At one end of the tank, there was a hinged wave generator powered by two 

 hydraulic cylinders. Wave form, height, length, period can be readily 

 varied. Maximum wave height is approximately 12 inches. At the other 

 end of the tank were three layers of wave absorbers to minimize wave 

 reflection. An observation window is installed at the side wall at the 

 test section near the middle of the tank. At this same location, a 

 portable truss was positioned across the tank. The truss provided a 

 mounting support for the models and wave gauges. The models were fastened 

 to aluminum plates suspended from the bottom members of the truss by 

 four steel rods. These rods are notched to provide the models with freedom 

 of horizontal movement. Three models were mounted near the center of the 

 tank along the testing section about three feet apart (Figure 12). Wave 

 forces on each model at directions parallel and normal to the waves were 

 measured by two sets of springs instrumented with two strain gauges. 

 These springs were supported by four rods fixed rigidly to the truss 

 (Figures 13 and 14) . A wave staff was mounted at the test section in 

 line with the models. The wave gauge output together with six strain 

 gauge outputs were conditioned and displayed on a multi-channel oscillogram. 

 These signals were also recorded on a magnetic tape recorder. 



Wave force measurements were obtained for waves having a wide range 

 of wave height, wave length, and the height to length ratio. Table 2 is 

 a summary of designed testing waves. 



A trial and error technique was necessary to adjust the wave properties 

 closer to values in Table 2. However, it is almost impossible to adjust 

 the wave height to a preset value. The actual wave measurements are listed 

 together with the test results in Table 3. 



Models were tested in three different orientations. They were first 

 mounted so that the flat side of the semi-circular model and the concave 

 side of the crescent shaped model were facing the impinging waves. The 

 second mounting orientation was 90° from the first orientation and the 

 third was 180° from the first. About twenty wave trains were tested in 

 each model orientation. 



Wave staff and wave force gauges were carefully calibrated before the 

 test started and the calibrations were checked after each series of tests 

 were completed. To calibrate force gauges, weights of one pound increment 

 were attached through a pulley system to the model mounting plates. Negative 

 wave forces were simulated by hanging weights at the upstream side of the 

 mounting . 



Oscillogram records were reduced by measuring the positive and the 

 negative peak forces averaged over five or six waves. No attempt was made 

 to analyze the wave forms. 



A samples of the oscillogram recordings is shown in Figure 15. Higher 

 frequency vibration noises are visible in the traces of wave forces. As 

 the lowest vibration frequency (crescent model) is about ten times higher 

 than the wave frequency, the effects of the noise signals can be eliminated 

 easily. In most records the noise level was relatively small. 



12 



