Monopiles supporting offshore wind turbines experience combined moment and horizontal loading which is both cyclic and complex – continuously varying in amplitude, direction and frequency. The accumulation of rotation with cyclic loading (ratcheting) is a key concern for monopile designers and has been explored in previous experimental studies, where constant-amplitude cyclic tests have shown rotation to accumulate as a power-law with cycle number. This paper presents results from laboratory tests in dry sand, which explore the rotation response to constant and variable amplitude, unidirectional and multidirectional cyclic loading. The tests are designed to inform model development and provide insight into key issues relevant to monopile design. Unidirectional tests show behaviour consistent with previous studies and provide a basis for interpreting more complex tests; multidirectional tests provide new insight into the monopile response to multidirectional cyclic loading; and multi-amplitude storm tests highlight salient features of the response to realistic loading. Tests are conducted in both very loose and dense sand, where the behaviour is found to be qualitatively similar.

中文翻译：

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砂土中复杂循环侧向荷载作用下的单桩旋转

支持海上风力涡轮机的单桩承受的力矩和水平载荷是周期性且复杂的–振幅，方向和频率不断变化。循环载荷（棘轮）对旋转的累积是单桩设计者的主要关注点，并且在先前的实验研究中已经进行了探索，在该实验研究中，恒定振幅循环测试显示旋转累积为具有循环数的幂律。本文介绍了在干沙中进行的实验室测试的结果，这些结果探讨了对恒定和可变振幅，单向和多向循环载荷的旋转响应。这些测试旨在为模型开发提供信息，并深入了解与单桩设计相关的关键问题。单向测试显示出与先前研究一致的行为，并为解释更复杂的测试提供了基础；多向测试为单向堆对多向循环载荷的响应提供了新的见解；多振幅风暴测试突出了对实际载荷响应的显着特征。在非常松散和稠密的沙子中进行测试，发现其行为在质量上相似。