اثر متقابل ساختار خاکی فونداسیون بر پاسخ لرزه ای توربین های بادی Effect of soil-foundation-structure interaction on the seismic response of wind turbines

1. Introduction Wind turbines are the world’s fastest-growing source of renewable energy across America and around the globe. In 2015, the US wind industry installed a total of 8598 Megawatts (MW) of new power capacity, a 77% increase over 2014 [1]. Decreasing number of prime sites with high wind availability and good access, coupled with increasing demand for higher power output has increased the need to use taller towers with longer blades especially in less windy sites [2]. In seismic regions, taller wind turbines develop large seismic forces that are sometimes bigger than the wind forces [3]. In such cases, an inaccurate estimate of the seismic force can result in either structural failure or uneconomic design. An important factor in estimating the seismic forces on wind turbines is the soil-foundation-structure interaction, which is affected by different parameters including turbine size, foundation type, and soil properties. This paper analyzes the soil-foundation-structure interaction effects on the seismic response of wind turbines. Three wind turbine capacities are selected for the study, namely, 65-kW (similar to the experimental model), and 1-MW and 5-MW (representing the current lower and upper threshold of utility scale sizes). In this study, horizontal-axis turbines with truncated cone steel towers were used. Foundation types are spread foundation, mono pile, pile group with cap, and anchored spread foundation. Soil effects are included using modulus of subgrade reaction and also explicit model. The finite element model developed using the ANSYS program was first validated using experimental data. Natural frequencies of numerical models are then examined using the Block Lanczos method with ANSYS program. Next, time history analysis is performed using the records from the 1992 Landers Earthquake and the generalized HHT-a formulation. Recommendations are provided to simplify the soil-foundation-structure interaction analysis of wind turbines subjected to seismic loading.