Abstract
Vibration characteristics and its growth mechanism of wind-excited ovalling vibration of thin circular cylindrical shell which has dimensions like silos were made clear by carrying out various kinds of wind tunnel tests. Followings are the main things measured by the tests. (1) Wind pressure characteristics acting on the circular cylindrical shell. (2) Static and dynamic response of wall of circular cylindrical shell. (3) Effects of additional air force caused by the vibration of wall. Wind tunnel tests were carried out using Eiffel type wind tunnel of Dept. of Architecture, Tohoku University, which has a working section of 6.5m in length and 1.0m by 1.4m in cross section. The approaching flow was uniform and its turbulence intensity was about 0.8%. In addition to this flow, we made four kinds of turbulent flows by using grids. Their turbulence intensity was 1.8, 4.8, 6.2 and 8.8%, respectively. Test models were made of polyester film with aluminum rings at both ends, and its diameter was 200mm, height was 400 and 600mm. As the results, the followings conclusions were obtained. (1) Circumferential distribution of static wind pressure coefficient depends not only on Renolds Number but also on the turbulence intensity of the approaching flow. (2) Vibration frequency and vibration mode of ovalling vibration is equal to the natural frequency and vibration mode of the circular cylindrical shell. (3) Vibration is caused by fluctuating wind pressure. But when turbulence intensity of the approaching flow is small, vibration amplitude grows suddenly at a certain wind velocity because of aerodynamic negative damping effect. There was no relation between vortex shedding and vibratiion frequency.
