slope toe were affected by this irregular rotation resulting from the 

 acceleration and load demand placed on the generator at startup. 



6. Generator Stroke . 



The generator stroke of 4.70 inches (11.94 centimeters) for the 1970 

 and 1971 experiments was chosen because several earlier experiments had 

 used that setting. This travel was obtained by adjusting the crankshaft 

 arm on each end of the generator to an eccentricity of 2.35 inches. The 

 maximum possible offset was 8.00 inches (20.32 centimeters), by means of 

 a threaded bar and locking assembly. For these generators, the eccentric- 

 ity was one-half the stroke. A photo of the eccentric assembly on one of 

 the generators is shown in Figure 12. 



The generated wave height (the height produced by the generator motion 

 before reflection) for the 1.90-second wave was determined before 1970 to 

 be 0.36 foot, but no documentation exists to prove how or when that value 

 was determined. The nominal incident wave height (generated height plus 

 re-reflected wave height) of 0.36 foot was determined by averaging all the 

 incident wave heights from the fixed-bed tanks from experiments 70X-06 and 

 70X-10 (Table 3). 



In 1972, the eccentricity settings were determined by a trial-and- 

 error procedure to generate a wave height for the selected wave period 

 which resulted in a wave with the same energy flux as the 1970-71 wave. 



V. WAVE HEIGHT DATA 



1. Data Collection . 



a. Wave Gages . Wave height in each test was measured with identical 

 instrumentation which consisted of a strip-chart recorder and FWK Model-1 

 CERC laboratory wave gages, with the necessary parallel wire probes, 

 cables, and connectors. Each set provided two channels of recording. The 

 operation and calibration of this apparatus were described by Stafford 

 (1972). 



Many of the delays and problems of instrumentation were caused by the 

 necessary daily assembly and disassembly of the equipment. Cables and 

 connectors were especially subject to wear, with resultant higher failure 

 than inplace instrumentation. However, this delay was minimized by avail- 

 ability of spare parts and prompt service from the CERC Instrumentation 

 and Equipment Branch, Research Division (CERRE-IN). 



b. Calibration . Proper gage calibration is essential in obtaining 

 accurate wave height data. About 20 to 30 minutes was required for the 

 instruments to reach an acceptable level of electrical stability between 

 power application and calibration. The calibration procedure by Stafford 

 (1972) was followed. Electrical interference, wind, and nonlinearity were 

 frequent problems in the calibration of the wave gages. The electrical 

 interference was part of the assembly problem and was solved by a thorough 



27 



