貨櫃船於頂浪中附加阻力之數值模擬

Numerical Simulation of Added Resistance in Head Waves for a Container Ship

耐海試驗的目的為預測船舶在波浪中的運動和阻力反應，作為實海航行的安全和效能指標。雖然以船模試驗方法己可準確求得船舶之波浪阻力性能，但過程將耗費大量的成本與研究周期，目前仍常用經驗法則估算。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1700 TEU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，目標為預估此船於台灣海峽波浪條件下之實航阻力。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。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航海餘裕。 The purpose of the seakeeping model test is to predict motion response which is important to estimate the safety and comfort indices in real sea operation. Although sea margin and waves and motions are closely related, a rough calculation of the former by empirical formula is typically sufficient. The goal of this paper is to test and demonstrate the capabilities of Reynolds-averaged Navier-Stokes equations (RANS) solver to evaluate added resistance in head waves with forward ship speed. The geometry of a real 1,700 TEU container ship was modeled. The bare hull resistance was first computed and verified with experimental data. To simulate regular waves, boundary conditions were set by the airy wave equation. Then the heave and pitch motions of the hull were simulated by applying the arbitrary Lagrangian-Eulerian (ALE) technique. The mean added resistance coefficients were carried out and applied to whole-year sea state statistics from the Taiwan Strait. Results showed that the motion responses were consistent with experiments while the sea margin of 20% was found to be overestimated than experimental prediction and potential theory but still lies within empirical estimation.