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題 名 | 初始均勻波列之非線性調變=Nonlinear Modulation of Initially Uniform Wave Trains |
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作 者 | 江文山; 黃煌煇; | 書刊名 | 海洋工程學刊 |
卷 期 | 3:2 2004.02[民93.02] |
頁 次 | 頁25-37 |
分類號 | 351.941 |
關鍵詞 | 均勻波列; 非線性調變; 副頻; Uniform wave trains; Nonlinear modulation; Sideband; |
語 文 | 中文(Chinese) |
中文摘要 | 本文於大型斷面水槽中以實驗方法研究初始均勻波列之波前演變及達穩態調變之特性。波浪是以活塞式造波機根據線性理論造出,沿水槽共佈置66支電容式波高計,同時量測波動傳遞過程中之變化。實驗條件之初始波列尖銳度(ka0)介於0.07~0.32。結果顯示由於振幅與週期調變合併作用的結果,使得波前中水位振幅較高者,相位速度較慢,而水位振幅較低者,相位速度較快,以致能量往高水位處集中而達到瞬間極大水位,ka0較大者波群中會發生碎波,之後波列呈現反調變情形。波前演變過程中,可以觀察到獨立波群的產生,然其並非發展的最終狀態,未碎波情況其演變緩慢,而碎波效應則有加速其演變的作用。經過充分時間發展,當波形達穩態調變時, 針對不同的初始波列尖銳度分別觀察到永久性與暫時性主頻下移現象,推測其與初始尖銳度及自然衍生之副頻頻率等有關,這點有待進一步研究。 |
英文摘要 | Experimental studies on the nonlinear wave trains evolution in deep water are conducted in a super long tank. Waves are generated by a piston-type wavemaker based on the linear wave theory. Totally, 66 Capacitance-type wave gages are installed along the wave flume to measure the wave profiles at different locations simultaneously. The initial wave steepnesses used in the experiments range from 0.07 to 0.35. Due to the joint effects of nonlinearity and frequency dispersion, the phase velocity and modulated wave period decrease as the modulated amplitude increases. That shifts the energy to the locations of higher water level and induces an extreme transient wave. Furthermore, wave envelope pulses are also observed in the uniform wave trains in the experiments. But they are not the end state of the wave trains evolution and will be further accelerated due to wave breaking events. After long time propagation, the wave train evolution may approach to the quasi-steady. During this stage, both permanent and temporary frequency downshifts, which depend on the magnitude of initial wave steepness, occur in the wave train evolution. Further studies to understand the mechanisms of different evolution type are ongoing |
本系統中英文摘要資訊取自各篇刊載內容。