Underwater Technology Vol 25 No 1

Autumn/Winter 2001

A Personal View

A Clarion call for clathrates

A Hunt

Technical Papers

Marine Aggregate Dredging in the UK: A Review

GH Singleton  

Abstract: In the 20th century, a marine industry evolved to dredge sand and gravel from the seabed around the United Kingdom, in order to provide an alternative source of aggregates for the construction industry.  Marine sand and gravel was also dredged for beach replenishment schemes around the UK coastline.  During the latter part of the century, there was an increased focus on coastal and marine issues generally, by both the public and regulatory authorities.  In the context of coastal and marine resource management, this paper reviews the recent developments that have taken place within the marine aggregate dredging industry and discusses the evolution of the institutional frameworks within which the industry operates.

 

Entrainment Thresholds of Naturally–shaped Fluvial and Marine Gravel (Granule) Sediments: A Laboratory Study

H Monteith  

Abstract: Using uniform beds and unidirectional flow conditions, the entrainment thresholds of naturally–shaped fluvial and marine gravels of granule size (2—2 mm) are determined by laboratory flume experiments.  Microscopic shape analysis shows that fluvial sediments are more angular than beach gravels.  For a given grain size, critical bed shear stress (to) in fluvial sediments is 47.6% lower than that recorded for marine gravels; efficiency of entrainment is related primarily to shape effects, in terms of protrusion.  This difference in the bed shear stress requirement for ‘threshold’ identifies the problems of adopting empirical relationships irrespective of environmental setting.

 

AUV Standardisation—Report on Workshop I Brown The Science of Decommissioning—Report on Conference

MJ Sayer and E Breuer

Book Review

NOAA Diving Manual: Diving for Science and Technology (4th Edn), by Ed James T Joiner

Reviewed by J Bevan

Underwater Technology Vol 25 No 2

Special Decommissioning Issue

Summer 2002

A Personal View

The future of exporting

K Forest

Technical Papers

Modelling the Behaviour and Environmental Impact of Cuttings Piles During Decommissioning

AO Tyler; ZA Sabeur and MC Hockley

Abstract: A model has been developed to predict the evolution of cuttings piles comprising discharged drilled strata and associated additives , under natural environmental forcing, and man–made operational disturbances.  The model uses a Lagrangian particle–tracking technique to represent the three–dimensional erosion and physical dispersion of particulate material.  The model is also able to represent chemical interactions and includes an ecotoxicological risk assessment approach.  The model has been run for illustrative disturbances arising from operational intervention on the cuttings pile and natural conditions of tidal/residual currents and storm waves.  Despite the uncertainties in input data, the model has demonstrated a capability to provide quantitative support to decision–making on options for future cuttings pile management. On–going studies are seen as contributing significantly to the refinement of the model and its use in modelling long–term evolution of cuttings piles.

 

Erosion of Cuttings Pile Sediments: A Laboratory Flume Study

KS Black, DM Paterson and IR Davidson  

Abstract: The best practical option for remediation of drill cuttings piles is directly contingent on a firm understanding of the properties and attributes of these sediments.  Whilst there is an increasing literature on the geochemical characteristics of cuttings piles, comparatively little is known regarding the transport by tidal currents and waves.  This paper reports some laboratory flume experiments conducted to ascertain the threshold entrainment shear stress (t crit) of drill spoil sediments from two locations (near to the drilling axis and outside the rig periphery) on the NW Hutton platform. t crit varies between 0.12—1.52 Nm־ and statistical  analysis shows a difference in sediment mobility wherein sediments farthest from of drilling axis are comparatively more stable.  Specialised low–temperature scanning electron microscopy (LTSEM) and compositional analysis of sediments (particle size, metal and organic content, inhabitant macrobenthos) are used to provide some insight into the differences between sites.  Swelling attributable to the greater clay content of sediment close to the drilling axis may, in part, explain the observations.  Comparison of the measured entrainment thresholds with both tidal and wave–induced bed stresses (separately) predicted using numerical models indicates that the sediments are unlikely to be moved by the prevailing tidal currents, but may be moved or agitated by extreme winter storms (wave height ~9—10m).  However , observations made during the flume experiments suggest a winnowing of the fine particles from the sediment matrix under sub–threshold stress, which may be important if these particles are geochemically reactive

 

Fundamentals of Drill Cuttings Pile Formation in the Sea

L Eames and D Vadnjal  

Abstract: The fundamental process of contaminated pile formation by depositing drill cuttings into the sea is discussed.  A new mathematical model of these processes is developed and tested against small–scale laboratory experiments.  the experimental study shows how the piles are formed by the development of a particle–laden plume descending to the sea flow which spreads laterally, over a considerable distance, as a particle–driven gravity current.  the model predictions are applied to interpret published field data measurements.  These results show that the thickness of drill cuttings piles decreases rapidly with distance from the initial source of cuttings and, that when natural biodegradation occurs, only a smaller fraction of the pile area or mass requires treatment.

 

A Multicapability Sensor for Hydrocarbons, Synthetic–based Fluids and Heavy Metals: Applications for Environmental Monitoring During Removal of Drill Cuttings Piles

D McStay, P Robertson, P Pollard, I Edwards, E Bonsen,A. Al–Obaidi and D Tait  

Abstract: As part of any drilling cuttings pile removal process the requirement for monitoring the release of contaminants into the marine environment will be critical.  Traditional methods for such monitoring involve taking samples for laboratory analysis.  This process is time consuming and only provides data on spot samples taken from a limited number of locations and time frames.  Such processes, therefore, offer very restricted information.  The need for improved marine sensors for monitoring contaminants is established.  We report here the development and application of a multi–capability optical sensor for the real–time in situ monitoring of three key marine environmental and offshore/oil parameters: hydrocarbons, synthetic–based fluids and heavy metal concentrations.  The use of these sensors will be a useful tool for real–time in situ environmental monitoring  during the process of decommissioning offshore structures.  Multi–capability array sensors could also provide information on the dispersion of contamination from drill cuttings piles either while they are in situ or during their removal.

 

A Novel Approach for the Study of North Sea Drill Cuttings Accumulations: The Combined Use of an ROV and Benthic Lander for In Situ Measurements

E Breuer, OC Peppe and GB Shimmield  

Abstract: Two benthic lander systems were used as part of a project investigating the geochemical characteristics of a North Sea drill cuttings pile.  Complications associated with deploying sampling gear in close proximity to the platform required an innovative technique to obtain the necessary measurements.  To achieve this goal, two deep–sea autonomous free fall vehicles (benthic landers) were adapted for deployment and transport by remotely operated vehicle (ROV).  The landers were fitted with a microelectrode profiling system for obtaining high–resolution oxygen, sulphide and pH profiles, and a rig to deploy gel proves into the sediment to examine dissolved trace metal profiles within the cuttings pile.  The use of an ROV for deployment of the landers enabled the simultaneous collection of data within a defined spatial context while providing real–time visual feedback of the landers operating on the seabed.  Eight deployments were made over 5 days, totalling over 100 hours of sampling time.  The successful deployment and retrieval of the instrumentation, the quality of data obtained and the limited disruptions to the ongoing ship operations demonstrate the value of the lander system as an efficient and versatile tool for in situ biogeochemical investigations in areas associated with sampling and measuring difficulties such as North Sea drill cuttings piles.

 

The Occurrence of the Coral Lophelia pertusa and other Conspicuous Epifauna Around an Oil Platform in the North Sea

JM Roberts  

Abstract: Lophelia pertusa is a cold–water coral most frequently reported on the shelf edge and offshore banks of the north east Atlantic.  The occurrence of this and other conspicuous large epifauna on moorings 2 km from an oil production platform in the North Sea were recorded from video surveys by remotely operated vehicle.  Sea anemones and soft corals were abundant and a total of 133 colonies of L. pertusa were observed.  These occurrences and those on the Brent Spar are the first documented reports of live L.pertusa in the North Sea. L.pertusa was restricted in its distribution to water >70 m, below the seasonal thermocline in the northern North Sea.  It is estimated that coral sampled from a single point mooring had a linear extension rate of at least 5 mm per year, a rate comparable with existing estimates.  It seems likely that these colonies will have originated from populations along the Atlantic margin with larvae transported into the northern North Sea in cooled Atlantic water, possibly via the east Shetland Atlantic Inflow current.  The implications of this finding in terms of the environmental sensitivity of this species remain unclear since it is not known to what extent that have been exposed to any drilling discharges.  It is possible that corals have persisted on and around oil industry installations as bottom trawling is excluded from the installation area.

 

Rigs to Reefs: A Critical Evaluation of the Potential for Reef Development Using Decommissioned Rigs

MDJ Sayer and MSP Baine  

Abstract: This paper reviews the effects existing platform and associated structures have on fish species of commercial importance and discusses what effect the decommissioning process could have on sold stocks in a North Sea context.  The success of the ‘rigs to reefs’ programme in the Gulf of Mexico has generated some interest in adopting a similar policy on some scale in the North Sea.  How this may be achieved following OSPAR 98/3 is reviewed.  Studies on the aggregations of fish species have estimated that less than 1.3% of North Sea saithe stocks and less than 0.25% of North Sea cod stocks are associated with oil and gas structures.  There is evidence to suggest that fish associated with platforms grow and taste better than offplatform fish, even though very small elevations in hydrocarbon contamination have been detected.  Whole ecosystem–based modelling approaches to fishery management indicate that total protection or regeneration of stocks is achieved only through significant area closures to the fishery.  The present area closed to the fishery is already maintaining the North Sea fisher status quo.  Converting existing structures into offshore reefs is considered unlikely to increase the present area of fishery exclusion nor improve  its productivity, even if it was possible under OSPAR 98/3.  There has been some speculation of a reef–dominated exclusion zone, whereby the reefs act as a central attractive feature.  Bringing the structures inshore for reef construction may have localised positive socio–economic impacts for coastal communities, but achieves no financial benefit for the production industries and does not remove any long–term liability.  Without significant levels of state support, both in the fields of construction and liability replacement, a programme of converting rigs into reefs will be difficult to achieve in the context of the North Sea.

 

Technical Notes: Sampling and Analysing Drill Cuttings

AC Skinner; D Long and GJ Tulloch  

Abstract:  The scientific study of drill cuttings on and from the seafloor requires that a number of technical challenges be overcome.  The location of the cuttings piles means that in situ measurement and sampling methodologies often have to be innovative in order to work around and within the platform structure and seabed installations.  In many respects, cuttings do not behave like sediments, so traditional survey and sampling technologies need adaptation to meet the challenges posed by the composition.  Sample handling procedures have to accommodate health and safety considerations additional to those normally associated with marine sampling.  Novel measurement techniques are required to analyse the material geotechnically and geochemically both in the field and in the laboratory.  The British Geological Survey has been involved in developing all of these aspects of cuttings pile surveys and analyses and aspects of this work are presented in this paper.

 

Decommissioning Pipelines and Subsea Equipment: Legislative Issues and Decommissioning Processes

JM Anderson

Abstract: The Oslo/Paris (OSPAR) Commission Decision 98/3 has placed an obligation on the UK effectively to preclude the disposal of offshore installations at sea.  Decision 98/3 has been enshrined in UK law under the Petroleum Act 1998.  However, the Decision does not apply to pipelines, and there are no international guidelines on the long–term decommissioning of pipelines.

The UK Government does provide some guidance on pipeline decommissioning on the UK continental shelf, both through the Guiding Principles, which provide the policy framework for decommissioning decisions, and in the Guidance Notes for Industry, which provide interpretation and guidance for decommissioning under the Petroleum Act 1998.  However, existing guidelines are concerned with the process of pipeline decommissioning, and the end point for these activities remains open.

This paper considers both the legal framework and the processes for decommissioning pipelines and subsea equipment.  Some key issues that need to be addressed are discussed.  There is still little by way of precedent for decommissioning pipelines, partly because most major pipelines have not yet reached the end of their economic life–span, but also because there is a conscious desire to defer pipeline decommissioning until the appropriate technology has been developed.  Furthermore, with little prescriptive guidance on pipelines, and uncertainty over future OSPAR considerations, there is little incentive for operators to face the challenges of pipeline decommissioning directly in the near future.

Underwater Technology Vol 25 No 3

Spring 2003

A Personal View

We can rewrite the story of 20 years of failure

J Hind

 

Umbilicals – Repair or Replace?  

Technical Papers

Time–lapse Photography in the Deep Sea

BJ Bett  

Abstract: Time–lapse photography (TLP) has been used in scientific applications for over 100 years, and has been used in deep–sea operations for the last three decades.  Here I review the use of TLP in deep–sea science by reference to case studies drawn from a 20–year history of ‘Bathysnap’ (Southampton Oceanography Centre’s TLP system) deployments in North East Atlantic.  Examples are given of echiuran feeding, xenophyophore growth, benthopelagic scavengers, and long–term studies of phytodetritus.  Although the technology for TLP will change over time, the concept remains of great value in studying the remote deep–sea environment.

Mapping the 3D Spatial Distribution of Dissolved Manganese In Coastal Waters Using an In Situ Analyser and the Autonomous Underwater Vehicle Autosub PJ Statham, DP Connelly, CR German, E Bulukin, N Millard, S McPhail, M Pebody, J Perrett, M Squires, P Stevenson and A Webb

Abstract:  An in situ dissolved manganese (Mc) analyser has been built and used with the autonomous underwater vehicle (AUV) Autosub.  The Mn analyser uses a continuous flow system to produce a coloured complex with Mn in seawater, which is measured in a flow–through detection cell.  The detection limit of the current system is 25 nmol dm –3, and using 10–s averaged data, the along–track resolution of the system is about 10 m.  The analyser was successfully used with Autosub in Loch Etive, Scotland, to define the three–dimensional distribution of dissolved Mn in sub–surface waters.  This application of AUV and sensor technologies in combination demonstrates the great power of the approach for determining the quasi–synoptic distribution of chemical species in environments (e.g. under ice, and horizontal space scales at depths of up to 500km) where more conventional approaches are not appropriate.

 

Development of the ‘Cocoon’ Subsea Fishing Protection System

JHA Baker  

Abstract: This paper describes a novel approach to protecting fishermen from the hazards of snagging on subsea christmas trees.  It presents the background to the development, and explains how the system works.  the fishing loads and the design philosophy are discussed.  The more general protection philosophy that follows from the design is also presented.,  The system is applicable to waters of any depth or location where bottom trawling is carried out.  A glossary is included at the end of the paper.

 

Technical Briefing: Energy Storage Systems for Unmanned Underwater Vehicles

SM Abu Sharkh and G Griffiths  

Introduction: The power source of an underwater vehicle is the main component that determines its range of travel and the tasks that it can perform.  Until recently, the choice of practical power sources for most applications has been limited to lead―acid and silver―zinc batteries are a well–established technology and are available at low cost.  However, they have a low energy density (~25 Wh kg –1).  Although silver―zinc batteries have a high energy density (~120 Wh kg –1), they are very expensive, costing 20 times the price of lead―acid.  They also have a very short life of 40―1–– cycles compared with 1000 cycles for lead―acid [1].

In recent years considerable research and development work has been done on advanced power sources for road electric and hybrid vehicles.  This ongoing work is motivated by environmentally driven legislation aiming at reducing the harmful emissions of conventional internal combustion engine vehicles (e.g. [2, 41]).

The power source should ideally have a high energy density, high power density (higher charge and discharge rates), low cost, long life, low maintenance, high efficiency and wide operating–temperature range.  It should also be safe and recyclable.  In addition to these requirements, which are similar to those for a road vehicle, there are additional considerations imposed by working in the underwater environment.  Ideally, the power source should be non–gassing and, in the case of batteries, the electrolyte should be spill–proof.  the operation of the power source should be independent of depth.

This paper presents a review of the features of different types of batteries (primary and secondary) and fuel cells that have been used in autonomous underwater vehicles (AUVs), highlighting their merits and operational and engineering issues that need to be considered when using them.  It also presents a survey of potentially promising alternative types of batteries and energy–storage systems including flywheel electromechanical batteries and supercapacitors.

 

Meeting Reports: Maritime World 2025: Future Challenges and Opportunities

INL Gallett

 

West Africa – The Oceanographic and Meteorological Conditions and their Challenges to the Oil and Gas Industry

INL Gallett

Book Reviews

The Diving Manual: An Introduction to Scuba Diving, by D Ellerby

Reviewed by J Bevan

 

Climate of UK Waters at the Millennium: Status and Trends, Editors G Alcock and L Rickards

Reviewed by WJ Gould

 

Waves in Ocean Engineering, by MJ Tucker and EG Pitt D Faulkner

Underwater Technology Vol 25 No 4

Winter 2003

A Personal View

Shortage of scientists and engineers for the offshore industries

I Gallett

Technical Papers

Reliability Capability Evaluation and Improvement Strategies for Subsea Equipment Suppliers

K Williams, N Robertson, C Roberts Haritonov and J Strutt  

Abstract: This paper presents the approach that BP and Boreas Consultants have taken to evaluate reliability capability and how this has been used to implement workable strategies to improve reliability in subsea equipment supplier federal contracts.  Key findings, lessons learned and strategy elements from this process are presented.

The paper will conclude with recommendations on how key elements of this strategy and the lessons learned from implementing it within federal contracts can be built upon to improve reliability capability throughout the subsea industry.  The application of reliability principles as the industry moves into the more dynamic environment of deepwater project specification and execution is specifically addressed.

 

On the Reliability of the Autosub Autonomous Underwater Vehicle

G Griffiths, NW Millard, SD McPhail, P Stevenson and PG Challenor  

Abstract: As autonomous underwater vehicles (AUVs) enter operational service, an assessment of their reliability is timely.  Using the Autosub AUV as an example, several design issues affecting reliability are discussed, followed by an analysis of recorded faults.  Perhaps contrary to expectations, failures rarely involved the autonomous nature of the vehicle.  Rather, faults were typical of those that occur with any complex item of marine electromechanical  equipment.  Reliability under various operating conditions was assessed using Weibull parametric models.  This reliability modelling was extended to the case of a vehicle operating under ice in order to estimate the probability of loss in situations where the support vessel could not gain access to a malfunctioning vehicle.

 

Retrieval of an Autonomous Underwater Vehicle: An Interception Approach

SM Ahmad, R Sutton and RS Burns  

Abstract: Guidance and navigation of airborne missiles has been reported extensively in the literature; however, little attention has been paid to the issue of guidance and docking of an autonomous underwater vehicle (AUV).  The retrieval of an AUV to a mother submarine (target) is conceived as a target interception problem and is considered herein.  The design problem is solved in two stages: first, the guidance technique is demonstrated assuming zero lag AUV dynamics; next, the AUV–controller dynamics is included in the guidance loop.  Thus, the issue of guidance, navigation and control is solved in a unified framework.  This is necessary for a realistic evaluation of the AUV–target engagement geometries.  Finally, the effectiveness of the guidance scheme in presence of disturbances is also illustrated.

 

Properties of Photopolymerisable Acrylic Adhesives for Underwater Bonding

PI Dolez, C Williams, A Goff and B. Love

Abstract: The bonding properties of two photopolymerisable acrylic adhesive formulations have been measured in terms of bonding strength in pure shear, which ranges between 2 and 6 MPa.  These resin systems have been developed ultimately for marine applications and have been designed to address very demanding requirements: underwater bonding in a very short time (less than a minute); at low temperatures (as low as 1°C); and on a wide range of marine surfaces.  The bonding strength dependence on curing time, curing temperature, substrate roughness and material for the two resin systems demonstrated their potential as marine adhesives.  Measurements of their shelf–life behaviour at various temperatures and of the water ageing of bonds are also reported.

Meeting Reports:

Emergency Recompression: Co–ordinating the Need…Revisited

J Bevan  

Introduction: The meeting was opened by the Chairman, David Elliott, Independent Consultant in Diving Medicine, and then the scheme was set by Martin Sayer of the Dunstaffnage Hyperbaric Unit, Oban.  As both a provider of emergency recompression treatment and a ‘diving contractor’, Martin Sayer was in a good position to offer an overall view.  He provided a brief and objective introduction to the several important issues the meeting would address.  Interestingly, he pointed out that for every one recompression treatment of an inland/inshore professional diver (or any other type of professional diver), the Dunstaffnage unit would treat some 30 recreational divers (including so–called ‘quasi–professional’ inland/inshore divers).  In terms of numbers of treatments, it was very clear that the recreational divers were the main source of patients.

Monitoring and Measuring the Underwater Environment IG Priede West of Shetland Drilling Operations – Validating Riser VIV Fatigue Life Predictions G Jeans

Book Reviews

Klinger’s Diving Machine, Editors M Fardell and N Phillips

Reviewed by J Bevan

 

Ocean Waves and Oscillating Systems: Linear Interactions Including Wave Energy Extraction, by J Falnes

Reviewed by D Faulkner

Underwater Technology Vol 24 No 1

A Personal View

Renewable Energies from the Sea: the Future for UK plc?

G Senior

Issues arising from the Westhaven Tragedy Concerning Fishing Gear and Pipeline Interactions

J Side  

Abstract: This paper reviews the findings of two inquiries into the loss of the fishing vessel, Westhaven.  It provides an account of international and UK law, and presents advice to be followed when fishing gear has snagged on a subsea pipeline.  Possible arrangements for provision of more detailed information on charts on pipeline burial and freespan status are discussed.  Finally the implications of the Westhaven tragedy for pipeline decommissioning and abandonment are examined.

 

A Method of Analysis for the Extreme Response of an Offshore Floating and Weathervaning Platform Subjected to Wave, Current and Wind from Different Directions

LH Khor and DNP Barltrop  

Abstract: This paper describes a study carried out to investigate the behaviour of a moored floating production and storage unit (FPSO) subject to wave, current and wind coming from different directions.  the main purpose is to investigate a methodology for designing the structure’s mooring system which allows for different environmental phenomena to come from different directions and to peak at different times.  Some results are presented to illustrate the effects of directionality and non–concurrency for the particular ship data assumed.

 

The Sensitivity of a Dispersion Model to Cuttings Settling Speeds

L Carles and I Bryden  

Abstract:  In order to determine the impacts from drilling operations, it is necessary to understand the physical dispersion of the drilling discharge into the sea.  The development of a waste dispersion model enables the prediction of the concentrations of drill–cuttings deposited on the seabed and the thickness of the cuttings pile (if present) on the seafloor.  Some models already exist and could easily be improved by using more appropriate equations for the settling speed of cuttings in the water.  In this paper, an existing simulation model is presented with its required input data and obtained output data.  Four different settling speeds equations are introduced in the described model to compare with the usually used equation.  Graphical data are produced and discussed for each test.  It was found that the settling speed equation chosen for a dispersion has a significant influence on the final output data.  Another common problem also comes from the nature of the input data required from the user.  These input requirements are not always in agreement with what the oil companies can provide.  Correlations between data needed for the simulation and data provided from oil companies could be determined through experiments.  A set of experiments is proposed in the last section of this paper.

 

Remote Intervention ’99 – The Deep Challenge – Report on Meeting

D Liddle

 

2nd Workshop on Subsea Pipelines – Report on Meeting

INL Gallett

 

Emergency Recompression: Co–ordinating the Need – Report on Meeting

D H Elliott  

Underwater Technology Vol 24 No 2

A Personal View

Got the Tee Shirt

B Loth

Buoyancy Mechanisms of Marine Organisms: Lessons from Nature

PJ Molloy and MJ Cowling  

Abstract:  This paper reviews how many pelagic organisms maintain their buoyancy in the ocean.  Although there are thousands of different species of marine organisms, ranging in size from microscopic plankton to squid, shark and the large whales, the mechanisms they use to avoid sinking are not as varied.  These mechanisms include: the exclusion of heavy ions to create a less dense liquid; enlarging the surface area of the organism to increase drag; the use of gas chambers; the use of low–density waxes and oils, and hydrodynamic planes.  Natural buoyancy systems are compared with those currently used in various underwater vehicles; in addition, the attempts being made to mimic the mechanisms present in nature are described.

 

Electric Field Signatures of Ships in Southampton Water

M Varney, S Batley and M Siddall  

Abstract: Continuous measurements of electric potentials were taken from a fixed point at the entrance to Southampton Water, adjacent to the Solent.  This provided a regular and wide spectrum of electric field sources for study.  Southampton Water has a considerable movement of vessel traffic entering and leaving the Port of Southampton, and a significant tidal movement each day.  Underwater electric fields were measured adjacent to a shipping channel of approximately 7 m depth.  Analysis of signals allowed various signatures and sources of electrical noise to be identified.  Regular ferry traffic allows the reproducibility of the sensor response to be examined.  This permits background sources of noise to be better identified and therefore increases the ability to discriminate the various signals of interest.

 

Fault Tolerant Control Strategies for Uninhabited Underwater Vehicles

AR Pearson, R Sutton, RS Burns , P Robinson, and A Tiano  

Abstract: Commercial, naval and scientific operational specifications for uninhabited underwater vehicles (UUVs) continue to become more challenging in line with the advances being made in control engineering.  In order to survive actuator and/or sensor failure during a mission, such vehicles need to possess a reconfigurable or fault tolerant control system.  This paper explains the basic principles of fault tolerant control systems.  It then reviews their application in the design of UUVs and other systems where it is considered a technology transfer is possible.

 

Deepwater Development Opportunities in Angola – Report on Meeting

M Hibbert

 

6th Atlantic Frontier Workshop: Waves, Steep Waves and Statistics – Operating in Harsh Environment – Report on Meeting

S Archer

 

$10 Oil: Is Underwater Robotics an Answer? – Report on Meeting

INL Gallett  

Underwater Technology Vol 24 No 3

Summer 2000

A Personal View

The Foresight Marine Panel

T Jones

ROV Image Scaling with Laser Spot Patterns

DA Pilgrim, DM Parry, MB Jones and MA Kendall  

Abstract: The use of remotely operation vehicles (ROVs) by ocean scientists has increased significantly during the last decade.  Of particular value and interest is the acquisition and analysis of subsea video images to obtain accurate measurements of seabed features, biota and manmade artefacts.  Video images obtained by ROVs have a variable perspective and scale but this problem may be solved by the use of structured lighting comprising an array of diode lasers.  A DOE Phantom XTL TOV has been fitted with a 5–spots diode laser system Abiss, and has been deployed in research programmes in Plymouth Sound and the River Dart.  An important aspect of these programmes is the development and perfection of verifiable measurement and sampling techniques, which may then be employed with confidence in inaccessible and hostile waters.

 

An Acoustic Beacon to Reduce the By Catch of Cetaceans  In Fishing Nets

D Newborough, AD Goodson and B Woodward  

Abstract: Acoustic beacons transmitting certain sound patterns underwater are known to have a deterrent effect on harbour porpoises and are a promising means of keeping these animals away from fishing nets.  The device described here has been successfully tested during sea trials in Scotland and Denmark and has been shown to reduce the by–catch of porpoises during a commercial fishing trial.

 

Reflections on the Legal Standing of Underwater Archaeology in the UK—Technical Briefing

G Momber  

Introduction:  In this paper the value of archaeology is discussed and its development in Britain outlined.  The contrasting development of archaeology both underwater and on land is examined to assess their relative positions in the profession.  Both terrestrial and maritime archaeology have undergone significant changes in structure over recent years, a review will given an insight into the status of archaeology today.

 

Deepwater Site Investigation—Report on Meeting P Harrington The Fiery Deep: Exploring a New Earth—Report on Meeting

INL Gallett

Book Reviews

The Eternal Darkness: A Personal History of Deepsea Exploration, by Robert D. Ballard with Will Hively

Reviewed by RA Mills

 

Decommissioning The Brent Spar, by Tony Rice and Paula Owen

Reviewed by AD McIntyre

 

The Restless Sea, by Robert Kunzig

Reviewed by AS Laughton  

Underwater Technology Vol 24 No 4

Winter 2000/2001

A Personal View

A tale of two industries

B Jones

Diverless Weld Inspection and Repair Using ECM/ACFM Techniques

D Clifton, F Mill, J Esnaola, R Kate and WD Dover  

Abstract: This paper describes the development and application of an integrated tooling/NDT system which provides the potential to undertake a weld inspection, carry out removal of the defective zone, and achieve validation of the repair, all within a single ROV deployment operation.  Removal of the defect zone is achieved using a novel application of the electrochemical machining process (ECM).  This system is integrated with the alternating current field measurement (ACFM) system, for crack detection, location and sizing.  The paper describes the development of electrochemical machining process models to cover situations encountered in automated weld sampling operations.  From these models, and data collected from experimental trials, it has been determined that the sampling/removal operation can be carried out at tool feed rates of up to 3 mm/min.  The model has been extended for determining the change in gap dimensions for the case of zero tool feed.  This relationship can be used as a control parameter when determining the degree of overcut required when inclusions are encountered and the tool is required to remain stationary for a certain duration.  Tank trials of the system have been carried out, successfully demonstrating effective operation of the integrated strategy in a submersed environment.

 

Experiments in the Guidance of Unmanned Underwater Vehicles

M Caccia, G Bruzzone and G Veruggio  

Abstract: This paper addresses the problem of the guidance of unmanned under3water vehicles (UUVs).  In the framework of a two–layered hierarchical architecture uncoupling the system’s dynamics and kinematics, a couple of guidance laws for approaching a target with the desired orientation and following an environmental feature have been designed with Lyapunov–based techniques.  Suitable acoustic–based estimators of the corresponding operational variables have been designed and integrated with the guidance and control system.  Experimental results of pool trials of a prototype UUV executing free–space manoeuvring and wall–following tasks are reported and discussed.

 

Some Results from the Analysis of Metocean Data Collected During Storms in the Northern North Sea

J Wolfram, B Linfoot and V Venugopal  

Abstract: This paper presents the results from statistical analyses of wave and wind data collected over a period from August 1994 to June 1998 at the North Alwyn, fixed, oil and gas platform in the northern North Sea.  Theoretical joint probability distributions of individual waveheight and periods are found to provide a poor fit to data sets obtained by aggregating the individual waves into bins defined by the significant waveheight.  Hs, and average zero–crossing period, Tz, of the 20–minute interval in which the waves were observed.  Better fits are obtained when empirical models are used for the join probability of individual waveheight and steepness, and a general bivariate Weibull model is presented that is conditional upon significant waveheight and average zero crossing period.  The JONSWAP spectrum peak enhancement parameter g is found to vary significantly for the storm seastates examined.

 

Subsea 2000: 2020–Focusing the Vision—Report on Meeting

D Liddle

 

Man–Made Objects on the Seafloor 2000—Report on Meeting

AL Rice

Book Review

Historic Shipwrecks: Discovered, Protected and Investigated, 1999 by Valerie Fenwick and Alison Gale

Reviewed by J Satchell

Underwater Technology Vol 23 No 1

AUV Technology Special Issue
Winter 1997/98

A Personal View

Observations for Ocean Forecasting

J Woods  

Technical Papers

Versatile Autonomous Submersibles–the Realising and Testing of a Practical Vehicle

N W Millard, G Griffiths, G Finegan, SD Mcphail, DT Meldrum, M Pebody, JR Perrett, P Stevenson and AT Webb

Abstract: Autonomous Underwater Vehicles are no longer engineering curiosities.  They have been under development since the 1970s, but the last three years, in particular, have seen significant advances towards their use in operational missions.  The state of the art for European and North American vehicles is summarised and the opportunities for future scientific missions are explored.  The UK Natural Environment Research Council (NERC) AUTOSUB project epitomises the progress made in AUV technology, and recent field trials in coastal waters are described.  Having proved its ability to gather scientific data autonomously, the vehicle is about to enter the next phase of performing operational scientific missions supported by appropriate technological upgrades.

 

Navigation and Control of an Autonomous Underwater Vehicle Using a Distributed, Networked, Control Architecture

SD McPhail and M Pebody

Abstract: The Ocean Technology Division of Southampton Oceanography Centre has designed, built and recently successfully field tested the AUTOSUB–1 autonomous underwater vehicle.  This paper describes the development, design and testing of the navigation and control systems. The system is based upon a modular, distributed architecture with fourteen network nodes carrying out the essential vehicle navigation, control, monitor and safety functions.  This paper will show how the use of this architecture has contributed to the speed of system implementation, test and integration, and will simplify the integration of future system enhancements. The navigation system uses the global positioning system (GPS) or differential GPS (DGPS) position fixes when surfaced, and dead–reckons when submerged using a Doppler velocity log.  Separate nodes control the vehicle depth, position and speed.  The mission control nodule is an event–driven command interpreter which co–ordinates activities and issues demands to the control nodes via the network.

 

The Mechanical Design and Implementation of an Autonomous Submersible

P Stevenson, D Graham and C Clayson

Technical Note

Use of Decompression Computers as Dive Profilers and Electronic Logbooks, and in the Management of Decompression Sickness Treatment

MDJ Sayer, GD Duncan, CM Wilson and AG Murchison

Abstract: This technical note gives examples of the categories and precision of some dive parameters recorded by new generation decompression computers.  Examples are also given in their use in generating electronic dive logs.  The ability to interrogate computers used by patients being treated for the effects of decompression sickness, can aid the management of that treatment, and is discussed.

Reports

Umanned Underwater Vehicle Showcase (UUVS)

CH Clayson and PG

Collar Oceans ’97. 500 Years of Ocean Exploration: Into the Next Millennium

B Woodward

Book Reviews

Handbook for ROV Supervisors

 

 

Underwater Robots

 

 

Coastal Environment: Environmental Problems in Coastal Regions

Underwater Technology Vol 23 No 2

Summer 1998

A Personal View

Shoals of Capricorn ­ a multidisciplinary approach

I Watt

Technical Papers

A Diver Observatory for in–situ Studies in Sublittoral Sediments

W Ziebis, T Pillen and B Unger  

Abstract: In marine sediments macrofaunal organisms often produce deep reaching tubes or burrows that greatly influence the biogeochemistry of the inhabited sediment (Hylleberg & Henriksen 1980, Aller 1982, Huettel 1990).  Among the burrowing organisms thalassinidean shrimps are a group of decapod crustaceans that are often abundant in coastal sediments (Suchanek 1985, Griffis & Suchanek 1993) and build complex burrow systems reaching up to 2.5m or more into the sediment (Pemberton et al. 1976).  Recent studies focused on the species Callianassa truncata that occurs at high densities (120 inc.m –2) in shallow–water sediments off the coast of the Italian island Giglio in the Mediterranean sea and constructs elaborate burrows to a sediment depth of 80–100 cm (Ziebis et al. 1996a).  Like many burrowing organisms its produces a ventilation current through its burrow system.  Many attempts to study this ventilation in laboratory systems were difficult due to the constraints of aquariums and the difficulty of measuring inside burrows without destroying the sediment structure (Witbaard & Duineveld 1989, Forster & Graf 1992, 1995).  Our interest was to gain information on the in situ burrowing behaviour and to find out how deep oxygen–rich water is actually pumped into the sediment by bio–irrigation and how this is affecting the sediment chemistry.

We report here the construction of a diver observatory and its deployment in the field for in situ investigations of deep–burrowing organisms and their effects on the sedimentary environment.  The large, hexagonal container (1.2m high, 2m diameter) was built of 6 transparent acrylic walls held by a stainless steel frame, and was covered by a lid made of PVC to avoid light penetration.  It was buried in the sediment so that the lid was level with the sediment surface.  The sediment from inside was removed to allow divers to enter through a door in the lid in order to perform observations and measurements from inside the observatory into the surrounding sediment.  We demonstrate the unique possibilities of observing the behaviour of burrowing animals in their natural habitat down to a sediment depth of 1m and show the opportunities of direct sampling of pore and burrow water in intact systems as well as detailed in situ measurements through silicone–filled ports in the walls of the observatory.

 

Hydrothermal Plume Detection in the Deep Ocean ­ A Combination of Technologies

RR Cave and CR German  

Abstract: Marine chemists, geologists and oceanographers have been studying the behaviour of hydrothermal plumes since the discovery of hot springs on the seafloor of the Pacific in 1977.  Scientists are now trying to assess the amount of hydrothermal activity in the deep ocean, both past and present, to get some idea of the impact of hydrothermal fluid on the oceans as a whole, on the composition of seawater and marine sediments, and on the behaviour of marine ecosystems.  Deep ocean hydrothermal vent sites tend to occur at plate tectonic boundaries.  This article concentrates on recent research along the Mid–Atlantic Ridge (MAR), close to the area of the Azores Triple Junction, where the African, Eurasian and N. American oceanic plates diverge.  The ridge in this area is broken up into several North–South trending segments, offset from each other by a series of East–West trending discontinuities.  The ability to deploy a platform combining instruments for real–time geological study of the seafloor and geochemical studies of the water column above it, simultaneously, has resulted in the discovery of a might higher incidence of hydrothermal venting along the MAR than previously supposed.  These improved techniques could now be applied to finding hydrothermal deposits in marginal basins where ore–grade deposits are known to accumulate.

 

Sonar Based Navigation System for an Underwater Vehicle

R Smith, A Frost and P Probert  

Abstract: This paper describes the design and development of a navigation system for a small remotely operated underwater vehicle (ROV).  The navigation system uses sonar to localise the vehicle with respect to underwater structures.

The navigation system has been successfully implemented.  This has required careful construction of an estimator.  Through implementation, we have shown that, with sufficient sensor information, a relatively straightforward vehicle model is sufficient.  This is beneficial both in reduced computation time, and since it involves a small number of easily measurable physical parameters.  Experimental results are shown for the localisation system combined with a simple control system.

Reports

Subsea Water Separation and Re–injection B Woodman New Government, New Prospects? The Future of the UK Oil and Gas Industry

G Senior

 

Deepwater Technology Symposium

LJ Ayling

 

Fully Subsea Production : Is it a Reality?

D Liddle

Book Reviews

Handbook of Seafloor Sonar Imagery

 

Construction Vessels of the World 98/9

 

Handbook for ROV Pilot/Technicians  

Underwater Technology Vol 23 No 3

Winter 1998/99

A Personal View

The UK Offshore Operators Association and their role in the offshore oil and gas industry

J May

Technical Papers

A Definitive Approach to Criticality Assessment as part of an Integrity Management Strategy for Submarine Pipelines

JHA Baker  

Abstract: This paper reviews risk, and the assessment of risk with regard to submarine pipeline systems, and highlights the shortcomings of both numerical risk assessment and simpler forms of criticality assessment, such as the use of the Boston Square.  An approach to criticality assessment is proposed in which three levels of any failure mode are defined, with consequence and likelihood assigned at each level, as a means of overcoming existing shortcomings.  It is demonstrated that the approach can be sued as a live integrity management tool throughout the operational life of a pipeline system.

 

Investigations on Carbon Dioxide/Oxygen Breathing Diesel Engines – Results from an International Collaborative Project

JG Hawley, GT Reader, M Zheng, IJ Potter and OR Frauvel  

Abstract: The capabilities of a diesel engine to operate on an atmosphere of 70 mol% carbon dioxide and 30 mol% oxygen when pre–heated to 150°C has been demonstrated.  The rated brake power is reduced by 20–23%, while brake–specific fuel consumption is increased by 23–28%.  The hypothesis that carbon dioxide is seriously affecting both pre– and post–ignition processes by slowing down reaction rates is presented.  Simulation work has shown that phenomenological models, when suitably modified, can predict brake performance parameters of engines operating on such atmospheres to within 5% within certain limitations.  Custom–derived ignition delay and heat release models have been successfully validated specifically for non–air diesel operation.

 

A New Instrument for Making In–situ Acoustic and Geotechnical Measurements in Seafloor Sediments

AI Best, JA Roberts and ML Somers  

Abstract: The SAPPA (Sediment Acoustic and Physical Properties Apparatus) is a new instrument designed for the rapid acquisition of seafloor geophysical and geotechnical data.  The present system can measure P–wave velocity and attenuation down to 1 m sub–bottom depth in sands and gravels, and the velocities of horizontally and vertically polarised shear waves at the surface.  Preliminary tests show that sufficient energy is produced to propagate P–waves at frequencies up to 10 kHz in water and S–waves at about 120 Hz through at least 1 m of wet sand.

Reports

The Fifth Framework Programme of the EU

CM Funnell

 

The Oceanographic and Underwater Robotics Industries in Asia: Report on an International Technology Service Mission to Korea and Japan, 8–19 June 1998

INL Gallett

 

Underwater Optics III D Pilgrim Harsh Operating Environments (Metocean Studies in the Atlantic Margin)

M Williams

 

Subsea Controls and Data Acquisition

M Sharman

Book Reviews

Three Miles Down

 

The Competent ROV Pilot/Technician

 

Competence With High Voltage AC Power Distribution for ROV Personnel  

Underwater Technology Vol 23 No 4

Spring 1999

A Personal View

$10 Oil ­ diversify or die

J Westwood

Technical Papers

Underwater Imaging Using Markov Random Fields with Feed Forward Prediction

MA Hodgetts, A Greig and A Fairweather  

Abstract: This paper presents a Markov Random Field (MRF) approach to the segmentation of underwater images as part of a total underwater imaging system.  The system uses image feed forward so that information from previous images can be applied to predict the next image in the sequence.  The predicted image is then used within an MRF framework to improve the image segmentation and, in doing so, the algorithm emulates aspects of the human visual system by combining what it sees with what it is expecting to see.  The overall method is outlined and the MRF segmentation is given in detail.  Improvement to image sequence scene interpretation are demonstrated from laboratory and underwater trials.

 

The Shape, Period and Wavelength of High Storm Waves

MJ. Tucker  

Abstract: It has been known for nearly 30 years that high waves in a linear sea have shapes which tend to that of the autocorrelation function.  This fact forms the basis of the Shell New Wave Theory, but its acceptance by the offshore industry has been slow.  For the present paper, 1000 random wave records have been simulated from a JONSWAP spectrum, and the highest wave in each record examined.  The results are used to demonstrate the validity of the concept and its limitations.  The statistics of the period and length of these individual high waves are examined together with the relationship between them.  Their mean zero–upcross period does not tend to T1 as has sometimes been stated, and in fact cannot be stated simply in terms of spectral moments.

 

Nomograms for Improving Diver Saftey

TG Anthony and BJ Horn  

Abstract:  Divers are increasingly required to perform ‘safety to life’ calculations which, if incorrect, may result in a serious incident.  The application of an ‘old fashioned’ manual computational technique, the Nomogram, is proposed as a cheap and simple tool for performing safety to life calculations.  the Nomogram is friendly to non–mathematicians, applicable to the marine environment and may significantly reduce the risk of calculation error.  Example Nomograms are illustrated and the advantages for improving diver safety presented.

Technical Note

Applying GIS and Digital Maps to Real–life Problems in the Coastal Zone

FL Frank

Abstract:  The Centre for Environment, Fisheries & Aquaculture Science (CEFAS) is an Executive Agency of the UK Government’s Ministry of Agriculture, Fisheries and Food.  Founded in 1902, it was formerly known as the Directorate of Fisheries Research.  It is now an internationally recognised centre of excellence for research, assessment and advice on fisheries management and environmental protection.  It is therefore both a producer and a user of a wide variety of spatial data.  This paper describes its progress is developing a range of PC–based geographic information systems for specific purposes and gives examples of how these systems can be used for managing and researching the marine and coastal environment.

Reports

Offshore Site Investigation and Foundation Behaviour: New Frontiers

JR Burland

 

Diverless Connection Technology

B Woodman and B Jones

 

Technology for Deep–Sea Geological Investigations: Developments, Applications and Results

D Evans, K Harrison and A Skinner

Book Reviews

Ship of Gold in the Deep Blue Sea

 

First Aid for Underwater Finds

 

The Ocean ­ Our Future. The Report of the Independant World Commission on the Oceans

Underwater Technology Vol 22 No 1

Summer 1996

A Personal View

An independent View of the Society

M Crawford

Technical Papers

Simplified First Order Motion Analysis of a Moored FPSO

D J Smith

Abstract: This paper presents a simplified method based on a barge shape, for predicting the first order motion response of a typical moored floating Production Storage and Offloading (FPSO) vessel.  The technique is suitable for use on a spread sheet and provides rapid optimisation for any given vessel and environment combination.  Results are presented from a three–dimensional diffraction program showing that a barge shape can be used to estimate the motions of a FPSO at an earlier stage of the design process.

 

Dynamic Seals in HP/HT Wells

R Shepherd and A Stevenson

Abstract: Emerging completion technologies are placing increased demands on seal systems required for downhole use.  The move towards higher production pressures and temperatures (HP/HT) means that seal design could become the limiting factor for the exploitation of HP?HT wells in the North Sea and elsewhere.  Current dynamic seal design practice is not supported by a fundamental base of knowledge, although there is experience and empirical data at existing operating conditions.  The basis for predicting seal behaviours under conditions more extreme than those currently experienced is therefore limited.  For this reason MERL has designed and built a new instrumented dynamic seal test facility to investigate the behaviours and mechanisms of failure of seals, under realistic conditions simulating downhole service.  The test facility that exists is unique in Europe and its function is illustrated by reference to typical results.

 

Avoiding the use of Exotic Materials in Pipeline Design

D H Demetriou

Abstract: The continued exploration and development of deepwater offshore oil and gas fields presents greater technical challenges to the pipeline engineer.  Such  wells tend to produce very corrosive wellstream fluids at high wellhead flowing temperatures.  This paper will examine aspects of pipeline materials selection based on corrosion resistance requirements.  A review of alternative pipeline materials is presented, together with limitations on the use of each material for corrosive service.  Finally, the paper will demonstrate how a re–evaluation of the traditional predictive models for assessment of corrosion rates, in wet CO2 gas pipelines, can avoid the use of high alloy carbon steels, or exotic materials.

 

A Technique for Monitoring the Settlement of Fouling Organisms at Exposed Subtidal Locations — Technical Note

IS Thompson et al

Meeting Reports

Underwater Research and Discovery

M Breen, C Johnston and S Marine

 

Offshore Mechanics and Arctic Engineering

DT Brown

Book Reviews

Remotely Operated Vehicles of the World

Reviewed by John Bevan

 

Anchor Handling Tugs and Supply Vessels of the World

Reviewed by John Bevan

 

Survey Vessels of the World

Reviewed by John Bevan

Underwater Technology Vol 22 No 2

Winter 1996–97

A Personal View

The future is subsea but not us for humans

Dr Rex Gaisford

Technical Papers

The Design and Evaluation of a Phase–Steered Parametric Sonar System Intended for Sediment Characterisation

JC Cook, AD Goodson, PA Lepper, B Woodward

Abstract:  The ultimate aim of the European Commission’s MAST–II REBECCA project was to study the viability of characterising sub–bottom sediment structures entirely by acoustic means.  Part of the system developed to attempt the realise this aim was a parametric sonar system.  The mode of operation was to insonify the sea bed at different incidence angles, using a variety of transmitted acoustic pulses, and subsequently to examine reflected and forward–scattered signals.  The paper describes firstly the transmitting system designed and developed at Loughborough University.  It then presents the results of static calibration tests in Lock Duich, Scotland and further results obtained during sea trials on two French research vessels off the coast of Brittany, when the parametric sonar array was integrated into a two–fish with an attached hydrophone streamer.  The sonar transmits a phase–steerable primary beam centred at 75 kHz and generates in the water useful secondary signals at typically 3 kHz to 7kHz, with a narrow sidelobe–free beam (2.5° x 2.5°), at Source Levels up to 196 dB re 1 mPa at 1m at 5 KHz.

 

Weather and Climate Variability Since Prehistoric Times and Recent Indications of Continuing Fluctuations in the N.E. Atlantic

N Lynagh

Abstract: Weather and climate are in a constant state of variation.  The time–scales over which these variations take place range from minutes to millennia and even longer.  Human experience of these variations spans only a very short period of time.  As a consequence, a change which is actually part of a long–period variation about the mean can easily be mistaken for a trend in the mean itself.  In recent decades significant variations in the wave climate of the N.E. Atlantic Ocean have been identified.  It is important to try to identify whether these changes are a variation about a steady mean or whether  they are indicative of a shift in the mean itself.  An examination of the varying climate of storm systems in the N.E. Atlantic helps to provide an understanding of why the wave climate appears to have changed.

 

Deepwater Geotechnical Investigations in the Gulf of Mexico

JH Pelletier, EH Doyle and RN Dutt

Abstract: This paper discusses Shell Offshore Inc.’s current deepwater Gulf of Mexico (GOM) geotechnical investigation practice.  The development of the geotechnical investigation prognosis and its components are outlined.  The paper discusses the range of water depths, site soils, platform types, investigation vessels , and in situ tools that have been used.  Both standard and advanced laboratory testing schemes are presented and their purposes discussed.  The importance of integrated geophysical studies for defining investigation scopes is highlighted.  The use of the data for the design of surface and subsea development structure foundations and exploration and production wells is reviewed.  The Mars Tension Leg Platform (TLP) site is provided as an example of an integrated geotechnical investigation.  Finally, the paper proposes directions for advances and development in geotechnical investigations and associated technology for the 21st century.

Meeting Reports:

Climate Change Offshore N.W. Europe ― An Assessment of the Impact of Changing Meteorological and Oceanographic (Metocean) Conditions on Offshore Activities

INL Gallett, D Thomas and A J Fyfe

 

Using the Marine Environment for the Greater God

AG Senior

 

An Update on Subsea Tree Technology

SA Hutton and H Howells

Book Reviews

International Offshore Engineering

Reviewed by C Kuo

 

Titanium Alloys in Subsea and Offshore Production Systems

Reviewed by WD Loth

Underwater Technology Vol 22 No 3

Summer 1997

A Personal View

From manganese nodules to Working Time Directives

A Read

Technical Papers

Extreme Value Analysis of the Structural Response of a Single Point Moored Vessel

J Bowers, I Morton and G Mould

Department of Management and Organisation, Faculty of Management, University of Sterling, Sterling, FK9 4 LA, UK

Abstract: Offshore system design requires an estimate of the extreme environmental conditions, typically based on the 50 year period values.  Where a single environmental variable dominates the system’s behaviour, a univariate extreme value analysis may be sufficient.  However, many systems are dependent on several aspects of the environment and a multivariate extreme value analysis is required.

One approach is the use of a response function to transform a bivariate environment to a single variable describing a critical force in the offshore system.  The resultant one dimensional problem is then explored using the standard techniques of univariate extreme value analysis.

This method, the ‘structural variable approach’ is applied in a bivariate extreme value analysis of a single point moored vessel and its dependence on wave height and period.  The 50 year return period steady drift force determined by this method suggests that the vessel will experience considerably greater forces than might be expected from a simple univariate extreme value analysis based on wave height alone.

 

Erosion Damage Mapping in a Standard 90 Degree Take–Off Subsea Christmas Tree Assembly

G Parslow, D Stephenson, J Strutt and S Tetlow

Abstract: School of Industrial and Manufacturing Science, Cranfield University, Cranfield, Bedfordshire, MK43 0AL, UK

It is increasingly recognised that erosion arising from sand production can be a significant problem in the production of petroleum fluids.  Since the quantitative analysis of the flow behaviour of entrained particles is extremely difficult, the traditional methods of estimating the rate of erosion occurring in well–head equipment has been based on the accumulation of experience and information on past equipment failure or damage.  The ability to  predict erosion rates in a new or modified system would provide the designer with an invaluable tool for estimating low erosion potentials within a cost effective and reliable design solution.

Here we present a set of results from an ongoing process of research examining erosion risk for various subsea component geometries. The set of data concerns a ‘T’ joint geometry, appropriate to both conventional and horizontal subsea Christmas tree configurations and demonstrates our use of a multi–layer paint erosion indication technique to produce highly visual and accelerated maps of erosion damage occurring in a three dimensional component model.  The paper also serves to introduce our exploratory investigations of computational fluid dynamics and fluid/particle flow dynamics visualisation as tools for modelling the erosion patterns observed.

 

Report of the Marine Technology Foresight Panel Working Group on Exploitation of Non–Living Marine Resources

C P Summerhayes, R Coles, B. Wheeler, M Baker, DS Cronan, R Burt, G. Griffiths, N Veck, D Anderson, H Young and M Murphy

Abstract:  As a contribution to the UK Government’s Technology Foresight programme, which aims to set priorities for research funding for the future through dialogue between industry, academia and Government, we have examined the non–living marine resources part of the Marine market sector.  Under this heading we identify substantial potential for growth in three target market areas:

A  offshore information and forecasting services

B  seabed survey in support of engineering of all kinds, military activity and transport

C  exploitation of deep waters beyond the edge of the continental shelf

 

Although the UK is already strong in several marine markets and in the science and technology necessary to underpin continued market success, we believe that substantial additional benefits will accrue to the UK if it increases its efforts so as to acquire a large fraction of the developing global markets in these three areas.  We have prioritised the technologies in which further investment in R&D is required if the UK is to achieve these benefits.

Reports

Near Seabed Geophysics and Geotechnics: What can they do for your next subsea pipeline project?

B Tollin

 

Towards 2000: Metres or Millenium?

J Sommerville and M Cook

 

ASPECT ’96: Advances in Subsea Pipeline Engineering and Technology

A Kyriacou et al.

 

Tax Pounds and Toxic Seas: Deep Water Containment of Pollutants

INL Gallett

Book Reviews

Sea Change : A Message of the Oceans

Reviewed by DA Pilgrim  

 

Dredging : A Handbook for Engineers

Reviewed by LJ Ayling

 

The Infernal Diver

Reviewed by RL Allwood

Underwater Technology Vol 22 No 4

Autumn 1997

A Personal View

The Marine Foresight Report D Goodrich

Technical Papers

Report of the Marine Technology Foresight Panel Working Group on Energy

D McKenzie

Introduction: The Marine Foresight Panel came about in 1995 to represent the cross–cutting interests of the Marine Markets as the sixteenth panel in the UK Government’s Technology Foresight exercise.  The Technology Foresight process was set up as a national consultation exercise to bring together industry, academia and government to determine where the country should invest its science, engineering and technology spending.

In view of the range and scope of technologies which underpin the marine industries in the United Kingdom this Foresight Panel was made up of five sub–groups, reporting to the Panel Chairman and resulting in a Final Report made up of their findings.  This paper is the second of two sub–group reports to be covered in Underwater Technology, selected for their interests to SUT members.

This report summarises the initial work of the Energy Sub–Group in identifying those areas in the fields of marine energy where there is high potential for innovative and economically  significant developments to be initiated, within the Foresight time–scale of 20―30 years, through research and applied technology. Is Abyssal Seafloor

 

Isolation an Environmentally Sound Waste Management Option?

DK Young and PJ Valent  

Abstract: This paper discusses the waste disposal concept of environmentally isolating industrial wastes (i.e. sewage sludge, fly ash from municipal incinerators, and dredged material) on the abyssal seafloor.  Environmental acceptability of this concept is compared with alternative oceanic waste management concepts of containment and dispersion.  Dredged material, containing contaminants with high particle affinities enabling potential toxins to be readily sorbed to sediment and be buried within the seabed, is ideally suited for abyssal seafloor isolation.  Sewage sludge, with low bulk densities, is better suited for disposal by dispersion.  Fly ash, containing high levels of heavy metals which can be mobilised under certain redox conditions, is a poor candidate for ocean disposal.

 

Marine Biological Mapping for Environment Management Using Acoustic Ground Discrimination Systems and Geographic Information Systems

J Davies, R Foster–Smith and IS Sotheran

Abstract: Effective marine environmental management requires base maps of biological resources.  Remote sensing techniques are one of the most cost–effective methods of resource mapping.  Sonar is the optimal method of remote sensing the seabed in turbid, temperate marine waters.  Acoustic group discrimination systems provide a relatively simple, low–cost method of sea bed mapping but are designed to map the physical environmental variables of topography and seabed type.  The BioMar project at the University of Newcastle–upon–Tyne has developed methods of analysing acoustic data in conjunction with biological information to produce biological resource maps.  These methods utilise geographic information systems (GIS).  These methods are described and illustrated with data from two case studies undertaken for the UK Government conservation agencies. Fuzzy Yaw Autopilots for Unmanned Underwater Vehicles Tuned Using Artificial Neural Networks R Sutton and PJ Craven

Abstract: This paper describes the application of neuro–fuzzy techniques in the design of autopilots for controlling the yaw dynamics of an unmanned underwater vehicle.  Autopilots are designed using an adaptive–network–based fuzzy inference system (ANFIS), a simulated annealing turning methodology, and a fixed fuzzy rule–based approach.  To describe the yaw dynamic characteristics of an unmanned underwater vehicle and realistic simulation model is employed.  Results are presented which demonstrate the superiority of the ANFIS approach.  It is concluded that the approach offers a viable alternative method for designing such autopilots.

Reports

Report of the Marine Technology Foresight Panel Working Group on Energy

D McKenzie

 

New Methods of Subsea Wellhead Control

W Andrews

 

Behaviour of Offshore Structures ’97

DT Brown

 

Denizens of the Deep: The Marine Life of the Atlantic Frontier

INL Gallett

Book Reviews

Regional Satellite Oceanography

Reviewed by DJT Carter

 

Sea Dumped Chemical Weapons: Aspects, Problems and Solutions

Reviewed by M Crawford

 

Oceanography

K Dyer

Underwater Technology Vol 19 No 1

Spring 1993

A Personal View

Maritime Technology in the MAST Programme

J Boissonnas  

Technical Papers

Addressing Training Needs in Europe: A Direction for the Marine Sector

JAT Grant

 

The Evolution of Divers’ Decompression Computers

NH Green and B Woodward

Abstract: Dive computers model the uptake and release of nitrogen in a diver’s tissues and are used routinely to monitor decompression status in terms of the allowable time a diver may stay at any particular depth.  Since the first appearance of multi–level decompression computers on the sports diving market in 1983, significant progress has been made towards improving divers’ safety.  This has been done principally by presenting decompression information such as dive time, no decompression stop time, depths at which decompression stops are made, repeat dive profiles, permissible and safe ascent rates, and other vital parameters such as air time remaining and air supply pressure.  The latest models can provide an accurate dive profile (depth against time) after the dive, a facility that is considered an important diagnostic aid after a decompression accident.  This paper considers the historical development of dive computers, how they work, how they differ in design, what features they offer and how divers’ expectations now make challenging demands upon manufacturers in terms of technical feasibility, ergonomic acceptability and human–computer interaction.  The new generation of dive computers will integrate conventional decompression computations with high resolution data–logging, environmental and physiological monitoring and extra functions such as underwater navigation capability.

 

Aspects of Remotely Operated Vehicle Control – A Review

HNR Fairbrother and BA Stacey

Abstract: This paper provides an introduction to the issues surrounding and impacting upon the design of control systems for Remotely Operated Vehicles  (ROVs).  The unique characteristics of ROVs are discussed from a control viewpoint, and methods are proposed for minimising the control problem at the design stage.  Mathematical modelling is briefly covered, and a brief tutorial–style review is given of current and proposed control techniques for use with ROVs.

 

Added Hydrodynamic Loading due to Sacrificial Anodes

MJ Downie, BA Murray, P Bettess and JV Haswell

Abstract: There is a scarcity of data relating to the hydrodynamic loading due to sacrificial anodes.  A method of calculating factors to apply to circular cylinder force coefficients, using the discrete vortex method is described.  The results are presented for uni–directional and oscillatory flows.  Equivalent force coefficients are calculated and used in a Morison–type analysis of a simple jacket structure in a current and in waves.  The overall in–line loading was found to be increased by as much as 9% in modest environmental conditions.

Meeting Reports

Offshore Site Investigation and Foundation Behaviour—Report on Conference

JB Burland

Protective Structures—Report on Seminar

JL Daeschler  

Book Reviews

Use and Misuse of the Seafloor, by Ed KJ Hsü and J Thiede

Reviewed by FG Larminie

Oxygen and the Diver, by K Donald

Reviewed by V Flook      

Underwater Technology Vol 19 No 2

Summer 1993

A Personal View

A Doctor Addresses Your Secret Fears

Dr B Loth

 

Whither Ocean Resources?

C Dudgeon

Technical Papers

Autonomous Control System (SPARCS) for Low–Cost Subsea Production Systems

M Theobald

Abstract: This paper describes a Subsea Powered Autonomous Remote Control System (SPARCS) which is designed to control subsea wells without the use of electrohydraulic control umbilicals.  With oil exploration moving towards marginal fields, and small fields connected to the existing infrastructure, SPARCS will provide a low cost solution for control of subsea developments.  This paper looks at each of the main system components and provides commercial justification for such a control system.  SPARCS is highly innovative in that it controls hydrocarbon wellheads without the use of control umbilicals.  The system’s electrical power subsea is produced by a turbine generator fitted to a water injection flowline or alternatively a thermo–electric generator fitted to a production flowline.  Hydraulic power for operating wellhead and downhole safety valves is produced from a subsea unit.  Communication signals for valve control and sensor monitoring use acoustic telemetry with seawater as the transfer medium.

 

The Offshore Aggregate Industry in the UK

R Fox

Abstract: The increasing demand for aggregates to supply the construction industry has resulted in an expanding marine dredging industry, and sand and gravel dredging now represents some 25% of total annual supplies.  This paper considers the history and development of offshore dredging, geological and technical considerations, licence procedures and problems, and the future of the offshore aggregate industry.

 

Comparison of Loads Predicted Using ‘Newwave’ and Other Wave Models with Measurements on the Tern Structure

JB Rozario, PS Tromans, PH Taylor and M Efthymiou

Abstract: Global wave loads measured on the Tern platform during a very severe storm have been compared with predictions made on the basis of three different models for wave kinematics.  The first is the ‘Newwave’ theory, a broadbanded, probabilistic–based model for the extreme waves of a random seastate.  The second model involves complex time–domain simulation of random directional seas.  Both these theories are used with the Morison equation and realistic force coefficients to predict global forces.  The third wave model is the Stokes fifth–order theory with artificial values for the force coefficients, as used in conventional design practice.  Both the Newwave theory and the random directional simulations lead to predicted base shear forces that are comparable to the measured values over a wide range.  If non–linear effects in the ocean surface are accounted for, then the Newwave theory predicts the base shear generated by the largest wave of the storm with a very high degree of accuracy.  In contrast, calculations based on the Stokes kinematics of conventional design practice overpredict the measured loads over the whole range studied.  It appears that Newwave is the most suitable available wave theory for routine use in the design and analysis of structures such as Tern.

Meeting Reports

Advances in Underwater Welding Technology—Report on Seminar

D Liddle

 

MAST Days and EUROMAR Market—Report on Conference

B Woodward Wave

 

Kinematics and Environmental Forces—Report on Conference

Book Reviews

Offshore Engineering, Eds. FLLB Carneiro, AJ Farrante, RC Batista and NFF Ebeken

Reviewed by G Owen

 

Composite Material Technology, Proceedings of the 14th Annual Energy–Sources Technology Conference, Houston, Texas, 1991, Eds. D Hui and TJ Kozik

Reviewed by WD Loth

Underwater Technology Vol 19 No 3

Autumn 1993

A Personal View

Ocean Politics

Prof Emeritus Alec Smith  

Technical Papers

Diving Science, the UK’s Place in Europe

NC Flemming

Abstract: There are about 3000 employed or university graduate student scientific divers in the European Community, and probably as many again with the status of undergraduate students who occasionally dive for research purposes or as voluntary assistants.  There is an additional population of amateur volunteers.  The number of scientific divers in the other European countries is not so clear, but probably a further 30–50%.  There are many ways in which scientific diving could benefit from various kinds of collaboration between European countries, and possibly from research funding or infrastructural funding on the European scale.  The UK has a good track record in international collaboration, although recent changes in legislation have made it difficult for foreign scientific divers to come and work in the UK.  The scientific diving community in the UK is one of the largest in Europe, and one of the best organised, although the demise of the Underwater Association was a serious blow.  Experience and ability in the UK will enable British scientific divers to play a strong role in European collaboration and large scale projects, and this situation should be developed to the full.  With our long coastline and extremely varied coastal conditions it would be sensible to offer British research diving facilities as convenient service sites for scientific research groups from throughout Europe, but this is not possible at present because of the legislation.  The Society for Underwater Technology (SUT) has an important potential role in attracting scientific divers so as to promote the community activities and membership participation in this field.

 

Underwater Terrain–Following Using Active Controls on a Towed Vehicle

JF Henderson & RC Wright

Abstract: A theoretical study has been made of the seabed terrain–following ability of a towfish, fitted with a seabed–sensing sonar and active controls.  Single cable and twin cable (with depressor) configurations have been compared and the effects of wave–induced towship motion have been included.  The results indicate that satisfactory terrain–following can be achieved, but that the anticipated advantages of the twin cable arrangement are not necessarily realised in practice because of motion coupling via depressor surge.

 

Designing Bubble–Free Profiles—Impossible?

V Flook and AO Brubakk

Abstract: We have developed a mathematical model of inert gas uptake and distribution based on the physiological characteristics of the human body.  Using the inert gas levels calculated by the model we have calculated total gas content of each tissue type taking account of metabolic gas exchange.  When the total gas pressure is greater than environmental pressure a bubble forms; the model calculates the change of volume of this separated gas phase.  These calculations are repeated at frequent intervals throughout the decompression procedure.  Thus, we have predictions of separated gas phase volume for any tissue of the body, at any point of the path from arterial blood to venous blood and tissue oxygen levels.  We have run this model to predict gas phase volume for a number of decompressions, carried out with pigs and with humans, in which we have used ultrasonic bubble detection.  The agreement between predicted separated gas volume and bubble count is very good.  The model enables us to examine the effect on bubble formation of changing major characteristics of the decompression profile.  Thus, we can begin to plan profiles with minimum bubble formation and compare predictions with bubble counts in pigs.  Ultimately we should be able to design bubble–free decompressions – but perhaps we are being too optimistic.

 

An Investigation into the Parametric Excitation of Suspended Loads During Crane Vessel Operations

FJ McCormick and JA Witz

Abstract: This paper investigates the parametric excitation of suspended loads during crane vessel operations.  Determination of the system’s behaviour is achieved by a time domain numerical integration of the equations of motion.  Growth of large amplitude oscillations of the suspended crane load is shown to occur in monochromatic and random sea states.  Results are presented and discussed in relation to their practical significance, and also to gain insight into the interesting characteristics of the non–linear, parametric equations of motion.

Meeting Report

Subsea International ’93—Report on Conference

F Knight, BA Jones and I Ball

Book Reviews

The Physiology and Medicine of Diving, 4th Edition, Eds. PB Bennett and DH Elliott

Reviewed by JD King

Underwater Technology Vol 19 No 4

Winter 1993–94

A Personal View

The Inter–Agency Committee for Marine Science and Technology

Prof IA Shanks  

Technical Papers

Tidal Stream Power for Orkney and Shetland?

IG Bryden

Abstract: This paper reviews a feasibility study into the use of tidal current driven electrical generators in the narrow channels around Orkney and Shetland.  The paper outlines the theory of tidal current generation and relates this to the geography of the two island regions. Marine Resource Atlases: the Implications for Policymakers and Planners J Ramster

Abstract:

Marine resource atlases provide a means of bringing together, in a convenient form for reference and planning purposes, the multiple uses of a sea area.  Digital versions – Geographic–Information Systems (GIS) – are now the rule rather than the exception and span the wide spectra of both users’ needs and technical development respectively.  The current situation in the United Kingdom, the Netherlands, Italy, North America, Food and Agriculture Organisation (FAO) of the UK and within the Private Consultancy area are described in turn and then the key question of whether or not decision–makers per se should manipulate data within a GIS–context is discussed.  It is suggested that technical advances over the next 3–5 yeras will make such a development inevitable and that this must be taken account of by marine resource atlas–makers.

 

Trends in the Wave Climate of the Atlantic and the North Sea: Evidence and Implications

RW van Hooff

Abstract: There is now extensive published evidence, based both on measurements and visual observations, that average wave heights over the North East Atlantic have increased moderately to considerably over the past two decades and this is also seemingly true for the North Sea.  This article reviews the available evidence and the implications for the design of marine structures.  In particular it notes that such increases in average height could have a substantial influence on fatigue loads affecting existing as well as future structures.  It therefore recommends further investigations, particular continued monitoring of the trend in wave climate to improve the general understanding of long term trends in weather severity and further research into the reasons for these trends.

 

Shell Cormorant CA–P1 Subsea Satellite Tree System: Post Operational Investigation

SA Cromar

Abstract: This paper details the findings of an investigation into the condition of the Cormorant CA–P1 Satellite Tree on recovery from the North Sea after eleven years of service as an oil and gas producer.  During this time the tree required no major workover operations, with the exception of a tree cap replacement.  The primary objective of the inspection work performed on the P1 tree was to investigate the general condition of key components and mechanisms after 11 years of continuous service.  Areas of particular interest were: the corrosion protection system, metal to metal seals and sealing surfaces, elastomer seals and sealing surfaces, gate valves and operators, alloy materials, the ‘Y’ spool and crown plug arrangement, and hydraulic control lines and couplers (tree to tree cap).  Additionally, the main block, flow loops and production flowlines were non–destructively examined for any loss of wall thickness, due to erosion/corrosion effects.  The paper concludes that the equipment performed well and makes recommendations on design and operational procedures for future subsea satellite production systems.

Meeting Reports

Subtech ’93—Report on Conference

R Allwood, S Cardno and D Wardle

 

The Use of 3D Seismic Data for Shallow Gas Investigations—Report on Seminar

J Squire

 

Development and Application of New Materials Offshore—Report on Seminar

LP Green

Underwater Technology Vol 18 No 1

Spring 1992

A Personal View

Subsea Technology – Opportunities for the Offshore Industry

JRS Morris CBE

Technical Papers

Encouraging Future Young Scientists – The View from One Research Laboratory

PA Hollow

Abstract: The Institute of Oceanographic Sciences Deacon Laboratory has been setting up links with schools to encourage pupils to consider careers in science and technology.  Initiatives have included school science projects, the supply of information for teachers, work experience for pupils and the publication of careers advice.  The need for such education links arose during the late 1980s and this article examines the background to this.  It describes the activities of the past two years and concludes that although assessment of these activities is difficult, the potential encouragement to young scientists is very valuable.

 

Day–to–Day Impact of Salmon Farming on the Work of the River Purification Boards

H Smith

Abstract: This paper is an attempt to clarify the role of the river purification boards in Scotland and to explain how legal control of the salmon farming industry was developed.  Estimates are made of the potential polluting impact of an industry that has grown dramatically over the last decade.  The author also identifies the pollution pathways arising from the industry, and differentiates between operations at land–based farms and floating cage farms.  Details are also given of the Clyde River Purification Board’s control policy and the self–monitoring requirements imposed on fish farming.  Finally, the author makes clear how the self–monitoring required by the boards relates to the charging schemes levied by all the boards on all discharges in respect of compliance and environmental monitoring.

 

Estimation of Extreme Wave Heights: A Review of Guidance Issued by the UK Department of Energy

N Hogben & DJT Carter

Abstract: The paper reviews the guidance on estimation of extreme wave heights issued by the UK Department of Energy in 1984 and 1990 with emphasis on the derivation, not previously published, of a key formula quoted but not explained in the 1990 issue.  It considers first the widely used simple approach underlying the data and associated guidance issued in 1984, and the reasons for the change to the different presentation based on a more complex analysis of the 1990 issue.  It then explains the 1990 analysis and discusses its implications in terms of a comparison between the 1984 and 1990 data charts for European waters.  A main finding of the paper is that due to fortuitous balancing of differences, the simple approach of 1984 and the more complex 1990 methods yield very similar results.

 

Advanced Power Systems for Autonomous Unmanned Underwater Vehicles

JG Hawley and GT Reader

Abstract: The underwater scientific, commercial and defence communities have long been aware of the potential uses of unmanned Autonomous Underwater Vehicles (AUVs) and the development of miniature high capacity computers and artificial intelligence systems has allowed more ambitious missions to be considered for such vessels.  However, to carry out these envisaged tasks new power systems will be required which are superior to those currently used in non–nuclear underwater vehicles.  Existing systems, almost exclusively, use lead–acid battery driven electric motors and the energy storage capacity of these systems is only sufficient for short reach missions.  Consequently, alternative power systems are being developed which make use of advanced batteries, fuel cells, semi–cells, radioisotopes and non–air breathing heat engines.  This paper details the power requirements for AUVs, examines the advanced power systems that are being developed for use in such vessels and describes the driving forces behind their possible realisation.

 

Physiological Monitoring by Underwater Ultrasonic Biotelemetry

B Woodward and R Sh. Habib

Abstract: Underwater ultrasonic biotelemetry is a branch of underwater technology concerned with the transmission of physiological information from a human or animal subject to some remote receiving station.  Here, we consider the transmission, reception and processing of signals from swimmers and divers, which includes signal formatting, multiplexing and encoding, transducers and power amplifiers, power sources, decoding and data analysis.  Applications include monitoring the heart rate, breathing rate and temperature of a patient in a swimming pool or a free–swimming diver in open water.  The most challenging problem addressed is how to transmit an electrocardiogram (ECG) signal in the severe multipath environment of a swimming pool.

Meeting Reports

Ocean Opportunities – Management for the Future (An address given at the SUT AGM, 12 December 1991)

Admiral Sir Lindsay Bryson

 

Advances in Diving Technology to 50 metres—Report on Seminar

M Johnson

Book Reviews

Marine Minerals in Exclusive Economic Zones, by DS Cronan

Reviewed by AJ Smith

Ocean Variability and Acoustic Propagation, by J Potter and A Warn–Varnas (Eds)

Reviewed by ML Somers

Underwater Technology Vol 18 No 2

Summer 1992

A Personal View

Industry now values collaborative research

T Veness  

Technical Papers

On–Site Tests for Underwater Video Picture Quality

RW Barrett, M Clarke and B Ray

Abstract: The majority of underwater operations involve the use of video for observing and recording.  This paper presents the results of a multi–sponsor project managed by The Marine Technology Directorate Ltd.  The objectives of the project were to develop a set of test procedures and quality acceptance thresholds to ensure that underwater videos shot on site will be fit for their intended purpose.  The tests were designed to be used and interpreted on site by non–specialist personnel.

 

Control System Design for High Pressure, High Temperature, Subsea Control Systems

M Theobald, M Fabbri and D Kirkman

Abstract: This paper examines the problems associated with subsea control systems when dealing with high pressures and temperatures.  It offers some overall design consideration to reduce the impact on umbilicals.  Key subsea components such as control valves and hydraulic connectors are examined in detail.  The authors conclude that existing design can be modified to withstand foreseeable higher pressures (up to 150°C).  The recommendation is made that long–term testing is carried out to prove key components.

 

Downhole and Subsea Completion Design for a High Pressure North Sea Gas Condensate Field

S Gomersall, K Sardar and G Rae

Abstract: This paper details the overall system design for a 15,000 psi subsea, gas condensate well in the North Sea.  Currently, significant industry interest exists in the technology required to complete wells of this type, which would enable substantial hydrocarbon reserves to be developed.  Subsea wells such as this have not yet been completed.

 

Engineering Technology and Aquaculture

MG Poxton

Abstract: Much of the information currently available on engineering technology for aquaculture is inadequate, having been empirically developed on a more or less trial and error basis.  Today, aquaculture remains an art with success largely resulting from the innate abilities of staff expert at animal husbandry, practising in open–water systems with good water quality.  The present state of the Atlantic salmon industry in Scotland – with over–production, low market prices, deterioration in environmental conditions, disease and many other problems – was both predictable and predicted.  However, this situation also applies to the production of salmon and other species in other countries, and is therefore regarded as a ubiquitous characteristics of the industry.  Before this situation can be improved, scientific and engineering technologies must be integrated and applied over a wide and diverse area.  Probably no single institute can muster enough resources to answer all the questions posed by this industry, indeed it probably would not be cost effective even to try to do so.  Consequently, collaboration is essential between scientists, engineers, economists and others from a wide range of institutions, together with the active participation of industrialists with sufficient financial resources to sustain long term programmes.

Meeting Reports

Subtech ’91—Back to the Future—Report on Conference

RG Birse, S Cardno and WE Mason

 

Automation of Remote Subsea Intervention—Report on Conference

J Turner

 

High Pressure/High Temperature Subsea Production Systems—Report on Seminar

GS Bonner

Book Reviews

Business Fundamentals for Engineers, by Chengi Kuo

Reviewed by RL Allwood

 

An Introduction to ROV Operations, by G Last and P Williams

Reviewed by DW Hartley

Underwater Technology Vol 18 No 3

Autumn 1992

A Personal View

Time for a Sea–Change in Engineering?

Prof JB Caldwell

Technical Papers

The Use of Exploration Geoscience Data in the Planning and Execution of Site Investigations for Offshore Development Facilities

MR Cook, JM Square and AW Hill

Abstract: Prior to development of an offshore hydrocarbon field, large sums of money are spent by operating companies on the acquisition and processing of exploration geoscience data.  These data, augmented by other publicly available data, can be cost–effectively integrated and reviewed to aid: field development conceptual design; selection of suitable sites for development facilities; and planning of detailed, site–specific, geotechnical and geophysical site investigations.  This paper illustrates the range of geoscience data that normally exists and the uses to which such data can be put.  A case history of two field development sites in the southern North Sea is presented, to emphasise the benefits of such a data review and the pitfalls that can occur if such a review is not undertaken.  The benefits of multi–use of existing data are summarised.  Recommendations are made for future geoscience data acquisition to provide further information for subsequent field development site investigations.

 

SWATH Vessel Engineering Science—State of the Art Seakeeping

T Downs

Abstract: Small Waterplane Area Twin Hull (SWATH) ships are an excellent example of how the physics of fluid flow is being exploited by naval architects: fluid/body interaction is engineered to the advantage of the ship.  They are a new breed of advanced ships receiving worthy attention.  The paper provides an overview and introduction to the principles of why SWATH ships behave as they do and how engineering scientists use frontier techniques to analyse them and produce design solutions.  The Navatek I, a Hawaiian passenger cruise vessel launched in 1990, is used as a case study for the ‘state of the art’ SWATH ship.  The aspects covered include motions, resistance, stability, seaworthiness, manoeuvring, structure, safety and missions.

 

Alternative Methods for Carbon Dioxide Removal in Diving Life Support Systems

R Hughes, DR Acharya and K Li

Abstract: The main objective of this investigation was to develop alternative, more efficient systems for carbon dioxide removal for diving operations and for small submersibles.  The methods studied included the use of absorbent liquids supported on porous solids which provided a regenerable system, and diffusion/permeation processes including, a) flat sheet membranes, and b) the use of hollow fibre permeators for gas separations.

 

Predicting the Fate of Oil Spilt at Sea

MV Leech and MI Walker

Abstract: Oil spilt at sea has the potential to cause signficant environmental damage.  In order to respond adequately and minimise such damage, it is essential to respond as quickly as possible.  The physical properties of oil undergo rapid changes once in the sea and many countermeasures are only useful for a short period of time before weathering processes make it difficult to deal with the slick.  Oil spill models have been developed to help speed response and to assist in pre–planning contingency efforts and training purposes.  Models can rapidly predict the movement, spreading and oil properties of a slick in the sea, providing advance warning to the authorities and helping to decide the most appropriate response.  This paper outlines some of the techniques behind oil spill modelling, concentrating particularly on the EUROSPILL model.  It is important to note that oil spill models represent an attempt to numerically simulate complex physical processes and are inevitably limited in their ability to predict the outcome of actual spills.  The quality of results from a numerical model is strongly influenced by the quality of the underlying algorithms and the quality of input data.

 

A Review of Equipment and Procedures for the ‘Lost Bell’ Situation

K Williams

Abstract: Diving bells are used extensively in the offshore industry for installation, inspection and maintenance of underwater structures and equipment.  The most dangerous scenario that can occur involving a bell is when it is impossible to bring it to the surface, either because the lifting system is broken or because the bell is trapped.  If the supply of breathing gas or heat from the surface has also been lost, then this is referred to as the ‘Lost Bell Situation’. This paper briefly looks at the factors which affect the life expectancy of a diver in this situation, and studies the current methods of rescue from a lost bell.  Alternative systems, which would reduce the danger to the divers and prolong their life expectancy are discussed and recommendations are made to facilitate their implementation.

Meeting Reports

Subsea Control and Data Acquisition—Report on Conference

R North

A Review of Current Developments in Offshore Ropes—Report on Conference

RL Allwood

Book Reviews

Water Baby—The Story of Alvin, by Victoria A Kahar

Reviewed by J Bevan

Tsunami Hazard: A Practical Guide for Tsunami Hazard Reduction, Ed. EN Bernard

Reviewed by D Pugh

Underwater Technology Vol 18 No 4

Winter 1992

A Personal View

The Pressure to Remain Ignorant

Dr Maurice Cross  

Technical Papers

Problems Associated with Seismic Facies Analysis of Quaternary Sediments in the Northern UK Continental Shelf

MS Stoker, FS Stewart, MA Paul and D Long

Abstract: Seismic facies analysis is increasingly being used in the interpretation of high–resolution seismic reflection data.  Existing depositional systems models, based primarily on seismic data, have been constructed on the basis that acoustic character can be directly correlated with relatively consistent lithologies and geotechnical properties.  However, borehole and shallow core data from the northern UK continental margin indicate significant inconsistencies in the use of the technique as a predictive tool.  Changes in acoustic texture can occur laterally and vertically, in both lithologically homogeneous and heterogeneous sequences.  Conversely, acoustic homogeneity does not necessarily imply a uniform sedimentary sequence.  The successful application of this technique can only be achieved by the integration of seismic data with other subsurface information, with interpretation based on sound geological concepts and models.

 

Oceanographic Equipment and Instrumentation: needs, trends and priorities

CP Summerhayes and D Girard

Abstract: Taking out the effect of inflation, oceanographic ships are now twice as costly and instrument systems are 10 times as expensive as they were 20–30 years ago.  The trend will continue as oceanography becomes a global science, and as the proposed Global Ocean Observing System (GOOS) becomes operational.  The growing requirement from all quarters for knowledge about the 70% of our planet that is covered by water demands increased investment in ever more complex and costly measuring systems.  To address the challenges of increased cost and complexity of operations and equipment, oceanographers must band together nationally and internationally to ensure that the slim resources available are used to best effect.  Collaboration is happening through bilateral agreements, through the design of large scale experiments like WOCE (the World Ocean Circulation Experiment) and the Ocean Drilling Programme (ODP) and through the planning of large scale operations, like GOOS.  Collaboration is fostered through the funding of Community Research Projects nationally, eg, by the Natural Environmental Research Council (NERC), and internationally, eg, via the CEC’s Marine Science and Technology (MAST) programme.  But more cooperation and better planning is urgently needed at the international level to reduce the rate of increase of operational and developmental costs and to get a maximum return of data and interpretation for the original investments.  High cost systems development is beyond national capabilities for the most part, requiring international cooperation and funding.  Discussions are needed in international forums (eg, Pan–European) to develop concensus and plans for collaborative action.

 

Evaluation of Hotspot Submarine Hydrothermal Mineralisation: the example of Pitcairn Island

DS Cronan, RA Hodkinson and O Stoffers

Abstract: A wide variety of state–of–the–art oceanographic survey, observation and sampling techniques have been employed to assess the marine mineral resource potential of the Pitcairn Island EEZ.  Results show that two large, hot–spot related, shallow submarine volcanic edifices occur some 80 km east–southeast of Pitcairn Island.  Both are covered by extensive hydrothermal mineral deposits, with one currently discharging hydrothermal fluids.  Studies suggest that sulphides may be buried just below the surface of the seamounts.  Many of the older seamounts within the Pitcairn EEZ are covered with relatively thick hydrogenous Mn–crusts.

Technical Note

High Pressure/High Temperature Reservoirs—an evaluation of the subsea control system problems

M Theobald and P Turner  

Meeting Reports

New Breathing Performance Standard for the Diving Industry—Report on Seminar

DE Elliott

14th International Congress on Acoustics—Report on Conference

B Woodward

Book Reviews

Management of Drilling Operations, by Ken Fraser

Reviewed by PA Strong

Dynamics of Fixed Marine Structures (Third Edition), by NDP Barltrop and AJ Adams

Reviewed by J Witz

Underwater Technology Vol 17 No 1

Spring 1991

A Personal View

EJ Risness

Technical Papers

Environmental Forces in Relation to Structure Design or Assessment (Part II)

JH Vugts

Abstract: Environmental forces are discussed in connection with the overall problem of the design of new, or the assessment of existing, structures.  It is essential to see environmental forces in this broader context and to integrate them with all the other aspects involved.  ‘Structures’ refers here in general to all types and applications – floating and bottom supported, compliant and fixed.  Where a discussion is aimed at a particular group, this is specifically identified, such as in the case of fixed space frame structures, to which special attention is paid.  Offshore structures engineering has, in many respects, become a mature discipline.  However, further developments are still necessary to fully benefit from the large increase in knowledge after so many years of research and development efforts, as well as from the accumulated experience with real platforms offshore.  This is in the best interest of safety, the extended use of existing structures and the more economical design of new ones.  The next major step is sometimes suggested to be structural reliability analysis, which would require both the loading and the structural models (describing generally elastic as well as rigid body properties) to become probabilistic.  In general, this is not yet considered to be within reach and is cautioned against.  However, the underlying principle is warmly supported and the introduction of concepts which are firmly based on reliability analysis methods is a realistic goal to aim for.  It is suggested that significant progress in this direction can be made by using loading models which incorporate the probabilistic features which reflect the random wave environment in a realistic manner, in combination with (nearly) deterministic structural models.  Where such loading models are not already current practice, they should be introduced forthwith.  This demands a truthful representation of random wave kinematics and realistic force coefficients, including the drag and inertia coefficients in Morison’s equation for fixed structures.  A perceived way forward is described and proposals are made on how to achieve this.

 

OSCR and Interocean S4 Current Measurements in Poole Bay

MJ Osborn

Abstract: The deployment and operation of a high resolution (1km) HF radar (OSCR) for the measurement of surface currents in Poole Bay, UK is described.  In addition, two pairs of Interocean S4 current meters (located 1m above the seabed and at mid–depth), plus a single S4 current meter (1m above the seabed) were deployed to provide information on the sub–surface flow.  Example OSCR data are presented to indicate the overall current regime in the area.  The data have been analysed to provide tidal and residual components of the observed current, information on the effect of wind stress on the surface waters and vertical variation in current speed and direction through the water column.  The results indicate the presence of predictable current shear with depth, that allows the surface tidal component to be extended to mid– and near–bed depths.

 

The Invention and Development of the Diving Helmet and Dress

J Bevan

 

The Cullen Report: Implications for the Standby Vessel Industry

J Daniel

 

Nitrox (Airox) – A Future Recreational Diving Gas

TR Hennessy

Abstract: If a nitrox mixture with an oxygen content greater than 21% is breathed instead of air during a dive, then it is possible to extend bottom times for a given decompression time or to reduce the amount of decompression time for a given bottom time.  In addition, the level of nitrogen narcosis suffered by a diver may be significantly reduced on deep dives.  A simple nitrox mixture is made by adding pure compressed oxygen to compressed air, known as oxygen–enriched air.  The use of such mixtures is increasing in the recreational diving public in Florida, USA, where it is available at many air filling stations.  However, there are new dive limits on these mixtures which are posed by the higher exposure to oxygen and the fact that there are no special–purpose decompression tables available.  The nitrogen–equivalent air depth N2/EAD) is normally used to convert standard air tables, but this method may not be correct for dives other than simple no–stop air dives.  The oxygen limits are discussed and the equivalent air no–stop table on 68%–32% nitrox is given for both USN Standard Air Tables and the BSAC’88 Tables.

Book Reviews

Using Oil Spill Dispersants on the Sea, Committee on Effectiveness of Oil Spill Dispersants. Marine Board Commission on Engineering the Technical Systems, National Research Council, USA

Reviewed by S Howard

 

Maintenance Dredging Reviewed by JG Edwards Developments in Tidal Energy

Reviewed by Gordon Senior CBE

Underwater Technology Vol 17 No 2

Summer 1991

A Personal View

C Kuo

Technical Papers

Application of a Remotely Operated Construction Vehicle

JS Wood

Abstract: One of the most innovative oilfield construction projects undertaken in recent years was the installation of a barrier wall around a North Sea platform.  Before the two semi–circular concrete walls could be installed, in water of more than 70m deep, the seabed around the platform required considerable preparation.  This work included the removal of scour–protection material from the periphery of the platform, debris removal from the seabed and sub–surface, and levelling an area more than 200m in diameter to an accuracy of ± 15cm, in order to generate a horizontal seabed foundation.  Most of this work was undertaken using a remotely operated construction vehicle, fitted with a number of specialised tools (Fig 1).  This paper describes the vehicle and its tooling, control systems and techniques which were developed for this project, and reports on the actual performance of the system on site.

 

Shoreline Wave Power on the Isle of Islay

TJT Whittaker

Abstract: The civil engineering construction of Britain’s first demonstration prototype wave power device, located on the Isle of Islay off the west coast of Scotland, was completed during November 1988.  The turbine generator was installed during December 1990.  After initial testing the station will supply power to the main electrical grid system.  During the preceding year the pneumatic power output was monitored.  Although there is considerable scope for improving the system, the initial results are very encouraging and the prototype should be capable of producing electricity for about 6 to 7 pence per kilowatt hour.  Initial design studies, based on the experience gained from the Islay project, indicate that larger systems could produce electricity at half this price during the capital payback period of 25 years, reducing to 2 pence per kilowatt hour for the remaining life of the structure.

 

Use of the BAT Probe for Shallow Gas Detection

NS Rad and T Lunne

Abstract: A new offshore tool has been developed which is capable of detecting and quantifying the content of gas either in free or dissolved form.  The tool is deployed in a similar fashion to other in situ tools (eg, the cone penetrometer) and is used to take samples of pore fluid (including any gas) at selected depths in the soil profile.  The pore fluid samples are analysed by gas chromatography onboard the survey vessel and the gas content can be determined within 15–20 minutes.  The trend of dissolved gas content with depth may be used to predict gas pockets ahead of the drill bit during soil investigation or drilling operations.  Thus blowouts may be prevented.  In addition, the in situ amount of gas in the soil can be determined.  Laboratory samples can then be restored to the in situ gas content as well as in situ stress conditions, and tests can be run to obtain correct soil parameters.  The article concludes with case histories from five soil investigations.

 

Remote Control Umbilicals for Subsea Control Systems

CJ Curran

 

Towed Production Systems – Further Developments in  Design and Installation

E Rooduyn

Abstract: In 1980 the first flowline bundles were fabricated onshore and towed to the field using the controlled depth tow method (CDTM).  In the past ten years the CDTM and other tow methods have become established and accepted techniques for the further development of satellite fields.  A logical new development is the full integration of the production system and flowline bundle as a towed production system (TPS), which avoids separate installation of the production system.  In particular, subsea hook–up and connection to the flowlines and umbilicals are no longer required.  The towed production system will be fabricated and fully tested onshore, before being towed offshore, securing maximum reliability.  The system offers maximum design flexibility and can be fine–tuned to suit a particular field development plan.  Substantial cost savings of up to 20% can be made with TPS and it can be designed for water depths up to 2000m.  The bundle can contain all types of flowlines and umbilicals, whereas the production system can contain manifolding, templates, emergency shutdown values and/or processing facilities.  The production system can be at either end of the bundles or at one or more intermediate locations.  This paper will review various concepts and examples ranging from simple lateral entry, integrated manifolding, and integrated manifolding combined with drilling slots, to the complex fully integrated production system.  The other end of the bundle can be fully integrated with the riser bases, direct pull–in structures to can even be an onshore facility.  Experience on projects applying various options of the towed production system will be highlighted, as well as further achievements in the design for deepwater applications.

Meeting Reports

Geotechnical Implications of Shallow Gas—Report on Half–day Seminar

SJ Wheeler

 

Integrated Approaches to Lower Cost Subsea Systems—Report on Conference

S Thurley

Book Reviews

Proceedings of the 9th International Conference on Offshore Mechanical and Arctic Engineering 1990 – Volume 1 Part A

Reviewed by Professor JR Chaplin

Proceedings of the 9th International Conference on Offshore Mechanical and Arctic Engineering 1990 – Volume 1 Part B

Reviewed by JA Witz

Engineering For Offshore Fish Farming, Proceedings of the Conference, organised by the Institution of Civil Engineers, 17–18 October 1990

Reviewed by RST Ferro

Underwater Technology Vol 17 No 3

Autumn 1991

A Personal View

C Lafferty

Technical Papers

The Performance and Potential Application to Diving Operations of a Regenerative Heat Exchanger in Air and Heliox to 31 Bar

A McLean, L Virr and R Hughes

Abstract: Respiratory heat loss is a major problem for divers in a hyperbaric environment.  A passive, regenerative heat exchanger may be used to reduce such heat loss, increasing the safety and comfort of the diver in both normal and emergency situations.  The development of sophisticated hyperbaric breathing simulators has allowed the gas temperature and flow characteristics of a diver’s respiratory system to be reproduced under simulated diving conditions with various workloads.  This proves an invaluable tool for obtaining performance data on potential systems and equipment.  Useful data have been obtained on the efficiency of a simple regenerator matrix, composed of stacked nylon mesh discs, under simulated operational conditions in air and heliox to 31 bar pressure.  Data directly pertinent to a diving scenario, based upon physiological and other relevant constraints, are given.  The role of such a regenerator as an integral part of an overall diver thermal protection system is discussed with reference to reduced diver heat loss, extended mission times and the possible benefits in terms of operating costs and logistics.

 

The Influence of Shallow Gas on the Geotechnical Properties of Fine–Grained Sediments

S Wheeler, G C Sills, WK Sham, SM Duffy and DG Boden

Abstract: In fine–grained sediments, undissolved gas occurs in the form of discrete gas bubbles that are much larger than the normal void spaces.  Results from a programme of experimental research indicate that these gas bubbles affect the geotechnical properties of the sediments, with important consequences for the performance of offshore foundations.  In particular, the undrained shear strength and undrained elastic moduli can be significantly reduced by the presence of gas bubbles, resulting in a decrease in the short–term ultimate load capacity of a foundation and an increase in the immediate settlement.

 

Real–Time Photogrammetry – A Technique for Today or Tomorrow?

J Turner, DJ Yule and J Zanre

Abstract: Photogrammetry has been in regular use since 1980 to produce three dimensional measurements underwater for a variety of tasks.  This paper will briefly summarise the history of the technique, from its inspection–orientated origins to the latest engineering–related, deepwater, ROV surveys, in order to analyse the strengths and weaknesses of the technique.  This analysis will introduce the technological improvements, leading to the satisfaction of market demands, that can be made possible with advancing technology.  The development of Real–Time Photogrammetry, from the feasibility study to offshore trials, will then be introduced, emphasising the enormous possibilities of the technique and its component technologies: electronic still imaging, digital image data transmission and storage, real time and still stereo viewing, and near instant three dimensional measurements of complex objects.  The by–products of the development will also be introduced, which include total electronic reporting systems and the database–controlled replay of visual data within a networked computer system, with suggestions as to how these could influence structural and pipeline inspection, as well as engineering surveys in today’s, as well as tomorrow’s, world.

 

The Impact of AP1 17 Standards on the International Subsea Industry

DA Price

Abstract: Against a background of increasing centralisation of standards in Europe to make ‘European Norms’ (ENs), the role of the Exploration and Production Forum in advising the American Petroleum Institute (API) on the international application of API standards will be described in this article.  The evolving international significance of API standards is a factor in the issue of new or updated API specifications, which more accurately reflect the functional standards required by oil companies for their operations worldwide.  API 17D – Subsea Trees and Wellheads is a good example of the results of this process.  API 17D can, and should, be regarded as an adequate basis for procurement of subsea hardware, needing only a minimum of additional field–specific data to fully describe the functional requirements.  Using 17D as a model, and building on a recent successful project which gathered information on the reliability of subsea umbilicals, a Joint Industry Project has commenced to prepare the basic material from which API 17E – Subsea Umbilicals will be developed.

Meeting Reports

Caribbean Oceanographic Resources Exploration (CORE)—Report on Conference D Seddon Oilfield Development in Environmentally Sensitive Areas—Report on Seminar JG Ingram Introduction to Subsea Processing and Separation—Report on Meeting

WG Edwards

Book Reviews

Modeling Marine Systems, Ed. AM Davis

Reviewed by D Pugh

 

Managing Troubled Waters: The Role of Marine Environmental Monitoring, by National Research Council

Reviewed by JR Turner

Underwater Technology Vol 17 No 4

Winter 1991

A Personal View

The Coastal Zone: Terra Incognita? Mare Incognitum?

PJ Cook

Technical Papers

The Ocean’s Role in Climate – Processes and Technology

G Griffiths

Abstract: The ocean is central to the climate system of the Earth.  The Intergovernmental Panel on Climate Change, in their Scientific Assessment (Ref 1) described the ocean as influencing the timing and patterns of climate change.  Global ocean processes mix surface waters down into the interior of the ocean, locking away the incident solar energy, and slowing the atmospheric warming.  Regional patterns of climate changes will be influenced by the global scale ocean circulation.  Ocean physics and ocean biology, from planktonic scale (10–5 m) to that of the global scale thermohaline circulation (108m), are therefore key elements in the Earth’s climate system.  Existing observation practices and methods for the ocean are far from sufficient to provide data at the spatial and temporal resolution needed for climate monitoring and forecasting.  Only through advances in technology can the data be acquired.  Innovative sensors using acoustics and optics, autonomous submersibles, and in situ long term moored and drifting instruments equipped with data telemetry will be needed to monitor the ocean.

 

An Automated System for Weld Sampling and Defect Removal

D Clifton, MB Barker, RW Gusthart and JA McGeough

Abstract: The sampling of defects from a wide range of structures is regularly carried out for metallurgical examination.  However, the present system of grinding is found to be somewhat cumbersome and lacking in precision.  This paper describes the successful application of electrochemical machining for removal of defects from a wide range of weld geometries.  The control strategy adopted has led to the construction of equipment which not only produces machined surfaces requiring little or no preparation prior to repair, but also enables the defect or sample to be removed without damaging the parent structure.  Furthermore, the forceless nature and portability of the equipment would be particularly beneficial when used in a subsea environment.

The Influence of Shallow Gas on Geotechnical Site Investigation MR Horsnell Abstract:

Offshore soils are normally considered as a two phase material, ie, soil and water.  Under certain geological and geochemical conditions, soils can be encountered which are three phase, ie, soil/water/gas.  Shallow gas can be either petrogenic or biogenic and, dependent upon the degree of concentration and pressure, may govern many aspects of subsequent development activities at an offshore location.  This paper describes the influence of such shallow gas on one such activity, ie, geotechnical site investigation.

 

Subsea Repair of Concrete Weight Coating on 30″ North Sea Pipeline

E Reker and H Dahlerup Koch

Abstract: The 30″ North Sea gas pipeline in the Danish sector had suffered damage to the concrete weight coating and the corrosion coating at several points on an exposed part of the pipeline.  This occurred in the vicinity of a subsea valve assembly protection cover which is located approximately 1.5km from the Tyra gas platform.  The damage was probably caused by trawlboards and other heavy fishing gear.  In order to repair the damage, several methods of repair were considered to find one which could provide the necessary mechanical protection and the required weight, as well as giving adequate corrosion protection to the bare metal areas on the pipeline.  Furthermore, the method had to be applicable with minimal pipe surface cleaning.  After thorough investigations of the alternatives, the choice was made to carry out the repair using a new product called Densit®.  Densit is a composite material made by mixing Portland cement with micro–silica and a superplasticiser.  The ultrafine micro–silica particles fill the voids between the cement grains, thus creating an extremely dense paste.  This high density gives the material a number of unique properties.  It can be pumped through long lengths of hoses, and will cure under water.  The paper describes the design, planning and repair work carried out on two sections covering the complete surface of 18m and 20m of the above mentioned pipeline, as well as the results of laboratory examination of the ability of the product to provide corrosion protection to bare metal areas.

 

Wellhead Protection at Gannet

B D Heal and L Naughton

Abstract: This paper describes the Gannet development and its extensive use of subsea production facilities.  It describes the consultations carried out with other seabed users, and the agreement on a protection philosophy for subsea wells using a combination of fishing exclusion zones and non–exclusion zones with ‘over–trawlable’ structures.  The functional requirements and design loads used for detailed design are outlined.  The paper also describes the structures and piles and how they meet the functional requirements.  It covers the model testing carried out to assess ‘over–trawlability’, and the changes that were made as a result.  The installation of the structures is also briefly described.

Meeting Reports

Scottish Mariculture—Report on Seminar AJ Smith A Review of Progress in Offshore Safety and Reliability Models (OMAE 90)

RG Tickell

Book Review

Underwater Electroacoustic Transducers, by D Stansfield

Reviewed by B Woodward

Underwater Technology Vol 16 No 1

Spring 1990

A Personal View

P Stibbons

Technical Papers

New Developments in the Inspection and Monitoring of Flexible Pipes

JM Neffgen

Abstract: In the past ten years flexible pipe has been increasingly utilised in floating production and marginal field developments, especially to accommodate dynamic motions and large pipeline misalignments.  The pipeline industry has begun to recognise the importance of this new technology and should therefore apply a better engineered approach towards assessing ultimate performance capability.  Due to the fact that flexible pipe is made from a composite, nonhomogeneous material construction, new developments with regard to inspection methodology and monitoring techniques are required in order to obtain meaningful data about the presence and significance of defects in the pipe, and relate these to overall integrity.  This paper outlines the prerequisites for the formulation of an inspection programme, and highlights progress in the development of state–of–the–art NDT methods.

 

Geological Investigations for Marine Aggregates Offshore East Anglia

DJ Harrison and DA Ardus

Abstract:  In the south–east of England, 25% of the demand for raw materials for the construction industry is met from marine dredged sand and gravel.  Future supplies of marine dredged aggregates will depend on the identification of resources and the licensing of reserves of marine sand and gravel.  Whereas a significant database exists on the extent of land resources of sand and gravel, information on the distribution, qualify and quantity of marine aggregate resources is sparse.  In recognition of the importance of marine aggregate supplies, the Crown Estate and the Department of the Environment have recently commissioned the BGS to undertake a programme of research designed to investigate offshore resources of sand and gravel.  In 1986 a desk study was undertaken to assess existing information relevant to marine aggregate resources in the southern North Sea.  Subsequently, an area off East Anglia was surveyed using geophysical techniques calibrated, in 1987, by sampling and coring.  The work has established the stratigraphy and lithology of the Holocene and underlying Pleistocene sediments and the distribution and potential quality of sand and gravel resources.  The determination of marine aggregate resource potential is demonstrably dependent on the development of an understanding of the regional geology of an area.  the purpose of this paper is to demonstrate the importance of geological studies in marine aggregate evaluation and to show how an understanding of the regional geology is fundamental to the efficient management and extraction of offshore sand and gravel deposits.

 

The Deep Ocean Option for Waste Disposal

Martin V Angel

Abstract:  The welcome announcement on 5 March 1990 by UK Minister for the Environment that shallow sea disposal of industrial wastes and sewage sludge is to cease by 1998, and similar disposal of raw sewage at some future date, starts the race to find acceptable alternatives.  These alternatives will have to be both economically affordable and environmentally friendly.  All the options presently adopted in the UK and on mainland Europe carry environmental penalties; the technologies needed for effective recycling are yet to be developed.  Deed oceans of abyssal depths 3000–6000m cover half the Earth’s surface; they are yet to be utilised by Man.  The increasing pressure on terrestrial resources created by population growth and industrialisation will soon force us to utilise the oceans more.

Disposal of large–bulk low–toxicity wastes direct onto the sea–bed at abyssal depths offers an option which promises to be environmentally safe and relatively inexpensive.  The acceptability of adopting such procedures is discussed and some criteria of acceptability suggested.  Existing knowledge of the deep ocean is sufficient to suggest that a pilot scheme could be started without risk.  However, monitoring would be necessary to ensure the method continues to comply with the criteria suggested.  Techniques for monitoring abyssal depths are now available.

 

A Novel Development in SONAR Beamforming

Dr IG Bryden and Dr AKT Lee

Abstract: This paper outlines research conducted into the development of a novel form of acoustic beamforming.  The principles of operation of the system are discussed and some future applications suggested.

 

A System to Measure the in situ Physical Properties of Marine Sediments

DG Huws

Abstract: A field proven seafloor system has been developed at UCNW, Bangor, enabling in situ geophysical measurements of bottom sediments to be taken.  The system comprises a seafloor sledge, on which are mounted two seismic sources and an electrical resistivity pad.  Attached to the rear of the sledge are six, equispaced, two–component, gimbal–mounted seismometers.  Ship deployment techniques have proved very important and these have been modified to maximise survey efficiency.  Results yielded include shear wave velocity, compressional wave velocity and apparent formation factor.  Given these data, it is possible to infer sediment dynamic elastic moduli and porosity values of the in situ seafloor material.  The commercial viability of this system is that it will enable the user to map out the spatial distribution of these parameters over a given site relatively quickly and economically.

 

The Supply and Training of Manpower for the Marine and Offshore Industries in the 1990s

M Staunton–Lambert

Abstract:  The recruitment and training of skilled manpower will represent a serious challenge to the marine and offshore industry in the 1990s.  Even if companies can recruit the type and numbers of skilled people they want, will they be able to keep them?

Workshop/Seminar Reports

Technology and the BRIDGE Initiative

Dt NGT Fannin

 

Tugs and Towage

D Maffin, J Kennedy and P Vallee

 

Underwater Salvage ― Location and Recovery

G Darling

Underwater Technology Vol 16 No 2

Summer 1990

A Personal View

JE Sloggett

Report Reviews

Marine Science and Technology in the UK ― A Report to Government from the Co–ordinating Committee on Marine Science and Technology (CCMST)

Gordon Senior CBE

Letters

A response to the review of his book ‘Remotely Operated Vehicles − Technologies, Applications and Markets’ in the SUT Journal Vol. 16

Paul Cunningham

Technical Papers

Snorre ― Subsea Control System

BD Boles and JA Johansen

Abstract: Saga Petroleum a.s. will utilize both tension leg platform and subsea production technologies for phased development of the Snorre field.  This paper describes the control system for the Snorre subsea production system.  General system requirements and equipment configuration of the subsea control system are presented, along with the current work status and an outline of future testing and installation activities.

 

Engineer Implications of Using Hydrogen as a Breathing Gas Constituent for Deep Diving

LE Virr

Abstract: The advantages of using hydrogen as a breathing gas constituent, namely low breathing resistance, anti–HPNS effect when mixed in suitable proportions with helium, availability and low cost are discussed.  The high flammability of hydrogen, its major disadvantage, is addressed in some detail and intrinsic safety curves for H2/air and H2/02 are presented, though the point is made that H2/air mixtures suitable for breathing at depths beyond, certainly, 200m are non–flammable because of the small percentage of oxygen present.  Other relatively minor disadvantages of hydrogen, namely greater respiratory heat loss and speech distortion compared with helium, are also considered and it is shown that the same problems exist with hydrogen as for helium but to a greater degree, calling for more precise control of breathing gas temperature and more exacting requirements for the design of communication system.  It is concluded that an intrinsically safe electrical system can be designed for communication and sensor applications for use in H2/02 mixtures, and that for many applications, optics technology offers a safe and viable alternative to electricity.

 

Sensing in Hostile Borehole Environments

PF Worthington

Abstract:  Downhole measurements provide a continuous record of sub–seabed characteristics and phenomena at in situ conditions.  The operating limits of most commercial facilities are around 170–200°C, with some tools being rated up to 260°C.  For high–temperature environments, quantified as 350–400°C, there are no commercial measurement facilities and only a few specialised tools exist.

In order to redress this situation, and thereby to prepare to meet the scientific challenges of the ‘nineties, initiatives are underway to develop operational high–temperature logging tools.  The magnitude and nature of this task are reviewed and realistic targets identified for the future availability of technology.  Important issues concern the relationship of these targets to drilling and coring practices: it is not feasible to develop a scenario for downhole measurements in isolation from the practicalities of borehole conditions and calibration needs.

In the past, scientific drilling programmes have largely relied upon oil industry technology for their downhole measurement capabilities.  This relationship is now changing.  During the ‘nineties it is expected that scientific drilling projects will provide the impetus for technological developments and advances in the ‘state of the art’ of borehole sensing.

 

‘ROHP’, A Remote Operated Hoisted (Underwater Inspection) Platform

HGH ten Hoopen and C van den Hil

Abstract:  The ROHP is a multipurpose underwater inspection system developed by Rijkswaterstaat North Sea Directorate and Seatec Underwater Systems in the Netherlands  The ROHP is specially designed for the Southern North Sea and other areas with severe underwater conditions, namely high current velocities and bad visibility.  The advanced techniques and controls allow the vehicle to operate as a very unique inspection and work platform.  Due to the big pay–load, an unlimited variety of tools and sensors can be fitted to execute any tasks within the capabilities of the system.  Built to the high demands of the working areas and their hostile environments, the ROHP system with its outstanding capabilities offers an attractive alternative to existing underwater systems.

Meeting Reports

Subsea Control and Data Acquisition ― Technology and Experience

I Ball, M Fabbri and M Murawiecki

 

Underwater Association Annual Symposium

Debby Seddon and Dr T Hennessy

 

Save Energy Devices

LJ Duckers

Underwater Technology Vol 16 No 3

Autumn 1990

A Personal View

Dr Harold Hughes

Technical Papers

Collecting and Observing Particles in the Ocean: Why and How

PP Newton

Abstract: Substances are transported through the oceans by a wide range of biological, chemical and physical processes.  Their mode and rate of transport, as well as their ultimate fate, is largely controlled by their partitioning between particulate and dissolved phases.  Such transport mechanisms are presently not well understood.  Studies of oceanic particles are generally limited by their low concentrations, necessitating the development of specialised instrumentation to enable their collection and observation whilst maintaining their integrity.  In this article, state–of–the–art instrumental methods are briefly reviewed, focusing on the principles, advantages, disadvantages and problems of each technique from a technological viewpoint; present studies in the N.E. Atlantic, as part of the Biogeochemical Ocean Flux Study, are discussed.

 

Comparison of Shear Moduli from Offshore Seismic Cone Tests and Resonant Column and Piezoceramic Bender Element Laboratory Tests

G de Lange, CH Rawlings and N Willet

Abstract:  The shear modulus (G) of a soil is a measure of its stiffness and is therefore a key soil parameter in many different geotechnical engineering applications where foundation soil–structure interaction is important.  The seismic cone is a new in situ device for the measurement of the low strain shear modulus, developed by Fugro–McClelland as an offshore site investigation technique that overcomes some of the disadvantages of site accessibility and deployment of cross–hole seismic testing, combining traditional cone penetrometer testing with geophysical property measurement in one tool.  A brief description of the development history of the seismic piezocone testing system is given.  The different modes of operation in offshore site investigations are outlined.  Laboratory tests which measure the shear modulus are the conventional low strain resonant column test and the piezoceramic bender element test as recently improved by the Norwegian Geotechnical Institute.  A brief description of these tests and the test conditions are given.  Results from the seismic cone, resonant column and piezoceramic bender element tests for a number of Norwegian North Sea sites in Quaternary soils are presented and the derived soil stiffnesses are compared.  It is concluded that the seismic cone test, when used in conjunction with resonant column and piezoceramic bender element tests, is a valuable new tool for accurate in situ seismic shear modulus testing in offshore site investigations.  Current research is focused on the integration of the in situ measurements into high resolution seismic surveys to enable quantitative analysis of the latter into geotechnical parameters.

 

The Central Brae Project Retrofit Riser Installation

R Farrow and N Cresswell

Abstract:  The Brae field, discovered in 1975, is located in block 16/7 about 42 nautical miles north west of the Occidental Piper field and 70 nautical miles north of the BP Forties field.  The Brae ‘A’ platform was installed in 1982.  First oil was exported in July 1983 and production rates of around 100,000 barrels per day have been achieved.  The Brae ‘B’ platform was installed in 1987 and first oil was achieved in April 1988.  The Brae ‘A’ and Brae ‘B’ platforms are connected to each other by a twin 18″ pipeline system.  From the Brae ‘B’ platform, oil is transported to Brae ‘A’ where it is combined with the processed Brae ‘A’ oil.  The combined oil is then transported via the 30″ submarine pipeline to BP’s Forties Charlie platform where it enters into BP’s 32″ submarine pipeline for transportation to the processing facility at Kinneil.  The Central Brae project is Marathon’s first sub sea development and has been managed by a dedicated team of engineers and support staff drawn from their respective discipline departments.  The Central Brae project is Marathon’s first sub sea development and has been managed by a dedicated team of engineers and support staff drawn from their respective discipline departments.  A major part of the project comprises the 6″ production, 4″ service, and 10″ water injection pipelines, the retrofit caisson riser and the chemical and control umbilicals.  Together these represent over a third of the total development  cost.  The development plan for Central Brae wa approved by the Brae group participants in October 1987, and Department of Energy approval was received in 1988.  This paper presents a general description of the project together with a more detailed account of the design, fabrication and installation of the retrofit caisson bundled rise system.

 

Multiple Product OTEC Project in Taiwan

Paul C Yuen, Shih–Chi Wang and Don E Lennard

Abstract:  Because of favourable geographic location and other reasons relating to energy utilization characteristics and technology development, the R.O.C. Energy Commission conceived and promoted a ‘multiple product Ocean Thermal Energy Conversion (OTEC)’ project in 1988 and prepared a development plan for this project in 1989.  The development plan outlined the steps necessary for the commercialization of OTEC plants in Taiwan.  Designing, building and testing of a 5MWe (net) pilot plant and an associated mariculture facility are the major elements proposed in the development plan.  This paper presents the scope and major objectives of the project, and describes the essential elements and tasks proposed in the development plan.  Baseline design, technical considerations, management plan, project schedule and follow up development are also discussed.

Meeting Reports

First French Conference Acoustics

Dr B Woodward

 

Safety in Offshore Drilling ― The Role of Shallow Gas Surveys

CD Green

 

Advances in Subsea Pipeline Engineering and Technology ASPECT ’90

Dr CP Ellinas

Book Reviews

Seakeeping: Ship behaviour in rough weather

Reviewed by Herbert Pearcey

 

Underwater Signal and Data Processing

Reviewed by B Woodward

 

A Pictorial History of Diving

Reviewed by Sir John Rawlins

Underwater Technology Vol 16 No 4

Winter 1990

A Personal View

Brian McCartney

Technical Papers

A Concept Exploration Model for Initial Design of Autonomous Underwater Vehicles

JR MacGregor, AC Brown, DD Blane

Abstract: A concept exploration model is an automated approach to producing balanced vehicle solutions.  This paper describes the structure of such a computer model designed for the synthesis of simple Autonomous Underwater Vehicles.  The required input data and the options available with the program are described .  The techniques employed to calculate the weights and volumes of all the component subsystems are outlined and the means of ensuring design balance is explained.  Sample program output is provided, together with typical results which illustrate the ability of the model to quantify the effects of altered design requirements on vehicle characteristics.

 

Environment Forces in Relation to Structure Design or Assessment − PART 1

Dr JH Vugts

Abstract: Environmental forces are discussed in connection with the overall problem of the design of new, or the assessment of existing, structures.  It is essential to see environmental forces in this broader context and to integrate them with all the other aspects involved.  ‘Structures’ refers here in general to all types and applications − floating and bottom supported, compliant and fixed.  Where a discussion is aimed at a particular group, this is specifically identified, such as in the case of fixed space frame structures, to which special attention is paid.

Offshore structures engineering has in many respects become a mature discipline.  However, further developments are still necessary to fully benefit from the large increase in knowledge after so many years of research and development efforts, as well as from the accumulated experience with real platforms offshore.  This is in the best interest of safety, the extended use of existing structures and the more economical design of new ones.  The next major step is sometimes suggested to be structural reliability analysis, which would require both the loading and the structural models (describing generally elastic as well as rigid body properties) to become probabilistic.  In general this is not yet considered to be within reach and is cautioned against.  However, the underlying principle is warmly supported and the introduction of concepts which are firmly based on reliability analysis methods is a realistic goal to aim for.  It is suggested that significant progress in this direction can be made by using loading models which incorporate the probabilistic features which reflect the random waive environment in a realistic manner, in combination with (nearly) deterministic structural models.  Where such loading models are not already current practice, they should be introduced forthwith.  This demands a truthful representation of random wave kinematics and realistic force coefficients, including the drag and inertia coefficients in Morison’s equation for fixed structures.  A perceived way forward is described and proposals are made on how to achieve this.

 

Evaluation of Marine Mineral Resources in the Exclusive Economic Zones (EEZs) of British Commonwealth Territories in the Pacific

DS Cronan, R Hodgkinson and S Miller

Abstract: Studies on polymetallic manganese nodules in some South Pacific EEZs show that nickel (Ni) and copper (Cu) reach their greatest combined abundances of over 2% between 2−8°S.  Cobalt (Co) reaches its greatest abundance of 0.6% south of 8°S.  Nodule abundances are greatest in the Co–rich are giving highest metal quantities per sq metre there, particularly of Co.  In Co–rich crusts, Co averages about 0.7%.  Much greater quantifies of valuable metals in the nodules than in the crusts suggest that the nodules represent a greater future metal resource than the crusts in the EEZs studied, even for Co.  Polymetallic sulphides consist of sulphides of iron (Fe), copper (Cu) and zinc (Zn) formed by hydrothermal processes, and occur in the EEZs of Fiji, Tonga and Papua New Guinea.  Related deposits occur in the EEZ of Pitcairn Island.  Enrichments of gold and silver are common in the deposits.

 

The Acoustic Properties of Marine Sediments

C McCann and DM McCann

Abstract:  Advances in instrumentation and computer technology now make it possible to measure the acoustic properties of marine sediments in situ and in real time.  It is thus timely to reassess both the state of our knowledge of the physical properties of these sediments and the possibility of using seismic measurements to routinely estimate porosity, permeability, etc.  In this paper the statistical relationship between compressional velocity and porosity published by Akal is critically discussed.  Experimental data relating acoustic attenuation to grain size are presented for unconsolidated sediments and compared with data for sedimentary rocks.  It is demonstrated that there is no extant theory which can account for these experimental data.

Technical Briefing

Deep Sea Oceanography in the 1990s

CP Summerhayes

 

Marine Science and Technology (MAST) Research Programme

MJ Staunton–Lambert

Meeting Reports

Advances in Subsea Cables

P Dick

 

Methane in Marine Sediments

A Judd

 

Environmental Forces on Offshore Structures and Their Prediction

Prof. J Chaplin

Book Reviews

Offshore Engineering, Volume 7

Reviewed by Dr RS Langley

 

Requiem for a Diver

Reviewed by J Hendrick