Rapid Deformation Calculation for Large Reflector Antennas:A Surrogate Model Method

The surface accuracy of the large-aperture reflector antenna has a significant influence on the observation efficiency.Recent researchers have focused on using the finite element(FE)simulation to study the effect of gravity and heat on the deformation distribution of the main reflector.However,the temperature distribution of the antenna is challenging to obtain,and it takes a long time for the FE simulation to carry out FE modeling and postprocessing.To address these limitations,this study presents a surrogate model based on Extreme Gradient Boosting(XGBoost)and deep Convolutional Neural Network(CNN)to get the deformation distribution of the main reflector quickly.In the design of the surrogate model,using the XGBoost algorithm and sparse sampling to solve the difficulty of obtaining the entire temperature distribution is first proposed,and then a deep CNN is developed for estimating deformation.Based on the effect of dynamic loads on the antenna structure,a diverse data set is generated to train and test the surrogate model.The results show that the surrogate model reduces the calculating time dramatically and can obtain the indistinguishable deformation compared to the FE simulation.This technique provides a valuable tool for temperature and deformation calculation of large-aperture antennas.

Micro-vibration Modeling and Verification of Shutter Mechanism of Survey Space Telescope

The scientific research mission of the Survey Space Telescope(also known as the China Space Station Telescope,CSST)imposes rigorous requirements on the observation precision.However,microvibrations generated by the shutter mechanism can seriously affect the performance of the highly precise and sensitive instruments onboard.This study presents a dynamic model and verifies its performance using experimental results.Indeed,a five-degreeof-freedom nonlinear dynamic model that considers all interference sources and bearing nonlinearity is established.The validity of the proposed model is verified using experimental measurements of the microvibration characteristics.The obtained results proved that the proposed dynamic model can accurately predict the characteristics of the microvibrations caused by the shutter mechanism in the design stage and provide a theoretical basis for the development of CSST.

Multimodality-based Wind Speed Forecasting Method for the Wind Resistance Control of Large Radio Telescope

A large,fully steerable radio telescope is susceptible to the wind load,leading to structure deformation andpointing deviation of the telescope.To effectively suppress the influence of dynamic wind load,the wind resistancecontrol of the telescope is carried out based on wind speed forecasting.This study developed a wind speedforecasting model to efficiently forecast the wind speed at the telescope position.The proposed model successfullyeliminates the random noise of the original wind speed,effectively extracts the wind speed features and solves theautomatic optimization of the hyperparameters of the forecasting network.This model significantly improves theaccuracy and reliability of wind speed forecasting.To verify the forecasting performance of the proposed model,the wind data from the Qitai Radio Telescope site is examined as a case study.The wind speed forecasting model’sMAE,RMSE and MAPE are 0.0361,0.0703 and 3.87%,respectively.The performance of the proposed modelmeets the requirements of wind resistance control and can provide data support for the radio telescope.

Simulation-driven Wind Load Analysis and Prediction for Large Steerable Radio Telescopes

Large steerable radio telescopes can rotate in azimuth and elevation,with various upwind postures and complex wind load characteristics.In order to obtain the wind load distribution on the reflector and the wind force coefficients in different upwind postures,this work took the reflector of the Qi Tai Telescope in Xinjiang as the object.The wind pressure distribution,drag coefficient,side force coefficient,lift coefficient,and total force coefficient of 361 groups of reflectors with different upwind postures were calculated and analyzed by a numerical simulation method.The results show that the force on the reflector when the concave surface faces the wind is significantly greater than when the convex surface faces the wind.The surrogate models for calculating wind force coefficients were established based on the polynomial response surface model(PRSM) and regularized minimumenergy tensor-product spline(RMTS).The adjusted R-squared of RMTS is 0.98,and the root mean square error is below 0.1,which proves RMTS is significantly better than PRSM.Compared with the numerical simulation values,the absolute errors of the drag coefficient,side force coefficient,lift coefficient,and total force coefficient of the reflector with azimuth and elevation of 45° predicted by RMTS are 0.02,0.027,0.032,and 0.046,respectively.The relative errors are 2.42%,2.76%,2.23%,and 2.43%,respectively.It is proved that the RMTS surrogate model is reliable and that the predicted data can fast provide sufficient information for the wind-resistant design of the large steerable radio telescopes.

Approximate Analytical Solutions for a Class of Laminar Boundary-Layer Equations

A simple and efficient approximate analytical technique is presented to obtain solutions to a class of two-point boundary value similarity problems in fluid mechanics. This technique is based on the decomposition method which yields a genera/analytic solution in the form of a convergent infinite series with easily computable terms. Comparative study is carried out to show the accuracy and effectiveness of the technique.

The Electromagnetic Characteristics of the Tianlai Cylindrical Pathfinder Array

A great challenge for 21 cm intensity mapping experiments is the strong foreground radiation which is orders of magnitude brighter than the 21 cm signal.Removal of the foreground takes advantage of the fact that its frequency spectrum is smooth while the redshifted 21 cm signal spectrum is stochastic.However,a complication is the nonsmoothness of the instrument response.This paper describes the electromagnetic simulation of the Tianlai cylinder array,a pathfinder for 21 cm intensity mapping experiments.Due to the vast scales involved,a direct simulation requires a large amount of computing resources.We have made the simulation practical by using a combination of methods:first simulate a single feed,then an array of feed units,finally with the feed array and a cylindrical reflector together,obtain the response for a single cylinder.We studied its radiation pattern,bandpass response and the effects of mutual coupling between feed units,and compared the results with observation.Many features seen in the measurement result are reproduced well in the simulation,especially the oscillatory features which are associated with the standing waves on the reflector.The mutual coupling between feed units is quantified with Sparameters,which decrease as the distance between the two feeds increases.Based on the simulated S-parameters,we estimate the correlated noise which has been seen in the visibility data,and the results show very good agreement with the data in both magnitude and frequency structures.These results provide useful insights on the problem of 21 cm signal extraction for real instruments.