利用CFD方法計算貨櫃船於規則波中附加阻力之研究

Abstract

隨著近年來世界經濟活動蓬勃發展，海上大型運輸工具之研發設計顯得日漸重要。雖然以船模試驗方法已可準確求得船舶之阻力性能，但過程將耗費大量的成本與研究周期。相對於現今已成熟發展之計算流體力學技術，數值計算方法可大幅降低成本和提高效率並能得到合理的結果。 本研究利用商用CFD軟體，以現有之1700TEU貨櫃船劍艏船型以縮尺比1/50為計算模型，模擬計算船舶在靜水與規則波下之航行阻力分析，目標為預估船舶之實航阻力。整體採用有限體積法搭配適用的紊流模型求解雷諾平均之涅維爾-史托克方程式，並利用流體體積法模擬自由液面之二相流。計算網格使用卡氏座標體積網格和邊界層柱狀網格，並加入艏艉重點局部加密以求得較精準之阻力結果。靜水計算分為船身固定與船身放開兩部分，計算之總阻力各與拖航水槽之船模試驗結果做進一步的比對與分析。船身固定部分誤差維持在4%以內;船身放開部分誤差則在3%以內。在規則波模擬部分則先以純線性波浪測試決定時間步距，配合適用波浪之網格佈置，接著放入船模模擬各波浪頻率中的阻力及運動。整體計算結果與船模試驗量測以及勢流理論計算結果比較，平均附加阻力趨勢可正確預估，運動反應部分則在定性及定量上皆與實驗吻合。最後配合實際海域海象波浪統計資料，此方法可保守推估船舶於實海上之附加阻力最大期望值。

This research describes that we apply the Computational Fluid Dynamics package software to simulate the resistance of hull in calm water and regular wave. We choose the 1700 TEU container ship with arrow bow at model scale 1/50 to be our model of computation. The goal of this research is to evaluate resistance of hull in real sea operation. A finite volume method is adopted to discretize the computationa domain and calculate the Reynolds-Averaged Navier-Stokes equation with suitable turbulence model. Free surface is modeled by using Volume-of-Fluid approach . We use the trimmer mesh and prism layer mesh of unstructural computational grid and add the local refinements to get the more accurate results. The part of calculation in calm sea is divided into hull fixed and hull free, and these results of resistance are compared with results of model test. The error of fixed state is in 4% and the error of free state is in 3%. In the part of regular wave, we decide the time step with pure linear wave firstly, and generate suitable grid for simulating wave. Then we add the model to calculate resistance and motion at each frequency. These calculated results are verified with experimental data and the results of potential theory . The trends of mean added resistance coefficients were evaluated correctly . the motion responses were well consistent with experiments qualitatively. Finally,The results were applied to whole-year sea state statistics from the Taiwan Strait,and this way can predict the maximum expected value of added resistance in real sea operation conservatively.