Study on Second-order Wave Exciting Forces on Cone Shaped Floating Bodies

The paper presents an experimental investigation of the first order and second order wave exciting forces acting on a body of simple geometry subjected to long crested irregular waves. The body is axis-symmetric about the vertical axis, like a vertical cylinder with a rounded bottom, and it is restrained from moving. Second order spectral analysis is applied to obtain the linear spectra, coherence spectra and cross bi-spectra of both the incident wave elevation and of the horizontal and vertical wave exciting forces. Then the linear and quadratic transfer functions (QTF) of the exciting forces are obtained. The QTF obtained from the analysis of irregular wave measurements are compared with results from experiments in bi-chromatic waves and with numerical predictions from a second order potential flow code.

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Wave forces on three-dimensional floating bodies with small forward speed

Journal of Fluid Mechanics ◽

10.1017/s002211209100006x ◽

1991 ◽

Vol 227 ◽

pp. 135-160 ◽

Cited By ~ 56

Author(s):

Jan Nossen ◽

John Grue ◽

Enok Palm

Keyword(s):

Velocity Potential ◽

The Body ◽

Wave Forces ◽

Forward Speed ◽

Floating Bodies ◽

Wave Drift ◽

Exciting Forces ◽

Wave Exciting Forces ◽

Wave Drift Damping ◽

The Mean

A boundary-integral method is developed for computing first-order and mean second-order wave forces on floating bodies with small forward speed in three dimensions. The method is based on applying Green's theorem and linearizing the Green function and velocity potential in the forward speed. The velocity potential on the wetted body surface is then given as the solution of two sets of integral equations with unknowns only on the body. The equations contain no water-line integral, and the free-surface integral decays rapidly. The Timman-Newman symmetry relations for the added mass and damping coefficients are extended to the case when the double-body flow around the body is included in the free-surface condition. The linear wave exciting forces are found both by pressure integration and by a generalized far-field form of the Haskind relations. The mean drift force is found by far-field analysis. All the derivations are made for an arbitrary wave heading. A boundary-element program utilizing the new method has been developed. Numerical results and convergence tests are presented for several body geometries. It is found that the wave exciting forces and the mean drift forces are most influenced by a small forward speed. Values of the wave drift damping coefficient are computed. It is found that interference phenomena may lead to negative wave drift damping for bodies of complicated shape.

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Computation of Hydrodynamic Interaction of Multiple Bodies in Waves With a Panel-Free Method

24th International Conference on Offshore Mechanics and Arctic Engineering: Volume 2 ◽

10.1115/omae2005-67316 ◽

2005 ◽

Author(s):

Wei Qiu ◽

Hongxuan Peng ◽

Sander M. Calisal ◽

Jianhong Wang

Keyword(s):

Hydrodynamic Interaction ◽

Gaussian Quadrature ◽

Time Domain Analysis ◽

Performance Study ◽

Floating Bodies ◽

B Splines ◽

Exciting Forces ◽

Wave Exciting Forces ◽

The Green Function ◽

The Time Domain

The hydrodynamic interaction of multiple floating bodies in waves has been computed in the frequency domain based on the panel-free method developed earlier for the time-domain analysis. The integral equations are first desingularized by removing the singularity in the Green function and then discretized by Gaussian quadrature over the exact geometry. Non-uniform rational B-splines (NURBS) surfaces are employed to represent the exact body surface. Robustness and accuracy of the method has been demonstrated by its application to vertically floating cylinders. Computed motions, hydrodynamic coefficients and wave exciting forces due to interactions are presented and compared with other published results. The numerical method has also been applied to the performance study of a wave energy converter. The computed results were compared with the experimental ones.

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Time-domain analysis of wave exciting forces on floating bodies at zero forward speed

Applied Ocean Research ◽

10.1016/0141-1187(89)90003-5 ◽

1989 ◽

Vol 11 (1) ◽

pp. 19-25 ◽

Cited By ~ 6

Author(s):

Robert F. Beck ◽

Bradley King

Keyword(s):

Time Domain ◽

Time Domain Analysis ◽

Domain Analysis ◽

Forward Speed ◽

Floating Bodies ◽

Exciting Forces ◽

Wave Exciting Forces

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Theory of Short Wave Excitation

Journal of Ship Research ◽

10.5957/jsr.1986.30.3.147 ◽

1986 ◽

Vol 30 (03) ◽

pp. 147-152

Author(s):

Yong Kwun Chung

Keyword(s):

Incident Wave ◽

Characteristic Length ◽

Finite Depth ◽

Short Wave ◽

The Body ◽

Wave Number ◽

Floating Body ◽

Wave Excitation ◽

Exciting Forces ◽

Wave Exciting Forces

When the wavelength of the incident wave is short, the total surface potential on a floating body is found to be 2∅ i & O (m-l∅ i) on the lit surface and O (m-l∅ j) on the shadow surface where ~b i is the potential of the incident wave and m the wave number in water of finite depth. The present approximation for wave exciting forces and moments is reasonably good up to X/L ∅ 1 where h is the wavelength and L the characteristic length of the body.

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Analysis on the Performance of Deckwetness of Sandglass-type and Cylindrical Floating Bodies

Journal of Ship Research ◽

10.5957/jsr.2016.60.3.145 ◽

2016 ◽

Vol 60 (03) ◽

pp. 145-155

Author(s):

Ya-zhen Du ◽

Wen-hua Wang ◽

Lin-lin Wang ◽

Yu-xin Yao ◽

Hao Gao ◽

...

Keyword(s):

Transfer Functions ◽

Linear Response Theory ◽

Second Order ◽

Irregular Waves ◽

Wave Loads ◽

Floating Bodies ◽

Drift Motion ◽

First Order ◽

Series Of Experiments ◽

Deck Wetness

In this paper, the influence of the second-order slowly varying loads on the estimation of deck wetness is studied. A series of experiments related to classic cylindrical and new sandglass-type Floating Production, Storage, and Offloading Unit (FPSO) models are conducted. Due to the distinctive configuration design, the sand glass type FPSO model exhibits more excellent deck wetness performance than the cylindrical one in irregular waves. Based on wave potential theory, the first-order wave loads and the full quadratic transfer functions of second-order slowly varying loads are obtained by the frequency-domain numerical boundary element method. On this basis, the traditional spectral analysis only accounting for the first-order wave loads and time-domain numerical simulation considering both the first-order wave loads and nonlinear second-order slowly varying wave loads are employed to predict the numbers of occurrence of deck wetness per hour of the two floating models, respectively. By comparing the results of the two methods with experimental data, the shortcomings of traditional method based on linear response theory emerge and it is of great significance to consider the second-order slowly drift motion response in the analysis of deck wetness of the new sandglass-type FPSO.

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Extreme Response of Very Large Floating Structure Considering Second-Order Hydroelastic Effects in Multidirectional Irregular Waves

Journal of Offshore Mechanics and Arctic Engineering ◽

10.1115/1.4001415 ◽

2010 ◽

Vol 132 (4) ◽

Cited By ~ 1

Author(s):

Xujun Chen ◽

Torgeir Moan ◽

Shixiao Fu

Keyword(s):

Second Order ◽

Irregular Waves ◽

Bending Moments ◽

Floating Structure ◽

First Order ◽

Fluid Forces ◽

Principal Coordinates ◽

Vertical Displacements ◽

Exciting Forces ◽

Nonlinear Fluid

Hydroelasticity theory, considering the second-order fluid forces induced by the coupling of first-order wave potentials, is introduced briefly in this paper. Based on the numerical results of second-order principal coordinates induced by the difference-frequency and sum-frequency fluid forces in multidirectional irregular waves, the bending moments, as well as the vertical displacements of a floating plate used as a numerical example are obtained in an efficient manner. As the phase angle components of the multidirectional waves are random variables, the principal coordinates, the vertical displacements, and the bending moments are all random variables. Extreme values of bending moments are predicted on the basis of the theory of stationary stochastic processes. The predicted linear and nonlinear results of bending moments show that the influences of nonlinear fluid forces are different not only for the different wave phase angles, but also for the different incident wave angles. In the example very large floating structure (VLFS) considered in this paper, the influence of nonlinear fluid force on the predicted extreme bending moment may be as large as 22% of the linear wave exciting forces. For an elastic body with large rigidity, the influence of nonlinear fluid force on the responses may be larger than the first-order exciting forces and should be considered in the hydroelastic analysis.

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First and Second Order Wave-Current Interactions for Floating Bodies

Volume 1: Offshore Technology ◽

10.1115/omae2012-83409 ◽

2012 ◽

Cited By ~ 2

Author(s):

Charles Monroy ◽

Yann Giorgiutti ◽

Xiao-Bo Chen

Keyword(s):

Field Method ◽

Boundary Integral ◽

Second Order ◽

Boundary Integral Method ◽

Diffraction Radiation ◽

Floating Bodies ◽

Order Problem ◽

First Order ◽

Wave Drift Damping ◽

Order Quantities

The influence of current in sea-keeping problems is felt not only for first order quantities such as wave run-ups in front of the structure, but also mainly for second order quantities. In particular, the wave drift damping (which is expressed as the derivative of drift force with respect to the current) is of special interest for mooring systems. The interaction effects of a double-body steady flow on wave diffraction-radiation is studied through a decomposition of the time-harmonic potential into linear and interaction components. A boundary integral method is used to solve the first order problem. Ultimately, a far-field method is proposed to get access to second order drift forces.

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