The Proceedings Fifth International Conference on Numerical Ship Hydrodynamics (1990) / Chapter Skim
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Interaction between Current, Waves and Marine Structures
Interaction between Current, Waves and Marine Structures
Pages 513-528
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From page 513... ...
It is shown numerically and analytically how problems with the mjterms can be avoided. Numerical results for horizontal and vertical mean wave forces on floating vertical cylinders of finite length are presented.
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From page 514... ...
, a non-dimensionalized frequency of oscillation, the roughness ratio and the ratio between the current velocity U and the maximum horizontal oscillatory ambient fluid velocity UM in the current direction. Obviously the flow will always separate from a body with sharp corners in any type of ambient flow.
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An example on calculations of the real part of the velocity potential due to a harmonically oscillating source satisfying either free surface condition (11)
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arise because the steady motion potential does not satisfy the body boundary condition on the instantaneous body surface correct to °((a) The derivation is based on a Taylor expansion, which means the formulation is breaks down at sharp corners.
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. When we have solved the equations of the first order motions, we can find the mean wave forces and moments correctly to o((a2)
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By time averaging equation (21) , assuming that SO is a horizontal plane at great depth and using boundary condition on S it follows that the mean wave drift forces can be written F = -p || ( ~ n + V V )
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. The mean wave forces can also be obtained by using direct pressure integration.
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nj ds (28) This formula is valid for a body without sharp corners, wall-sided at the free surface and when As satisfies the rigid free surface condition.
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What we have done now is to analytically isolate the difficulties with the mj-terms. This procedure is also valid when ship motions at forward speed is evaluated.
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~ ~ 1~/,~ =~ 0 3~ 0~ 0~ 11~ 9 Fig. 10 Numerical results of horizontal driftforces F2 for U/~i ~ 0.000 U/~ ~ 0.0479 with direct pressure integration method and a method based on conservation of momentum' and energy.
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14 Numerical results of vertical mean wave forces F3 with direct pressure integration method and a method based on conservation of momentum and energy Data presented as a function of R/6L (AL defined in the figure 11)
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A method to calculate mean wave forces based on conservation of fluid momentum is presented. It is demonstrated that a direct pressure integration method can lead to large errors in prediction of mean wave forces when the body has sharp corners.
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1981, Contribution a ['etude Theorique et Experimentale des Efforts du Second Ordre et du Comportement Dynamic d'une Structure Marine Sollicitee par une Haul Reguliere et un Courant, These de Docteur Ingenieur (Ecole Nationale Superieure de Mechanique)
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3) The authors experienced some problems even for the zero speed case in determining the wave drift forces based on the pressure integration, because of the presence of sharp corners.
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From page 527... ...
If one should calculate the wave drift damping coefficient that is proportional to the slow drift velocity, the two approaches should be equal. However if one want to study wave current interaction and in particular the wave elevations around the structure, the two different approaches are different.
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