Experimental Investigation of The Harmonics Generated by Wave over A Submerged Rectangular Obstacle

• Main Authors: lin chi tsang, 林其蒼
• Other Authors: 林銘崇
• Format: Others
• Language: zh-TW
• Published: 2003
• Online Access: http://ndltd.ncl.edu.tw/handle/88846115395222339777

碩士 === 國立臺灣大學 === 工程科學與海洋工程學系 === 91 === Abstract The incoming waves undergo strong nonlinear deformations at the obstacle when the wave amplitude is finite. An infinite number of super-harmonic waves are prominent at obstacle’s lee side. The second- and third-harmonic wave amplitudes are, in previous literature, in several examples found to be comparable to the incoming wave amplitude. In addition, Phase-locked-mode harmonics and free-mode harmonics play an important role in energy transform. The aim of this paper is thus to investigate experimentally the decomposition phenomenon of a nonlinear wave train passing over a submerged obstacle with spatial and temporal measurements. Spatial, as well as temporal, non-linear surface measurements are made using a technique which was originally proposed by Perlin et. al.(1993).This technique employs cylindrical lenses to magnify the verti-cal dimension, high-speed imaging system, facilitating the measurement of the disparate scales with a vertical surface-elevation resolution on the order of 0.0156cm/pixel.Thus, high-frequency waves are measured accu-rately in space and time. Time series of spatial surface-elevation meas-urements are presented. In addition, the height effects of submerge obstacle have been dis-cussed in previous literature systematically. So, we just discuss the width effects of submerge obstacle on the energy transfering from primary wave to its higher harmonics. Taking advantage of spatial information of wave trains, we can find that nonlinear effect would influence generation of free and force harmonic waves.