Search our collections

The stress contributed by nutrients to the coral reef ecosystem is among many problems that may be resolved using the coastal ocean observing system (COOS) being developed by various institutions. Traditional nutrient sampling has been inadequate to resolve issues on episodic nutrient fluxes in reef regions due to temporal and spatial variability. This paper illustrates sampling strategy using COOS information to identify areas that need critical investigation. The area investigated is within the Puerto Rico subdomain. Nutrient profile results from the region indicate nitrate is undetectable in the upper 50m due to high biological consumption. The strong vertical fluctuation in the upper 50m demonstrates a high anomaly in temperature and salinity and a strong cross correlation signal. High chlorophyll a concentration corresponding to seasonal high nutrient influx coincides with higher precipitation accumulation rates and apparent riverine input from the Amazon and Orinoco rivers. Non-detectability of nutrients in the upper 50m is a reflection of poor sampling frequency or the absence of a highly sensitive nutrient analysis method to capture episodic events. Thus this paper explores the range of depths and concentrations that need to be critically investigated to determine nutrient fluxes nutrient sources and climatological factors that can affect nutrient delivery. It also provides insight into needed sampling rates and temporal and spatial domain choices. Finally it demonstrates a scientific reconnaissance for a field study that is now possible wit92313 Developments affecting classification requirements for high-speed craft R Curry ; D Novak ; B Menon et al.

Int Symp held in London on the 6-7 October 1986 Papers are Deepwater development - the operator's view Conceptual designs for deepwater salm-tanker systems Overview of deeper water mooring and anchoring systems Deepwater fixed steel platforms Development of an articulated launch barge Analysis of multiple barge - tow configurations for deepwater towers The design of deepwater jackets - dynamic effects The sea tower design of a deepwater jack-up mobile drilling/production unit Deepwater tension leg platform designs A 350m North Sea guyed tower - design and model testing Results of a joint semisubmersible/submersible wave drift force project Time domain simulations of couples responses of the moored buoy and the mooring lines in deep sea Predicting the strength of welded stiffened cylinders A strategy for establishing safety margins for floating platforms without weight penalties The dynamics of deep water pipelaying Assessment of station keeping capability of dynamically positioned vessels The behaviour of shallow draft offshore structures and service vessels in deeper water Innovative centre column semi's for deep water drilling An integrated approach to sub-sea intervention Experience with the design and installation of flexible pipes in deepwater developments

The majority of images being captured during oceanographic cruises are now digital (digital video and still image digital video) and it is now also the standard for AUVs (autonomous undersea vehicles) and ROVs (remotely operated vehicles). NOAA's (the National Oceanic and Atmospheric Administration) OE (Office of Ocean Exploration) has embarked on an effort to support a national strategy for exploring the ocean. An important part of this effort is the establishment of a data management capability for data sets that will be captured and made available for timely access by a variety of users. A large and important subset of these data is digital imagery and video. To support all data producing line offices the NOAA data management infrastructure must be expanded to accommodate these data as well as storing classifying processing archiving and providing users with innovative functional access. A methodology is introduced to enable video data and its associated metadata to be centrally managed and archived by a dedicated facility under the aegis of NOAA's Central Library. This effort is also consistent with the OE Data Management Strategy. Also discussed are the various digital video recording and editing techniques new data asset and media management techniques video data volume estimates and perceived video data management requirements. A series of visits that were carried out at several organisations to determine the extent of their involvement in video data management processes is also described and discussed.

Over the last ten years the numbr of floating assets has increased significantly for most operators. Many of these are in remote areas where a thoroughly planned and executed integrity management becomes all the more critical. Several of these fields are also in harsh environments with limited weather windows for routing maintenance. Some are in deepwater and have a very complex field architecture putting a higher demand on the integrity planning. Several of the assets especially the FPSO units are converted tankers with a long cumulative service life with its associated structural integrity challenges. All of these factors call for a well-planned integrity management system to ensure asset integrity and minimise production downtime. This paper provides a broad overview of a general framework adopted by EMPC (ExxonMobil Production Company) to promote and achieve performance excellence in asset integrity management across their global network of production operations. The general scope of the integrity and reliability management framework are discussed and also the organisation and the process by which the plan is executed the primary tools used including the RBI (risk-based inspection) plan the performance indicators used to measure the effectiveness of the program and the overall assessment and feedback used for continuous improvement of the system.

The problem of channel allocation in the frequency domain for underwater networks is considered. In this paper underwater networks with multiple sensors that report data to a single sink node are considered and the use of FDMA as a channel access method is advocated. In order to assign channels to users in an efficient way a number of allocation methods are compared that explicitly account for the underlying channel attenuation and noise model. A simpler case is inspected where the number of channels is equal to the number of users and a known algorithm is described which finds an optimal channel allocation in a max-min fair sense. It is then explored how the channel assignment problem changes. Finally suitable heuristic methods are proposed that allow effective solutions to be found without the complexity of an exhaustive exploration of all possible assignments. The results show that considerable advantages can be gained in terms of both minimum capacity and fairness even with heuristic methods with a proper choice of the assignment options. Future directions of work include the definition of a completely distributed MAC protocol based on the channel assignment ideas deployed here as well as the evaluation of the same ideas using realistic modulation formats.

Improper mixing of saline water and freshwater can result in stratification within the mouth of an estuary. A weir in front of the estuary mouth forms an entrapped saline wedge. When dissolved oxygen in the saline wedge goes beyond permissible limits and can endanger marine life. The anaerobic decomposition of organic matter at the bottom results in noxious environmental conditions. Similar problems are being faced at River Lagan bay in Northern Ireland. The use of propeller washes on a stratified flow system is discussed. These are applied to develop a technique to eliminate saltwater. Conductivity velocity and temperature at different points along the depth in a stratified flow system were observed in detail during this research. The testing procedure is described. Using the flume arrangement an artificial stratified condition close to natural conditions was produced and tested in the laboratory under different sets of experiments. Results and analysis are presented. These show that the propeller rotating at a higher speed was more effective at mixing stratified layers than the propeller rotating at a lower speed. Results also showed that an increase in propeller-tip clearance from the saltwater layer reduced the rate of erosion of saltwater. Conclusions are drawn.

An important element in the design of offshore structures is the estimation of extreme response statistics. For drag-dominated structures like jacket structures and jack-up structures there has not been available a simple accurate and fast method for estimating the extreme response values. There are in particular two different aspects of this problem that have caused this lack of easily accessible methods. Firstly there are the non-linear characteristics of the drag force itself. Secondly due to the fact that the structures considered are bottom-fixed there is the added complexity of the inundation effect. These two complications make simple approximations very hard to achieve if accurate results are required. The aim here is to develop a simple robust and general method which makes it possible to tackle all non-linear effects without any simplification beyond those implicit in any computer model. This is achieved by combining Monte Carlo simulations with a CPU timesaving extrapolation technique. The resulting method has the advantage that it ties up easily with present day design practice which to a large extent is based on providing design characteristic values using time domain simulations in combination with the environmental contour line principle. A brief explanation of the environmental contour line method is given later in the paper. A brute force approach used in design is also presented. The method proposed opens up the possibility to predict simply and efficiently long-term extreme response statistics which is an important issue for the desi88812

Model tests simulations and offshore measurements are complementary and need to be used in combination to come to a reliable evaluation of an offshore structure. As an example of such integrated use this paper presents the overall methodology as it has been developed to investigate the loading and response of the South Arne platform. After discussing the specific roles of model tests simulations and offshore (full-scale) measurements for the evaluation of offshore structures in general the paper applies this integrated methodology to the investigation of the loading and structural response of the South Arne platform with the aim of extending the platform's capabilities. The South Arne platform deck is supported by a combination of a large volume concrete GBS (gravity-based structure) and a slender steel lattice structure. This resulted in a unique project including the novel combination of small-scale tests of the complete structure (GBS and lattice tower) with large-scale component testing of parts of the lattice tower to limit and quantify scale effects on these slender members. The paper discusses the different phases (and scale) of model testing and also highlights the related FE (finite element) and diffraction calculations and offshore (full-scale) measurements.

The first series-built large marine diesel engine with electronically controlled common-rail injection entered service in September 2001. This Sulzer 6RT-flex58T-B engine is providing excellent service to the owner's satisfaction. The experience with this engine over the past 2.5 years is reported together with the relatively few problems encountered and the necessary modifications and improvements introduced so far. Meanwhile another five Sulzer RT-flex engines have entered service including four vessels powered with the new RT-flex60C type. The corresponding short experience is reported briefly. The mechanical and hydraulic functions of the RT-flex system are described as well as a detailed description of the process for development and industrialisation of the Sulzer RT-flex IV system for large-bore engines. The RT-flex common-rail system has a high degree of redundancy both intrinsic from the common-rail concept and built in the design. This redundancy and the related safety aspects are addressed. The redundancy is of particular merit for the larger vessels especially tankers for which the Sulzer RT-flex84T-D engine is being developed. A short insight is given to the extended endurance testing of the RT-flex components being an important contribution to success. Also included is an outlook to the RT-flex specific performance data and its benefits such as alternative tuning options and present and future possibilities of extended NOx emission reduction. This high potential for emission control is based on an unsurpassed degree of flexibility of the systX17952 The evolution of the TLP

A critical factor while drilling extended reach wells is the weight of the drill string used in the high inclination angle section of the well. One solution for this is the use of drill pipes made of alternative materials lighter than the conventional steel drill pipes for example titanium and aluminum. However titanium is avoided due to its high cost. Russia has recently manufactured drill pipes using aluminum alloys of the system Al-Cu-Mg similar to alloys 2024 used in airplanes. These pipes present a reasonable commercial cost. They are composed of an aluminum pipe and a steel connector in the tool-joint. Drill pipe fatigue damage occurs under cyclic loading conditions due to for instance rotation in curved sections of the well. In fact material fatigue is considered to be one of the main reasons for drill pipe failures. Usually failure mechanisms are occur in the transition region between tool joint and pipe. Several mechanical and metallurgical factors affect the fatigue life of drill pipes. The former are mainly geometric discontinuities inherent to design or corrosion pits and slip marks. The latter are related to the size and distribution of crystalline grains phases and second phase particles (inclusions). The aim of the study is to analyse the fatigue behaviour of aluminum drill pipes under combined tension and cyclic bending loads with emphasis on the detrimental effect of the stress concentrations in the tool-joint region. The experimental work comprises small-scale and full-scale tests. The material S-N diagram and the aluminum mechanical properti94778 Experimental and numerical investigation of a trimaran in calm water

The shell structural roller gate gives the best water closing performance of all structural types. In particular it has greater structural stiffness than the girder type. This is why the shell structural roller gate is applied to large-scale closing gates that need a long span. The steel water gate experiences variable water pressure due to the gap between the water level in the sea and balancing reservoir. This can cause fatigue damage cracks in the gate lip. In order to find the precise cause of this damage various investigation programs were carried out including observation with microscope and measurement of stress and water level. By analysing the results of these investigations comprehensively it was concluded that the cyclic loading on the gate lip at ground surface had caused this damage and it was established that the relationship between sea water level and stress occurs at damaged point. The damaged part was subsequently replaced with new reinforced element. In addition to check the effect of this measure the crack growth estimation was calculated using FLARP a numerical simulation code developed by the authors. As a result of the numerical simulation the crack growth curve became visible quantitatively and it was confirmed that the measures undertaken would prevent the fatigue crack reoccurring under the assumed loading conditions.

This book aims to provide an overview of the main activities involved in financing the international petroleum industry. It begins with an introduction to the nature and structure of the industry and a brief history of its financing. This leads to a more detailed discussion of the contrast between the approach adopted by the small independent companies and the large international companies towards financing their activities. The emphasis of third part is on non-recourse financing. It covers specific aspects of project financing and considers the risks involved in various projects within the industry in relations to the approach to security for loan finance used by bankers and other financing bodies. The relevance of taxation and insurance to the petroleum industry is then analysed in detail, and the book concludes with a section outlining the export credit arrangements and the various sources of finance that apply to the petroleum industry. This book is of particular interest not only to executives in the oil industry, personnel in banks and other financial institutions, government official and politicians with an interest in the international petroleum industry, but also to academics and students at graduate schools of business studying and researching the nature of financial management in various industries.

Marine risers are used in a number of marine developments and marine surveys such as offshore drilling marine oil production development of OTEC and so on. Marine risers are being used in deeper and deeper waters therefore it is necessary to improve the accuracy of the numerical calculations for design. A model test is described which examines characteristics of VIV (vortex-induced vibrations) of tubing in water e.g. a marine riser and considers VIV characteristics from experimental results. Rigid circular cylinders are used for the model experiment because it is assumed that the model is a part of a marine riser. The test models are suspended in still water through a flat spring and hence VIV can be found with hydroelasticity in spite of a rigid circular cylinder. This is a forced oscillation test in still water. The circular cylinders for the model test have drafts of 30 cm 60 cm and 80 cm and diameter of 5 cm and 8 cm. The models are oscillated with periods of 0.5 s to 4.6 s and with about 7 cm amplitude of the oscillation. In uniform flow there is just one velocity of which flow causes the VIV lock-in. However it is confirmed that there are several cases of experimental models in whicX37853

Fretting fatigue (FF) is probably the most insidious of all the fracture processes that affect engineering components. A great amount of phenomenological data has been gathered in the past 40 years and as many as 50 parameters are known to affect FF behaviour. This paper briefly discusses some of the more frequently studied parameters such as fretting wear fretting corrosion relative slip between component surfaces and temperature and time effects together with the more important aspects of the surface traction force and the surface normal applied pressure between components. Finally the cyclic stresses that are common to all conventional fatigue (F) and fretting fatigue studies are also discussed. Although the FF cyclic stress limit can be a factor of 10 (or more) lower than the conventional F limit with the latter itself being substantially less than the yield stress of the fretted material this paper explores previously-unknown links between FF and F behaviour. In particular both microstructural fracture mechanics (MFM) and linear elastic fracture mechanics (LEFM) theories are invoked which explain previously-anomalous test data. This approach introduces a comparison between a fretting fatigue threshold (FFTH) and the conventional fatigue threshold (FTH) both of which are material grain size dependent; a parameter that is seldom if ever quoted in scientific papers on fatigue fracture. Surface strain concentration studies and fracture mechanics evaluations of FF lifetimes under laboratory conditions have completed the first stage of a comprehensive assessment of FF behaviour in an aerospace matX32269

Results of extensive towing tank measurements with the AXE bow model and the same model with a conventional bow are presented and compared. Tests are carried out in calm water to measure the calm water resistance the sinkage and the trim of the designs. In addition ship motion measurements are carried out primarily in head wave conditions which are aimed at validation of the computational results presented in a previous paper which were obtained from calculations with the non-linear code FASTSHIP. In addition a number of numerical simulations are carried out with these two designs in moderate to high stern quartering sea states using the non-linear code FREDYN of MARIN. The aim of these calculations is to compare both designs with respect to their motions in following waves (not available during the tests) and on their possible sensitivity for the broaching phenomenon and-or heavy rolling in those conditions. The results of these tests and calculations and the comparisons between the two designs are presented and discussed. It is concluded that the application of the AXE bow concept shows very good promise for optimising the sea-keeping behaviour and operability of fast patrol boats in a seaway.

Historically the UK MoD has maintained a significant salvage capability. Military salvage requirements in the marine environment have always been an essential component of the military effect and closely associated with war fighting capability. With the end of the Cold War came the decision to dispose of much of the UK salvage equipment and place much greater reliance on the commercial sector to provide platforms and plant. Increased defence costs and the drive to reduce staff numbers generated a new range of problems. The advent of the global terrorist threat and the return to the concept of global expeditionary littoral warfare has also generated a new paradigm for military salvage activity. Publication of the UK Defence Industrial Strategy proposes a move away from the pure thrust of competitive tendering for capability acquisition. This is primarily driven by the dwindling volume of government resource committed to the defence sector the massive long-term capital investment required for military hardware and the need for the commercial sector to work in partnership rather than in competition. This change has been matched by very significant evolution in the commercial salvage sector which is increasingly facing similar problems and having to move in the same direction. Here some of the current strategic developments in the military sector are translated together with the opportunity they represent to the commercial salvage sector.

As the exploitation and production activities of petroleum in deeper waters has increased there has been a greater tendency to use FPSOs (floating production systems) based for instance on moored ships or semi-submersible platforms as opposed to fixed structures used in still water levels up to 400 meters. The behaviour of permanently moored floating systems is dictated not only by the hydrodynamic behaviour of the hull and the hydrodynamic-structural behaviour of the mooring system but also by the hydrodynamic-structural behaviour of the array of risers. The implementation and application of modal analysis during nonlinear time-domain dynamic simulations of floating offshore systems is presented. The simulations are carried out by a fully coupled non-linear time-domain analysis methodology which considers the interaction between the hydrodynamic behaviour of the hull and the structural-hydrodynamic behaviour of the mooring lines and risers. Considering the non-linear variation of the stiffness and added mass of the floating system with time the objective is to assess the variation of the natural periods of vibration for the 6-DOF of the floating system (surge sway heave roll pitch and yaw). To achieve this the generalised eigenvalue problem associated with the system is assembled and the Generalized Jacobi Method is used to solve this problem and determine natural periods of the system at selected time intervals during the dynamic simulation. Case studies are selected to assess the variation with time of the natural periods considering two different tX16337

The implementation of a modelling infrastructure is described. This implementation was necessary to transition a Gulf of Mexico model called PDOM-A (the Princeton-Dynalysis Ocean Model) with assimilation from a research mode to a model that produced twice-daily 48-hour forecasts for the Gulf of Mexico at the NAVOCEANO (Naval Oceanographic Office) MSRC (major shared centre). PDOM-A's model forecasts are provided to the oceanographic community via the MEL (Master Environmental Library) as data and depicted on the NGLI (Northern Gulf of Mexico Littoral Initiative). MEL is a DMSO (defence modelling and simulation office)-sponsored one-stop site for ordering environmental information. As part of the NGLI Program forecasts from the model are also used to specify outer boundary conditions for a regional model for the Mississippi Bight called ECOM (estuarine and coastal ocean model). The modules that comprise the PDOM system and the connecting logs and data files provide a robust environment for operational models. Each module performs a series of functions. As needs change additional functions can be added to that module. The modules in the infrastructure are: the Gather Environmental Data Module; the Environmental Data Processing Module; the Expert the Modeller Module; the Model Data Preparation Module; the Model Simulation Module; and the Model Post-Processing and Skill Assessment Module. These modules and the motivation for the PDOM modelling infrastructure are described.

In maritime warfare torpedoes pose an important threat to ships and submarines and therefore their early detection is crucial in order to evade them on time. A MTDA (modified torpedo detection algorithm) that improves upon the range estimates of an earlier (TDA (torpedo detection algorithm) is introduced. The original TDA detects the presence of a direct path and a surface reflected path for a torpedo acoustic tonal using the FOS (fast orthogonal search) algorithm. In the original TDA the candidate functions used by FOS were sinusoidal functions at a constant frequency. Using the frequencies of the direct and reflected path signal the TDA estimated the torpedo range. It is known that the frequency of the direct path and reflect path signal will vary in time. It is also well known that correlating a received signal with the expected signal results in the lowest probability of error in detection (matched filter). Thus in this work the candidate functions used by FOS are functions whose frequencies vary in time (chirp signals) as theoretically expected for the direct and reflected path signals. Also the FOS algorithm is modified to fit the direct and reflected paths in pairs. The pair of frequencies that fit the highest energy is determined to be the direct and reflected path signal and the range used to generate that candidate pair is used as the range estimate. The MTDA algorithm is simulated for a torpedo approaching a receiver at several angles and the range estimations are shown. These results are compared with the earlier TDA are sX35644 Improved viability of FPSO developments for HP/HT fields by use of subsea HIPPS

In the past 10 years it has become apparent that the US depends upon a workforce with strong scientific and mathematical skills as well as the ability to apply these skills to emerging technologies. Since deficiencies exist in these areas US Maths and Science educational reform has led to the establishment of National Education Goals (US Code Title 1 Section 102 National Education Goals). Goal Number 5 states 'US students will be first in the world in Mathematics and Science achievement.' With this goal in mind NAVOCEANO (the Naval Oceanographic Office) established a new educational initiative called OCEANS ALIVE (oceanographic career enhancement and naval science: adventurous learning in variable environments). OCEANS ALIVE aims to inform and interest middle and high school students and teachers in operational Naval oceanography. During a three-day voyage aboard a state-of-the-art oceanographic survey ship students learn practical applications of Maths and Science principles and also become aware of career opportunities in the multi-disciplined field of oceanography. OCEANS ALIVE provides a combination of lectures and hands-on learning experiences aboard ship to show students that Maths and Science skills are needed to think creatively to make decisions and to solve problems. The programme content is described.