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Please use this identifier to cite or link to this item: http://ntour.ntou.edu.tw:8080/ir/handle/987654321/35336

Title: 以布斯尼斯克模式探討群波與花蓮港亞重力波的關係
Investigations on the relationship between group waves and infragravity waves in the Hualian Harbor based on Boussinesq wave model
Authors: Tzu-Li Yang
楊自立
Contributors: NTOU:Department of Marine Environmental Informatics
國立臺灣海洋大學:海洋環境資訊學系
Keywords: Boussinesq模式;亞重力波;離岸堤;孔隙層
Boussinesq model;infragravity waves;offshore breakwater;porosity layers
Date: 2012
Issue Date: 2013-10-07T02:53:54Z
Abstract: 颱風時期在花蓮港內長週期振盪問題自第四期工程後已持續數年,每當颱風來襲時停泊於港內的船隻就可能會發生斷纜事故。過去經由分析花蓮港波浪實測資料、水工模型模擬以及數值模擬方式,對其發生亞重力波機制有初步的了解,並依各種不同的假設提出解決的辦法,而群波的波降或波升作用可能會引發亞重力波,本文將以丹麥水利研究所(DHI)所發展的布斯尼斯克波浪模式(MIKE21-BW)來探討群波是否為颱風時期形成花蓮港內長週期能量共振現象的主因。 本文使用交通部運輸研究所港灣技術研究中心所提供的2005年海棠颱風實測水位資料,經由頻譜分析後取兩相近尖峰週期的波浪能量重新造出群波,使用此群波與實測波浪輸入港內後,兩者的模擬結果與實測港內8號碼頭位置的波浪週期與波浪能量相近,另外將颱風波浪頻譜以30秒做分界分別輸入BW模式模擬,從模擬結果發現在使用週期小於30秒的颱風波浪為入射波時,在港內產生亞重力波的能量比使用長於30秒以上的颱風波浪還要大。 為了緩和在港內產生的長波,我們發現模擬颱風波浪進入港內的情形中,在港內碼頭以及防波堤處設置使波浪反射率減低的孔隙層,港內的亞重力波能量就會減少;另外模擬外海波浪進入花蓮港及其附近地形,在港口外灘線設置平行海岸的離岸堤後,港內的長週期能量也隨之下降。 關鍵字:Boussinesq模式、亞重力波、離岸堤、孔隙層
It is well known that there are infragravity waves in the Hualien Harbor during the passage of typhoons. The infragravity waves may cause cable breakage for the moored ships in the harbor. Past physical experiments and numerical simulations have been conducted by many researchers, trying to understand the cause of the Infragravity waves inside the harbor. Group wave is one of the possible sources for the infragravity waves, and the waves from offshore typhoons often consist of group waves. In this study, we used the Boussinesq model developed by Danish Hydraulic Institute (MIKE21-BW) to investigate whether there is a connection between group waves outside the harbor and the infragravity waves inside the harbor. The infragravity waves can be triggered by the set-down (or set-up) bound to the wave groups. After analyzing the wave records measured outside the harbor during the passage of the Typhoon Haitang in 2005, we found two peak wave periods in the spectrum that can be combined into group waves. We first used the combined group waves and then measured waves as the incident waves to the wave model. Results showed that both simulated waves inside the harbor are similar, and they also agreed with the measured waves inside the harbor. Then we filtered the waves measured outside the harbor into one contains waves with period less than 30s and one with period longer than 30s. These two wave trains were used as incident waves to the BW model separately. The results showed that the typhoon waves with period less than 30 second cause higher infragravity wave energy inside the harbor than using typhoon waves with only waves longer than 30s. To mitigate the long waves inside the harbor, we found that, using measured typhoon waves as incident waves, the infragravity wave energy inside the harbor can be reduced, if the porosity layers are added to the harbor structures such as wharves and breakwaters. Also if the offshore breakwaters were added to the beach outside the harbor entrance, the simulation showed that the long wave energy inside the harbor can also be reduced. Key words : Boussinesq model, infragravity waves, offshore breakwater, porosity layers
URI: http://ethesys.lib.ntou.edu.tw/cdrfb3/record/#G0M95840007
http://ntour.ntou.edu.tw/handle/987654321/35336
Appears in Collections:[海洋環境資訊系] 博碩士論文

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