A Refined Study On Evolutions Of Snow On Building Roofs Considering Wind And Heat Combined Effects

Snow-induced engineering disasters in China are widely distributed,frequently occur.The damage and collapse accidents of buildings are accordingly increasing,causing disaster preventions and mitigations of importance and urgency.The root cause of the accident is the unclear understanding of the process of the snow evolution under the impacts of environmental factors,i.e.wind,snow,and temperature.At this stage,more attention has been focused on studying the snowdrift in the field of building,while the coupling of snow and heat has seldom been discussed.Herein,To investigate the mechanism of snow evolutions considering wind and heat coupling effects,scholars and engineering practitioners usually consult specifications or industry standards to obtain relevant meteorological parameters(data),in which the normalized statistical data are often independent statistics,and without considering the joint effect of meteorological parameters.In terms of the relevant research,the choice of research methods has remarkably identity,which needs to be innovated urgently.In detail,the experiments carried out mostly rely on the use of particle ?pre-laying‘technology in traditional wind tunnel facilities,and the numerical simulations are mainly based on the model developed under the Euler-Euler(E-E)framework.However,there are some limitations in the application of those above methods to the research considering wind and heat coupling effects.It is urgent to put forward a new method with comprehensive factors and advanced technical means.Based on this,taking the joint analysis of meteorological factors as the prerequisite for the knowledge of snow evolution,a set of new similarity criteria and the CFD-DEM method have been proposed to investigate the snowfall and snowdrift.Then,combining it with the calibrated(via field measurements)snowmelt model,the whole process of wind-snow-heat coupling can be analyzed in this study.(1)Based on the observation data of ground meteorological stations in northern China in recent 50 years,the meteorological factors that have a significant impact on snow evolutions are selected to carry out the joint analysis of factors,the significance test,and the feature classification.The spatial distribution of meteorological processes unfavorable to the distribution of snow on the roof,namely the preferential deposition,the uneven snowdrift and snowmelt,are accordingly obtained.Based on the principle of feature identity,the meteorological characteristic maps of related typical snow evolution modes are drawn via proposed cluster analysis,which can guide the design of building engineering.(2)Aiming at the key issues of the combined wind and snow tests,after a review of the test similar criteria limitations,a set of new test similarity criteria that consider the whole process of snowfall and snowdrift events are derived and introduced.Guidance can be given to the achievement of the test in the realms as diverse as the test particle selection,the determination of wind speed and snow intensity,and the particle movement(transport).The accuracy and advancement of the proposed similarity criteria are prototyped via several benchmark models in a meteorological wind tunnel.Then,experimental studies are carried out to explore the development of wind and snow environments,as well as snowfall deposition modes on building roofs,which the applicability of criteria can be accordingly verified in the complex flow field environment around buildings.(3)Based on the Euler-Lagrangian(E-L)frame,snow can be treated as individual particles,by combining the computational fluid dynamics(CFD)and the discrete element method(DEM),a coupling method that can consider the collision and bonding of particles is proposed to describe real physical motions of snow particles.The physical properties and model inputted parameters of snow particles are calibrated in low-temperature experiments.The snow erosion and deposition around a prototype cube are used as the reference to check the accuracy of the CFD-DEM method.Taking the high and low roof buildings as the research object,the simulation method is further used to simulate the wind-induced snow transport in the field of the building.By changing the relevant parameters of DEM,i.e.roof materials and water content of snow,their effects on snow distribution on the building roofs can be achieved.(4)Based on the achievement of the snow melting measurement,the effects of thermal factors on snow physical properties and snow load are discussed.To consider the temperature dependence of heat transfer in snow medium,a thermal constitutive of the snow medium is accordingly proposed and introduced into the establishment of the snowmelt model,meaning that the finite element thermal analysis is accordingly carried out.Then,Using the technology of the ?birth and death‘ element,the visualization of the physical property changes of the snow medium can be achieved.Following the principle of heat transfer,the CFD-DEM coupling method is supplemented with the energy exchange process.By connecting it with the above snowmelt model,the whole process analysis of snow evolutions on the roof considering wind and heat coupling effects can be achieved.The long-period change of the shape of the deposited snow,the averaged snow depth,and snow temperature on the roof can be reproduced to predict the thermal coefficient and the snow evolution result.