Twenty-Fourth Symposium on Naval Hydrodynamics (2003) / Chapter Skim
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Development, Validation, and Application of a Time Domain Seakeeping Method for High-Speed Craft with a Ride Control System
Development, Validation, and Application of a Time Domain Seakeeping Method for High-Speed Craft with a Ride Control System
Pages 475-490
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From page 475... ...
It is designed to take ship hulls with lifting surfaces into account. Validation results are presented for three basic cases: damping forces on an oscillating lifting surface operating beneath a free surface, wave excitation forces on a lifting surface advancing in waves and wave induced motions of a destroyer hull form operating in head seas.
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From page 476... ...
Incident waves from arbitrary directions are present. All vorticity in the flow is restricted to a thin region consisting of the outer skin of the lifting surface and its wake sheet.
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From page 477... ...
For lifting surfaces, it does not have an unique solution for the conditions implied so far. A wake model needs to be established where conditions are specified which relate to the vortex strength at the trailing edge and the location and shape of the wake sheet.
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From page 478... ...
By using doublet elements on the lifting surface and (equivalent) vortex ring elements on the wake sheet with strength ~ as a discretization of a continuous vortex sheet and by transferring each time step the nett circulation at the trailing edge elements into the wake elements, these requirements are satisfied.
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From page 479... ...
The first term on the right hand side denotes the normal velocity components due to body motions and incident waves, the second and third terms denote the normal induced velocity due to wake vortex elements and lifting surface doublet panels, the fourth and fifth terms account for the normal induced velocity components due to the memory effect of hull and lifting surface source panels, the sixth term accounts for the normal induced velocity components due to the memory effect of waterline source panels and the last term on the right hand side accounts for the normal induced velocity due to the memory effect of lifting surface and wake sheet doublet panels. The vector V denotes the velocity components due to the body translational velocities, Vb= (u,v,w)
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From page 480... ...
The concept of influence coefficients is again used, for determining the induced velocities due to wake sheet elements at the lifting surface collocation points. Furthermore, the integration of the aG flat terms with respect to time can be performed analytically for wake sheet vortex elements since the distance between body collocation points and wake elements is constant for each (~)
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From page 481... ...
The terms on the right hand side of Of are time derivatives of the memory integral and can be evaluated in a similar way as the free surface Green function terms. Furthermore, relations between the source strength and the corresponding potential and the source strength and the normal velocity component are used to obtain a relation for the A contribution: (T)
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From page 482... ...
Lifting surface below free surface As a first validation case a comparison is made between experimental and computed results for the lift of an oscillating hydrofoil below the free surface. Experimental results are obtained from Kyozuka (1992~.
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From page 483... ...
6 Pitch response of DOGS 1 destroyer in head waves. High speed mono hull ferry The next case concerns a high speed (FnL=0.67)
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From page 484... ...
Figures 8 and 9 show the heave and pitch response in head waves, without T-foils. It is seen that without transom stern flow model the peak pitch response is significantly overestimated.
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From page 485... ...
In waves, the vortex strength of the forward foil wake sheet will vary in time and in space. The aft foil lift force and its phase relative to the motion of the ship will be modified continuously.
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From page 486... ...
are given with and without viscous damping in the vertical plane. It is clear that adding viscous damping is necessary for an adequate prediction of the peak responses.
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From page 487... ...
Computed results for damping and wave excitations forces on a lifting surface advancing below a free surface are in fair agreement with experimental data. Next the heave and pitch motions for a destroyer hull form sailing in head waves are adequately predicted.
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From page 488... ...
Future developments include a more accurate evaluation of the free surface Green function for shallowly submerged panels by using a combination of analytical and numerical integration and the inclusion of viscous damping for roll, sway and yaw motions. ACKNOWLEDGEMENTS The author gratefully acknowledges the permission of Rodriguez Engineering SrL.
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From page 489... ...
van, "Computational Methods for Hydrofoil Craft in SteadY and Unsteady Flow" Ph.D. Thesis , , Delft University of Technology, Department of Naval Architecture and Marine Engineering, March 1999.
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From page 490... ...
It is possible to approximate the real wake sheet shape in a nonlinear method, including wake sheet roll-up, but at a substantial computational burden. Experimental results on the interaction between two tandem foils running in head waves show that a fixed position forward foil wake is allowed for small to moderate heave and pitch motions.
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