Experiments on nonuniform currents are desirable. They would be 

 particularly valuable in showing how eddies and turbulence accompanying 

 the currents modify refraction by the currents. If in some 

 circumstances the eddies and turbulence dominate the waves, prevailing 

 views on the relevance of refraction will need to be revised. 



Detailed measurements of the type being done by Kemp and Simons 

 (University College London, personal communication, 1981) are very 

 important for applications. There should be more attempts to measure 

 waves and currents which are not collinear. Such measurements should be 

 possible in existing large wave basins also equipped for generating 

 currents. 



There are many other fields of science and engineering employing 

 wave theory (e.g., quantum physics, radio propagation, plasma physics, 

 internal waves in atmosphere and ocean, acoustics and seismology). It 

 could be very valuable if workshops were arranged to enable 

 practitioners in these fields to see what can be learned from their 

 different disciplines. For example, Blokhintsev (1956) was the first 

 (in 1946) to correctly deal with radiation stress in acoustics, and 

 later Longuet-Higgins and Stewart (1960, 1961, 1962, 1964) and others 

 independently introduced it to water waves. 



IV. CONCLUSIONS 



This review of wave-current interaction shows that there is a good 

 theoretical framework for the refraction of water waves by large-scale 

 currents which are uniform in depth. However, with minor exceptions, 

 the theory has only been applied to very simple current distributions 

 and has not been subject to rigorous experimental or field verification. 

 Even so, it is clear that simple current fields can strongly refract 

 waves, and both observations and experiments show changes in wave 

 properties qualitatively consistent with theory. A start has been made 

 on treating refraction and diffraction caused by both depth and 

 currents, using a computer. 



Effects caused by varying velocity with depth is given some 

 emphasis. The major effects of interaction with waves in this case are 

 the way in which the change in the velocity field affects the mean 

 bottom stress and hence influences the mean current, and the strong 

 effect of surface shear on wave breaking. 



Once wave and current properties are known, their major engineering 

 applications are to the prediction of forces on structures and sediment 

 transport. Both of these applications involve a triple interaction 

 problem: waves, current, and structure; or waves, current and sediment. 

 Yet even the double interaction cases (waves and structure; or waves and 

 sediment) still require fundamental research. 



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