Numerical Study Of Wind Effects,Wind–driven Rain Effects And Fluid–structure Interactions On Structures

Retractable roof structures break traditional concepts of indoo r and outdoor space,which can free indoor activities from weather restrictions and ambient conditions.Thus,such structures have gained great popularity among designers.The length of retractable roofs increases with the demand for more flexible and ligh t construction,and such requirements normally result in the characteristics of higher flexibility,lighter mass,lower natural frequency and smaller damping of retractable roof structures.As a result,large span retractable roof structures are becoming m ore sensitive to wind actions than traditional structures.Additionally,large span retractable roof structures are usually used for low–rise buildings and locate within the lower part of the atmospheric boundary layer,hence,experiencing stronger gusty wind with higher turbulence intensity.Therefore,this paper investigates the wind and wind–driven rain(WDR)effects on a large span retractable roof stadium by combined studies of wind tunnel experiment and numerical simulations.Results of this study can be used to guide the wind resistance design of this type of building in future.In addition,large span retractable roof structures and hig–rise buildings are wind–sensitive structures,and obvious fluid–structure interactions(FSI)are observed when wind blows over the building.Vibrations of large span retractable roof structures and hig–rise buildings are usually generated by fluctuations of wind,thus causing the damage of the building surface envelope.Therefore,this study proposes a FSI algorithm based on OpenFOAM,and investigates the interactions between wind and a high–rise building.The numerical results are compared with corresponding aeroelastic wind tunnel test results to validate the applicability and accuracy of the numerical method.The main research contents and achievements are as follows:(1)A combined study of wind tunnel experiment and large eddy simulation(LES)for evaluation of wind effects on a large span retractable roof stadium was performed.Based on the advantages of Computational Fluid Dynamics(CFD),the LES with usage of the inflow turbulence generator DSRFG and the dynamic SGS model was conducted for both the scaled(1:200)and prototype(1:1)stadium.The effectiveness and reliability of the adopted LES techniques ha d been verified by detailed comparisons with the model test results.The adopted LES techniques had been proven to be an effective tool for evaluations of wind effects on buildings with complex geometries in high Reynolds number turbulent flows.Through the cross–validation of results between the LES and wind tunnel experiment,it was found that the model test fails to capture the maximum and minimum values of pressure coefficients due to limited number of pressure taps on scaled model.Significant differences were observed in terms of pressure coefficients and flow fields between different roof states.(2)The turbulent dispersion of raindrops was integrated into the Eulerian multiphase model to investigate the WDR effects on a rectangular cross –section.Especially,the influences of the turbulent dispersion are discussed in detail by comparing the WDR simulation results for the cases with and without consideration of the turbulent dispersion in terms of WDR flow fields,volume fraction,specific catch ratio,catch ratio,rain loads and aerostatic force coefficients.The results indicate that the turbulent dispersion for a certain range of raindrop size is needed to be taken into account for obtaining accurate WDR simulation results.(3)In the light of design scheme and actual usage,the roof of the large–span retractable roof stadium is closed when it rains.So,WDR simulations on the closed roof state of the large span retractable roof stadium were conducted based on the LES method(including the DSRFG approach and the new dynamical SGS model)together with the revised Eulerian multiphase model.A validation study based on available field measurements of WDR and detailed analysis of the simulation results demonstrated that the numerical methods adopted in this paper are effective tools to predict the WDR effects on a large–scale complex structure in high Reynolds number turbulent flows.Both mean and instantaneous WDR effects in terms of volume fraction,specific catch ratio,rain loads on the roof were presented and discussed.In addition,detailed analysis of time histories of specific catch ratio were conducted,which can be used as a reference for the study of preventing erosion and degradation of building materials and ensuring safety and durability of building s in their life cycle.(4)Structural responses of the retractable roof subjected to wind and WDR actions were determined by the dynamic analysis of the stadium in time domain.Four different load sources were considered in the dynamic analysis: the scaled wind tunnel experiment(wind actions only),the full–scale LES simulation(wind actions only),the wind actions extracted from the WDR simulations,and the WDR(combined effects of wind and rain).WDR–induced and wind–induced mean and RMS structural responses of the retractable roof were analyzed in this paper for comparison purposes.The comparison studies validated that the simulation methods adopted in this paper are useful tools in predicting the structural responses of a large span roof with complex geometries.The scaled wind tunnel experiment may underestimate the wind–induced structure responses due to the Reynolds number effects,especially for structures with complex geometries in high Reynolds number turbulent flows.Wind phase only has obvious effect on fluctuations of small raindrops,whereas,rain phase has significant influence on fluctuation of wind phase in WDR simulation.The high frequency part of wind pressure increases remarkably when interactions between wind phases and rain phases are considered,which leads to a significant increase in the fluctuating response of the structure,including RMS displacement and acceleration.In view of this,two–way coupled simulation of wind and rain is essential for accurate predictions of WDR effects on buildings.Rain loads have little contribution to the WDR–induced responses compared to wind–induced loads in WDR simulations.Particularly,the extreme structural responses of the large span roof mainly occur in the central part,implying that the central part of this type of roof may be the most vulnerable region to structural damage during violent storms or severe WDR events,which should draw attentions from engineers and designers involved in designing this type of stadium.(5)In addition,large span retractable roof structures and hig–rise buildings are wind–sensitive structures,and obvious FSI are observed when wind blows over the building.Therefore,a fluid–structure interaction algorithm based on OpenFOAM togrther with the inflow turbulence generator DSRFG was proposed to investigate interactions between wind and a high–rise building.The numerical results were compared with the corresponding aeroelastic wind tunnel test data to verify the feasibility of the fluid–structure coupling algorithm.