| Thunderstorm downburst is a strong downdraft air impinging on the ground during the thunderstorm, with an extremely high velocity generated close to the surface, which leads to the destruction of quantities of structures. Currently, the research of the downburst mainly focused on the wind field characteristics of stationary downbursts, while little study have been done towards the wind field characteristics of non-stationary downburst, the loading and wind-induced response of downburst. In this article, the wind field of thunderstorm downburst, wind-induced response and windage yaw of the transmission lines were studied.In the process of wind field research, with the application of the downburst test equipment, the stationary downburst with various surface roughness and non-stationary downburst with a given surface roughness of0.3679m were obtained. Accordingly, vertical profile of both the horizontal and vertical velocity, together with their relevant turbulence intensity were improved as well as the dependent changing rules of which on the surface roughness and the radial distance. In addition, the maximum velocity profile and time histories of horizontal velocity of the non-stationary downburst at various height levels was gained, based upon which there is a detailed study of the dependent changing rules of the time histories of horizontal velocity on the height and the difference between the maximum velocity profiles of two analogies of downbursts mentioned above.In view of the fact that analysis found that classical deterministic stochastic hybrid method has some limitation and could not be used in all cases, a revised DSHM was imposed in this article. In combination the fluctuating component given by the revised DSHM with the time history of structural average force under non-stationary downburst obtained through CFD or wind tunnel test, the time history of total wind load could be presented.For the windage yaw research of conductors with a transverse structural feature under the non-stationary downburst, Fluent moving grid technique based CFD simulation was implemented to generalize the time history of conductor’s average load in the moving process of the non-stationary downburst. Then, the revised DSHM was used to gain the time history of total wind load. In contrast the results of the conductors’ windage yaw under the non-stationary downburst calculated by ANSYS with the code, it was revealed that the computation of the downburst exceeded the code by a large margin, thus the span reduction was appropriately amended.Regarding the transmission tower with a vertical structural feature, the wind load under stationary and non-stationary downburst was earned through force test. Accordingly, the radial and vertical distribution of the wind load under stationary downburst was analyzed to obtain the relevant static response characteristics of the transmission tower; moreover, the peak wind load as the change of the wind angles in various conditions under non-stationary downburst was analyzed and meanwhile the tower was divided into several segments, with the time history of wind load of every segment calculated by the revised DSHM, according to which the quasi-stationary and vibration response was figured up.The ratio of max wind-induced response and max static response under non-stationary downburst is defined as wind vibration coefficient.The former is obtained with considering the turbulent wind.At y=0Djet, wind vibration coefficient in x directionis under0°rotation angle is bigger in the bottom than that in the top.The values are1.51and1.21.But under90°rotation angle,wind vibration coefficient in y direction in the bottom is closed to that in the top.They are1.41and1.47.The displacement is bigger under the wind load based on the code than that in downburst,but it is not right to conclude that the wind load given by code is safe. |
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