CFD-DEM modeling of snowdrifts on stepped flat roofs

Zhao, Lei,Yu, Zhixiang,Zhu, Fu,Qi, Xin,Zhao, Shichun Techno-Press 2016 Wind and Structures, An International Journal (WAS Vol.23 No.6

Snowdrift formation on roofs should be considered in snowy and windy areas to ensure the safety of buildings. Presently, the prediction of snowdrifts on roofs relies heavily on field measurements, wind tunnel tests and numerical simulations. In this paper, a new snowdrift modeling method by using CFD (Computational Fluid Dynamics) coupled with DEM (Discrete Element Method) is presented, including material parameters and particle size, collision parameters, particle numbers and input modes, boundary conditions of CFD, simulation time and inlet velocity, and coupling calculation process. 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. The numerical method is 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.

CFD-DEM modeling of snowdrifts on stepped flat roofs

Lei Zhao,Zhixiang Yu,Fu Zhu,Xin Qi,Shichun Zhao 한국풍공학회 2016 Wind and Structures, An International Journal (WAS Vol.23 No.6

Snowdrift formation on roofs should be considered in snowy and windy areas to ensure the safety of buildings. Presently, the prediction of snowdrifts on roofs relies heavily on field measurements, wind tunnel tests and numerical simulations. In this paper, a new snowdrift modeling method by using CFD (Computational Fluid Dynamics) coupled with DEM (Discrete Element Method) is presented, including material parameters and particle size, collision parameters, particle numbers and input modes, boundary conditions of CFD, simulation time and inlet velocity, and coupling calculation process. 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. The numerical method is 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.

Grinding Marks on Ultra-Precision Grinding Spherical and Aspheric Surfaces

Bing Chen,Bing Guo,Shichun Li,Zhaohui Deng,Qingliang Zhao 한국정밀공학회 2017 International Journal of Precision Engineering and Vol.4 No.4

Grinding marks are regard as a great obstacle to manufacture spherical and aspheric surfaces with higher surface quality, lower energy and wastage. The scallop-height was studied for optimizing the grinding parameters firstly to reduce its effect on grinding marks. Secondly, the expression of grinding points distribution was established to characterize the grinding marks caused by the radial run-out of grinding wheel. And then, the aspheric grinding experiments of monocrystalline silicon were carried out to investigate the influence of grinding marks on surface quality. The experiments revealed that the remarkable grinding marks with patterned grinding points distribution would cause more fractures and roughness, deeper grooves, and more inhomogeneous surface quality compared with the weak grinding marks. The discriminating standard of grinding marks was established, and the grinding parameters were optimized for homogenizing the grinding points distribution by this discriminating standard to reduce the grinding marks in actual grinding process. Finally, the large size infrared lens was ground with high surface quality by the optimized grinding parameters, and the results of surface quality demonstrate that the discriminating standard was effective. This research provides references and ideas for grinding aspherical surface with high surface quality and efficiency, low energy and wastage.

Experimental Study on Existing RC Circular Members Under Unequal Lateral Impact Train Collision

Khalil AL-Bukhaiti,Liu Yanhui,Zhao Shichun,Hussein Abas,Xu Nan,Yang Lang,Yan Xing Yu,Han Daguang 한국콘크리트학회 2022 International Journal of Concrete Structures and M Vol.16 No.5

With the fast growth of high-speed rail in recent years, derailment has become the first hidden danger of high-speed rail transportation. The high-speed train passes near the station building. So the train may derail and hit the station building. Building a high-speed railway station usually uses a reinforced concrete structure. As a result of high impact energy on the impact body, the reinforced concrete (RC) member may fail; the impact point is near the member's foot; the structural member's constraint can be considered fixed support. This paper investigates the dynamic behavior of four types of circular reinforced concrete members under unequal lateral impact loads. The RC member's failure mechanism and dynamic response addressed the significance of unequal lateral impact load. The usual circular reinforced concrete members are used as the model to perform the drop-weight impact test. The specimens' crack pattern, failure mechanism, impact, deflection, and strain time–history curves are obtained. Findings show that between the impact point and the adjacent support, shear fractures occur that fail in shear mode. Shear cracks are based on impact velocity, longitudinal reinforcement ratio, and stirrup ratio. One type is more destructive to members and nodes. A shear fracture occurs when a longitudinal reinforcement fractures towards the closer support. The effects of impact velocity, longitudinal reinforcement ratio, and stirrup ratio on the dynamic impact response are studied. The experimental results may help improve structural member impact resistance. The critical section (right side) computed the static shear resistance using shear force, whereas the maximum external load resistance determines static bending moment resistance. Understanding how circular members fail to be subjected to unequal lateral impact loads provides insight into circular RC members' impact design and damage evaluation.

An Application of BP Neural Network to the Prediction of Compressive Strength in Circular Concrete Columns Confined with CFRP

Khalil AL-Bukhaiti,Liu Yanhui,Zhao Shichun,Hussein Abas 대한토목학회 2023 KSCE Journal of Civil Engineering Vol.27 No.7

The neural network comprises many neurons with extensive interconnections operatingparallel and performing specific functions. This paper establishes a BP neural networkprediction model for the compressive strength of CFRP-confined concrete based on a largenumber of experimental data to study the predictive ability of the BP neural network on thecompressive strength of CFRP-confined concrete and the output performance of the neuralnetwork model. The model is based on a BP neural network that has been trained using manyexperimental data. An investigation is being conducted on the effect of different datacombinations on the accuracy of the predictions made by the neural network model. Thehigh-precision BP network model is created into generic and simplified formulae for applicationconvenience. These formulas are developed based on the theory of neural networks. Theneural network models' findings and the empirical formulae for making predictions arecompared and discussed. The BP neural network accurately predicts the compressive strengthof CFRP-confined concrete, with over 90% of its data points having less than 15% error. Incomparison, the regression model shows less accuracy, with less than 70% of its data pointshaving an error within 15%. Compared to traditional regression models, the simple linearequation derived using Purelin instead of Sigmoid as the transfer function only adds a constantterm. The average value of prediction/test results is 1.011. The analysis results show that BPneural network can extract the input and output parameters' data information well and obtaina high-accuracy prediction model. The coefficient of variation is 0.112, which indicates thatthe prediction accuracy and stability are greater than average.

Wind tunnel tests and CFD simulations for snow redistribution on 3D stepped flat roofs

Zhixiang Yu,Fu Zhu,Ruizhou Cao,Xiaoxiao Chen,Lei Zhao,Shichun Zhao 한국풍공학회 2019 Wind and Structures, An International Journal (WAS Vol.28 No.1

The accurate prediction of snow distributions under the wind action on roofs plays an important role in designing structures in civil engineering in regions with heavy snowfall. Affected by some factors such as building shapes, sizes and layouts, the snow drifting on roofs shows more three-dimensional characteristics. Thus, the research on three-dimensional snow distribution is needed. Firstly, four groups of stepped flat roofs are designed, of which the width-height ratio is 3, 4, 5 and 6. Silica sand with average radius of 0.1 mm is used to model the snow particles and then the wind tunnel test of snow drifting on stepped flat roofs is carried out. 3D scanning is used to obtain the snow distribution after the test is finished and the mean mass transport rate is calculated. Next, the wind velocity and duration is determined for numerical simulations based on similarity criteria. The adaptive-mesh method based on radial basis function (RBF) interpolation is used to simulate the dynamic change of snow phase boundary on lower roofs and then a time-marching analysis of steady snow drifting is conducted. The overall trend of numerical results are generally consistent with the wind tunnel tests and field measurements, which validate the accuracy of the numerical simulation. The combination between the wind tunnel test and CFD simulation for three-dimensional typical roofs can provide certain reference to the prediction of the distribution of snow loads on typical roofs.