electric recorders; however, the scale effects due to variations in the 

 concentration of entrained air in model waves, compared to prototype 

 waves and the difficulties of generating model waveforms that correspond 

 to the complex wave spectra of prototype waves, cause large variations 

 in individual pressure measurements that are difficult to interpret as 

 prototype shock pressure impulses. Research is needed to accurately 

 determine the effects of model scale and operating procedures on the 

 model-to-prototype transference equations for breaking wave pressures. 



(3) Floating Breakwaters . Scale effects in the oscillating 

 characteristics of floating structures are negligible if care is taken 

 to construct the breakwater geometrically and dynamically similar. The 

 elastic and weight properties of the mooring lines can be modeled with 

 enough accuracy in most cases. The largest errors that occur in this 

 type of model study are those obtained by using monochromatic waves and 

 the necessity of using two-dimensional rather than three-dimensional 

 model structures. Most tests of floating structures are conducted in 

 this manner for economic necessity. Studies are needed to determine the 

 variations in test results for floating breakwaters with and without 

 mooring restraints, for the conditions of two-dimensional, monochromatic 

 waves compared with those using selected wave spectra and three-dimensional 

 floating structures. 



(4) Pneumatic Breakwaters . A considerable number of model and 

 prototype studies have been done to determine the efficacy of pneumatic 

 breakwaters. However, the prototype tests were not performed over a 

 sufficient range of the primary variables, and the model studies have 

 not been conducted so that accurate transference equations with known 

 scale effects can be determined. Additional research is urgently needed 

 to determine scale effects with sufficient accuracy that the design engi- 

 neer can calculate, for a proposed installation, the quantity of free air 

 that must be delivered by a compressor to the manifold system to obtain 

 the required reduction in wave height to ensure satisfactory mooring con- 

 ditions. These scale-effect tests should be performed under the suggested 

 program of tests outlined in Section VI, 2, f. 



(5) Hydraulic Breakwaters . Hydraulic breakwaters are similar to 

 pneumatic breakwaters in that the mechanism that effects a reduction in 

 wave height is a system of horizontal currents. Scale-effect tests are 

 needed to obtain accurate data concerning the discharge of water from the 

 orifices of the manifold system required for the required reduction of 

 wave heights. However, the tests required are not as numerous or as 

 complicated as those needed for pneumatic breakwaters. The scale-effect 

 tests for hydraulic breakwaters should follow the suggestions given in 

 Section VI, 2, g. 



4. Model Operation . 



a. Selection of Test Conditions . In general, test conditions selected 

 for model studies concerning the stability of coastal structures are deter- 

 mined by the type of structure under consideration, the purpose and scope 



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