海陸交界的近岸邊，是人類活動最頻繁的地區，海域的開發與近岸結構物的建立大多集中在此。而近岸之海床係有坡度之淺水區，波列在此區域之演化特性與深海大為不同，因此對波浪在淺水區的傳播特性若有更進一步的瞭解對近岸結構物的設計及海岸地形之變化將有很大之助益。

　　本文利用在成大水工試驗所之大型斷面水槽，對三種不同之初始波浪型態；即規則波、三成分波(一主頻、兩副頻)及兩波波群所做的波浪試驗，探討其初始非線性參數在不同底床坡度(1/10、1/20)下，波列在等深水及斜坡段之演變情形。在本文中，將各波浪型態依照波浪尖銳度參數(ka)大小各挑選三種典型的波列，分別記錄其在兩種坡度下行進之水位變化並利用傅立葉轉換來進行分析，透過頻譜圖來觀察波浪在等深段與斜坡段行進時，波浪內部之成分波演變情形。

　　由實驗結果獲知非線性波列其時空演化特性因波浪型態、波浪尖銳度、底床坡度及時空差異而有不同之結果。初始非線性參數較小之規則波及三波條件在等深處並無非線性演化現象，但於斜坡上方會產生明顯的二階及三階諧波量。而當規則波在波浪尖銳度參數大時，其在等深段之演變則會遵循副頻不穩定理論而導致碎波並伴隨能量往低頻轉移，而波列在等深段若因有碎波發生而產生了主頻下移之現象時，其在斜坡段因淺化效應所衍生之倍頻為主頻下移後頻率之倍頻，並非在初始主頻之倍頻處。在三波試次中，波浪尖銳度參數越大會使波列之調變現象越明顯，波列在等深段之碎波後能量會往主頻之低副頻轉移。波列在斜坡上行進時，因淺化影響所激發之倍頻處也會自然衍生出副頻。而在兩波試次方面，在等深段行進時，兩波之交互作用會明顯產生兩主頻相減(fu-fl)成分波及高主頻加上兩主頻頻差(2 fu-fl)之成分波，並於進入斜坡區段後，其兩主頻之各倍頻(2 fl、2 fu)及兩主頻合成(fu+fl)之成分波能量明顯增加。

　The characteristics of wave trains in shallow water are quite different from which in deep water. Therefore, further investigations on the characteristics of wave propagation in shallow water are necessary to design suitable coastal structures. For this purpose, a series of experiments were conducted in a super tank (300m*5m*5.2m) on slopes of 1/10 and 1/20 at Tainan Hydraulics Laboratory (THL).

　Three kinds of wave trains (regular wave, three wave, and bichromatic wave) with a large range of initial nonlinear parameters (k0a0) were conducted in the constant deep water depth and then progressing on slopes of 1/10 and 1/20. The wave surface elevations were recorded by 93 wave gauges and analyzed by using the Fast Fourier transform (FFT) to investigate the evolution of corresponding spectrum on slopes. In order to describe the evolvement of the wave trains, nine testing runs were examined in the thesis.
The results show that the evolutional characteristics of nonlinear waves depend on the initial wave types, wave steepness, bottom slopes and time and space distributions. There is no non-linear development in deep water under conditions of smaller wave steepness parameters (k0a0~0.1) for regular waves and three waves. However, as the wave trains progress on the slope, the energy of second and third harmonics grows obviously. Additionally, under conditions of larger wave steepness, regular wave trains in deep water will be unstable due to side-band instability and lead to frequency-downshift accompanying wave breaking. The energy of fundamental frequency will be transferred to lower frequency band of the spectrum. When wave trains progress on slope, the second or third harmonics derived from the shoaling effect will be at the double or triple of downshifted frequency, not the initial fundamental frequency.

　During three wave testing runs, the larger wave steepness parameters, the more obvious extent of wave modulated; the energy of the broken wave in deep water will shift toward the lower side-band frequency. When waves proceed on slopes, the double fundamental frequency derived from shoaling effect will also derive its two side-bands.
For bichromatic waves, the evolution of specific Fourier components were examined, including two carriers(fl、fu), higher imposed side-band(2fu-fl), bounded long wave(fu-fl), double frequency of two carriers(2fl、2fu), compound of two carriers(fu+fl) and component of fu+2fl. When waves propagate in deep water, the energy of bounded long wave and higher imposed side-band will increase obviously. Additionally, the energy will grow obviously at the double Fourier component of two carriers and compound of two carriers as wave progresses on the slopes.

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