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 ]ones
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
