長波之理論推導與試驗研究由來已久。淺水長波與近岸輸砂機制相關，進而對岸線侵蝕、港口航道淤塞、近岸汙染物擴散有很大影響；深水長波與波群演進密不可分。遠處看似均勻的線性波浪，經過一段距離傳動後，可能產生非線性長波成份使得在深海上航行之漁船、軍艦失事。以上再再顯示長波研究對海洋工程的重要性。然而相對於重力波長波具有較長週期及小振幅的特性，宜以較長試驗水槽及較精密的量測儀器進行試驗。本研究針對雙主頻波設計一系列52個試次的試驗，以精度0.5mm之波高計及多點式資料收錄系統（Multi-Nodes Data Acquisition System）於國立成功大學水工試驗所300m長水槽中進行。

　　為探討二階長波傳動機制，宜先全盤瞭解群波中各成份傳動特性。以離散傅利葉轉換分析水位訊號得振幅能譜，52個試次結果可依五個成份波（兩主頻、兩副頻及長波）在空間上的特性歸納成五種類型，文中建議應以個別無因次頻率差當作區分指標。

　　本文在長波上的研究結果顯示長波能量在空間上的演變具規則可逆性，比較有無碎波的試次，可發現有碎波時，長波能量會較大。本研究並發現Longuet-Higgins and Stewart (1962)幅射應力理論無法描述碎波帶下游長波與波形傳動變形的關係。

　　經由本論文量測實驗與分析，有助於瞭解長波生成機制進而對海洋工程發展有所貢獻。

　　The generation of long waves has been studied for many years. No matter in shallow water or in deep water, it has been recognized as an important role in coastal and ocean engineering. A series of systematic and well-controlled experiments were conducted in a super tank with length of 300m at Tainan Hydraulics Laboratory (THL).

　　The evolution of Fourier components including two carriers, two imposed side-band, and long wave was examined one by one. Fifty-two cases are classified into five types. Cases of type I non-breaking perform weakly non-linearity and cases of type II non-breaking show strong non-linearity. Near-recurrence, belonging to type I non-breaking actually, is specially selected because of the spatially reversible phenomenon. On the other hand, the simple periodicity is irreversibly lost in type I breaking but it remains in type II breaking. Moreover, indexes are suggested when classifying the cases of bichromatic wave. Results reveal that the bounded long wave remains limited periodic in space. Comparing cases in non-breaking and breaking, long wave energy with breaking is larger than it without breaking. Furthermore, the radiation stresses theory can not satisfactorily describe long waves in breaking cases. Above results advance the ocean engineering a lot in the generation of long waves.

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