Research On Modeling And Parameter Inversion Of Moving Downburst And Wind-Induced Response Of Transmission Tower Line System

With the aggravation of climate change,thunderstorms and other extreme weather are increasing.A downburst is a kind of disastrous wind formed by a strong downdraft impacting the ground in thunderstorm weather,which has high frequency and destructive and poses a great threat to the wind resistance safety of engineering structures,especially the transmission tower line system.With the constant development of power grid construction,the total length and space coverage of transmission lines are significantly improved.At the same time,the probability of encountering downbursts and other extreme weather conditions is also greatly increased.In recent years,although some achievements have been made in the research of downburst wind field and the wind-induced response of the transmission tower,there are still some problems to be solved urgently due to the complexity of downburst and its load mechanism.This thesis carried out in-depth and systematic research on the moving downburst’s wind field characteristics,analysis model,parameter inversion,and the wind-induced response of transmission tower-line system.The major contents and achievements are summarized as follows.（1）Based on the impinging jet test device with a movable nozzle,the stationary and moving downburst wind fields are simulated,and the cobra wind speed probe is used to collect the wind field information.For moving downburst,the time-varying mean wind velocity is extracted from the total wind time history by signal processing,and then the non-stationary fluctuating wind speed is separated.Through the analysis of wind speed time history,the vertical,radial,and transverse distribution characteristics of horizontal mean wind velocity in stationary and moving downburst are given,and the fluctuating wind characteristics in the two kinds of wind fields are compared,including turbulence intensity,power spectrum,and probability density distribution.The results show that the difference between stationary and moving downburst is mainly reflected in the mean wind characteristics,and the velocity distribution is affected by the ratio of the storm moving velocity to jet velocity(V_tr/V_jet).（2）Based on the impinging jet model,the large eddy simulation method is used to carry out CFD numerical simulation research on stationary and moving downbursts.The development process,time-varying characteristics of wind speed,and wind profile characteristics of stationary and moving downburst are compared,the influence of V_tr/V_jeton the wind field structure is discussed,and the applicability of the vector superposition principle in the simulation of moving downbursts is verified.The results show that the time history of wind speed and direction obtained by numerical simulation of moving downburst is in good agreement with the measured records.In the early stage and mature stage of wind field development,the wind speed distribution is different.The movement of the storm makes the near-surface wind field lose its central symmetry,and a bow-shaped extreme wind speed area appeared in front of the storm.With the increase of V_tr/V_jet,the non-central symmetry of the wind field become more obvious.The radial position of the maximum horizontal wind speed in front of the storm gradually approaches to the center of the storm,and the peak wind speed gradually strengthens,while the wind speed distribution behind the storm presents the opposite change pattern;The principle of vector superposition is not fully applicable to the simplified analysis of mobile downburst.When V_tr/V_jet is large,the principle of vector superposition will cause large errors.（3）The existing stationary and moving downburst radial wind profile models are sorted out,and the shortcomings of the existing models are pointed out.Then,the vector superposition principle is abandoned in the moving downburst wind field,and an improved empirical model suitable for both stationary and moving downbursts is proposed from the formation process of wind field.Based on the CFD numerical simulation results,the model is improved.Finally,the effectiveness of the improved empirical model is verified by comparing it with the existing model and CFD results.（4）A reconstruction model of the horizontal wind speed field of the downburst is proposed.The horizontal wind speed is decomposed into the vector superposition of the downburst radial wind speed and the ambient wind,and the intensity attenuation of the storm is considered.Then,an analysis framework for the inversion of downburst wind field parameters is established,and a rapid identification method of wind field parameters based on the genetic algorithm and nonlinear programming is proposed.Finally,through the parameter inversion of several sets of time history data,the accuracy and efficiency of the proposed method are verified.（5）The finite element model of a single tower and the tower-line system is established.Based on the improved empirical model,Wood model,and the fluctuating wind simulation method proposed by Chen et al.,the time history of downburst wind load is generated.Using the time-domain dynamic analysis method,the wind-induced responses of a single tower and the tower-line system are studied,and the dynamic amplification factors are given.The influence of the tower line coupling effect on the dynamic response of the tower is discussed.In addition,the sensitivity of wind-induced response of the tower line system to the height of maximum horizontal wind speed and V_tr/V_jet is also discussed.The results show that the background response of a single tower and tower line system is dominant under a downburst,and the dynamic amplification factor of fluctuating wind is 1.3.The responses of the tower line system first increase and then decrease with the increase of the height of the maximum horizontal wind speed,and monotonously increase with the increase of V_tr/V_jet.When evaluating the critical load case of the transmission tower under the downburst,the moving effect of the storm should also be considered as an important factor.