船舶碎冰区斜航运动的水动力导数预报

Prediction for hydrodynamic derivatives of ships in oblique motion under brash ice conditions

摘要:

目前敞水水动力导数的研究较为成熟,冰水耦合后的船舶水动力导数研究尚处于起步阶段。为求解碎冰工况下冰水耦合后船舶斜航运动水动力导数,使用CFD软件STAR-CCM+中DEM颗粒模拟碎冰粒子,开启DEM模块下双向耦合模式,通过动量、能量交换达到冰块与水耦合作用,并选用小漂角工况分别为0°、2°、4°、6°、8°进行了斜航运动数值模拟。忽略自由液面的影响。分别计算敞水工况以及碎冰工况下船舶所受的侧向力以及转艏力矩,通过对各漂角下无因次后的力以及力矩拟合从而求解出各个水动力导数。考虑冰块的干扰具有随机性所以采用干扰后的力以及力矩最大值以及最小值分别求解对应的水动力导数,形成一个水动力波动区间,更为真实地预报冰水耦合下的船舶水动力导数。通过计算结果表明,敞水工况下船舶各部分水动力导数值与模型统计公式计算值相差不大,冰水耦合后部分水动力导数波动区间端点值出现正负,冰水耦合后水动力导数随机性较大。

Abstract:

The current research on the hydrodynamic derivatives in open water is relatively mature, but the research on the hydrodynamic derivatives under ice-water coupling is still in infancy. In order to solve the hydrodynamic derivatives of a ship in oblique motion after ice-water coupling under brash ice conditions, the DEM particle of the CFD software STAR-CCM+ was used to simulate brash ice particles. The momentum and energy exchange was performed to achieve the coupling effect between ice and water by turning on the two-way coupling mode under the DEM module. The small drift angles of 0°, 2°, 4°, 6°, and 8° were selected for the numerical simulation of oblique motion. The effect of the free surface was ignored. The lateral force and turning moment of the ship under open water conditions and brash ice conditions were calculated respectively. The hydrodynamic derivatives were obtained by fitting the dimensionless force and moment at each drift angle. Considering the randomness of the brash ice interference, the maximum and minimum values of the force and moment after the interference were used to solve the corresponding hydrodynamic derivatives, so as to form a hydrodynamic fluctuation interval, which can more accurately predictthe hydrodynamic derivatives of the ship under ice-water coupling. Calculation results show that the hydrodynamic derivatives of the ship at each part under open water conditions were not significantly different from those calculated by the statistical model. The end values of the fluctuation interval of some hydrodynamic derivatives after ice-water coupling were positive and negative. Hydrodynamic derivatives were more random under brash ice-water coupling.