基於對疊船模的Wigley修正船型尺度效應及形狀因子數值模擬

NUMERICAL STUDY ON SCALE EFFECT AND FORM FACTOR OF MODIFIED WIGLEY HULL WITH DOUBLE-MODEL ARRANGEMENT

本研究使用理論船型Modified Wigley Hull討論現行阻力推估方法ITTC 1978的使用極限，藉以分析形狀因子於不同尺度和船體形狀的影響。在5種不同方塊係數條件下，獲得25種相異的船形，並且使用商用計算流體力學軟體STAR-CCM+模擬船體流場以及計算船體所受的黏性阻力。為計算形狀因子，本研究驗證對疊船模用於計算黏性阻力項的準確程度。本研究使用的平板阻力曲線為ITTC 1957-2D、ITTC 1957-3D、Grigson、ATTC、Kastui，以及系列經由數值計算獲得的平板阻力曲線。藉由形狀因子針對不同船形和尺度評估各平板曲線公式的適用性。當船型為Modified Wigley Hull系列，即使不同方塊係數條件下，若具有相同的出水角，可獲得相近的形狀因子。在平板阻力曲線適用性，較小的出水角（＜52.5°）以ATTC的阻力曲線預測形狀因子為佳；較大的出水角（＞52.5°）則以Katsui的平板阻力曲線預測形狀因子為優。

A theoretical hull series is employed in this study to evaluate the ITTC 1978 extrapolation method, in order to understand the impact of the scale and hull form on the form factor. Modified Wigley hull is chosen as the hull series utilized in this study, where 25 different hull forms are generated for 5 different block coefficients. The commercial computational fluid dynamics software, STAR-CCM+, is applied to calculate the viscous drag via flow simulations. First, this study validates the accuracy of form factor prediction with a double-model arrangement. After that, the suitability of different flat plate friction lines was appraised with diverse behavior of the form factor under varied hull forms, scale, trying to derive regression formula for each flat plate friction lines. The flat plate friction lines employed in this study are ITTC 1957-2D, ITTC 1957-3D, Grigson formula, ATTC 1947, Kastui formula, and the flat plate friction line calculated by this study. In conclusion, if the series is Modified Wigley Hull form, the form factor is similar as long as their entrance angles are same regardless of distinct block coefficients. As for the suitability of the flat plate friction line, it ends up that the ATTC one is suitable for low run angle (<52.5°), and that Katsui one is suitable for high run angle (>52.5°).