Process for analysis of wind-induced vibrations of antennas. A two-way Fluid-Structure Interaction simulation in Ansys Workbench, validated with wind tunnel testing.

Abstract

Deflection and vibrations of antennas that are a part of a transmission line result in a significant drop in performance. This is due to the performance being highly dependent on whether the antenna lobe hits the target. A small deflection of the antenna structure caused by wind load results in a great deflection of the antenna lobe. In this project, a simulation process is developed to predict the wind-induced vibrations of Ericsson’s antenna structures. The process uses a two-way Fluid-Structure Interaction setup, which couples a structural and a fluid solver. To validate the simulation process, wind tunnel testing at Chalmers University of Technology was conducted. The testing included cases of constant wind load, different angles of incoming wind and hammer impulse tests. A damping ratio of 2.78% was calculated from the experimental data using the method of logarithmic decrement. A method for creating a fluid domain was developed to resolve the turbulent flow around the antenna using the criteria set by the LES model. The simulation results were compared to the experimental data and correlated well in frequency. Certain patterns of the deflection of the antenna from the experimental testing were well captured by the simulation process. The computational time of the simulation process was optimised by increasing the time step size. The larger time step size resulted in a decrease of almost one-third of the computational time of a finer time step size without losing considerable accuracy. The decreased computational time is favourable when using this process in the industry.