Search our collections

Problems of drilling in argillaceous laminated shales (ranging from clay-rich gumbo to highly cemented siltstones) are discussed with particular attention to borehole instability arising from insufficient hydrostatic support on the borehole wall. The appropriate choice of drilling fluid to overcome these difficulties includes consideration of: Oil Based Muds (OBM); Water Based Muds (WBM) with and without the addition of salt lime potassium gums; and the more recently developed Silicate Based Muds (SBM). Case studies in which sodium chloride/sodium silicate muds were used to drill the upper gumbo sections of a well in the Gulf of Mexico and a cretaceous chalk/cromer knoll/triassic claystone sequence in the southern North Sea are reported.

The move towards more-electric and all-electric power platforms on naval vessels has brought with it a number of unique technical challenges. One such challenge is the effective modelling and computer simulation of a fully integrated electro-mechanical system containing prime movers electrical generators electrical distribution system power electronic drives and electrical motors. There is currently no single simulation system environment which can effectively address a fully integrated more-electric system. This paper address some of the issues mentioned here through a case study of a large-scale naval electric power system ranging from steady-state simulation of the bulk electrical power system through to detailed simulation of a variable-frequency power electronic drive.

A simulation model for the overall ship propulsion plant system has been extended by an additional model for the PI governor of the propulsion diesel engine. Detailed steady state simulations at full load and at various part loads were performed for the validation of the accuracy of the predicted results. Transient simulations of the complete propulsion system with: changes in engine speed setpoint considering PI control and propeller law load; and constant speed set point using experimentally derived varying load and PI control were also performed. Simulation tests were performed for a 9K90MC-VI MAN B&W marine diesel engine fitted on a ship of Hapag Lloyd Container Lines. The transient simulation with the changes in engine speed setpoint considering PI control and propeller law load was used in order to fine tune the simulated PI governor. The same governor was applied to a case simulating powerplant operation in rough seas and was found to safely control the engine speed.

The slope stability at Ormen Lange gas field is considered. This is a major concern for field development work. The area under consideration is large and has been extensively mapped with 2D and 3D seismic profiling. The number of geotechnical borings is limited and integration of geological geophysical and geotechnical information was required to develop a geotechnical model of the area. Stability analyses have been carried out for critical sections of the headwalls. These involved long-term drained analyses under gravity loading and undrained analyses considering the effects of earthquake-loading and possible influence from field installations like rockfill supports for pipelines and anchors. The focus is on explanation of slide mechanisms involved in the Storegga slide and comparison of the stress-strain-strength conditions in the headwall at the time of the slide and today. Since work is still ongoing and also under review and the conclusions presented are considered to be preliminary.

The sloshing in LNG tanks has attracted attention over recent years mainly due to the market developments and changes in the design and operation of LNG ships. In designing LNG insulation Mark 3 systems it is essential to estimate the stress level that can occur in the structures due to the extreme loading such as sloshing loading which can be local high and transient. The effect of the flexibility of the stiffened panel and impact-loading patch on the stresses level of insulation system is investigated. The results are presented in the form of the dynamic amplification factor. For impulse type sloshing pressures relative to the steel plate the steel plate behaves as a rigid support resulting in vertical responses that exhibit a limited variation over the area.

Symp held in London 7 - 9 March 1978 Papers are Operational requirements and choice of craft The offshore tapestry and the 200 mile exclusive economic zone Offshore capabilities required to meet governments increased responsibilities and tasks Seakeeping and the small warship Small warships in the Royal Navy and the Fishery Protection Task A hydrofoil fisheries patrol vessel for the United Kingdom The amphibious hovercraft as a warship General design aspects of small fast warships Planing hull feasibility model Its role in improving patrol craft design An experimental investigation on the roll stability of a semi displacement craft at forward speed Structural design and materials for small warships A navigation and action information system for offshore task forces Weapon electronics in small fast warships and security vessels Arming the light naval craft Air defence of small fast warships The compact gas turbine for powering small fast ships The diesel engine for powering high speed craft Controllable pitch propellers for small fast warships and patrol craft

Varied observations over Oregon's continental shelf illustrate the beauty and complexity of geophysical flows in coastal waters. Rapid creative and sometimes fortuitous sampling from ships and moorings has allowed detailed looks at boundary layer processes internal waves and coastal currents including how they interact. These processes drive turbulence and mixing in shallow coastal waters and encourage rapid biological responses yet are poorly understood and parameterized. The work presented in this article represents examples of efforts by many physical oceanographers to quantify small-scale coastal-mixing processes so that their effects might be included in regional circulation models. After some introductory information new perspectives on cross-shelf structure are outlined. Next a look is taken at the bottom Eckman layer followed by nonlinear internal waves form drag the role of internal waves in shear-enhancement of the coastal jet and consequences.

An improved distribution of multi-disciplinary observatories will bring about improved investigations of the Earth's structure and dynamics. SN-1 (submarine network-1) the first node of the Italian seafloor observatory network was successfully deployed in October 2002 and recovered in May 2003. During this time it carried out a 130-day mission collecting high quality seismic gravimetric and environmental data. It will eventually be connected to an underwater cable of INFN by a junction box. In this way the observatory will be powered from on land and will provide real-time data. The connection will make SN-1 the first European seafloor real-time observatory.

Mobil has two sour gas fields in Alabama: Mary Ann and Mobile OCS Block 823. The hydrogen sulphide content of Mary Ann is about 5 mol% while that of Mobile 823 is about 150 ppm. The different development methods chosen for the fields are evaluated. The design for Mary Ann included offshore cooling separation and dehydration of the gas to allow carbon steel materials to be used for the surface and pipeline components. Silica gel was chosen for the dehydration process. A corrosion inhibition system was employed to protect the carbon steel equipment upstream and to dissolve any sulphur deposits on the platform. Glycol was chosen for Mobile 823's dehydration process. Because Mobile 823 was more remote and the hydrogen sulphide concentration was lower it was possible to flare the low-pressure off-gases eliminating the need for compression requirements. The operating history of each field is described and a cost comparison is made. The conclusions highlight the selection criteria for dehydration.

With the introduction of welding to shipbuilding it was necessary to control the out-of-plane distortions resulting after the welded plates cooled. The post-welded behaviour can have a critical influence on the strength of the steel structure. Initial research has lead to over 15 critical parameters which have to be taken into account when estimating the maximum post-welded deflection. This large number of parameters makes it difficult to introduce a methodology to account for all the critical weld parameters. In the USSR one approach was to develop an integrated framework to include the critical welding parameters. From this standpoint of ship production it is useful to understand this Soviet approach and to see examples of its use. The Soviet procedure for calculation of deflection due to butt welding is introduced and the graphical aids used in this procedure are presented together with a worked example using this procedure for a butt welded plate. This approach can be used in developmental efforts to establish a practical and reliable code for post-welded deformation estimation.

In general terms spatial memory is the ability to acquire and retain associations of environmental features in order to allow an organism to navigate effectively through space. Animals of various species use memory for spatial locations every day in order to gain food or return home. Spatial memory for navigation is an area both of interest and of controversy. There are various theories postulated to try to explain spatial learning. The ability of rats is investigated to localise a reward hidden at specific distances within a simple directionally polarised environment. Pre-exposure to stimuli was hypothesised to promote learning. Deviant distance was used as a measure. Results suggested that pre-exposure has a positive effect on learning to acquire a task but once learning has been achieved the subjects are able to transfer their learning across different situations. The method and procedure are described and results presented and discussed.

For marine reserves to function as effective harvest refuges for exploited species the reserve must protect a substantial proportion of the population for an indefinite period of time. As most marine reserves are space-limited the buildup and equilibrium population sizes of mobile species will be influenced by the size and boundary conditions of the refuge. A logistic rate model is used to predict equilibrium population sizes in a marine harvest refuge based on species-specific dispersal dynamics and the spatial configuration of the refuge. After some introductory information a look is taken at the methods covering the equilibrium population model species' life histories/dispersal dynamics study site and model simulations. Next results are given. Performance of the model and assumptions of the model are each discussed in turn. Lastly conclusions are drawn.

This study examines a representative segment of ship collision investigation data based on the Safety Board’s marine investigation experience. The study identifies some leading causes of ship collisions and assesses the results of the Safety Board’s collision prevention recommendations made to Federal agencies and to maritime organisations. The study found that human error in the predominant cause of ship collisions and that specialised marine accident data which underscore the human factor in the cause of ship collisions need to be collected. Many of the Safety Board’s past recommendations aimed at improving steering gear reliability will be resolved as the Coast Guard implements US steering gear regulations in consonance with the current IMCO revisions to the 1974 SOLAS Convention. The Inland Navigational Rules Act of 1980 is responsive to many of the Safety Board’s recommendations to upgrade navigation rules. The study recommends additional measures to increase the effectiveness of the ship’s bridge watch team, and the collection of data concerning the human factors that contributes to the cause of ship collisions.

This paper focuses on how enhanced co-operation and interaction between the research operational and industrial communities can help break down boundaries to better leverage advancements in platforms and sensors and to more rapidly transition instrumentation from the bench top to real-world applications. Existing success stories in the research to operations transition can be used to help establish processes and mechanisms that will enable more rapid and efficient transition of technology through the "valley of death". This paper also discusses ways to help ensure that the oceanographic tools needed by the operational community are in the visionary pipeline of the research community.

This paper describes analytical investigations into springing effects on a high speed target passenger vessel. The work has been carried out using a finite element model of the whole ship. For this a typical loading condition has been set up. After the calculation of the Stillwater condition hydrodynamic added masses according to Lewiss theory have been defined. They have been used first for the computation of the natural frequencies of the modes shapes of interest. Afterwards wave load cases have been generated with respect to springing excitation. The springing calculation has been performed using the eigen-mode superposition method. The evaluation has been done with respect to global deformations vibration velocities as well as stresses in way of deck and bottom. The work has been carried out within the framework of the European research and development project FasdHTS.

The wave forcing and motion response of a small size TLP is investigated with particular focus on sum frequency effects related to the restrained modes heave roll and pitch. The fluid loading is obtained from a second order diffraction code and the stochastic response in a random sea state is estimated using a Volterra series representation of the response process. Although the wave loading is assumed to be a second order process the dynamical system as such is a damped linear mass-spring system. Numerical results are presented both in terms of power spectra and as extreme value predictions. In the latter case three different methods are compared and evaluated.

Simulation of dynamic effects in seastates is an extremely useful tool in designing ships with better seakeeping and increased on board safety. However an examination of existing intact stability rules shows that most ships gain sufficient safety level only due to the fact that damage stability requirements overrule intact criteria. The intact stability code is considered and whether the existing stability rules meet the requirements of today's fleet. It is concluded that the weather criterion is the limiting criterion which does not represent a reasonable safety level for these types of ships and allows ships to the designed with insufficient safety in rough weather. An approach is presented to demonstrate this.

In the offshore industry when a structure's tubular joints have to be reinforced due to last minute alteration and-or additional loading conditions there are several methods available such as reinforced joints by gusset internal ring stiffeners and doubler plates etc. A new method to reinforce X joints is presented which depends on the connection between the pontoon and the leg of a semi-submersible. As a part of the whole research this paper extends a numerical study to consider sleeve reinforced X-joints subject to compression load through systematic variation of the main geometric parameters. The load transferring mechanisms and failure modes of such joints with different sleeve size are investigated and compared to corresponding un-reinforced joints. Within the range of geometric parameters investigated the sleeve is observed to provide strength enhancement up to 200% for the corresponding un-reinforced joint. Design recommendations are provided for this joint type.

Intl Conf held at the University of Strathclyde on 16-18 June 1986 Papers are Stability requirements for semi-submersibles; a designer's veiwpoint A new theory and its application for stability criteria covering wave-induced tilt pheonomena in semi-submersibles Wind loads in floating offshore structures Inclining tests in service Mobile platform stability; the MOPS projects Semi-submersible research and its applications The study of a new procedure for assessing stability of ships and offshore structures Hydrodynamic model studies of the Ocean Ranger Marine Disaster A method of simultaneous measurement of directional wave spectra surface current and rig motion A data system for improving safety and availabilty of moored floating structures Transient motions of a semi-submersible after damage Dynamic positioning of a semi-submersible - resulting of scale model tests and computer simulations Propulsive aspects of dynamically positioned semi-submersibles

Acoustic remote sensing such as high-resolution multi-beam and sidescan sonar provides new means for in-situ observation of the seabed. Statistical characterisation of these high-resolution sonar images is important for a number of practical applications such as marine geology commercial fishing offshore oil prospecting and drilling. The proposed methods for the classification of sonar image in various types of seafloor (rocks mud sand etc.) are generally based on the BS (backscattered) intensity models. Several parametric families of probabilistic distribution functions have been suggested such as the Rayleigh distribution the K distribution the Weibull distribution. These first order statistics are not sufficient when the high-resolution sonar image involves textures. Here the analysis of texture characteristics in sonar images is further investigated for seabed characterisation issues. A general framework is proposed to evaluate similarities from co-occurrence statistics between seabed textures within sonar images.