|Abstract: ||本文主要目的是利用以速度勢為基底函數而滿足Dirichlet內表面邊界條件方程式之高階偶流小板法,建立一套高效率及高精確度直接求解船體表面速度勢的方法,以便往後在計算螺槳對船體表面激振力之非定常問題,可比以速度為基底者節省大量計算時間.在幾何表面之近似方面,本文採用二次拋物面近似法,解決了低階平板法小板間之不連續性,較準確地模擬真實物體之曲面外形.在奇異點分佈強度方面,於拋物面小板上作二次拋物面偶流分佈,改善了低階法小板與小板間之奇異點分佈強度不連續的缺點,且可得到小板上每一點之奇異點分佈強度值,故可較準確地描述局部流場變化較大的情形.最後本文計算有理論解之球體外表面速度勢,證實僅需於四之一圓上分佈18個小板,其結果即接近於理論解 .並證明本方法比以線性源流強度分佈之高階小板法準確.另外對於外形複雜之船體勢流場亦可準確計算.|
The purpose of this study is to use the potential based higher order doublet method, which satisfies the Dirichlet internal boundary condition, to establish a efficient and accurate method in solving the velocity potential of the ship body directly. The method, can save significant computing time for the calculation of the pressure fluctuation on ship hull induced by a cavitating propeller. Concering geometry simulation, a second order approximation to the true surface is used, which can overcome the geometry leakage problem of the flate panel method. For the doublet strength, the quadratic distribution of the constant distribution method. Finally, the velocity potential of sphere is calculated and compared with the analytical solution. The numerical results by using only eighteen doublet panels to simulate the 1/4 sphere are close to analytical solution very well. However, to get same numerical results, thirty-three second order source panels with linear singularity distribution are needed. Besides, the velocity potential of complicated geometry, such as full ship, is also calculated and compared with that calculated by second order source panel with linear singularity distribution. Both results are almost the same.