This paper discusses a statistical second-order two-scale（SSOTS） analysis and computation for a heat conduction problem with a radiation boundary condition in random porous materials.Firstly,the microscopic configur...This paper discusses a statistical second-order two-scale（SSOTS） analysis and computation for a heat conduction problem with a radiation boundary condition in random porous materials.Firstly,the microscopic configuration for the structure with random distribution is briefly characterized.Secondly,the SSOTS formulae for computing the heat transfer problem are derived successively by means of the construction way for each cell.Then,the statistical prediction algorithm based on the proposed two-scale model is described in detail.Finally,some numerical experiments are proposed,which show that the SSOTS method developed in this paper is effective for predicting the heat transfer performance of porous materials and demonstrating its significant applications in actual engineering computation.展开更多
Numerical simulation based on computational fluid dynamics （CFD） is a useful approach for quantitatively investigating the underlying thermal-mechanical conditions during FSW, such as temperature field and material ...Numerical simulation based on computational fluid dynamics （CFD） is a useful approach for quantitatively investigating the underlying thermal-mechanical conditions during FSW, such as temperature field and material deformation field. One of the critical issues in CFD simulation of FSW is the use of the frictional boundary condition, which represents the friction between the welding tool and the workpiece in the numerical models. In this study, three-dimensional numerical simulation is conducted to analyze the heat transfer and plastic deformation behaviors during the FSW of AA2024. For comparison purposes, both the boundary velocity （BV） models and the boundary shear stress （BSS） models are employed in order to assess their performances in predicting the temperature and material deformation in FSW. It is interesting to note that different boundary conditions yield similar predictions on temperature, but quite different predictions on material deformation. The numerical predictions are compared with the experimental results. The predicted deformation zone geometry by the BSS model is consistent with the experimental results while there is large difference between the predictions by the BV models and the experimental measurements. The fact that the BSS model yields more reasonable predictions on the deformation zone geometry is attributed to its capacity to automatically adjust the contact state at the tool/workpiece interface. Based on the favorable predictions on both the temperature field and the material deformation field, the BSS model is suggested to have a better performance in numerical simulation of FSW than the BV model.展开更多
This essay studies various family-related factors that influence a child’s academic achievement in school in P.R. China. The factors are illustrated under three categories: the family’s social class and education, e...This essay studies various family-related factors that influence a child’s academic achievement in school in P.R. China. The factors are illustrated under three categories: the family’s social class and education, early home environment and family material condition. The author discusses the relevant factors by way of relating the knowledge of social environment to his own experiences as a student and then teacher in China. The essay closes with a discussion directing the public’s attention to the concern about home-related factors influencing a child’s academic achievements in school.展开更多
To solve the problem of condensation at the radiant cooling terminal,a novel radiant cooling terminal(NRCT)based on the moisture buffering effect is proposed.The NRCT combines traditional radiant cooling terminals wit...To solve the problem of condensation at the radiant cooling terminal,a novel radiant cooling terminal(NRCT)based on the moisture buffering effect is proposed.The NRCT combines traditional radiant cooling terminals with solid humidity conditioning materials(HCM).On this basis,a coupled anti-condensation regulation strategy between the NRCT and the fresh air system was constructed,which utilizes the moisture buffering effect of the HCM to extend the condensation time,and reserves sufficient time for active intervention of personnel and feedback adjustment of the fresh air system.Then,the indoor air parameters are restored to normal design values as a result of the fresh air system.Meanwhile,the HCM releases the adsorbed water vapor,thereby enabling the completion of the desorption process.Using numerical simulation methods to study each step of the anti-condensation regulation strategy,the results indicate that the NRCT can effectively prevent condensation,and it can ensure that condensation does not occur within 20 min after the window is opened,even under extreme weather conditions.Moreover,the anti-condensation effect improves with the thickness increase of the HCM.However,when ensuring the prevention of condensation while expecting the best moisture adsorption effect,there is an optimal value for the thickness of the HCM.Increasing the fresh air supply volume can enable the HCM to complete the desorption process more quickly.In the final steady-state operation process,the HCM can continue to release moisture,achieving sustainable utilization of the HCM.In actual operation,the operational duration of the fresh air system during the moisture desorption process can be regulated by tracking the relative humidity of the outlet to ensure that the HCM completes the adsorption and desorption cycle.This anti-condensation regulation strategy can provide effective guarantee for the non-condensing operation of radiant cooling terminals.展开更多
基金Project supported by the China Postdoctoral Science Foundation(Grant Nos.2015M580256 and 2016T90276)
文摘This paper discusses a statistical second-order two-scale（SSOTS） analysis and computation for a heat conduction problem with a radiation boundary condition in random porous materials.Firstly,the microscopic configuration for the structure with random distribution is briefly characterized.Secondly,the SSOTS formulae for computing the heat transfer problem are derived successively by means of the construction way for each cell.Then,the statistical prediction algorithm based on the proposed two-scale model is described in detail.Finally,some numerical experiments are proposed,which show that the SSOTS method developed in this paper is effective for predicting the heat transfer performance of porous materials and demonstrating its significant applications in actual engineering computation.
基金supported by the National Natural Science Foundation of China(Grant No.51375259 and Grant No.51705280)the Ministry of Science and Technology of China(Grant No.2012ZX04012-011)+1 种基金Special Program for Applied Research on Super Computation of the NSFC-Guangdong Joint Fund(the second phase,Grant No.U1501501)the Tsinghua National Laboratory for Information Science and Technology
文摘Numerical simulation based on computational fluid dynamics （CFD） is a useful approach for quantitatively investigating the underlying thermal-mechanical conditions during FSW, such as temperature field and material deformation field. One of the critical issues in CFD simulation of FSW is the use of the frictional boundary condition, which represents the friction between the welding tool and the workpiece in the numerical models. In this study, three-dimensional numerical simulation is conducted to analyze the heat transfer and plastic deformation behaviors during the FSW of AA2024. For comparison purposes, both the boundary velocity （BV） models and the boundary shear stress （BSS） models are employed in order to assess their performances in predicting the temperature and material deformation in FSW. It is interesting to note that different boundary conditions yield similar predictions on temperature, but quite different predictions on material deformation. The numerical predictions are compared with the experimental results. The predicted deformation zone geometry by the BSS model is consistent with the experimental results while there is large difference between the predictions by the BV models and the experimental measurements. The fact that the BSS model yields more reasonable predictions on the deformation zone geometry is attributed to its capacity to automatically adjust the contact state at the tool/workpiece interface. Based on the favorable predictions on both the temperature field and the material deformation field, the BSS model is suggested to have a better performance in numerical simulation of FSW than the BV model.
文摘This essay studies various family-related factors that influence a child’s academic achievement in school in P.R. China. The factors are illustrated under three categories: the family’s social class and education, early home environment and family material condition. The author discusses the relevant factors by way of relating the knowledge of social environment to his own experiences as a student and then teacher in China. The essay closes with a discussion directing the public’s attention to the concern about home-related factors influencing a child’s academic achievements in school.
基金supported by the National Natural Science Foundation of China[No.52276179]the Natural Science Foundation of Jiangsu Province[No.BK20231425]。
文摘To solve the problem of condensation at the radiant cooling terminal,a novel radiant cooling terminal(NRCT)based on the moisture buffering effect is proposed.The NRCT combines traditional radiant cooling terminals with solid humidity conditioning materials(HCM).On this basis,a coupled anti-condensation regulation strategy between the NRCT and the fresh air system was constructed,which utilizes the moisture buffering effect of the HCM to extend the condensation time,and reserves sufficient time for active intervention of personnel and feedback adjustment of the fresh air system.Then,the indoor air parameters are restored to normal design values as a result of the fresh air system.Meanwhile,the HCM releases the adsorbed water vapor,thereby enabling the completion of the desorption process.Using numerical simulation methods to study each step of the anti-condensation regulation strategy,the results indicate that the NRCT can effectively prevent condensation,and it can ensure that condensation does not occur within 20 min after the window is opened,even under extreme weather conditions.Moreover,the anti-condensation effect improves with the thickness increase of the HCM.However,when ensuring the prevention of condensation while expecting the best moisture adsorption effect,there is an optimal value for the thickness of the HCM.Increasing the fresh air supply volume can enable the HCM to complete the desorption process more quickly.In the final steady-state operation process,the HCM can continue to release moisture,achieving sustainable utilization of the HCM.In actual operation,the operational duration of the fresh air system during the moisture desorption process can be regulated by tracking the relative humidity of the outlet to ensure that the HCM completes the adsorption and desorption cycle.This anti-condensation regulation strategy can provide effective guarantee for the non-condensing operation of radiant cooling terminals.
