Effect Research Of Dense Truss To Averaged Wind Pressure On Large-span Roof With Sub-domain Method

Large-span roofs are quite sensitive to the effects of the wind because of their long spans and flexible structures.So the average wind load on it is one of the most important factors of structure safety.Long-span roofs usually use dense truss for the supporting structure.Also the truss is complicated and slender,it is close to the roof and the effect to the airflow field around the roof can not be ignored.However,the two major ways of wind engineering research:wind tunnel and numerical simulation are difficult to consider the effect.Because in wind tunnel experiment,the truss used to be dealt with high approximation,or even is ignored due to the reduced scale.And it is almost impossible to build the truss model in numerical simulation for engineering structure for the reason of building difficulty and enormous mesh.So it is necessary to find a new way to improve the numerical accuracy.This paper made a deduction of improved SSTκ-ωturbulent model from the Fluid Dynamics with a reference to the idea of canopy flow and a secondary development of commercial software CFX by FORTRAN Language,then compute the average wind pressure on the large-span roof with Sub-domain Method to consider the truss effect equivalently,so as to make a precision improvement of CFD simulation.The research work of this dissertation is mainly focused on the following aspects:1.Improved SSTκ-ωturbulent model is deduced from the Fluid Dynamics to be the Theoretical basis of Sub-domain Method.With a reference to the definition of wind resistance in the field of Canopy Flow,the truss resistance is added to Reynolds Averaged Equation. Then on the basis of the deduction of improved Standard k-εModel,it is deduced the improved SSTκ-ωturbulent model used by this thesis.2.The feasibility and detailed suggestion of Sub-domain Method is given by basic research of combined structure of standard cube and simplified truss,for cube model is similar to low large-span coliseum.Firstly,both RNGκ-εmodel and SSTκ-ωmodel are used to make a numerical simulation of cube to indicate that SSTκ-ωmodel has b better accuracy to predicate the wind load in the field of Civil Engineering.Then simplified truss is combined with the cube to consider the truss effect of averaged wind pressure on the roof. Secondly,it is considered the effect of mesh number in sub-domain,section type of sub-domain and experiment factorλe and suggestion for the three factors about Sub-domain method are also provided.Finally,the change of wind load on roofs is given while the resistance item,turbulent energy item and dissipation item is changed individually.3.Sub-domain Method is used to compute the averaged wind pressure on the typical simple grandstand cantilevered roof with suggestions proposed above,so the reliability of suggestions to consider the effect of dense truss on large-span roof has been checked.Many kinds of truss type are chosen to combine with grandstand roof:simple truss on front edge, truss on both front and back edge and crossing truss.And each of above model has both simplified and real truss model.Then rules of truss effect of roof wind pressure are concluded on different models under three different wind directions:0,45 and 90.Finally,the improvement of numerical accuracy with Sub-domain Method is ensured after comparing the results of Sub-domain Method,real truss model and no truss model.4.Primary application of Sub-domain Method on practical structure.Shanghai Hongkou Stadium is chosen to compute with Sub-domain Method.Then the wind pressure result is compared with that of no truss numerical simulation and wind tunnel.It can be concluded that Sub-domain Method improves the numerical accuracy in practical application.