Wind-induced vibration of a square cylinder suspended by parallel elastic strips with nonlinear stiffness

A series of wind tunnel tests is conducted to investigate the wind-induced vibration of a square cylinder suspended by four parallel elastic strips. The elastic strip-suspended experimental setup, which provides the square cylinder with a cubic hardening nonlinear stiffness, is more convenient than existing nonlinear setups (e.g., the numerical computer-controlled feedback nonlinear setup or the physical magnet-induced nonlinear setup) and can be readily achieved in any wind tunnel. A theoretical formula is deduced for the nonlinear restoring force provided by parallel elastic strips, and the theoretical formula is validated against experimental measurements. The considered square cylinder exhibits vortex-induced vibrations (VIVs) at low wind velocities while galloping vibrations occur as the wind velocity becomes higher. The critical wind velocity for galloping instability can be remarkably reduced by adding two fins at the trailing-edge corners of the square cylinder. The influences of the pretension force of the elastic strips and the configuration of the trailing-edge fins on the vibration amplitude and kinetic energy of the square cylinder are also investigated.