Nonlinear impulse of ocean waves on floating bodies

2012 ◽  
Vol 697 ◽  
pp. 316-335 ◽  
Author(s):  
Paul D. Sclavounos
Keyword(s):  
Time Derivative ◽  
Ocean Waves ◽  
The Body ◽  
Offshore Wind ◽  
Floating Body ◽  
Offshore Platforms ◽  
Wave Loads ◽  
Floating Bodies ◽  
Bernoulli’S Equation ◽  
Hydrostatic Force

AbstractA new formulation is presented of the nonlinear loads exerted on floating bodies by steep irregular surface waves. The forces and moments are expressed in terms of the time derivative of the fluid impulse which circumvents the time-consuming computation of the temporal and spatial derivatives in Bernoulli’s equation. The nonlinear hydrostatic force on a floating body is shown to point vertically upwards and the nonlinear Froude–Krylov force and moment are derived as the time derivative of an impulse that involves the time derivative of a simple integral of the ambient velocity potential over the time-dependent body wetted surface. The nonlinear radiation and diffraction forces and moments are expressed as time derivatives of two impulses, a body impulse and a free surface impulse that represents higher-order wave loads acting along the body waterline. Numerical results are presented illustrating the accuracy of the new force expressions. Applications discussed include the nonlinear seakeeping of ships and offshore platforms and the extreme wave loads and responses of offshore wind turbines.

scholarly journals Karhunen–Loeve representation of stochastic ocean waves

2012 ◽  
Vol 468 (2145) ◽  
pp. 2574-2594 ◽  
Author(s):  
Paul D. Sclavounos
Keyword(s):  
Wind Turbines ◽  
Ocean Waves ◽  
Offshore Wind ◽  
Yield Enhancement ◽  
Energy Yield ◽  
Offshore Platforms ◽  
Stochastic Representation ◽  
Nonlinear Loads ◽  
Floating Offshore Wind Turbines ◽  
Order Of Magnitude

A new stochastic representation of a seastate is developed based on the Karhunen–Loeve spectral decomposition of stochastic signals and the use of Slepian prolate spheroidal wave functions with a tunable bandwidth parameter. The new representation allows the description of stochastic ocean waves in terms of a few independent sources of uncertainty when the traditional representation of a seastate in terms of Fourier series requires an order of magnitude more independent components. The new representation leads to parsimonious stochastic models of the ambient wave kinematics and of the nonlinear loads and responses of ships and offshore platforms. The use of the new representation is discussed for the derivation of critical wave episodes, the derivation of up-crossing rates of nonlinear loads and responses and the joint stochastic representation of correlated wave and wind profiles for use in the design of fixed or floating offshore wind turbines. The forecasting is also discussed of wave elevation records and vessel responses for use in energy yield enhancement of compliant floating wind turbines.

scholarly journals Viscous-flow-based investigation of Cloaking phenomenon among multi-floating bodies and experimental verification

2019 ◽  
Vol 272 ◽  
pp. 01016
Author(s):  
Z K Wang ◽  
G H He ◽  
Z G Zhang ◽  
Y H Meng
Keyword(s):  
Experimental Research ◽  
Scattered Wave ◽  
Floating Body ◽  
Offshore Platforms ◽  
Floating Bodies ◽  
Cfd Simulations ◽  
Wave Drift ◽  
Real Coded Genetic Algorithm ◽  
Drift Force ◽  
Interaction Problem

The safety of mooring systems on offshore platforms seems more and more significant with the utilization of offshore space and resources, so the reduction of wave drift force is the key issue in this wave-body interaction problem. The wave drift force acting on the inner floating body surrounded by multiple small floating bodies can be reduced obviously with the occurrence of a phenomenon, which is called the Cloaking phenomenon. The Cloaking phenomenon refers to the reduction or complete elimination in amplitude of the scattered waves. In this paper, a real-coded genetic algorithm was used to optimize the parameters of outer floating bodies to minimize the scattered wave energy, and then the wave drift force acting on the inner body can be reduced. Furthermore, associated CFD simulations and experimental research were conducted with the above optimized parameters to investigate and verify the Cloaking phenomenon more systemically. It is shown that the wave drift force acting on the inner floating body in the Cloaking configuration can be reduced obviously both in numerical and experimental research, and the reduction of the wave drift force is closely related to the change of wave field around the structure.

scholarly journals Numerical Simulation of Fully Nonlinear Interaction Between Regular and Irregular Waves and a 2D Floating Body

2019 ◽  
Author(s):  
Haoran Li ◽  
Erin E. Bachynski
Keyword(s):  
Numerical Results ◽  
The Body ◽  
Body Motion ◽  
Irregular Waves ◽  
Floating Body ◽  
Computational Time ◽  
Wave Loads ◽  
Nonlinear Loads ◽  
Fully Nonlinear ◽  
Irregular Wave

Abstract A fully nonlinear Navier-Stokes/VOF numerical wave tank, developed within the open-source CFD toolbox OpenFOAM, is used to investigate the response of a moored 2D floating body to nonlinear wave loads. The waveDyMFoam solver, developed by extending the interDyMFoam solver of the OpenFOAM library with the waves2Foam package, is applied. Furthermore, a simple linear spring is implemented to constrain the body motion. An efficient domain decomposition strategy is applied to reduce the computational time of irregular wave cases. The numerical results are compared against the results from potential flow theory. Numerical results highlight the coupling between surge and pitch motion and the presence of nonlinear loads and responses. Some minor numerical disturbance occurs when the maximum body motion response is achieved.

Drift Motion of Floating Bodies Under the Action of Green Water

2021 ◽  
Author(s):  
Sasan Tavakoli ◽  
Luofeng Huang ◽  
Alexander V. Babanin
Keyword(s):  
Numerical Simulations ◽  
Water Waves ◽  
The Body ◽  
Green Water ◽  
Floating Body ◽  
Floating Bodies ◽  
Drift Motion ◽  
Upper Deck ◽  
Steep Waves ◽  
The Impact

Abstract Numerical simulations are peformed to model the dynamic motions of a free floating body exposed to water waves. The solid body has low freeboard and draft, and its upper deck can be washed by the steep waves. Thus, the green water phenomenon occurs as large waves interact with the floating body. The aim of the research is to improve the understanding of the green water emerging above the upper deck of a floating plate. A thin floating body with barriers is also modeled. For the case of the body equipped with barriers, no green water occurs. Green water has been seen to affect the wave field and the dynamic motions of the plate. It is observed that when water can wash the upper surface of the floating object, drift speed is slightly decreased as a proportion of the energy of waves is dissipated above the body. Water waves are seen to impact the upper surface of the thin floating body as the green water flows over its upper deck. Furthermore, water is seen to impact the plate as its front edge re-enters the water. The first water impact only occurs when the floating body is not equipped with any barrier. By sampling the numerical simulations, it is observed that the non-dimensional value of the impact pressure, resulting from the green water, is larger for the case of smaller wavelength.

scholarly journals Computational Methods for Moving and Deforming Objects in Extreme Waves

2019 ◽  
Author(s):  
Arthur E. P. Veldman ◽  
Henk Seubers ◽  
Matin Hosseini ◽  
Xing Chang ◽  
Peter R. Wellens ◽  
...  
Keyword(s):  
Well Being ◽  
Simulation Method ◽  
Engineering Problem ◽  
The Body ◽  
Green Water ◽  
Wave Forces ◽  
Offshore Platforms ◽  
Wave Loads ◽  
Floating Platform ◽  
Offshore Industry

Abstract Wave forces can form a serious threat to offshore platforms and ships. The damage produced by these forces of nature jeopardizes their operability as well as the well-being of their crews. Similar remarks apply to coastal defense systems. To develop the knowledge needed to safely design these constructions, in close cooperation with MARIN and the offshore industry the numerical simulation method ComFLOW is being developed. So far, its development was focussed on predicting wave loads (green water, slamming) on fixed structures, and for those applications the method is already being used successfully by the offshore industry. Often, the investigated object (ship, floating platform) is dynamically moving under the influence of these wave forces, and its hydrodynamic loading depends upon the position of the object with respect to the oncoming waves. Predicting the position (and deformation) of the body is an integral part of the (scientific and engineering) problem. The paper will give an overview of the algorithmic developments necessary to describe the above-mentioned physical phenomena. In particular attention will be paid to fluid-solid body and fluid-structure interaction and non-reflecting outflow boundary conditions. Several illustrations including validation, will demonstrate the prediction capabilities of the simulation method.

On the Lagrange’s Method for Floating Bodies

2006 ◽  
Author(s):  
Keyvan Sadeghi
Keyword(s):  
Kinetic Energy ◽  
Mechanical Energy ◽  
Equations Of Motion ◽  
Equation Of Motion ◽  
The Body ◽  
Floating Body ◽  
Floating Bodies ◽  
Lagrange’S Equation ◽  
Lagrange’S Method ◽  
Linear Radiation

It is shown that, in the context of a linear theory, all fluid radiation actions on a floating body can be solely represented by a part of the fluid mechanical energy corresponding to the wetted surface of the body. In this regard, it is indicated that the linear radiation damping can be expressed by a fluid kinetic energy which has a bilinear form. Then from the Lagrange’s equations of motion, an equation of motion is derived that is called the conjugate Larange’s equation of motion. A variant of Hamilton’s principle is also introduced as the variational generator of the conjugate Lagrange’s equation of motion.

Study on Influence of Geometrical Dimensions of Floating Bodies on Cloaking Phenomenon

2016 ◽  
Author(s):  
Zhigang Zhang ◽  
Guanghua He ◽  
Xiaoqun Ju ◽  
Dong Yu
Keyword(s):  
Wave Interaction ◽  
Floating Body ◽  
Geometrical Parameters ◽  
Offshore Platforms ◽  
Ocean Engineering ◽  
Floating Bodies ◽  
Floating Structures ◽  
Wave Drift ◽  
Drift Force ◽  
Geometrical Dimensions

Mooring offshore floating structures such as offshore platforms in large waves and winds, against the drift force and rotational moments are challenging in offshore engineering and ocean engineering. To investigate these kind of problems named positioning problems accurately, not only in hydrodynamic forces of first order but also in time-averaged steady forces of second order named wave drift force need to be taken into account. That arranging of several small cylinders regularly on a circle concentric with a fixed floating body is considered to reduce the wave drift force. Fortunately, a Cloaking phenomenon occurs at certain conditions with proper geometrical dimensions of floating bodies, which can reduce the wave drift force acting on bodies, perfectly even to zero. In this paper, with a combination of higher-order boundary element method (HOBEM) and wave-interaction theory, the influences of geometrical parameters of outer surrounding cylinders on the wave drift force of floating bodies are systematically investigated and discussed.

Investigation of a Novel Wave Energy Generator Using Dielectric Elastomer

2020 ◽  
Author(s):  
Changqing Jiang ◽  
Seiki Chiba ◽  
Mikio Waki ◽  
Koji Fujita ◽  
Ould el Moctar
Keyword(s):  
Wave Energy ◽  
Ocean Waves ◽  
High Energy ◽  
Absorption Efficiency ◽  
High Energy Density ◽  
Floating Body ◽  
Dielectric Elastomers ◽  
Direct Drive ◽  
Floating Bodies ◽  
Optimal Arrangement

Abstract The type of electroactive polymer, known as dielectric elastomers, has shown considerable promise for harvesting energy from environmental sources such as ocean waves, wind, and human motions, etc. The high energy density and conversion efficiency of dielectric elastomers (DEs) can allow for very simple and robust “direct drive” generators. In such generators, a DE transducer is directly driven by the up and down motions of waves. These generators can be simple, low-cost and robust. The efficiency of a wave energy convertor using DEs was confirmed by our previous experimental work. In this study, a wave energy convertor using DEs was numerically investigated as a moored floating body. First, the numerical model is validated against existing benchmark experiments. Then the moored floating body is numerically modelled, and the simulated results are compared to physical wave tank tests. The analyzed conditions vary from single body, two bodies with different intervals, and three bodies. The fluctuation, energy absorption efficiency, as well as the influence of multiple moored floating bodies on each other are discussed. The purpose of present work is to clarify the influence of floating body intervals and number of floating bodies on the motions, the mooring tensions, as well as the power generation efficiencies for a plurality of floating bodies arranged in a series in head seas. This kind of optimal arrangement is expected to be popularized in the future, which may contribute to the increasing demand of renewable energy solutions.

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.

Impact of ocean waves on offshore wind farm power production

2021 ◽  
Author(s):  
Porchetta Sara ◽  
Muñoz-Esparza Domingo ◽  
Munters Wim ◽  
van Beeck Jeroen ◽  
van Lipzig Nicole
Keyword(s):  
Wind Farm ◽  
Power Production ◽  
Ocean Waves ◽  
Offshore Wind ◽  
Offshore Wind Farm
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