bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numerical Simulation of Vortex Induced Vibrations for Marine Risers Subjected to Sheared Flow
Authors: Van den Abeele F. , Vande Voorde J. , Kara F. 
Published: November 2013

The increasing demand for oil and gas, currently estimated at 135 million barrels of oil equivalent per day, keeps pushing the boundaries of offshore engineering into ever deeper waters. Exploration and production activities in the Gulf of Mexico, for instance, are performed in water depths exceeding 3000 meters. For such deepwater developments, the suspended length of the marine risers adds up to several kilometers. When designing and installing risers in (ultra)deep water, the length/diameter aspect ratio of the marine riser can exceed L/D > 1000, and the features of the fluid flow in depth direction can no longer be neglected. Indeed, both the magnitude and the direction of the current change with water depth, giving rise to higher harmonics in the VIV response.
The prediction of vortex induced vibrations for deepwater risers is very challenging, owing to the fact that the incident flows are non-uniform and the associated fluid structure interaction phenomena are highly complex. These complex conditions give rise to a non linear coupled system with a large number of degrees of freedom, which depends on several physical and mechanical parameters.
In this paper, 3D CFD calculations are performed to evaluate the effect of the third dimension for risers subjected to uniform flow and sheared currents. For a uniform current velocity at the inlet boundary, it is shown that vortex shedding in the wake of long slender tubulars can give rise to the development of vortices with horizontal axis, resulting in a fluctuation of the flow in the Z-direction. These three dimensional vortices are strong enough to modulate the vortex shedding on the riser as a function of depth. The 3D simulations with uniform current velocity are then compared to marine risers subjected to sheared currents. It is shown that the presence of sheared currents invokes a shift in both phase and frequency of the vortex shedding.
An Integrated Approach for the Representation of Concrete Gravity Based Foundations for Offshore Wind Turbines
Authors: Philippe Maxime , Borgarino Bruno , Kotronis Panagiotis , Ducrozet Guillaume 
Published: November 2013

This paper describes a novel approach to efficiently simulate the structural dynamics of a concrete Gravity Based Foundation (GBF). In this time-domain analysis, the GBF is subjected to loads applied by the turbine, wave loads and the influence of the soil structure interaction is taken into account. Wind turbine loads are computed using the aeroelastic software FAST and expressed at the connection point between the turbine and the GBF Wave loads on the GBF are computed using a potential, nonlinear wave model. Nonlinear soil-structure interaction is modelled with the use of a macro-element specifically developed for shallow foundations. Finally, the structure itself is modelled using an Euler-Bernoulli multifiber beam, which allows representing the reinforced concrete sections.
It is shown that the numerical model is able to efficiently simulate the behaviour of a GBF foundation under nonlinear irregular wave forces and loads transmitted by the turbine. It reproduces nonlinear phenomena such as a decrease in material stiffness due to damage and permanent strains but also the GBF displacements considering soil structure interaction.
Comparison Between Static, Forced Oscillation and Free Oscillation Model Tests for the Assessment of Galloping Instability at High Reynolds Numbers
Authors: Cinello Alexandre , Pétrié François , Rippol Thierry , Molin Bernard , Damblans Guillaume 
Published: November 2013

Galloping may take place for non-circular cross sections, such as an ice-coated electric power line or a riser bundle, under current action. This type of instabilities occurs at lower frequency than Vortex Induced Vibrations but with unbounded amplitude, and might be detrimental for riser integrity.
In a recent joint industry project, the CITEPH “Gallopan” project, galloping instabilities were investigated for two types of cylinders: an academic square cylinder and a generic riser tower cross section. Model tests and numerical computations were performed to assess the propensity of both cylinders to gallop.
Experiments on the square cylinder are reported here. Three types of tests were performed in steady flow: loads measurement on fixed cylinder, at various headings; loads measurement on the cylinder with over imposed cross-flow harmonic oscillations; free transverse oscillations. By using analytical calculations, the ability to predict galloping instability occurrence and amplitude, of each of the three above methods, was compared.
Compared to typical results found in literature, these experiments were conducted at a larger scale, and thus with Reynolds number closer to on-site values, i.e. over 105.
Sea State Estimation Based on Ship Motions Measurements and Data Fusion
Authors: Drouet Céline , Cellier Nicolas , Raymond Jérémie , Martigny Denis 
Published: November 2013

In-service monitoring can help to increase safety of ships especially regarding the fatigue assessment. For this purpose, it is compulsory to know the environmental conditions encountered: wind, but also the full directional wave spectrum. During the EU TULCS project, a full scale measurements campaign has been conducted onboard the CMA-CGM 13200 TEU container ship Rigoletto. She has been instrumented to measure deformation of the ship as well as the sea state encountered during its trip. This paper will focus on the sea state estimation.
Three systems have been installed to estimate the sea state encountered by the Rigoletto: An X-band radar from Ocean Waves with WAMOS® system and two altimetric wave radars from RADAC®.
Nevertheless, the measured significant wave height can be disturbed by several external elements like bow waves, sprays, sea surface ripples, etc… Furthermore, ship motions are also measured and can provide another estimation of the significant wave height using a specific algorithm developed by DCNS Research for the TULCS project.
As all those estimations are inherently different, it is necessary to make a fusion of those data to provide a single estimation (“best estimate”) of the significant wave height. This paper will present the data fusion process developed for TULCS and show some first validation results.
A Low Motion Floating Platform for Offshore Wind Resource Assessment Using Lidars
Authors: Nicholls-Lee Rachel 
Published: November 2013

With offshore wind becoming a key source of renewable energy there exists a requirement for the acquisition of meteorological information at the sites allocated for development. Installation of a conventional, static, meteorological mast is costly. Multiple masts are required to obtain data at several positions in a large offshore wind farm, which further increases the cost of gathering such data. A structure that has mobility for relocation about the site has the potential to reduce costs whilst improving data capture coverage. As such, an instrumentation platform in the form of a floating structure which can be moved easily is desirable.
This work discusses the development of a low-motion, lightweight, floating platform with tunable motion response as a basis for a repositionable meteorological measurement station. Wind speed and direction measurements are acquired at a range of heights in the atmosphere through the use of a pulsed Lidar (light detection and ranging) system. The motions of the platform have been analyzed both numerically and experimentally, and the performance of the platform in a range of seas is good.
Random Wave Forces on Monopile Wind Turbine Foundations: A Comparison of Wave Models
Authors: Zheng Xiang Yuan 
Published: November 2013

The wave forces on a monopile are compared among the classical random wave models and the state-of-the-art fully nonlinear random wave model. Forces are calculated in terms of Morison’s equation up to the wave crest zone. Linear random wave model with constant stretching, second-order random wave model with linear extrapolation from the still water level and, the third-order nonlinear wave model are adopted in time-domain simulations.
The simulation results show that the third-order random model is able to produce accurate predictions of extreme wave crest and quasi-static wave forces when compared with the fully nonlinear model. The linear random model with constant stretching behaves better than the commonly used Wheeler stretching. The second-order random wave model is suggested to enter the mainstream application of industrial design for shallow-water offshore structures as it provides wave forces whose quality is only inferior to the third-order model, but with much less computational effort than both the third-order model and the fully nonlinear model.
A Detailed Investigation of the Nearshore Wave Climate and the Nearshore Wave Energy Resource on the West Coast of Ireland
Authors: Gallagher Sarah , Tiron Roxana , Dias Frederic 
Published: November 2013

The western coast of Ireland possesses one of the highest wave energy resources in the world and consequently is a promising location for the future deployment of Wave Energy Converters (WECs). Most wave climate studies for this region have focused primarily on the offshore area since it enjoys higher energy densities. However, recent studies have shown that nearshore locations offer a similar potential for the exploitation of wave energy as offshore sites [13]. Furthermore, the proximity of WEC devices to the shore will likely reduce losses in power transport, and facilitate access for maintenance activities.
In this context, we analyse the wave climate over a ten year period for several nearshore sites off the Irish West Coast. The wave climate is estimated using a spectral wave model, WaveWatch III, forced with wind and spectral wave data from the ECMWF (European Centre for Medium Range Weather Forecast) operational archive. The wave model is validated with wave buoy data from intermediate to shallow depths (< 60 m).
Our focus is on two aspects of the wave climate resource assessment. Firstly, we characterise the directionality of the wave energy resource (mean direction, directional spread) which affects the site selection, design and performance of nearshore WECs. Secondly, we discuss the climate data from the perspective of accessibility for maintenance. When selecting sites for the deployment of WECs, a balance needs to be found between two opposing criteria: the existence of sufficiently long, continuous time intervals of calm sea states (weather windows) which are necessary for maintenance activities to take place, and a high, consistent level of wave energy density, essential for economically viable wave energy extraction.
A Probabilistic Metocean Model for Mooring Response in Gulf of Mexico Hurricanes
Authors: Mathisen Jan , Hørte Torfinn 
Published: November 2013

Hindcast data for a specific location is utilised to develop a joint probability function for the metocean variables that are expected to have a significant effect on mooring line tensions for a floating platform moored at that location. The main random variables comprise: peak significant wave height, peak wind speed, peak surface current speed, peak wave direction, peak wind direction and peak current direction, where “peak” indicates the maximum intensity of the metocean effect during a random hurricane. The time lead of peak wind relative to peak waves and the time lag of peak current after peak wind are included as random variables. It is also necessary to describe the time variation around the peak events. Simple models are assumed based on inspection of the time variations during severe hurricanes. Only the part of the hurricane during which the significant wave height exceeds 80% of the peak value is taken into account. The duration of this interval is included. Linear variation is assumed for the directions, hence the rates of change of the 3 directions are included. A linear (triangular) plus parabolic model is assumed for the time variation of the intensities of the 3 metocean effects around their respective peaks. A single parameter is required to define the proportion of linear and parabolic models for each effect and the values of this parameter for each of the 3 metocean effects are also included as random variables.
A random hurricane can be drawn from this metocean model, such that the time variation of the metocean actions is deterministic once the values of the random variables have been selected. The overall duration of the hurricane is split into short intervals, each of 15 minutes duration, such that stationary response may be assumed during each short interval. The extreme value distribution of line tension during each short interval is obtained. These distributions are combined to obtain the extreme distribution of line tension during the hurricane. Second order reliability methods are applied to integrate over the distribution of the metocean variables and obtain the distribution of extreme tension during a random hurricane. The annual frequency of hurricanes is used to derive the annual extreme value distribution of line tension.
The model is intended for the reliability analysis of the ultimate limit state of mooring lines, but may also be applicable to other response variables. The present paper is primarily concerned with the metocean model, but it is intended to include sample results for the extreme line tension.
Finite Element Analysis of Subsea Pipelines Subjected to Underwater Explosion
Authors: Van den Abeele F. , Verleysen P. 
Published: November 2013

Underwater mines and explosives, left in ports and harbours after World War II, can still pose a threat to subsea pipelines. In case of an accidental explosion, or even during controlled detonation, such explosives can cause significant damage to subsea pipelines. To assess the safety of pipelines exposed to an underwater explosion, finite element analyses are performed to predict the transient response of the pipeline to an acoustic pressure shock wave.
This type of problem is characterized by a strong coupling between the structural response of the pipe and the acoustic pressure on the wetted interface between the pipe surface and the surrounding seawater. The spherical pressure wave induced by an underwater explosion is characterized by a very steep wave front, where the maximum pressure is attained over an extremely short rise time. The pressure then drops off exponentially over a significantly longer period of time. As a result, the structural behaviour is a combination of a long time response, dominated by an added mass effect (low frequency), a short time response, governed by radiation damping (high frequency), and an intermediate time-frequency response, where both added mass and radiation damping effects are present.
In this paper, a finite element model is presented to simulate the transient response of a subsea pipeline subjected to an underwater explosion. The close coupling between acoustic pressure and structural response gives rise to numerical challenges like the accurate formulation and representation of the shock wave, the mesh requirements for the acoustic domain, and the position of the surface based absorbing radiation boundaries. An explicit dynamic solver is used to tackle these challenges, and to predict the behaviour of subsea pipelines exposed to an underwater explosion. The numerical results are compared to published experimental data, and can be used to assess the safety of submerged pipelines in the vicinity of explosives.
Wave Drift Forces on Three Barges Arranged Side by Side in Floatover Installation
Authors: Xu Xin , Yang Jianmin , Li Xin , Lu Haining 
Published: November 2013

Floatover is a new method for installing integrated topside of a spar platform. It has several obvious advantages such as less time and cost compared with derrick lifting. In general, the floatover installation consists of three procedures: firstly a single barge is used for long-distance transportation of the topside in order to get good stability; secondly two barges take place of the single barge for floatover installation near the operating site; finally the topside is transferred from the two barges to the spar hull and the installation is completed. Between the first and second procedures, the case occurs that the single transportation barge is sided left and right by two floatover barges in the second procedure with close proximity. This case is concerned by many designers and operators for the security problem brought by possible large relative motions and forces of the three barges in side by side configuration.
The hydrodynamics of side-by-side barges are much more complex than that of a single barge in waves. In numerical simulation, it is a challenge to consider all effects including the hydrodynamic interactions, the shielding effects, the viscous effects and the wave resonance effect which has been observed in the gaps between the barges and has a significant impact on wave drift forces. In this paper, motion responses and wave drift forces were calculated in frequency domain for both the multi-body system and the single body. Far-field, middle-field and near-field method were all carried out to calculate wave drift forces. Numerical analysis was executed using potential flow code WAMIT. Corresponding model tests were also performed in the Deepwater Offshore Basin in Shanghai Jiao Tong University. Comparison between numerical and experimental results shows that numerical results agree well with the experiment and that middle-field method has better convergence than near-field method. The comparison between the multi-body system and single body shows that the hydrodynamic interactions (including wave shielding effect and Helmholtz resonance of water in the gaps) are remarkable and motion responses in the multi-body system are larger than single barge at some frequencies.
Riser Resistance to In-Service Fatigue Loading
Authors: Iob Francesco , Mecozzi Elisabetta , Di Vito Luigi , Darcis Philippe , Marines-Garcia Israel , Quintanilla-Carmona Hector M. 
Published: November 2013

Riser systems are subjected to complex loading spectra induced by sea states. The complex loading spectrum differs sensibly from the constant amplitude loading commonly adopted for qualification of the product (riser pipe and its girth welds).
The present work deals with numerical calculations of the actual loading spectrum experienced by a Steel Catenary Riser when adopted in different scenarios, Gulf of Mexico (GoM) and West of Africa (WoA). Sensitivity analyses have been performed to evaluate the influence on applied fatigue loading of different parameters, like: water depth, seabed stiffness, hang-off angle.
The variable amplitude loading, derived from in-service conditions, has been applied to laboratory scale, full thickness specimens from X65 SCR girth welds. The fatigue performance of these samples has been compared to analogous samples subjected to constant amplitude loading. The samples subjected to in-service loading conditions exhibited a lower fatigue performance than in constant amplitude.
To allow a comparison with common qualification procedure under constant amplitude, full scale testing of SCR girth welds have been performed on resonance machine by in-service loading spectra rearranged in constant amplitude blocks. Laboratory full thickness specimens have been adopted to compare the girth weld fatigue performance when subjected to the original cycle-by-cycle sequence and the in-blocks rearranged sequence.
Validation of CFD for the Determination of Damping Coefficients for the Use of Wave Energy Converters Modelling
Authors: Thilleul Olivia , Babarit Aurélien , Drouet Aurélien , Le Floch Sébastien 
Published: November 2013

Diffraction-radiation codes enable to model the behaviour of Wave Energy Converters (WEC) and seakeeping of ships on many sea-states with very little computational time. However, the viscous effects are neglected and therefore the simulations lead to relatively inaccurate values. The inaccuracy mainly occurs at the resonance frequency, especially in roll motions for which viscous effects are of major importance. Classically, the viscous effects are represented by adding viscous damping coefficients obtained either from experimental data or analytical approaches based on numerous approximations.
In order to improve the accuracy of the diffraction-radiation solvers, the damping coefficients can also be calculated from Computational Fluid Dynamics (CFD) simulations. The first part of this paper presents the three CFD solvers and turbulence models used in this validation study: ICARE and ISIS-CFD are developed by Ecole Centrale de Nantes and Star-CCM+ is a general purpose solver developed by CD-adapco. For each case, a preferred solver is chosen and a second solver is used for verification in most cases.
The second part briefly presents the theory that obtains drag coefficients in oscillatory flows, which are closely related to damping coefficients in waves. Each of the three following parts introduces the experimental test cases to which numerical results are compared to. The numerical parameter convergence study leads to a choice of around 200 timesteps per period with an adapted mesh enabling to obtain drag coefficients with errors lower than 5%. A mesh convergence study in the wake area leads to a mesh refinement of around 2 to 2.5 % of the body characteristic length. In order to reduce the computational time, the total number of cells can be decreased by mainly refining locations where specific flow detachment occurs, such as body corners or sharp edges. Turbulence models are also varied. Validation results are finally presented in terms of single or coupled damping coefficients and added mass coefficients. They are presented for various non-dimensional numbers such as Keulegan-Carpenters and Reynolds number.