Dynamic wind loads on heliostats

This PhD thesis describes a methodology to determine dynamic wind loads on solar concentrators known as Heliostats. The methodology, which relies on numerical simulations, has been applied to a conventional heliostat design to predict the response of the structure subjected to the turbulent atmospheric boundary layer (ABL). Large-eddy simulations (LES) have been performed on a simplified model of a heliostat at different elevation angles to predict the time-dependent wind loads. Based on wind data analysis and information from the literature, the ABL has been reproduced at the inlet boundary of the flow simulations by generating synthetic turbulence via the Vortex Method. A detailed finite-element (FE) model of an 8 m^2 heliostat has been generated and validated with measurements by means of modal analysis. The results from the modal analysis helped to identify the modes most likely to be excited by fluctuating wind loads. The FE model in combination with the damping coefficients determined experimentally have been used to develop a dynamic FE model of the heliostat. The time signals of the pressure loads from the LES have been used as boundary condition in dynamic FE simulations to compute the response of the structure under critical wind conditions. By analyzing the transient FE results, it was found that the contribution of inertial forces and resonance effects is significant in the reaction loads. Moreover, a simplified procedure known as the Admittance Method was applied to the heliostat to estimate statistically the response of the structure. The method works in the frequency domain and uses transfer functions to determine the spectral distribution and statistical values of the loads and displacements. Using the load spectra, time signals have been recovered by inverse Fourier transform that provide valuable information for fatigue analysis. In addition, the admittance method was used in combination with wind data to predict the optical error, known as slope error, of the heliostat induced by the dynamic wind loads. It was found that the yearly average slope error is insignificant for the operating point considered compared to reference values from the literature