用势流和计算流体动力学模型比较三自由度圆柱形点吸收体波浪-结构相互作用动力学
Comparison of wave-structure interaction dynamics of a submerged cylindrical point absorber with three degrees of freedom using potential flow and computational fluid dynamics models
摘要：
在本文中，我们比较了垂荡，浪涌和俯仰动力学的淹没圆柱形点吸收器，模拟使用势流和完全解决计算流体动力学（CFD）模型。势流模型基于时域Cummins方程，而CFD模型使用虚拟域Brinkman惩罚（FD/BP）技术。使用动力输出（PTO）装置将水下圆柱体拴在海床上，动力输出装置可抑制转换器的升沉、纵荡和俯仰运动，并吸收所有三种模式的能量。结果表明，势理论过度预测的升沉和纵荡运动的振幅，而它的结果在一个完全淹没的轴对称转换器的一个微不足道的俯仰。它还低估了浮标的缓慢漂移，而CFD模型能够可靠地捕捉到这一点。此外，我们使用完全解析的CFD模拟来研究三个自由度（DOF）圆柱形浮标在不同PTO系数、浮标质量密度和入射波高度下的性能。它表明，PTO系数预测的线性势理论是次优的波的中度和高陡度。当PTO阻尼选择为高于预测值时，波吸收效率显著提高。不同质量密度的浮标的模拟表明，低质量密度的转换器在其PTO和系泊缆中具有增加的张力。此外，质量密度也影响装置的共振周期的范围。最后，不同波高的模拟表明，在较高的高度，波的转换器的吸收效率降低，大部分可用的波能保持未被吸收。
英文摘要：
In this paper we compare the heave, surge, and pitch dynamics of a submerged cylindrical point absorber, simulated using potential flow and fully-resolved computational fluid dynamics (CFD) models. The potential flow model is based on the time-domain Cummins equation, whereas the CFD model uses the fictitious domain Brinkman penalization (FD/BP) technique. The submerged cylinder is tethered to the seabed using a power take-off (PTO) unit which restrains the heave, surge, and pitch motions of the converter, and absorbs energy from all three modes. It is demonstrated that the potential theory over-predicts the amplitudes of heave and surge motions, whereas it results in an insignificant pitch for a fully-submerged axisymmetric converter. It also under-estimates the slow drift of the buoy, which the CFD model is able to capture reliably. Further, we use fully-resolved CFD simulations to study the performance of a three degrees of freedom (DOF) cylindrical buoy under varying PTO coefficients, mass density of the buoy, and incoming wave heights. It is demonstrated that the PTO coefficients predicted by the linear potential theory are sub-optimal for waves of moderate and high steepness. The wave absorption efficiency improves significantly when higher than the predicted value of the PTO damping is selected. Simulations with different mass densities of the buoy show that converters with low mass densities have an increased tension in their PTO and mooring lines. Moreover, the mass density also influences the range of resonance periods of the device. Finally, simulations with different wave heights show that at higher heights, the wave absorption efficiency of the converter decreases and a large portion of available wave power remains unabsorbed.
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