Determination of Aerohydrodynamic Performance of ACVs 



Pressure scales linearly, and the height scales linearly ; 

 atmospheric pressure is not scaled in any facility, at least it is not 

 scaled at speeds appropriate for ACV. The situation is such that if 

 you consider this effect, the natural frequency of the system is 

 scaled linearly while for Froude scaling it varies as the square root 

 of your scale ratio. Therefore you have shifted natural frequency 

 coincidence well out of proportion, depending upon your scale ratio. 

 In addition, the relative damping, that is the matter of so-called 

 relative to critical damping, also changes due to scaling because of 

 the operation pressure system. The resulting question is, what con- 

 sequence does this have upon the motion ? 



Some results have been obtained based on analysis and simu- 

 lation work, and have been published in the open literature, on this 

 particular point. It shows the following. You can predict the vertical 

 acceleration responses from tests in waves at model scale at atmos- 

 pheric pressure. Unfortunately the prediction is unconservative. You 

 think you are getting by with a certain acceleration, and if you work 

 out the equations which you validated by your original procedure to 

 correlate with your testing at non-scaled atmospheric pressure, you 

 then scale the atmospheric pressure to simulate real life and your 

 accelerations are larger. However I do not say that there is no busi- 

 ness for towing tanks in getting information for ACV. I do say there 

 is business for theoreticians, together with towing tanks, to get the 

 right information. 



REPLY TO DISCUSSION 



Vjacheslav N. Treshchevsky 



Kryloff Research Institute 

 Leningrad^ U.S.S.R. 



I am grateful to you for your comment. I would say that the 

 problems of scale effect which you mention are taken into acount 

 and special experiments have been and are being made in order to 

 exclude wide errors connected with the scale effect in various types 

 of experiments. 



You mentioned the negative value of the term corresponding 

 to mass which is on one of the illustrations. It is difficult to explain 

 it quite correct, I think the reason of the phenomena is in the inter- 



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