bluuebunny/crossref_metadata_2025 huggingface dataset:
Field Observations of Wave-Induced Set-Up on the French Aquitanian Coast
Authors: Heidarzadeh Mohammad , Bonneton Philippe , Bonneton Natalie , Tissier Marion
Published: February 2010

We report and analyze extreme wave-induced set-up heights obtained during a large international field experiment on the Atlantic coast of France. The field experiment associated with a large storm with the maximum offshore wave height of more than 12 m, enabled us to record extreme set-up heights up to 2 m. Such extreme data which are necessary for developing further numerical and analytical studies in this field, were lacking in the literature. Our data agrees reasonably well with existing set-up data reported from other coasts in the world. A good correlation was observed between set-up and offshore wave height. Similar to other coasts, the setup-offshore wave height relationship was linear up to a value of about 1 m. Nonlinear behaviour was observed for higher setup values. This study will help to further improve and validate the existing analytical and numerical solutions.
Mathematical Models for Model-Based Control in Offshore Pipelay Operations
Authors: Jensen Gullik A. , Fossen Thor I.
Published: February 2010

This paper considers mathematical models for model-based controller design in offshore pipelay operations. Three classes of models for control design are discussed, real-world models suitable for controller design verification, controller and observer models which are used on-line in the control system implementation. The control application place requirements on the model with respect to the computational time, dynamic behavior, stability and accuracy. Models such as the beam model, two catenary models, as well as general finite element (FE) models obtained from computer programs were not able to meet all of the requirements, and two recent dynamic models designed for control are presented, which bridge the gap between the simple analytical and more complex FE models. For completeness, modeling of the pipelay vessel, stinger and roller interaction, soil and seabed interaction and environmental loads are discussed.
Evaluation of Linear and Nonlinear Hydrodynamic Coefficients of Underwater Vehicles Using CFD
Authors: Ray Amit , Singh S. N. , Seshadri V.
Published: February 2010

Hydrodynamic coefficients (HDCs) in the equations of motion for trajectory simulation of any underwater vehicle are inherent characteristics of the body geometry. At the concept design stage of underwater vehicles, there is a requirement for affordable and efficient use of general-purpose CFD tools to get a first estimate of the HDCs, with greater accuracy than empirical methods, but at lesser cost and time than model testing. This paper reports the prediction of values of straight-line and rotary HDCs for a submerged axisymmetric body of revolution using a general-purpose RANSE solver and with modest, readily available computational facilities. Various alternatives for grid generation and grid size have been compared and a solution strategy evolved to optimize requirements of accuracy, time and computational resources. Linear and nonlinear HDCs for straight-line and rotary motions were obtained by curve-fitting of the forces and moments plotted against angle of attack and angular velocity. To compute rotary HDCs, an approach was evolved to define a circular domain and effectively simulate the motion of a model in Rotating Arm captive model tests. Results were compared with experimental results from Planar Motion Mechanism tests of the same body. The trends in variation of forces and moments are captured well by computations. Accuracy obtained for yaw moment HDCs is comparable to the uncertainty levels from model tests. It is shown that CFD techniques offer flexibility for computing nonlinear coefficients as well, by simulating combinations of linear and angular velocities.
A Joint Numerical and Experimental Study of a Surging Point Absorbing Wave Energy Converter (WRASPA)
Authors: Bhinder Majid A. , Mingham Clive G. , Causon Derek M. , Rahmati Mohammad T. , Aggidis George A. , Chaplin Robert V.
Published: February 2010

This paper presents the findings from using several commercial computational fluid dynamics codes in a joint numerical and experimental project to simulate WRASPA, a new wave energy converter (WEC) device. A series of fully 3D non-linear simulations of WRASPA are presented. Three commercial codes STAR-CCM, CFX and FLOW-3D are considered for simulating the WRASPA device and final results are presented based on the use of Flow-3D. Results are validated by comparison to experimental data obtained from small scale tank tests undertaken at Lancaster University (LU). The primary aim of the project is to use numerical simulation to optimize the collector geometry for power production over a range of likely wave climates. A secondary aim is to evaluate the ability of commercial codes to simulate rigid body motion in linear and non-linear wave climates in order to choose the optimal code with respect to compute speed and ease of problem setup. Issues relating to the ability of a code in terms of numerical dissipation of waves, wave absorption, wave breaking, grid generation and moving bodies will all be discussed. The findings of this paper serve as a basis for an informed choice of commercial package for such simulations. However the capability of these commercial codes is increasing with every new release.
Wave Radiation and Shear Instability in Rotating Stratified Flow
Authors: Pinilla Camilo E. , Chu Vincent H.
Published: February 2010

The paper shows how the shear instability is suppressed by the wave radiation, and how a window of instability exists in a rotating stratified flow. Direct numerical simulations (DNS) are conducted of the nonlinear transition from the linear instability in a model of ocean current in the rotating Earth. The base flow is a jet of the hyperbolic-secant velocity profile. The depth varies across the jet initially following a hyperbolic-tangent profile for geostrophic balance between Coriolis force and the lateral pressure gradient. The geostrophic balance is maintained throughout the simulation as the shear flow is modified by the nonlinear development. An accurate, and robust, computational scheme is used to solve the governing equations for the DNS. Time integration of the equations has been carried out using the fourth-order Runge-Kutta scheme. A third-order upwind bias finite difference approximation known as QUICK (Quadratic Upstream Interpolation of Convective Kinetics) is employed for the spatial discretization. The numerical oscillations are controlled using a flux limiter for Total Variation Diminishing (TVD). The concept of radiation damping is introduced for interpretation of the simulation results. In the DNS of the shear instability in the rotating shear flow, the radiation damping is observed to approach a minimum at a critical Rossby number Ro = 4. A corresponding maximum instability occurs at the critical Rossby number. A significant fraction of available energy to the shear instability is lost due to wave radiation from the shear flow. The maximum instability, the wave radiation and the nonlinear transition from the instability are the dynamic events that leads to heat and mass exchanges and the formation of rings and eddies across the ocean currents.
Morphodynamic Simulation at the South Branch of Yangtze Estuary
Authors: Zhou Xiaoyan , Zanke Ulrich , Yan Yixin , Zheng Jinhai
Published: February 2010

In this paper a numerical morphodynamic model TIMOR3 has been introduced and applied to simulate the morphological response to the water and sediment changes in the Yangtze River Estuary. TIMOR3, coupled with Hydrodynamic Model and Wave Model, is used to simulate a long-term and huge area of the morphological changes in the Yangtze River Estuary. A detailed investigation was made to the south branch where the Deepwater Channel Navigation Project is under construction. The effect of the project in different phases with different water depth has been simulated and analyzed.
Analysis of the Roll Decay Motion for a Patrol Boat by URANS Simulations
Authors: Broglia Riccardo , Muscari Roberto , Di Mascio Andrea
Published: February 2010

The simulations of the flow around a vessel of the Italian Navy in free roll decay have been carried out by the numerical solution of the Reynolds Averaged Navier-Stokes equations. The focus is on the analysis of the roll motion coefficients (damping and period of oscillations) at different Froude and Reynolds numbers. To this aim, numerical simulations were carried out at three different speeds, with corresponding Froude numbers equal to 0.160, 0.227 and 0.337, and Reynolds numbers ranging from 4.073 106 to 1.300 107 at model scale. Computations were carried out by means of an in-house unsteady RANS solver; the scheme is based on a finite volume discretization, and it is globally second order accurate. The free surface is handled by means of a suitable single phase level set algorithm; moreover, Chimera overlapping grid capabilities have been implemented in the code, which has been also efficiently parallelized. An analysis of the roll motion, longitudinal and lateral forces and roll moment is carried out for the different speeds considered. A preliminarily grid convergence analysis is also performed.
Design Challenges and Experience With Controlled Lateral Buckle Initiation Methods
Authors: Sinclair Forbes , Carr Malcolm , Bruton David , Farrant Tim
Published: February 2010

Subsea pipelines are increasingly being required to operate at higher temperatures and pressures. The natural tendency of such a pipeline is to relieve the resulting high axial stress in the pipe-wall by buckling. Uncontrolled buckling can have serious consequences for the integrity of a pipeline. An elegant and cost-effective design solution to this problem is to work with rather than against the pipeline by controlling the formation of lateral buckles along the pipeline. Controlled lateral buckling is a relatively new design option which has matured as more projects have adopted the approach. As with all new design techniques, knowledge and understanding has improved and evolved with design application, installation and operational experience. Methods used to control the formation of lateral buckles include snake lay, vertical upsets, localised weight reduction and local seabed imperfections. Selecting the right buckle initiation method for a flowline can be a complex issue which is influenced by the flowline type, operating conditions, environmental conditions and pipe-soil interaction. Detailed lateral buckling design is normally concerned with achieving reliable buckle formation, minimising the peak strains in the flowline (local buckling) and controlling through life girth weld fatigue. However, as lateral buckling design has progressed, other design challenges have become apparent, which must be considered during design. This paper discusses commonly used buckle initiation methods and focuses on the key design challenges associated with lateral buckling, in the light of feedback from operational experience of recently installed flowlines. Many of the design challenges are common to all initiation methods, such as pipe-soil interaction or girth weld fatigue. However, there are a number of issues which can be specific to a particular buckle control method or pipeline project, these can include sour service operating conditions or complex flow assurance implications. The paper highlights key information required for lateral buckling design and outlines typical test programmes performed to support the design process. Crucially, many of the flowline design issues identified in this paper have been identified as a result of lessons learnt from operational experience. This affirms the importance of rigorous visual inspection and survey to monitor the performance of flowlines during the first months and years after start-up.
Design Synthesis of a Wave Energy Converter
Authors: Beatty S. J. , Hiles Clayton , Nicoll Ryan S. , Adamson James E. , Buckham Bradley J.
Published: February 2010

A demonstration ocean wave energy project is planned for Hesquiaht Sound, British Columbia, Canada in 2010. This project is led by SyncWave Systems and involves the University of Victoria, Dynamic Systems Analysis Ltd. and Marinus Power. The design process for this demonstration wave energy converter (WEC) including site selection, linear dynamics, control system scheduling and non-linear dynamics modelling is presented. The WEC is a heaving point absorber that extracts energy through the relative motion between two axisymmetric bodies and utilizes an internally housed mechanical system with adjustable inertia characteristics for frequency response tuning. Site selection for the device was completed by using an established wave propagation model to translate off-shore sea conditions calculated from WAVEWATCHIII (WW3) into near-shore conditions. By analysis of the predicted near-shore conditions a suitable location with a frequently energetic sea state was chosen. The design process of the WEC consists of a linearized dynamics model to optimize the controller and a nonlinear dynamics model to analyze the mooring and hull components. The resulting unit effectively captures energy from the prevailing sea-states while ensuring adequate survival capability.
Climatologically Modeled Wave Field Analyses in the Western South Atlantic
Authors: Ribeiro Eric Oliveira , Andrioni Marcelo , Martins Renato Parkinson , Grossmann Matheson Guisela , Alves Jose´ Henrique , Nunes Luis Manoel Paiva
Published: February 2010

Wave height, period and direction are basic parameters for designing off-shore structures. Besides this direct application, knowledge of the regional characteristics of a wave field can also help in the selection of optimal regions for wave power energy plant design and installation. A wave climatology based on data generated by a WAVEWATCH III model simulation (NOAA WW3) for the Brazilian coast was analyzed and validated against statistical values derived from opportunity vessel measurements. The hindcast covered the period from January 1997 to December 2005 in a region between 5°N – 40°S and 10°W – 65°W. The grid used was uniform with a 0.25° spacial resolution. The boundary conditions were obtained from NOAA WW3 operational model and the atmospheric forcing from NOAA GFS model. The model results were calibrated with field data and detailed information about the simulation can be obtained in Alves et al. (2008) and Alves et al. (in press). Monthly averages of significant height, period and wavelength were calculated using 3 hour time resolution fields. Since a simple mean direction has small physical representativeness, the predominant direction (moda) and associated persistency were obtained from the data. The results were then compared with values from the U.S. Navy Marine Climate Atlas of the World. This Atlas has four points located within the selected model grid region. These points showed good agreement with wave period, height and direction persistency based on the WW3 simulation results. The wave climatology showed that the predominant wave direction from April to July was from S and SE in southern Brazil, associated with swells related to cold fronts. The S and SE swells were also responsible for the largest mean wave height (2.1 m) observed in the climatology. Another result that was validated with the literature was the E and NE predominant wave direction during the austral summer. This phenomenon is associated with winds originated from the South Atlantic High Pressure Center, which is a semi permanent high pressure center near Trindade Island. The wave climate in northern Brazil showed a predominant direction from the N during January to March, associated with the northern hemisphere winter storms. During the remaining months of the year, the predominant wave direction is E and NE associated with trade winds. The model results are still in a processing phase to produce extreme values, which will be more useful for coastal and off-shore structure design.
Directional Extreme Current Profiles Based on Complex Empirical Orthogonal Functions (C-EOF) for Offshore Design
Authors: Lima Jose Antonio Moreira , Ribeiro Eric Oliveira , Ceccopieri Wellington , Grossmann Matheson Guisela
Published: February 2010

This paper presents a methodology to estimate deep water design current profiles using Complex Empirical Orthogonal Function (C-EOF) and a structural reliability response based model. The advantage of C-EOF is the capability of directly obtaining directional extreme current profiles. It is estimated that most of the variability of the southeast Brazil current system can be explained by the first two EOF modes. The first mode associated with the southwestward Brazil Current (BC) and the second mode with the northeastward Intermediate Western Boundary Current (IWBC). Thus, only two series of C-EOF amplitudes can be used in the response based technique to estimate the 100-y extreme current values. The methodology can also be used with more EOF modes if required to properly represent the current data. The probabilistic cumulative functions are based on extreme value distributions such as Gumbel or Weibull, and Lognormal for conditional distributions. The evaluation of estimated distribution parameters are carried out using Kolmogorov-Smirnov goodness-of-fit hypothesis tests and correlation coefficients for each directional sector.
Global Hydroelastic Analysis of Pontoon-Type VLFS
Authors: Jiao L. L. , Greco M. , Faltinsen O. M.
Published: February 2010

A two-dimensional composite strategy given by Greco et al. [1] is applied to couple a linear global solution with a nonlinear local analysis. Globally a linear hydroelastic analysis is performed by an accurate Beam-On-Elastic-Foundation (BOEF) method. A parameter analysis of hydroelastic response of the structure is also carried out. Locally, a two-dimensional fully-nonlinear numerical wave tank (NWT) in combination with a Boundary Element Method (BEM) is developed to estimate the interaction between regular waves and the structure restrained from rigid and elastic motions. The effect of air cushion is considered. Present results are compared with experimental data and other numerical solutions.
Robust Tracking Control of Autonomous Underwater Vehicles in the Presence of Disturbance Inputs
Authors: Singh S. , Sanyal A. , Smith R. , Nordkvist N. , Chyba M.
Published: February 2010

An autonomous underwater vehicle (AUV) is expected to operate in an ocean in the presence of poorly known disturbance forces and moments. The uncertainties of the environment makes it difficult to apply open-loop control scheme for the motion planning of the vehicle. The objective of this paper is to develop a robust feedback trajectory tracking control scheme for an AUV that can track a prescribed trajectory amidst such disturbances. We solve a general problem of feedback trajectory tracking of an AUV in SE (3). The feedback control scheme is derived using Lyapunov-type analysis. The results obtained from numerical simulations confirm the asymptotic tracking properties of the feedback control law. We apply the feedback control scheme to different mission scenarios, with the disturbances being initial errors in the state of the AUV.
The Evolution of Free Standing Risers
Authors: Tellier Elizabeth , Thethi Ricky
Published: February 2010

Deepwater riser selection is a complex evaluation of technical and commercial project drivers. The free standing hybrid riser (FSHR) has evolved in the last 10 years through major use in West Africa and is now gaining serious consideration in other deepwater provinces. The key benefit of the free standing riser is that the steel riser vertical section is offset from the vessel using flexible jumpers, thereby decoupling the riser from vessel dynamic motion. Early FSHR configuration took the hybrid bundle tower form. The very first free standing riser system, installed in 1988, consisted of the Placid hybrid bundle in the Gulf of Mexico. In the late nineties, a hybrid bundle tower was chosen for the Girassol development in West Africa. Since then, the industry has sanctioned numerous developments using multiple single line freestanding risers. Optimization of the FSHR is continuing with new concepts such as the Grouped SLOR developed to offer the combined benefits of both the bundle and single line multiple arrangements. This paper will describe how the FSHR configuration has evolved to meet increasing industry demands over the past 10 years and will discuss the future of this type of riser system. Increasing applications in ultra deepwater regions, hurricane prone locations and tiebacks to existing payload limited production vessels will be discussed with riser system architecture described including interfaces with the vessel and seabed.
Bending Stiffener Design Through Structural Optimization
Authors: Tanaka Rafael Loureiro , da Silveira Lauro Massao Yamada , Novaes Joa˜o Paulo Zi´lio , de Barros Eduardo Esterqui , Martins Clo´vis de Arruda
Published: February 2010

Bending stiffeners are very important ancillary equipments of umbilicals or flexible risers, since they protect the lines from overbending. Their design however is a complex task, since many load cases must be taken into account; the structure itself has a section that is variable with curvilinear coordinate. To aid the designer in this task, optimization algorithms can be used to automate the search for the best design. In this work an optimization algorithm is applied to the design of the bending stiffener. First, a bending stiffener model is created, which is capable of simulating different load case conditions and provide, as output, results of interest such as maximum curvature, deformation along the stiffener, shear forces and so on. Then, a bending stiffener design procedure is written as an optimization problem and, for that, objective function, restrictions and design variables defined. Study cases were performed, comparing a regular design with its optimized counterpart, under varying conditions.
Experimental Investigation of Fracture in Wrinkled Pipelines Under Monotonic Axial and Bending Deformation
Authors: Ahmed Arman , Aydin Mehmet , Cheng J. J. Roger , Zhou Joe
Published: February 2010

Buried pipelines, used by petrochemical industries in North America for transporting oil and derivatives, are often subjected to large deformations resulting from geoenvironmental factors such as: geotechnical movements, thermal strains, and internal fluid pressure. Exceeding the critical deformation limit of these pipes initiates wrinkles and further increase may result in fracture; thus jeopardizing the safe operation of a field pipeline. A recent field fracture and failed laboratory specimens under monotonic load history addresses the necessity of conducting a full-scale test program for the better understanding of the complete post-wrinkling behaviour and failure modes of wrinkled pipes under similar loading condition inducing axial and bending deformation. Six tests with two sizes of pipe (NPS16 and NPS20), representative of those used in pipelines for transmission of hydrocarbons, were performed. Only one of the tests were found to yield the desired failure mode and hence chosen to present and discuss in this paper in detail to understand the tearing mode of failure. However, test results in general had shown that both X60-grade and X65-grade steel pipelines generally exhibited a ductile behavior after wrinkling. Eventually, these line pipes failed in a deformation mode due to excessive cross-sectional deformation and several occurrences of rupture at the wrinkle face of the bent pipe were observed.
Permafrost Thawing-Pipeline Interaction Advanced Finite Element Model
Authors: Xu Jianfeng , Abdalla Basel , Eltaher Ayman , Jukes Paul
Published: February 2010

The increasing energy demand has promoted the interest in exploration and field development in the Arctic waters, which holds one quarter of the world’s petroleum reserves. The harsh conditions and fragile environment in the arctic region introduce many challenges to a sustainable development of these resources. One of the key challenges is the engineering consideration of warm pipelines installed in permafrost areas; found mainly in shallow waters and shore crossings. Evaluations have to be made during the pipeline design to avoid significant thaw settlement and large-scale permafrost degrading. In this paper, a three-dimensional (3D) finite element (FE) model was developed to study the interaction between buried pipelines transporting warm hydrocarbons and the surrounding permafrost. This interaction is a combination of several mechanisms: heat transfer from the pipeline, results in permafrost thawing and formation of thaw bulb around the pipeline. Consequently, the thaw settlement of soil beneath the pipeline base results in bending strains in the pipe wall. For safe operations, the pipe should be designed so that the induced strains do not exceed the ultimate limit state conditions. The developed model helps in accurate prediction of pipe strains by using finite element continuum modeling method as opposed to the more commonly used discrete (springs) modeling and hand calculations. It also assesses the real size of the thaw bulb and the corresponding settlement at any time, thus preventing an over-conservative design.
Characterization of Measured VIV for Free Spanning Pipelines
Authors: Aglen Ida M. , Larsen Carl M. , Nielsen Finn Gunnar
Published: February 2010

As the search for oil and gas takes place on increasing water depths, the traditional production systems based on fixed or floating platforms becomes increasingly costly. A good alternative to the traditional production systems are subsea to shore solutions, where pipelines transport the product to a land terminal for processing. One of the main challenges of documenting pipeline integrity in subsea to shore solutions is related to fatigue induced by vortex induced vibrations (VIV). Rough and uneven seabed introduce free spans that can be short or long, have small or large clearance and can have a large variety of boundary conditions at the shoulders. Hence, there is a need for methods that can give reliable estimate for fatigue damage under all realistic conditions. This paper investigates the measured VIV for a free spanning pipeline model. The model has L/D ratios from 72 to 350 and includes both single and multi-spans. It is exposed to uniform current and is free to vibrate in both cross-flow (CF) and in-line (IL) direction. Bending strains are measured in CF and IL direction at ten locations along the pipe. The observed cross-sectional trajectories are analyzed, with particular focus on the complex interaction between CF and IL VIV, and the significance of higher order response components. The purpose of this investigation is to understand the behaviour of the free spanning pipelines with respect to response amplitudes, frequency and modal composition, and also to identify characteristic cross section trajectories for further investigation. This work is a continuation of the earlier published results by Nielsen et al. [1] and Soreide et al. [2].
Experimental Investigation of Vortex-Induced Vibration Responses of Tension Riser Transporting Fluid
Authors: Zhang Yongbo , Meng Fanshun , Guo Haiyan
Published: February 2010

This paper presents the test results of a vertically tensioned riser model under vortex-induced vibrations. The influence of internal flowing fluid and top tensions on the riser behavior is investigated. Twelve strain gauges were mounted on the riser and both the in-line and cross-flow responses at locations were measured. The frequency spectrum and amplitude response were derived from the strain date. The influences of internal flow and top tensions on two kinds of model risers are analyzed and some conclusions are drawn.
Effect of Relative Density on the Wave-Induced Liquefaction in Seabed Around a Breakwater
Authors: Tomi Yuichiro , Zen Kouki , Chen Guangqi , Kasama Kiyonobu , Yahiro Yuichi
Published: February 2010

The liquefaction of seabed induced by ocean waves is considered to be one of the influential phenomena related to damages of coastal marine structures such as the floating of pipelines, the settlement of concrete blocks and the reduction of pile foundation resistance, etc, since the liquefied seabed loses its shear strength and then easily and drastically deforms. A model flume was newly developed to simulate the wave-induced liquefaction in seabed around a breakwater with a reduced model scale against the caisson type breakwater widely used in Japan. The dimension of developed flume was the length of 6.0m, the width of 0.4m and the depth of 0.9m. As for geotechnical parameters affecting the wave-induced liquefaction of seabed around the model breakwater, the effect of seabed density on liquefaction was highlighted in this paper in terms of the generation of pore water pressure in seabed and the settlement of seabed surface. The experiment was carried out under the following conditions; the wave period was 1.0s, the incident wave height was 55mm, the depth of water was 170mm, the thickness of permeable layer was 350mm and the relative density was between 20% and 60%. In order to satisfy similarity law in 1g gravitational field, the polymer fluid was used to decrease the permeability of model seabed. As the result from this study, the following conclusions were obtained; 1) When water was used as a fluid, the liquefaction due to the residual excess pore water pressure happened in the sand bed with the relative density of 23%. However, the liquefaction did not happened in the sand bed with the relative density more than 30%, 2) When the polymer fluid is used for reducing the permeability of model seabed, the generation of pore water pressure ratio becomes larger and the dissipation time of generated pore pressure becomes longer compared with the case using water, 3) When the relative density of seabed was between 20% and 40%, the liquefaction induced by the residual excess pore water pressure was observed in the deep area of model seabed while the shear failure of seabed was observed in the shallow area of model seabed, 4) When the relative density was between 50% and 60%, the liquefaction due to the residual excess pore water pressure was not observed in the present experimental conditions.
Wave-Vessel Interactions in Beam Seas
Authors: Spentza Eirini , Swan Chris
Published: February 2010

This paper concerns the nonlinear interaction of waves with a floating vessel. A detailed experimental study has been undertaken in a 3-D wave basin, using a scaled model tanker subject to a variety of incident wave conditions. The vessel, which is free to move in heave, pitch and roll, has a draft of 14m (at full-scale) and is subject to a range of incident wave periods propagating at right angles to the side shell of the vessel. Measurements undertaken with and without the vessel in place allow the diffracted-radiated wave field to be identified. The laboratory data indicate that the diffracted-radiated wave pattern varies significantly with the incident wave period. Detailed analysis of the experimental results has identified a hitherto unexpected second-order freely propagating wave harmonic generated due to the presence of the vessel. Given its frequency content and its relatively slow speed of propagation, this harmonic leads to a significant steepening of the wave field around the vessel and therefore has an important role to play in terms of the occurrence of wave slamming. Physical insights are provided concerning the latter and the practical implications of the overall wave-structure interactions are considered.
Specifications for a Subsurface Ice Intelligence System
Authors: Eik Kenneth , Lo̸set Sveinung
Published: February 2010

In connection with offshore activities in waters exposed to sea ice and/or icebergs, ice management (IM) systems need to be applied. An ice intelligence system is one of several required elements in an IM system. This paper presents possible solutions for Subsurface Ice Intelligence Systems (SIIS). Capabilities of technology for sonars, unmanned underwater vehicles, and communication nodes are highlighted and need for further development is commented.
A Review of Hydrodynamic Effects on Bottom-Fixed Offshore Wind Turbines
Authors: Merz Karl O. , Moe Geir , Gudmestad Ove T.
Published: February 2010

Recent and historical literature regarding hydrodynamics has been reviewed, with offshore wind turbine support structures in mind. Under conditions of separated flow, several relevant phenomena have been noted which are not covered by the commonly-used Morison equation: 1. damping of structural vibration or slow-drift motion; 2. the interaction of structural vibration and vortex shedding; 3. loads near the free-surface; and, 4. burst motions, caused by impulse-like loading from steep waves. References have been given to books and articles that describe the phenomena in more detail. A form of the Morison equation is proposed which has separate empirical coefficients for each of the velocity and acceleration terms. The coefficients can be determined from existing test data with use of least-squares error minimization. A simplified form of the equation provides a means to obtain conservative bias on both the applied load (bias towards a high drag coefficient) and damping (bias towards a low drag coefficient). Further investigation into free-surface and burst motion (ringing) phenomena is recommended, considering a slender wind turbine monotower in 20 to 50 m water depth.
Simulations of Ductile Tearing at Large Strains of Biaxially Loaded Pipes
Authors: Dybwad Jacob , To¨rnqvist Rikard , O̸stby Erling , Thaulow Christian
Published: February 2010

The purpose of the present paper is to present results from analyses of ductile tearing of biaxially loaded pipes subjected to large scale yielding. The paper deals with three dimensional finite element modelling of pipes with a circumferentially orientated surface crack, where the analyses aim to reproduce the crack propagation behaviour of six full scale bend tests of x-65 seamless pipes with different levels of internal overpressure. The tests were performed as a part of the joint industry project Fracture Control - Offshore Pipelines. Ductile tearing is taken into account by using the Gurson-Tvergaard-Needleman formulation, where calibration of the material model parameters is done by reproducing the fracture toughness test of a SENT-specimen of the same material with finite element modelling. The following simulations of the pipes show a good correspondence with the full scale test results, where both the global response and the ductile tearing from the crack are captured. One important result of the study is that the Gurson-Tvergaard-Needleman parameters that were calibrated against the SENT-specimen could successfully be used for the ductile tearing simulation of the full scale pipes.
PDEG-B Overall Design and Installation Challenges
Authors: Tanscheit Peter , Sriskandarajah T. , Xavier Marcelo , Solano Rafael Familiar , Braga Vini´cius Rodrigues
Published: February 2010

PDEG-B was an EPIC project including three gas and three rigid oil export pipelines for the Marlim, Roncador and Barracuda fields in Campos Basin, Rio de Janeiro, Brazil. A total pipeline length of 165km and 14 tie-in structures located at the ends and along the pipelines were installed as part of the scope. Project comprised 10.75″ and 12.75″ API 5L X65 pipelines installed in water depths ranging from 100m to 1400m using the reeling method. Both Subsea7 reel vessels Seven Navica and Seven Oceans laid pipe in two independent installation campaigns. Installation started mid 2006 and the last pipeline section was laid down late 2007/early 2008. All pipelines were fabricated at Subsea7 spool base located in UBU, Espi´rito Santo, Brazil, and more than 15 trips of the pipelay vessels were necessary to complete the installation. During the engineering phase, potential for upheaval and lateral buckling was identified on the longer oil lines and potential for pipeline walking on the shorter oil line, resulting in the development of specific design mitigation measures. Furthermore, thermal expansion and free span analysis were also combined and used to assess the behavior of the free spans during the operation phase, in order to define the method and scope for free span rectification. Three of the longer lines extended from shallow to deep waters including several wall thickness transitions along their total length. The external coating of the pipelines comprised an anti-corrosion protection layer and a further thermal insulation layer was required for the oil lines. Different materials were used in used in conjunction with extensive PQT program for qualification with respect to the technical requirements and installation methods. Challenges in pipeline fabrication included planning to produce proper line pipe welding misalignment at girth welds and qualification of welding procedures for sour service. Large pipeline end and in-line subsea structures were specified for this project. PLEM’s in excess of 40Te launched as 1st end directly connected to the pipeline, and ILT’s weighing up to 33Te were deployed from the Seven Navica and Seven Oceans pipelay vessels, requiring reliable and field proven standards of engineering. The main objective of this paper is to provide relevant overall high level and general information on the topics mentioned above, based on the experience acquired during the project.
Progressive Wave Simulation Using Stabilized Edge-Based Finite Element Methods
Authors: Elias Renato N. , Gonc¸alves Milton A. , Coutinho Alvaro L. G. A. , Esperanc¸a Paulo T. T. , Martins Marcos A. D. , Ferreira Marcos D. A. S.
Published: February 2010

Flows involving waves and free-surfaces occur in several problems in hydrodynamics, such as sloshing in tanks, waves breaking in ships and motions of offshore platforms. The computation of such wave problems is challenging since the water/air interface (or free-surface) commonly present merging, fragmentation and cusps, leading to the use of interface capturing Arbitrary Lagrangian-Eulerian (ALE) approaches. In such methods the interface between the two fluids is captured by the use of a marking function which is transported in a flow field. In this work we simulate these problems with a 3D incompressible SUPG/PSPG parallel edge-based finite element flow solver associated to the Volume-of-Fluid (VOF) method [1]. The hyperbolic equation for the transport of the marking function is also solved by a fully implicit parallel edge-based SUPG finite element formulation. Global mass conservation is enforced adding or removing mass proportionally to the absolute value of the normal velocity at the interface. The performance and accuracy of the proposed solution method is tested in the simulation of progressive waves and the interaction of a fixed cylinder with a progressive wave.
Prediction on Hydrodynamic Performances of Propeller by OpenFOAM
Authors: Li Wei , Yang Chi , Yu Lijun , Wang Guoqiang , You Yunxiang
Published: February 2010

In this paper the flow around a propeller is simulated by open source CFD tool-OpenFOAM. In order to validate the availability of OpenFOAM code in the field of propeller theory, the steady hydrodynamic performances of DTMB P4119 propeller is predicted. The discrete schemes are second order upwind. The grids are generated by GAMBIT software. The dependence of grid number and adaptability of turbulent model are studied. Compared with the experimental data, it shows that the OpenFOAM code can be used effectively to predict the hydrodynamic performances of the propeller in practice. It can be developed further to study more complex flow phenomena such as cavity flow and other unconventional propulsors.
Hydraulic Characteristics of Artificial Reefs Using the Oyster Shell
Authors: Sohn ByungKyu , Lee Jeong-Woo , Won Seung-Hwan
Published: February 2010

For settlement and growth of shellfish and seaweed, artificial reefs have been deployed in the Korea waters for last thirty years. Nowadays, according to whitening phenomenon, the construction of seaweed beds becomes important; therefore, the role of artificial reefs is more emphasized. In addition, the recycle of shellfish wasters become an environmental issue; hence, among the wasters, oyster shells have been used as parts of a new artificial reef, namely OS-type artificial reefs. However, it is required to investigate their stability and functionality before deploying the reefs in fields. This study presents the stability (sliding and overturning) tests of the artificial reefs using oyster shell. For the tests, hydraulic experiments have been done in a 2-D flume. From the experiments, it is shown that how stability parameters such as surf similarity parameter, water particle velocity, wave pressure, etc. affect the sliding and overturning. These results give ones guideline for installation of artificial reefs in fields.
The Application of Strain-Based Design to Pipelines and the Requirements on Pipe Materials
Authors: Chen Hongyuan , Ji Lingkang , Xie Wenjiang , Xiong Qingren , Li Weiwei
Published: February 2010

With the sharply rising demand of oil and gas, the pipeline industry has been experiencing a rapid development in recent years. Pipelines in the areas of ground movement from slope instability, seismic sideslip, loess collapse, mining subsidence, frost heave and thaw settlement in discontinuous permafrost can experience displacement-controlled plastic strain. The current paper describes the application of strain-based design of pipelines and introduces relevant codes, standards, and criteria of other countries. Some major issues in strain-based design such as geologic conditions, strain limits, mechanical performance, etc., are mentioned. The prospect of strain-based design of pipelines is discussed with reference to the geologic conditions and the state of the pipeline industry. Finally the requirements on parameters of line pipe materials, including yield stress, yield and tensile strength ratio, stress ratio, weld mismatch, anisotropy etc., and their influence on strain-based design are discussed.
Methods to Reduce Lateral Noise Propagation From Seismic Exploration Vessels
Authors: Ayers Ray R. , Jones Warren T. , Hannay David
Published: February 2010

This paper covers the development of methods and equipment for reducing lateral noise propagation from seismic exploration vessels operating in the Alaskan Beaufort and Chukchi Seas. Oil exploration activities are currently taking place or are planned, and there is a need for creating methods and equipment to reduce lateral noise propagation from seismic exploration. This project is supported by the U.S. Minerals Management Service, which has the responsibility and authority to ensure that oil and gas exploration and production activities are conducted in a safe and environmentally sound manner. This research effort includes a literature synthesis and review to identify existing seismic exploration technologies (airguns) and involves developing promising methods and technologies that could potentially reduce the lateral propagation of sound from those airguns. Three principal areas have been explored: (a) Attenuating lateral noise with air bubble curtains, like has been shown in the literature, or with some special bubble curtain material, acting as a more solid curtain-like barrier, (b) Making arrays more directional, and thus narrow the cone of sound, and (c) Changing the structure of the airguns to reduce high frequency sound (noise) while maintaining the strong source signal needed for exploration purposes. This paper (a) describes our preliminary findings in each of the above areas and (b) shows that deploying bubble curtains outboard of the seismic arrays towed by the same exploration vessel can potentially produce the sought-after noise reduction, while the minimizing impact on the traditional seismic exploration operations.
A Fast Convergent Modal-Expansion of the Wave Potential With Application to the Hydrodynamic and Hydroelastic Analysis of Floating Bodies in General Bathymetry
Authors: Belibassakis K. A. , Athanassoulis G. A.
Published: February 2010

A non-linear coupled-mode system of horizontal equations has been derived with the aid of Luke’s (1967) variational principle, modelling the evolution of nonlinear water waves in intermediate depth and over a general bathymetry Athanassoulis & Belibassakis (2002, 2008). Following previous work by the authors in the case of linearised water waves (Athanassoulis & Belibassakis 1999), the vertical structure of the wave field is exactly represented by means of a local-mode series expansion of the wave potential. This series contains the usual propagating and evanescent modes, plus two additional modes, the free-surface mode and the sloping-bottom mode, enabling to consistently treat the non-vertical end-conditions at the free-surface and the bottom boundaries. The coupled-mode system fully accounts for the effects of non-linearity and dispersion. The main feature of this approach that a small number of modes (of the order of 5–6) are enough for the precise numerical solution, provided that the two new modes (the free-surface and the sloping-bottom ones) are included in the local-mode series. The consistent coupled-mode system has been applied to numerical investigation of families of steady nonlinear travelling wave solutions in constant depth (Athanassoulis & Belibassakis 2007) showing good agreement with known solutions both in the Stokes and the cnoidal wave regimes. In the present work we focus on the hydroelastic analysis of floating bodies lying over variable bathymetry regions, with application to the non-linear scattering of water waves by large floating structures (of VLFS type or ice sheets) characterised by variable thickness (draft), flexural rigidity and mass distributions, modelled as thin plates of variable thickness, extending previous approaches (see, e.g., Porter & Porter 2004, Belibassakis & Athanassoulis 2005, 2006, Bennets et al 2007). Numerical examples are presented, showing that useful results can be obtained for the analysis of large floating elastic bodies or structures very efficiently by keeping only a few terms in the expansion. Ideas for extending our approach to 3D are also discussed.
Numerical Simulation of Diffusion of CO2 Released by Thirty Ships in Mesoscale Deep Ocean
Authors: Sato Toru , Iida Taiki , Jeong Se-min , Hirabayashi Shinichiro
Published: February 2010

Among possible carbon capture and storage methods to mitigate the global warming, the direct injection of CO2 into the deep ocean by the moving ship method, is considered to be a feasible way and expected to minimize its environmental impacts on marine organisms in the vicinity of the injection points. In this study, a simple but effective numerical model for the given practical scenario of very large system was developed with adopting moving and nesting grid technique and low-wavenumber forcing technique. The calculated results show that the maximum change of additional PCO2 is lower than a non-observed effect concentration, +5,000 μatm, in the both small and mesoscale domains. This indicates that the scenario of 30 ships with different length of injection pipes injecting total CO2 of 50 million t/yr and moving in the 110 × 330 km operation area is efficient and effective. The developed techniques demonstrated its efficiencies and applicability to give an outline for the optimization of the CO2 ocean sequestration system, by which biological impacts should be minimized and insignificant.