Study On Wind-induced Dynamic Responses Of The Foundation Of Mountainous Large-scale Horizontal-axis Wind Turbine

For the past few years, many large and medium-sized cities in China have witnessed serious air-quality problems. The shortcomings of coal based thermal power have become increasingly evident, and the utilization of hydropower is close to saturation. Therefore,wind power as a representative of the new energy, is now becoming a strong complement to the electric power resources. In the past, the exploration of wind resources in China was mainly concentrated in three northern areas and the southeast coastal region. But recently, in order to narrow the regional energy disparity and stimulate the sustainable development of the economy in the central and southern China, the development of wind power in these mountainous and hilly areas has drawn great attention from the public, as well as the government. However, the design theory of the mountainous wind turbine foundation is still not mature enough, and the irrational design of foundation has caused several collapse accidents of wind turbine. Thus, it is extremely necessary to study the interaction mechanism between residual soils and spread foundation in an inland wind field, and explore the wind-induced dynamic responses of mountainous wind turbine foundation under random wind loads. Based on above backgrounds, the following research work has been carried out in this paper:(1) Subgrade pressures, foundation settlements and tower strains of several wind turbines were tested in a wind field, and the changing behaviors and the distributions over time were summarized. The results show that the values and distributions of subgrade pressures have a great relationship with velocities and operating conditions, and the subgrade pressure may be agreed with the trapezoidal or parabola distribution, and even close to the slower “N” distribution. The measured magnification factors of subgrade pressures which caused by superstructural dynamic loads on the edge of the foundation can reach 1.05, which contributes to the variation of the actual distribution shape of subgrade pressures compared to the assumed ideal distribution plane. Also, the mathematical model for settlement prediction was obtained by fitting a large number of measured settlement data.(2) Based on similarity theory and dimensional analysis method, model tests were conducted in which a 1/10-scale model of the mountainous wind turbine foundation subjected to random wind loads adopting rational similarity constants, and the dynamic responses of the wind turbine foundation were monitored. The experimental results showthat subgrade pressures, strains, horizontal displacements and settlements of the wind turbine foundation are significantly influenced by the horizontal random wind loads, and compared with considering the change of fluctuating wind speed alone, the dynamic responses of wind turbine foundation caused by the random loads that taking into account the variation of both average wind and fluctuating wind are more significant.(3) The stress and deformation of the wind turbine foundation under random wind loads was analyzed by means of numerical method, and the numerical model was verified by comparing the numerical results with the model tests data, and then further studies on the dynamic responses of the wind turbine foundation were performed using the numerical model. The numerical analyses indicated that the magnification factor of subgrade pressure on the leeward side of the foundation is ranging from 1.15 to 1.23, the magnification factor of basement stress is from 1.16 to 1.24, and the magnification factor of foundation settlement is over 1.12 under the random wind loads with the average wind speed of 11m/s. It is also shown that foundation overturning is a general failure mode in terms of mountainous wind turbine, and it should be paid much attention when designing and constructing.