In the second case the velocity fields of the two waves are of the 

 same order of magnitude. Interaction equations are derived, and it is 

 noted that they are identical to equations for capillary-gravity wave 

 interaction derived by Kawahara, et al. (1975). The equations are not 

 interpreted physically. 



Coastal Engineering Significance . This type of problem is important in 

 the wave-current context since it demonstrates the fact that the current 

 field is itself affected by the waves. Analysis of this type of problem 

 has proceeded much farther than that of any other wave-current 

 interaction problem. Further study of work such as this may increase 

 understanding of the general problem of wave-current interaction. 



19. HEDGES, T.S., BURROWS, R., and MASON, W.G., "Wave-Current Inter- 

 action and its Effect on Fluid Loading," MCE/3/79, Department of 

 Civil Engineering, University of Liverpool, England, Dec. 1979. 



Keywords. Currents, Unidirectional; Forces on Cylinders; Forces on 

 Structures; Review; Spectra; Statistics; Theory. 



Discussion. The report starts with a simplified review of wave-current 

 interaction and waves propagating in a single direction onto a current 

 with the same or opposite direction. Attention is drawn to the high- 

 frequency limits of a spectrum and its "equilibrium range" due to 

 breaking. Several examples are given of transformed spectra and of 

 waves generated on a current. 



The above spectra are then used in a variety of calculations for 

 the probability distributions of horizontal forces on vertical 

 cylinders. These calculations use the results of Borgman (1965, 1967), 

 which are based on the Morison equation for the drag. A further section 

 then uses these results and considerations of wave climate to make long- 

 term force distribution estimates. 



Coastal Engineering Significance. This report gives a convenient up-to- 

 date summary of methods that are used to estimate forces on structures 

 in the presence of waves and currents. There are a considerable number 

 of simplifications in the analysis, e.g., unidirectional currents and 

 waves, Gaussian statistics, and Morison's equation. However, in con- 

 sidering general cases it would not be possible to progress far without 

 them. The variety of examples may be useful for getting an appreciation 

 of the subject. 



20. HUANG, N.E., et al., "Interaction Between Steady Non-Uniform 

 Currents and Gravity Waves with Applications for Current Measure- 

 ments," Journal of Physical Oceanography , Vol. 2, No. 4, Oct. 

 1972, pp. 420-431. 



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