箭艏於貨櫃船線形最佳化設計應用之研究

Abstract

提高能源利用效率是目前科技發展的趨勢,尤其以大型貨櫃輪等巨大海上耗能的交通工具為首要目標。船形精進可以在排水 量 (或 載 貨 量 )維 持 下 , 讓 總 阻 力 降 低 以 達 到 節 省 能 源 的 效 果 。 本 研究修改一艘現行的球艏貨櫃輪前半段線型成為箭艏,使之在靜 水性能維持不變的條件下,可以降低靜水狀態之興波阻力。同時 探討主要影響興波阻力性能的關鍵參數。 首先將船形幾何形狀予以參數化,並探討各個參數與興波阻 力的關係,利用最佳化的方法改變每個參數以逐步降低興波阻力 係數進而找到箭艏船形的最佳結果。為了縮短計算的流程,所以 在設計階段使用勢流計算,再將興波阻力係數較低的船形進行黏 性流計算,以確定在靜水情況下的總阻力。 本研究成果使得箭艏船形的興波阻力係數在勢流計算下比 母船球艏船型減少了 10%,但經過黏性流場計算,總阻力部分仍 然比原有球艏船型高出 2%,而其中壓力項仍然比球艏版本多出 4%。在本研究中使用最佳化演算法找到數個有效影響興波阻力 係數的參數。傳統球艏改成箭艏之後缺少一個可以消去艏波的機 制,因此艏波較大造成額外的壓差阻力是箭艏船型在靜水情況下 總阻力較大的主因。

Containerships with bulbous bow are the major type in the sea transportation and have been proved well over decades. An aim of our modeling was to reform the bulbous bow of a 1700 TEU containership into an arrow bow. Second, we would like to find the key geometric parameters of the arrow bow that affect the hydrodynamic performance. The geometry was fully parameterized, while keeping the principle dimensions and afterbody geometry the same. Non-uniform Rational B-spline theory was applied on the forebody sections to guarantee surfaces with high-order smoothness. An optimization algorithm was used to find the relationship between the parameters and the wave-making resistance coefficient. For increasing computing pace ,in optimal process only evaluated Wave-making performance by potential flow theory, and was compared to the conventional one. The outstanding geometries were selected, and then evaluated the total resistances by CFD. Fifteen versions of arrow bows were made, and six of them were calculated by CFD. The minimum Cw was 10% less than the original, but the total resistance is 2% higher. The main contribution to the increment of the total resistance is the pressure term, which is 4% larger than the bulbous one. Also, the wave elevations of the arrow bow were inspected two times larger at the fore perpendicular. During the process, four parameters were found to affect Cw effectively. The parametric modeling process of the arrow bow of containerships may provide the basis in the designing stage. But the mechanism to reduce the wave peak at the FP needs to be studied further.