不同強制運動模式對船體橫移水動力係數之影響

INFLUENCE OF DIFFERENT CAPTIVE MODEL TESTS ON SWAY HYDRODYNAMIC DERIVATIVES

船體的運動方程式可利用強制運動之測量結果建立。本研究以實驗的方式探討靜水條件中，船體在不同強制運動狀態下的船體受力並分析水動力係數。實驗以一艘貨櫃船型分別進行不同漂移角的OTT試驗（oblique towing test），及不同橫移幅度的PMM（planar motion mechanism）動態Pure Sway試驗，量測船體受到的縱向力、橫向力、扭矩。將量測到之船體受力數值代入運動方程式進行傅立葉分析與數值擬和以求得水動力係數。本研究比較Pure Sway試驗進行單次試驗（single run，SR）、多次試驗（multiple run，MR）及OTT試驗之過程與橫移速度相關水動係數之差異。結果顯示MR較SR受單次試驗數值異常影響較小；OTT與Pure Sway所得橫向速度一次方相關之水動力系數、數值較接近；Pure Sway橫向速度三次方相關之水動力係數、與OTT試驗及前人結果相差較大，推測Pure Sway較無法表現橫移速度三次方之特徵。

The equations of motion for a ship can be established using measurement results from captive model tests. This study experimentally investigates the hydrodynamic forces acting on a ship hull under various captive motion tests in calm water to determine the hydrodynamic derivatives. Experiments were conducted using a container ship model to perform OTT (oblique towing test) at different drift angles and PMM (planar motion mechanism) Pure Sway tests with varying sway amplitudes. The longitudinal force, lateral force, and yaw moment acting on the hull were measured. The measured force data were applied to the equations of motion, utilizing Fourier analysis and numerical fitting to derive the hydrodynamic derivatives. This study compares the procedures and the resulting sway hydrodynamic derivatives obtained from Single Run (SR) and Multiple Run (MR) Pure Sway tests, as well as those from OTT. The results indicate that the MR method is less susceptible to anomalies in individual test data compared to the SR method. The linear sway derivatives , obtained from OTT and Pure Sway tests show close agreement. However, the cubic sway derivatives , derived from Pure Sway tests differ significantly from those obtained via OTT and results from previous studies, suggest-ing that the Pure Sway test may not effectively capture the characteristics associated with the cubic terms of sway velocity.