Performance of a Wedge‐Type Absorbing Wave Maker

Design criteria for absorbing wave makers are presented and their implementation illustrated by reference to the conversion of a conventional wave maker with a wedge‐type paddle. Measurements obtained with both regular and irregular waves demonstate that the requried feedback loop in the wave maker's control circuit can be successfully based on a conventional wage gage. Furthermore, it is shown that good absorption characteristics can be achieved with a lessthan‐perfect circuit design. Comparison of results obtained both with and without absorption highlight some of the dangers of investigating the behavior of reflective coastal structures in a laboratory channel equipped with a conventional wave maker. It is shown that the multiple reflection of irregular waves between a test structure and a nonabsorbing wave maker can produce systematic changes in the incident wave climate that it would be difficult to rectify. Generally the full consequences of such changes will be unknown but they could be very serious. Thus, it is strongly recommended that tests on reflective structures should be carried out only with absorbing wave makers.