Effect of Frequency Ratio on Dynamic Responses of Sand Under Wind Turbine Loading
The soil sample is subjected to a coupling effect of wind and wave action with various frequencies during the operation of offshore wind turbines.A series of tests were conducted to investigate the influence of the frequency ratio between wind and wave loads on sand using a multi-directional cyclic simple system(VDDCSS).The effect of frequency ratio on the dynamic strain,pore water pressure,and dynamic strength of sand was analyzed.The test results show that the development of shear strain is affected by the bidirectional frequency coupling and the combination of x and y-direction stress caused by the frequency ratio.At a CSR of 0.15,the bidirectional frequency coupling effect is greater than the stress combination effect.With the increase of the stress level(at a CSR of 0.20 or 0.25),both the frequency coupling effect and the stress combination effect are strengthened.At a low-stress level,the pore pressure curve of the failed specimen is"upward concave"and the frequency ratio has little effect on the pore pressure development of other specimens.As the stress level increases(at a CSR of 0.20 or 0.25),the final value of pore pressure umax increases with increasing CSR.Except for the samples corresponding to a fr of 1.00 and 10.00,the dynamic strength of others soil samples decreases with the increase of fr and CSR.At a f of 5.00,the sample has a large strain,a high pore pressure value,and a low dynamic strength,which is related to the superposition effect of the two-way frequency coupling and stress combination.
cyclic simple shearfrequency ratiodynamic strainpore water pressuredynamic strength
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