bluuebunny/crossref_metadata_2025 huggingface dataset:
Reliability Analysis of Ultimate Strength of a Capesize Bulk Carrier in Hogging and Alternate Hold Loading Condition
Authors: Shu Zhi , Moan Torgeir
Published: January 2011

This paper deals with the structural reliability analysis (SRA) of ultimate strength of a Capesize bulk carrier in hogging and alternate hold loading condition (AHL). The ultimate strength in hogging and AHL condition is very important for the safety of bulk carriers since the local loads due to internal cargo loads and external sea pressure can reduce the ultimate bending capacity. In the present paper, the characteristic ultimate bending capacity of the subject bulk carrier is investigated by nonlinear finite element (FE) analysis and the characteristic value of the global and local loads are determined in accordance with the Common Structural Rules for bulk carriers (CSR-BC). The uncertainties associated with the loading capacity and load effects are appropriately modelled. The First Order Reliability Method (FORM) is adopted to calculate the annual probability of failure of this bulk carrier in hogging and AHL condition. The effect of heavy weather avoidance on the global and local loads is also evaluated in the SRA. The results show that the local loads have a significant impact on the failure probability of such vessels in the hogging and AHL condition.
Numerical Investigation of Sloshing in a Tank: Statistical Description of Experiments and CFD Calculations
Authors: Iwanowski Bogdan , Lefranc Marc , Wemmenhove Rik
Published: January 2011

Numerical study of liquid dynamics in an LNG tank is presented. The available data from large scale (1:10) sloshing experiments of 2D section of an LNG carrier reveal large scatter in recorded values of peak pressures. The experimental data is analysed from statistical point of view in order to obtain distributions of the pressure peaks. Then the entire experimental data record is reproduced numerically by CFD simulations and it is shown that pressure peaks obtained numerically display scatter of values as well. A statistical description of the numerically obtained record is provided and compared with description derived from the experimental data. The applied CFD code ComFLOW solves Navier-Stokes equations and uses an improved Volume of Fluid (iVOF) method to track movement of fluid’s free surface. Two different fluid models, single-phase (liquid+void) and two-phase (liquid+compressible gas) can be applied, the latter model being capable of simulating bubbles and gas entrapped in liquid. For low tank filling rate discussed in the paper (10%) the single-phase approach is sufficient. Comparison of statistical properties of experimental and numerical records is offered.
Global Responses of Struck Ships in Collision With Emphasis on Hydrodynamic Effects
Authors: Jia Huirong , Moan Torgeir
Published: January 2011

Hydrodynamic effects in ship collisions are usually considered by increased inertia force in the form of the equivalent added mass. It is necessary to reasonably estimate the equivalent added mass to calculate energy absorbed by ships in collisions. In this paper, motion equations in the horizontal plane for the struck rigid ship are first established considering hydrodynamic effects in the form of added mass, linear and quadratic damping. The equivalent added mass are obtained in three ways and analyzed. It is shown that the equivalent added mass for the sway motion depends on not only the duration of collision impact, impact force, but also the collision position, while the equivalent added mass for the yaw motion could be assumed to be independent of the collision position. In addition, a simple formula is proposed to relate the equivalent added mass for part of the vessel to that of the whole vessel, provided that the underwater area of the transverse section is known. As a consequence, it is possible to estimate rigid hull girder responses based on the simplified methodology, which could be used in design and probabilistic collision analyses. In the end, the hull girder responses are estimated considering both a flexible and rigid vessel. Comparisons are made between rigid and flexible hull girder responses.
Development of 3-D Numerical Wave Tank and Applications on Comb-Type Breakwater
Authors: Fang Zhuo , Cheng Liang , Zhang Ningchuan
Published: January 2011

In this study, a 3-D numerical wave tank is developed, based on a commercial computational fluid dynamics (CFD) package (FLUENT) to predict wave forces on coastal and offshore structures. A source wave-generation method is introduced to FLUENT through user-defined functions to generate incident waves. Spongy layers are used on both upstream and downstream sides of the wave tank to reduce the effects of wave reflections and secondary wave reflections. Various wave trains, such as linear monochromatic waves, second order Stokes waves and irregular waves were generated by using different source functions. It is demonstrated through numerical examples that the source wave-generation method can accurately generate not only small amplitude waves but also nonlinear waves. The present numerical wave tank is validated against standing waves in front of a vertical breakwater. Interactions between waves and a comb-type breakwater are simulated using the present model. The numerical results are compared with physical experimental results. It is found that the present numerical wave tank simulated the wave and breakwater interactions well.
Code Verification, Solution Verification and Validation in RANS Solvers
Authors: Ec¸a Lui´s , Vaz Guilherme , Hoekstra Martin
Published: January 2011

The maturing of CFD codes for practical calculations of complex turbulent flows implies the need to establish the credibility of the results by Verification & Validation. These two activities have different goals: Verification is a purely mathematical exercise that intends to show that we are “solving the equations right”, whereas Validation is a science/engineering activity that intends to show that we are “solving the right equations”. Verification is in fact composed of two different activities: Code Verification and Solution Verification. Code Verification intends to verify that a given code solves correctly the equations of the model that it contains by error evaluation. On the other hand, Solution Verification intends to estimate the error of a given calculation, for which in general the exact solution is not known. Validation intends to estimate modelling errors by comparison with experimental data. The paper gives an overview of procedures for Code Verification, Solution Verification and Validation. Examples of the three types of exercises are presented for simple test cases demonstrating the advantages of performing Verification and Validation exercises.
Failure Mode and Sensitivity Analysis of Gas Lift Valves
Authors: Gilbertson Eric , Hover Franz , Colina Ed
Published: January 2011

Gas-lifted oil wells are susceptible to failure through malfunction of gas lift valves. This is a growing concern as offshore wells are drilled thousands of meters below the ocean floor in extreme temperature and pressure conditions and repair and monitoring become more difficult. Gas lift valves and oil well systems have been modeled but system failure modes are not well understood. In this paper a quasi-steady-state fluid-mechanical model is constructed to study failure modes and sensitivities of a gas-lifted well system including the reservoir, two-phase flow within the tubing, and gas lift valve geometry. A set of three differential algebraic equations of the system is solved to determine the system state. Gas lift valve, two-phase flow, and reservoir models are validated with well and experimental data. Sensitivity analysis is performed on the model and sensitive parameters are identified. Failure modes of the system and parameter values that lead to failure modes are identified using Monte Carlo simulation. In particular, we find that the failure mode of backflow through the gas lift valve with a leaky check valve is sensitive to small variations in several design parameters.
Guideline for Offshore Floating Wind Turbine Structures
Authors: Ronold Knut O. , Hansen Vigleik L. , Godvik Marte , Landet Einar , Jo̸rgensen Erik R. , Hopstad Anne Lene H.
Published: January 2011

Floating offshore wind turbines is a field undergoing major development. Several companies and research institutes worldwide are engaged in research programs, pilot projects and even planning of commercial floating wind farms. Developing standards for design of floating wind turbine structures and a framework for prevailing rules are crucial and necessary for the industry to continue to grow. Det Norske Veritas (DNV) is an international provider of offshore standards for both the oil and gas industry and the wind energy industry. The standard DNV-OS-J101 “Design of Offshore Wind Turbine Structures” provides principles, technical requirements and guidance for design, construction and in-service inspection of offshore wind turbine structures. As a first step towards updating this standard to fully cover floating wind turbine structures, a DNV Guideline for Offshore Floating Wind Turbines has been established. This development is based on identification of current floating wind turbine concepts and the guideline includes an evaluation of what is required to make DNV-OS-J101 suitable for floating wind turbine structures. This paper presents the highlights of the new DNV Guideline for Offshore Floating Wind Turbine Structures.
The Design and Analysis of Pile Protection Devices for the Qiantang River Bridge
Authors: Pan Jin , Wu Weiguo , Xu Mingcai
Published: January 2011

According to the Qiantang River Bridge project, the pile structures are adopted as protection devices for bridge piers. Because the pile structures are not contact with bridge piers, the traditional design method of impact force control is no longer applicable. Therefore, this paper studies on the large deformation characteristics of piles, takes the interaction between the piles and soil into account by “m” method, puts forward a new anti-collision design method, and at last determined the form and dimension of pile structures. LS-DYNA, a nonlinear explicit dynamic finite-element code, was used for analysis. The protection devices are used to Qiantang River Bridge, and then some useful conclusions were achieved.
On the Understanding of Non-Stationary VIV of Slender Beams
Authors: Larsen Carl M. , Wu Jie , Lie Halvor
Published: January 2011

VIV of slender beams at high mode order will appear as a non-stationary response process. Amplitudes, dominating frequency and mode composition are seen to vary in time, but so far we do not have a complete understanding of this process. One approach is to attempt to understand and model the physical mechanism behind the observed behaviour, but an alterative is to establish a simplified model that can be used for fatigue calculations. The purpose of the present paper is to compare the dominant response frequencies that have been observed in large scale tests of a flexible beam to the discrete response frequencies that are predicted by an empirical model for prediction of VIV. Use of wavelet and modal analyses on experimental data makes it possible to describe the time variation of the peak frequency, and hence also the relative period of time this frequency falls into discrete frequency bins. An empirical model is also proposed for calculation of relative duration of competing response frequencies. The observed frequencies can hence be compared to the results from the proposed model. The conclusion is that the model identifies the domination response frequencies with satisfactory accuracy. The range of calculated discrete response frequencies is larger than for the discrete peak frequencies identified from the experiments. But the observed response process has a broader frequency band than the variation of the peaks. Hence, the results from the analysis seem to agree well with observations. Further analyses are, however, still needed in order to verify the proposed model.
Non-Linear Finite Element Drop Collision Simulation of the Anti-Collision Device Hitting a Bridge Pile Cap
Authors: Peng Sheng , Wu Weiguo , Pan Jin , Xia Ziyu
Published: January 2011

This paper recites the non-linear dynamic finite element simulation to the whole collision process of the collision between the anti-collision equipment and the bridge pile cap in the rough waves and surge with an example, basing on the solving technique of explicit non-linear finite element method and the mechanism in bridge-anti-collision equipment collision, including the process of building a reasonable FEA model and the numerical calculation and analysis of the collision process in considering the hydrodynamics influence by non-linear finite element analysis code MSC.Dytran / Patran. Described in detail attached to the collision analysis needs to consider such as determination of element size control, the selection of material models and failure criteria, the definition of contact and friction and so on. It is pointed that local strength of the anti-collision equipments and the bridge pile caps, as well as the collision impact force in the rough seas and surge. On the basis of numerical simulation, the general laws and characteristics of the impulse response of collision are achieved, which can be extended to the design of the bridge anti-collision devices and reinforcement for pier caps with providing a range of meaningful conclusions.
Ship Track Impacted by Incident Waves
Authors: Lin Ray-Qing , Klamo Joseph
Published: January 2011

Correctly predicting the track of a ship when impacted by incident waves is one of the most important tasks in accurately simulating seakeeping performance. This is especially difficult during a storm surge in coastal regions, where the bottom topography rapidly changes. In fact accurately predicting a ship track in calm water has not been completely solved. Most recently, Lin et al. integrated the total forces and moments over an actual ship hull and rudders in a fully nonlinear ship motion model named the Digital, Self-consistent Ship Experimental Laboratory (DiSSEL) by using finite element/finite difference in calm water (Lin et al. 2005 [1], Lin and Kuang, 2006 [2], 2008 [3], 2009 [4]; Lin et al., 2009 [5]). The new method is not only accurate, but also computationally efficient. As part of a continuing effort, in this study, the incident wave impact is now included. The incident wave impact on the ship hull and rudders is integrated over the actual wetted surfaces at each time step, based on the ship position. First, the numerical simulations are benchmarked using existing experimental data for an experimental hull form. The DiSSEL simulations agree well with the experimental data. Based on the simulations, we explore the physics to gain an understanding into the possible factors that cause changes to the ship tracks. For example, why will the turning circle of a ship with constant rudder angle and ship speed, in the presence of waves, sometimes be a spiral while other times remain a circle? Finally DiSSEL will be coupled with the coastal wave model by Lin and Perrie (1997, 1999) [6], [7], to predict the ship track in a coastal region impacted by a storm surge. Future improvements to DiSSEL will include the incorporation of a propeller model. Since a model for the propellers has not yet been implemented, the influence of the propeller slipstream on the rudder is currently handled by empirically modifying the effective inflow velocity into the rudder to account for the acceleration of the flow by the propeller.
A Novel Concept for Floating Offshore Wind Turbines: Recent Developments in the Concept and Investigation on Fluid Interaction With the Rotating Foundation
Authors: Vita Luca , Zhale Frederik , Paulsen Uwe S. , Pedersen Troels F. , Madsen Helge A. , Rasmussen Flemming
Published: January 2011

This paper describes the recent developments regarding a new concept for deep sea offshore vertical axis wind turbines. The concept utilizes a cylindrical foundation rotating in the water. The 2D Navier-Stokes solver EllipSys2D has been used to investigate the interaction between the rotating foundation and a water flow stream passing the turbine. Lift and drag forces, and the friction moment on the rotating foundation of the turbine have been computed. The calculations are repeated for different operating conditions of the wind turbine on a range of rotational speeds. The Reynolds number, based on the diameter of the foundation, is 5×106.
Prediction of Wave Impact Pressures on Horizontal Plate
Authors: Meng Yanqiu , Chen Guoping , Yan Shichang
Published: January 2011

An optimal design of deck of jetty, platform and similar ocean structures requires detailed knowledge on wave impact pressure which affects its function. Investigations on wave induced impact pressures on deck were carried out by using physical model studies. The influences of wave and structure parameters on wave impact pressures were investigated. It is found that the wave impact pressure increases with increased deck clearance. The increasing trend continues up to the relative deck clearance Δh/η = 0.3–0.8, and then the impact pressure starts to decrease after that deck clearance. The wave steepness has some effect on the wave impact pressure, but the trend of variation is not consistent for different wave condition. The maximum impact pressure occurs when the ratio of wave length to deck width equals 3.97. Increase of wave period results in increase of the distance between the location of the maximum impact pressure and the seaward end of deck. Based on analysis of the physics of the wave structure interaction, empirical formula was proposed to estimate wave impact pressure on deck.
Novel Technique for SCR Porch Location Screening
Authors: Yue Bin , Campbell Mike , Walters David , Thompson Hugh , Raghavan Kamaldev
Published: January 2011

For a spread moored FPSO, the determination of feasible SCR hangoff locations is usually performed considering numerous load combinations including different riser hangoff locations, vessel drafts, wave heights, periods and directions and current profiles. Due to the riser response sensitivity to the random waves multiple three hour random sea realizations are also typically used to capture the worst riser response. Thus, large numbers of load cases have to be performed. The amount of computational resources needed to obtain the results is substantial and sometimes prevents the work from completion in a timely manner. Furthermore, significant effort needs to be invested in organizing and understanding the results. This paper introduces the concept of developing Porch Location Envelopes (PLE) which considerably simplifies the understanding of all results, and recommends an approach that drastically reduces the time in obtaining those results. The PLE for a given SCR is defined as the limiting riser hangoff locations for a range of vessel motions. The PLE is determined using rigid body vessel motion transformation and relationships between porch motions and riser response characteristics. By utilizing the approach provided in this paper, the feasible SCR hangoff locations can be determined for each riser using only a limited number of riser strength analyses.
Calculation of Manoeuvring Forces on Submarines Using Two Viscous-Flow Solvers
Authors: Vaz Guilherme , Toxopeus Serge , Holmes Samuel
Published: January 2011

Submersibles used for exploration, maintenance and naval warfare have to be both manoeuvrable and easy to control. Simulation of the trajectory for these vessels requires the accurate determination of the hydrodynamic forces and moments which are determined by model-testing, empirical methods or a combination of both. CFD can play a role here by permitting an easier and more accurate determination of these loads. In this paper we focus on the accurate prediction of the manoeuvring forces of free swimming streamlined submersibles (submarines) using CFD. We compare simulations of a standardised well-known submarine shape (DARPA SUBOFF) for two configurations, one bare hull (AFF-1) and one fully-appended hull (AFF-8), under different inflow angles. The viscous-flow solvers used are the finite volume solver ReFRESCO developed by MARIN, and the finite element commercial solver AcuSolve. Verification studies are performed and the numerical results are validated with the experimental data available in the literature. The influence of different turbulence models is investigated and results obtained with a RANS (Reynolds-Averaged-Navier-Stokes) approach are compared with the theoretically more realistic DDES (Delayed-Detached-Eddy-Simulation) results. The influence of the appendages on the forces and flow fields is also investigated and analysed. As a last example, results of a forced pitch motion including dynamic effects are presented.
9.13 Inch Gas Export Flexible Pipe Prototype Development for Ultra Deep Water Projects in the Brazilian Pre-Salt Area
Authors: Pires Fabio , Clevelario Judimar , Sheldrake Terry , Falca˜o Gelson , Souza Italo , Tan Zhimin , Lu Jing
Published: January 2011

Although commercial operation of the Brazilian pre-salt cluster has already commenced with both the TUPI EWT and the TUPI Pilot projects employing both 4-inch and 6-inch flexible pipes, forthcoming developments will require the consolidation of large diameter pipeline technology to make fluid exportation feasible, since the pre-salt cluster is located approximately 300km offshore in water depths reaching up to 2500m. This paper discusses the main technological challenges and summarizes the development process of a 9.13-inch flexible pipe designed to function within the operating envelope expected for the TUPI Pilot project.
Investigation on the Effects of Risers in the Dynamics of Floating Systems
Authors: Rateiro Felipe , Malta Edgard Borges , Fujarra Andre´ L. C. , Prata Vieira Daniel , Nishimoto Kazuo
Published: January 2011

This paper presents the experimental results obtained from the model tests performed at the IPT (State of Sa˜o Paulo Technological Research Institute) towing tank, located in Sa˜o Paulo, Brazil. The model used was the semi-submersible ITTC-SR192, at a scale 1:105. The main focus of this study is the analysis of the risers influence on the floating unit dynamics, taking into account damping effects caused by the lines. In order to establish basis of comparison the tests were performed with and without risers. These were modeled as a group of large diameter hoses that are able to provide a significant increment in the damping of the system. By such approach, it was possible to evaluate the changes on the dynamic behavior of the unit induced by the presence of risers. As an additional investigation tool, these results were analyzed with the aid of the software Numerical Offshore Tank (Tanque de Provas Nume´rico - TPN), which is a dynamic simulator of offshore systems based on parallel-processing developed by means of a partnership between the University of Sa˜o Paulo, Petrobras and other Brazilian research institutions. By means of the comparisons between the model tests results with and without risers and of the results from the numerical tool, TPN, the dynamic behavior of the floating unit was investigated in terms of the effects caused by the presence of risers, which is a very relevant subject as offshore industry walks towards ultra-depth waters.
Flexible Pipe Systems Configurations for the Pre-Salt Area
Authors: Clevelario Judimar , Pires Fabio , Barros Claudio , Sheldrake Terry
Published: January 2011

Unbonded flexible pipes are being considered as an actual solution for the following developments for the Brazilian Pre-Salt area. This technology is already being successfully used in the first EWT installed in the Brazilian Pre-salt and being qualified for the first Pre-salt Pilot Project development. However, unlikely the current project developments in water depths around 1500m, the free catenary configuration is not always an applicable option not only due to the 2500m water depth but also to the presence of contaminants such as CO2 and H2S in the conveyed fluids which in certain applications make the use of conventional high strength steels unfeasible, making the use of sour service armour wires mandatory. This paper presents the result of the global and local analysis performed for different applications such as 4″ gas lift, 6″ water injection, 6″ production and 9.13″ Gas export structures designed specifically for the ultra deep water in Brazilian Pre-Salt area. The aim of this study was to verify the feasibility of the free hanging catenary configuration and determine the most suitable flexible pipe system configuration for different applications, confirming that the flexible pipes are an adequate solution for the Pre-Salt even when the service life requirements exceeds 20 years and associated safety factors.
Evaluation of Weld Root Failure Using Battelle Structural Stress Method
Authors: Hong Jeong K.
Published: January 2011

Weld related fatigue failure is one of the most common concerns in welded structures. From the fatigue design point of view, weld toe failure is preferable to weld root failure. Base plate thickness is a controlling parameter for weld toe failure, while weld metal size is a controlling parameter for weld root failure. However, controlling the weld metal size is not easy because the actual weld penetration and weld leg size vary along a weld and from weld to weld. Therefore, analyzing fatigue test data for weld root failure tends to enlarge scatter band due to variability in weld penetration and weld leg size when the nominal weld size is considered. The structural stress based weld fatigue master S-N curve adopted by 2007 ASME section VIII Div. 2 and new API 579/ASME FFS-1 was constructed by incorporating only clearly defined weld toe fatigue data. In this article, a simplified structural stress procedure was developed and a design master S-N curve for weld root failure was established based on the published fatigue test data. Consequently, the mean design master S-N curve for weld root failure is downshifted relative to the mean master S-N curve for weld toe failure, and has a wider scatter band. To be conservative, a crack path along weld throat is recommended for structural stress calculation. Also, the transverse shear stress effects on structural stress calculation can be ignored.
Vortex-Induced Vibrations and Wake Structures of Isolated Plain and Straked Cylinders Mounted on a 2DOF Elastic Base
Authors: Korkischko Ivan , Freire Cesar M. , Meneghini Julio R. , Franciss Ricardo
Published: January 2011

This paper presents experimental results concerning the response of plain and straked circular cylinders. The isolated cylinders are mounted in a two degrees of freedom elastic base. Two straked cylinders are tested and they have the same pitch p = 10d and two different heights h = 0.1d and h = 0.2d. The longitudinal and transverse amplitude responses and wake structures of plain and helically straked cylinders are compared. The wake visualization uses the stereoscopic digital particle image velocimetry (SDPIV) technique. Comparing to the plain cylinder response, the p = 10d and h = 0.1d strakes moderately reduce the maximum amplitude response, while the p = 10d and h = 0.2d strakes suppress the vortex-induced vibrations. The strake effectiveness is directly related to the strake height. The Reynolds number varies from 1000 up to 7500 in the experiments.
Improved SCR Design for Dynamic Vessel Applications
Authors: Yue Bin , Campbell Mike , Walters David , Thompson Hugh , Raghavan Kamaldev
Published: January 2011

Design of Steel Catenary Risers (SCR) has seen increasing challenges in deep water applications due to higher pressures, vessels with more dynamic motions and severe weather conditions. In the Gulf of Mexico, the SCR is sometimes designed with little margin due to harsh environment. In West Africa, SCRs may be infeasible with turret moored Floating Production Storage and Offloading (FPSO) System, and are often limited to a narrow hang-off range near the Center of Gravity (CoG) with spread moored FPSO. Freestanding hybrid risers are feasible solutions for many fields in West Africa. However, the freestanding riser cost is generally considered much higher than that of an SCR. Hence, there is a need to improve SCR performance in dynamic vessel applications. This paper presents the development of Shaped SCR configuration that has significantly improved performance and minimal cost increase compared to an SCR. Compared with a conventional Lazy Wave SCR, the riser configuration has increased installation flexibility and decreased cost as it is installable via J-lay or S-lay. The configuration is developed and assessed for a spread moored FPSO in West Africa. The strength and fatigue response is compared with those of a simple SCR and Lazy Wave SCR. The key considerations in developing the configurations are discussed. This paper also presents the use of upset ends to improve riser fatigue performance. This is achieved due to reduced bending and tension stress ranges resulting from thicker pipe ends, as well as to reduced Stress Concentration Factors (SCF) resulting from forging process.
A TLP Solution for 8000 Ft Water Depth
Authors: Bian Xiaoqiang Sean , Leverette Steven J. , Rijken Oriol R.
Published: January 2011

A Tension Leg Platform (TLP) solution is proposed for dry tree applications in ultra-deep water depths (∼8000 ft). Major challenges for a TLP associated with the ultra deep environment are addressed with an innovative air spring – mass vibration absorber (VAB) system introduced by SBM Atlantia. The tendon system for the TLP therefore is able to scale essentially linearly with the water depth, instead of quadratically for a conventional TLP. This paper details the integrated platform design issues, including the hull, tendon design and the coupled motion analysis approach. It also discusses the system weight and dimension scales for typical applications and the constructability in terms of their upper bound limits compared with existing platforms. A design example is presented for the offshore Brazil Santos Basin environment at 8000 ft water depth with consistent current and relatively large fatigue sea states.
Feedback Analyses of Pipeline Embedment Over As-Laid Survey Results
Authors: Carneiro Daniel , Gouveia Joa˜o , Parrilha Rafael
Published: January 2011

The as-laid embedment is a key parameter in the design of non-buried rigid pipelines. Large discrepancies are observed, for example in the number and length of predicted free spans, or in the global response to thermo-mechanical expansion, when this parameter is misevaluated. The employment of wide ranges to cover the uncertainties and ensure safety may hugely increase the project costs by mitigating what could not be an actual concern. Conversely, there is no reliable method to accurately predict this embedment. The large strains imposed to the soil dishearten the use of finite element analyses, while physical model tests are as well subjected to the scatter in soil parameters along pipeline route (increased by the sampling under harsh conditions); and mostly to the dynamic motions that occur during the lay process which are difficult to quantitatively foresee. This last effect causes pipelines to embed deeper, as the seabed soil is both softened and physically displaced by the pipeline motion. Engineering practice has been using empirical models, which are always subjected to calibration and applicability range issues. This paper presents the results of feedback analyses of six rigid flowlines (ranging from 174mm to 353mm diameter) recently installed on clayey seabed offshore Brazilian coast, in water depths between 1087m and 1628m. The embedment values, measured by as-laid surveys, were used to reassess model parameters calibration. Results indicate encouraging agreement with published works. Statistical treatment of the data led to smooth distributions, which might be useful in future projects employing probabilistic design approach.
Crushing and Wet Collapse of Flowline Carcasses: A Theoretical-Experimental Approach
Authors: Pesce Celso P. , Martins Clo´vis A. , Gay Neto Alfredo , Fujarra Andre´ L. C. , Takafuji Fernanda C. M. , Franzini Guilherme R. , Barbosa Teo´filo , Godinho Carlos A.
Published: January 2011

The present paper brings together theoretical predictions and experimental results, comparing crushing tests results as well as carcass wet collapse tests. The theoretical models are of two kinds: (i) numerical (FE) and (ii) analytical. The first kind is a restricted 3D version of a finite element model. The second kind is based on classic assumptions of equivalent ring behavior. Discussion is made on the real yield stress value to be adopted, as well as on the pertinence of geometric hypotheses. Sensitivity analyses, regarding ovalization and helical pitch are also presented.
Crushing Tests of Flowlines Internal Layers: An Experimental Approach via Optical Motion Capture and Image Processing
Authors: Fujarra Andre´ L. C. , Gonc¸alves Rodolfo T. , Pesce Celso P. , Silva Marcelo R. , Godinho Carlos A. F.
Published: January 2011

New optical measurement approach for crushing tests of flow lines internal layers is detailed, based on an accurate tracking of the deformed carcass section through image processing. The results are compared to those from standard procedures based on discrete measurements using calipers. The new approach shows to be not only appropriate for the standard measurement requirements but also enables a comprehensive understanding of the crushing behavior.
On the Calibration of Coefficients of Friction for Pipeline-Seabed Interaction
Authors: Datye Deepak V.
Published: January 2011

Subsea pipelines placed on the seabed can buckle due to thermal and mechanical loads. This buckling, and the associated pipe walking phenomena, can lead to large stresses in the pipe sections and at the pipe end attachments. These high stresses need to be accounted for in pipeline design. An accurate simulation of pipeline buckling for design purposes requires a rational representation of the nonlinear large deformations of the underlying soil, which entails a large 3D problem to be solved with repeated remeshing in the Lagrangian setting. However, it is possible to reduce this effort and forgo the direct modeling of the underlying soil by modeling the pipe as a beam, the seabed as a surface, and the resistance offered by the soil to the pipe through an appropriate contact interaction behavior between the pipe and the seabed. This contact interaction behavior can be expressed through variable coefficients of friction between the pipeline and the seabed. In this paper the Coupled Eulerian-Lagrangian technique is used to evaluate the resistance offered by the plastic soil to the pipeline; the resistance data are then used to calibrate these coefficients of friction, which are in turn used in an implicit dynamic analysis for simulating the buckling deformations of a representative pipeline, modeled as a beam, in contact with the seabed, which is modeled as a surface.
Numerical Modelling in Turbines for OWC Systems: Application to a Radial Impulse
Authors: Gonza´lez Juan G. , Pereiras Bruno , Castro Francisco , Rodri´guez Miguel A.
Published: January 2011

This work is focused on radial impulse turbines for an Oscillating Water Column (OWC) which is one of the alternatives to the Wells turbines traditionally installed in the OWC systems. All self-rectifying turbines work under special conditions due to the bi-directional flow caused by OWC. But a radial impulse turbine has another special point: it works alternatively as an inflow/outflow turbine, so that its behavior is not symmetrical as is expected in axial turbines for OWC (Wells and axial impulse turbines). The complete CFD analysis we have made of a radial impulse turbine is described. The model was created for a specific turbine but can be adapted for any self-rectifying turbine. We have studied the turbine by means of a one-dimensional study and a 3-D model solved with FLUENT® software, and the results were validated with experimental data extracted from the bibliography. This model allowed us to analyse both the classical dimensionless parameters and the flow pattern. Moreover, we have introduced a special definition for the reaction degree in order to analyse the process of the energy conversion.
Validation of Vortex Induced Vibration With One Degree of Freedom
Authors: Pacheco Sicilia , Vitola Marcelo A. , Wanderley Juan B. V. , Sphaier Sergio H. , Levi Carlos A.
Published: January 2011

The vortex induced vibration is an important problem for the offshore industry, due to the frequent use of structures, such as risers and umbilicals. In the last decade, the use of numerical methods to study the vortex induced vibration has increased. Some disagreement between numerical and experimental results has been verified in the literature. In the present work, the numerical model solves the Reynolds average Navier-Stokes equations using an upwind and a Total Variation Diminishing (TVD) conservative scheme, written in curvilinear coordinates. The turbulent flow in the wake of the cylinder has been modelled using the k–ε model. The cylinder is supported by a spring and a damper and free to vibrate in the transverse direction. Results obtained for phase angle, amplitude, frequency, and lift coefficient are compared to experimental data from Morse et al. [1]. The results indicate that the two dimensional simulation represents better the behaviour of cylinder displacement obtained experimentally using the unattached or attached end plate setup used by Morse et al. [1]. These results suggest that some difference between experimental and numerical data could be associated with the end condition used in the experiments. For the case using the unattached or attached end plate the difference in the peak amplitude between experimental and present results seems to be related with the initial condition adopted.
Probabilistic Fatigue Safety Analysis of Oil and Gas Risers Under Random Loads
Authors: Khan Rizwan A. , Ahmad Suhail
Published: January 2011

Marine riser is an important component of oil and gas drilling and production system. It is essentially a slender pipe conveying fluid between well-head and floating production unit. They are formed out of three basic types of configuration namely, free hanging, “lazy-wave (SWLR)” riser. Risers are subjected to varied static, quasi-static and dynamic forces. For the safety of design, the behavior of the riser under these forces is thoroughly investigated. 3D Nonlinear dynamic analysis of riser is obtained in the time domain using finite element software package ABAQUS/Aqua. The response histories so obtained are employed for the study of fatigue reliability analyses of riser. It is based on a bi-linear relationship to model fatigue crack growth and incorporates a failure criterion to describe the interaction between fracture and plastic collapse. Uncertainty modeling, especially of fatigue crack growth parameters, is undertaken using bi-linear crack growth relationship. Results pertaining to fatigue reliability and fatigue crack size evolution are presented using Monte Carlo Simulation. The bi-linear crack growth models are found to lead to higher fatigue life estimation. Sensitivity behavior pertinent to limit state adopted has been thoroughly investigated. These findings implicate inspection schemes for components of the marine structures to ensure minimization of the surprises due to wide scatter of the fatigue phenomenon in marine environment.
FourStar™ Dry-Tree Semisubmersible Development
Authors: Williams Neil , Leverette Steve , Bian Sean , Large Sean , Cao Peimin
Published: January 2011

This paper discusses the development of a dry-tree semisubmersible (DTS) platform concept appropriate for deployment in non-hurricane/non-cyclonic environments worldwide, and the verification of the concept through wave basin model tests. An example configuration is presented for an application in 2,100 m water depth offshore Brazil.
Preliminary Concept and Feasibility Studies on Ocean Energy Device Design From Used Ships
Authors: Mukherjee Debanjan , Mansour Alaa E.
Published: January 2011

The process of decommissioning ships, usually followed by ship scraping, is associated not only with significant costs but also with many environmental and toxic hazards. Thus, re usability of such ships will offer more advantages than recycling its steel. This paper proposes reusing a post-service life vessel by converting it into an Ocean Wave Energy Device. A systematic study on the preliminary estimation of energy extraction levels from ocean waves is presented, with some discussion on the energy of a ship-shaped body in motion in irregular seas. Heave motion was found to be more favorable for such applications. Thereafter concept designs have been proposed for the device, and the designs have been analyzed in terms of the extent of relative motion and power that could be obtained from each of them. Numerical simulation techniques have been used to generate the results. Through this analysis, it has been established that the idea of constructing such a device is feasible. The relatively slower but high-force systems can use a hydraulic take-off unit instead of electrical inductance generators. The mooring system has also been identified as a separate design problem. Further design issues including optimizing the different parameters, cost analysis and fabrication issues have not been considered — this work is aimed to provide the starting point of the design exercise.
Piston Mode and Sloshing Resonances in a Damaged Ship
Authors: Kong X. J. , Faltinsen O. M.
Published: January 2011

This work investigates the motions of a damaged ship in regular beam sea waves. The ship geometry including the damaged compartment (with opening) is modeled by using a unified approach called Hull Reshaped Method [1] and the hydrodynamic problem is solved by applying a 3D potential flow code. Linear hydrodynamic coefficients and excitation loads together with experimental nonlinear viscous roll damping are used in the calculations of the motion response functions. In addition to the natural roll resonance, the piston mode and sloshing resonances are numerically observed. By applying simplified theoretical analysis, these two resonances are further confirmed for a damaged ship with opening in the hull defined by the SOLAS rule [2]. The resulting physical problems, for instance, dry bottom, roof impact and possible structural failure in the damaged compartment are predicted from the simulations.
Splash Zone Lifting Analysis of Subsea Structures
Authors: Sarkar Arunjyoti , Gudmestad Ove T.
Published: January 2011

The lifting analysis of a subsea structure determines the maximum allowable design sea state in which the structure can be installed safely. Normally, such analysis on the structure at the splash zone governs the expected largest forces in the hoisting system and in turn the allowable sea state since the water particle kinematics is larger in the splash zone. In this paper, the DNV Recommended Practice for Modelling and Analysis of Marine Operation (DNV-RP-H103, April 2009) is discussed with emphasis on the hydrodynamic coefficients and analysis methodology for the splash zone lifting analysis. An approach is suggested here to take into account the free surface proximity effect on added mass of flat surfaces in the absence of test results. Discussions on the following points are also included: • For structures which show restricted sea state due to large double pendulum motion and consequently high dynamic tension in the crane wire, a solution could be obtained by lowering the sling angles. • For inertia dominated structures, the drag coefficients should be chosen with caution unless experimental results are available since the drag may induce unrealistic damping in the system. • For the structural design of large subsea structures, the design DAF for submerged condition should be chosen from a preliminary lifting analysis result. The current industrial practice of using DAF = 2 with respect to the static submerged weight could be increased following the analysis result to optimise the use of the crane capacity by achieving a higher design sea state. • For lifting analysis of structures with large added mass / submerged weight, modelling of winch speed may represent a worse loading case as compared to the case with zero winch speed in the splash zone. • For the splash zone analysis, correct modelling of the stiffness of the crane structure along with the wire is important. The assumption that the crane structure is rigid may lead to unrealistic analysis results. Experimental programmes to obtain further information on the amplitude dependent characters of the hydrodynamic coefficients, the stiffness and the damping of the Crane, the wires etc are furthermore recommended.
Analysis, Design, and Evaluation of the UC-Berkeley Wave-Energy Extractor
Authors: Yeung Ronald W. , Peiffer Antoine , Tom Nathan , Matlak Tomasz
Published: January 2011

This paper evaluates the technical feasibility and performance characteristics of an ocean-wave energy to electrical energy conversion device that is based on a moving linear generator. The UC-Berkeley design consists of a cylindrical floater, acting as a rotor, which drives a stator consisting of two banks of wound coils. The performance of such a device in waves depends on the hydrodynamics of the floater, the motion of which is strongly coupled to the electromagnetic properties of the generator. Mathematical models are developed to reveal the critical hurdles that can affect the efficiency of the design. A working physical unit is also constructed. The linear generator is first tested in a dry environment to quantify its performance. The complete physical floater and generator system is then tested in a wave tank with a computer-controlled wavemaker. Measurements are compared with theoretical predictions to allow an assessment of the viability of the design and future directions for improvements.
The Visual Information Derived From the Stereo Camera System Mounted on the Underwater Vehicle
Authors: Ishibashi Shojiro , Yoshida Hiroshi , Hyakudome Tadahiro
Published: January 2011

The visual information is very important for the operation of an underwater vehicle such as a manned vehicle and a remotely operated vehicle (ROV). And it will be also essential for functions which should be applied to an autonomous underwater vehicle (AUV) for the next generation. Generally, it is got by optical sensors, and most underwater vehicles are equipped with various types of them. Above all, camera systems are applied as multiple units to the underwater vehicles. And they can construct a stereo camera system. In this paper, some new functions, which provide some type of visual information derived by the stereo vision system, are described. And methods to apply the visual information to the underwater vehicle and their utility are confirmed.
Computation of Ship-to-Ship Interaction Forces by a 3D Potential Flow Panel Method in Finite Water Depth
Authors: Zhou Xueqian , Sutulo Serge , Guedes Soares C.
Published: January 2011

The double-body 3D potential flow code developed earlier for computing hydrodynamic interaction forces and moments acting on the hulls of the ships sailing in close proximity with neighbouring ships or some other obstacles, is extended to the shallow water case. Two methods for accounting for the finite water depth were implemented: use of truncated mirror image series, and distribution of an additional single layer of sources on parts of the seabed beneath the moving hulls. While the first method does only apply to the flat horizontal seabed, the second one can also deal with the arbitrary bathymetry situations. As appropriate choice of the discretization parameters can significantly affect the accuracy and efficiency of the second method, the present contribution focuses on comparative computations aiming at defining reasonable dimensions of the moving panelled area on the sea bottom and maximum admissible size of the bottom panel. As result, conclusions concerning optimal parameters of the additional set of panels are drawn.