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桥梁模型的独特大水平响应机理，将桥梁和山体模型简化为悬臂梁和圆锥体。改变桥梁模型在山丘尾流中的位置和水平倾斜角，并测量响应。山的直径为4.5H，以H为高度。悬臂梁模型的长度为H，位于0.123H的高度。当模型位于距山中心背风3.3H左右时，水平响应变大。当悬臂模型的风偏角为40度时，响应也变大。响应的峰度有时达到4至4.5。通过一系列的流场显示实验，提出了轴向倾斜40 ~ 50 °的锥形涡的形成，并认为这些涡是引起大水平响应的可能原因，同时测量了响应和脉动风速。并根据大响应的发生情况进行条件采样，以明确引起大响应的脉动风速特性。这是由于作用于倾斜40度左右的桥梁模型上的脉动风速产生了较大的响应，被认为与流动显示实验中的旋涡结构相对应的情况，另一方面，也有没有观测到这些脉动风速特性或实验结果再现性不好的情况。考虑到流动条件等的敏感影响，现在正在寻找原因。还将使用同步压力测量实验来测量气动力特性。

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.