bluuebunny/crossref_metadata_2025 huggingface dataset:
A Numerical Study on the Performance of Composite Foundation System With Piles and Cushion
Authors: Cui Chun-yi , Li Jun , Luan Mao-tian , Li Mu-guo , Sun Zhan-qi
Published: January 2011

For the reason that composite foundation can fully realize the potential of bearing capacity of subsoil and reinforcement, it has been widely applied in modern foundation engineering of coastal area. However, knowledge towards the mechanism and the performance characteristics of composite foundation is not mature enough. Thus more intensive and further study is required on the design and construction methods. In this paper, elasto-plastic numerical computation is conducted by developing elasto-plastic FE model in plane stress state, together with adopting Mohr-Coulomb yield criterion to describe the elaso-plasticity of subsoil and Coulomb contact pair theory with penalty algorithm to simulate the discontinuous contact behavior of foundation and soil, as well as using infinite element in model boundary to avoid static boundary effect. Based on the elasto-plastic numerical model of composite foundation with piles and cushion used above, the characteristics of internal forces and deformation of composite foundation system including raft, cushion and piles are analyzed. Furthermore, the respective effect of raft foundation, cushion and piles on the durability and performance of whole composite foundation system is discussed. On the basis of computational results and theoretical analyses, several conclusion remarks are drawn to provide certain references for related construction and design practice.
Nonlinear NWT Simulation for Oscillating-Water-Column Wave Energy Converter
Authors: Koo Weoncheol , Kim Moo-Hyun
Published: January 2011

A two-dimensional time-domain, fully nonlinear numerical wave tank (NWT) technique based on potential theory, the mixed Eulerian-Lagrangian (MEL) approach, and the boundary element method was developed and applied to a land-based oscillating water column (OWC) system with compressed air inside the chamber. The nonlinear free-surface inside the chamber was specially treated to represent both the viscous effect of the water column motion and the pneumatic pressure of the time-varying airflow velocity in the chamber. The developed NWT was verified through comparison with viscous-flow-based numerical and experimental results by Liu et al. (2008) with and without air ducts. The NWT simulations correlated well with experimental values with tuned viscous damping coefficient for a variety of wave conditions. The fully nonlinear simulations were also performed with irregular wave input, so that the developed numerical tool can be practically used for the optimal design of land-based OWCs.
CFD Modeling of Corrugated Flexible Pipe
Authors: Jaiman Rajeev K. , Oakley Owen H. , Adkins J. Dean
Published: January 2011

The objective of this paper is to present Computational Fluid Dynamics (CFD) modeling of fully developed turbulent flow through a flexible corrugated pipe and to investigate the pressure drop reduction potential of liners. This work also aims to establish a framework to be used in large scale numerical simulations of the offshore transfer of cryogenic fluids. A 3-D CFD approach is considered more appropriate than 2-D axisymmetric one, since the wavy corrugation profiles lead to a great deal of internal turbulent structures for high Reynolds number over Re > 106. Three geometries of the bellows’ (corrugation) depth are considered to determine the potential value of a cryogenic liner, corrugation filler or geometric variations for the 16″ pipe. The reduction in cost and complexity of developing a robust cryogenic liner or corrugation filler, plus eventual certifications, would be significant and needs to be worth the improvement (decrease) in pressure drop. We conduct a straight pipe corrugation depth study for pressure drop (deep corrugation, shallow corrugation and liner), and include suitable mesh convergence and unsteady simulations. We also attempt to validate the friction coefficient data with the empirical formulas and recent experimental tests. Operational cryogenic transfer flow rates ranging from Q = 1000 m3/h to Q = 5000 m3/h are considered.
Vortex Induced Vibration Analysis of a Complex Subsea Jumper
Authors: Holmes Samuel , Constantinides Yiannis
Published: January 2011

Jumpers are typically short sections of curved pipe spanning production riser elements on the sea floor. When in areas of significant currents these jumpers are subject to vortex induced vibration (VIV). The complex shape of the jumper means that numerical methods are usually needed to solve for the vibration modes of the jumper. Furthermore, the fluid flow around the jumper is also complex so that traditional methods of VIV analysis used for risers are not applicable to jumpers. Here we use a CFD code in a fully coupled analysis to predict vibration response and strain of a typical subsea jumper. A separate finite element analysis is used to calculate the eigenvalues and eigenvectors of the jumper system for input into the CFD analysis. The resulting method is economical and practical for design analyses.
Real-Time Analysis of Higher Order Ship Motion Spectrum
Authors: Iseki Toshio
Published: January 2011

The real-time algorithm of higher order spectral analysis is proposed in order to investigate the non-linear and non-stationary ship motions. The algorithm is based on the time-varying vector auto-regressive (TVVAR) modeling and can be considered as an extension of the instantaneous cross spectral analysis. The TVVAR model is fitted to the data using the Kalman filter algorithm and the instantaneous higher order spectra can be evaluated by using the TVVAR coefficients. In order to examine the validity of the proposed algorithm, numerical simulations of the real-time estimation of higher order spectra was carried out based on the full scale ship motion data. The accuracy of the proposed algorithm was investigated by comparing with the stationary analysis based on the FFT. Furthermore, the algorithm was extended to the trispectral analysis and a result was shown to demonstrate the usefulness of the proposed algorithm.
Ship Motion Predictions: A Comparison Between a CFD Based Method, a Panel Method and Measurements
Authors: Huijsmans R. H. M. , van ‘t Veer R. , Kashiwagi M.
Published: January 2011

In the past 50 years the research into the behavior of ships in seaway has shown a great deal of progress. From analytical solutions of 2-d hydrodynamics as derived by Ursell in 1949 to complex 3-d CFD numerical solutions that can be used nowadays. The first consistent approach for ship motions in time domain was derived by prof. T.F.Ogilvie [] as presented in his seminal paper in Bergen in 1964. Throughout the years however ship hull forms developed and the need for validation of computational procedures for the calculation of the ship motions has never gone away. In this paper we present a selection of results of a benchmark study performed by some 12 companies and universities using their state of the art computational tools. In this benchmark study the results of model tests of a modern container vessel are used. The results presented in this paper show that the panel method as described in this paper, based on the disturbed steady flow, leads to acceptable transfer functions for ship motions. The CFD approach used in this paper also produces acceptable motion transfer functions. However the results from the CFD computation for the internal load transfer functions do show a larger scatter when comparing with the results from model test.
Two-Dimensional Vessel-Motion/Liquid-Sloshing Interactions and Impact Loads by Using a Particle Method
Authors: Lee B.-H. , Park J.-C. , Kim M.-H.
Published: January 2011

The violent free-surface motions interacting with floating vessels containing inner liquid tanks are investigated by using the newly developed Moving Particle Semi-implicit (MPS) method for 2-dimensional incompressible flow simulation. In the present numerical examples, many efficient and robust algorithms have been developed to improve the overall quality and efficiency in solving various highly nonlinear free-surface problems and evaluating impact pressures compared to the original method proposed by Koshizuka and Oka (1996). For illustration, the improved MPS method is applied to the simulation of nonlinear floating-body motions, violent sloshing motions and corresponding impact loads, and vessel motions with inner liquid tanks. It is seen that the roll amplitudes can be significantly reduced due to the presence of the sloshing tank when the excitation frequencies are away from the lowest sloshing natural frequencies. The developed numerical tools can be used to the study of vessel motions with liquid cargo or design of passive anti-rolling devices.
Numerical Analysis for Pipeline Installation by S-Lay Method
Authors: Wang Li-Zhong , Yuan Feng , Guo Zhen
Published: January 2011

S-lay method is widely used in pipeline installation from shallow water to deep water for decades. However, previous researches on S-lay method are not so complete because they are based on some assumptions, such as calm water and rigid seabed, which make the results deviate from precision. In this paper, a novel numerical model for analyzing pipelines in the S-lay problem is proposed to investigate the overall configuration, internal forces and strain of the pipeline taking into account the influence of ocean currents and seabed stiffness. Such a model is of great advantage because it can properly consider many influential factors in the real situation, including the variation position of the liftoff point, the change of stinger radius, the influence of ocean currents, seabed stiffness and the strain of the pipeline. Moreover, the solution process of this model is easy and not time consuming, so it is suitable for engineering application.
Business Risk Management Applied to Offshore Pipeline Field Development
Authors: Gan Lihua
Published: January 2011

A world class project must have a disciplined business risk management. As a good project manager, he should manage project risk successfully. Through business risk management, he can identify risk of the project, find the cause of all business risks, then define the influence of all risks. He can take measures to avoid, transfer, and mitigate the risk. A field development includes production facilities, risers and pipelines and subsea wells, in which the pipelines and risers connect the subsea wells and production facilities to transfer oil and gas. The cost of offshore pipelines and risers is major. In the following we shall take offshore pipeline and riser as a case study to practice the principal of business risk management step by step. It has been demonstrated that the method may be applied to maximize the returning for the stakeholders in an offshore field development. However, it is suggested to accumulate and update the data bases required for an accurate statistical evaluation.
Cavity Flow in a Boundary Layer
Authors: Yoon Bum-Sang , Semenov Yuriy A.
Published: January 2011

A numerical-and-analytical method for solving cavity flows in a vortex incidence flow is proposed. The continuous vorticity arbitrary displayed in the flow field is replaced by discrete vortex lines coinciding with stream lines. The flow between these lines is assumed to be vortex free. The problems of the flow in channels formed by stream/vortex lines and the problem of the cavity flow in a jet of a finite width connected to each other by the derived interaction conditions are solved by using complex variable theory. The numerical procedure is based on the method of successive approximations and adopted to investigate the effect of the velocity gradient in a boundary layer on parameters of the cavity flow. The presented calculations show that, at some fixed cavity length, the cavity number and drag coefficient decreases with the increase of the boundary layer width.
Suppressing Vortex-Induced Vibrations of Long Flexible Riser by Multiple Control Rods
Authors: Wu Hao , Sun Dapeng , Lu Lin , Teng Bin , Zhang Jianqiao , Xie Bin
Published: January 2011

Experimental investigations on a passive control method for suppressing VIV of long flexible riser are presented in this work. A riser model with L/D (slenderness ratio) of 1750 was horizontally installed on a carriage and uniform current was simulated by towing the riser using the carriage in a wave tank, which leads to the Reynolds numbers ranging from 103 to 104. Four slender control rods with diameter d = 0.25D were placed parallel to the riser at uniform angle (i.e. at 90° intervals around the riser circumference). Different pitch distances l/D = 0.813, 1 and 1.188 were considered in this work, where l is the center-to-center distance between control rod and riser model. Strain along the riser and tension were measured by Fiber Bragg Grating and tensionmeter, respectively. The experimental results indicate that the response characteristics of a riser model with multiple control rods are quite distinct from that of a bare riser. Multiple control rods can suppress VIV response significantly, and their performance is mainly dependent on the pitch distance. It is found that the spatial maximum standard deviation of strain decreases about 84% due to the existence of control rods. The optimal pitch distance is found to be l/D ≤ 1. Moreover, spectrum analysis shows that the dominate frequency increases linearly with the increasing of flow velocity, for both the bare riser and the riser with control rods, while the frequency band of the suppressed riser becomes broader compared with the bare riser. It is also observed that the tension of the riser is slightly increased due to the presence of four rods, but not sensitive to the pitch distance.
Numerical Study of a Semi-Displacement Ship at High Speed
Authors: Sun Hui , Faltinsen Odd M.
Published: January 2011

A numerical analysis of a semi-displacement ship at high forward speed is performed by using a 2D+t theory. Time dependent two-dimensional (2D) boundary value problems are solved in space-fixed vertical planes by a Boundary Element Method (BEM). The steady advancing of the ship in the calm water is simulated, although the theory is also capable of solving the unsteady problem with forced oscillations in heave and/or pitch. The numerical results for the steady motions are compared with Keuning’s experiments [1]. The sectional vertical forces along the ship and the wave elevation around the ship hull are presented. The effects of non-viscous flow separation and the three-dimensional effects at the transom stern are discussed.
Design of Pipelines Against Ice Scour: Effects of Seabed Geology
Authors: Konuk Ibrahim , Yu Shenkai
Published: January 2011

In recent years, several computational models were published for the analysis of pipelines subjected to ice scour. With one exception, most of these models assumed uniform seabed soil properties. This paper studies the effects of different seabed soil stratigraphies on the ice scour process. Influence of various stiffer and softer soil sequences on the pipeline stresses are analyzed. Effects of reworking or remolding of soils by recurrent scours are studied. The question of existence of limiting scour depths is explored by examining the interaction forces between the seabed soils and the ice keel during the scour process.
Prediction of Motions and Loads for Floatover Installation of Spar Topsides
Authors: Koo Bonjun , Magee Allan , Lambrakos Kostas , Beyko Eleni , Sablok Anil
Published: January 2011

There are several substantial advantages to installing integrated topside onto a Spar using floatover method, particularly for large topsides which exceed the single lift capacity of the available heavy lift derrick barge fleet. These advantages include schedule and cost savings for the integration and commissioning of modules on land rather than at sea. Uncoupling the deck fabrication schedules from the availability of heavy lift vessels is another advantage. The performance of a successful floatover installation requires adequate design and analysis of each phase of the floatover installation, and a sufficient weather window in which to perform each phase. Design of floatover installation includes: a) Global motions / mooring analysis to determine motions and loads on mooring lines, fenders, and structural members, b) Structural design including structural integration of the topsides with the barges and shock cell design on the Spar and barges, and c) Operational procedures for mating and barge separation. Validated analysis tools are essential to ensure adequacy in the design of all stages in the floatover operation. This paper presents data from floatover installation model tests, performed at OTRC (Texas A&M University, College Station, Texas, USA), and results from numerical analysis tools for motion and load predictions. The scale of the model tests was 1:60, and the simulated topside was approximately 18,000Te. The simulated environmental conditions included expected upper limit operational sea states for the Gulf of Mexico. The details of the model tests are described in Ref [1]. The analytical challenges related to floatover installation simulations are several and include multi-body hydrodynamics, and prediction of relative motions and interface loads during the mating operations. Available numerical analysis tools include the time domain multi-body proprietary code MLTSIM, and WAMIT, a frequency domain potential code that is widely available in the industry. The validation of MLTSIM involves viscous damping, multi-body hydrodynamic interaction, and simulation of impact forces. This paper presents the results from the validation on the basis of full scale, and quantifies the accuracy of predictions by comparing the measured and predicted motions and loads.
A Hybrid Framework for Free-Surface Flows With Irregular Solid Boundaries
Authors: Zhang Qinghai
Published: January 2011

The author presents a hybrid continuum-particle framework (HyPAM) consisting of three components. The first is a second-order interface tracking method: the Polygonal Area Mapping (PAM) method [Zhang and Liu 2008. J. Comput. Phys. 227(8):4063–4088], which represents material areas explicitly as piecewise polygons and utilizes polygon-clipping algorithms from computational geometry. In addition to its mesh-topology independence, the PAM method is free of numerical diffusion and tracks interfaces with or without singularities naturally and accurately. Both numerical experiments and theoretical analyses show that the PAM method is superior to existing VOF methods. The second component is a hybrid formulation for free-surface flows [Zhang and Liu 2009. J. Comput. Phys. 228(4):1312–1342]. A graph-based algorithm decomposes the water phase into a continuum zone and a particle zone, where the Euler equations and the free fall of rigid bodies are used as the governing equations, respectively and separately. The third component is the Explicit Jump Approximation (EJA) method for handling irregular solid boundaries in viscous flows [Zhang and Liu 2010. J. Comput. Phys. in press]. An analysis shows that the widely-used linear and quadratic ghost-cell approaches (GCA) are inconsistent and first-order accurate, respectively. As a remedy, the jump corrections at the solid-fluid interface are explicitly approximated and incorporated into the discretization of the Laplacian operator to obtain second-order convergence. Further developments of HyPAM include a fourth-order Navier-Stokes solver with adaptive mesh refinement (AMR), incorporating a particle method, and multi-material three-dimensional interface tracking.
Regeneration of Fishing Ports as Tourism Industry in Republic of Korea
Authors: Jung Wonjo , Kondo Takeo , Yamamoto Kazukiyo , Lee Hanseok
Published: January 2011

Factor analyses were performed on fifty eight national fishing ports in Korea, excluding ones on remote islands, with respect to their latent tourism potential, and they were classified as historical/cultural type, fisheries industry-oriented type, tourism development type, nature preservation type, or fishing port-dependent type. Then, cluster analyses were performed to examine these fishing ports from the perspectives of fisheries industry/preservation type and recreation/development type. Results of analyses on tourism characteristics of fishing ports according to the typology indicated regionally uneven trends. In addition, the results of our analyses on the fishing ports with respect to latent tourism potential and tourism structural characteristics showed that the most important contributing factors were production quantity of fisheries products and moorage facilities, followed by nature tourist sites, harbor fixed-water area, and outlying facilities, in that order. Therefore, in developing fishing ports for tourism in the future, political measures are required to enhance fisheries industry bases for maintaining the function of fishing grounds, and, additionally, projects for improving the environment, such as purification of harbor water, are necessary.
Ultimate Strength of a Capesize Bulk Carrier in Hogging and Alternate Hold Loading Condition
Authors: Shu Zhi , Moan Torgeir
Published: January 2011

The ultimate hull girder strength of a Capesize bulk carrier under combined global and local loads in hogging and alternate loading condition (AHL) is evaluated using nonlinear finite element (FE) analysis with ABAQUS software. A three-cargo-hold FE model with fine mesh in the middle cargo hold is developed for the nonlinear FE analysis. The initial geometrical imperfections are introduced in the double bottom of the middle cargo hold. Both material and geometrical nonlinearities are taken into account in the FE model. The most critical situation for the longitudinal strength assessment of bulk carriers in hogging is the AHL condition with middle cargo hold empty under combined global and local loads. The local loads, i.e. the external sea pressure and internal cargo pressure are adopted according to Common Structural Rules for bulk carriers (CSR-BC). The ultimate hull girder strength with various local pressure load levels is investigated for the heavy cargo AHL in hogging condition. It is found that the ultimate strength of the hull girder can be significantly reduced due to the action of the local pressure loads compared with that obtained under pure hogging bending.
Review of the Effect of Hydrogen Gas on Fatigue Performance of Steels
Authors: Zhang Yan Hui
Published: January 2011

To develop hydrogen energy, it is important to understand the effects of hydrogen on mechanical properties in all applications — production, transportation, storage and fuel cells. Although a considerable amount of work has been carried out on hydrogen related embrittlement, there is comparatively less work on the effect of a hydrogen environment on fatigue performance of steels. It is essential to carry out comprehensive and coordinated research to understand how a component is affected when exposed to a hydrogen environment, how to prevent or minimise the failure probability, and finally to gather critical data to develop design guidance and government regulations to ensure safe operation of infrastructures involving hydrogen environment. The paper reviews the effect of a gaseous hydrogen environment on fatigue endurances and fatigue crack growth rates of steels, identifies the major factors promoting hydrogen effects and reviews the requirements for carrying out fatigue tests in hydrogen environment. The review covers degradation on fatigue performance of many variables including steel grades, ΔK magnitude, hydrogen partial pressure, loading frequency, gas composition, stress ratio, microstructures, base and weld metals and temperature. The mechanisms responsible for the accelerated crack growth rates in hydrogen environment and the implication of the degradation on fatigue design are also discussed. It was found that, unlike hydrogen embrittlement, fatigue performance of steels in hydrogen is degraded in both ferritic and austenitic steels, and in both low and high strength steels. The degradation by hydrogen gas is more pronounced with respect to fatigue crack growth rate than fatigue endurance of steels. Based on the results of the review, recommendations are made with respect to further research work required.
Pitch/Roll Static Stability of Tension Leg Platforms
Authors: Xu Ning , Zhang Jun
Published: January 2011

Severe hurricanes in recent years have raised concerns about the safety and the robustness of the Tension Leg Platform (TLP) concept in the deep water Gulf of Mexico. This study investigates the static stability of different types of TLPs representing those deployed in the Gulf of Mexico, under three different scenarios. That is, a TLP with an intact tendon system, a partially damaged tendon system, and a completely damaged tendon system. The two types of TLP chosen for this study are the conventional four-leg TLP (C-TLP) and the Mono-column TLP. To avoid buckling and yielding occurring in a tendon, the maximum righting moment provided by an intact or partially damaged tendon system is reached when the tension in one or more tendons on the down tension leg becomes zero or when the tension in one or more tendons on the up tension leg reach the yielding strength. This definition leads us to identify the most sensitive directions of met-ocean conditions to a TLP with an intact or partially damaged tendon system. Hence, our finding may also be used in the study on the dynamic simulations of a TLP. The righting moments of each TLP in the three different scenarios are respectively computed and compared with related wind-induce static upsetting moment at certain velocities. By comparing their ratios, the static stability of a TLP and the redundancy of its tendon system may be revealed, which has important implication to its design.
Analysis of Practical Examples of Experienced-Based Marine Education for Marine Space Utilization
Authors: Chiu Hsien-Yu , Kondo Takeo , Yamamoto Kazukiyo , Miyazaki Wataru
Published: January 2011

Environmental education is being promoted worldwide and is the subject of active effort in Japan as well. However, many environmental education programs focus on land-based systems, and currently only few schools have programs on the marine environment. Toward the goal of developing an educational game for advancing marine environmental education, we assessed the current state of environmental education and conducted basic research on existing educational games. The current state of environmental education indicated a need for developing educational games with a marine environmental theme to be linked with outdoor hands-on activities. As for the game itself, a card game is likely to be a suitable basic format because it can be used regardless of physical setting and also because the use of a variety of cards can be effective in maintaining continued interest and developing the capacity to understand the annual cycle of the natural environment. We also developed a region-specific card game whose objectives were to understand the region’s organisms and the relationship between people and the environment.
Inplace Model Test Result Correlation of Multi Column Floater (MCF): Drilling and Production Unit
Authors: Tahar Arcandra , Finn Lyle
Published: January 2011

This paper presents the comparison of model tests and numerical results of Multi Column Floater (MCF). MCF is a new drilling and production deep-draft semisubmersible platform developed by Horton Wison Deepwater in Houston. A vertically restrained well deck or Multi Riser Buoyancy Can (MRBC) configured in the center of the MCF is technology enabler for dry tree semisubmersible. The MRBC independently supports and tensions the production and drilling risers. The production risers may be a combination of dry tree risers and subsea tree tubing risers. Inplace model tests were carried out at the FORCE Technology basin during the period September-October, 2007 for the internal study. The test emphasis was to understand the physical behavior of MCF at model scale so that a thorough correlation study could be carried out. MCF mooring stiffness, riser stiffness, natural periods and mass properties of the model were closely matched with target full-scale properties. Guide loads and relative motions between MRBC and hull were measured to obtain model-scale behavior. A wide range of sea states and towing speeds were covered in the test programs. Detailed comparison summarizing the statistical quantities of interests as well as time series and spectral plots are included in this paper. RAO and free decay comparisons are also described.
Comparative Analysis on Fatigue Damage of Deepwater Hybrid Mooring Line
Authors: Qiao Dongsheng , Zheng Changxin , Li Binbin , Ou Jinping , Zhai Gangjun
Published: January 2011

In the deepwater exploitation of oil and gas, the replacement of polyester rope for the wire in chain-wire-chain mooring line is proved to be fairly economic. Previous studies are mainly conducted to hydrodynamic analysis and dynamic response calculation, but there are few studies on the fatigue damage analysis of hybrid mooring line. Take the mooring system of a Spar platform as the research object, and the multi-component mooring lines are usually made up of chain-wire-chain. The representative mooring line has been considered while other conditions are kept unchanged, and top end tension-static offset characteristic curve of the two mooring lines are consistent as much as possible, meanwhile the polyester rope is adopted as the substitute for the wire, then the comparative calculation on fatigue damage of deepwater hybrid mooring line is carried on. The analysis of Spar platform response is carried out in which the wave force is calculated under diffraction theory. After the establishment of two-dimensional nonlinear finite element dynamic model of the hybrid mooring line, the calculation on stiffness of the hybrid mooring line is accomplished through the iterative method based on the empirical formula proposed by Del Vecchio in 1992. The mooring line and seabed interaction is based on the hypothesis of rigid seabed. The fluid drag force and inertia force on the mooring line are calculated according to the Morrison formula. The dynamic analysis is executed through time-domain nonlinear finite element method accounting for the response of the Spar platform which is calculated as above. The stress time histories of the hybrid mooring line in each short-term sea state of South China Sea area are calculated, and then the rain flow counting method is employed to obtain the fatigue load spectrum in each short-term sea state. The Miner linear cumulative law model is used to compare the fatigue damage of the hybrid mooring lines in long-term sea state which consists of tens of short-term sea states. The results show that the using of polyester rope as the substitute for the wire can significantly improve the fatigue resistance.
System Effects in Fatigue Design of Long Pipes and Pipelines
Authors: Lotsberg Inge , Mo̸rk Kim , Valsga˚rd Sverre , Sigurdsson Gudfinnur
Published: January 2011

In fatigue design of steel structures the hot spot area is normally limited in size. In pipelines and cylinders used for transportation and storage of compressed natural gas the hot spot area can extend to several kilometers along a seam weld subjected much to the same stress range. The fatigue capacity for large diameter pipes is reduced as the weld length is increased. The seam weld in pipes is subjected to a significant stress range normal to its weld toes when it is subjected to varying internal pressure from start and stop of gas transportation through pipelines and from filling and emptying of cylinders. A reliable methodology is required for fatigue design of long pipes in order to meet target safety level at an acceptable cost. This includes description of physical models that represents actual long term fatigue capacity of the pipes subjected to varying internal pressure. The design methodology includes length of welds, fabrication tolerances, fabrication methodology and non destructive testing. It also involves definition of characteristic values for loading and capacity in addition to a recommended Design Fatigue Factor to be used in fatigue design. Alternative fatigue design procedures require different Design Fatigue Factors to achieve a required target safety level for pipelines and cylinders used for transportation of gas. These issues are further considered in this paper.
Computation of Slamming Forces on 3-D Bodies With a CIP Method
Authors: Yang Qingyong , Qiu Wei
Published: January 2011

This paper presents the numerical solutions of slamming problems for 3D bodies entering calm water. The highly nonlinear water entry problems are governed by the Navier-Stokes equations and were solved by a Constrained Interpolation Profile (CIP)-based finite difference method on a fixed Cartesian grid. In the computation, the 3D CIP method was employed for the advection calculations and a pressured-based algorithm was applied for non-advection calculations. The solid body and the free surface interfaces were captured by density functions. For the pressure computation, a Poisson-type equation was solved at each time step by the Conjugate Gradient iterative method. Validation studies were carried out for a 3D wedge entering calm water and the entry of a sphere into calm water at both vertical and horizontal velocities. The predicted hydrodynamic forces on the wedge and the sphere were compared with experimental data.
TLP: A Dry Tree Solution for Pre-Salt in Santos Basin
Authors: Moraes Alves Luiz Henrique , de Oliveira Goulart Roberto , Martins Mourelle Marcio , Poll Philip
Published: January 2011

The purpose of this paper is to describe the conceptual TLP designs for the pre-salt area in Santos Basin, which is one of the alternative Dry Tree solutions evaluated for this area. The TLPs were evaluated for 2,200 m of water depth for Santos Basin environmental conditions, where extreme values for wave and wind are significantly higher than for Campos Basin. Three different TLP scenarios have been studied for specific process plants and number of dry completion wells (TTRs). Both wellhead platforms and full production, drilling and quarters platforms have been considered. Characteristics of hull dimensions are shown for the three scenarios with comparisons to existing TLP installations from other worldwide locations. Possible Brazilian construction sites, transportation, integration and installation are discussed. TLP motions, tendon tensions and other performance results are summarized and compared to design criteria. Composite tendon material was investigated and compared with steel tendons in terms of hull size and installation procedure. Main results of TTR analyses are presented, including strength, stroke, fatigue and interference between risers during operation and installation.
Numerical Study on Circulation and Thermohaline Structures With Effects of Icing Event in the Caspian Sea
Authors: Kitazawa Daisuke , Yang Jing
Published: January 2011

A hydrostatic and ice coupled model was developed to analyze circulation and thermohaline structures in the Caspian Sea. The northern part of the Caspian Sea freezes in the winter. Waters start icing in November and ices spread during December and January. The northern part of the Caspian Sea is covered by ices in severe winters. Ice-covered area is at its maximum during January and February, and then ices begin melting in March and disappear in April. The occurrence of ices must have significant effects on circulation and thermohaline structures as well as ecosystem in the northern Caspian Sea. In the present study, formation of ices is modeled assuming that ices do not move but spread and shrink on water surface. Under the ices, it is assumed that the exchange of momentum flux is impeded and the fluxes of heat and brine salt are given at sea-ice boundary. The ice model was coupled with a hydrostatic model based on MEC (Marine Environmental Committee) Ocean Model developed by the Japan Society of Naval Architect and Ocean Engineers. Numerical simulation was carried out for 20 years to achieve stable seasonal changes in current velocity, water temperature, and salinity. The fluxes of momentum, heat, and salt were estimated by using measurement data at 11 meteorological stations around the Caspian Sea. Inflow of Volga River was taken into account as representative of all the rivers which inflow into the Caspian Sea. Effects of icing event on circulation and thermohaline structures were discussed using the results of numerical simulation in the last year. As a result, the accuracy of predicting water temperature in the northern Caspian Sea was improved by taking the effects of icing event into account. Differences in density in the horizontal direction create several gyres with the effects of Coriolis force. The differences were caused by differences in heat capacity between coastal and open waters, differences in water temperature due to climate, and inflow of rivers in the northern Caspian Sea. The water current field in the Caspian Sea is formed by adding wind-driven current to the dominant density-driven current, which is based on horizontal differences in water temperature and salinity, and Coriolis force.
Fracture Toughness Evaluation for Welded Joints of High Strength Steel Through CTOD Test
Authors: Gan Jin , Yu Qiming , Wu Weiguo , Le Jingxia
Published: January 2011

This paper presents the method and procedure of CTOD test which are used for the toughness evaluation for welded joints. Two types of high strength steel (E38 and E43) are chosen as the object of fracture toughness evaluation. The contents of CTOD test include three-point crack tip open displacement (CTOD) bending tests for base metal (BM) specimens, weld position (WP) specimens and heat-affected zone (HAZ) specimens of the high strength steel, considering different thickness of steel plate and different test temperature (−20°C and 20°C). The CTOD test can achieve the P-V curves of samples, and the CTOD values are calculated. On the basis of the above work, the results of toughness evaluation are obtained. Meanwhile, some factors which affect the toughness of high strength steel are discussed in this paper, such as thickness of steel plate and test temperature, and many valuable conclusions are achieved.
A Comparison of Some Multivariate Weibull Distributions
Authors: Leira Bernt J.
Published: January 2011

Three different possible choices of statistical models for multivariate Weibull distributions are considered and compared. The concept of “a correlation field” is introduced and is subsequently applied for the purpose of comparing the different models. Linear combinations of Weibull distributed random variables are considered, and expressions for the corresponding probability density functions are established. Furthermore, a simplified procedure for approximating the resulting density function is described. Comparison is made between the statistical moments of increasing order for the specific case of two Weibull components. This example of application arises e.g. in connection with mechanical design of a column which is subjected to a bi-axial bending moment.
Uncertainties of Joint Long-Term Probabilistic Modelling of Wind Sea and Swell
Authors: Bitner-Gregersen Elzbieta M.
Published: January 2011

In several practical applications joint environmental description is required. In the last years increasing attention has been given to importance of inclusion of wind sea and swell components in a joint environmental model. Presence of wind sea and swell will affect design and operability of fixed and floating offshore structures as well as LNG terminals. In the present study joint environmental description has been established for three locations: Southern North Sea, Northwest Shelf of Australia and off coast of Nigeria. Hindcast data have been used in the analysis. Uncertainties related to the proposed fits are discussed focusing particularly at wind sea and swell modelling. Attention is given to location specific features of the wave climate and adopted partitioning procedure for the wave components. Implication of the uncertainties for design of marine structures is shown. An approach for joint environmental description for marine operations is proposed.
Model Test Investigation of LNG Tandem Offloading With Dynamic Positioned Shuttle Tankers
Authors: de Wilde Jaap , Serraris Jorrit-Jan , de Ridder Erik-Jan , Be´cel Marie-Laure , Fournier Jean-Robert
Published: January 2011

LNG FPSOs are being developed for production and processing of gas in remote offshore locations. The floating production unit is positioned over the reservoir and replaces the offshore platform, the pipeline to shore, the onshore LNG plant and the jetty. Alternatively, the LNG FPSO can be utilized to liquefy and export the associated gas, produced by one or several production units. Side-by-side offloading and stern-to-bow (tandem) offloading are the main options for the direct transfer of the cryogenic product from the FPSO to the LNG shuttle tanker. For stern-to-bow we can further distinguish between a hawser mooring (passive) or a dynamic positioned shuttle tanker (active). Experience suggests that the side-by-side operation is limited to relative benign metocean conditions, whereas a stern-to-bow arrangement allows for offloading in more severe sea states in which larger maneuverability area and large capacity mooring equipments are required. This paper discusses a first investigation of LNG stern-to-bow offloading with dynamic positioned shuttle tankers, based on a basin model test program. The shuttle tanker was controlled by a full closed loop DP system which is largely identical to real DP systems, including extended Kalman filtering, PID control and thruster allocation. The modeling of the azimuthing thrusters, rudder and main propeller is discussed in the paper, as well as the modeling of the relative position between the two ships. Some results of the model test program are presented.
CFD Hydrodynamic Analysis of a Torpedo Anchor Directional Stability
Authors: de Carvalho e Silva Daniel Fonseca
Published: January 2011

The geometry of offshore anchors is usually determined from a geotechnical perspective. This paper presents the proposal of simple modifications on a torpedo anchor to improve its hydrodynamic performance concerning its directional stability. Additionally, the study of a real case torpedo deformation is presented. Although the directional stability investigation requires a dynamic analysis, the CFD simulations were performed on a steady state regime to show for which inclinations the anchor tends to recover the vertical position. The trajectory was investigated through a simplified dynamic model and compared with field measurements.
Time Domain FEA for Riser VIV Analysis
Authors: Sidarta Djoni E. , Finn Lyle D. , Maher Jim
Published: January 2011

Risers are often subjected to non-linear boundary conditions, such as soil-SCR interaction and interaction between risers and the guides in the vessel, which often have gaps and non-linear stiffness. Also, current profiles may vary in direction through depth. In these cases, time domain FEA could represent the problems better than frequency domain analysis. Several computer codes are available for cross-flow VIV analysis using time domain FEA. This paper introduces SimVIV, a time domain computer code for cross-flow VIV and in-line VIV analysis. The algorithm used in SimVIV for cross-flow VIV analysis is consistent to the one used in the Highly Compliant Rigid Riser Joint Industry Project (HCR Riser JIP). The algorithm for in-line VIV is an added feature in this code, and for this initial attempt, this covers only in-line VIV that has about twice the frequency of the cross-flow VIV. This paper presents the results of SimVIV to predict cross-flow VIV and in-line VIV for model tests that have been done at the Delta Flume of Delft Hydraulics (May 2003). The results in general show good comparison to the measured data.
A Simple Alternative Method to Estimate the Collapse Pressure of Flexible Pipes
Authors: Nogueira Victor Pinheiro Pupo , Netto Theodoro Antoun
Published: January 2011

Offshore oil and gas production worldwide constantly moves to deeper water with increasing flexible pipe operational severity. Failure mechanisms, i.e., sequences of events which may lead to failure, are nowadays more likely to happen. Therefore, it is important to develop reliable numerical tools that can be used in the design stages or during service-life to assess the structural integrity of pipes under specific operational conditions. This work presents a methodology to develop simple finite element models capable to reproduce the behavior of structural layers of flexible pipes under hydrostatic pressure up to the onset of collapse. The models use beam elements and include contact between layers, nonlinear kinematics and material behavior. Different configurations were analyzed: carcass-only, and carcass plus pressure armor with dry and wet annular. The dependability of the numerical models is assessed in light of experimental tests on flexible pipes with 4 and 8 inch nominal internal diameters. Relevant geometric parameters and material properties of each specimen were measured and subsequently used in the models to reproduce the physical experiments. The metallic inner carcass and pressure armor layer manufacturing processes cause a high degree of stress-induced material anisotropy. Due to the inherent difficulty to determine the non-homogeneous elastic-plastic material behavior of the wires’ cross-sections, a novel alternative method was used to estimate their average stress-strain curves up to moderate strains (2%). Good correlation was obtained between experimental and numerical results. The applied methodology proved to be simple and yet efficient and reliable for the estimation of the collapse pressure of flexible pipes.
Vortex-Induced Vibrations of Risers Due to FPDSO Heave Motions
Authors: Lei Song , Zhang Wenshou , Yue Qianjin
Published: January 2011

Based on the concept design of FPDSO, mechanical model of risers with variable tension is presented, and fluid forces and submerged weight are considered. The dynamic analysis is done to research the influence of FPDSO heave motion to vortex-induced vibrations. The numerical results reflect that risers have large response under the combined action of “lock in” and parametric resonance, and amplitude of heave motion has little effect on the vibrations; tension due to heave motion can significantly increase the forces of the risers.
Coupled Dynamic Analysis of a Moored Spar Platform in Time Domain
Authors: Yang M. D. , Teng B.
Published: January 2011

A time-domain simulation method is developed for the coupled dynamic analysis of a spar platform with mooring lines. For the hydrodynamic loads, a time domain second order method is developed. In this approach, Taylor series expansions are applied to the body surface boundary condition and the free surface boundary condition, and Stokes perturbation procedure is then used to establish corresponding boundary value problems with time-independent boundaries. A higher order boundary element method is developed to calculate the velocity potential of the resulting flow field at each time step. The free-surface boundary condition is satisfied to the second order by 4th order Adams-Bashforth-Moultn method. An artificial damping layer is adopted on the free surface to avoid the wave reflection. For the mooring-line dynamics, a geometrically nonlinear finite element method using isoparametric cable element based on the total Lagrangian formulation is developed. In the coupled dynamic analysis, the motion equation for the hull and dynamic equations for mooring lines are solved simultaneously using Newmark method. Numerical results including motions and tensions in the mooring lines are presented.