Kichiro Kimura

Characteristics of buffeting forces on flat cylinders

Experiments were conducted to clarify the characteristics of the buffeting forces on cylinders with flat hexagonal and rectangular cross sections. For the buffeting lift forces, the spanwise correlation was found to be larger than that of the fluctuating wind velocity, which was in accordance with the previous researches. The power spectra of the buffeting lift force acting on a cross section were smaller than the analytical result, and the difference was larger for smaller-scale turbulence. For the buffeting drag forces on rectangular cylinders, the experimental and conventional analytical result generally agreed. Discussions are given to explain these characteristics and to improve the accuracy of the buffeting force formulation by introducing an aerodynamic admittance which considers the effects of the three-dimensional fluctuating velocity field.

An experimental study on vortex-induced vibration of a circular cylinder tower at a high wind speed

A wind-tunnel experiment using a circular cylinder tower rocking model is conducted to study the characteristics of the across-wind response. Special attention is paid to the vortex-induced vibration which occurs at a wind speed higher than the occurrence wind speed of the ordinary vortex-induced vibration. Included in this study are the discussions on the effects of the turbulence of wind and the damping of the model. The wavelet analysis clarifies that the tip-associated vortices which are formed rather intermittently around the model top are concerned with the cause of the vibration.

Numerical study on the suppression of the vortex-induced vibration of a circular cylinder by acoustic excitation

Abstract In order to investigate the possibility of suppressing flow-induced vibration of structures by applying periodic excitation such as a sound wave to the flow around the structures, numerical simulations of the vortex-induced vibration of a circular cylinder were carried out when a periodic velocity excitation was applied to the flow at two locations on the cylinder surface. A FEM based on the ALE formulation was employed to simulate the vortex-induced vibration, with the time integration being carried out by the predictor-corrector method. The results revealed that the excitation with the transition wave frequency is the most effective in changing the flow characteristics around the cylinder and the characteristics of the vortex-induced vibration. These changes appear to be caused by the promotion of the vortex growth in the early vortex formation behind the cylinder.