I-Min Yang 



(2) Since the main purpose of this paper is to present an approach 

 to find the nonlinear, asymmetrical motion of a moored ship, I have 

 omitted the discussion of determining the hydrodynamic coefficients. 

 In fact, I just used the data discussed in published papers. 



(3) The effect of nonlinearity depends heavily on the nonlinear sys- 

 tem. If the nonlinearity in the force -displacement relationship is very 

 large, like the case of mooring lines, the resonant period determined 

 by linear analysis is quite different from that determined by nonlinear 

 analysis. For example, in one case I considered, it may shift from 



20 seconds to 50 seconds. 



(4) This paper discussed an analytical approach to investigate the 

 motion of a moored ship. It seems to me that the lack of figures does 

 not affect the understanding of this approach. 



DISCUSSION 



Ernest O. Tuck 



University of Adelaide 

 Adelaide 3 Australia 



I do not want to let one of Dr Saint-Denis's remarks pass. I 

 forget which point number it was but it was the business about the ex- 

 citing force being of only one type when he thought it ought perhaps to 

 be of several types. I think this is quite erroneous. There is no rea- 

 son to believe that the excitation is anything but the most general li- 

 near excitation in this particular problem. From my reading of the 

 paper there is an input frequency-dependent phase as well as input 

 amplitude, so I think that that particular point put by Dr Saint -Denis 

 should not be allowed to stand. 



Another point of his was that there is nothing new in this paper 

 and I think that is quite wrong. I think myself that it is quite a good 

 paper. I think Dr Yang explained about the matrix K^ . The fact that 

 it is diagonal does not necessarily mean that one is considering only 

 self -linearities. I think that some of this criticism is simply misplac- 

 ed and that the people making the criticism should read the paper a 

 bit more carefully. 



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