Numerical Simulation Of Wind Loads On Low-rise Buildings Under Construction With Closely-knitted Safety Nets

With the rapid development of the national economy,numerous buildings have sprung up.Most of the studies on wind resistant design are focused on in-service buildings.Research on wind loading and wind effect on buildings in the construction stage is still far from enough.With the frequent occurrence of construction safety accidents,the research on the safety of buildings in the construction stage should be given sufficient attention.At the same time,the main cause of wind damage is the collapse of a large number of low-rise buildings under the action of typhoons.Therefore,it is necessary to systematically investigate the the wind loading and its distribution on low-rise buildings in order to propose effective wind-resistance measurement.Computational fluid dynamics is the core of the computational wind engineering research field.It is designed to study the phenomena of wind loading on the surface of buildings and the flow of air around buildings.Based on the FLUENT 14.0.0 software platform,the wind field and wind pressure distribution of low-rise buildings under construction with closely-knitted safety nets in the atmospheric boundary layer were performed by numerical simulation,statistical analysis and comparison.The main research content is as follows:(1)The description of FLUENT theory for numerical simulation of wind field and wind loading on buildings is introduced,which includes three basic control differential equations for viscous fluids and various turbulence models for simulating wind fields.Meanwhile the main feature for major types of turbulence models are also specified.The discretization method for control equations in CFD is summarized.Finally the common discrete format of FVM and the solution method of discrete equations are discussed.And the User-Defined Function(UDF)is introduced in more detail.(2)The TPU aerodynamic database established by the Tokyo Polytechnic University is briefly introduced,and the section on the low-rise building aerodynamic database is highlighted.In the TPU aerodynamic database,a scaled model of low-rise building structure with flat roof with Breadth/Depth/Height=160:400:160 and a scale ratio of 1/100 is selected.The three-dimensional mesh model is established by Gambit 2.3.16 software.The establishment of numerical wind tunnel model and the related work of grid discretization,boundary condition setting,near-wall treatment and solution setting are introduced in detail.The distribution of wind pressure on the construction surface of the low-rise building in the atmospheric boundary layer is numerically simulated.The wind speed profile U(z),the distribution of turbulent kinetic energy k and dissipation rate ? at the incoming flow boundary are all realized by UDF programming and FLUENT hooking.The CFD analysis results from the standard k-? model and realizable k-? model are described and compared with the experimental data from TPU aerodynamic wind tunnel database.Thus the verification and the validation of proposed CFD analyzed methods in the dissertation are performed.(3)The definition,properties,momentum equation,porous jump model,and solution method of the porous media model are introduced in detail.The wind tunnel experiment of dense-mesh safety net,the determination of two important parameters for porous media in FLUENT are specified.The CFD numerical simulation for the performance of dense-mesh safety nets by the porous media model,and the calculation of drag and lift wind loading coefficients are highlighted.Using the comparative analysis method,the effect of setting up the four-sides scaffolding on the average wind pressure coefficient of a building surface was investigated.Meanwhile the average wind coefficient of the surface of the main building was numerical analyzed when different types of safety nets are covered.Finally,the wind pressure characteristics of the main building surface with different layouts of scaffolds were studied.(4)The wind pressure characteristics of the covered net under different working conditions are all analyzed.The relationship between the pressure drop and the free flow velocity for some the two types of safety nets was created by FLUENT numerical simulation results on some monitoring points.The trend line from numerical simulation results was compared with the effective data obtained from the wind tunnel experiment,which could verify the feasibility of the porous media model in modeling the physical property of dense-mesh safety net.Finally the mean wind pressure coefficient of the dense mesh safety net under the conditions of overlaid scaffolding around the main building was performed,and the numerical simulation results were compared with the corresponding data from the design specification for safety nets.Furthermore,the proposed value of the wind loading on the scaffold is proposed for a covered scaffold design based on CFD analyzed results.The research results from this study would provide theoretical references and guideline for engineering practice for wind resistant design of low-rise building and its surrounding safety nets in construction stage.