FPSO内孤立波载荷实验观测及理论预报模型研究

利用大型密度分层水槽开展了下凹型内孤立波作用在FPSO上的载荷特性系列实验;并依据实验工况,考虑KdV、eKdV和MCC内孤立波理论的适用性条件,数值研究了FPSO内孤立波载荷成分构成;基于实验结果和载荷成分构成,建立了FPSO内孤立波载荷的理论预报模型.研究表明:FPSO内孤立波水平载荷由粘性力和Froude-Krylov力组成,而垂向载荷主要为垂向Froude-Krylov力;Froude-Krylov力可通过动压力沿FPSO浮体湿表面积分得到,粘性力则通过经实验回归的摩擦系数Cf、形状修正因数K乘以内孤立波诱导水质点切向速度沿FPSO浮体湿表面积分得到.系列实验结果得出:摩擦系数Cf和形状修正因数K与雷诺数Re、KC数和流体层深度比h1/h有关;摩擦系数与Re呈自然对数关系;而形状修正因数K与KC数呈幂函数关系.理论预报模型预报的水平载荷、垂向载荷结果均与系列实验和数值结果吻合较好,并且发现随着内孤立波振幅的增加,载荷幅值近乎线性增加,而且上层流体深度对水平力幅值有明显的影响.

Experimental Investigation and Simplified Prediction Model Study of Internal Solitary Wave Forces on FPSO

The forces exerted by internal solitary waves (ISWs) on FPSO were investigated. A series of depression ISWs were generated by a double-plate wave maker in a density stratified two-layer fluid within a 30-meter-long wave flume. The forces on a fixed FPSO model were measured. Combined with the laboratory experiments, a numerical flume taking the applicability of ISWs theories into con-sideration was adopted to study the force components. Based on the experimental data and the force composition, the theoretical simplified prediction model for FPSO ISW loads was established. It is shown that the horizontal load consists of two parts:the Froude-Krylov force, which can be calculated by integrating the dynamic pressure induced by ISW along the FPSO wetted surface, and the viscous force, which can be obtained by multiplying the friction coefficient Cf, correction factor K and the inte-gration of particle tangential velocity along the FPSO wetted surface. The vertical load is mainly the vertical Froude-Krylov force. It is concluded from the experimental results that the friction coefficient Cf and correction factor K are regressed as a relationship of Reynolds number Re, Keulegan-Carpenter number KC and layer depth h1/h. Moreover, the friction coefficient Cf follows the natural logarithmic function with Re, while the correction factor K follows four power function with KC number. The force prediction was also performed based on the regression formulas and pressure integral. The predicted results agree well with the experimental and numerical results. The maximum forces increase linearly as the ISWs amplitude increases. Besides, the upper layer thickness has an obvious influence on the extreme value of the horizontal forces.