Research On Wind Load Characteristics And Structural Response Of TM65m Radio Telescope

Shanghai Tianma Telescope(TM65m in short)is a fully movable parabolic antenna structure with complex body shape.It has long natural vibration period,which means flexible structure.And it has various windward attitudes,causing complicated distribution of wind load.Therefore its pointing precision and surface shape accuracy are sensitive to wind effect.So,it is necessary to take a combination of experimental measurement and simulation to study the wind load and wind-induced vibration response of the structure.This article takes TM65 m as the main research object,taking the surface precision of the reflector and the pointing accuracy of the antenna as the main concerns,and mainly carries out the following research work:In order to understand the wind environment in which the TM65 m is located,and to provide reference data for wind load input for further structural wind response analysis,the wind speed and wind direction data measured on the TM65 m site were statistically analyzed,and the average wind speed as well as average wind direction and distribution were obtained.The wind speed data with higher collection frequency in some periods was used for frequency analysis.The spectrum of the fluctuating wind speed was obtained and compared with the commonly used fluctuating wind speed spectrum curves.Finally,the Davenport spectrum was selected as the reference spectrum and the parameters were modeled.Combined with the correction,the fitted expression of the measured wind speed spectrum was obtained,which provided support for subsequent structural wind load simulation and response analysis.Using the method of on-site wind speed measurement,structural response measurement and structural finite element simulation,the influence of average wind load on the main reflector's surface shape accuracy and antenna pointing accuracy of TM65 m were analyzed.Firstly,the measured wind speed and wind direction data were converted into average wind load data,and the average wind response of the TM65 m structure was simulated and compared with the measured slope data of the inclinometer at the same time,the same position,and with the same physical quantity.The two were in good agreement.Afterwards,based on the finite element simulation method of actual measurement and verification,the variations of surface shape accuracy and antenna pointing accuracy of the TM65 munder different windward attitudes and different wind speeds were analyzed.It was found that the average wind load had less influence on the surface shape accuracy.However the influence on the pointing accuracy,especially the pitch pointing accuracy,is greater.The analysis results provide a good reference for the evaluation of the surface shape accuracy and antenna pointing accuracy.Based on the CFD large eddy simulation method,a linear filter method was used to generate the fluctuating wind speed time history of the inlet,and the pulsating wind load of the TM65 m main reflector was numerically simulated.The fluctuating wind pressure data of the reflector surface was obtained;the time-averaged wind was further calculated.The pressure distribution was compared with the results of previous studies.The results showed that the two were in good agreement and verified the validity of the simulation results.Further statistical analysis of the obtained fluctuating wind pressure data has obtained the distribution of fluctuating wind loads in the frequency domain,providing a reference for further structural wind-induced vibration analysis.Finally,using the simulated wind pressure time history,the TM65m's nonlinear dynamic time history analysis was performed to obtain the structural displacement response and its effect on the surface shape accuracy and antenna pointing accuracy when considering the dynamic effect of the wind.The wind-induced displacement dynamic response of the structure is mainly concentrated in the first-order natural vibration frequency of the structure.The characteristics of the surface shape accuracy and the pointing accuracy in the frequency domain are consistent with the displacement response.Comparison with the average wind load response provides a more comprehensive reference for the evaluation and correction of observation accuracy.