| Under the background of the comprehensive promotion of renewable energy development and the gradual saturation of onshore wind energy,the development of offshore wind energy is increasingly important.With the gradual development of shallow water offshore wind energy,the development of offshore wind energy is moving towards deep water areas,which is the main trend of future development.In order to ensure the safety and normal operation of offshore wind turbines,it is necessary to analyze their seismic performance.Tripod foundation overcomes the disadvantages of low lateral stiffness,obvious lateral displacement,and large scour impact of single pile foundation.It is a type of offshore wind turbine foundation that is more suitable for construction in deeper waters.However,compared with single pile foundation,the application history of tripod foundation is relatively short and the structural form is more complex,which makes the research on the seismic performance of tripod offshore wind turbines relatively lacking,especially the research combined with shaking table tests.Therefore,it is necessary to combine shaking table tests to carry out research on the seismic performance of tripod foundation considering pile-soil interaction.Based on the above reasons,a 1:20 scale model shaking table test and finite element simulation of the tripod support offshore wind turbine,as well as a full-scale tripod offshore wind turbine seismic research considering pile-soil interaction,were conducted.The main research contents include:(1)design a blade scaled model and carry out a shaking table test.The main content of the test includes using white noise sweep frequency to determine the dynamic characteristics of the structure,and calculate the dynamic response of the structure under seismic action with an acceleration amplitude of 0.6g;(2)use the general finite element software ANSYS Mechanical to carry out elastic time history analysis on the scale model and compare it with the test results to verify the accuracy of the modeling method;(3)establish two full-scale offshore wind turbine unit models,named OWT-1 and OWT-2(OWT is the abbreviation of offshore wind turbine),and use ANSYS Mechanical to carry out time history analysis to the fully constrained model,separated model and integrated model,which were three method to simulate pile-soil interaction.Compared the calculation results of the three models,and analyze the influence of SSI effect on the structural dynamic response;(4)Adjusted the foundation soil among composite,loess,clay and loamy,and researched soils’ effect on natural frequency and acceleration response of offshore wind turbine.The main conclusions drawn from the research were as follows:(1)Under the Kobe wave and Taft wave,the acceleration response of the tower in the X and Y directions presented a trend of increased firstly and then decreased from bottom to top.and the maximum acceleration response occurs at the bottom of tower;the acceleration response along Z direction distributed uniformly,and the amplification factor of the acceleration is relatively low.The acceleration response of the tower under San Fernando wave distributed uniformly among the tower,and the amplitude is relatively large.The average acceleration along X、Y and Z under San Fernando wave were increased by 64.52%,109.33%,and 269.81% compared with the Kobe wave,and increased by 70%,86.91%,and 184.06% compared with the Taft wave.(2)The blades had a significant influence on the dynamic characteristics of the structure,which made natural frequency of the structure decreased 3.82%～16.04%.In addition,the first two frequencies of the structure without blades were basically same,while the frequencies of the structure with blades were different.Under the condition with lateral brace,the difference between first two frequencies was 2.65% referred to first frequency;under the condition without lateral brace,the difference between the two in the condition of no inclined braces on the pile side is 5.88% referred to first frequency.(3)Compared the dynamic characteristics and dynamic response of the model with and without lateral braces,it founded that the natural frequency,damping ratio,and dynamic response of the structure were all decreased in the condition without lateral braces.The first two natural frequencies were respectively reduced by 7.71% and 10.53%,and the damping ratio was reduced from 0.033 to 0.021,which decreased of about 36.4%;the amplitude of acceleration of each measuring point on the tower decreased by 6.83%～67.94%.(4)The dynamic characteristics and response results of the finite element simulation were in good agreement with the test results.The error of natural frequency were about 3.04%～7.72%.The maximum error of acceleration was about 7.69%.(5)In the working condition considering pile-soil interaction,the natural frequencies of all levels of the structure were reduced,and the reduction amplitude of high-order modes is higher than that of low-order modes.In the analysis of OWT-1 and OWT-2 wind turbine,when using the separated model for calculation,the first frequency was respectively reduced 0.08%and 2.72% compared with the fully constrained model,and the maximum reduction occurred in the 7th and 8th mode,with a reduction respectively of 13.36% and 13.11%;when using the integrated model for calculation,the first frequency was respectively reduced by 0.04% and3.48% compared with the fully constrained model,and the maximum reduction occurred in the7 th and 8th mode,with a reduction respectively of 16.24% and 24.91%.(6)Compared the separated model and integrated model,it can be found that the natural frequencies calculated by the separated model were between the integrated model and the fully constrained model.In the calculation of OWT-1 and OWT-2 wind turbines,the separated model respectively increased by 3.74% and 7.30% compared with the integrated model.(7)The pile-soil interaction reduced the acceleration response of the structure and increased the displacement response.In the OWT-1 model,for the Kobe wave,when used the separated model and integrated model to analysis,the average acceleration response decreased by 7.87% and 10.45%,and the average displacement response increased by 7.83% and 12.80%.For the San Fernando wave,when using the separated model and integrated model to analysis,the average acceleration response decreased by 6.51% and 9.98%,and the average displacement response increased by 3.48% and 12.80%. |
PDF Full Text Request