bluuebunny/crossref_metadata_2025 huggingface dataset:
Stress Development Inside Large Diameter Pipe Piles Using a Soil Plug Forcing System
Authors: Fischer Jan , Henke Sascha , Höhmann Sebastian
Published: August 2013

It is well known that soil plugging inside tubular steel piles will only appear in rather small diameter piles during impact driving. Therefore, large open ended steel piles, which are often used for the fixation of offshore buildings, such as wind farms, are highly unlikely to develop an internal soil plug. To take advantage of a soil plug, where a significant rise in the piles’ bearing capacity generally appears, a large diameter pipe-pile with an inner steel ring was designed by the third author. The location of the steel ring was determined by the soil formation in situ. To avoid increasing pile driving energy, the internal ring should dip into dense soil conditions only for the last few decimeters of driving. In October 2010, a full scale test was performed in the harbor of Hamburg, using two tubular piles with an outer diameter of 1220 mm. One pile was equipped with an inner steel ring as described above. The second pile was a typical tubular pile without any attached systems. To better compare the results, both piles were driven next to each other. Both piles were equipped with internal total stress and pore water pressure sensors at the pile tip to investigate the radial stress development during and after installation. Acceleration and strain at the pile head were measured to predict the bearing capacity. Using the numerical analysis program CAPWAP (Case Pile Wave Analysis Program) [15], the distribution of shaft and toe friction can be determined additionally. Furthermore, the internal soil movement was surveyed during driving. The results of the measurements showed, that when using an inner steel ring, a significant rise in internal radial stresses and the piles’ bearing capacity occurs.

To better understand the stress development inside and outside the two investigated piles during driving, a numerical back-calculation of the recorded measurements was performed. The results of the full scale and numerical simulations, with a particular focus on the use of an internal steel ring to force the soil to plug behavior in large diameter pipe piles, is presented in the following paper.
Slender Buoy FSHR Vortex Induced Rotations
Authors: Minguez Matthieu , Luppi Ange , Berger Anthony
Published: August 2013

The paper addresses the Flow Induced Response (FIR) of a sub-surface Buoyancy Can (BC) and more particularly the yaw motions possibly due to the current vortices.

2D Computational Fluid Dynamic (CFD) simulations have been performed to analyse the turbulent flow regime over a BC. Thereafter 1 DOF and 2 DOF BC responses i.e. yaw and cross flow responses are analysed.

Focusing on the yaw behaviour, a lock-in has been observed from which yaw rotations develop. The Yaw and Cross Flow (CF) appear to be coupled. As already mentioned in [8], the presence of yaw tends to weaken the CF vortex induced motions (VIM). When the 2 DOF natural periods are somehow closer, the CF response tends to be recovered.
Numerical Analysis of Residual Stresses in Hyperbaric Welding
Authors: Ren Xiaobo , Akselsen Odd M. , Ås Sigmund K. , Nyhus Bård
Published: August 2013

Hyperbaric welding residual stress is one of the main concerns for deep water operation. This study presents the numerical investigation of residual stresses in hyperbaric welding by using WeldsimS code. The pressure range investigated in this study is from 3 to 35 bar, which corresponds to 30 to 350 msw (Meters of Sea Water). Experiments results indicate that the welding procedure might be significantly influenced within the pressure range studied. A 2D axisymmetric model has been considered in this study to simulate circumferential welding of a pipe. Phase transformations and transformation plasticity during the welding procedure have been taken into account. The main aim of the study is to predict the hyperbaric welding residual stresses. The temperature evolution and the micro-structure were also studied. Results show that residual stresses induced by hyperbaric welding are significant within the pressure range investigated, which should be assessed for the sake of structural integrity.
Nonlinear Decomposition of Transmitted Wave Trains Behind Submerged Reef Structures Using “Nonlinear Fourier Transform”: The Nonlinear Spectral Basic Components
Authors: Bruehl Markus , Oumeraci Hocine
Published: August 2013

The nonlinear Fourier transform (NLFT) is introduced as an alternative analysis method for nonlinear waves in shallow water. In physics the NLFT is the application of the inverse scattering transform (IST) for the solution of the Korteweg-deVries (KdV) equation that gouverns the evolution of waves in shallow water. In coastal and ocean engineering the NLFT can be regarded as an extension of the conventional Fourier transform (FT) as it uses nonlinear shallow water waves (cnoidal waves) as basic components for the spectral decomposition and explicitly considers the nonlinear wave-wave interactions during the analysis. A first description of the numerical implementation and its application for the analysis of soliton fission over and behind submerged reefs is given in a former paper [1]. This paper presents a closer view on the interpretation of both types of spectral basic components of the nonlinear decomposition: solitons and nonlinear oscillatory waves.
Occurrence of High Amplitude VIV With Time Sharing
Authors: Swithenbank Susan B. , Larsen Carl Martin
Published: August 2013

When using the theory of Time Sharing of frequencies for predicting damage and fatigue from Vortex-Induced Vibrations (VIV), the percent of time that a riser is vibrating with high amplitude VIV will significantly influence the fatigue rate of a riser. To accurately predict the fatigue of a riser using time sharing or another stochastic prediction method an accurate model is needed for the percent of time spent at these high amplitude vibrations.

Using multiple laboratory tests with both sheared and uniform flow, the percent of time that each section of a pipe vibrated at high amplitude was determined. The larger issue was determining the factors that control the percentage of time at high amplitude vibration. Energy in the system was determined to be the largest influence on the percentage of time. At both low levels and high levels of energy the system had a low percentage of high amplitude VIV. A middle set of energy is the condition that produced high amplitude VIV for the largest percentage of time.
Predicting Wind Loads on Typical Offshore Vessels Using CFD
Authors: Koop Arjen , Rossin Bruno , Vaz Guilherme
Published: August 2013

Within the OO1 and OO2 “Offloading Operability” JIPs, wind-tunnel measurements were carried out to determine the wind loads on a number of vessels, e.g. Membrane (Prismatic) and Moss (Spherical) type LNG Carriers, Shuttle tanker and FPSO. Furthermore, wind velocity measurements were performed in the wake of the FPSO. For all these vessels CFD calculations are carried out using MARIN’s in-house code ReFRESCO. In [9] the sensitivity of the CFD results was investigated for various parameters, such as grid resolution, grid type, flow solver and geometric simplifications. In this paper it is shown that the calculated forces are very dependent on the atmospheric velocity profile used in the calculations. Therefore, different profiles are first compared with the profile measured in the wind tunnel. Then, the development of the profile in the CFD calculations is investigated. Using the appropriate grid resolution and the correct velocity profile, the wind loads on 5 different vessels are calculated for the angles 0 to 180 degrees in steps of 10 degrees. Overall, the calculated force coefficients agree well with the measurements for all vessels. Furthermore, the wind velocity distribution in the wake of the FPSO shows a good agreement with the velocity measurements. The location and shape of the wake are predicted accurately and the calculated velocities show reasonable agreement with the measured velocity distribution. From the results presented in this paper we conclude that with ReFRESCO the wind loads on typical offshore vessels can be predicted with reasonable accuracy in a cost-efficient manner. The accuracy of the calculated velocity fields is such that these can be used in prediction methods to obtain shielding effects on vessels positioned in the wake.
Rankine Source Method for Seakeeping Predictions
Authors: Söding Heinrich , von Graefe Alexander , el Moctar Ould , Shigunov Vladimir
Published: August 2013

Model tests are usually used for the traditional seakeeping predictions (transfer functions of ship motions and loads in regular waves). Experience shows that numerical solution of Reynolds-averaged Navier-Stokes equations (RANSE) can provide accurate results for this task, however, such computations require too much computational time for the required large number of the loading conditions, ship speeds and wave directions and periods. Traditionally, potential flow methods are used for such computations at early design stages. Although potential flow methods can produce results very quickly for large number of conditions, viscosity effects (most important for the roll motion) have to be taken into account using measurements or RANSE computations.

Rankine source method, applied to seakeeping problems perhaps for the first time by Yeung [1] to oscillating ship sections, is increasingly used in practical seakeeping analysis. This paper presents a three-dimensional Rankine source code GL Rankine. Patch method is used instead of the usual collocation method to satisfy boundary conditions on the solid body surface. Periodic flow due to waves is linearized with respect to wave and motion amplitude, taking into account interactions between the nonlinear steady flow and periodic flow due to waves and ship motions. The steady flow solution accounts for the nonlinear free-surface conditions, ship wave and dynamic squat. The paper shows results of the method for ship motions in waves in comparison with model measurements and RANSE simulations.
Viscous-Flow Calculations on an Axial Marine Current Turbine
Authors: Otto William , Rijpkema Douwe , Vaz Guilherme
Published: August 2013

In this paper, the flow over a marine current turbine is studied. As a test case, the benchmark turbine published in [1, 2] is selected. A bibliography review shows a variety of numerical methods applied to this specific turbine, of which a viscous-flow RANS approach seems to be the best suitable for simulations over a broad range of inflow conditions. Therefore, MARIN’s RANS solver ReFRESCO is used to study the flow over this turbine. ReFRESCO results show a good agreement with the experiments, the calculated results and associated uncertainties overlapping the model-tests results. A numerical procedure is followed to estimate these calculation uncertainties, including an estimation for the numerical, domain and geometrical uncertainties. The flow-field analysis reveals significant viscous effects. Large separation zones at the suction side of the blade are seen in the model-scale results. At model scale, the turbulence level indicates that the turbine is operating in the transitional regime between laminar and turbulent flow, leading to early flow separation. Calculations at full scale show a large scale effect. The separation zones present at model scale are significantly smaller at full scale, resulting in a higher power production and axial loading. This is explained by the fully-turbulent boundary layer.
A Rankine Panel Method for Added Resistance of Ships in Waves
Authors: Söding Heinrich , Shigunov Vladimir , Schellin Thomas E. , el Moctar Ould
Published: August 2013

A new Rankine panel method and an extended RANS solver were employed to predict added resistance in head waves at different Froude numbers of a Wigley hull, a large tanker, and a modern containership. The frequency domain panel method, using Rankine sources as basic flow potentials, accounts for the interaction of the linear periodic wave-induced flow with the nonlinear steady flow caused by the ship’s forward speed in calm water, including nonlinear free surface conditions and dynamic squat. Added resistance in waves is obtained by pressure integration method. The time domain RANS solver, based on a finite volume method, is extended to solve the nonlinear equations of the rigid body six-degrees-of-freedom ship motions. The favorable comparison of panel and RANS predictions demonstrated that the Rankine method is suitable to efficiently obtain reliable predictions of added resistance of ships in waves. Comparable model test predictions correlated less favorably although overall agreement was felt to be acceptable, considering the difficulties associated with procedures to obtain accurate measurements.
Effects From Fully Nonlinear Irregular Wave Forcing on the Fatigue Life of an Offshore Wind Turbine and its Monopile Foundation
Authors: Schløer Signe , Bredmose Henrik , Bingham Harry B. , Larsen Torben J.
Published: August 2013

The effect from fully nonlinear irregular wave forcing on the fatigue life of the foundation and tower of an offshore wind turbine is investigated through aeroelastic calculations. Five representative sea states with increasing significant wave height are considered in a water depth of 40 m. The waves are both linear and fully nonlinear irregular 2D waves. The wind turbine is the NREL 5-MW reference wind turbine. Fatigue analysis is performed in relation to analysis of the sectional forces in the tower and monopile.

Impulsive excitation of the sectional force at the bottom of the tower is seen when the waves are large and nonlinear and most notably for small wind speeds. In case of strong velocities and turbulent wind, the excitation is damped out. In the monopile no excitation of the force is seen, but even for turbulent strong wind the wave affects the forces in the pile significantly. The analysis indicates that the nonlinearity of the waves can change the fatigue damage level significantly in particular when the wave and wind direction is misaligned.
Ocean Eddies’ Influence on Lula Field, Santos Basin, Brazil
Authors: Andrioni Marcelo , Moreira Lima Jose Antonio , Guerra Luiz Alexandre , Ribeiro Eric Oliveira , Paiva Nunes Luis Manoel , Ceccopieri Wellington , de Souza Rego Valéria , de Oliveira Silas Manoel
Published: August 2013

Current data measured by an instrumented mooring line deployed at the Santos Basin, in a water depth of 2200 m, show a mean velocity of 0.20 m/s with no preferential direction. Extreme current events detected were associated with the presence of a pair of eddies with a dipole configuration. The jet stream created by the interaction of the cyclone-anticyclone pair was able to generate speeds up to 1.2 m/s at the first hundred meters of the water column. An investigative study with sea surface height anomaly fields processed from environmental satellites clearly shows the eddy structure during extreme current events.
Inline-Crossflow Coupled Vortex Induced Vibrations of Long Flexible Cylinders
Authors: Zheng Haining , Modarres-Sadeghi Yahya , Dahl Jason , Triantafyllou Michael S.
Published: August 2013

The inline motion of long flexible cylinders caused by Vortex Induced Vibrations (VIV) has been long neglected due to its small amplitude compared to the cross-flow response amplitude. However, the inline motion has a major impact on fatigue life due to its higher frequency (second harmonic) and more importantly, because it triggers a third harmonic stress component in the crossflow direction along with a broad-band frequency stress component. We introduce an inline response prediction module to VIVA, a VIV response prediction program widely used in the offshore industry, to be able to consequently predict the higher harmonic and chaotic VIV response characteristics of flexible cylinders. Extensive forced inline and combined inline-crossflow experiments were employed to provide hydrodynamic coefficient databases for input to VIVA, in addition to existing crossflow hydrodynamic coefficients. The Norwegian Deepwater Programme (NDP) experimental data were used to validate this prediction methodology.
The Stabilizing Effects of U-Tanks as Passive and Controlled Anti-Rolling Devices
Authors: Ribeiro e Silva Sergio , Vásquez Guillermo , Guedes Soares C. , Marón Adolfo
Published: August 2013

In this study a U-type tank, consisting of two lateral reservoirs connected by means of an horizontal channel, is considered either as a passive or controlled anti-rolling device for ships.

Initially, forced oscillation tests have been conducted at CEHIPAR for the U-type tank on a moving platform for different frequencies and also for different amplitudes of the pure roll forced motions adopting two distinct configuration: passive and controlled by means of two air valves installed on top of two lateral reservoirs. The most important aspect was to obtain a large set of roll restoring moments, for both passive and controlled configurations, which could give a discrete distribution of the roll restoring moments along the entire range of wave frequencies of interest. On a first study, a detailed account of model tests was presented, the method of analyzing the experimental results was discussed, and the experimental data of the U-type tank was compared with results from Lloyd’s linear frequency domain model, where non-linear effects with the amplitude of the forced motions was thoroughly addressed.

In this paper, the stabilizing effects of the same U-tank installed onboard a typical containership has been first analyzed with two distinct tools: WaMIT wave interaction 3D analysis software, and the two degrees-of-freedom numerical model referred above. In second place, the experimental data of the controlled U-type tank has been compared and contrasted with results from a nonlinear time domain model, where the controller of the air valves has been also included. Therefore, some preliminary conclusions could finally be drawn about the stabilizing effects of U-type tanks as passive and controlled anti-rolling devices.
Numerical Simulation of Ship Dynamics for Application in a Weather Routing System
Authors: Lin Yu-Hsien , Fang Ming-Chung
Published: August 2013

In order to enhance the efficiency and safety of a ship sailing in rough seas, the authors aim to develop a ship dynamic performance system, which can be used to predict ship motion responses, wave loads as well as quasi-mean added resistance. Two-dimensional strip theory discretized by the source distribution method is implemented to calculate Response Amplitude Operators (RAOs) for 6 DOF motion as well as the wave loads for the vertical shear force and bending moment. In addition, the ITTC directional wave spectrum of the short-crested wave adopts the one-hundred years return sea state as the input for testing the sea-keeping performance. Subsequently, we developed a database for a specific ship to realize the relationship between the sea-keeping performance and a combination of wave headings and ship speeds. Since the calculation of hydrodynamic coefficients correspond to the instantaneous hull form below the free surface (draft), the B-spline curve fitting technique based on the fourth order Runge-Kutta method is introduced to describe the relative wave heights together with second order nonlinear forces.
Wave Loads on a Monopile in 3D Waves
Authors: Nielsen Anders Wedel , Schlütter Flemming , Sørensen Jacob V. Tornfeldt , Bredmose Henrik
Published: August 2013

During the last decades more and more wind farms have been erected offshore. Most of these wind farms are located at relatively shallow water. The majority of the offshore wind turbines are founded on monopiles. Many of these offshore wind farms are exposed to large and steep waves, in some cases even breaking waves. The loads on the piles caused by waves can be significant and a better knowledge of the forcing caused by real sea states, including irregular waves and directional spreading is required to optimize the design.

The present physical model tests have been conducted in order to determine the effects of wave directionality and breaking of irregular waves. Piles with and without secondary structures have been tested. The waves were shoaled over a sloping bed and the pile was placed at two different positions with varying bed slopes. The three forcing components (Fx, Fy, Fz) were measured at the bottom of the pile during the experiments.

Breaking waves occurred around the pile in most of the tests and significant slamming forces were observed in the cases where breaking waves hit the pile which is well known from the literature. The experimental results indicated that the slamming force may be reduced when the wave spreading is increased, similar to the case of non-breaking waves.
Aero-Elastic-Floater-Mooring Coupled Dynamic Analysis of FOWT (Floating Offshore Wind Turbine) in Maximum Operation and Survival Conditions
Authors: Bae Y. H. , Kim M. H. , Yu Q. , Heo J. K.
Published: August 2013

Increasing numbers of FOWTs (floating offshore wind turbines) are planned in the coming years due to their high potential in massive generation of clean energy from ocean-wind. In the present study, a numerical prediction tool has been developed for the fully coupled dynamic analysis of an FOWT system in time domain including aero-loading, blade-rotor dynamics and control, mooring dynamics, and platform motions so that the influence of rotor-control dynamics on the hull-mooring performance and vice versa can be assessed. Hywind spar design with 5MW turbine is selected as an example, and two different environmental conditions, maximum operational and survival conditions, are applied for this study. The maximum operational condition means the maximum environmental condition that wind turbine can work normally, and the survival condition represents the extreme situation without any blade-turbine operation. Through this study, it is seen that the design environments for different structural components of FOWT can be different. The developed technology and numerical tool are readily applicable to the design of any future FOWTs in any combinations of irregular waves, dynamic winds, and steady currents.
Reliability Analyses of Clay-Embedded Offshore Pipelines Under Vertical Buckling Considering Lower-Bound Pipe-Soil Capacity
Authors: Valle-Molina Celestino , Alamilla-López Jorge , Najjar Shadi S. , Silva-González Francisco
Published: August 2013

This paper presents the reliability formulation and analyses for studying and quantifying probabilistically the impact of the main parameters involved in the upheaval buckling of offshore buried pipes due to high pressure high temperature conditions (HPHT) on the reliability of the pipeline. Pipelines are considered installed in a clayey trench and naturally covered. The limit state function is established in terms of the vertical pipe-soil capacity and vertical loading. A lower-bound capacity of the pipe-clayey soil system is included in the reliability analysis in order to represent more realistic conditions with regards to the uncertainty in the capacity. The lower-bound capacity is the smallest possible physical limit of the pipe-soil capacity. Reliability assessments using the main parameters that control the vertical buckling in terms of loading and capacity were performed. Consequently, the variations of the reliability index (β) with the vertical imperfection (δ) and the ratio of the cover height (depth of pipe embedment) to the pipe diameter (H/D) were quantified. The reliability index was evaluated by means of Monte Carlo simulations. The inclusion of the lower-bound capacity by means of a left-censored lognormal distribution was found to increase in some cases the values of β.
Comparative Study of Spar-Type Wind Turbines in Deep and Moderate Water Depths
Authors: Karimirad Madjid , Moan Torgeir
Published: August 2013

This paper compares the dynamic responses and performance of two spar-type wind turbines, DeepSpar and ShortSpar, in deep and intermediate water depths, respectively. The oil and gas industry has implemented spar platforms in deep water areas. Spar platforms show good hydrodynamic performance due to their deep draft. The same idea is applied to offshore wind turbines to present a reliable concept. Hywind is an example of a successful offshore wind turbine based on the spar concept in deep water. The good performance of spar-type wind turbines motivates us to study the feasibility of using these turbines in moderate water depth. Spar-type 5-MW wind turbines in deep and moderate water depths are compared. The power performance, dynamic motions, tension responses, accelerations, structural shear forces and bending moments are studied. Simo/Riflex/TDHMILL3D is used to perform the coupled wave- and wind-induced analyses. Simo/Riflex, developed by MARINTEK, is a commercial tool for analyzing the coupled wave-induced responses of moored offshore structures. TDHMILL3D, is an external DLL that accounts for spar motions while calculating the aerodynamic thrust at each time step using the turbine characteristics and relative velocities. Different environmental conditions are used to compare the responses. The results show that spar-type wind turbine in the moderate water depth exhibits good performance and that its responses are reasonable compared to those of spar-type wind turbine in deep water. This finding indicates the feasibility of implementing the same rotor-nacelle assembly for both concepts. The total mass (the structural mass plus the ballast) of the ShortSpar is 35% less than that of the DeepSpar, while the statistical characteristics of the power generated are almost the same. The reduced mass of the ShortSpar helps to achieve a more cost-effective solution for floating wind turbines in moderate water depth.
State-of-Art on Vortex-Induced Motion: A Comprehensive Survey After More Than One Decade of Experimental Investigation
Authors: Fujarra André L. C. , Rosetti Guilherme F. , de Wilde Jaap , Gonçalves Rodolfo T.
Published: August 2013

After one decade of experimental investigation, the Vortex-Induced Motion – VIM phenomenon deserves a comprehensive survey concerning the advances related to its understanding, mainly under the consideration of the fundamental aspects that keep it in a close relationship to the dynamic behavior of the same phenomenon acting on slender bodies, the well known Vortex-Induced Vibration – VIV. A considerable amount of results can be found in the literature, although there are few works dealing with a general view of the problem. Probably, the main reason for such a large amount of works with no interaction between themselves and, consequently, without a common understanding about VIM might be due to its technological origin, featured by huge platforms with a variety of geometrical details, which ends up placing the researches more on the field of the faithful reproduction of the features in small-scale and less on the global understanding of the phenomenology regardless the floating system, e.g. a spar platform, a monocolumn or even a semi-submersible or a tension-leg platform. Obviously, no one should disagree that there is part of the research that must keep a faithful relationship with the full scale, however, in most of them it is possible to identify the common fundamentals concerning the fluid-structural interaction. The aim of the present work is to address a comprehensive evaluation of the experimental investigations during the past decade on the VIM, trying to gather a general understanding about its phenomenology including some comparisons to VIV. As a result, some relevant aspects are pointed out for a more prospective way of research.
An Investigation on the Excitation of Yaw Parametric Resonance of a Tension Leg Platform
Authors: Cruz Roberto Edward , Neves Marcelo A. S. , Rivera Luis Alberto , Esperança Paulo T. T.
Published: August 2013

The paper summarizes some aspects of a series of model experiments conducted with a Tension Leg Platform (in fact a Tension Leg Wellhead Platform) in close proximity with a FPSO emphasizing the types of coupled motions taking place. It is observed that as the yaw motion develops increasing amplitudes the sway motion is reduced, pointing out to an interesting exchange of energy between the sway and yaw modes. This should be recognized as a revealing aspect of strongly non-linear coupled parametric resonant motions. A mathematical model is proposed to describe the main aspects of the two-body moored system and hydrodynamic interactions. In principle a 12-DOF model is contemplated. Numerical simulations are compared to the time series obtained from the experiments showing adequate agreement. However, in this paper the essential coupling of sway and yaw is distinguished in order to typify the Mathieu-type instability as being the main mechanism behind the onset of large yaw motions of the TLP unit.
Nonlinear Effect on Wave-Structure Interaction
Authors: Chen J. M. , Liang D.
Published: August 2013

Accurate prediction on the behaviour of the nonlinear waves in a coastal environment is vital to the safe design and performance of coastal defence. This paper is concerned with the description of tsunami wave-island interaction, and includes both linear and nonlinear modelling of the maximum free surface motion arising within distorted flow field. A deterministic nonlinear effect on the predicted maximum runup is examined using a Boussinesq-type model. Statistics of the predicted maximum leading-crest motion are obtained and discussed in light of linear diffraction theory. The results show that the predicted maximum runup and free surface motion by the quaternary-islands is affected by nonlinear wave transformation. The numerical simulations suggest that the present model describes the wave field very accurately even for extreme events. The present study provides a critical insight into the free surface elevation maxima at surf zone, thus safeguarding the structure design.
N-Wave Runup Statistics at Surf Zone Using Boussinesq-Type Model
Authors: Chen J. M. , Liang D. , Rana R.
Published: August 2013

A TVD Lax-Wendroff scheme solves the Boussinesq-type equations is presented, extensively validated, and clearly demonstrated to be a robust and efficient engineering tool to simulate the physical processes involved in the tsunami wave runup and interaction of the propagating solitary waves with the idealized coastal beaches. To better understand the physical processes of the tsunami wave runup at surf zone, a parametric study concerning N-wave runup is carried out. For all cases investigated, the qualitative features of the propagating N-waves remain unaltered, even for the large wave events. The relative maximum runup height and wave steepness are found to be strongly correlated and appeared to be linearly asymptotic in form. Also, the severity of extreme wave attack is found to be a function of beach slope for a given extreme event. The numerical simulations reveal the significance of the nonlinear wave effects on the predicted maximum N-wave runup heights, which provide guidance in selecting the design height of coastal defence structures and specifying the clearance distance between the shoreline and infrastructure.
Two- and Three-Dimensional Simulations of the Flow Around a Cylinder Fitted With Strakes
Authors: Carmo Bruno S. , Gioria Rafael S. , Korkischko Ivan , Freire Cesar M. , Meneghini Julio R.
Published: August 2013

Two- and three-dimensional simulations of the flow around straked cylinders are presented. For the two-dimensional simulations we used the Spectral/hp Element Method, and carried out simulations for five different angles of rotation of the cylinder with respect to the free stream. Fixed and elastically-mounted cylinders were tested, and the Reynolds number was kept constant and equal to 150. The results were compared to those obtained from the simulation of the flow around a bare cylinder under the same conditions. We observed that the two-dimensional strakes are not effective in suppressing the vibration of the cylinders, but also noticed that the responses were completely different even with a slight change in the angle of rotation of the body. The three-dimensional results showed that there are two mechanisms of suppression: the main one is the decrease in the vortex shedding correlation along the span, whilst a secondary one is the vortex wake formation farther downstream.
Numerical and Experimental Investigation of a Novel Wave Energy Converter
Authors: Rogne Øyvind Ygre , Ersdal Svein , Moan Torgeir
Published: August 2013

This paper deals with the numerical and experimental work carried out as part of the development of a new wave energy converter device suggested by Aker Solutions. The device consists of one catenary moored platform hinged to several smaller buoys. Energy is extracted through the relative rotation in the hinges. Model tests have been carried out in a towing tank with the aim to verify the use of linear hydrodynamic theory as a mean to predict the annual mean power production. The mathematical model of the device relies on linear hydrodynamic theory, and the commercial BEM code WAMIT is used to obtain the hydrodynamic coefficients. The equation of motion is formulated using generalized coordinates and Lagrange equation. The non-linear characteristics of the pneumatic cylinders, used to represent the power take-off forces in the model tests, necessitate the use of a time domain model. The convolution integral representing the radiation forces is replaced by an approximate state-space model, which is obtained using an frequency domain identification method.

The results show that the simulation model overpredicts the mean absorbed power by approximately 20% in sea states that result in moderate hinge response, whereas in one particular sea state that produce large hinge response, and consequently large power absorption, the overprediction is as large as 49%. This trend is expected, since large hinge response imply that the linear assumption is violated.
Oil Skimming Efficiency of the SOS: Scaling From GeoSim Model Tests to Full Scale Prototype Operations
Authors: Clauss Günther F. , Kosleck Sascha , Sprenger Florian , Grüter Laura
Published: August 2013

The severe ecological and economical aftermath of the 2010 ‘Deepwater Horizon’ catastrophe in the Gulf of Mexico clearly shows the insufficiency of current oil recovery systems which cannot operate in wave heights above 1.5m. To prevent emulsification and weathering processes, it is necessary to skim the oil film off the sea surface shortly after the accident. The autonomous SOS (Sea State-independent Oil Skimming System) developed within the framework of the research project SOS3 features high transit velocities, the capability of operating in rough seas and a massive intake of oil polluted water — and is therefore a unique technology. The oil water separation process of the SOS is purely based on hydrodynamic principles involving vortex evolution and a special flow pattern inside the internal moon pool. These requirements for efficient oil skimming operations depend on various hydrodynamic effects that would imply model testing in compliance with Froude’s and Reynolds’ law simultaneously — a physically impossible condition. Therefore GeoSim model tests with the SOS at model scales of 1:16, 1:25 and 1:36 are conducted with discrete particles of the correct density substituting the oil phase. The tendencies in flow pattern evolution and oil skimming efficiency are compared and extrapolated to full scale. Results from open water tests with the prototype of the SOS in the mouth of river Elbe serve for validation of the extrapolated results.
Experimental Comparison of Three Floating Wind Turbine Concepts
Authors: Goupee Andrew J. , Koo Bonjun , Kimball Richard W. , Lambrakos Kostas F. , Dagher Habib J.
Published: August 2013

Beyond many of the Earth’s coasts exist a vast deepwater wind resource that can be tapped to provide substantial amounts of clean, renewable energy. However, much of this resource resides in waters deeper than 60 m where current fixed bottom wind turbine technology is no longer economically viable. As a result, many are looking to floating wind turbines as a means of harnessing this deepwater offshore wind resource. The preferred floating platform technology for this application, however, is currently up for debate.

To begin the process of assessing the relative advantages of various platform concepts for floating wind turbines, 1/50th scale model tests in a wind/wave basin were performed at MARIN (Maritime Research Institute Netherlands) of three floating wind turbine concepts. The Froude scaled tests simulated the behavior of the 126 m rotor diameter NREL (National Renewable Energy Lab) 5 MW, horizontal axis Reference Wind Turbine attached via a flexible tower in turn to three distinct platforms, these being a tension leg-platform, a spar-buoy and a semi-submersible. A large number of tests were performed ranging from simple free-decay tests to complex operating conditions with irregular sea states and dynamic winds. The high-quality wind environments, unique to these tests, were realized in the offshore basin via a novel wind machine which exhibited low swirl and turbulence intensity in the flow field. Recorded data from the floating wind turbine models include rotor torque and position, tower top and base forces and moments, mooring line tensions, six-axis platform motions and accelerations at key locations on the nacelle, tower, and platform. A comprehensive overview of the test program, including basic system identification results, is covered in an associated paper in this conference.

In this paper, the results of a comprehensive data analysis are presented which illuminate the unique coupled system behavior of the three floating wind turbines subjected to combined wind and wave environments. The relative performance of each of the three systems is discussed with an emphasis placed on global motions, flexible tower dynamics and mooring system response. The results demonstrate the unique advantages and disadvantages of each floating wind turbine platform.
Analysis of Roll Motion due to Asymmetric Bilge Keels
Authors: Tom Nathan , Seah Robert , Roddier Dominique
Published: August 2013

Traditional frequency domain based vessel motion analyses operate under the assumption that the roll damping contribution from the port and starboard bilge keels are equivalent. In this work, we examine the roll motion of a vessel with bilge keels of unequal length using a novel methodology. Experiments conducted during the FPSO Roll JIP suggest that waves approaching from port versus starboard will induce different motion amplitudes due to the unequal bilge keel length. We examine the results from different approaches, comparing the computed response from a frequency domain analysis against those provided by a time domain model using Orcaflex with bilge keel represented by drag elements.
Experimental and Numerical Study of the Flow Around a Semi-Submerged Rectangular Cylinder
Authors: Arslan Tufan , Malavasi Stefano , Pettersen Bjørnar , Andersson Helge I.
Published: August 2013

The present work is motivated by phenomena occurring in the flow field around structures partly submerged in water. A three dimensional unsteady flow around a rectangular cylinder is studied for four different submergence ratios by using computational fluid dynamics (CFD) tools with LES turbulence model. Simulation results are compared to particle image velocimetry (PIV) measurements at Reynolds number Re = 12100 and Froude number Fr = 0.26. Focus in our investigation is on the characterization of the behaviour of vortex structures generated by separated flow. Another target in the study is to obtain better knowledge of the hydrodynamic forces acting on a semi-submerged structure. Computed force coefficients are compared with experimental measurements.
Improvement of Fatigue Crack Growth Simulation Based on the Strip Yield Model Considering the Strain Hardening Effect of Materials
Authors: Gotoh Koji , Harada Keisuke
Published: August 2013

This paper presents an improved numerical simulation procedure for fatigue crack growth based on the strip yield model with a weight function. In the previous numerical model, one-dimensional bar elements plugged up the chink corresponding to the virtual crack opening displacement in the plastic zone to describe the crack wake over fatigue crack surfaces. However, this numerical simulation method gives poor growth estimations under large variable loading histories, e.g. spike overloading. It is possible that insufficient consideration of the strain hardening effect of materials leads to excess crack closure. The authors develop the numerical simulation model of fatigue crack growth by considering the strain hardening effect of materials using the modified strip yield model. Numerical simulations of fatigue crack growth under many types of loading are performed to investigate the validity of our new proposed model. Comparison of proposed simulation results with previous results and with experimental measurements confirms the superiority of the proposed method.
Numerical Analysis of Hydrodynamic Performance of Backward Bent Duct Buoy (BBDB)
Authors: Koo W. C. , Kim S. J. , Kim M. H.
Published: August 2013

The hydrodynamic performance of Backward Bent Duct Buoy (BBDB), a floating-type wave energy converter, was evaluated in the time-domain simulation by using a two-dimensional fully-nonlinear numerical wave tank (NWT) technique. The developed NWT was based on potential theory, boundary element method with constant panels, and the mixed Eulerian-Lagrangian (MEL) approach to capture the nonlinear free-surfaces. The viscous damping at the chamber entrance due to oscillating water column and the shape of body causing generation of vortex shedding were modeled and applied to the free surface boundary condition inside the chamber. The calculated surface elevations inside the chamber with open chamber condition were compared with experimental data to select a proper viscous damping coefficient. Then, the surface elevations with a tuned viscous damping coefficient were calculated for various wave conditions. The results of linear and nonlinear time-domain simulation with two different corner-shaped BBDBs were compared to investigate the mean drift force of BBDB. Energy conservation in the computational domain was checked for all cases.
Numerical Calculation of the Viscous Hydrodynamic Forces on a KVLCC Hull Sailing Along Channel Bank
Authors: Lou Peng-yu , Zou Zao-Jian
Published: August 2013

In restricted waters, ships often need to navigate along banks of the waterways. In such case, the hydrodynamic lateral force and yaw moment acting on the ships will be induced due to the asymmetric flow about the ship hull. Accurately predicting these force and moment is of practical significance to ensure a safe navigation and can provide some guidance on correct manoeuvring and control of ships in restricted waters. In the present paper, to study the bank effects on the hydrodynamic forces acting on a ship manoeuvring in restricted waters, the viscous flow around an unappended ship sailing in a straight course along the channel bank and simultaneously undergoing sway motion is numerically simulated by using a CFD-based viscous flow solver. The steady and unsteady RANS equations in conjunction with a RNG k-ε turbulence model are solved by using the dynamic mesh technique and UDF (User-Defined Function). Numerical study is conducted for a KVLCC model. The hydrodynamic lateral force and yaw moment acting on the hull are calculated at different ship-to-bank distance and different water depth. By comparing the numerical results, the effects of ship-to-bank distance on the hydrodynamic forces are analyzed.
Numerical Simulation of Turbulent Flow Around Podded Propeller in Azimuthing Conditions
Authors: Shamsi Reza , Ghassemi Hassan
Published: August 2013

This paper investigates the numerical modeling of turbulent flow and hydrodynamic analysis of podded propeller in open water and azimuthing conditions. The RANS (Reynolds-Averaged Navier Stokes) based solver is used in order to study the variations of hydrodynamic characteristics of podded propeller at various angles. The variations of thrust and torque coefficients as functions of the advance coefficient are obtained at various yaw angles. Turbulent flow around the propeller and pod are presented. At first, the propeller is analyzed in open water condition in absence of pod and strut. Next flow around pod and strut are simulated without effect of propellers. Finally, the whole unit is studied in zero yaw angle and azimuthing condition. These investigations are performed for two podded propulsor configurations: puller and pusher. Total forces on the unit in each direction and propeller torque are computed for a range of advance coefficients from 0.2 to 1. Yaw angle of pod are modified from +15° to −15° by increments of 5°. Computational results are examined against with available experimental data. Characteristic parameters including torque and thrust of propeller, axial force, and side force of unit are presented as functions of advance coefficient and yaw angle. The performance curves of the propeller obtained by numerical method are compared and verified by the experimental results. The results show that the propeller thrust, torque, and podded unit forces and moments in azimuthing condition depend on propeller advance coefficient and yaw angle.
Detailed FSI Analysis Methodology for Subsea Piping Components
Authors: Chica Leonardo , Pascali Raresh , Jukes Paul , Ozturk Burak , Gamino Marcus , Smith Kevin
Published: August 2013

Flow Induced Vibration (FIV) is one of the important phenomena that contribute to failure of subsea piping components. This paper addresses a detailed methodology to analyze the structural response caused by unsteady multiphase flow within a pipe. This fluid-structure interaction (FSI) study was conducted in a two-bend model of a rigid M-shaped jumper to estimate the stresses and pressure fluctuations and determine the level of risk of failure.

Initially, a risk assessment method was carried out to determine the likelihood of failure (LOF) due to flow induced turbulence. Following the screening method, a detailed “two-way coupling” FSI study is recommended. Coupling the Finite Element Analysis (FEA) program with the Computational Fluid Dynamics (CFD) program allows to perform the following assessments:

• Strength check (Allowable stress);

• Fatigue analysis, and;

• Engineering criticality assessment of welds.

The two-way coupling analysis also compares the structural natural frequencies to the slug frequencies. Depending on the percentage difference between the two frequencies, a conclusion can be drawn in terms of level of risk and address whether assessing FIV fatigue damage should be required for future examination.
Experimental Study of the Coupled Hydrodynamics of a DP Barge Operating Close to a FPSO
Authors: Vieira Daniel P. , Tannuri Eduardo A. , Silva João Luis B. , Ferreira Marcos D.
Published: August 2013

The coupled hydrodynamic of a DP Barge operating close to a FPSO is evaluated. Experimental tests in a wave basin were performed to obtain the system dynamic behavior for several relative positions and environmental incidences. Two small scale models with factor 1:48 were tested in three different relative positions, five incidence angles and two irregular seas. The industry experience in operating barges was used to provide the insight to select these configurations. The DP Barge model was equipped with a dynamic positioning (DP) system, in order to keep its position relative to the FPSO. The FPSO model uses a scaled spread mooring system. Motions for DP Barge only were also obtained. Discussions are centered in reduction or amplification of DP Barge motions due the FPSO presence. Results are presented in terms of motions significant amplitude and RAO curves. A numerical model was evaluated and its results compared with the experiments. Some considerations, problems and conclusions about the operation were also obtained. These discussions complement the study presented by Vieira et al. (2011), which explored this operation numerically. A companion paper (Tannuri et al., 2012) will discuss the effects of the hydrodynamic coupling on the DP performance of the barge.