Ramamonjiarisoa (1973) and Coantic and Favre (1973) presented a 

 similar figure, which does not duplicate any of the data by Hidy and 

 Plate, and showed by numerous laboratory and field wave-generation 

 spectra that the width of the dimensionless spectriim peak is broader 

 for ocean than laboratory waves. 



Colonell (1972), in describing a new wind-wave research facility at 

 the University of Massachusetts, stated: "...While it is not claimed 

 to be a replica of the ocean environment, it does provide a reasonable 

 simulation of ocean surface characteristics...." 



Differences between wind-generated waves in the laboratory and field 

 result from two fundamental causes. A wave-generating region 100 to 200 

 meters (330 to 660 feet) in length is extremely short for natural con- 

 ditions, and extremely long for a laboratory. Consequently, the lab- 

 oratory-generated waves correspond to very short fetches at prototype 

 scale, or they must be generated by very low windspeeds; thus, only very 

 short waves with low wave heights can be obtained. The resulting waves 

 are generally too small to permit accurate measurement of their effects. 

 For such waves, surface-tension effects can distort laboratory results. 

 Both air and water must be confined in the laboratory. This confinement 

 leads to the growth of turbulent boundary layers , not present at pro- 

 totype scale, on the sides and roof of the wind tunnel. Boundary layers 

 also form on the sides and may form on the bottom of the wave flume. 

 These side boimdary layers may be either viscous or turbulent depending 

 on conditions, and they have no counterpart at prototype scale. These 

 extraneous boundary layers in both air and water give rise to other 

 phenomena (not present in the prototype scale) which significantly affect 

 the exchange of momentum between air and water, and suppress other phenomena 

 now believed to be important in nature. The importance of the secondary 

 phenomena on wind-wave generation in the laboratory was not clearly 

 recognized until about 1972. 



Agreement between the spectra of wind waves generated in the laboratory 

 and wind waves observed in nature should be improved by vising a programable 

 wave generator to produce an initial wave field which is acted on by the 

 wind. This procedure is now being used by several coastal engineering 

 laboratories. It appears that programable wave generators, with or with- 

 out wind, lead to improvement in modeling natural waves. It has not been 

 established that any quantitative improvement in modeling wave conditions 

 of engineering importance can be achieved by adding a wind tunnel on top 

 of a wave tank equipped with a programable wave generator. The capabilities 

 of programable wave generators have not been fully exploited. The further 

 development of more versatile wave generators and, if possible, develop- 

 ment of a technology for establishing surface currents in the wave channels 

 appear to offer more potential benefits for engineering application to 

 coastal engineers for the costs involved than the construction of a wind- 

 wave research facility. 



Possible uses of a combination wave channel and wind tunnel in coastal 

 engineering research and difficulties which must be overcome to obtain 

 satisfactory results, are discussed later in this report. 



