Reprinted from ‘Proceedings of the Royal Society of London’ 
Series A No. 963 vol. 175 pp. 409-421 July 1940 
The pressure of water waves upon a fixed obstacle 
By T. H. Havetock, F.R.S. 
(Received 29 March 1940) 
The diffraction of plane water waves by a stationary obstacle with vertical 
sides is examined, in particular the variation of amplitude along the sides 
and the average steady pressure due to the wave motion. Results similar 
to those in other diffraction problems are obtained for an infinite plane and 
for cylinders of circular or parabolic section, and approximations are made 
for sections of ship form. The examination was made in view of possible 
applications in the problem of a ship advancing through a train of waves, 
and the results are discussed in relation to the average additional resistance 
in such circumstances. It appears that the mean pressure obtained on 
diffraction theory from the second order terms can only account, in general, 
for a small proportion of the observed effect; the motions of the ship, 
and in particular its oscillations, are essential factors in the problem. 
1. The problem to be considered is the resultant fluid pressure upon an 
obstacle held in position in a train of plane waves advancing over the surface 
of the water. In a previous paper (1937) I considered the additional 
resistance on a ship moving through waves, the work being restricted to the 
first order effect, a purely periodic force which may have an amplitude 
comparable with the resistance to the ship in still water; further, for the 
type of ship considered, the usual approximations were made and these 
included neglecting the effect of reflected or scattered waves as being of the 
Vol. 175. A. (18 July 1940) 
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