Research On Large-eddy Simulation Of Wind Effects On High-rise Building Structures And Its Applications

The structure of super high rise buildings has the characteristic of large flexibility,light in weight,long natural period of vibration and small damping ratio.With the increase of height,wind load becomes the key load of controlling the safety and comfort of super high rise buildings.The constantly emerging of super high rise buildings helps improving the research and development of structural wind engineering,and as one of the main research methods of wind engineering,numerical simulation has received more and more attentions from researchers.Recently,the wind resistant design of super high rise building structure proposes higher requirements to numerical simulation.Engineer and designer hope that they can use numerical simulation as a tool to analyze the distribution of wind pressure on building surfaces and the wind-induced response of building structure precisely.Therefore,large eddy simulation(LES),as unsteady method of numerical simulation,has become a research hotpot of computational wind engineering(CWE).The work of this paper was mainly to study the theory of LES and numerical simulation technique,and then applied the LES technique to the analysis of air flow around tall buildings,which aimed to explore a high accuracy and high efficiency numerical method for wind-resistance analyses of building structures.The content of this paper includes the following aspects:(1)The study of LES basic theory and method.Firstly,the research of the key technique of LES——inflow turbulence generator was made to study and analyze the basic principle of this technique.Based on the Random Flow Generation(RFG)and researches of previous studies,some modifications was made to proposed an new improved inflow turbulence generator——the Narrowband Synthetic Random Flow Generator(NSRFG),and simulations was made to validate the applicability and effectiveness of the proposed method.Based on the new inflow turbulence generator of LES,the whole research frame of this paper was built,which includes: 1)the numerical simulation of standard building model;2)the research of engineering case of super high building;3)research on parameter comparisons of wind effect on tapered super-tall buildings;4)the processing and analyzing method of the distribution of wind pressure and wind-induced response,etc.(2)The study of LES of the turbulent flow around the CAARC(Common wealth Advisory Aeronautical Research Council)standard building model.Based on the proposed NSRFG technique,the LES evaluation of the turbulent flow around the CAARC standard building model was made.Comparison of the distribution of wind pressure and wind induced responses between the numerical simulation and the wind tunnel test which was conducted in the wind tunnel laboratory of South China University of Technology(SCUT),was made to illustrate its feasibility and effectiveness.Meanwhile,cross comparisons between the NSRFG method and the consist discretizing and synthesizing RFG(CDRFG)method,which was proposed by Aboshosha(2015)recently,indicated that the improved method has advantages of higher accuracy and computational efficiency.(3)Large eddy simulation of wind induced response on Nanning Wuxiang ASEAN Tower.This part of the paper put the Nanning Wuxiang ASEAN Tower with the height of 528 meters as a case,and used the proposed NSRFG in the Large eddy simulation to study the wind-induced response of Nanning Wuxiang ASEAN Tower.The base moments and displacements of the structure had been calculated.The comparison of the results between numerical simulation and high frequency force balance(HFFB)wind tunnel testing was also presented to indicate the effectiveness and accuracy of the numerical method.The results showed that the base moment spectra in along-wind and across-wind directions between numerical simulation and wind tunnel test were in good agreements,but there was still discrepancy in torsional direction.The results showed that although there was still discrepancy in computational results between numerical simulation and wind tunnel test,the basic laws were in good agreements.Besides,the numerical method of this paper was able to predict the vortex shedding frequency of the building model that was close enough to the wind tunnel test results,which can produce valuable reference to structural design of the building.(4)LES research on wind effect on tapered super-tall buildings.The proposed NSRFG technique was employed to LES study the wind effects on four tapered building models with different tapers,which aimed to compare the difference of different taper on wind loads and wind-induced responses of high building structures.Numerical simulation showed that the distributions of the average and fluctuating pressure on building surfaces were similar,while for the wind-induced response,the peak base bending moment(BBM)of different models in across wind direction decreased remarkably with the increasing of the taper.Therefore,a building with bottom-up gradually shrinking and an appropriated taper shape can effectively decrease the aerodynamic wind load and wind induced responses in across-wind direction.In addition,results from the numerical simulation were coincided with that from the wind tunnel test in the whole,which indicated that based on the improved inflow turbulence generator in this paper,LES would have higher accuracy and can provide valuable reference to the aerodynamic shape optimization of super-tall buildings.