DYNAMIC WIND-INDUCED VIBRATION AND FATIGUE DAMAGE ANALYSIS OF HELIOSTAT STRUCTURES

A typical heliostat consists of a supporting column, a torsion beam, a truss, a drive unit and a mirror. Heliostat structures, which are normally deployed in open rural areas, subject to strong wind and suffer from significant wind-induced vibration. A refined finite element model (FEM) of a typical heliostat was established for structural and fatigue analysis. The heliostat has a large mirror of 8 m×8 m size and a 5 m high column. Wind tunnel tests were carried out to measure fluctuating wind pressure on the mirror. The measured wind pressure was converted into time histories of wind forces, which were then applied to the FEM model of the heliostat. Subsequently, wind-induced dynamic responses of the heliostat structure were analyzed using the FEM model in the time domain for various cases of different wind angles and the elevation angles of the mirror. Finally, fatigue damage analysis of the key parts of the heliostat was performed in the time domain as well as in the frequency domain by employing four methods, i.e., the time domain rain-flow method, the equivalent stress method, the equivalent narrow band method and the equivalent wide band method. The comparison of fatigue damage results demonstrated the effectiveness of the frequency domain methods. The equivalent narrow band method and the equivalent wide band method showed advantages in computational efficiency and relatively good accuracy in the estimation of wind-induced fatigue damage of heliostat structures.