The Mechanical Behavior Analysis For An Electromagnetic Launcher

The electromagnetic launcher can be used in many areas such as aerospace,transportation,scientific research and national defense and military,because it can realize the instantaneous high-power conversion of electromagnetic energy into kinetic energy.Compared with the traditional launch technologies,the electromagnetic launcher has many advantages such as clean,high efficiency,sustainable,pollution-free and ultra-high speed due to the use of electromagnetic energy,while in the meantime,because of the extremely-strong electromagnetic environment during launch process,the launcher will experience the unprecedented mechanic problems of the structural response and the strong coupling of electric-magnetic-thermal-mechanical Multiphysics.The mechanic problems govern the life and accuracy of the launcher,but the current research and design of the electromagnetic launcher are mostly focused on the electromagnetic field,and lack the consideration of the mechanical characteristics for the electromagnetic launcher.In order to understand deeply the mechanical characteristics of an electromagnetic launcher and to facilitate the design of the launcher with excellent performance,this dissertation adopts the research paradigm of the practical engineering problem—the mechanical model—the mathematical model—the computational solution—discipline and scheme in applied mechanics,to conduct the comprehensive research on the mechanical behavior of electromagnetic launcher.For the mechanics problems of the electromagnetic launcher,the interaction between structural components is not considered in the dynamic characteristics problem of the structural components,the mechanical behavior is not considered or not in-depth considered in the multi-physics coupling problem,and the boundary conditions of the sliding-contact lubrication model of launcher are not suitable.This dissertation carries out detailed research on modeling motion of structural components in mutual influence,modeling multi-field coupling response as well as modeling multi-field of the lubricating fluid layer in contact interface,to establish a multi-level mechanical model framework for describing the electromagnetic launcher.The model of structural components motion in mutual influence is mainly based on the rigid body kinematics,solid linear elastic theory and Euler-Bernoulli beam theory.The model is validated by comparing with theoretical and experimental data.It can show the basic motion characteristics of structural components such as the armature,rail and barrel,and describe the dynamic laws of structural components in mutual influence.The model is innovative by considering the dynamic characteristics of the armature-rail-barrel structure in mutual influence and the closer-reality distribution of rail current due to the skin effect,as well as the non-linearity effect of rail vibration on the electromagnetic moving load amplitude.The model analysis shows that the rail vibration has an impact on the armature exit-speed and the barrel end-displacement.In order to reduce the influence of the rail vibration,the insulator material with appropriate stiffness can be selected,or a smallestmuzzle-displacement barrel can be designed according to the armature mass,stiffness and distance attributes of the barrel containment structure.The multi-field coupling response model takes into account the discontinuity of interfacial magnetic field and temperature,as well as the contact problem under the relative high-speed sliding of the armature-rail,to establishes the solution method different from normal contact problem for the jumping boundary of the magnetic field,temperature field and the displacement contact boundary in extremely high-speed contact interface,so that the definite solution problem for the electromagnetic field,temperature field,and elastic stress field are formulated under high-speed sliding.The jumping boundary of magnetic field is different from that the normal component of the magnetic induction intensity for the general contact medium is continuous at the interface,and the normal component of the magnetic induction intensity will interrelate the conductivity properties of the specific contact material;The jumping boundary of temperature field should consider the non-ideal contact resistance heat and the high-speed friction heat;The displacement contact boundary will involve nonintrusion of mutually contacting bodies.The model analysis shows that the electromagnetic rail launcher has the extraordinary magnetic and thermal environmental conditions,which causes the initial parts of the launch rail to be damaged easily,and the von mises stress in the corresponding position exceeds the yield limit of the material.The rail damage can be reduced by using a larger rail size.The multi-field model for the lubricating liquid layer in contact interface abandons the unrealistic assumption that the temperatures at the armature contact interface,the liquid layer and the rail contact interface are the same in previous research,and the temperature with different distribution conditions at the armature-rail interface during high-speed sliding are specifically considered.By using the custom finite element codes developed for the electricmagnetic-thermal-mechanical-flow multi-field coupling computation,the quantitative characteristics of the multi-field liquid layer and the lubrication behavior at different layer thicknesses can be analyzed,and the positive effect of lubricant layer on reducing the structure thermal damage can be shown.The model analysis shows that the predicted temperature of the liquid layer will decreases about a half when the temperature with different distribution conditions at the armature-rail interface during high-speed sliding are considered,so that the temperature at the armature contact interface can be reduced by more than 48%,and the temperature inside the armature can be reduced by 25%.The mechanical model framework for the electromagnetic rail launcher developed in this dissertation realize the quantitative simulation and analysis of the structure and multi-field characteristics.The meaningful results obtained lay the foundation for the in-depth research of the mechanical theory for the electromagnetic launcher,and provide the necessary theoretical value for the engineering design in the launcher.