timing with an electric stopclock graduated in hundreds of a second. An 

 error of 0.2 second per 20 revolutions resulted in an error of ±0,01 sec- 

 ond in the wave period. 



4. Wave Period . 



The original plan for the 1970 tests called for a wave period of 1.88 

 seconds. However, early in experiment 70X-10 it became difficult to main- 

 tain this period due to wear of the varidrive. After 14 testing hours, 

 the period was changed to 1.90 seconds. Wave periods of 3.75, 2.35, 1.50, 

 and 1.90 seconds were selected for the 1972 experiments to provide a wide 

 range of wave energy densities. These four wave periods had all been 

 used during longshore transport tests in the early 1960 's by Fairchild 

 C1970a). 



5. Problems Encountered in Operation . 



The complexity of the wave generators and their control mechanisms 

 virtually assured some operational difficulties; i.e., the generator would 

 not "lock in" with the control mechanism, or the generator would run with 

 an irregular angular velocity. The lock-in problem generally occurred on 

 damp, rainy days. Balancing the control adjustment did not always solve 

 the problem, especially when humidity or rain resulted in voltage leakage 

 in the control circuits. Depending on the degree of voltage leakage, the 

 solution ranged from repeated attempts at locking in the generator to 

 waiting for the equipment to dry out, perhaps until the following day. 

 The procedure for locking in the generator is discussed in Appendix B. 



The corrective procedure for irregular rotation was the adjustment of 

 the balance control in a clockwise direction until operation appeared uni- 

 form. The appearance of uniform rotation was not proof that the rotation 

 was uniform. Due to the complexity and many steps of power transfer in 

 these generators, the presence of uniform angular rotation with any degree 

 of certainty has always been in doubt. Further, it was largely a matter 

 of test personnel vigilance whether or not the optimum rotation was main- 

 tained. A further risk existed that, should the irregular rotation not be 

 corrected, the irregularity would increase until the servomechanism would 

 lose control completely. In this event, the generator would "run free" at 

 whatever speed, or period, the power of the main drive mechanism would 

 allow. For the 2,35-inch (5.97 centimeters) eccentric setting (1970 and 

 1971), the period was about 1.25 seconds. Any prolonged interval, expe- 

 cially one of unknown duration of these "run away" waves on the beach, would 

 have been disastrous to the experiment. However, all occurrences were 

 observed and corrected within 1 minute except an occurrence of 5- to 10- 

 minute duration in experiment 71Y-06. 



Initial irregular bulkhead motion had an undesirable effect on the 

 first waves of each test run. Even with optimum control adjustment, the 

 irregular motion was quite pronounced until the generator stabilized. 

 Examination of the initial wave record from each test of 1970 and visual 

 observation indicated that at least the first five waves arriving at the 



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