| Summary: | 博士 === 國立臺灣大學 === 工程科學及海洋工程學研究所 === 101 === This study used wavemaker system and high speed camera tech with optical system to take wave passed over a step construct images at the fundamental fluid mechanics lab, department of Engineering Science and Ocean Engineering, NTU. And used the image processing techniques with edge detection and digitize to analysis the free surface elevation. In the Full-scale image, using LabView successfully developed multi-section image connection technique with edge detection. By measuring enlarge Y axis image to observe the physical phenomenon details when the wave passed over the submerged dike, at the same time, the digital free surface data could be totally analysis the wave phenomenon by using Matlab to develop 2DFFT and 1DMWT.
Multi-section Full-scale measure techniques by using high speed camera, it''s better than the low sampling CCD camera and wave gages because of its higher sampling and space resolution. The enlarge Y axis error is less than 2 pixels at connecting surface, and almost no error at time. Otherwise, the propose method could decompose the waves of incident, reflect, even the free and bound wave of higher harmonics. By this method also useful to deal with the complex nonlinear harmonic waves interaction and had been good validation.
Finally, this study focused on research the effects of generating higher harmonics waves by different width (Bx) of step obstacle.The point view of energy(amplitude) and energy flux(E*Cg) by determining the spatial distribution of energy flux(E*Cg) and take the result to parameter optimation. Setting a threshold of generated second harmonics wave by using incident wave Ursell number and introduced a parameter(Bx/λi)±n, n=0.09. And the viewpoint of energy flux, the results were obtained n=+0.39 and n=-0.32 at generating bound wave and free wave. In this research also bring up a simulation of math model to describe the relationship of spatial amplitude between first and second harmonics. At the simulation spatial domain, the curve decay rate of amplitude can''t be neglect because the friction effects. At the last, we discussed the effects of reflect(Kr)、transmission(Kt) and energy dissipation(Kd) at Step1 and Step2 when waves propagate over a submerged. And our results were quite reliable and could be provided to numerical researchers to examine their models.
|
|---|
