bluuebunny/crossref_metadata_2025 huggingface dataset:
Calculation of Wave-Induced Shallow Stratum Seabed Slides in the Subaqueous Yellow River Delta
Authors: Xu Guohui , Wang Xin , Wei Congcong , Fu Zibu , Zhao Qingpeng
Published: February 2010

Wave-induced seabed slide could happen even at very gently sloping silty seabed. Based on the wave-seabed interaction, the safety coefficient calculation model of wave-induced gentle seabed slides in the seabed instability was carried out using limit equilibrium method, Bishop Method, in this paper. The calculated results shows that the effective internal cohesion c′ and the effective internal friction angle φ′ affect the location of slip surface and the magnitude of the safety coefficient significantly. The safety coefficient rises linearly with the increases of c′ and φ′ at a fixed depth. The results fit reasonable well with the slide calculation results from a wave flume experiment in laboratory. Additionally, it was concluded that the silty seabed tended to slide under wave actions at the depth less than 5 meters in the Yellow River Subaqueous Delta.
Skin Friction of Taper-Shaped Piles in Sands
Authors: Manandhar Suman , Yasufuku Noriyuki , Shomura Kazutaka
Published: February 2010

The main theme of this paper is to evaluate the skin friction and unit skin friction of different types of pile on a defined model ground. The typical silica sands were selected to make model ground at high relative densities of 80% and 60% respectively at confining pressure of 50 kPa to perform the pile load test on selected two different model ground. Model ground has been prepared by free falling of sand through sieve on the chamber to meet the required relative densities. Relative densities have acquired after evaluating desired height and area of nozzle through which dry sands fall. To fulfill the requirement, different types of tapered piles were selected to perform the pile load test. Straight and different types of tapered pile have driven in silica sands respectively at relatively high densities. Experimental results have showed that the skin friction of straight pile is considerably low with compared to tapered pile and wedging effects can be clearly seen towards the depth of penetration. In conclusion, it is clearly seen that the skin friction of tapered pile can be improved with increasing tapering angles. Higher the angle the greater the skin friction. Further, lateral stresses around the pile increases laterally during loading. Lateral stresses are increased with increase on amounts of pile expansion. The skin frictions of tapered piles have pressing effect and soil tamping effect.
Nonlinear Ship Motion Computations Using a Time-Domain Body-Exact Slender-Body Approach
Authors: Bandyk Piotr J. , Beck Robert F.
Published: February 2010

This paper continues the development of a computationally efficient potential flow code using a time-domain body-exact strip theory approach. The exact body boundary conditions and linearized free surface conditions are used. Present results include further improvements, validations, and comparisons. Two different formulations to obtain the forces on the vessel are studied: pressure and momentum. Panel distribution techniques, critical for large amplitude motions, are discussed. The slender-body assumption requires finding the longitudinal interaction between sections to compute the hydrodynamic forces. Finally, an equation of motion solver is implemented to predict the six degree-of-freedom motions of the vessel in regular waves, including nonlinear effects.
Numerical Simulations of Dynamic Embedment During Pipe Laying on Soft Clay
Authors: Wang D. , White D. J. , Randolph M. F.
Published: February 2010

Prediction of the as-laid embedment of a pipeline, which affects many aspects of pipeline design, is complicated by the dynamic motions that occur during the lay process. These motions cause pipelines to embed deeper than predicted based on static penetration models, as the seabed soils are both softened and physically displaced by the pipeline motion. This paper describes the results of 2D numerical analyses using a large displacement finite element approach aimed at quantifying pipeline embedment due to cyclic lateral motion at various fixed vertical load levels. The validity of the numerical results is first assessed by comparison with published data from centrifuge model tests in two different types of clay. A parametric study varying the normalized vertical load is then presented, which suggests a simple approach for estimating an upper limit to the dynamic embedment.
Laboratory Study on the Relationships Between Suspended Sediment Concentration and Electrical Conductivity
Authors: Dai Qian , Shan Hongxian , Jia Yonggang , Meng Xiangmei , Li Honglei , Cui Wenlin
Published: February 2010

In order to find a simple, continuous method to determine the suspended sediment concentration in a high turbidity region, experiments were conducted to look for relationships between suspended sediment concentration and electrical conductivity. Sediments were sampled from the Yellow River Delta and a conductivity sensor was used to measure the electrical conductivity of different sediment content seawater. The influencing factors such as temperature and salinity are also investigated. The results show that good linear relationships exist between suspended sediment concentration and electrical conductivity; salinity and temperature have some influence on electrical conductivity, and salinity is the most important influencing factor and temperature takes the second place. Basically, the general linear regression formulas between suspended sediment concentration and electrical conductivity can be drawn with variable salinity and temperature. The relationships suggest that it is feasible to measure suspended sediment concentration in situ using electrical conductivity sensors.
Wave Devouring Propulsion System: From Concept to Trans-Pacific Voyage
Authors: Terao Yutaka
Published: February 2010

In the spring of 2008, the Mermaid II began her historic voyage from Hawaii to Japan. According to the log of the vessel, the journey took 110 days and covered about 7800 km. The successful conclusion of the voyage demonstrated the possibility that Wave Devouring Propulsion System (WDPS) could be adapted to practical use. In order to capitalize on the success of this voyage, the author intended to design and tested a new WDPS hull within a year to build it. A WDPS is a thrust generator for a vessel that converts wave forces directly into forward thrust. Additionally it efficiently reduces hull pitch and roll motion, while also performing as a motion stabilizer. The Mermaid II, which is equipped with a WDPS, incorporates a specially designed catamaran hull form and twin hydrofoil system. A solid hydrofoil system that captures wave forces is set on the underside of the bow of the vessel. Those hydrofoils are connected to the hull with pin joints and are supported by soft springs that provide foil pitch restoring force.
Arctic Pipeline Design Challenges and Current Practices: Ice Scour
Authors: Konuk Ibrahim
Published: February 2010

Analysis methods used for the design of offshore pipelines against ice scour are reviewed. Implications and impact of their limitations on pipeline design are discussed. Alternative analysis methods are proposed to address the shortcomings of the current engineering design and analysis practices.
Numerical Study of Large Amplitude Ship Motion With Forward Speed in Severe Seas
Authors: Hong D. C. , Sung H. G. , Hong S. Y.
Published: February 2010

A three-dimensional time-domain calculation method is of crucial importance in prediction of ship motion with forward speed in a severe irregular sea. The exact solution of the free surface wave–ship interaction problem is very complicated because of the extremely nonlinear boundary conditions. In this paper, an approximate body nonlinear approach based on the three-dimensional time-domain forward-speed free-surface Green function has been presented. It is a simplified version of the method known as LAMP (Lin and Yue 1990) where the exact body boundary condition is applied on the instantaneous wetted surface of the ship while free-surface condition is linearized. In the present study, the Froude-Krylov force and the hydrostatic restoring force are calculated on the instantaneous wetted surface of the ship while the forces due to the radiation and scattering potentials on the mean wetted surface. The time-domain radiation and scattering potentials have been obtained from a time invariant kernel of integral equations for the potentials. The integral equation for the radiation potential is discretized according to the second-order boundary element method (Hong and Hong. 2008). The diffraction impulse response functions of the Wigley seakeeping model are presented for various Froude numbers. A simulation of coupled heave-pitch motion of the Wigley model advancing in regular head waves of large amplitude has been carried out. Comparisons between the fully linear and the present approximate body nonlinear computations have been made at various Froude numbers.
Investigation of Impact of New Design Code on Riser System Design
Authors: Yu Alan , Stanton Paul , Cheng Yongming
Published: February 2010

Top tensioned risers are fluid conduits from subsea equipment to surface floating production platforms. The advantages of using top tensioned risers are the ability to drill and complete through the production riser, ease of access of the production trees for gas lift operation, and the simplicity of workover and redrill. The integrity of a riser system plays an important role in deepwater developments. Top tensioned risers (TTRs) and steel catenary risers (SCRs) have been widely used with floating production systems such as Spars and TLPs. API RP 2RD [1] has been used to guide riser system design for the last decade. API RP 2RD is being revised as a code (ISO 13628-12) that will also be adopted as a new API code. This paper investigates the impacts of the new design code on the riser system design. This paper first discusses the differences between ISO/WD 13628-12 and the existing API RP 2RD code, particularly the section on design criteria for pipes. The Holstein top tensioned riser system is chosen as an example to evaluate the riser system design impacts. The risers have been installed and successfully producing oil since 2005. The results of the nonlinear finite element program ABAQUS used to analyze the Holstein top tensioned risers were evaluated according to the API RP 2RD. The same analytical results are used for evaluating the impact of the proposed ISO 13628-12 in the area of stress evaluation.
Investigating a Near-Bed Submarine Pipeline in a Current
Authors: Lin Mian , Cao Yulong , Li Lei , Huang Guojun
Published: February 2010

This paper considers the lift forces acting on a pipeline with a small gap between the pipeline and the plane bottom or scoring bottom. A more reasonable fluid force on the pipeline has been obtained by applying the knowledge of modified potential theory (MPT), which includes the influences of the downstream wake. By finite element method, an iteration procedure is used to solve problems of the nonlinear fluid-structure interaction. Comparing the deflection and the stress distributions with the difference sea bottoms, the failure patterns of a spanning pipeline have been discussed. The results are essential for engineers to assess pipeline stability.
Hydroelastic Motion of Aircushion Type Large Floating Structures With Several Aircushions Using a Three-Dimensional Theory
Authors: Ikoma Tomoki , Masuda Koichi , Rheem Chang-Kyu , Maeda Hisaaki , Togane Mayumi
Published: February 2010

This paper describes hydroelastic motion and effect of motion reduction of aircushion supported large floating structures. Motion reduction effects due to presence of aircushions have been confirmed from theoretical calculations with the zero-draft assumption. A three-dimensional prediction method has been developed for considering draft influence of division walls of aircushions. It is investigated that hydroelastic motion reduction is possible or not by using the three-dimensional theoretical calculations. In addition, the aircushion types are supported by many aircushions which are small related to wavelengths. The Green’s function method is applied to the prediction method with the linear potential theory in which effect of free water surfaces within aircushions are considered. Hydroelastic responses are estimated as not only elastic motion but also a vertical bending moment. From the results, the response reduction is confirmed, in particular, to the vertical bending moment in wide wavelength range and in whole structure area.
Real-Time Estimation of Directional Wave Spectra Using Non-Stationary Ship Motion Data
Authors: Iseki Toshio
Published: February 2010

The Bayesian modeling procedure is modified for real-time estimation of directional wave spectra using non-stationary ship motion data. The assumption of stationary stochastic processes is applied to the seaway, but not to ship response because it also depends on ship maneuvers. Ship response is strongly affected by changes in the encounter angle and frequency of waves. Therefore, it is need to be a real-time algorithm that can deal with non-stationary stochastic processes and estimate the directional wave spectra. In the proposed algorithm, the iterative calculations of the non-linear equations were optimized and the convergence was not achieved at every time step, but was achieved gradually over several time steps. In order to examine the reliability of the proposed method, real-time estimation was conducted by using the data of onboard experiments. Comparisons between the results of the proposed algorithm and a wave monitoring radar system show good agreements.
Prediction of Current Load Using Computational Fluid Dynamics
Authors: Kim Joo Sung , Hong Chun Beom , Lee Dong Yeon , Ahn Sung Mok
Published: February 2010

The use of CFD based on Reynolds-averaged Navier-Stokes equations is examined to predict the current load acting on ships in operation. CFD results agree well with experimental data from wind tunnels and a water basin, where the main features of the test conditions are modeled appropriately in a numerical simulation. It is found that measurement in the water basin (Samsung Ship Model Basin) is the most reasonable method to obtain the current load, at least at a model scale. Otherwise, measurements in a wind tunnel should be carried out more carefully so as to avoid the friction effect of the tunnel bottom on inflow, as this effect is considerable. Conclusively, the CFD method is a viable approach for the prediction of the current load on ships.
Dynamic Behavior of a Submersible Fish Cage
Authors: Lee Chun Woo , Lee Gun Ho , Choe Moo Youl , Song Dae Ho , Hosseini Seyed Abbas
Published: February 2010

Fish cage system is influenced by various external forces from the ocean environments, and the movements and the deformation of the cage by these external forces affect the safety of the cage itself, as well as that of the cultured organisms. In this research, submersible fish cage was designed to endure less physical stress by harsh sea conditions, and to keep the organisms in safer life by reducing the stress through exposure and movement. The submersible cage system consists of netting, mooring ropes, floating collar, floats, sinkers and anchors. Mass-spring model was used to predict the dynamic response of the cage subjected to tidal currents and waves. Computer simulation was performed for fish cage at the surface and submerged positions to investigate the dynamics of the motion and to calculate mooring line tensions. As expected, the average tension value of the mooring line for the submerged cage were less, being 64% of what we got in the case of surface position under the current velocity of 0.5 m/s combined with the waves. As the waves was used in combination with the current velocity of 1.0 m/s, the average tensile load for the submerged cage showed 85% of the value for the floating cage. The simulation results provide an improved understanding of the dynamic behaviors of the structure and their capability to withstand in subject to sever environmental loadings, and also valuable information on the optimized design of the cage system exposed to the open ocean environmental factors.
Prediction of Vortex-Induced Vibration of Flexible Riser Using an Improved Wake-Oscillator Model
Authors: Chen Wein-min , Zhang Liwu , Li Min
Published: February 2010

Based on improving the wake-oscillator model, an analytical model for vortex-induced vibration (VIV) of flexible riser under non-uniform current is presented, in which the variation of added mass at lock-in and the nonlinear relationship between amplitude of response and reduced velocity are considered. By means of empirical formula combining iteration computation, the improved analytical model can be conveniently programmed into computer code with simpler and faster computation process than CFD so as to be suitable to application of practical engineering. This model is validated by comparing with experimental result and numerical simulation. Our results show that the improved model can predict VIV response and lock-in region more accurately. At last, illustrative examples are given in which the amplitude of response of flexible riser experiencing VIV under action of non-uniform current is calculated and effects of riser tension and flow distribution along span of riser are explored. It is demonstrated that with the variation of tension and flow distribution, lock-in region of mode behaves in different way, and thus the final response is a synthesis of response of locked modes.
ECA of Pipeline With Girth Weld Strength Mis-Matching Subjected to Large Strain
Authors: Yang Zhengmao , Kumar Shashi , Tronskar Jens P.
Published: February 2010

In recent years, the strain based design for pipeline has been widely accepted by the industry, but the definition of a rational flaw acceptance criteria for girth welds subjected to axial strain within the context of the existing codified fracture mechanics based assessment procedures is problematic since these are essentially stress based. To extend the FAD method to the large strain conditions, several challenges i.e. weld strength mismatching, fracture toughness, and welding residual stresses have to be understood. With appropriate modifications as per DNV-RP-F108 [1], the assessments procedure detailed in BS7910 document for stress based situations have been used successfully for several projects to develop acceptance criteria for pipeline installation involving plastic straining. But only weld metal strength over-match comparing with base metal is considered in DNV-RP-F108 [1]. High strength line pipes are required to reduce the transmission cost of natural gas in long distance and internal clad with corrosion resistant alloy (CRA) is used for transportation of sour gas. Steel manufactures have developed such line pipes to develop new oil and gas field. The inconel filler metal was selected as weld consumable for the production girth weld in the lay budge. From the all weld tensile tests, it was found that the yield strength of the weld is under-match comparing the base metal, and the pipeline maybe subjected to a strain level up to 1.0% due to the lateral buckling. In this research the effect of weld strength mismatching on the structural integrity of the pipeline subjected to large strain was studied. The Engineering Critical Assessment (ECA) was performed to derive the critical flaw acceptance criteria for the AUT system. The segment tests and numerical analysis were performed to validate the assessment procedure, and the finite element analyses of the pipeline girth weld with surface crack in the weld centre were carried out to investigate the effect of bi-axial loading on the ECA results.
Bragg Reflection of Water Waves in a Rectangular Channel
Authors: Yu Jie , Howard Louis N.
Published: February 2010

A series of corrugations on the bottom of a layer of water of otherwise uniform depth can have a cooperative effect on incident water waves. The phenomenon is well-known, called Bragg reflection or Bragg resonance. These effects on the normal modes of oscillation in a rectangular tank with corrugated bottom are studied using an asymptotic theory, and by developing an exact theory. The exact theory confirms the essential correctness of the asymptotic results for the slowly varying aspects of the motions. The rapidly varying components are, however, important to the flow near the boundaries. Higher order Bragg resonance, i.e. when the spacing of corrugations is an integer (greater than 1) multiple of half the water wavelength, is examined and the solution regimes (resonance tongues) are constructed using the exact theory.
Advances in Deepwater Steel Catenary Riser Technology State-of-the-Art: Part II—Analysis
Authors: Song Ruxin , Stanton Paul
Published: February 2010

The Steel Catenary Riser (SCR) concept offers advantages over other riser concepts and has been widely deployed worldwide. The first deepwater SCR was installed in the Gulf of Mexico in 1994. Since then, more than 100 SCRs have been installed for many types of deepwater floaters (Spars, TLPs, SEMIs, and FPSOs) in the deepwater fields of West of Africa, the Gulf of Mexico (GoM), and Offshore Brazil. As the second of two companion papers, this paper presents the state-of-the-art of key analysis techniques of deepwater SCRs while the first paper addresses the design methodology [R. Song, P. Stanton, Ref. 4]. First of all, the procedure for analysis of deepwater SCRs is discussed and presented in more detail than given in the first paper and is also illustrated in an analysis flowchart. Wave theory applicable to deepwater SCR analysis and time domain vs. frequency domain analysis approaches are described and discussed. More focus is given to the strength analysis including discussion and comparison of regular wave and random wave approaches. Attention is paid to the vortex induced vibration (VIV) analysis including discussion of modal response analysis and VIV parameter selections. For SCRs on semisubmersibles and FPSOs, vessel heave-induced VIV needs to be taken into account, and a corresponding time-domain approach is presented. Similarly, for Spars and deep draft semisubmersibles, vortex-induced motion (VIM) fatigue damage of SCRs is discussed in more detail. Particular attention is also given to the analysis of SCR compression in the touch-down zone (TDZ) and corresponding acceptance criteria are presented. The application of fracture mechanics to engineering criticality assessment (ECA) is explored. Two examples of deepwater SCRs corresponding to a semi and a Spar are given to illustrate the presented methodology.
On the Coupled Extensional–Torsional Response of Flexible Pipes
Authors: Merino He´ctor E. M. , de Sousa Jose´ R. M. , Magluta Carlos , Roitman Ney
Published: February 2010

In this paper, the coupled extensional-torsional behavior of a 4″ flexible pipe is studied. The pipe was subjected to pure tension and two different boundary conditions were considered: ends free and prevented from axially rotating. The response of the pipe is predicted with a three-dimensional nonlinear finite element (FE) model. Some aspects of the obtained results are discussed, such as: the effect of restraining the axial rotation at the extreme sections of the model; the effect of friction or adhesion between the layers of the pipe on the induced axial rotation (or torque) and elongation; and the reduction to simple plane behavior usually assumed by analytical models. The numerical results are compared to the ones measured in experimental tests performed at COPPE/UFRJ. Reasonable agreement is observed between all results pointing out that the analyzed pipe is torque balanced and that friction mainly affects the axial twist or torque led by the applied tension. Moreover, the cross-sections of the pipe remain straight with the imposed load, but different axial rotations are found in each layer.
Simple Tool for Prediction of Green Water and Bow Flare Slamming on FPSO
Authors: Stansberg Carl Trygve , Berget Kjetil
Published: February 2010

A practical method for prediction of green water and wave impact on FPSO’s in steep irregular waves is described. The relative wave elevation and kinematics are found from combining ship motions, wave diffraction and nonlinear irregular waves. Water heights on deck and related velocities are estimated by simple analytical formulas originally derived from dam-breaking theory but modified in this work to take into account a non-zero water velocity input and the effects from a dynamic and finite wave-determined water reservoir. A bulwark is also included. Deckhouse slamming and bow flare slamming loads are computed by simple formulas from the local velocities and, in the latter case, also the relative angle between the water surface and the flare. Verification against more advanced models and to model test data show promising results. The method is being implemented into a simple research-type software tool.
A Comparative Buckling Study for the Carcass Layer of Flexible Pipes
Authors: Neto Alfredo Gay , Martins Clo´vis de Arruda
Published: February 2010

When there are some failures on the external plastic layer of a flexible pipe, a high value of hydrostatic pressure can be transferred to its interlocked carcass layer, maybe causing a collapse. So it is necessary to predict on the design of a flexible pipe the maximum value of pressure that would be acceptable to avoid collapse of the carcass layer. That value depends on the imperfections on the internal diameter due to fabrication uncertainties. To study that problem, two numerical finite element models were created and used to simulate external pressure loading condition. The first model is a full 3D approximation, composed by solid elements. The second one is a 3D ring approximation, still made by solids. An analytical model using an equivalent thickness approach for carcass was done. A good correlation between analytical and numerical models was achieved for pre-buckling behavior, but analytical buckling behavior was not the same as numerical values predictions. Discussions about these differences are done.
A Comparison Between BS7448-CTOD and ASTM E1290-CTOD in Linepipes
Authors: Kayamori Yoichi , Inoue Takehiro , Tagawa Tetsuya
Published: February 2010

ASTM E1290 previously used the plastic hinge model for the calculation of CTOD, but has changed its CTOD calculation to J-based conversion since 2002. In this study, the ratio of ASTM-CTOD to BS-CTOD was analytically predicted and experimentally evaluated in linepipes. It was demonstrated that the CTOD ratio changed according to CTOD itself, and took a minimum in a CTOD ratio curve. The minimum value of the CTOD ratio was lower than 1 for low yield-to-tensile ratios, but higher than 1 for high yield-to-tensile ratios. The CTOD ratio tends to be higher than 1 for high CTOD caused by plastic instability, but around or less than 1 for low CTOD possibly caused by brittle fracture in X65 and X80. A CTOD transformation equation, which was proposed by the authors, can transform BS-CTOD into ASTM-CTOD with reasonable accuracy.
Time Trace Window Based Approach for SCR Strength Analysis in Ultra Deepwater of Gulf of Mexico
Authors: Chen Jack , Cao Peimin , Zhu Huadong , Jukes Paul
Published: February 2010

For a steel catenary riser (SCR) in the ultra deep water of the Gulf of Mexico (GOM), the areas of major concern from a dynamic stress response point of view are the sagbend region near the touchdown and the region below the hang-off at the SCR top where local bending must be accommodated. Usually global strength (stress/strain/buckling) analysis focuses primarily on the sagbend region, while more detailed analysis associated with design of the riser hang-off assembly concentrates on the SCR top region. The global strength design of the SCR is controlled by dynamic response in the sagbend region, which is primarily driven by the host vessel motions. Vessel motions are in turn induced by metocean conditions such as hurricanes and winter storms. Given the random nature of the ocean waves, to obtain statistically sound results, random wave simulations involving multiple (usually ten (10)) three (3) hour realizations have been a well accepted practice by the offshore industry. Just as waves in an extreme or survival storm event are randomly distributed, stress (and strain) response events are randomly distributed as well. For a comprehensive design, there will be far more than one sea state to be analyzed with each sea state undergoing multiple three (3) hour simulations. In addition, the design often progresses iteratively, i.e., there will be several cycles of analyses to be performed before the final design can be concluded. Therefore, the overall computational resources in terms of time and data storage are quite significant. This paper presents the methodology that significantly reduces the computer simulation time without compromising the analysis accuracy for the strength analysis of the SCR. The paper uses the example of a SCR in the ultra deepwater of the GOM attached to a DeepDraft Semi™ designed by SBM Atlantia Inc. The methodology builds on time traces of the host vessel motions, and the correlation between the vessel/porch motion and the SCR sagbend response. Generally the maximum riser sagbend stress occurs when the wave pushes the vessel, then the riser porch toward its touchdown point (slack position). One vessel/porch motion characteristic — the downward speed at the riser porch dominates the SCR sagbend response. By screening the downward speeds at the riser porch under slack condition, the time at which the sagbend response (stress/strain/buckling) peaks is identified. A time trace window containing the peak time and with band width of about 200 seconds is located and the SCR global dynamic analysis is performed based on this time trace window. In some scenarios, up to five (5) windows associated with the top five (5) downward speeds at the riser porch for one realization are needed to capture the peak stress response in the SCR sagbend.
Extra High-Pressure High-Temperature (XHPHT) Flowlines: Design Considerations and Challenges
Authors: Jukes Paul , Eltaher Ayman , Sun Jason , Harrison Gary
Published: February 2010

Development of deep water oil reservoirs in the Gulf of Mexico may encounter conditions where the flowline product temperatures approach 177°C (350°F), water depths range to 3000 m (10,000 ft), and tie-back distances up to 40 miles are presently being considered. These high flowline temperatures, water depths and distances, present real challenges to the design of flowlines. The objective of this paper is to present the design considerations and challenges of designing for extra high pressure high temperature (XHPHT) conditions. For such conditions, a pipe-in-pipe (PIP) flowline system with thermal expansion management, and a limit state-based design are viable solutions. This paper is split into three main parts and covers (i) design challenges and how they are overcome, (ii) finite element analysis design methods, and (iii) qualification testing of PIP components. The first section presents the main design issues, and challenges, of designing flowlines for deepwater and high-temperature conditions. The paper discusses aspects of controlling the large axial loads, such as thermal expansion management using buckle initiators and end constraints for flowlines, and presents current methods. The second section describes the use of advanced finite element analysis (FEA) tools for the design and simulation of PIP systems, and presents local and global FEA models, using ABAQUS, to investigate the limit state design of XHPHT flowlines. A 3-D helical response of the inner pipe subjected to high temperature, and the sequential reeling and lateral buckling of flowlines is also discussed. The final section of the paper describes the qualification testing to be undertaken on PIP components to ensure structural integrity and long-term thermal and structural performance. Qualification testing for PIP components for 177°C (350°F) service is discussed, and includes the testing of centralizers, waterstop seals, thermal insulation and loadshares. This paper is based on both theoretical and practical research work.
Development and Validation of a Coupled Eulerian Lagrangian Finite Element Ice Scour Model
Authors: Abdalla Basel , Pike Kenton , Eltaher Ayman , Jukes Paul , Duron Billy
Published: February 2010

Pipelines in the arctic offshore must be installed and buried below the seabed to avoid direct contact, and to mitigate the effects of strains induced by soil displacement below the ice keel scour depth. A three-dimensional (3D) finite element (FE) model that utilizes the Coupled Eulerian Lagrangian (CEL) formulation has been developed to provide direct and explicit estimation of pipe stresses and strains. The CEL formulation is novel, and no published work has attempted to explore its capabilities and potential for ice scour modeling to date. The developed model will be helpful in solving some of the uncertainty regarding pipeline burial depth, potentially resulting in major trenching cost savings. In order to gain confidence in this numerical modeling technique, a systematic validation effort was carried out, whereby numerical predictions of subgouge displacements were compared with measured data from centrifuge tests and other published empirical and numerical data. Sensitivity analyses were then performed to investigate the effect of the scouring keel geometry, depth, and attack angle on the induced subgouge soil displacements. Preliminary conclusions were drawn and presented in this paper.
VIV Force Identification Using Classical Optimal Control Algorithm
Authors: Wu Jie , Mainc¸on Philippe , Larsen Carl M. , Lie Halvor
Published: February 2010

Due to the difficulty of direct force measurements in vortex induced vibration (VIV) experiments with long elastic cylinders, accelerometer and bending strain measurement are available. Still, obtaining information on the force is of great interest to researchers. The work presented in this paper follows the same principle as Mainc¸on (2004), who estimated external forces acting on a riser subjected to VIV from measured response by using a classical optimal tracking algorithm. The objective of this study is to first present a method for extracting VIV forces from measured data with long elastic riser models subjected to current. The second objective is to extract first order (primary) cross-flow force coefficients by a combined use of modal filtering. The algorithm minimizes the sum of the squares of the discrepancies between measured and predicted response plus a constant times the sum of squares of the external forces, while satisfying the system’s dynamic equilibrium equation. FEM discretization of the riser with Euler beam elements leads to a stiffness and mass matrix. The dimension of these matrixes is reduced by eliminating the rotation degree of freedom using master-slave condensation, which greatly facilitates the matrix iteration. Displacement is used in this study as input to the algorithm to identify forces. The method is verified against synthetic measurement data. The results showed the algorithm’s capability to accurately estimate the input forces from noisy measurement data. The method is applied to the data from a rotating rig test to identify hydrodynamic forces in primary cross-flow vortex shedding frequency range. The emphasis is on extracting force coefficient database. One important finding is that the high mode component of the force contributed little to the response, while it resulted in complication of the coefficient data base. Therefore, they are neglected by filtering the measurement with modal analysis before the use of inverse force estimation. The excitation and added mass coefficients are calculated and their contour plots are generated. Comparisons with existing data are investigated.
Numerical Simulations of Tsunami Wave Generation by Submarine and Aerial Landslides Using RANS and SPH Models
Authors: Das Kaushik , Janetzke Ron , Basu Debashis , Green Steve , Stamatakos John
Published: February 2010

Tsunami wave generation by submarine and aerial landslides is examined in this paper. Two different two-dimensional numerical methods have been used to simulate the time histories of fluid motion, free surface deformation, shoreline movement, and wave runup from tsunami waves generated by aerial and submarine landslides. The first approach is based on the Navier-Stokes equation and the volume of fluid (VOF) method: the Reynolds Averaged Navier-Stokes (RANS)-based turbulence model simulates turbulence, and the VOF method tracks the free surface locations. The second method uses Smoothed Particle Hydrodynamics (SPH)—a numerical model based on a fully Lagrangian approach. In the current work, two-dimensional numerical simulations are carried out for a freely falling wedge representing the landslide and subsequent wave generations. Numerical simulations for the landslide-driven tsunami waves have been performed with different values of landslide material densities. Numerical results obtained from both approaches are compared with experimental data. Simulated results for both aerial and submerged landslides show the complex flow patterns in terms of the velocity field, shoreline evolution, and free-surface profiles. Flows are found to be strongly transient, rotational, and turbulent. Predicted numerical results for time histories of free-surface fluctuations and the runup/rundown at various locations are in good agreement with the available experimental data. The similarity and discrepancy between the solutions obtained by the two approaches are explored and discussed.
Transfer of Boussinesq Waves to a Navier-Stokes Solver: Application to Wave Loads on an Offshore Wind Turbine Foundation
Authors: Christensen Erik Damgaard , Bredmose Henrik , Hansen Erik Asp
Published: February 2010

Wave load and wave run-up is a very important issue to offshore wind turbine foundations. These are often installed in relatively shallow water on for instance sand banks. Therefore the non-linear shoaling and subsequently the force and run-up are important to address. The paper presents a method to combine a Boussinesq model with a CFD model. This gives an accurate tool to estimate wave loads on the foundations at acceptable computational times.
Reducing Hydroelastic Response of Interconnected Floating Beams Using Semi-Rigid Connections
Authors: Wang Chien Ming , Riyansyah Muhammad , Choo Yoo Sang
Published: February 2010

This paper is concerned with the hydroelastic response of interconnected beams by a mechanical joint. A frequency domain approach is developed for the hydroelastic analysis. The fluid is modelled as an ideal fluid, whereas the beam is modelled by the Euler-Bernoulli beam theory. The boundary element method (BEM) and finite element method (FEM) are applied to solve the governing equations of fluid motion and beam equation of motion, respectively. This study investigates the design of the mechanical joint in reducing the hydroelastic response. The design involves varying the rotational stiffness and the location of such a mechanical joint to obtain a significant reduction of the hydroelastic response of the interconnected beams that model a longish very large floating structure (VLFS).
The Study of the Influence of Different Drained Conditions for Seabed Stability Under Wave Loading
Authors: Chien Lien-Kwei , Yang Chi-Ling , Tseng Wen-Chien
Published: February 2010

A series of partial drained dynamic triaxial test were performed to understand the seabed stability under wave induced wave loading. In order to evaluate the real behavior of the strength of sea bed soil under wave action, the field sands in Kinhu were adopted in the study. The specimens were prepared by multi-pluviation through water method to simulate the particle aggregation in-situ. The marine soils stress states were simulated by Ko consolidation in laboratory. Moreover, the stability of marine sands is discussed under different drained conditions by using flow valve to control the soil drained states. In this study, the typhoon waves induced loading were simulated in small amplitude wave and Stoke’s 2nd order wave theory to evaluate the cyclic stress ratio in sea bed. From the test results found that the marine soil was liquefaction immediately by using the Stoke’s 2nd order theory. The drained efficiency is defined in this study. The relationship between strain, cyclic numbers, and cyclic stress ratio (CSR) were discussed under different drained efficiency conditions. Under the drained efficiency is 86% and the number cycle is one, the double amplitude strain (DA) of seabed soil will induce 10% by Stoke’s 2nd order wave theory induced the cyclic shear stress ratio. But under the drained efficiency is 100%, the DA of seabed soil will only induce 7%. Combined with the time concept of wave action, when the seabed soil reach to DA = 10% under wave loading, the time of wave action request 1296 sec. From the results indicated that the drained efficiency have significantly influence on deformation resistance of sea bed soil. Therefore, the study analysis could be provided the reference for near shore structure design and engineering practice, and reduce storm induced damages.
Benchmark Study Between CFD and Model Tests on a Semi-Submersible Crane Vessel
Authors: Ottens Harald , van Dijk Radboud , Meskers Geert
Published: February 2010

Accurate assessment of current loads on offshore vessels is required to determine operability of heavy lift and pipe lay operations. Whereas in the past only semi-empirical methods or model tests were suitable to obtain these data, CFD has recently become available as engineering tool to assess current loads on offshore structures. CFD has the potential to assess current loads more flexible in a numerical manner. Although the application of CFD has proven its value in assessment of ships resistance and VIV calculations, CFD is still not yet a fully proven method to calculate the current loads on offshore structures. Therefore validation of the results is further required to reach general acceptance of this method for offshore applications. HMC took the initiative to compare and validate CFD results with its model test data of current loads on one of its semi-submersible crane vessels. In this paper a comparison of CFD results with model test data of the current loads of a semi-submersible crane vessel is presented. The CFD calculations are performed as blind computations, so the model tests results were unknown. Afterwards the CFD results are compared with the results of the model tests. Based on both data sets lessons learned are addressed to improve the CFD computations as well as practical aspects and limitations of current load model testing. Furthermore, the possibilities to use CFD to scale the results of the model tests to full scale are explored. Based on this comparison CFD appears to be a complementary, flexible and reliable tool in assessing the current loads on mission critical vessel operations.
Advanced Hybrid Joining Technology
Authors: Shkolnikov Vladimir M. , Hostetter Gabriel J. , McNamara David K. , Pickens Joseph R. , Turcheck Stanley P. , Dance Bruce G. I.
Published: February 2010

The paper summarizes results of an engineering investigation on advanced joining technology for hybrid (composite-metal) structures. Polymer Matrix Composites (PMC) used in structural applications are known to reduce structure weight, lower life-cycle cost and, in case of a floating platform, improve the deadweight/displacement ratio. While beneficial, PMC applications for large hull structures have certain limitations in size and volume of seamless structural component without using joints. A hybrid hull that consists of both metal and composite structural members potentially enables desirable enhancements of structural efficiency, but robust joining between those heterogeneous structures must be employed. A recently completed feasibility study has been performed involving a novel hybrid joining concept-technology based on a combination of conventional adhesive bonding with novel metal surface preparation. Computer simulation of the joint structural behavior and failure, development of a material processing procedure based on adaptation of Vacuum-Assisted Resin Transfer Molding (VARTM) process to manufacturing of a large hybrid structure, fabrication of pilot joint test articles, and tensile testing of those to failure, have been performed as part of the feasibility study. Two sets of the hybrid joint were tested, the novel joint being developed and its conventionally bonded analogue without the novel surface preparation considered as a base-line joint. The tests resulted with 48%-increase of load-bearing capability of the novel joint and a good match between generated computed and experimental data.
Thruster Interactions on Autonomous Underwater Vehicles
Authors: Palmer Alistair R. , Hearn Grant E. , Stevenson Peter
Published: February 2010

Autonomous underwater vehicles are a developing technology capable of undertaking a wide variety of different tasks. The development of these vehicles is aided by the use of simulations of their performance. These simulations require accurate modelling of the propulsion and control devices employed to calculate the response of a vehicle to different situations and control strategies. Simulations of underwater vehicles tend to include models of the dynamic performance of the thrusters employed, however, the simulations neglect some of the hydrodynamic interaction effects. These interaction effects include thruster–hull and thruster–thruster interactions similar to those encountered on dynamic positioning surface vessels. This paper assesses these effects for autonomous underwater vehicles and, where appropriate, suggests models for use in simulations.
Landslide Tsunamis Propagating Along a Semi-Plane Beach
Authors: Sammarco Paolo , Renzi Emiliano , Lecouvez Matthieu
Published: February 2010

A forced three-dimension analytical model is developed to investigate the main characteristics of landslide tsunamis propagating on a semi-plane beach. The method of separation of variables and the Fourier transform are employed to obtain the solution in the form of an eigenfunction expansion. Parametric discussion and further comparison with the model of a uniformly sloping beach are finally made.