bluuebunny/crossref_metadata_2025 huggingface dataset:
A Boundary Element Method for Dynamic Analysis of Elastic Structures Subjected to Axial Flow
Authors: Ugˇurlu Bahadir , Ergin Ahmet
Published: October 2008

A boundary element method is presented to investigate the dynamic behavior of elastic structures partially or completely in contact with uniform axial flow. In the analysis of the linear fluid-structure interaction problem, it is assumed that the fluid is ideal and its motion is irrotational. Furthermore, the elastic structure is assumed to vibrate in relatively high-frequencies, so the infinite frequency limit condition is imposed for fluid free surface, which is satisfied implicitly by using method of images. When in contact with the flowing fluid, the structure is assumed to vibrate in its in vacuo eigen-modes that are obtained by using a finite element software. The wetted surface of the structure is idealized by using appropriate hydrodynamic panels and a boundary element method is formulated for velocity potential function, which is taken as linearly varying over the panels. Using the Bernoulli’s equation, the dynamic fluid pressure on the elastic structure is expressed in terms of potential function, and the fluid-structure interaction forces are calculated as generalized added mass, hydrodynamic damping and hydrodynamic stiffness coefficients, due to the inertia, Coriolis and centrifugal effects of fluid, respectively. Solution of the eigenvalue problem associated with the generalized equation of motion gives the dynamic characteristics of the structure in contact with fluid. As an application of the method, the dynamics of a simply supported cylindrical shell subjected to internal flow is studied. The predictions compare quite well with the previous results in the literature.
Interoperability in the Context of Marine Geosensors
Authors: Waldmann Christoph , Diepenbroek Michael , Schindler Uwe , Visser Ubbo
Published: October 2008

The strategy to observe geophysical and biochemical processes in the world oceans will be subjected to significant changes within the upcoming years by complementing current point sampling campaigns at certain time instances with permanent possibly cabled observatory stations. This is underlined by the outcome of the ESONET study, an EU funded project, which states a strong need for permanent observation stations in the Open Ocean and coastal waters to monitor the health of the oceans around Europe and detect potential environmental hazards. As these stations will be connected with the main land via submarine cables or via satellite communication systems it is possible to collect scientific data in real time and also to interact with the instrument to control the sampling process. Here the concept of interoperability becomes a necessity as the inventory of sensors is changing permanently due to the scientific demands and maintenance and service needs. Additional to that there are marine sensors in particular for measuring biochemical parameters where only experts are able to identify, connect and interpret the signals of the sensors. When setting up the new, costly infrastructure of marine sensor networks it is advisable that the sensor data can be detected and interpreted also by people from outside the research community to ensure an optimal use and a widespread availability to public institutions and private companies. In the context of hazardous events like Tsunamis waves the necessity is obvious as immediate, real-time information is crucial for efficient disaster management. Moreover, if we provide formal semantics on the sensor, the signals could also be understood from machines. This would gives us new opportunities with the sensor networks, e.g. identify “foreign” sensors, automatically interpret signals from own and foreign sensors, plausibility controls for the quality of the data, etc. This paper connects the actual needs for the construction of marine sensor networks with the technologies that are available from the Web community to outline a general scheme for implementing interoperability in Marine Geosensor networks and systems.
A Numerical Shallow Water Model Based on the Non-Orthogonal Curvilinear Grids
Authors: Tong Chaofeng , Meng Yanqiu
Published: October 2008

According to the transformation relationships between the Cartesian coordinates and the general curvilinear coordinates, the governing equations of the model are derived as the forms in the general curvilinear coordinates from those in the Cartesian coordinates. In the model, the contravariant velocities are adopted as the independent variables in non-orthogonal grids. The momentum equations keep strongly conservative forms and the boundary conditions can be given easily. The model used a staggered grid arrangement. The discrete equations are solved using the SIMPLIC algorithms. The numerical model has been validated against the bifurcated flow of which the diversion angle is 30 degree. Compared with the measured values, the numerical shallow water model is shown to be capable of simulating the water domains with irregular boundaries.
Deployment of a Completion Riser Management System Incorporating Advanced On-Board Riser Numerical Analysis: Key Issues and Benefits
Authors: Lang Donogh W. , Huxtable John , Lim Roland , Lane Michael
Published: October 2008

With development occurring in increasingly challenging environmental conditions, including Arctic locations, the potential benefits of riser monitoring for completion/workover operations with open sea completion risers are becoming more apparent. This is particularly the case when monitoring is combined with an on-board numerical riser model that can provide real-time operational guidance to rig personnel. The use of a Riser Management System (RMS) with these capabilities presents opportunities for significant cost savings from a maximized operational window and enhanced safety and riser integrity. This paper describes an RMS that has been supplied for a completion/workover riser application in the Barents Sea. The RMS comprises riser-mounted strain gauge instrumentation connected via data acquisition hardware to a topside PC. Data is also acquired from other vessel systems, e.g. Environmental Monitoring System (EMS), Drilling Control System (DCS) and Workover Control System (WOCS). The RMS incorporates an advanced finite element (FE) numerical model of the riser system, which coupled with the measured riser response data is used to predict the operating envelope for the vessel under the prevailing metocean conditions in pseudo-real time. This capability represents a key feature of the RMS and is used to provide operational guidance to rig personnel. The RMS also includes a riser joint tracking feature that automatically records the measured fatigue damage for the instrumented riser joints and the fatigue damage predicted by the riser numerical model for the non-instrumented riser joints. The paper describes the key features of the RMS, with particular emphasis on the procedure used to determine the riser response from a limited number of riser strain measurements using the FE numerical model of the riser. Experience with deployment of the system and its use in practice is described and some of the key benefits are highlighted.
Time Domain Computation of Riser VIV From Vessel Motions
Authors: Cheng Yongming , Lambrakos Kostas F.
Published: October 2008

Intermittent riser VIV behavior caused by vessel motions can affect both riser strength and fatigue life. There are frequency domain codes available that are used routinely to calculate riser fatigue damage from VIV due to currents. These codes are often adapted to calculations of the vessel motion VIV and fatigue damage. The adaptations reduce the intermittent VIV to steady state VIV by assuming an appropriate time invariant velocity profile over the length of the riser. However, since vessel motions cause a relative velocity profile over the riser that varies with time, and the VIV response is intermittent, a time domain VIV code is best suited for such an analysis. The paper demonstrates the use of Technip’s time domain riser VIV code ABAVIV to calculate steel catenary riser VIV response and fatigue damage due to vessel motions. Since time domain analysis is computer time intensive, the paper also outlines an efficient methodology to perform these calculations. The analysis example in the paper is based on surge, pitch, and heave motions which are the most important vessel motions for the riser fatigue damage near the touch down region. The ABAVIV code accounts for the nonlinear structural characteristics of the SCR, and the unsteadiness of the VIV phenomenon for the present application.
Tension Leg Platform Survivability Analysis
Authors: Mansour Alaa M. , Huang Edward W. , Phadke Amal C. , Zhang Shaosong S.
Published: October 2008

In this paper, the survivability of a tension leg platform (TLP) under severe environmental conditions has been investigated. Survival conditions related to tendon damages are considered. Tendon damage conditions include tendon slacking condition, unpredicted increase in wave/wind condition after one tendon is removed and sudden tendon breakage. The effect of column spacing on the TLP survivability is also investigated and presented in this paper. Numerical results are presented for the tendon tension time histories including any tendon down-stroke or unlatching events. Based on the analysis results, recommendations are made to improve the survivability of the TLP under extreme environmental conditions.
A Method to Implement the Random Signals for Time Varying Offshore Wave Height During Storm Condition in an Intra-Wave Period Wave Model
Authors: Zhu Yuliang , Pan Shunqi , Fernando Premanandan T. , Zhou Xiaoyan
Published: October 2008

In this paper, a method to implement the surface elevation at the offshore boundary during storm conditions is presented in the intra-wave period wave model. At storm condition, the offshore incident significant wave height is time varying. In the case of time varying incident wave height, the JONSWAP energy spectrum can be manipulated as follows: H1/32s(f). s(f) is the energy density function for a unit wave height. During a storm event not only the offshore boundary significant wave heights but also the peak frequency varies. If we choose a mean peak frequency during a storm event, s(f) can be calculated for the mean peak frequency for the storm event. The amplitudes of the component waves for the random signals are calculated from the unit energy density function s(f), and the phase angle of the component wave, So we can numerically generate surface elevation time series for the time varying offshore wave heights. The method was verified in the intra-wave period wave model using field measurements at Sea Palling site Norfolk UK.
New Methods to Solve High Order Potential Used in Calculating Non-Linear Wave Loads
Authors: Nihei Yasunori , Bao Weiguang , Kinoshita Takeshi
Published: October 2008

In the present study, non-linear wave loads such as the wave-drift force, wave-drift damping and wave-drift added mass, acting on the body is considered based on the potential theory. To investigate non-linear wave loads, consistent perturbation expansion by means of two small parameters, i.e. the incident wave slope and the low frequency body motion, is performed on a moving frame (body-fixed) coordinate system. To avoid complicated free surface integrals as much as possible, new approach for the higher order potential in the interaction problem of low frequency motion and waves is suggested in the present work. Instead of integrals, derivative operators are defined to obtain special solutions efficiently.
Model Testing of Dynamic Characteristics of Compliant Buoyant Towers
Authors: Dryne Jackson , Maeda Katsuya , Xia Jinzhu
Published: October 2008

Rigorous deepwater wave-basin tests for a series of reduced (1/80) scale model compliant buoyant towers (CBT) have recently been conducted in the Deep-Sea Basin at the National Maritime Research Institute (NMRI) in Tokyo, Japan. The models have been designed to comply with the theoretical conditions of the hydro-elastic similitude. The models are based on a conceptual prototype CBT design suited for the Vincent Field situated on the North West Shelf of Western Australia. The research has been funded by the Australian Research Council. Three parameters, namely, seabed stiffness, additional buoyancy and platform payload, were varied to investigate how each influence the performance of the CBT. Only one portion of the tests conducted at the NMRI is reported here. These include results and findings from free decay and load-deflection tests that were performed to achieve the structure’s natural periods, modal dampening factors and the tower’s global stiffness. These dynamic characteristics and responses obtained from the tests are compared with their finite element analysis (FEA) counterpart.
Multi-Objective Optimisation of Orthogonally Tophat-Stiffened Composite Laminated Plates
Authors: Maneepan K. , Shenoi R. A. , Jeong H. K. , Blake J. I. R.
Published: October 2008

This paper deals with the multi-objective optimisation of an orthogonally tophat-stiffened composite laminated plate. The plate is simply supported around all its edges and subjected to a uniform lateral pressure load. Genetic algorithm (GA) technique is employed as the optimisation tool. As objective functions, both structure weight and manufacturing cost, with respect to a set of practical stiffness and strength constraints (maximum stress criterion), are considered. Structural analysis of the plate is performed using a combination of elastic grillage solutions and an equivalent elastic property approach. Through the unique solutions in conjunction with the GA, it is possible to produce layer by layer optimisation results for the laminated plate, the web, the crown and the overlaminate of the plate. Therefore, the present optimisation framework is capable of dealing with a large number of design variables such as different fibre materials, fibre volume fractions, fibre orientations and geometric values.
In-Situ Uniaxial Compression Tests of Level Ice: Part I — Ice Strength Variability Versus Length Scale
Authors: Shafrova Svetlana , Moslet Per Olav
Published: October 2008

Field programs of the ice strength determination through the uniaxial compression tests were carried out on the landfast level ice both in the Van Mijenfjorden and in the Adventfjorden on Svalbard, Norway in 2004 and 2005. The ice strength was examined in relation to the different length scales. The step (horizontal distance) between the ice samples was continuously reduced in order to find out how the ice strength variability develops. The spatial variation of the physical properties of the ice such as temperature, salinity, density has been measured. The typical ice strength variability for the areas larger than 40 m2 is found about 20–30 % for the vertical ice cores of the certain depth from the ice cover surface. For the horizontal ones it is slightly less about 10–20 %.
In-Situ Uniaxial Compression Tests of Level Ice: Part II — Ice Strength Spatial Distribution
Authors: Shafrova Svetlana , Moslet Per Olav
Published: October 2008

Part I of this paper describes in-situ field tests of ice strength estimation in relation to the different length scales. Part II deals with the spatial heterogeneity of the ice strength in landfast level ice for the different tests areas. The paper presents a statistical analysis of the ice strength distribution for a Point-area, for a line and for an area in the ice cover. The ice strength distribution for a Point-area varied seasonally. It was estimated in terms of the coefficient of variation about 24.9% at the end of the season. For the coldest months the ice strength variability was around 40%. For the test area the strength spatial variability for the ice samples from the certain ice depth below the ice cover surface was about 19.4% for warm ice and 35.8% for cold ice. The ice strength heterogeneity for a line was determined of 14.4% in case of warm ice.
Finite Element Analysis of Residual Stresses in TT-Welded Joint of a Fixed Jacket Platform
Authors: Rostami Kh. , Gharabaghi A. R. M. , Chenaghlou M. R. , Arablouei A.
Published: October 2008

Welded steel tubular joints are the kind of connections used extensively in the construction of fixed jacket platforms. The welding process creates considerable tensile residual stresses near the toe of TT-joint due to the rapid cooling and contraction of final welding layers. Welding produces thermal stresses that cause structural distortions, which influence the buckling strength of the structure. In this study thermal elasto-plastic analysis is carried out using ANSYS finite element techniques to evaluate the thermo-mechanical behavior and the residual stresses of the TT-joint. Moreover, the technique of element birth and death is employed to simulate the weld filler variation with time in TT-joint. The results show the considerable tensile residual stress near the weld toe that it may cause crack initiation in this region and threats the fatigue life of joint.
Design Aspects of Winterized and Arctic LNG Carriers: A Classification Perspective
Authors: Mahmood Mutmaz , Revenga Arturo
Published: October 2008

It is anticipated that Russia will be one of the major suppliers of LNG to meet energy demand in Europe and in the United States in the future. As a result, large quantities of gas will be transported from Russia through seaborne trade by LNG ships. Due to the geographical location of large gas fields in Russia, these LNG ships will need to be designed to specifically operate in severe weather conditions. Meeting the transportation challenge demands an analytical and a more comprehensive and systematic approach to the management of the risks. More detailed analysis has been made possible through developments in computing and modeling technology. That technology plays an essential role in addressing the key safety issues associated with emerging LNG transportation needs in the Arctic trade. In addition, the application of risk assessment methodology in the evaluation of novel concepts permits a better understanding of the risks associated with LNG shipping in arctic waters and its integration into design technical standards, survey requirements and operational practices. The paper will discuss various aspects of the ship design and operational requirements from a Classification perspective. Particular consideration will be given to issues such as the strength of the hull structure to endure ice loads on deck, ice breaking capabilities and the design of the containment system to withstand the dynamic loads envisaged under harsh weather conditions, in particular sloshing loads. In addition the paper will cover requirements for safety equipment and systems under freezing condition and the propulsion systems for ships in this trade. The paper will summarize the latest Classification technology initiatives to support the development of standards for the design, construction and maintenance of an LNG carrier operating in a harsh cold weather environment.
Bio-Inspired Locomotion for Underwater Exploration and Investigation
Authors: Kirchner Frank , Fechner Sascha , Spenneberg Dirk
Published: October 2008

We present ideas on using bio-inspired locomotion concepts for robotic underwater applications. The technology of land-based bio-inspired walking robots improved a lot in the last decade; systems like The SCORPION [1], Rhex or DANTE II have proven that high mobility in rough terrain can be achieved. Walking is a locomotion technique which can be found in underwater animals like lobsters, crayfish, or prawn. These animals can be found in the littoral zone of the oceans and rivers, which are a very challenging environment. Crayfish and prawn can live in rough terrain like the slope of a black smoker, too. They are especially able to adapt to irregular ground contours, current, wave action and surge. For example, lobsters can navigate around obstacles such as rocks, crevices and seaweed. Lobsters flourish in the benthic and littoral environments and have developed robust control systems for locomotion, sensing, and searching behavior. These control systems present a proven solution [2, 5, 11]. No artificial wheeled or swimming system is able to navigate as robustly as lobsters or crayfish in such underwater environments. Thus studying the behavior of animals in the littoral zone and using their control principles for robots seems to be a promising way to close this gap. Therefore we analysed past research in this direction, e.g. the ARIEL and the NEU Lobster project and propose new ideas based on our existing systems [1, 3, 15] for a robust underwater walking platform. We present a possible control concept for such an underwater walking system. Furthermore we discuss possible application scenarios like mine detection or environmental monitoring and non-littoral applications like inspection and maintenance of underwater structures and buildings or service for offshore wind energy parks.
Structural Reliability Analysis of Pipes Subjected to Multiple Strain Cycles: Application to Reeling Process
Authors: Ernst Hugo A. , Passarella Diego N. , Bravo Richard E. , Daguerre Federico
Published: October 2008

The reeling process is one of the most important methods for offshore installations of linepipes. Pipe segments are welded onshore and subsequently bent over a cylindrical rigid surface (reel) in a laying vessel. The pipe is significantly cyclically strained. Due to the high loading condition, the high costs of operations and the severe failure consequences, it is necessary to guarantee the integrity of the components during the process. Conventional defect assessment procedures are not explicitly developed for situations with large cyclic plastic strains. In previous work, a fracture mechanics based methodology was developed to obtain an appropriate specific method to assess the structural reliability of reeled pipes. A description of the material resistance toughness and the crack driving force evolution through strain cycles was proposed. This methodology was experimentally verified. In order to expand this model, in this work the case where several reeling cycles are applied is considered. In addition to the fracture mechanics methodology previously developed, a fatigue crack growth (FCG) formulation controlled by ΔJ parameter was developed. This formulation accounts for the crack growth produced during subsequent reeling cycles. Several fatigue laws and methods to calculate ΔJ were evaluated. An experimental program was carried out. Girth welded joints from two different seamless steel pipes were analyzed. Monotonic and cyclic fracture mechanics tests were performed using single edge notch tension (SENT) specimens. Cyclic tests were used to determine experimentally the cyclic crack growth. Experimental measurements were compared to predicted fatigue crack growths for different ΔJ calculation methods and fatigue laws. Comparison between theoretical and experimental results led to the selection of the most realistic fatigue law. A methodology to assess the reliability of pipes during multiple reeling cycles, based on fracture and elastic-plastic fatigue crack growth, was developed. A particular case of interest was presented, tolerable defect sizes were determined for different number of applied reeling cycles. The proposed methodology seems to be an accurate method to assess cases where multiple plastic cycles are taken into account.
Some Statistical Properties of Random Waves in a Sea Storm
Authors: Arena Felice , Pavone Diego
Published: October 2008

In this paper some statistical properties of random waves in a sea storm are investigated. The classical Borgman’s approach is applied to obtain the analytical expressions of both the probability PK(H) that in a sea storm only K waves higher than a fixed threshold H occur, and the probability P≥K(H) that in a sea storm at least K waves higher than a fixed threshold H occur, with K = 1, 2, 3,… Moreover, it is shown that, if the number K is negligible in comparison with the number of waves occurring in the storm, the results may be expressed in an integral form. This integral form is very useful to particularize both PK(H) and P≥K(H) for a storm with a triangular time history. Finally, the results are validated with Montecarlo simulations of random waves in a sea storm of given time history.
Bio-Optical Sensors Onboard Autonomous Profiling Floats
Authors: Zielinski Oliver , Cembella Barbara , Heuermann Ru¨diger
Published: October 2008

The perspective of an array of thousands of floats drifting in the world ocean offers the possibility to monitor global ocean currents via the distribution of oceanographic parameters like temperature and salinity (WOCE – ARGO programme). Deploying these floats with advanced bio-optical sensors for the detection of bio-geochemical parameters offers a potential for large scale assessment of the pelagic primary productivity and the bio-geochemical processes involved. Technical specifications to be met by these sensors will be: low power consumption, long-term stability and reliability, standardized interfaces and protocols together with an intelligent data handling. However, these requirements also demand sophisticated capabilities of the float as a platform. Enhanced interfaces, algorithmic power and memory including new telemetry and docking solutions are necessary to provide a flexible and yet reliable platform for bio-geochemical sensors onboard floats. Within this work an overview of bio-optical sensors, which were integrated in autonomous profiling systems, will be given. This introduction will be followed by first results from hyperspectral irradiance and radiance data from the Navigating European Marine Observer (NEMO) float which were obtain during a two-day lake experiment. Finally, future integrations of sensors and general requirements for floating profiling drifter in the context of coastal and open ocean observatories will be discussed.
Forces of Random Wave Groups on Vertical Cylinders
Authors: Pavone Diego , Arena Felice
Published: October 2008

The paper analyses the diffraction problem of two bottom mounted vertical circular cylinders. The randomness and directional spreading of sea waves are taken into account and a new procedure is proposed to estimate the largest forces on the bodies when extreme waves occur. Firstly extreme forces on the array of cylinders are obtained in two cases: - when a large crest occurs at a given point in the undisturbed wave field (which is the incident wave field in diffraction conditions); - when a large crest-to-trough wave height occurs in the undisturbed wave field. Finally, it is investigated where extreme crests or crest-to-trough heights should occur in order to produce the maximum value of the force on a cylinder. It is shown that, because the second condition is always the most conservative, it is the most suitable to predict design conditions.
Nonlinear Dynamic Analysis of Pile Foundation Embedded in Sand Subjected to Strong Ground Motion Using Fiber Elements
Authors: Asgarian B. , Boroumand M. , Soltani R. H.
Published: October 2008

In this paper Fiber Element is used for modeling soil–pile interaction during earthquakes. In this model, both pile and surrounding soil are modeled using fiber elements. This model is developed using DRAIN–3DX software. In this method, behavior of soil is assign to fiber elements using p-y curves. In order to consider effects of free field soil on the motion, EERA and NERA software are used. In this paper pile behavior embedded in sandy soil subjected to strong ground motion were analyzed and compared with available experimental results. The model can be used for soil – pile – structure interaction analysis of jacket type offshore structure.
Water Absorption Effect on Syntactic Foam Thermal Insulation of a Flexible Pipe
Authors: Chalumeau Alain , Felix-Henry Antoine
Published: October 2008

Thermal insulation of a flexible pipe for deepwater applications is generally obtained by spiraling syntactic foam extruded tapes around the pipe core, in between two thermoplastic sheaths. As water tightness of the insulating annulus can frequently not be guaranteed, water absorption and the effect on thermal properties of insulating material have to be determined, so as to be taken into account for Overall Heat Transfer Coefficient calculation of the flexible pipe. It is required to demonstrate the overall suitability of a specific insulating material for a given application. The first part of this paper describes accelerated fresh water absorption tests and subsequent thermal conductivity measurements, conducted on polypropylene syntactic foam filled with glass micro-spheres. Based on test data in the 50°C–100°C temperature range, a prediction model has been established to calculate water absorption for service life as long as 20 years. A relationship between thermal conductivity variation and water content has been demonstrated, so that thermal conductivity of material exposed to water can be calculated versus temperature and time of exposure, for design purpose. The second part describes the full scale thermal tests that have been performed by Technip, in order to compare the measured thermal properties and heat losses of the flexible pipes in vertical or horizontal positions, with the computer calculations. Finally, based on lab test ageing and full scale tests on non aged flexible pipe, Technip is able to predict the full thermal behaviour during all the lifetime of the pipe.
Experimental Evaluation of a Dynamic Positioning Thruster Prohibited Operating Zone Using Stereoscopic Particle Image Velocimetry (SPIV)
Authors: El Lababidy Said A. , Bose Neil , Liu Pengfei
Published: October 2008

The knowledge of the effects of the wakes from Dynamic Positioning (DP) thrusters and the practical need to describe and predict their impact is fundamental in the assessment of design loading on slipstream-submerged structures (moorings, risers, and equipment) associated with offshore floating systems. In particular, with the increasing importance and application of DP thrusters in the offshore industry, the designer as well as the operator must have more information about thruster-structures interaction effects and the safest location of DP thrusters regarding to any submerged structures. This paper contributes at this knowledge by experimentally evaluating of a DP thruster model far wake induced load. This is by evaluating the DP thruster wake thrust and force loading distribution and propagation, when operating with and without a nozzle, at high loading conditions (J = 0 and J = 0.4) and up to 15 diameters downstream of the model. Experiments were performed using a Stereoscopic Particle Image Velocimetry (SPIV) at the Italian Ship Model Basin (INSEAN) large cavitation tunnel. This paper evaluates the safest location of DP thruster when operating with and without a nozzle.
Qualification of Welding Procedures for ExxonMobil High Strain Pipelines
Authors: Hukle Martin W. , Hoyt Douglas S. , LeBleu James B. , Dwyer John P. , Horn Agnes M.
Published: October 2008

Weld procedure qualification methodologies for ExxonMobil high strain pipelines are presented. ExxonMobil has been involved in the design and construction of high strain pipelines for both onshore and offshore applications. These projects have included onshore applications involving potential seismic activity (fault displacement and soil liquefaction) as well as arctic applications that may involve displacements associated with frost heave and thaw settlement. Recent offshore installations have been designed and constructed to accommodate potential displacement caused by ice scour. Some of these installations have been designed to accommodate in excess of 3% longitudinal tensile strain demand. A critical element of the overall pipeline design is the qualification and validation of acceptable strain capacity for the pipeline girth welds. A girth weld qualification test program, based on large scale proof testing (i.e., curved wide plates) has been developed and executed.
Designed-Oriented Methods of Ultimate Hull Girder Strength
Authors: Qi Enrong , Cui Weicheng
Published: October 2008

Based on long-time theoretical and experimental work in authors group, assessment methods of ultimate strength of ship hulls are analyzed and improved. Nonlinear finite element analysis method (FEM), idealized structural unit method (ISUM), simplified method (SM) and analytical method (AM) are integrated into a software system of direct calculations of large tankers. Using this software system, a comparative calculation is performed on ultimate hull girder strength of a 300,000dwt double hull tanker and the calculation results are also compared with the single step procedure of Common Structural Rules for double hull tankers (JTP CSR).
On the Lagrange’s Method for Floating Bodies
Authors: Sadeghi Keyvan
Published: October 2008

It is shown that, in the context of a linear theory, all fluid radiation actions on a floating body can be solely represented by a part of the fluid mechanical energy corresponding to the wetted surface of the body. In this regard, it is indicated that the linear radiation damping can be expressed by a fluid kinetic energy which has a bilinear form. Then from the Lagrange’s equations of motion, an equation of motion is derived that is called the conjugate Larange’s equation of motion. A variant of Hamilton’s principle is also introduced as the variational generator of the conjugate Lagrange’s equation of motion.
Probabilistic Assessment of Hull Girder Strength and Stiffness
Authors: Arason Magnu´s , Kent John S.
Published: October 2008

The paper summarises recent work on a probabilistic prediction of hull girder strength and stiffness. This addresses a requirement within the UK Ministry of Defence to introduce structural reliability based methods for naval ship structures, which can have benefits in design as well as inservice assessment. A Monte Carlo simulation scheme, which samples a number of probability distributions, has been developed for application with an ultimate strength prediction tool. This tool uses 2D representation of hull girder sections. The section models are divided into regions that are assumed to have the same statistical properties within each simulation cycle. It is demonstrated that a lognormal distribution describing the ultimate strength of a hull girder section can be derived with relatively little computational effort. The results indicate that whilst standard deterministic strength predictions fall below mean values, there is a significant probability that actual hull girder strengths may be lower. This is of the order of 5%. Modelling uncertainties associated with the simplified strength prediction method are also outlined and quantified. The same method can be used for calculating hull section modulus. Results can be used directly when transforming measured strains to applied bending moments as part of work on load prediction and validation of hydrodynamic tools. The work presented forms part of a larger research programme that aims to produce recommendations for a limit state based assessment of hull girder strength against wave induced bending.
Reel Installation of 15” Clad Steel Pipeline With Direct Electrical Heating and In-Line T
Authors: Endal Geir , Nupen Oddbjo̸rn , Sakuraba Masahiro , Kondo Katsuji
Published: October 2008

The Norne Satellite project in the Norwegian Sea involved installation of a 9 km long 15” thermally insulated clad steel production pipeline. The pipeline is equipped with Direct Electrical Heating for hydrate control and an in-line T for connection of a mid-line reservoir. The installation was performed in 2005 with the reel ship “CSO Apache” after completion of comprehensive qualification programs. The Norne Satellite project represents a step forward in sub-sea pipeline technology, with the following main firsts: • Reeling of clad steel pipeline. • Direct Electrical Heating of clad steel pipeline. • Direct Electrical Heating of pipeline with in-line T. • AUT of clad steel girth welds. This paper presents experiences from the qualification and installation works.
Extreme Waves and Stochastic Wave Groups
Authors: Fedele Francesco , Tayfun M. Aziz
Published: October 2008

We introduce the concept of stochastic wave groups to explain the occurrence of extreme waves in nonlinear random seas, according to the dynamics imposed by the Zakharov equation (Zakharov, 1999). As a corollary, a new probability of exceedance of the crest-to-trough height which takes in to account the quasi-resonance interaction is derived. Furthermore, a generalization of the Tayfun distribution (Tayfun, 1986) for the wave crest height is also proposed. The new analytical distributions explain qualitatively well the experimental results of Onorato et al. (2004, 2005) and the numerical results of Juglard et al. (2005).
Effects of Geometric and Operating Parameters on the Separation Performance of Air-Injected De-Oil Hydrocyclone
Authors: Zhao Lixin , Jiang Minghu , Li Feng , Song Hua , Liu Shumeng
Published: October 2008

A new type hydrocyclone, air-injected de-oil hydrocyclone (AIDOH), was developed. Basic separation principle of the AIDOH, prototype structure, experimental technical process and facilities are introduced. The effect of different geometric parameters, including vortex finder diameter and length, micro-pore diameter, and different operating conditions, such as flowrate, split ratio, gas-liquid ratio, and air-injecting position, were studied. Laboratory experiments were carried out first to provide basis for field tests. The field research indicates that, for around 1000 mg/l polymer-flooding oily produced-water, the optimum flowrate is 4.20 m3/h for the testing prototype, the split ratio should be 30%; gas-liquid ratio 0.45. It also shows that 20–40 µm micro-pore materials are optimum diameter for hydrocyclonic separation enhancement Research indicates that the AIDOH has satisfied separation effect, which is feasible for emulsified oil treatment. The AIDOH will have better application prospect in petrochemical, environmental field, especially for offshore application, to reduce space occupied by normal water treatment facilities.
Springing Response Statistics of Tethered Platforms in Random Waves
Authors: Teigen P. S. , Gaidai O. , Naess A.
Published: October 2008

The paper investigates the wave forcing and motion response of a small size TLP, 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.
Development of the New Aquaculture Fishcage for Open Ocean Areas
Authors: Jeong S. J. , Shin J. K. , Lee J. Y. , Yoon J. H.
Published: October 2008

Until now, Korean aquaculture industry has been grown largely in quality and quantity. However, an increase of quantity has caused lots of problems like sea pollution lately. Nearly 82% of Korean aquaculture farms had been installed mainly at inshore of the southern sea, so, sewage, factory wastes, high density of farms at the limited area and autoinfection have deteriorated inshore fisheries. Now, the open sea has been on the rise for the solution to these problems since it has clear seawater that will expect to decrease the environmental pollution with much current. As a matter of fact, it is impossible to move the existing fish cages to the open sea due to the rough environmental conditions such as higher waves, strong currents etc.; therefore, it is necessary to develop new fish cage equipment that will fully meet the open sea conditions. In this research, the theoretical study and experimental analysis have been carried out for the structural fish cage design which is feasible for the open sea.
Experimental Research on Flow Induced Oscillation of Circle Cavity With Free Surface
Authors: Yao Xiong-Liang , Kang Zhuang , Xu Wei-Jun , Dai Wei , Pang Fu-Zheng
Published: October 2008

With the help of empirical mode decomposition method this flow noise experiment was investigated in the towing tank. The key part of the EMD method is that with which and complicated data set can be decomposed into a finite and often small number of ‘intrinsic mode functions’. By the comparative method, the acoustic data have been collected with and without the cavity in all conditions respectively. After the proceeding of empirical mode decomposition, the intrinsic mode functions of the acoustic data have been gotten, and then do the PSD spectrum of each IMF. Compare the difference of each PSD spectrum between the result of with and without cavity, the flow noise which result from the cavity can be got. In this experiment, when the flow velocity is from 0.4m/s to 0.6m/s, the resonance phenomenon is observed. It appears the water in the cavity is up and down in the deep direction. This is so-called “Piston” phenomenon. The fluid fluctuating force in the cavity is a harmonic force. The frequency is the same with the resonance frequency and the value level is greater. When the flow velocity is more than 0.8m/s, there is no resonance phenomenon any more, under the help of EMD method, the fluctuating force which is consist of the shear layer oscillation and the water oscillation can be gotten.
Pipeline Unburial Behaviour in Loose Sand
Authors: Schupp J. , Byrne B. W. , Eacott N. , Martin C. M. , Oliphant J. , Maconochie A. , Cathie D.
Published: October 2008

Small diameter pipelines are routinely used to transport oil and gas between offshore production plants and the mainland, or between remote subsea well-heads and a centralised production facility. The pipelines may be placed on the soil surface but it is more usual that they are placed into trenches, which are subsequently backfilled. For the buried pipelines a well established problem has been that of upheaval buckling. This occurs because the fluid is usually pumped through the pipes at elevated temperatures causing the pipeline to experience thermal expansion which, if restrained, leads to an increase in the axial stress in the pipeline possibly resulting in a buckling failure. A secondary phenomenon that has also been identified, particularly in loose silty sands and silts, involves floatation of pipelines through the backfill material, usually shortly after burial. At the University of Oxford a project sponsored by EPSRC and Technip Offshore UK Ltd has commenced to investigate in detail the buckling and floatation problems. The main aim of the research programme is to investigate three-dimensional effects on the buckling behaviour. The initial experiments involve the more typical plane strain pipeline unburial tests to explore the relationship between depth of cover, uplift rate, pipeline diameter and pullout resistance under drained and undrained conditions. The second and main phase of experiments involves inducing a buckle in a model pipeline under laboratory conditions and making observations of the pipe/soil response. This paper will describe the initial findings from the research including a) plane strain pipe unburial tests in loose dry sand, and, b) initial small scale three-dimensional buckling tests. The paper will then describe the proposed large scale three-dimensional testing programme that will be taking place during 2006 and 2007.
CFD Analysis, Measurements and Applicable Fields on Hydrocyclonic Separation Technology Research
Authors: Zhao Lixin , Jiang Minghu , Liu Shumeng , Song Hua
Published: October 2008

The structure, separation principle, varieties, and application fields of hydrocyclones are introduced first. Based on Computational Fluid Dynamics (CFD) method, by using FLUENT pack, the flow field inside hydrocyclones were studied and analyzed. Velocity distribution and flow path line characteristics of the hydrocyclone were mainly studied, especially when the operating parameters changed. By using a Laser Doppler Anemometer (LDA), the simulation results were verified to some extent, which is beneficial to further understanding of hydrocyclonic separation mechanism and its research. In addition, the application aspects and main results of CFD analysis on hydrocyclonic technology study are discussed, such as Locus of Zero Vertical Velocity (LZVV), recirculation flow, and short circuit flow (SCF) inside hydrocyclones. The CFD methods can be applied on the velocity field and density field distribution characteristics research, separation mechanism analysis, separation efficiency prediction, and so forth. The CFD analysis of flow field simulation, efficiency prediction, and part erosion study on hydrocyclonic optimization design are introduced. The CFD application outlook and future work are also addressed.
Aided Inertial Navigation System Solutions: Application for Synthetic Aperture Sonar
Authors: Ho¨lscher-Ho¨bing Ursula , Larsen Mikael Bliksted
Published: October 2008

Future naval systems for MCM will include a family of advanced underwater vehicles: AUV’s, towed vehicles, inspection ROV’s, expendable mine disposal vehicles etc. Navigation system technical requirements range from low cost for disposable vehicles in high quantity production to state-of-the-art autonomous navigation in support of AUV’s and high resolution Synthetic Aperture Sonar (SAS) for mine hunting. Using modern development tools and floating point embedded processors it was possible to create a generic implementation of the conventional Aided Inertial Navigation System (AINS) framework. The proven framework and real-time embedded software/hardware ensures optimum fit of navigation systems technical requirements via complete freedom in choice of navigation sensors, aiding techniques and operational procedures. This paper describes the underlying navigation system framework and in particular the first real-time embedded application within an underwater vehicle: Extremely high performance relative navigation in support of SAS processing for detection of buried mines.