Study to Clarify The Mechanism of Uniquely Large Horizontal Bridge Response Located in The Wake of aHill

为了阐明孤立山体尾流中的桥梁模型观测到的独特的大水平响应的机理，将桥梁和山体模型简化为悬臂和锥体。改变了桥梁模型在山体尾迹中的位置和水平斜角，并测量了响应。山体直径为4.5h，高度为H。悬臂模型的长度为H，位于0.123H的高度。当模型位于山丘中心下风向3.3H附近时，水平响应变大。当悬臂模型的风偏角为40度时，响应变大。反应的峰度有时达到4到4.5。通过一系列的流动可视化实验，提出了轴线倾斜角为40~50度的锥形涡旋的形成，并认为这些涡旋可能是水平响应大的可能原因，然后同时测量响应和脉动风速，并根据大响应的发生进行条件采样，以阐明引起大响应的脉动风速特征。其中一些情况下，作用在40度左右的斜锋线的桥梁模型上的脉动风速引起了较大的响应，这被认为与流动显示实验中提出的涡旋结构相对应；另一方面，也有一些情况下，这些脉动风速特性没有被观察到，或者实验结果的重现性不好。考虑到流动条件等敏感因素的影响，现找出了原因。同时，利用同步测压实验测量了气动力特性。

This study was conducted to clarify the mechanism of uniquely large horizontal response observed with a bridge model located in the wake of an isolated hill.The bridge and hill models were simplified as a cantilever and a cone. The location of the bridge model in the wake of the hill and horizontal skew angle were varied and responses were measured. The diameter of the hill was 4.5H, taking H as the height. The length of the cantilever model was H and it was located at height of 0.123H. The horizontal response became large when the model when the model was located around 3.3H leeward from the hill center. Also the response became large when the cantilever model had wind skew angle of 40 degrees. The kurtosis of the response sometimes reached to 4 to 4.5. With a series of flow visualization experiment, the formation of conical vortices that has the axis with skew angle of 40 to 50 degrees was suggested, and these vortices were thought to be the possible cause of large horizontal response.Then the response and fluctuating wind velocity were measured simultaneously, and conditional sampling based on the occurrence of large responses was conducted to clarify the fluctuating wind velocity characteristics causing the large response. These were some cases where fluctuating wind velocity that acts on the bridge model with skew front line of around 40 degrees caused large responses, and that was considered to correspond to the vortex structure suggested in the flow visualization experiment.On the other hand, there were other cases where these fluctuating wind velocity characteristics were not observed, or reproduction of the experimental results was not good. The cause is now sought considering sensitive effects by flow condition etc. Also the aerodynamic force characteristics are to be measured using simultaneous pressure measurement experiment.