scholarly journals Investigation of Focused Wave Impact on Floating Platform for Offshore Floating Wind Turbine: A CFD Study

2019 ◽  
Author(s):  
Yang Zhou ◽  
Qing Xiao ◽  
Yuanchuan Liu ◽  
Atilla Incecik ◽  
Christophe Peyrard
Keyword(s):  
Potential Theory ◽  
Wave Theory ◽  
Second Order ◽  
Floating Platform ◽  
Wave Impact ◽  
Pitch Motion ◽  
Irregular Wave ◽  
Wave Parameters ◽  
Motion Responses ◽  
Focused Wave

Abstract Most existing research related to a semi-submersible offshore floating platform focuses on the wave-structure interaction under either a regular or irregular wave condition. In order to numerically model the irregular wave impact on a semi-submersible platform hydrodynamic response with a low computational cost, in this study, a focused wave is utilized. The platform under this consideration is the DeepCwind semi-submersible platform. A high fidelity CFD numerical solver based on solving Navier-Stokes equations is adopted to estimate the dynamic response and the hydrodynamic loading of the platform. The focused wave is firstly generated based on a first order irregular wave theory in a numerical wave tank and validated against the linear wave theory results. Next, for CFD coding validation, the surface elevation of a fixed FPSO model associated with a focused wave is calculated and compared with the benchmark results. At last, the dynamic responses of the platform are numerically simulated under various focused wave parameters, and the results are compared with those obtained from an in-house potential flow theory tool at Électricité de France (EDF). It is found that the predicted CFD surge motion responses are close to those achieved with the second order potential theory while differ from the results obtained using linear potential theory. As to the pitch motion, differences are observed between two results, due to the different methods used for second order loads and viscous effects calculation. Turning to the results under different wave parameters, the surge and heave motion responses increase as the wave period goes up. However, the pitch motion is not affected significantly by varying wave periods. It may be due to the fact that the low-frequency effects have limited impact on the pitch motion. The strong nonlinearity at extremely large wave amplitude will be the task in our near future study.

Second-Order Slowly Varying and Mean Value of Pitch Motion of the Sandglass-Type Floating Body With Dynamic Positioning System

2017 ◽  
Author(s):  
Linlin Wang ◽  
Wenhua Wang ◽  
Yazhen Du ◽  
Yi Huang
Keyword(s):  
Pitch Angle ◽  
Experimental Tests ◽  
Mean Value ◽  
Second Order ◽  
Floating Body ◽  
Positioning System ◽  
Pitch Motion ◽  
Dynamic Positioning System ◽  
Irregular Wave ◽  
Metacentric Height

This paper takes the presented concept of sandglass-type floating body as the research object. The shape of new sandglass-type floating body has extended oblique characteristic, which may result in special performance and the problem of pitch (or roll) motion. From the experimental tests, it can be found that its pitch natural frequency is small and the second order slowly varying pitch motion in irregular wave is significant, which may cause an unintentional interaction between the pitch and surge motions. Additionally, the floating body with small-waterplane-area and low metacentric height may have obvious mean pitch angle with wind moment under harsh sea condition. To solve the above two problems, numerical simulations have been conducted with two sea conditions. Lastly, based on the existing technique, the problems are solved and the positioning accuracy can be satisfied well for the harsher sea condition.

Non-Linear Wave Diffraction Around a Moored Ship

2004 ◽  
Author(s):  
J. Zang ◽  
R. Gibson ◽  
P. H. Taylor ◽  
R. Eatock Taylor ◽  
C. Swan
Keyword(s):  
Wave Diffraction ◽  
Scattering Problem ◽  
Wave Interaction ◽  
Wave Structure ◽  
Second Order ◽  
Linear Wave ◽  
Wave Impact ◽  
Non Linear ◽  
Focused Wave ◽  
Run Up

The objective of this research, part of the FP5 REBASDO Programme, is to examine the effects of directional wave spreading on the nonlinear hydrodynamic loads and the wave run-up around the bow of a floating vessel (FPSO) in random seas. In this work, the non-linear wave scattering problem is solved by employing a quadratic boundary element method. An existing scheme (DIFFRACT developed in Oxford) has been extended to deal with uni-directional and directional bi-chromatic input wave systems, calculating second-order wave diffraction under regular waves and focused wave groups. The second order wave interaction with a floating vessel in a unidirectional focused wave group is presented in this paper. Comparison of numerical results and the experimental measurements conducted at Imperial College shows excellent agreement. The second-order free surface components at the bow of the ship are very significant, and cannot be neglected if one requires accurate prediction of the wave-structure interaction; otherwise a major underestimation of the wave impact on the structure could occur.

Second Order Wave Diffraction Around a Fixed Ship-Shaped Body in Unidirectional Steep Waves

2006 ◽  
Vol 128 (2) ◽  
pp. 89-99 ◽  
Author(s):  
J. Zang ◽  
R. Gibson ◽  
P. H. Taylor ◽  
R. Eatock Taylor ◽  
C. Swan
Keyword(s):  
Free Surface ◽  
Wave Diffraction ◽  
Scattering Problem ◽  
Wave Interaction ◽  
Wave Structure ◽  
Second Order ◽  
Wave Impact ◽  
Focused Wave ◽  
Run Up ◽  
Steep Waves

The objective of this research, part of the EU FP5 REBASDO Program, is to examine the effects of second order wave diffraction in wave run-up around the bow of a vessel (FPSO) in random seas. In this work, the nonlinear wave scattering problem is solved by employing a quadratic boundary element method. A computer program, DIFFRACT, has been developed and recently extended to deal with unidirectional and directional bichromatic input wave systems, calculating second order wave diffraction loads and free surface elevation under regular waves and focused wave groups. The second order wave interaction with a vessel in a unidirectional focused wave group is presented in this paper. Comparison of numerical results and experimental measurements conducted at Imperial College shows excellent agreement. The second order free surface components at the bow of the ship are very significant, and cannot be neglected if one requires accurate prediction of the wave-structure interaction; otherwise a major underestimation of the wave impact on the structure could occur.

Numerical Modeling Using CFD and Potential Wave Theory for Three-Hour Nonlinear Irregular Wave Simulations

2017 ◽  
Author(s):  
Aldric Baquet ◽  
Jang Kim ◽  
Zhenjia (Jerry) Huang
Keyword(s):  
Numerical Modeling ◽  
Potential Theory ◽  
Wave Spectrum ◽  
Nonlinear Effects ◽  
Wave Theory ◽  
Breaking Waves ◽  
Wave Crest ◽  
Fully Nonlinear ◽  
Irregular Wave ◽  
Stokes Waves

In this paper, we focus on the modeling of a fully-nonlinear, steep, irregular wave field of three-hour duration without structures in it. The fully-nonlinear effects are considered in the wave simulations using computational fluid dynamics (CFD), as well as potential theory. The overall approach for the numerical modeling is described in the paper. The Euler Overlay Method (EOM) is used to incorporate incoming waves, nonlinear effects, and CFD simulations in the numerical modeling. For computational efficiency, we also use potential theory to model the fully-nonlinear waves. Numerical damping was applied locally around the breaking region to enable simulations for large breaking waves. To compensate for energy loss in the numerical simulations, energy compensation factors of wave spectral frequency components are applied to the input wave spectrum. Results of convergence study, validation against high-order Stokes waves and fully-nonlinear irregular wave with prescribed target spectrum, as well as comparison between numerical wave crest distributions and those from multiple realizations of wave calibration tests are presented.

Analysis of the Motion Response of Trimaran Based on Directional Spectrum

2016 ◽  
Author(s):  
Shuzheng Sun ◽  
Hui Sun ◽  
Jide Li ◽  
Xiyang Liu ◽  
Wenlei Du
Keyword(s):  
Wave Theory ◽  
Operating Conditions ◽  
Analysis Method ◽  
Towing Tank ◽  
Motion Response ◽  
Directional Spectrum ◽  
Irregular Wave ◽  
Motion Responses ◽  
Seakeeping Performance ◽  
Comparison Of The Results

The seakeeping performance of trimaran is crucial to its design and development. A series of trimaran model tests for seakeeping performance are conducted in towing tank. Directional spectrum theory and long-crested wave theory are introduced to the spectrum analysis method so as to analyze the motion response of trimaran. The comparison of the results gaining from two theories and those achieving from the long-crested irregular wave tests is carried out. By statistical analysis, there is a big difference between the motion responses of trimaran according to different wave theories in several operating conditions. The characteristics of trimaran motion responses under different course angles are studied. Compared with long-crested wave theory, directional spectrum theory is introduced as a more accurate approach to research the seakeeping performance of trimaran.

Analysis of the First Order and Slowly Varying Motions of an Axisymmetric Floating Body in Bichromatic Waves

2013 ◽  
Vol 135 (1) ◽  
Author(s):  
João Pessoa ◽  
Nuno Fonseca ◽  
C. Guedes Soares
Keyword(s):  
Vertical Cylinder ◽  
Vertical Axis ◽  
Second Order ◽  
The Body ◽  
Floating Body ◽  
Drift Motion ◽  
First Order ◽  
Motion Responses ◽  
Simple Geometry ◽  
Good Agreement

The paper presents an experimental and numerical investigation on the motions of a floating body of simple geometry subjected to harmonic and biharmonic waves. The experiments were carried out in three different water depths representing shallow and deep water. The body is axisymmetric about the vertical axis, like a vertical cylinder with a rounded bottom, and it is kept in place with a soft mooring system. The experimental results include the first order motion responses, the steady drift motion offset in regular waves and the slowly varying motions due to second order interaction in biharmonic waves. The hydrodynamic problem is solved numerically with a second order boundary element method. The results show a good agreement of the numerical calculations with the experiments.

A Second Order Lagrangian Model for Irregular Ocean Waves

2005 ◽  
Vol 128 (3) ◽  
pp. 177-183 ◽  
Author(s):  
Sébastien Fouques ◽  
Harald E. Krogstad ◽  
Dag Myrhaug
Keyword(s):  
Specular Reflection ◽  
Fluid Velocity ◽  
Equations Of Motion ◽  
Wave Theory ◽  
Ocean Waves ◽  
Second Order ◽  
Lagrangian Model ◽  
Lagrangian Description ◽  
Linear Wave ◽  
Irregular Solution

Synthetic aperture radar (SAR) imaging of ocean waves involves both the geometry and the kinematics of the sea surface. However, the traditional linear wave theory fails to describe steep waves, which are likely to bring about specular reflection of the radar beam, and it may overestimate the surface fluid velocity that causes the so-called velocity bunching effect. Recently, the interest for a Lagrangian description of ocean gravity waves has increased. Such an approach considers the motion of individual labeled fluid particles and the free surface elevation is derived from the surface particles positions. The first order regular solution to the Lagrangian equations of motion for an inviscid and incompressible fluid is the so-called Gerstner wave. It shows realistic features such as sharper crests and broader troughs as the wave steepness increases. This paper proposes a second order irregular solution to these equations. The general features of the first and second order waves are described, and some statistical properties of various surface parameters such as the orbital velocity, slope, and mean curvature are studied.

Second-order Wagner theory of wave impact

2006 ◽  
Vol 58 (1-4) ◽  
pp. 121-139 ◽  
Author(s):  
A. A. Korobkin
Keyword(s):  
Second Order ◽  
Wave Impact ◽  
Wagner Theory

Spectral Analysis of Irregular Wave Impact on the Structure in Splash Zone

2002 ◽  
Author(s):  
Bing Ren ◽  
Yongxue Wang
Keyword(s):  
Spectral Analysis ◽  
Wave Height ◽  
Incident Wave ◽  
Impact Pressure ◽  
Splash Zone ◽  
Spectral Moment ◽  
Wave Impact ◽  
Large Wave ◽  
Irregular Wave ◽  
The Impact

The spectral analysis from experimental data of irregular wave impact on the structures with large dimension in the splash zone is presented. The experiments were conducted in the large wave-current tank in the State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology. In the experiment, the target spectrum is JONSWAP spectrum, the significant wave height H1/3 is in the range from 0.1m to 0.3m, and the peak period of spectrum Tp in the range from 1.0s to 2.0s. The ratio of s/H1/3, which refers to the clearance of the subface of the structure above still water level (s) to the incident wave height, is between −0.1 and 0.4. The spectral analysis results of the irregular wave impact pressure on the subface of the structure under various case studies are presented. The distribution of spectral moment of the impact pressure on the structure along the subface is given. And the influence of different incident wave parameters and relative clearance s/H1/3 on the average spectral moment of impact pressure are discussed.

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