Development of Measuring System for Stability of a High-Speed Craft Using an Unmanned Towing Carriage

大坂府立大学拖曳实验室研制了船舶运动和高速船受力的测量系统，利用该系统对滑行艇在静水中前进速度高达Fn=6.0时的纵向动力不稳定性或称“鼠泊”现象进行了实验研究，并对船舶运动进行了测量，揭示了“鼠泊”现象的特征和条件。结果表明，在任意航速下，垂荡与纵摇的相位差约为90 °，通过模型试验和强迫运动试验，研究了垂荡与纵摇的耦合恢复系数随航速的增加而减小，当Froude数大于0.6时，垂荡恢复系数变为负值，其中动力分量在总力中占主导地位。这表明，系泊是一种自激振荡，由于升沉和纵摇运动之间的能量交换。模拟的升沉和纵摇振幅与实测结果吻合较好。

Measuring systems for ship motions and forces acting on high-speed craft have been developed in the towing tant of Osaka Prefecture University.Using the system, experimental investigations are performed on the longitudinal dynamic instability, or porpoising, of a planing craft at high advanced speed up to Fn=6.0 in calm water.Measurements of ship motions are carried out to reveal the characteristics and conditions of porpoising. The results show that the phase difference between heave and pitch is about 90 degrees at any advanced speed.Captive model tests and forced motion tests are carried out to clarify the influence of the restoring, damping and added mass forces on the dynamic instability, The results show that the coupled heave restoring coefficient from pitch motion decreases with advanced speed and becomes negative at Froude number higher than 0.6, where the dynamic component in the total force are dominant. This suggests that the porpoising is a self-excited oscillation due to the energy exchange between heave and pitch motions.Porpoising of the model ship are numerically simulated using a non-linear equation with measured non-linear hydrodynamic and hydrostatic coefficients. The simulated heave and pitch amplitudes are in good agreement with the measured results.