Effects of scour on the natural frequency of offshore wind turbine structures

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Journal of Vibration and Shock ›› 2020, Vol. 39 ›› Issue (22) : 16-22.

CHEN Chen，MA Hongwang，LI Yutao，LU Zhiyue

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Abstract

The majority of offshore wind turbines(OWT)are supported by large diameter monopiles.Scour caused by seawater affects the dynamic characteristics and mechanical property of the wind turbine, and its impact on the structural natural frequency is especially significant.Therefore, it is necessary to study the effect of scour on the natural vibration frequency of OWT monopile foundations.First, the effects of scouring depth, sand density and pile embedding depth on the natural frequency of monopile foundations were studied by model test.Then, a three-dimensional finite element model of monopile was established by ABAQUS and the reliability of the numerical model was verified by comparison between the simulation results and model test results.Finally, taking a project as an example, a variety of measures to reduce the natural frequency caused by scour were analyzed.It is shown that, with the increase of scour depth, the natural frequency of the monopole foundation will gradually decrease, and the looser the sandy soil is and the shallower the embedded depth is, the more obvious the decrease is.With the same amount of steel consumption, increasing the embedded depth, wall thickness and pile diameter all can increase the natural frequency of the structure, but increasing the pile diameter has the most obvious effect.It is suggested that the decrease of natural frequency caused by scour can be compensated by increasing pile diameter in practical engineering design to meet the design requirements.

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offshore wind turbines / monopiles / scour / natural frequency / ABAQUS

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CHEN Chen，MA Hongwang，LI Yutao，LU Zhiyue. Effects of scour on the natural frequency of offshore wind turbine structures[J]. Journal of Vibration and Shock, 2020, 39(22): 16-22

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