| Snowdrift formation on roofs especially on long-span lightweight roofs is a major problem in snowy and windy areas.In recent years,with the global warming,news about structural damages due to snowdrifts were reported commonly.Investigations also showed the main reasons for these accidents were big snow loads,non-uniform accumulation of snow and coupling effects of wind-snow-structure.Meanwhile,In snowy and windy areas,blizzards are often accompanied with strong snowdrifts around buildings,resulting in seriously unbalanced snow distribution around buildings.The planning of buildings in such areas should also consider the positions of snowdrifts in respect to outdoor facilities such as doors,roads and car sheds carefully.If such planning is done properly,the reliability of emergency escape routes would be improved and the costs of snow removal could be reduced.At present,nationally and internationally,studies on low rise buildings are less,and the achievements were more confined to individual specific engineering application,lacking of the distribution characteristics and laws.Therefore,deep and systematical researches on snowdrift on low-rise building with typical roofs have important engineering significance and academic value.This dissertation carried out systematical researches on snowdrift formation on typical roofs,snowdrift formation around buildings and numerical simulation method of snowdrift,the details are as follows:1.Snowdrift on typical roofs.Snowdrift formations on stepped roof,flat roof,pitched roof and arched roof have been investigated by field measurement.The influence of parapets have also been investigated.Some design recommendations have been given by comparing measured results with load codes including China,America Canada and Europe.Parametric studies have been done by wind tunnel tests,including the influence of wind speed and windward side width on snowdrift formations on the lower roof of stepped roof building,the influence of wind speed and downwind direction length on snowdrift formations on flat roof.Snowdrift formations on pitched roofs on the condition of different wind speed and slope 10° and 20° respectively have also been studied.Snowdrift formations on one span,two spans and three spans of 20°pitched roofs have been studied,the effect of wind speed has also been investigated.2.Snowdrift around buildings.Snowdrift formations around buildings including flat roof,pitched roof and stepped roof have been investigated by field measurement.The influence of parapets have also been investigated.Snowdrift formations around a single cube model,serial and parallel products 2 cube models,one behind two front 3 cube models have been studied.Wind directions divided into 0° and 180° have also been studied on one behind two front 3 cube models.3.Numerical simulation method of snowdrift.A new snowdrift modeling method by using CFD(Computational Fluid Dynamics)coupled with DEM(Discrete Element Method)has been built basing on summarizing CFD and DEM related theories,including material parameters and particle size,collision parameters,particle numbers and inputmodes,boundary conditions of CFD,simulation time and inlet velocity,and coupling calculation process.The numerical method was applied to simulate the snowdrift on a typical stepped flat roof.The feasibility of using coupled CFD with DEM to study snowdrift is verified by comparing the simulation results with field measurement results on the snow depth distribution of the lower roof.The effect of snow on the flow field characteristics has also been discussed.Not only is the two-way coupling between wind and snow particles which includes the transient changes in snow surface topography,but also the cohesion and collision between snow particles are taken into account. |
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