Besah and Liu 



DISCUSSION 



Reuven Leopold 



U.S. Navy Naval Ship Engineering Center 

 Hyattsville 3 Maryland 3 U.S.A. 



Thank you. I haye a few more questions. 



The authors stated that predicted mode shapesand frequencies 

 are nearly always accurate when 3-D hydro -loading is used. Could 

 they elaborate on the techniques used ? How many modes were extract- 

 ed per typical model, and what is the cost and length of calculation 

 time for such an effort ? 



REPLY TO DISCUSSION 



Peter K. Besch 



Naval Ship Research and Development Center 

 Bethesda, Maryland^ U.S.A. 



We have extracted ten modes for each strut at each speed. The 

 accuracy would normally only remain good through four or five modes. 

 But we have found that it is only necessary to analyze the first four 

 modes to conduct the stability analysis. Therefore the accuracy of 

 higher modes would not be particularly important in our flutter analy- 

 sis. The calculation is fairly efficient in that one detailed flutter ana- 

 lysis can be conducted in approximately ten minutes, on a CDC 6700 

 computer. 



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