bluuebunny/crossref_metadata_2025 huggingface dataset:
Combined Seakeeping and Maneuvering Analysis of a Two-Ship Lightering Operations
Authors: Skejic Renato , Berg Tor E.
Published: January 2011

Hydrodynamic interaction effects between two ships going ahead in regular deepwater waves were numerically studied during typical maneuvers for ship-to-ship (STS) operations, such as lightering, replenishment, etc. Such maneuvers are usually classified as potentially hazardous situations, due to the possibility of collision between the two vessels when they are operating in close proximity. Since the collision hazard is usually even greater in bad weather conditions, knowledge of the maneuvering capabilities of two ships in a seaway must be available in order to ensure safe and efficient STS operation. In this study, a combined seakeeping and maneuvering analysis of two ships involved in typical lightering operation was performed using a unified seakeeping and maneuvering theory developed by Skejic and Faltinsen [1, 2]. The unified theory integrates seakeeping and maneuvering analysis by using a two time scale assumption and modular concept. This approach allows the maneuvering behavior of the two ships involved in lightering operation in waves to be successfully described. The seakeeping analysis for both vessels uses Salvesen-Tuck-Faltinsen [3] (STF) strip theory for deep water by assuming that there are no hydrodynamic interaction in waves between the two ships. The regular wave field effects upon the involved vessels are described by the mean second-order wave loads. They can be estimated by using one of the available near/far field theories (Salvesen [4] and Faltinsen et al. [5]) that take the complete wave length range of interest for a considered STS maneuver into account. When the incident wave length is short relative to the ship length, the asymptotic theory by Faltinsen et al. [5] is used. The predicted mean second-order wave loads according to these theories are shown in the case of turning maneuver of a ‘MARINER’ type of a ship in specific wave conditions. The maneuvering module of the unified theory model is based on generalized slender-body theory, while calm-water interaction forces and moments between the two ships are estimated using Newman and Tuck [6] theory. Automatic steering- and speed-control algorithms for both ships (Skejic et al. [7]) are employed to achieve high-precision and collision-free lightering maneuvers in waves. This is illustrated by a numerical simulation involving ‘Aframax’ and ‘KVLCC’ (type 2 – Moeri tanker [16]) types of ships. Finally, from the perspective of marine safety and reliability, the future requirements and recommendations for typical lightering operations in a seaway are discussed.
A Simplified Approach to Wave Loading for Fatigue Damage Analysis of Monopiles
Authors: Thomassen Paul E. , Krokstad Jo̸rgen
Published: January 2011

The monopile is the dominating substructure concept used for offshore wind turbines. Offshore wind farms have so far been built at a depth of up to 24m. As the importance of wave loads increase when deeper waters are considered for wind farms, it becomes increasingly important to correctly and efficiently include wave loading in structural analysis. Also, for deeper waters monopiles are expected to gradually become less economical compared to alternative substructure concepts, and wave loading is important to rate different alternatives. Although monopiles is the focus of this paper, the methodology presented is largely relevant to alternative substructure concepts. A rational and efficient methodology is suggested to construct a scatter diagram based on growth curves, wind speed, fetch, and the duration of winds. First, a scatter diagram for wind speed is generated based on the 1-year and 50-year wind speeds. The wave scatter diagram is then constructed using growth curves and considering the average duration of winds compared to the length of the wave growth phase. Wave loading is discussed in the context of the wave climate found most relevant for fatigue loading. Drag effects are ignored due to low Keuligan-Carpenter (KC) number. For short wave periods, diffraction effects should be considered, but they are nevertheless ignored as very little of the fatigue damage occur for these periods. An analytic expression for the mudline moment amplitude is used to find the stress range for a regular wave. Fatigue damage and fatigue life is calculated using the SN-approach. The results indicate that wave loading can be very important for fatigue damage in an analysis also including wind loading and dynamic effects.
Research on Collision Strength for Deep Sea Submersible Structures
Authors: Lin Yi , Feng Guoqing , Ren Huilong , Yu Hao
Published: January 2011

Collision is one of the common accidents during the lifetime of deep sea submersibles. Now scholars have paid more and more attention to research on collision strength. The FEM is adopted to simulate the collision between two submersibles in this paper. Based on the research on some key collision indices, plastic energy absorption, collision force and critical collision speed, the approach of assessing collision strength was obtained. Besides, we discuss the motion lag of the submersibles and consider the impact of some collision parameters, such as water pressure, impact position, angle, and radius of indenter. Finally, some significant conclusions were made.
Analysis on Motions and Green Water of FPSOs in Shallow Water With Non-Collinear Environments
Authors: Guo Bin , Xiao Long Fei , Yang Jian Min
Published: January 2011

The paper presents motions and green water of a FPSO in shallow water with different wave headings. In non-collinear directions of wind, waves and current, the FPSO does not always encounter head waves, which probably induces specialties in motions and green water especially because of the complexity of shallow water hydrodynamics. Time-domain numerical simulation and model test are carried out in order to analyze motions of a single-point moored FPSO. Green water and wave run-up along the side of a fixed FPSO are simulated in a 3-D numerical wave tank, and results are compared with that of model tests. It is shown that the influence of the yaw angle on motions of a FPSO is considerable and green water occurs more frequently around the mid-ship when the FPSO encounters a big wave heading. In the same water depth, roll and pitch motions of the FPSO under higher wave are lower instead but green water occurs; in the same wave situation, the motions of the FPSO in a lower water depth are lower, but green water occurs more severely. In general, water depth has an important influence on green water of FPSOs in shallow water. The hydrodynamic character of large floating structures in shallow water, especially the green water, should be taken into account carefully for determining the design load and freeboard of a large floating structure.
Safety as Objective in Multicriterial Structural Optimization
Authors: Zanic Vedran , Kitarovic Stanislav , Prebeg Pero
Published: January 2011

Multicriterial design methodology with safety as one of the design objectives is presented. The aim of the paper is to analyze the influence of safety based design objectives on generated nondominated designs on the Pareto frontier. Possible improvements in nondominated designs are investigated by comparison to ones obtained with the standard design procedure when safety criteria are used as design constraints only. It is assumed that safety based objectives and targets act as attractors, driving nondominated designs along the constant cost/weight contours in design space towards its safer regions. Global safety objectives (for hogging/sagging modes), are based on the maximization of ultimate longitudinal strength in vertical bending calculated via the extended IACS incremental-iterative method. Applied compound safety measures for gross-panel (stiffened panel with associated girders) are based upon 34 failure modes, belonging to serviceability/collapse subsets. Objectives based on the maximization of safety measures are applied together with standard design objectives such as minimization of initial cost and weight. The following problems were solved with different sets of objectives: (a) minimize cost and weight objectives subject to safety constraints (used for reference), (b) only the maximization of local safety measures is added to (a) as additional objectives, (c) only the maximization of global safety measures is added to (a) as additional objectives, (d) maximization of safety measures ad (b) and (c) are added to (a) as additional objectives. For each of the problems (a–d) the developed design procedure is executed. It contains two basic tasks for structural design of realistic (non-academic) problems: (1) multicriterial optimization with topology / geometry design variables; (2) multicriterial optimization of gross-panels with scantling / material design variables. Design procedure steps are executed using a fast and balanced collection of analysis and synthesis modules/methods of the OCTOPUS design system: • Determination of design load sets; • MOGA / MOPSO based generation of nondominated designs for the selected ship structure; • For each design the following analysis blocks are executed: – calculation of ship’s primary and racking response fields, – calculation of ship’s ultimate longitudinal strength, – calculation of serviceability and collapse safety criteria on the gross-panel level. Comparisons of results, based on generated Pareto hyper-surfaces and on subset of preferred designs, are given for problems (a–d). Insights into the results of optimization process, using 5-D graphics for design and attribute spaces, are also presented. Design problems of modern RoPax and SWATH structures are used in case studies.
Numerical Simulation of Fatigue Crack Growth Based on Strip Yield Model Considering Work Hardening of Materials
Authors: Gotoh Koji , Harada Keisuke
Published: January 2011

This paper presents the improved numerical simulation of fatigue crack growth considering the crack opening / closing behaviour based on the strip yield model with the stress intensity factor weight function. The mechanical property in the primitive model corresponds to rigid-plastic material and is replaced to the elastic - perfectly plastic material in order to describe the elastic behaviour of material around a crack tip during the unloading process. However, the simulation model based on the elastic - perfect plastic material gives poor growth estimations under rapidly changing of loading histories, e.g. the spike loading. The possibility is pointed out that insufficient considerations of work hardening effect of materials lead the excess crack closure in the numerical simulations. Authors propose the improved numerical simulation fatigue crack growth considering the work hardening effect of materials in this paper. Comparison of proposed simulation results with previous ones and with measured results confirms the primacy of proposed method over previous ones.
Typhoon Energy Utilization Using Mega-Yacht System
Authors: Terao Yutaka
Published: January 2011

Typhoon, hurricane or tropical cyclone are characterized by the release of large amounts of latent heat of condensation. Even if an average typhoon has 1018J energy which is enough for annual Japanese electric power. Therefore until now, none of human beings can utilize this huge ocean energy. If we could develop a system that drawn out power from the typhoon or as such high wind energy resources, we could obtain clean and abundant energy. In this research proposes the concept of a sailing type power plant, designed as a mega sailing yacht with some underwater power generators. This power plant operates under the high wind energy area with its hard sails and the underwater propeller generators yield electric power, which will be stored by batteries or H2 conversion. Our feasibility study shows that using the 1000 mega yacht fleet, the annual power in Japan can be easily obtained with no CO2 emission. In this paper discuss our concept with the mega-float wind power concept and the results of model test in the tank.
Assessment of the Uncertainties Introduced by Different Fatigue Damage Models for Ship Structural Details
Authors: Garbatov Yordan , Guedes Soares C.
Published: January 2011

The objective of this work is to assess the uncertainties introduced by different approaches for fatigue damage of ship structural details including discrete, closed-form and spectral approaches. The fatigue life is predicted by S-N approach based on the long-term notch stress range. The influence of ship main characteristics, operational profile based on a mission or loading condition, wave climatic data including the use of different scatter diagrams, wave spectra, heading distributions and consider the random origin of the mean stress effect, imperfection, weld shape improvement, hot spot calculation and resulting notch stress concentration factors to the fatigue life of a but welded ship structural component are accounted for.
Analysis of Nonlinear Dynamic Response of Mooring Lines in Deepwater
Authors: Zhang Su-xia , Tang You-gang , Liu Xi-jun
Published: January 2011

Nonlinear motion equations of cable is reduced with the assuming of linear constitutive relation, and simplified further according to propagation characters of stress wave. The loading acting on quasi-static cables are analyzed and the detailed expressions are given. The displacement, stress and strain in mooring line in deep water are calculated in this paper, and the nonlinear propagation characters of stress and strain, the motion characters and the effect of drag force reduced by fluid on the dynamic tension in cable are analyzed respectively. The results show that, the stress in cable propagating from exciting end to fixed end and there is a difference in phase. At the same time, the stain in cable different point is also different. At the point with maximum tension, the normal motion is double-period and the tangential motion is quasi-periodic. The tension in cable is effected by tangential and normal drag.
Optimal Set-Point Chasing of Position Moored Vessel
Authors: Fang Shaoji , Blanke Mogens , Leira Bernt J.
Published: January 2011

Dynamic positioning of surface vessels moored to the seabed via a spread mooring system are referred to as position mooring (PM), the main objective of which is to keep the vessel within a small radius from a given position while preventing mooring line breakage. When environmental loads become high, position mooring systems apply thruster forces to protect mooring lines and position accuracy may need be relaxed. This paper suggests a new position chasing algorithm that works entirely online, is optimal according to a criterion and can protect any number of mooring lines simultaneously. Tensions of all mooring lines are included in a cost function where the criticality for each mooring line determine individual weights. With this strategy, external environment effects are included directly by without needing predefined tabular settings of environmental loads as in earlier approaches. There is no limitation to the number of mooring lines that can be close to critical tension. A reliability index is used as weight to include the dynamic influence of mooring line tension. Detailed simulations illustrate the features and advantages of the new method and results are compared with those of a fixed weight algorithm.
Assessment of SYMS Survival Limit for “Peng Bo” FPSO During Installation
Authors: Phadke Amal C. , Liao Shihwei , Chen Donghui
Published: January 2011

The ConocoPhillips “Peng Bo” FPSO in Bohai Bay, China, is one of the largest FPSOs in the world. It was installed in early 2009 and first oil was achieved in May 2009. The FPSO is moored to a jacket platform in about 27m water depth via a Soft Yoke Mooring System (SYMS). The mooring system consists of two yoke arms (port and starboard) connected at the jacket end to a turn-table that sits on a main bearing at the top of the jacket. The other ends of the yoke arms are integrated with two large ballast tanks which are attached to two pendulums supported by a rigid frame mounted on the forward end of the FPSO. The ballast weights give rise to the necessary system surge restoring force while the turntable and bearing allow the FPSO to weathervane. The yoke arms and ballast tanks are pre-installed with empty ballast tanks mounted on two temporary support barges while awaiting the arrival of the FPSO. Upon arrival, the ballast tanks are attached to the pendulums from the FPSO side. The tanks are then filled with solid concrete ballast to achieve the design weight. Before the tanks are completely filled, the SYMS may not have sufficient restoring force in partially filled condition to prevent excessive pitching of the yoke arms and severe bearing load on the jacket beyond the design limit due to large FPSO offset in the event of an unforeseen storm event. An analysis was carried out to estimate the maximum bearing load and yoke arm pitch angle when the ballast tanks were 0%, 25%, 50%, and 75% full for 10-year and 100-year return period events. This paper describes the analysis methodology and results from the analysis. The overall project and installation experience are also discussed.
Computation of Fully Nonlinear Wave Loads on a Large Container Ship by CIP Based Cartesian Grid Method
Authors: Hu Changhong , Sueyoshi Makoto , Miyake Ryuji , Zhu Tingyao
Published: January 2011

A Cartesian grid method with CIP (Constraint Interpolation Profile [1]) based flow solver has been developed and applied to many strongly nonlinear free surface problems. In this paper we present a research on applying the method to predict nonlinear wave loads on a container ship, which is advancing at a constant forward speed in regular waves with large amplitudes. Numerical computations are carried out on a head sea case and a bow sea case. The computed frequency response characteristics for the ship motions and the wave loads including vertical bending moments on the cross-sections and hydrodynamic pressures on the hull, are compared to a model test result and the result obtained by two potential flow based numerical methods. The nonlinear features of the numerical results are discussed.
Arc Stability Indexes Evaluation on Underwater Wet Welding
Authors: Pessoa Ezequiel C. P. , Ribeiro Leandro F. , Bracarense Alexandre Q. , Dias Weslley C. , Andrade Luciano G. D. , Liu Stephen , Santos Valter R. , Monteiro Mauri´cio J.
Published: January 2011

Underwater wet welding (UWW) with shielded metal arc welding (SMAW) is employed basically in repairs of offshore structures, including platforms, ships and others. The main problems of this type of welds are related, of course, with water presence in the electric arc that causes higher cooling rates, Oxygen and Hydrogen availability in the arc atmosphere and arc instability. Many of research and test welding programs in laboratory are undertaken in shallow water performed by automatic devices using hyperbaric chambers to simulate depths. Also, welding arc signals are acquired using data acquisition systems and the arc stability is estimated through indexes calculated from values acquired and analyzed. It is very well known the reduced stability of the wet welding process at shallow depths — less than approximately five meters. So this effect would be considerable significant since it can be used to make correlations between the arc stability indexes and the welds quality results. The main objective of this work was to evaluate the efficiency of the most used arc stability indexes reported in the literature in detect the arc instability effect of shallow water wet welding. Bead-on-plate welds had been made using a gravity feeding system device inside a hyperbaric chamber, applying straight polarity (DCEN) in ASTM A36 steel plates, using the same weld parameters in two different depths, 0.5 and 20.0 meters. Rutile, basic and oxidizing commercial electrodes types prepared for UWW with 3.25mm rod diameter were used. Visual analysis, bead morphology and arc stability were the criteria used to evaluate the weld quality. The voltage and current arc signals were acquired at 10 KHz rate. The arc stability indexes measured were average voltage and current and its standard deviation, S (Imax/Imin) parameter, voltage and current square mean, arc “re-ignition” voltage and current, metal transfer time and its deviation, metal transfer frequency and its deviation, short circuit time and its deviation and the voltage versus current graph area. The results shown that none of the stability indexes tested has been shown to indicate, alone, a good relationship to the surface appearance obtained for the three electrodes studied. The rutile type electrode was the only one that clearly produced better weld appearance at 20 meters than in shallow water depth. The rutile and oxidizing electrodes showed better surface appearance with the increased number of short circuits. For the rutile electrode, the globular transfer mode with high voltage were directly related with poor weld bead surface appearance.
Comprehensive FEA of Thermal Mitigation Buoyancy Module (TMBM)–Soil Interaction Using the Coupled Eulerian–Lagrangian (CEL) Method
Authors: Pike Kenton , Duan Gang , Sun Jason , Jukes Paul
Published: January 2011

Thermal expansion and global buckling is a critical design aspect for subsea flowline systems subjected to high pressure and high temperature (HPHT). In the Gulf of Mexico, HPHT oil/gas production is becoming exceedingly common as drilling and production depths extend deeper. Advanced finite element analysis becomes essential for flowline expansion and buckling design which is highly dependent on pipe-soil interaction behavior. For decades, pipe-soil interaction has been the focus of many research studies and joint industry projects. For HPHT flowline systems, thermal mitigation is decisive for safe design. Thermal mitigation acts to control global buckling at designate locations and avoid buckling in unknown locations. Thermal mitigation results in significant cost savings by lowering the welding class besides the buckling locations and increases safety in terms of local buckling, fracture, and fatigue. One widely used thermal mitigation method involves attaching a buoyancy module around a segment of the flowline. In this paper the Coupled Eulerian Langrangian (CEL) finite element (FE) formulation is utilized to simulate the interaction between soil and the thermal mitigation buoyancy module (TMBM). The paper demonstrates the capability of the CEL FE method to simulate large soil deformation without the numerical difficulties that are commonly associated with other numerical formulations e.g. ALE (Arbitrary Lagrangian Eulerian) or more conventional Lagrangian. Initially, a three dimensional (3D), continuum, FE model is used to establish the variation of initial embedment along the length of the buoyancy and adjoining pipe. The study then establishes the lateral displacement/resistance relationships under different levels of contact pressure and soil embedment for a series of buoyancy-soil interaction segments, also using the CEL FE method. Current practice for global pipeline thermal expansion FEA is to utilize the same friction model for both buoyancy-soil interaction and pipe-soil interaction. The obtained buoyancy-soil interaction model from the current study is to be used as input to the global FE model to more precisely simulate flowline lateral buckling behavior. This paper presents a practical application of the current state of the art in modeling large soil deformations in providing an improved approach for modeling buoyancy-soil interactions in the global FEA of pipeline thermal expansion and lateral buckling.
Non-Linear Initialization in Three-Dimensional High Order Spectra Deterministic Sea State Modeling
Authors: Perignon Yves L. , Bonnefoy Felicien , Ferrant Pierre , Ducrozet Guillaume
Published: January 2011

This study deals with the initialization of three-dimensional wave field computations. We carry out such simulations with an HOS model developed at LMF-ECN since 2002 and based on the work of West et al. (1987) and Dommermuth & Yue (1987). In such models, initial conditions for three-dimensional realistic sea state computation are obtained by linearly distributing energy density spectrum. This however implies a relaxation of the non-linear effects as proposed by Dommermuth (2000) for bi-dimensional monochromatic wave train and Tanaka (2001), over several tenths of wave periods. The present work tests those former initialization methods and exposes an alternative initialization based on a non-linear three-dimensional approach. Non-linear interaction processes are both accounted in the spectra of elevation and potential of velocity, in accordance with the formulation of Dalzell (1999) at second order in wave steepness. Non-linear energy calculation is then addressed and the efficiency of the methods as well as their possible impact on properties and statistics of the wave field are investigated.
Best Practice Riser Integrity Management and Its Applicability to Greenfield and Brownfield Developments
Authors: Botto Adriana , Hull Meghan , Singh Binder , Golczynski Tommy , Wittkower Bob
Published: January 2011

An improved approach is presented for the cost efficient, reliable development and implementation of a holistic Integrity Management (IM) plan for risers systems. Examples based on project experience are provided, illustrating how this process can be applied to Green and Brownfields alike. Flexible Pipe, Top Tension Risers (TTR) and Steel Catenary Riser (SCR) major hazards will be evaluated for a new development tie-in to existing facility, as major material compatibility threats may arise. Consideration regarding available mitigation measures will be discussed. This process will also identify synergies in the planning and scheduling of integrity management activities that can help achieve significant cost benefits through optimized mobilizations with other offshore interventions. The intent is to retain focus on practical retention of technical integrity throughout the riser lifecycle, while emphasizing that integrity management is a dynamic process that takes advantage of best practices from both analysis and operations personnel. Similarly, good interface between design and operations teams can ensure better co-operation between the CAPEX and OPEX cost centers. This then ensures design personnel have the data required to better optimize immediate life cycle ‘fitness for purpose’ as well as future reassessment capabilities of the system.
Numerical and Experimental Analysis of a Novel Wave Energy Converter
Authors: Rhinefrank Ken , Schacher Al , Prudell Joe , Cruz Joao , Jorge Nuno , Stillinger Chad , Naviaux David , Brekken Ted , von Jouanne Annette , Newborn David , Yim Solomon , Cox Dan
Published: January 2011

A novel point absorber wave energy converter (WEC) is being developed by Columbia Power Technologies, LLC (CPT). Numerical and physical experiments have been performed by Columbia Power, Garrad Hassan and Partners (GH) and Oregon State University (OSU). Three hydrodynamic modeling tools including WAMIT, GH WaveFarmer, and OrcaFlex are used to evaluate the performance of the WEC. GH WaveFarmer is a specialized numerical code being developed specifically for the wave energy industry. Performance and mooring estimates at full scale were initially evaluated and optimized, which were then followed by the development of a 1/33rd scale physical model to obtain comparable datasets, aiming to validate the predictions and reduce the uncertainty associated with other numerical model results. The tests of the 1/33rd scale model of the CPT WEC were recently carried out at the multi-directional wave basin of the O.H. Hinsdale Wave Research Laboratory (HWRL), in conjunction with the Northwest National Marine Renewable Energy Center (NNMREC) at OSU. This paper presents details of the modeling program and progress to date. Emphasis is given to the coupling of WAMIT with GH WaveFarmer for performance estimates and the coupling of WAMIT with the OrcaFlex model for mooring load estimates. An overview of the novel 3-body WEC, including operation and mooring system, is also presented. The 1/33rd scale model functionality is described including an overview of the experimental setup at the basin. Comparisons between the numerical and experimental results are shown for both regular and irregular waves and for several wave headings and dominant directions using a number of spreading functions. The paper concludes with an overview of the next steps for the modeling program and future experimental test plans.
Time-Domain Simulation of a Multi-Body Floating System in Waves
Authors: Yu Xiaochuan , Falzarano Jeffrey M. , Su Zhiyong
Published: January 2011

It is important to study multi-body dynamics when analyzing the transfer of cargo between ships and platforms at sea. The hydrodynamic interactions should be considered in an accurate way to predict the relative motions between them. In this paper, the response amplitude operators (RAOs) of a single vessel will be compared with those of a multi-body system, considering different spacing between them. Further, the coupled hydrodynamic interactions among multiple vessels in close proximity are studied. Various levels of approximation, including the constant coefficient method (CCM) and the impulse response function (IRF) method, are employed to model the hydrodynamic interactions. Finally, the comparison between a single vessel and multi-body time domain simulation is also given.
Piper Alpha and the Evolution of Inherently Safe Design and Integrity Management: An Overview of Interpretations and Lessons Learned
Authors: Singh Binder , Jukes Paul , Wittkower Bob , Poblete Ben
Published: January 2011

The development of Inherently Safe Design, Corrosion and Integrity Management as a genuine combined engineering discipline has evolved largely over the past 30 years or so, with significant acceleration and urgency after the Piper Alpha offshore disaster in the North Sea in 1988. The concepts and practices have matured with many significant changes implemented across the world offshore regions. Even after more than 20 years, the emanating point for sweeping changes has been the Cullen Report and the UK North Sea industry. This paper offers an interpretation of the early and later lessons learned, as applicable and relevant to deepwater and by analogy arctic offshore assets and pipelines, whereupon conditions are harsh and accessibility very limited. The particular focus is on the so called ‘secondary tier’ points related to materials performance, corrosion, and integrity; the understanding monitoring and control of such matters and failures can be critical in reconstituting integrity, if pragmatic life cycle safety and performance are to be recognized. It is argued that modes of failure such as those related to loss of material properties, corrosion, erosion, environmental cracking, and other degradation phenomena, have become far more critical in deepwater and arctic projects. This is mainly due to repair, retrofit, or re-habilitation being invariably far too costly if not virtually impossible in practice. The authors’ use career wide experiences post Piper Alpha to highlight the worries and concerns offering rational pragmatic solutions, illustrated through related case histories. Conclusions and recommendations are based on predictions, interpretations, and viable solutions. Additionally, industry disconnects between technology transfer under this tutelage are identified. The new methods of ‘concurrent design’ and inherently safe design are discussed, and in the context of mechanical, materials, and corrosion engineering advances are related to the use of Key Performance Indicators (KPIs) and Key Failure Indicators (KFIs), for best life cycle integrity and knowledge management. This approach is considered very important for deepwater and arctic assets where ‘surprise’ failures, environmental and political ‘snafus’ are not really an option, and thus more purposeful design investment at CAPEX is vital rather than at OPEX, and the ‘gray’ zone between the two cost centers must be therefore be better reconciled, perhaps it is argued through the concept of an extended CAPEX.
Fatigue Strength Assessment for High Strength Steel Welded Joints
Authors: Kim Ho Jung , Kang Sung Won , Lee Jae Myung , Kim Myung Hyun
Published: January 2011

The aim of the present paper is to investigate and to compare the fatigue characteristics of butt welded joints made of high strength steel with tensile strength 700MPa. The influence of different back plate materials and the groove shapes of copper backing are investigated. Various backing methods have been used in the steel construction industries, but steel backing, which is the most frequently used, sometimes is not capable of providing sufficient fatigue strengths for welded joint, particularly for high strength steel. Therefore, alternative backing methods have been investigated in order to improve the fatigue strength by employing ceramic backing, CMT (Cold Metal Transfer) [1] and copper backing. The main objective of the work is to estimate the fatigue test results for improving fatigue strength by comparing different backing materials and groove shapes. A series of fatigue tests with different types of backings has been carried out to obtain the fatigue life of butt welded joints. It was observed that the fatigue behavior of welded joints can be substantially improved by changing back bead shapes. The result has shown that the back bead shape of copper backing is better than others except for that of CMT, accompanied by improved fatigue strength.
Physical Modelling of Hydrodynamic Loads on Piggyback Pipelines in Combined Wave and Current Conditions
Authors: Brankovic´ Masˇa , Zeitoun Hammam , Sutherland James , Pearce Andrew , Jacobsen Vagner , Sabavala Hosi , To̸rnes Knut , Cumming Gary , Willcocks John
Published: January 2011

One of the aspects of pipeline design is ensuring pipeline stability on the seabed under the action of environmental loads. During the 1980s, significant efforts were made to improve the understanding of hydrodynamic loads on single pipeline configurations on the seabed (Reference 1). The stability of piggyback (bundled) pipeline configurations is less well understood, with little quantitative data readily available to the design engineer for practical application in engineering problems (References 2–6). This paper describes an extensive set of physical model tests performed for piggyback on-seabed and piggyback-raised-from seabed (spanning or lifting pipeline) configurations to determine hydrodynamic forces in combined wave and current conditions. The piggyback is nominally in the 12 o’clock position. The well-established carriage technique was used, in order to obtain data for use in full-scale stability modelling. The model tests are benchmarked against existing test data, to confirm the validity of the test method. Key findings are presented in terms of non-dimensional coefficients, and force time histories for the vertical and horizontal forces. A brief interpretation of the hydrodynamic load behaviour of the Piggyback System is provided by considering the physical flow mechanisms causing the force time history variation; furthermore the influence of the seabed separation on the piggyback loads is also discussed.
Extreme Storm Wave Histories for Cyclic Check of Offshore Structures
Authors: Hagen O̸istein , Solland Gunnar , Mathisen Jan
Published: January 2011

Offshore platform resistance to cyclic storm actions is addressed. In order to achieve the best economy of the structure especially when assessing existing structures, the ultimate capacity of the structure is utilized. This means that parts of the structure may be loaded into the non-linear range and consequently the load-carrying resistance of the structure against future load cycles may be reduced. In such cases it is required to carry out a check of the cyclic capacity of the structure. Such checks are required in the ISO 19902 code for Fixed Steel Offshore Structures. The paper presents a proposal for how a load history for cyclic checks can be established. The method is in line with what is included in the NORSOK N-006 standard on “Assessment of structural integrity for existing load-bearing structures”. The load-history for the waves in the design storm may be expressed as ratio of the dimensioning wave. The ratio will be different for check of failure modes where the entire storm will be relevant such as crack growth, compared to failure modes like buckling where only the remaining waves after the dimensioning wave need to be accounted for. Using simple order statistics and simulation, the statistics for the ith (Hi), i = 1, 2, 3, 4 etc. highest wave in the storm is studied in some detail, assuming that the maximum wave (H1) is equal to an extreme wave obtained by a code requirement. Environmental contours for the pair (H1,H2) are established by Inverse FORM for design conditions. Further, the long term statistics for load effects that are expressed as a function of H1, .., H4, i.e. L = f(H1, .., H4), are determined. The R-year value LR for the load effect L is determined by structural reliability techniques, and the most probable combination (design point) (H1*, .., H4*) for L = LR is determined. The design point values Hi*, as well as the design point value for the significant wave height, are determined for different load effects, and their characteristics for different types of load effects are discussed. The paper gives advice also on how to establish the magnitude for the remaining waves in the storm.
Effects of the Yield Criterion on Predicted Fracture Responses of Pipelines Subjected to Large Plastic Deformation With and Without Internal Pressure
Authors: Kane Alexandre , O̸stby Erling , Lademo Odd-Geir , Berstad Torodd , Hopperstad Odd Sture
Published: January 2011

The structural integrity of offshore pipelines is of vital importance for safe oil and gas transport. To ensure the required safety level, non-linear Finite Element (FE) analyses are necessary to perform fracture assessment of pipes under various, realistic loading conditions. Many standard material models, as found in commercial FE codes, pre-suppose the yield criterion of von Mises. This choice provides in many cases reasonable accuracy, certainty and engineering designs, but for some materials and application areas, it is much too inaccurate. In this work, 3D elastic–plastic FE simulations of pipes with internal surface cracks have been carried out. The aim of the work is to evaluate the influence of the yield criterion on the predicted fracture response. Analyses are performed on pipes loaded in tension, with and without internal pressure. The model shows that the yield surface shape may have a significant effect on the predicted evolution of Crack Tip Opening Displacement (CTOD). If the internal pressure is weak, a reduction in strain capacity is observed when the yield surface shape is varied from the rounded von Mises towards the cornered Tresca-like yield surface.
ASDD Technology in Deepwater Drilling and Its Process of Commercialization
Authors: Guo Yong-feng , Ji Shao-jun , Tang Chang-quan
Published: January 2011

The paper had discussed on a new technology and equipment in deepwater engineering, ASDD (Artificial Seabed Deepwater Drilling), and its process of commercialization in COSL of China. The concept of ASDD had put forwarded by a Norway engineer in 1993, and COSL had introduced it to China since 2004 from Europe, which has been built the cooperation with a company from Norway to develop ASDD not only the technology but also equipment. The advantages of ASDD is both reduce cost of drilling in deepwater and use common semi submersible to replace of expensive platform in deepwater drilling until water depth of 1500 m. A series of tests and simulations had been done both abroad and domestic by COSL and two large trial operations had been gone in South China Sea between 2008 and 2009. The trial well operation had been completed in Apr. of 2009, and COSL dispatched many huge vessels, including to Nanhai V, which is one of the hugest semi submersible in Aria, and AHVs that power is over 10,000 HP, such as Nanhai 212, Nanhai 213, Nanhai 216 and so on. The trial well had taken great success. It is obvious that COSL intend to carry out process of commercialization for ASDD, and the two commercial wells had been planed to drill in South China Sea in 2010.
Towards a Unified Fatigue Life Prediction (UFLP) Method for Marine Structures: An Overview
Authors: Cui Weicheng , Wang Fang , Wang Xiaoping
Published: January 2011

Marine structures such as ships and offshore platforms are mostly made of metals and designed with damage tolerance. This design philosophy requires accurate prediction of fatigue crack growth under service conditions. Now more and more people have realized that only a fatigue life prediction method based on fatigue crack propagation (FCP) theory has the potential to explain various fatigue phenomena observed. However, it is not the case that any type of FCP theory can work. As a matter of fact, from the very fundamental question of fatigue crack driving forces to the more complicated fatigue crack growth rate expressions all are needed critical examination. In the past several years, the group led by the authors have made some efforts in developing a unified fatigue life prediction (UFLP) method for marine structures. By unified method the authors mean that the method should be able to explain all the observed fatigue phenomena. In this paper, an overview of these researches is carried out and our main research results are presented.
Extreme Value Analysis of the Response of a Turret-Moored FPSO
Authors: Sagrilo Lui´s Volnei Sudati , Naess Arvid , Gao Zhen
Published: January 2011

One of the standardized procedures used in the design of floating systems and their mooring and production lines is the so-called short-term design approach where the system is analyzed for some specific extreme environmental conditions. Along with this procedure, a nonlinear time-domain coupled dynamic analysis, considering the floater and its risers and mooring lines, is nowadays feasible to be employed in the design practice. One important and challenging aspect of this process is concerned with the estimation of the characteristic short-term extreme values of the system response parameters based on the sampled time-series. In this paper a common procedure used to establish these extreme values for floater system response parameters, which is based on a Weibull distribution model for the time-series peaks, is reviewed in the light of a recently proposed approach based on a general parametric model for the average conditional exceedance rate of peaks. It is shown that the former model corresponds to a particular case of the latter one. Numerical results are presented for the response parameters of a turret-moored FPSO considering a short-term coupled analysis of the whole system under an extreme environmental condition of wind, wave and current. Specifically, the extreme response of surge motion, top tension of the most loaded mooring line and DnV’s utilization factor for the most critical section of a 8″ SLWR (Steel Lazy Wave Riser) are investigated.
Kinetic, Dynamic and Energy Characteristics of Vortex Evolution on Bragg Scattering of Water Waves
Authors: Hsu Tai-Wen , Ou Shan-Hwei , Tsai Chin-Yen , Lin Jian-Feng
Published: January 2011

The vortex generation and dissipation under Bragg scattering of water wave propagation over a series of submerged rectangular breakwaters are investigated both numerically and experimentally. A Reynolds Averaged Navier-Stokes (RANS) model combined with a k–ε turbulence closure is applied to simulate the entire vortex evolution process as water waves pass over a series of artificial rectangular bars. The Particle Image Velocimetry (PIV) is also used to measure the velocity field in the vicinity of the obstacles. The numerical model is validated through the comparisons of water surface elevations and velocity field with the measurements. The mechanism of vortex evolution and its influence on the interaction of water waves with submerged structures for both cases of resonance and non-resonance were studied. Wave reflection coefficients for both resonant and non-resonant cases were calculated and compared with experiments and solutions based on the linear wave theory. It is also found that the calculated vortex intensity at the last bar is only one third of that at the leading bar for the near-resonant case. The local kinetic energy is also found to attain its minimum value at a place where potential energy became larger in Bragg scattering of water waves.
Probabilistic Evaluation of Collision Between DP Shuttle Tanker and Geostationary FPSO in Direct Offloading
Authors: Chen Haibo , Lerstad Arve , Moan Torgeir
Published: January 2011

A geostationary FPSO does not weathervane like a turret-moored ship-shaped FPSO. The offshore industry has limited experience for direct offloading from such geostationary installations in the North Sea. In recent years direct offloading operations from geostationary FPSOs by DP shuttle tankers, have been developed, and key operational principles for such a system are presented in this paper. Probabilistic modeling of the collision risk between shuttle tanker and geostationary FPSO in direct offloading is presented, followed by a case study. It is found that the collision risk level is much lower in the direct offloading than in the tandem offloading. The results demonstrate that the direct offloading approach is a promising concept with inherent safety designed in the operations, i.e. the positioning philosophy of the shuttle tanker and a large separation distance.
Experimental and Numerical Study of the Depth Effect on the First Order and Slowly Varying Motions of a Floating Body in Bichromatic Waves
Authors: Pessoa Joa˜o , Fonseca Nuno , Guedes Soares C.
Published: January 2011

The paper presents an experimental and numerical investigation on the motions of a floating body of simple geometry subjected to harmonic and bi-harmonic waves. The experiments were carried out in three different water depths representing shallow and deep water. The body is axis-symmetric about the vertical axis, like a vertical cylinder with a rounded bottom, and it is kept in place with a soft mooring system. The experimental results include the first order motion responses, the steady drift motion offset in regular waves and the slowly varying motions due to second order interaction in bi-harmonic waves. The hydrodynamic problem is solved numerically with a second order boundary element method. The results show a good agreement of the numerical calculations with the experiments.
Acoustic analysis of the vocal tract during vowel production by finite-difference time-domain method
Authors: Takemoto Hironori , Mokhtari Parham , Kitamura Tatsuya
Published: January 2011

The vocal tract shape is three-dimensionally complex. For accurate acoustic analysis, a finite-difference time-domain method was introduced in the present study. By this method, transfer functions of the vocal tract for the five Japanese vowels were calculated from three-dimensionally reconstructed magnetic resonance imaging (MRI) data. The calculated transfer functions were compared with those obtained from acoustic measurements of vocal tract physical models precisely constructed from the same MRI data. Calculated transfer functions agreed well with measured ones up to 10 kHz. Acoustic effects of the piriform fossae, epiglottic valleculae, and inter-dental spaces were also examined. They caused spectral changes by generating dips. The amount of change was significant for the piriform fossae, while it was almost negligible for the other two. The piriform fossae and valleculae generated spectral dips for all the vowels. The dip frequencies of the piriform fossae were almost stable, while those of the valleculae varied among vowels. The inter-dental spaces generated very small spectral dips below 2.5 kHz for the high and middle vowels. In addition, transverse resonances within the oral cavity generated small spectral dips above 4 kHz for the low vowels.