WIND- GENERATED WAVES FOR LABORATORY STUDIES 



by 

 D. Lee Harris 



I. INTRODUCTION 



The need for imderstanding and controlling or moderating the effects 

 of wind-generated waves is one of the most distinctive requirements of 

 coastal engineering. There is also a need to design, build, and maintain 

 structures for the protection of low- lying coastal areas from storm 

 surges. The meteorological, hydraulic, and sedimentary processes involved 

 are variable, complex, and often deductive. Theoretical development and 

 engineering judgment have proven inadequate for most of the needed designs 

 and laboratory studies of many of the processes involved have been 

 required to provide design guidance. Thus, laboratory facilities for 

 studies of coastal processes have become important coastal engineering 

 tools. Long, narrow channels with a mechanical wave generator at one end 

 and a beach or stilling basin for absorbing the wave energy at the other 

 end, are used for testing wave forces on slopes and component members of 

 marine structures. The application of wave channels for testing components 

 of structures is analogous to the aeronautical engineer's use of wind 

 tunnels for testing aircraft components. Wave channels are also useful 

 for testing instabilities of revetments, breakwaters, seawalls, and reser- 

 voirs to wave action. Wide, shallow basins (usually with wave generators, 

 and occasionally with tide generators at one side and absorber beaches 

 around most of the remaining periphery) are used for modeling partial or 

 entire harbor complexes and studying beach processes. Both types of lab- 

 oratory facilities are also used for many other purposes. 



Although the mechanically generated waves used in most wave channels 

 and basins are generally more regular and symmetric than the waves encoun- 

 tered in nature, experimental results obtained have greatly reduced the 

 uncertainty in predicting the effectiveness of many engineering designs and 

 the consequent cost of building structures which are not adequate for 

 their purpose, or structures which are more massive and expensive than they 

 need to be. 



Success with relatively simple channels and basins in which measurements 

 of the effects of small water waves or small-scale structures are used to 

 predict the effects of big waves on prototype structures stimulates the 

 coastal engineer to think of small-scale studies involving both wind and 

 waves which might be used to improve the knowledge of wind-generated waves 

 for engineering studies and perhaps to evaluate the combined effects of 

 wind and waves on marine and coastal structures. Plate and Nath (1969) 

 explicitly suggested this possibility. Shemdin (1972) discussed an experi- 

 ment based on this concept. Bole (1973) discussed many physical processes 

 of engineering importance which might be studied effectively in a combina- 

 tion wave tank-wind tunnel. Bole also listed many difficulties which must 



