Numerical Simulation of Sediment Transport in Coastal Areas (Ii)-1

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基本資料

Project title

Code/計畫編號

MOST103-2221-E022-016-MY2

Translated Name/計畫中文名

海岸泥沙運動數值模擬 (II)-1

Project Coordinator/計畫主持人

Shih-Feng Su

Funding Organization/主管機關

National Science and Technology Council

Co-Investigator(s)/共同執行人

謝志敏

Department/Unit

Department of Maritime Information and Technology,NKUST

Website

https://www.grb.gov.tw/search/planDetail?id=11273453

Year

2015

Start date/計畫起

01-08-2015

Expected Completion/計畫迄

31-07-2016

Bugetid/研究經費

585千元

ResearchField/研究領域

海洋科學

波浪作用下泥沙的懸浮及運動規律是海岸動力學和海岸工程中的重要研究課題。波浪與泥沙之間的相互作用問題是個普遍存在而又難以處理的問題，因此對其相互作用的研究具有重要的意義和工程應用價值。但由於波浪與泥沙相互作用具有極強的非線性，用線性勢流理論進行研究難以得到滿意的結果。因此採用粘性流數值模擬方法來研究此問題，將是一種更爲直接和有效的方法。本計畫為了獲得更準確的模擬，在前人的研究成果基礎上，擬用完整的 Reynolds Averaged Navier-Stokes 方程式，作為紊流流場的控制方程式，使用 k 紊流模式來閉合 Reynolds 平均 Navier-Stokes 方程式，不同於前人採用勢流的觀點或未考慮紊流效應；自由液面採用流體體積方法來處理。在結構物及複雜邊界的處理預計採用嵌入邊界法 (Embedding Boundary Method) 和巢狀卡式網格系統。本計畫擬發展 RANS波浪泥沙數值模式，進行波浪通過不同型態之泥沙底床之流場模擬。本計畫為三年計畫，第一年主要工作發展 2D數值模式探討波浪作用下泥沙運動之數值模式，探討不同特性泥沙 (懸浮質、泥質) 之運動特性。目前進度已經發展出二維波浪泥沙運動數值模式，今年度為第二個執行年度，第二年利用利用第一年發展的二維波浪泥沙運動數值模式，探討沙漣底床和斜坡底床之漂沙引起的地形變動。第三年發展三維波浪泥沙運動數值模式，探討三維波浪在斜坡上之沖刷問題以及三維波浪與直立圓柱引發的沖淤問題。本計畫主要探討波浪通不同海床時，渦流生成與減衰在不同波浪條件之影響。主要針對波浪通過泥沙海床之渦流生成及其特性，分析渦流與波能消滅之關係，藉由渦流生成位置、渦流大小、渦流強度、渦心的移動、渦流能量及渦流生成與消散之運動行為。此外，計畫中也將探討波浪和泥沙互制之流場型態、速度場、剪應力、濃度分佈、底床變動、紊流特性和壓力場等。上述數值計算結果對瞭解波浪與泥沙運動交互作用的特性，將有所助益。 The research on suspension and motion laws of sediment under waves are important both in the coastal dynamics and coastal engineering. Since problems arising from wave interaction with sediment are often encountered but difficult to deal with, research on the interaction between them has important implication and great applied value in engineering. Due to the various difficulties that could be expected in carrying out field observations, we propose to conduct the study using numerical model. Since full understanding into the problem of interaction between waves and sediment transports can hardly be attained by linear potential theory, our numerical flume is based on viscous fluid theory to deliver an effective and direct approach for solving the problem sought after. Previous studies on the interaction between wave and sediment have neglected the viscous effect, hence without the effect of turbulence. Instead, our project proposes a new numerical model incorporating fluid viscosity, high nonlinearity and turbulent. An effective numerical model capable of simulating the vortex formation and dissipation processes as waves over seabeds will be developed. The RANS (Reynolds Averaged Navier-Stokes) equations will be used as the governing equations for turbulence and with the k- model to calculate the flow field around the sandbeds for various incident wave conditions. The proposed model will differ from the conventional way which ignores fluid viscosity and turbulence in the physical condition. As a result, the model will be more authentic. The proposed numerical model aims to solve the RANS equations for the mean flow field using a modified k turbulence model. In order to update the free surface configuration at each time step, the Volume of Fluid (VOF) method will be implemented. Coupling the VOF, the embedding method, and a nested grid system, the treatment of free surface problem and complex bottom topography can be easily reached. The proposed model will be used to study several different physical conditions, i.e. waves propagating over sand beds, the dynamic interaction between waves and the muddy seabed, sand ripples, as well as waves across a sloping sand bed. Suspended sediment motion in the boundary layer under waves will be studied. The proposed work is expected to complete within three years. In the first year, we developed the 2D numerical model for simulating the vertical sediment transport and bed evolution under the waves over sand beds. Up to the present, the numerical model is extended to include sediment model. In the second year, wave propagation over a mudded seabed to be followed by numerical simulation for wave propagation over rippled sand beds and slopping sand beds. In the third year, a 3D numerical simulation will be conducted for wave interaction a slopping sand bed and 3D wave interaction with a cylinder. This project will investigate the effects of vortex generation and dissipation arising from a number of physical factors, such as different wave conditions and various conditions of the sand seabeds, while waves interacting with the sand seabeds. Moreover, the project would focus on the mechanism of vortex generation and its characteristics and analyze the relation between vortex motion and energy dissipation, with specific attention to the physical process of vortex formation, size of vortex, strength and energy, together with the details of movement of the vortices. Information of the wave field will be used to estimate energy dissipation due to the existence of sand beds, and to analyze the relation between energy dissipation and vortex characteristics. In addition, thee complex three-dimensional flow patterns, the velocity, the shear stress, sediment concentration, the vertical profiles of the suspended sediment concentration, the bed form, the turbulence characteristic, and pressure fields will be discussed. The results generated from the numerical study will provide a better understanding to the counter interaction between the wave and sediment transports in the flow field.

Keyword(s)

wave
sediment concentration
RANS equations
Volume of Fluid

DSpace CRIS

Numerical Simulation of Sediment Transport in Coastal Areas (Ii)-1

基本資料

Description