This work aims to establish a suitable numerical simulation model for hybrid laser-electric arc heat source welding of dissimilar Mg alloys between AZ31 and AZ80. Based on the energy conservation law and Fourier’s la...This work aims to establish a suitable numerical simulation model for hybrid laser-electric arc heat source welding of dissimilar Mg alloys between AZ31 and AZ80. Based on the energy conservation law and Fourier’s law of heat conduction, the differential equations of the three-dimensional temperature field for nonlinear transient heat conduction are built. According to the analysis of nonlinear transient heat transfer, the equations representing initial conditions and boundary conditions are obtained. The “double ellipsoidal heat source + 3D Gaussian heat source”combination was chosen to construct the laser-electric arc hybrid heat source. The weld bead morphologies and the distribution of temperature, stress, displacement and plastic strains are numerically simulated. The actual welding experiments were performed by a hybrid laser-electric arc welding machine. The interaction mechanism between laser and electric arc in the hybrid welding of Mg alloys is discussed in detail. The hybrid heat source can promote the absorption of laser energy and electric arc in the molten pool, resulting in more uniform energy distribution in the molten pool and the corresponding improvement of welding parameters. This work can provide theoretical guidance and data supports for the optimization of the hybrid laser-electric arc welding processes for Mg alloys.展开更多
A three-dimensional(3-D)global hybrid simulation is carried out for the generation and structure of magnetic reconnection in the magnetosheath due to interaction of an interplanetary Tangential Discontinuity(TD)with t...A three-dimensional(3-D)global hybrid simulation is carried out for the generation and structure of magnetic reconnection in the magnetosheath due to interaction of an interplanetary Tangential Discontinuity(TD)with the bow shock and magnetosphere.Runs are performed for solar wind TDs possessing diFFerent initial half-widths.As the TD propagates through the bow shock toward the magnetopause,it is greatly narrowed by a two-step compression processes,a "shock compression" followed by a subsequent "convective compression".In cases with a relatively thin solar wind TD,3-D patchy reconnection is initiated in the transmitted TD,forming magnetosheath flux ropes.Multiple components of ion particles are present in the velocity distribution in the magnetosheath merging,accompanied by ion heating.For cases with a relatively wide initial TD,a dominant single X-line appears in the subsolar magnetosheath after the transmitted TD is narrowed.A shock analysis is performed for the detailed structure of magnetic reconnection in the magnetosheath.Rotational Discontinuity(RD)/TimeDependent Intermediate Shock(TDIS)are found to dominate the reconnection layer,which and some weak slow shocks are responsible for the ion heating and acceleration.展开更多
针对高速电机和飞轮储能系统等对空间利用率要求较高的场合,提出一种新型异极径向混合磁轴承(heteropolar radial hybrid magnetic bearing,HRHMB).首先,建立该磁轴承的等效磁路模型,通过解析磁场得出其电流刚度、位移刚度及电磁力,并...针对高速电机和飞轮储能系统等对空间利用率要求较高的场合,提出一种新型异极径向混合磁轴承(heteropolar radial hybrid magnetic bearing,HRHMB).首先,建立该磁轴承的等效磁路模型,通过解析磁场得出其电流刚度、位移刚度及电磁力,并通过有限元仿真验证其有效性;然后,在相同约束条件下与传统偏置磁轴承进行对比,分析磁轴承的刚度特性和空间利用率;最后,通过有限元仿真研究新型磁轴承径向两自由度间的电磁力耦合,并与传统磁轴承进行对比.研究结果表明:在相同承载力等约束条件下,该新型磁轴承的体积仅为传统磁轴承的0.87倍,其电磁力在控制电流和转子位移影响下的相对误差值为6.5%,而传统磁轴承的电磁力相对误差为13.6%,表明新型磁轴承径向两自由度的电磁力耦合小于传统磁轴承,解耦效果良好.展开更多
基金Project(52004154) supported by the National Natural Science Foundation of ChinaProject(ZR2020QE002) supported by the Shandong Provincial Natural Science Foundation,ChinaProject(6142005190208) supported by the National Key Laboratory Foundation of China。
文摘This work aims to establish a suitable numerical simulation model for hybrid laser-electric arc heat source welding of dissimilar Mg alloys between AZ31 and AZ80. Based on the energy conservation law and Fourier’s law of heat conduction, the differential equations of the three-dimensional temperature field for nonlinear transient heat conduction are built. According to the analysis of nonlinear transient heat transfer, the equations representing initial conditions and boundary conditions are obtained. The “double ellipsoidal heat source + 3D Gaussian heat source”combination was chosen to construct the laser-electric arc hybrid heat source. The weld bead morphologies and the distribution of temperature, stress, displacement and plastic strains are numerically simulated. The actual welding experiments were performed by a hybrid laser-electric arc welding machine. The interaction mechanism between laser and electric arc in the hybrid welding of Mg alloys is discussed in detail. The hybrid heat source can promote the absorption of laser energy and electric arc in the molten pool, resulting in more uniform energy distribution in the molten pool and the corresponding improvement of welding parameters. This work can provide theoretical guidance and data supports for the optimization of the hybrid laser-electric arc welding processes for Mg alloys.
基金Supported by NSF grant ATM-0646442 to Auburn University and the National Natural Science Foundation of China(NSFC) grant 40640420563 to Wuhan University
文摘A three-dimensional(3-D)global hybrid simulation is carried out for the generation and structure of magnetic reconnection in the magnetosheath due to interaction of an interplanetary Tangential Discontinuity(TD)with the bow shock and magnetosphere.Runs are performed for solar wind TDs possessing diFFerent initial half-widths.As the TD propagates through the bow shock toward the magnetopause,it is greatly narrowed by a two-step compression processes,a "shock compression" followed by a subsequent "convective compression".In cases with a relatively thin solar wind TD,3-D patchy reconnection is initiated in the transmitted TD,forming magnetosheath flux ropes.Multiple components of ion particles are present in the velocity distribution in the magnetosheath merging,accompanied by ion heating.For cases with a relatively wide initial TD,a dominant single X-line appears in the subsolar magnetosheath after the transmitted TD is narrowed.A shock analysis is performed for the detailed structure of magnetic reconnection in the magnetosheath.Rotational Discontinuity(RD)/TimeDependent Intermediate Shock(TDIS)are found to dominate the reconnection layer,which and some weak slow shocks are responsible for the ion heating and acceleration.
文摘针对高速电机和飞轮储能系统等对空间利用率要求较高的场合,提出一种新型异极径向混合磁轴承(heteropolar radial hybrid magnetic bearing,HRHMB).首先,建立该磁轴承的等效磁路模型,通过解析磁场得出其电流刚度、位移刚度及电磁力,并通过有限元仿真验证其有效性;然后,在相同约束条件下与传统偏置磁轴承进行对比,分析磁轴承的刚度特性和空间利用率;最后,通过有限元仿真研究新型磁轴承径向两自由度间的电磁力耦合,并与传统磁轴承进行对比.研究结果表明:在相同承载力等约束条件下,该新型磁轴承的体积仅为传统磁轴承的0.87倍,其电磁力在控制电流和转子位移影响下的相对误差值为6.5%,而传统磁轴承的电磁力相对误差为13.6%,表明新型磁轴承径向两自由度的电磁力耦合小于传统磁轴承,解耦效果良好.
