A form o£ scale effect in models where intermediate and long waves 

 are investigated is caused by the reflection of wave energy from the 

 ocean boundaries of the model. It is common practice to use wave absorb- 

 ers around the ocean boundaries of the model and in front of the wave 

 generator. If these absorbers are not adequate, the wave energy that 

 is radiated from the harbor and wave reflections from breakwaters and 

 adjacent beaches will be trapped in the ocean basin part of the model 

 and will distort the amplification factors or the frequency- response 

 curves of the harbor basins. Considerable work relating to this problem 

 has been accomplished by Ippen and Raichlen (1962), Goda and Ippen (1963), 

 Ippen and Goda (1963), Keulegan (1968), and others, but satisfactory de- 

 sign procedures to ensure sufficient absorption of wave reflections from 

 the ocean boundaries of harbor wave action model studies of intermediate- 

 and long-period waves are not presently available. 



Another form of scale effect in intermediate- and long-period wave 

 action models is the differences in the response characteristics of har- 

 bor basins, model-to-prototype, caused by the lack of similarity in the 

 dissipation of wave energy in harbor basins. Lee and Raichlen (1971) 

 described this problem and concluded that sufficiently accurate answers 

 are not currently available to design engineers and that additional re- 

 search in this area is needed. 



4. Model Construction and Operation . 



a. Construction . Harbor wave action models are constructed in shel- 

 ters to provide protection against the elements and to ensure that air- 

 flow across the water surface does not form ripples or small gravity 

 waves. Such extraneous waves are within the range of wave heights meas- 

 ured in the model, and may, therefore, interfere with obtaining accurate 

 test data. The height of shelter for this type of model should be such 

 that good photos of wave patterns can be obtained. Except for models of 

 small harbors with limited problem areas, camera heights of 30 to 40 feet 

 are preferred. Harbor wave action models are constructed of sheet steel, 

 sheet aluminum, or masonite templets graded to an accuracy of about ±0.002 

 foot. The templets are placed about 2 to 3 feet apart in the offshore 

 ocean areas where the depth contours are generally regular and there are 

 no abrupt bottom slopes, and about 0.5 to 1.5 feet apart in the more rug- 

 ged and irregular parts of the harbor area. The space between the tem- 

 plets is filled to about 0.2 foot of the top with sand, the sand is 

 compacted, and the remaining space between the sand bed and the tops of 

 the templets is filled with a cement mortar mix using mason sand with 

 one part cement and three parts sand. Because wave height reduction 

 with distance traveled in harbor wave action models occurs primarily by 

 energy loss in the viscous boundary layer at the rigid bottom, and be- 

 cause dissipation of energy is not a function of bottom roughness if the 

 roughness elements do not extend beyond the viscous boundary layer, a 

 slick, metal-troweled finish of the cement mortar mix is unnecessary. A 

 semislick finish is usually used. Figure 4-7 shows a harbor model under 

 construction where masonite screeds were used in the offshore areas and 



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