Experimental and Numerical Studies on Wave Breaking over Sloping and Bar/Step-Type Profiles

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Project title

Code/計畫編號

NSC99-2221-E127-005

Translated Name/計畫中文名

波浪通過斜坡底床、沙洲和平台之碎波試驗量測與數值模擬

Funding Organization/主管機關

National Science and Technology Center for Disaster Reduction

Co-Investigator(s)/共同執行人

歐善惠(計畫主持人)

Department/Unit

Department of Environmental Science and Occupational Safety and Hygiene Graduate school of Environmental Management

Website

https://www.grb.gov.tw/search/planDetail?id=2153894

Year

2010

Start date/計畫起

01-08-2010

Expected Completion/計畫迄

31-07-2011

Co-Investigator(s)

Tai-Wen Hsu

Bugetid/研究經費

848千元

ResearchField/研究領域

土木水利工程

本計畫擬利用模型試驗及數值模式求解探討規則波浪和不規則波浪通過斜坡底床、沙洲和平台之波流場變化情形，進而分析波浪通過斜坡底床、沙洲和平台後之碎波現象。試驗部分擬在二維波浪斷面水槽進行，利用質點影像測速儀 (Particle Image Velocimetry, PIV) 及氣泡影像測速儀 (Bubble Image Velocimetry, BIV) 研究波浪通過斜坡底床、沙洲和平台附近之流場與波形變化，研究渦流生成、減衰及其特性，分析渦流與波能消減之關係，並進一步探討波浪通過三種不同形狀之海床碎波後之波流場變化及能量消散。根據試驗結果，本研究擬擴充 Hsu 等人 (2004) 之雷諾平均納維爾-斯托克斯 (Reynolds Averaged Naiver-Stokes, RANS) 方程式之紊流數值模式，自行發展一完整之波浪碎波數值模式，藉以探討波浪和斜坡底床、沙洲及平台互制時，液面的變化及內部流場的運動特性。數值模式採用有限體積法，求解RANS方程式，以期能夠呈現波浪場中非線性與黏性效應的影響，同時配合 k − ε 紊流模式來模擬紊流效應。固體邊界條件係採用嵌入邊界法 (Embedding Method, EB)，此法仍保留卡氏座標之運算，但將邊界視為兩向流，解除速度邊界在方格網分量的問題，提高數值在不規則邊界解析度，其中時間差分項以顯式法 (explicit method) 來離散，壓力場則藉著預測-修正方式 (predictor-corrector procedure) 來建立，配合交錯網格系統，採用不等間距網格。自由液面採較高階數之分段線性界面計算方法-流體體積法 (Volume of fluid with piecewise linear interface calculation, VOF/PLIC)，以模擬波浪之變形。本模式與傳統方法之最大不同係使用 RANS 模擬波浪與斜坡底床、沙洲和平台之互制，並探討波浪碎波之模擬，完整地考慮非線性、黏性和紊流效應，以展現波浪碎波後流場和能量減衰的變化。本計畫執行成果將可較客觀提供風浪模式源項之碎波和能量消散兩個參數之決定公式，提高模式預報之能力。本計畫將與澳洲旋濱大學A.V.Babanin教授合作，Babanin教授負責碎波減衰函數之探討，合作成果將有助於風浪數值模式參數之決定。 Using a 2-D numerical model within the framework of the present proposal, extensive numerical simulations of Reynolds averaged Navier-Stokes (RANS) equations and simultaneous experimental measurements using PIV/BIV (particle/bubble image velocimitry) are intended to be performed in order to gain significant insight into various complex flow phenomena surrounding the sloping and bar/step-type bottoms owing to its interaction with an oncoming wave. Nonlinear effects in the nearfield of the bottom configurations such as vortex formation, turbulence and wave overtopping/breaking are intended to be investigated in a greater detail. In the numerical modeling, the transient evolution of the free-surface is opted to be captured by suitably incorporating a VOF/PLIC (Volume of fluid with piecewise linear interface calculation) method in combination with the higher order weighted essentially non-oscillatory schemes. Capillary effects will be taken into account, so as to include concentrated nonisotropic stresses near the interface. The wall boundary condition is described by the embedding (EB) method developed by Ravoux et al. (2003). In the EB method, the solid boundary is accounted for by adding a force field to the flow phase in the computed cells that are fully or partially occupied by the solid phase. Therefore, there is no need to impose boundary conditions on the body surface since the velocity components are made vanish within the bodies as a part of the solution. Results concerning time evolution of the water surface elevation and velocity field are intended to be extracted for both regular and irregular waves, revealing how an initial steep wave undergoes breaking and successive splash-up cycles. Breaking processes, including overturning, splash-up and air entrainment, and breaking induced vortex-like motion and the associated energy dissipations are opted to be investigated. This research project will be carried out jointly with Professor A.V. Babanin of the Swinburne University of Technology, Australia. The results will provide a modified energy dissipation function in the source terms of the wind wave model to enhance the predictability of the model.

Keyword(s)

質點影像測速儀
氣泡影像測速儀
三維雷諾平均納維爾-斯托克斯
流體體積法
人工潛礁
PIV
BIV
RANS
VOF
artificial reefs

DSpace CRIS

Experimental and Numerical Studies on Wave Breaking over Sloping and Bar/Step-Type Profiles

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