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

Drilling and production of oil by semi submersible take place in many locations throughout the world. Generally, floating structures play an important role in exploring the oil and gas from the sea. The force and motion prediction of offshore structures may be carried out using time domain or frequency domain models or model tests. In this paper the frequency domain analysis used because it is the simplified and linearized form of the equations of motion. The time domain analysis, unlike frequency domain models, is adequate to deal with non-linearities such as viscous damping and mooring forces, but it requires sophisticated solution techniques and it is expensive to employ. In this paper, the wave exciting forces of a free floating semi-submersible were carried out using 3D source distribution method within the scope of the linear wave theory. The results obtained from computations were also compared with the results obtained using commercial software MOSES and WAMIT.

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Time-domain analysis of side-by-side floating bodies by the three-dimensional hybrid Green function method

Ships and Offshore Structures ◽

10.1080/17445302.2020.1742493 ◽

2020 ◽

pp. 1-13

Author(s):

K. Tang ◽

Q. Z. Zhen ◽

L. Hong ◽

D. P. Jiang ◽

X. Chen ◽

...

Keyword(s):

Green Function ◽

Time Domain ◽

Function Method ◽

Three Dimensional ◽

Time Domain Analysis ◽

Domain Analysis ◽

Floating Bodies ◽

Green Function Method

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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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