工學院: 工程科學及海洋工程學研究所指導教授: 丁肇隆; 楊智傑趙偉廷Chao, Wei-TingWei-TingChao2017-03-022018-06-282017-03-022018-06-282016http://ntur.lib.ntu.edu.tw//handle/246246/271430本研究中利用一系列的水槽試驗，探討非線性波浪通過一矩形潛堤所造成的諧和波生成、振幅調變(重現距)以及能通量的變化。總共有45組不同的實驗條件，包括不同的入射振幅、頻率(0.8、1.0及1.25 Hz)以及潛堤結構，其中包含四組堤寬及三組堤高(或堤上水深)。利用非侵入式影像量測系統紀錄7.8 m範圍的波形變化，拍攝時間長度為21.8 s。 自由液面量測資料進一步利用二維快速傅立葉轉換以及一維毛利小波轉換分析各諧和波頻率的振幅變化。提出一參數描述二階諧和波在堤上之生成。此外，研究發現影響諧和波生成最重要的因子為入射波的Ur數以及堤上水深，而堤寬的影響並不顯著。二階諧和波振幅調變的現象(即重現距)主要是受到自由及強迫波成份波長的影響，利用毛利小波轉換或是3階Stokes理論分散關係式即可準確計算其平均波長。主頻波受到三、四階或更高倍頻諧和波生成的影響，其振幅之重現距分佈呈現與二倍頻不同。最後，提出平均能通量的觀點，重新說明重現距的現象，並定義出一最佳化參數。在能通量觀點下，探討波浪通過潛堤時，在堤頭與堤尾所造成之反射率、透射率與能量消散的影響。A series of flume experiments were conducted to investigate the harmonic generation, wave height modulation (i.e., recursion) and the variation of energy flux of nonlinear waves passing over a submerged step. A total of 45 experimental conditions were considered, including several different incident amplitudes, periods (0.8, 1.0 and 1.25 Hz) and bottom configurations, i.e., four step widths and three step heights (or submergence depths). The waveforms across a 7.8-m-long segment were recorded over a period of 21.8 sec using a non-intrusive imaging system. The measured surface elevations were further analyzed to reveal the amplitude variations of harmonic frequencies based on the 2D Fast Fourier and 1D Morlet wavelet transforms. A set of parameters was proposed to depict the generation of second-harmonic waves at the step crest. Overall, it was found that the most influencing factors for harmonic generation are the Ursell number of incident waves and relative height of the obstacle while the relative step width yields an insignificant impact. The wave height modulation (i.e., recursion) of second harmonic is affected mainly by the wavelengths of its free and bound components, which are accurately estimated from the Morlet wavelet transform analysis and third-order Stokes dispersion relation. The amplitude of primary wave exhibits a different recursion pattern due to the generation of the third and forth harmonics. In the end, the concept of average energy flux is clarified the recursion phenomenon and take the result to parameter optimization. In the point of energy flux, we discussed the effects of reflection (Kr), transmission (Kt) and energy dissipation (Kd) at the lee side and weather side when waves propagate over a submerged.4907921 bytesapplication/pdf論文使用權限: 同意有償授權(權利金給回饋學校)諧和波生成重現行為堤上水深Ur數3階Stokes理論分散關係式平均能通量harmonic generationrecursion behaviorsubmergence depthUrsell numberthird-order Stokes dispersion relationaverage energy fluxthesis10.6342/NTU201603613http://ntur.lib.ntu.edu.tw/bitstream/246246/271430/1/ntu-105-D98525003-1.pdf