A shallow draft cylindrical barge type floater with footing close to the water surface was experimentally evaluated in waves to investigate non-linear motion characteristics. The floater was designed to be used as an option for FOWT—floating offshore wind turbines. The non-linear mechanism can be promoted due to the viscous force that acts on the footing edges and the footing interaction with the free surface. In general, the observed non-linear viscous damping is modeled as a force proportional to the square of the relative velocity between the floater and the water. Therefore, the viscous damping levels is expected to increase, and the response in waves, to decrease. However, an increase in motion responses was observed for a broad range of wave periods. An attempt was made to clarify the hydrodynamic mechanism by comparing wave tank experiments, numerical calculations by CFD—computational fluid dynamics codes, and linear potential theory codes. Regular wave tests for three different wave height conditions were carried out, including free decay tests in still waters. For CFD simulations, the OpenFOAM code was selected. For potential theory simulations, the WAMIT code was chosen. As a result of the research, three points could be highlighted and discussed: first, the hydrodynamic phenomenon that contributed to the non-linear motion of the floater was identified; second, the increase and coupling of the motions response of heave and pitch motions; and finally, the phenomenon that the footing held water mass and lifted it to the water surface. The CFD calculations were able to get good qualitative results compared with the experiments and confirmed the use of CFD as a useful tool to capture the non-linear hydrodynamic phenomenon. The linear potential theory was not able to capture the phenomenon discussed herein.

中文翻译：

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波浪中FOWT的浅吃水圆柱形驳船型浮子的非线性运动特性

在波浪中实验性地评估了立足于水面的浅吃水圆柱形驳船型漂浮物，以研究非线性运动特性。该浮子旨在用作FOWT的选件-浮式海上风力涡轮机。由于作用在基脚边缘上的粘性力以及与自由表面的基脚相互作用，可以促进非线性机制。通常，将观测到的非线性粘性阻尼建模为与浮子与水之间的相对速度的平方成比例的力。因此，预期粘性阻尼水平会增加，而波浪响应会下降。但是，在宽范围的波浪周期中都观察到了运动响应的增加。试图通过比较波箱实验来阐明流体力学机理，CFD进行的数值计算-计算流体力学代码和线性势能理论代码。进行了三种不同波高条件的常规波浪试验，包括在静水中的自由衰减试验。对于CFD模拟，选择了OpenFOAM代码。对于潜在的理论模拟，选择了WAMIT代码。作为研究的结果，可以强调和讨论三点：首先，确定了导致浮子非线性运动的流体动力学现象；第二，升沉和俯仰运动的运动响应的增加和耦合；最终，这种现象是立足点支撑了水团并将其提升到水面。与实验相比，CFD计算能够获得良好的定性结果，并确认使用CFD作为捕获非线性流体动力学现象的有用工具。线性势能理论无法捕获本文讨论的现象。