OCEAN WAVE SPECTRA 
AND SHIP APPLICATIONS 
Ming-Shun Chang 
Naval Shtp Research and Development Center 
Bethesda, Maryland, U.S.A. 
ABSTRACT 
This paper presents the results of two studies : one 
dealing with the analytical representation of unidi- 
rectional wave spectra, and the other dealing with 
experimental determination of directional wave spec- 
tra. 
(1) A two-parameter wave-spectrum formulation 
for determining the seakeeping qualities of ships was 
evaluated by application to hindcast data for the 
North Atlantic Ocean. Computations indicate that the 
two-parameter representation does not properly dis- 
tribute wave energy over the full range of wave fre- 
quencies. 
(2) An experiment was conductedina large seakeep- 
ing basin toassess techniques for determining direc- 
tional wave spectra from wave elevation measure- 
ments obtained with sonic probe arrays. The mea- 
surements were found to be sufficiently accurate for 
analysis of the wave directions, when the direction- 
al spectra are approximated bya ninth-order Fourier 
series. 
INTRODUCTION 
In order to describe the properties of ocean waves, one consi- 
ders the seaway as a random process having a spectral representa- 
tion. The spectrum of ocean waves is two-dimensional, and thus it is 
a function of both wave frequency and wave direction. It is difficult to 
obtain a directional wave spectrum, and in many applications the 
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