一方向型吊屋根のフラッタに関する基礎的研究 : 壁付吊屋根のフラッタの発生機構について

Abstract

Aerodynamic responses for elastic membranes are investigated for the. purpose of elucidating the mechanism of single-degree-of-freedom flutter of suspended roofs with walls (one-way-type). Elastic membranes and rigid plates, which form roofs and grounds of suspended roofs, respectively, are attached to the upper and the lower surfaces of each prismatic bar with 〓-section having width-to-height ratios, of 4, 5 and 8, in the experimental models. The model is mounted horizontally in the working section, and both sides of the model is fixed to the tunnel wall. The main results obtained are summarized in the followings. 1) The single-degree-of-freedom flutter for models without ground occurs in a restricted range of wind speed centered around the one at which the frequency of vortex shedding coincides with a natural frequency of each model. The characteristic responses, which are simillar in trend to those for spring-mounted rectangular prismatic bars with the same elongated cross-sections, indicate that the instability observed is occurred by the vortex excitation. 2) The responses for models with ground are also simillar in trend to those without ground. Therefore, it can be concluded that the instability observed in suspended roofs is caused by the vortex excitation. The vortex excitation of elongated bluff cross-sections is known as flutter coupled with the impinging-shear-layer instability. Elastic membranes comprising cavity floors are also susceptible to the same vortex excitation. The responses of elastic membranes of this cabity type obtained in the experiment are simillar in trend to those for suspended roofs, which is another evidence for the validity of the concluding remark 2). mentioned above.