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The Reflection of Irregular Waves by Perforated Breakwater with a Rock-Filled Core
|Contributors: ||NTOU:Department of Harbor and River Engineering|
Irregular wave;Wave chamber;Reflection;Multi-domain BEM;Breakwater;Porosity;Friction coefficient;Regular wave;Velocity potential
|Issue Date: ||2012-04-13T01:20:03Z
|Abstract: ||摘要:通常透水結構物要較傳統不透水結構物好且經費較節省，主要是它們具有下列特 性：因為具有孔隙易附著生物對生態較為有善破壞較少；組成元件可以容易在陸地上建 造；可以快速安裝施工；所需維護費用較少；孔隙間海水可以流通對水質較好；損壞時 易於修補恢復性高。填充式透水防波堤，其消波機制最主要特性即在於利用介於透水薄 板與塊石間之水流黏滯性來消減波能。 由過去研究結果顯示大多以規則波進行探討與實驗，規則波無法模擬實際海面狀 況，因此本計畫採用不規則波為入射波浪，利用永井(1972)等能量波譜分割法，將不規 則波視為由不同週期之成分波所組合而成，再利用線性疊加的方法求出不規則波通過填 充式透水防波堤反射率及透過率，數值計算結果更能符合實際海域狀況。 本計畫數值模式採用多重領域邊界元素法(Multi-domain BEM)為基礎，以 Bretshneider 波譜為入射波波譜，模擬不規則波通過填充式透水防波堤後，探討其反射 率及透過率變化；另外，藉由改變透水防波堤之相對堤長、堤高、沒水深度、塊石孔隙 率、薄板透水參數及塊石摩擦係數等，找出最佳反射率及透過率之配置。採用填充式透 水防波堤，節省材料，施工方便，所需成本較少；就消波效果及經濟性方面評估，填充 式透水防波堤為一較理想之消波結構物。|
abstract:The porous structures are considered as a good and cost-effective substitute for the conventional type of structures. The porous structures have gained significance in the recent years because of their basic advantage, such as: (1) eco-friendliness (2) easy on-land fabrication (3) quick construction (4) less maintenance (5) mobilization and (6) retrieval. Recently perforated caissons are often used to construct vertical breakwaters and wharfs in coastal engineering as they can effectively reduce the wave reflection and wave forces on the structures. The breakwater consists of a perforated front wall of thin thickness, a core region of width B containing large diameter rock filled, and an impermeable back wall. An important characteristic of such breakwater is that wave energy is dissipated within the front permeable wall by viscous effects. Most of the research results were investigated and experimented by regular waves, however, under certain circumstances, the regular waves can’t simulate the actual sea status. Thus, this project applies the irregular waves as incident waves, using Nagai’s(1972) spectrum resolution method, and consider the irregular waves as the combination of the various regular waves. Also it is expected to have more precise result comparing to the actual status by linear superposition to obtain the reflection and transmission of irregular waves. The numerical model is based on multi-domain boundary element method and Bretschneider spectrum as incident waves to reproduce the variation of the reflection and transmission when the irregular waves go through perforated breakwater with a rock-filled core. Furthermore, by changing the relative length, height, submerged depth, porosity ratio, porous effect parameter and the linearized resistance coefficient of porous medium to predict the best reflection and transmission. Moreover, under the same construction, if using perforated breakwater with a rock-filled core, save material, easy for construction and cost effective. Therefore, from the perspective of effect of wave dissipation and economy, the perforated breakwater with a rock-filled core is an ideal construction for wave dissipation. It is shown that the rock-filled increase wave reflection on the breakwater as compared to the same breakwater without the rock-filled but also reduces the wave force on the breakwater.
|Appears in Collections:||[河海工程學系] 研究計畫|
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