| 摘要: | 本研究以三維不可壓縮流模式Splash3D為基礎，發展可模擬泥石流、山崩型海嘯、以及局部沖刷之模式。Splash3D模式以PLIC法(Piecewise Linear Interface Construction)及流體體積法(Volume of Fluid, VOF)，求解Navier-Stokes方程式。該模式在發展之初，僅適用於模擬牛頓流體之行為。然而如泥、粉砂、黏土、土壤等具有複雜之流變特性之物質，因無法精確地以牛頓流體進行描述，應是將其視作具黏滯性之非牛頓流體。因此本研究拓展原有之Splash 3D模式，使其能進一步模擬非牛頓流體之運動行為。此一新模式名為「不連續雙黏性流模式」(Discontinuous Bi-viscous Model, DBM)，可適用於研究泥石流、山崩型海嘯以及局部沖刷模擬。
DBM模式中將物質視為非牛頓流體，以降伏應變率 (Yield strain rate) 為分界，可分為固化區(Plug zone)及液化區(Liquefied zone)，此時所對應之應力值即為該物質之降伏應力(Yield stress)。模式須輸入四個主要參數，分別為降伏應變率、降伏應力、固化區黏滯度及液化區黏滯度。藉由調整降伏應變率與降伏應力，甚至能將模式轉換為傳統之賓漢流模式或牛頓流體模式。此外，本研究亦新增內部造波功能，以實現規則波與不規則波之輸入。
此DBM模式除耦合多項功能外，更經過全面且縝密的驗證，包含理論解與實驗解之比較。比對項目如泥石流、造波波型、受力分布與沖刷坑發展等，各項目都呈現良好之一致性。本論文亦模擬與討論三個DBM模式之應用，其一為模擬1966年美國德州之石膏尾礦潰壩案例；二為海底山崩所致之海嘯模擬，此例中山崩物質組成將視為非牛頓流體；第三則為局部沖刷模擬，如單樁風機受洋流作用，或是複雜橋墩結構受河流影響下之沖刷發展。此模式於上述應用皆有良好成果並套用於國內數項工程計畫，細部討論亦於文中展現。
;Natural materials such as muds, silts, clays, and soils are generally cohesive non-Newtonian fluids with complex rheological properties, which a Newtonian model cannot characterize precisely. This study adopts a three-dimensional model, Splash3D, which resolves the Navier-Stokes equations with PLIC-VOF surface-tracking algorithm. However, the original version of Splash3D is only available for Newtonian fluid prediction. One of the main contributions of this study is compiling a non-Newtonian fluid model into Splash3D model. This non-Newtonian fluid model is named Discontinuous Bi-viscous Model (DBM), which deals with the rheology feature of natural materials. This compiled model is used to study mudflow, landslide tsunami, and scouring problems.
DBM illustrates a discontinuity in the stress-strain relation of the mixture, which contains both solid and liquid phases (un-yield/plug and yield/liquefied phases). A yield strain rate is introduced as the indicator to identify the slip surface, which separates the un-yield and yield region. The new version of DBM can switch to the conventional Bingham model flexibly, where the yield strain rate equals zero. DBM includes four variables as yield stress, yield strain rate, plug zone viscosity, and liquefied zone viscosity, which a rheometer can measure. In addition, the internal source wave maker, which can deliver both regular and irregular waves, is also integrated into the model.
The coupling model is carefully validated with theoretical solutions and laboratory data, including the mudflows, wave generations, force calculation, and scour profiles. All of them get good agreements. This study provides three major applications and discussions of DBM. The first is the mudflow of the gypsum tailings dam in East Texas in 1966. The second is the submarine landslide tsunamis in which the volume of submarine material is treated as a rheological material. The third is the local scour around complex bridge piers caused by river floods and the scouring nearby a mono-pile wind turbine caused by ocean waves. The model is also employed to undertake some important projects in Taiwan. The results are acceptable compared with the survey data. Detailed discussions are presented in the contents. |
