A uniform transient temperature field model of electrical contacts operation was found by analyzing the process of closing arc constriction resistance Joule heat ~ breaking arc. Essential parameters of Ag/La2NiO4 elec...A uniform transient temperature field model of electrical contacts operation was found by analyzing the process of closing arc constriction resistance Joule heat ~ breaking arc. Essential parameters of Ag/La2NiO4 electrical contact material for transient temperature field calculation were obtained through tests of electrical contact experimental instrument under 18 V DC in different cur- rents, other correlation experiments, and calculation anal- ysis. The finite element method was applied to solve the transient temperature field, and the features and distribution of the transient temperature field were obtained. The condition of material erosion and mass transfer can be forecasted by those calculation results. It is beneficial to research about the lifetime of Ag/La2NiO4 electrical material.展开更多
Previous failure analyses of bridges typically focus on substructure failure or superstructure failure separately. However, in an actual bridge, the seismic induced substructure failure and superstructure failure may ...Previous failure analyses of bridges typically focus on substructure failure or superstructure failure separately. However, in an actual bridge, the seismic induced substructure failure and superstructure failure may influence each other. Moreover, previous studies typically use simplified models to analyze the bridge failure; however, there are inherent defects in the calculation accuracy compared with using a detailed three-dimensional （3D） finite element （FE） model. Conversely, a detailed 3D FE model requires more computational costs, and a proper erosion criterion of the 3D elements is necessary. In this paper, a multi-scale FE model, including a corresponding erosion criterion, is proposed and validated that can significantly reduce computational costs with high precision by modelling a pseudo-dynamic test of an reinforced concrete （RC） pier. Numerical simulations of the seismic failures of a continuous RC bridge based on the multi-scale FE modeling method using LS-DYNA are performed. The nonlinear properties of the bridge, various connection strengths and bidirectional excitations are considered. The numerical results demonstrate that the failure of the connections will induce large pounding responses of the girders. The nonlinear deformation of the piers will aggravate the pounding damages. Furthermore, bidirectional earthquakes will induce eccentric poundingsto the girders and different failure modes to the adjacent piers.展开更多
The idea of functionally gradient material (FGM) theory was used to design ceramic nozzle based on the erosion wear behaviors of the ceramic nozzles and the out- standing properties of FGM. The purpose is to reduce th...The idea of functionally gradient material (FGM) theory was used to design ceramic nozzle based on the erosion wear behaviors of the ceramic nozzles and the out- standing properties of FGM. The purpose is to reduce the tensile stress at the entry region of the nozzle during sand blasting processes. The design theory and methods of gradient ceramic nozzle were proposed. The physical, micromechanical, and composition distribution models of gradient ceramic nozzle were established. The optimum composition distribution of the gradient ceramic nozzle material was determined from the solution of the multi-objective optimization calculation by constructing the models of the composition distribution versus the structural in- tegrity of the compact in fabricating process. Results showed that compressive residual stresses appeared at the entry area of the gradient ceramic nozzle. The optimized component distribution exponent p is 0.5. An SiC/(W,Ti)C gradient ce- ramic nozzle material was synthesized by hot-pressing according to the design result. Results showed that the surface Vickers hardness of the FGM-1 gradient ceramic nozzle materials was greatly improved in comparison with that of the other layers.展开更多
Due to the surface protection structure of wind turbine blades,coating plays a key role in ensuring the surface quality of blades and improving the working performance of wind turbine.In this paper,a simplified method...Due to the surface protection structure of wind turbine blades,coating plays a key role in ensuring the surface quality of blades and improving the working performance of wind turbine.In this paper,a simplified method of finite element simulation on blade coating of wind turbine is carried out by means of theoretical analysis and computer software simulation.The influence of particle erosion velocity,mass flow rate and particle diameter was made clear on the coating erosion.This will provide a theoretical reference for improving the cover technique of wind turbine blade coating and improving the coating reliability.展开更多
Rill erosion models are important to hillslope soil erosion prediction and to land use planning.The development of rill erosion models and their use has become increasingly of great concern.The purpose of this researc...Rill erosion models are important to hillslope soil erosion prediction and to land use planning.The development of rill erosion models and their use has become increasingly of great concern.The purpose of this research was to develop mathematic models with computer simulation procedures to simulate and predict rill erosion.The finite element method is known as an efficient tool in many other applications than in rill soil erosion.In this study,the hydrodynamic and sediment continuity model equations for a rill erosion system were solved by the Galerkin finite element method and Visual Cþþprocedures.The simulated results are compared with the data for spatially and temporally measured processes for rill erosion under different conditions.The results indicate that the one-dimensional linear finite element method produced excellent predictions of rill erosion processes.Therefore,this study supplies a tool for further development of a dynamic soil erosion prediction model.展开更多
Debris flows in their natural environments are made up of different sediment sizes,even though they are often considered to be uniform in numerical studies.This prompted the present study to investigate the behaviors ...Debris flows in their natural environments are made up of different sediment sizes,even though they are often considered to be uniform in numerical studies.This prompted the present study to investigate the behaviors of debris flows with nonuniform sediment composition.A model is developed to investigate nonuniform debris flows and the characteristic behavior of their compositions.The model’s framework of mass and momentum equations and mass exchange with the bed are solved using the shock-capturing finite volume method.The model is first tested with a uniform sediment laboratory experiment,where there is a good agreement.The model is then tested against two flume experiments with different bed water content and porosity.The model performed well in both cases,however,the slight underprediction in the second case can be associated with the complexity of debris flows which may not be fully captured by physical equations.The model is further used to investigate different compositions of debris flows including mixed grain sizes,mean size,fine and coarse sediment size,and no erosion/deposition.The modeling of the mixed grain sizes produced a more accurate result,and this justifies the consideration of nonuniform sediment sizes in the numerical studies of debris flows.To enhance the understanding of frontal coarsening and rear fining in experimental debris flow,the model is also used to investigate cases with different sediment compositions,and the model was able to reproduce the frontal coarsening and rear fining observed in experiments.展开更多
基金financially supported by the National Science Foundation of China-Yunnan United Foundation(No.U0837601)the National Natural Science Foundation of China(No.51267007)the Natural Science Foundation of Yunnan Province(No.2010CD126,No.2012FB195)
文摘A uniform transient temperature field model of electrical contacts operation was found by analyzing the process of closing arc constriction resistance Joule heat ~ breaking arc. Essential parameters of Ag/La2NiO4 electrical contact material for transient temperature field calculation were obtained through tests of electrical contact experimental instrument under 18 V DC in different cur- rents, other correlation experiments, and calculation anal- ysis. The finite element method was applied to solve the transient temperature field, and the features and distribution of the transient temperature field were obtained. The condition of material erosion and mass transfer can be forecasted by those calculation results. It is beneficial to research about the lifetime of Ag/La2NiO4 electrical material.
基金National Program on Key Basic Research Project of China(973) under Grant No.2011CB013603the National Natural Science Foundation of China under Grant Nos.51427901,91315301 and 51408410the Natural Science Foundation of Tianjin,China under Grant No.15JCQNJC07200
文摘Previous failure analyses of bridges typically focus on substructure failure or superstructure failure separately. However, in an actual bridge, the seismic induced substructure failure and superstructure failure may influence each other. Moreover, previous studies typically use simplified models to analyze the bridge failure; however, there are inherent defects in the calculation accuracy compared with using a detailed three-dimensional （3D） finite element （FE） model. Conversely, a detailed 3D FE model requires more computational costs, and a proper erosion criterion of the 3D elements is necessary. In this paper, a multi-scale FE model, including a corresponding erosion criterion, is proposed and validated that can significantly reduce computational costs with high precision by modelling a pseudo-dynamic test of an reinforced concrete （RC） pier. Numerical simulations of the seismic failures of a continuous RC bridge based on the multi-scale FE modeling method using LS-DYNA are performed. The nonlinear properties of the bridge, various connection strengths and bidirectional excitations are considered. The numerical results demonstrate that the failure of the connections will induce large pounding responses of the girders. The nonlinear deformation of the piers will aggravate the pounding damages. Furthermore, bidirectional earthquakes will induce eccentric poundingsto the girders and different failure modes to the adjacent piers.
基金the Specialized Research Fund for Doctoral Program of Higher Education (Grant No. 20030422105)the Natural Science Founda-tion of Shandong Province (Grant Nos. Y2004F08, Z2003F01)the Program for New Century Excellent Talents in University (Grant No. NCET-04-0622)
文摘The idea of functionally gradient material (FGM) theory was used to design ceramic nozzle based on the erosion wear behaviors of the ceramic nozzles and the out- standing properties of FGM. The purpose is to reduce the tensile stress at the entry region of the nozzle during sand blasting processes. The design theory and methods of gradient ceramic nozzle were proposed. The physical, micromechanical, and composition distribution models of gradient ceramic nozzle were established. The optimum composition distribution of the gradient ceramic nozzle material was determined from the solution of the multi-objective optimization calculation by constructing the models of the composition distribution versus the structural in- tegrity of the compact in fabricating process. Results showed that compressive residual stresses appeared at the entry area of the gradient ceramic nozzle. The optimized component distribution exponent p is 0.5. An SiC/(W,Ti)C gradient ce- ramic nozzle material was synthesized by hot-pressing according to the design result. Results showed that the surface Vickers hardness of the FGM-1 gradient ceramic nozzle materials was greatly improved in comparison with that of the other layers.
基金the National Natural Science Foundation of China(No.51365031)the Wind and Solar Energy Utilization Technology Provincial and Minis try Co-construction of Key Laboratory Open Fund of Ministry of Education(No.201607)。
文摘Due to the surface protection structure of wind turbine blades,coating plays a key role in ensuring the surface quality of blades and improving the working performance of wind turbine.In this paper,a simplified method of finite element simulation on blade coating of wind turbine is carried out by means of theoretical analysis and computer software simulation.The influence of particle erosion velocity,mass flow rate and particle diameter was made clear on the coating erosion.This will provide a theoretical reference for improving the cover technique of wind turbine blade coating and improving the coating reliability.
基金supported by the National Natural Science Foundation of China under Project no.40635027,and No.51321001.
文摘Rill erosion models are important to hillslope soil erosion prediction and to land use planning.The development of rill erosion models and their use has become increasingly of great concern.The purpose of this research was to develop mathematic models with computer simulation procedures to simulate and predict rill erosion.The finite element method is known as an efficient tool in many other applications than in rill soil erosion.In this study,the hydrodynamic and sediment continuity model equations for a rill erosion system were solved by the Galerkin finite element method and Visual Cþþprocedures.The simulated results are compared with the data for spatially and temporally measured processes for rill erosion under different conditions.The results indicate that the one-dimensional linear finite element method produced excellent predictions of rill erosion processes.Therefore,this study supplies a tool for further development of a dynamic soil erosion prediction model.
基金the National Natural Science Foundation of China(Grant Nos.12172331,11872332)the Natural Science Foundation of Zhejiang(Grant No.LR19E090002)the HPC Center of Zhejiang University(Zhoushan Campus).
文摘Debris flows in their natural environments are made up of different sediment sizes,even though they are often considered to be uniform in numerical studies.This prompted the present study to investigate the behaviors of debris flows with nonuniform sediment composition.A model is developed to investigate nonuniform debris flows and the characteristic behavior of their compositions.The model’s framework of mass and momentum equations and mass exchange with the bed are solved using the shock-capturing finite volume method.The model is first tested with a uniform sediment laboratory experiment,where there is a good agreement.The model is then tested against two flume experiments with different bed water content and porosity.The model performed well in both cases,however,the slight underprediction in the second case can be associated with the complexity of debris flows which may not be fully captured by physical equations.The model is further used to investigate different compositions of debris flows including mixed grain sizes,mean size,fine and coarse sediment size,and no erosion/deposition.The modeling of the mixed grain sizes produced a more accurate result,and this justifies the consideration of nonuniform sediment sizes in the numerical studies of debris flows.To enhance the understanding of frontal coarsening and rear fining in experimental debris flow,the model is also used to investigate cases with different sediment compositions,and the model was able to reproduce the frontal coarsening and rear fining observed in experiments.
