在數值模擬領域中，含自由液面流場的問題求解一直都是具有難度，若此類型之流場又加入結構物則會使之更加複雜。在前人的研究中，利用等位函數法模擬氣液二相流問題已發展的相當成熟，若再配合浸沒邊界法求解流體結構物互制的問題，則能探討氣、固、液體的流動問題。
本文模擬之案例探討不同的結構物對於自由液面以及流況變化的影響為何，採用之案例為均勻流流經橋墩及橋台等結構物；本文研究中，在求解等位函數法時，空間項與時間項分別採用WENO法及三階Runge-Kutta法來離散。而在求解三維不可壓縮Navier-Stokes 方程式的部分，則是利用投影法導出壓力的Poisson方程式，使得連續方程式能夠自動滿足，當壓力解出後即可以二階顯式Adams-Bashforth法求解運動方程式。結構物則利用浸沒邊界法，以虛擬力的方式來處理，計算成果藉由3D效果來呈現，本模式對於整體流況的計算以及自由液面之模擬，都可以獲得良好的結果。

In the numerical simulation, the problem what have free surface always be difficult. If the flow field joins the structure and it will be more complicated. In previous studies, the problem used level set method to simulate gas-liquid two-phase flow is quite mature. If the immersed boundary method is used, and it can explore the flow problems of gas, solid and liquid.
Our examination probes the effects of different structures for the free surface and the flow conditions change. The cases in our examination are always uniform stream flowing through the pier and abutment structures. In solving the level set method, space and time discretization are using WENO method and the third-order Runge-Kutta method. The Projection Method is applied to obtain the pressure Poisson equation such that the continuity equation satisfies. When the pressure is solved, we can solve the equations of motion from second-order explicit Adams- Bashforth method. The immersed boundary method is used to treat the structures to solve the virtual force. The calculation results of flow fields are shown by 3D Tecplot software. In this study, both the calculation of the overall flow conditions and the simulation of free surface can obtain good results.