Arc erosion morphologies of Ag/MeO（10） electrical contact materials after 50000 operations under direct current of 19 V and 20 A and resistive load conditions were investigated using scanning electron microscope（SE...Arc erosion morphologies of Ag/MeO（10） electrical contact materials after 50000 operations under direct current of 19 V and 20 A and resistive load conditions were investigated using scanning electron microscope（SEM） and a 3D optical profiler（3DOP）. The results indicated that 3DOP could supply clearer and more detailed arc erosion morphology information. Arc erosion resistance of Ag/SnO_2（10） electrical contact material was the best and that of Ag/CuO（10） was the worst. Arc erosion morphology of Ag/MeO（10） electrical contact materials mainly included three different types. Arc erosion morphologies of Ag/ZnO（10） and Ag/SnO_2（10） electrical contact materials were mainly liquid splash and evaporation, and those of Ag/CuO（10） and Ag/CdO（10） were mainly material transfer from anode to cathode. Arc erosion morphology of Ag/SnO_2（6）In_2O_3（4） electrical contact materials included both liquid splash, evaporation and material transfer. In addition, the formation process and mechanism on arc erosion morphology of Ag/MeO（10） electrical contact materials were discussed.展开更多
Nonlinear solution of reinforced concrete structures, particularly complete load-deflection response, requires tracing of the equilibrium path and proper treatment of the limit and bifurcation points. In this regard, ...Nonlinear solution of reinforced concrete structures, particularly complete load-deflection response, requires tracing of the equilibrium path and proper treatment of the limit and bifurcation points. In this regard, ordinary solution techniques lead to instability near the limit points and also have problems in case of snap-through and snap-back. Thus they fail to predict the complete load-displacement response. The arc-length method serves the purpose well in principle, received wide acceptance in finite element analysis, and has been used extensively. However modifications to the basic idea are vital to meet the particular needs of the analysis. This paper reviews some of the recent developments of the method in the last two decades, with particular emphasis on nonlinear finite element analysis of reinforced concrete structures.展开更多
A transient finite element model has been developed to study the heat transfer and fluid flow during spot Gas Tungsten Arc Welding （GTAW） on stainless steel. Temperature field, fluid velocity and electromagnetic fie...A transient finite element model has been developed to study the heat transfer and fluid flow during spot Gas Tungsten Arc Welding （GTAW） on stainless steel. Temperature field, fluid velocity and electromagnetic fields are computed inside the cathode, arc-plasma and anode using a unified MHD formulation. The developed model is then used to study the influence of different helium-argon gas mixtures on both the energy transferred to the workpiece and the time evolution of the weld pool dimensions. It is found that the addition of helium to argon increases the heat flux density on the weld axis by a factor that can reach 6.5. This induces an increase in the weld pool depth by a factor of 3. It is also found that the addition of only 10% of argon to helium decreases considerably the weld pool depth, which is due to the electrical conductivity of the mixture that increases significantly when argon is added to helium.展开更多
A matrix whose entries are +,-, and 0 is called a sign pattern matrix. Let k be arbitrary positive integer. We first characterize sign patterns A such that .Ak≤0. Further, we determine the maximum number of negative ...A matrix whose entries are +,-, and 0 is called a sign pattern matrix. Let k be arbitrary positive integer. We first characterize sign patterns A such that .Ak≤0. Further, we determine the maximum number of negative entries that can occur in A whenever Ak≤0. Finally, we give a necessity and sufficiency condition for A2≤0.展开更多
This study examines the hydrodynamic performance of short-crested wave interaction with a new porous cylindrical structure by using the scaled boundary finite element method （SBFEM）, which is a semi-analytical techn...This study examines the hydrodynamic performance of short-crested wave interaction with a new porous cylindrical structure by using the scaled boundary finite element method （SBFEM）, which is a semi-analytical technique combining the advantages of the finite element method and the boundary element method and with its own special features as well. The cylindrical structure consists of dual arc-shaped porous outer cylinders circumscribing an impermeable inner cylinder. A central feature of the newly extended method is that two virtual outer cylinders extending the arc-shaped porous outer cylinders with the same centre are introduced and variable porous-effect parameters are also introduced for the two virtual cylinders, so that the final SBFEM quation still can be handled in a closed-form analytical manner in the radial direction and by a finite element approximation in the circumferential direction. The entire computational domain is divided into two bounded and one unbounded domains, and a variational principle formulation is used to derive the SBFEM equation in each sub-domain. The velocity potential in bounded and unbounded domains is formulated using sets of Bessel and Hankel functions respectively, and the unknown coefficients are determined from the matching conditions. The results of numerical verification show that the approach discretises only the outermost virtual cylinder with surface finite-elements and fewer elements are required to obtain very accurate results.Influences of the incident wave parameters and structural configurations on the hydrodynamics are examined.展开更多
基金Project(2012QNZT003)supported by the Fundamental Research Funds for the Central Universities,ChinaProject(2012M521542)supported by the Postdoctoral Science Foundation of China+1 种基金Project(14JJ3014)supported by the Hunan Provincial Natural Science Foundation of ChinaProject(BSh1202)supported by the Zhejiang Provincial Postdoctoral Scientific Research Foundation of China
文摘Arc erosion morphologies of Ag/MeO（10） electrical contact materials after 50000 operations under direct current of 19 V and 20 A and resistive load conditions were investigated using scanning electron microscope（SEM） and a 3D optical profiler（3DOP）. The results indicated that 3DOP could supply clearer and more detailed arc erosion morphology information. Arc erosion resistance of Ag/SnO_2（10） electrical contact material was the best and that of Ag/CuO（10） was the worst. Arc erosion morphology of Ag/MeO（10） electrical contact materials mainly included three different types. Arc erosion morphologies of Ag/ZnO（10） and Ag/SnO_2（10） electrical contact materials were mainly liquid splash and evaporation, and those of Ag/CuO（10） and Ag/CdO（10） were mainly material transfer from anode to cathode. Arc erosion morphology of Ag/SnO_2（6）In_2O_3（4） electrical contact materials included both liquid splash, evaporation and material transfer. In addition, the formation process and mechanism on arc erosion morphology of Ag/MeO（10） electrical contact materials were discussed.
文摘Nonlinear solution of reinforced concrete structures, particularly complete load-deflection response, requires tracing of the equilibrium path and proper treatment of the limit and bifurcation points. In this regard, ordinary solution techniques lead to instability near the limit points and also have problems in case of snap-through and snap-back. Thus they fail to predict the complete load-displacement response. The arc-length method serves the purpose well in principle, received wide acceptance in finite element analysis, and has been used extensively. However modifications to the basic idea are vital to meet the particular needs of the analysis. This paper reviews some of the recent developments of the method in the last two decades, with particular emphasis on nonlinear finite element analysis of reinforced concrete structures.
文摘A transient finite element model has been developed to study the heat transfer and fluid flow during spot Gas Tungsten Arc Welding （GTAW） on stainless steel. Temperature field, fluid velocity and electromagnetic fields are computed inside the cathode, arc-plasma and anode using a unified MHD formulation. The developed model is then used to study the influence of different helium-argon gas mixtures on both the energy transferred to the workpiece and the time evolution of the weld pool dimensions. It is found that the addition of helium to argon increases the heat flux density on the weld axis by a factor that can reach 6.5. This induces an increase in the weld pool depth by a factor of 3. It is also found that the addition of only 10% of argon to helium decreases considerably the weld pool depth, which is due to the electrical conductivity of the mixture that increases significantly when argon is added to helium.
基金Supported by Shanxi Natural Science Foundation(20011006)
文摘A matrix whose entries are +,-, and 0 is called a sign pattern matrix. Let k be arbitrary positive integer. We first characterize sign patterns A such that .Ak≤0. Further, we determine the maximum number of negative entries that can occur in A whenever Ak≤0. Finally, we give a necessity and sufficiency condition for A2≤0.
基金supported by the National Natural Science Foundation of China (Grant Nos. 51121005 and 51138001)the China-Germany Joint Research Project (Grant No. GZ566)
文摘This study examines the hydrodynamic performance of short-crested wave interaction with a new porous cylindrical structure by using the scaled boundary finite element method （SBFEM）, which is a semi-analytical technique combining the advantages of the finite element method and the boundary element method and with its own special features as well. The cylindrical structure consists of dual arc-shaped porous outer cylinders circumscribing an impermeable inner cylinder. A central feature of the newly extended method is that two virtual outer cylinders extending the arc-shaped porous outer cylinders with the same centre are introduced and variable porous-effect parameters are also introduced for the two virtual cylinders, so that the final SBFEM quation still can be handled in a closed-form analytical manner in the radial direction and by a finite element approximation in the circumferential direction. The entire computational domain is divided into two bounded and one unbounded domains, and a variational principle formulation is used to derive the SBFEM equation in each sub-domain. The velocity potential in bounded and unbounded domains is formulated using sets of Bessel and Hankel functions respectively, and the unknown coefficients are determined from the matching conditions. The results of numerical verification show that the approach discretises only the outermost virtual cylinder with surface finite-elements and fewer elements are required to obtain very accurate results.Influences of the incident wave parameters and structural configurations on the hydrodynamics are examined.
