Experimental and numerical determination of the shoreline motion during the run-up of tsunami waves on a plain beach

Within this master thesis the behaviour of long periodic waves during their run-up on a plain beach was investigated via physical and numerical modelling. In the experimental part, for seven leading depression, non-breaking sine waves with surf similarity parameters between 3.1 and 15.6 the wave velocity, wave height and run-up on a plain beach were determined. In addition, the motion of the initially still shoreline, i.e. run-up/ run-down process, run-up/ run-down velocity, wave acceleration, maximum run-up and maximum run-up velocity, was determined via two high-speed cameras. Comparison of the aforementioned characteristics with the theory revealed good agreement; deviations can mostly be attributed to experimental performance. For wave generation a new volume driven wave generator was used. Long waves are generated by a pair of high capacity pumps under control of a proportional-integral-derivative controller (PID-controller). While rotating clockwise or counterclockwise water is pumped into the propagation section or extracted from it. Thereby, waves of arbitrary length can be generated. Using the relatively new strategy of observing the shoreline motion via optical measurements gave a comparatively exact shoreline position during wave run-up. In contrast, determination of the shoreline position during run-down was less exact due to missing evidence indicating the distinct position of the shoreline. In general, the experimentally determined shoreline position agreed with the theoretical approach. The maximum run-up/ run-down occurred for waves with surf similarity parameters between 3 and 6 (interval in which transition from breaking to non-breaking occurs). The magnitude of the theoretical breaking point increased for decreasing wave non-linearity A/h. For surf similarity parameters greater equal of the theoretical breaking point and for increasing surf similarity parameters the normalized run-up and magnitude of normalized run-down decreased. The maximum run-up/ run-down was proportional to wave non-linearity, i.e. the normalized run-up and magnitude of normalized run-down decreased with increasing wave amplitude as predicted by theory. The agreement of experimental and theoretical maximum run-down/ run-up depended on tuning of the PID controller and the resulting actual curve. For longer waves suboptimal tuning of the PID controller resulted in riding waves.

Klappentext

Master's Thesis from the year 2014 in the subject Geography / Earth Science - Oceanography, grade: 1.7, University of Hamburg (Institute of Oceanography Hamburg), course: Physical Oceanography, language: English, abstract: Within this master thesis the behaviour of long periodic waves during their run-up on a plain beach was investigated via physical and numerical modelling. In the experimental part, for seven leading depression, non-breaking sine waves with surf similarity parameters between 3.1 and 15.6 the wave velocity, wave height and run-up on a plain beach were determined. In addition, the motion of the initially still shoreline, i.e. run-up/ run-down process, run-up/ run-down velocity, wave acceleration, maximum run-up and maximum run-up velocity, was determined via two high-speed cameras. Comparison of the aforementioned characteristics with the theory revealed good agreement; deviations can mostly be attributed to experimental performance. For wave generation a new volume driven wave generator was used. Long waves are generated by a pair of high capacity pumps under control of a proportional-integral-derivative controller (PID-controller). While rotating clockwise or counterclockwise water is pumped into the propagation section or extracted from it. Thereby, waves of arbitrary length can be generated. Using the relatively new strategy of observing the shoreline motion via optical measurements gave a comparatively exact shoreline position during wave run-up. In contrast, determination of the shoreline position during run-down was less exact due to missing evidence indicating the distinct position of the shoreline. In general, the experimentally determined shoreline position agreed with the theoretical approach. The maximum run-up/ run-down occurred for waves with surf similarity parameters between 3 and 6 (interval in which transition from breaking to non-breaking occurs). The magnitude of the theoretical breaking point increased for decreasing wave non-linearity A/h. For surf similarity parameters greater equal of the theoretical breaking point and for increasing surf similarity parameters the normalized run-up and magnitude of normalized run-down decreased. The maximum run-up/ run-down was proportional to wave non-linearity, i.e. the normalized run-up and magnitude of normalized run-down decreased with increasing wave amplitude as predicted by theory. The agreement of experimental and theoretical maximum run-down/ run-up depended on tuning of the PID controller and the resulting actual curve. For longer waves suboptimal tuning of the PID controller resulted in riding waves.