Abstract Multi-mode wave energy converters are able to generate power from multiple degrees-of-freedom, typically delivering increased power absorption from ocean waves compared to devices operating in heave or surge only. However, the control of such systems is complex due to strong coupling between different degrees-of-freedom. This study aims to understand the effect of both linear and nonlinear pitch-surge hydrodynamic coupling on the performance of a submerged cylindrical wave energy converter. Results showed that when nonlinear coupling effects were considered, pitch had a much larger effect on device performance than what was predicted from a linear model. The maximum power that could be absorbed by the device at lower frequencies was significantly reduced as pitch amplitude increased. In terms of control, from linear theory, for any given pitch amplitude and phase, only the surge amplitude and phase was required to tune the device for maximum power absorption from the wave. However, when a nonlinear model was used, results showed that proper tuning of the pitch phase was also required to achieve maximum power absorption. As the pitch amplitude increased, nonlinear hydrodynamic effects caused by the combined pitch-surge motions became more significant, which in turn affected power estimates. Care should therefore be taken, since linear hydrodynamic models could potentially provide misleading predictions regarding the performance and control of multi-mode wave energy converters.

中文翻译：

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俯仰-浪涌耦合对水下圆柱波换能器性能的影响

摘要 多模式波浪能转换器能够从多个自由度产生功率，与仅在波浪或浪涌中运行的设备相比，通常可以从海浪中吸收更多的功率。然而，由于不同自由度之间的强耦合，这种系统的控制很复杂。本研究旨在了解线性和非线性俯仰-喘振流体动力耦合对水下圆柱形波浪能转换器性能的影响。结果表明，当考虑非线性耦合效应时，间距对器件性能的影响比线性模型预测的要大得多。随着音调幅度的增加，设备在较低频率下可以吸收的最大功率显着降低。在控制方面，从线性理论，对于任何给定的音高幅度和相位，只需要浪涌幅度和相位来调整设备以获得最大的波吸收功率。然而，当使用非线性模型时，结果表明还需要适当调整音调相位以实现最大功率吸收。随着俯仰幅度的增加，由俯仰-喘振组合运动引起的非线性水动力效应变得更加显着，进而影响功率估计。因此应该小心，因为线性流体动力学模型可能会提供关于多模波浪能转换器的性能和控制的误导性预测。结果表明，还需要适当调整音调相位以实现最大功率吸收。随着俯仰幅度的增加，由俯仰-喘振组合运动引起的非线性水动力效应变得更加显着，进而影响功率估计。因此应该小心，因为线性流体动力学模型可能会提供关于多模波浪能转换器的性能和控制的误导性预测。结果表明，还需要适当调整音调相位以实现最大功率吸收。随着俯仰幅度的增加，由俯仰-喘振组合运动引起的非线性水动力效应变得更加显着，进而影响功率估计。因此应该小心，因为线性流体动力学模型可能会提供关于多模波浪能转换器的性能和控制的误导性预测。