Forces on an A.C.V. Executing an Unsteady Motion 



DISCUSSION 



Jorgens Strom-Tejsen 



Naval Ship Research and Development Center 

 Bethesda s Maryland s U.S.A. 



I should like to take the opportunity to ask Dr Doctors a few 

 questions about the work he has carried out. Dr Doctors has shown 

 in his paper that by smoothing the pressure distribution some of the 

 very pronounced humps and hollows in the resistance curve disappear. 

 This is the case in particular at the lower Froude numbers, whereas 

 at the higher Froude numbers the last hump seemed to have been af- 

 fected very little. I would like to ask Dr Doctors if he has any similar 

 experience when rounding the corners of the surface of a big shift ? 

 One would expect that rounding the corner, actually using the right 

 angle, a pressure platform would be round the corner, and in a simi- 

 lar way the humps and hollows at the lower Froude numbers would 

 disappear. 



This brings me to another question. Actually, the linearised 

 wave resistance theory being used, we can only expect it to be accu- 

 rate at the highest Froude numbers, whereas going down to the lower 

 Froude numbers, on the assumptions we make, namely, that the wave 

 slope is low is not valid any longer. Has it any importance at all, this 

 smoothing or rounding away of the corner ? If this is not so at the 

 lower Froude numbers, the wave resistance theory would not hold at 

 all any how. 



We saw some rather interesting figures showing the effect 

 when the surface effect shift was at the yaw angle or drift angle. In 

 some cases the side force was negative and in other cases it was po- 

 sitive. This means that in certain cases the surface effect shift would 

 heel to one side and in other cases it would heel to the other side. I 

 wonder if Dr Doctors could clarify this sine convention, and give us 

 an idea about whether it is heeling away, or in what way it is heeling, 

 relative to the drift angle he has been using. 



Finally, I would like to indicate that at the Naval Ship Research 

 and Development Center we have made some somewhat similar com- 

 putations, using pressure distribution, not smooth but actually using 

 a staircase variation so that the pressure distribution is varied from 



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