Dynamic Fatigue Damage And Vibration Reduction Of Offshore Wind Turbine Structures By Bucket Foundation

As a large land and large ocean country,China has a wide range of marine strategic interests.Managing and building a strong marine power and developing new marine energy are inevitable and urgent requirements of the new era.Offshore wind energy holds merits such as better quality of the wind resources,larger suitable free area to install and close to the north area of China,which can not only make full use of ocean resources,but also accelerate the pace of green power generation in China.Bucket foundation structure provides a brand-new idea for efficient,low-cost and large-scale construction of offshore wind power with its superior performance,high cost performance and short construction period.At present,problems like how to reflect the dynamic characteristics and long-term dynamic characteristics of the offshore wind turbines(OWTS)supported by the bucket foundation,how to accurately predict the structural fatigue life under complex ocean cyclic loading and how to effectively control the structural vibration in extreme situations,are the main and difficult points.Therefore,this paper has conducted in-depth research on the key issues of the about OWTS,involving prototype observation,laboratory test,theoretical derivation and numerical simulation.The corresponding research and innovative results are as follows:(1)Based on the field observation data,the vibration response characteristics and the influence of foundation parameters of the OWTS under different operating conditions were analyzed.Firstly,the vibration characteristics of offshore wind turbine under different working conditions were counted.The structural dynamics characteristics were studied.Then based on the prototype observation data,a joint simulation method based on MATLAB and ABAQUS treating the particle swarm optimization algorithm(PSO)as the core was proposed to optimize the inversion of the complex layered foundation parameters of the bucket foundation.The elastic modulus and compressive modulus conversion coefficient of complex layered soil were within the range of [5.6,6.0].Finally,based on a large number of finite element simulations,an empirical formula for the equivalent stiffness of the bucket foundation-soil interaction was established by analogy method and regression analysis.(2)Based on the bucket foudation model test in the laboratory,the behavioral changes of long-term cyclic action of the bucket foundation were studied.The test was carried out under the condition of 1 gravity.The bucket foundation model was placed in saturated sand and subjected to cyclic loading.The long-term behavior changesof the bucket foundation model were investigated by different load conditions.And,a neural network regression analysis method was established to analyze the influencing factors.And,the natural frequency of the structure increased by about 20% to 40% with the excitation number and densification in the bucket foundation.Then,the Monte Carlo method was used to establish the random distribution field of soil stiffness,and the influence of foundation stiffness degradation on the bucket foundation model was analyzed.(3)Researches on the vibration fatigue of the OWTS supported by the bucket foundation and fatigue crack propagation were conducted.Firstly,joint probability of wind and wave was constructed based on the published statistics data.Then,the aerodynamic load on the wind turbine,tower and hydrodynamic load on the foundation were detailed analyzed,and coupled dynamic analysis system of OWTS was established.Next,fatigue damage analysis based on time-frequency domain calculation method,which was fouced on the complex joint segments in three bucket foundation structures.The joint simulation method of FAST and ABAQUS was built,and the fatigue crack growth at the joints was predicted,according to the statistical hot spot stress distributions.(4)Based on theoretical derivation and numerical simulations,research on passive vibration control of the OWTS was carried out.Passive control dampers such as traditional tuned mass dampers(TMD),multi-tuned mass dampers(MTMD),and new eddy-current dampers(ECD),the principles of vibration control were summarized.Based on the stochastic process method as path integration and modified Monte Carlo method,the equivalent offshore wind turbine supported by bucket foundation-TMD random dynamic response was analyzed.Based on laboratory tests,the influencing factors and vibration reduction effects of ECD damping were verified.Finally,the damping effect of the passive dampers in the extreme wind conditions of the OWTS was explored by constructing finite element model for the Xiangshui offshore wind turbine engineering reducing the vibration amplitude by 13.4% to 38.8%,and increasing the anti-fatigue capability by 36%~51%.