Eighteenth Symposium on Naval Hydrodynamics (1991) / Chapter Skim
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Effect of Viscous Damping on the Response of Floating Bodies
Effect of Viscous Damping on the Response of Floating Bodies
Pages 149-156
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From page 149... ...
A method of matching precalculated results for separated oscillatory flow past an isolated edge at each vortex shedding region of the outer potential flow field of the body in waves has been extended to three-dimensional floating bodies by two different methods. In the first method the pressure field due to a local separated flow computed by a discrete vortex method, is applied at all vortex shedding edges of the hull.
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From page 150... ...
The outer flowfield associated with the incident wave field and general motion of the body is solved with a full bound ary integral method. Since this r.`ethod is based on inviscid potential flow theory which cannot model flow separation, the flow field is singular along the lengths of bilges and other shedding 'edges.
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From page 151... ...
For each wave frequency the total potential may be written in terms of the separate potentials for the undisturbed incident wave, the wave scattered by the body considered to be fixed and rigid, and the waves radiated by the body in its six degrees of freedom, where it is understood that the real part only of the potential is considered: 6 do e + ~ (j Hj + ¢7 edict (2) j=1 The potential satisfies the linearised free surface condition `,,2 ¢,j + g 6~/by = 0, j = 0 ...
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From page 152... ...
. It is convenient in the present panel method to represent the dipole by a piecewise constant distribution of source dipole density aligned in the direction normal to the panel surface, and hence to the vortex dipole direction, with the panel lying along the external bisector of the edge angle.
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From page 153... ...
Experimental data contain ing sufficient information to compute these cases however are scarce. Three cases have been studied, the first and second being cases of barge response in beam seas and the third a forced roll case.
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From page 154... ...
'Jajce potential theory result without vortex damping is shown calculated by the present thriee dimensional potential panel method. the agreement between the predicted and measured damping coefficients is very good when the vortex panels are incorporated in the computation.
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From page 155... ...
-· - , ~ = 0.05 red., - + - , ~ = 0.10 red.,-x-, ~0.20 red. Results for three different forced roll amplitudes have been plotted and it is apparent that the vortex panel method does predict the increase in hydrodynamic damping with amplitude quite accurately.
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From page 156... ...
The matched edge technique has been applied to both cases, the forced roll calculations being reported in a previous paper. The viscous edge panel technique has so far been applied to the case of forced roll only.
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