The Large Wave Flume at the O.H. Hinsdale Wave Research Laboratory houses a piston wavemaker with a built-in active absorption system designed by MTS Systems Corporation. The performance of the active absorption system has not been properly assessed yet. This thesis evaluates the performance of the MTS active absorption system in parallel with a new system designed at Aalborg University called AwaSys7.
The results of this thesis have a direct impact on the quality of data collected in future experiments.
The collection of high-quality data in a wave laboratory is vital for coastal engineering design testing and expanding our understanding of physical ocean processes. Confidence in data is obtained by working with a reliable wave generator, particularly if an active absorption system is present and whose capabilities are known. It is understood that experiments requiring regular and irregular waves are impacted by re-reflection from the wave board if an active absorption system is not present or poorly designed. The presence of re-reflected waves leads to a build-up of energy, altering the desired sea state the experimental model is tested in.
The experiment at the Large Wave Flume tested a series of regular and irregular wave conditions in a highly reflective environment. The flume was equipped with five resistance wave gauges and eight ultrasonic wave gauges.
The performance of the two systems for the regular wave cases was based on calculated reflection coefficients, uniformity of incident waves, and the length of time required to eliminate the existing waves in the flume after testing was completed. For irregular wave cases the change in variance during simultaneous generation and absorption and its exponential decrease at the culmination of generation were used.
The performance parameters were calculated using a mixture of methods including zero down crossing analysis and the separation of incident and reflected waves conducted with the program WaveLab3.
The results show that the AwaSys active absorption system outperforms MTS for the irregular wave cases. However, neither system was able to remain stable for the entire duration of all of the irregular wave conditions. Both AwaSys and MTS had similar performance for the regular wave cases, but there was a trend in favor of AwaSys for all but one tested frequency.