SIMULATIONOFDYNAMIC ARMATURE MOTION INA RAILGUNWITH COUPLINGOFELECTROMAGNETIC, THERMAL AND STRUCTURAL EFFECTSUSINGSHIFTEDFINITEELEMENT FIELDS+

physics viaa relatively straightforward Fortran-like scripting language. A movingarmature railgun code(called HERB)has beendeveloped forcoupled electromagnetic, thermal and I.BACKGROUND structural fields using thegeneral purpose codeANSYS astheunderlying computational engine. ThisanalysisTherailgun problem isaninherently 3-dimensional usesshifted electromagnetic fields tosimulate thevelocity (3D)dynamic problem requiring notonlya detailed effects associated withsuchmotion(akin toEMAP3D electromagnetic analysis todetermine thearmature and [1]). Specifically, thevelocity effects areproduced bythe rail dynamics butalso simultaneous thermal andstructural shift ofthemagnetic vector andscalar potential fields, the analyses thatinturncansignificantly modifythe temperature andstructural fields, andtherespective electromagnetic problem ontimescales muchless than element material attributes. Thecylindrical symmetry of theprojectile rail transit time. Thethermal andstructural themodelallows ustoemploy 3Dfinite element bricks. aspects becomeevenmoreimportant attheweaponlevel Thesehaveanadvantage overtetrahedral elements by currents (multi-mega-amperes) presently envisioned. allowing veryhigh aspect ratios tomodellonger stretches Thus, anyrealistic analysis requires afully self-consistent oftheproblem notintheimmediate vicinity ofthe treatment ofall three physics regimes. armature ortheendoftherails, withaminimal number of Prior tothedevelopment ofHERB,theonlyother elements, thereby reducing boththemodelsize andthe meanstodosuchanalyses laywiththeEMAP3Dcode required computational time.Thearmature motion is developed attheUniversity ofTexas, Austin atthe calculated self-consistently fromtheelectromagnetic Institute forAdvanced Technology (IAT). forces on thearmature; however, thearmatureis An impetus forthedevelopment ofsuchacapability stationary. Instead theelectromagnetic, thermal and wasthatmuchofthepotentially interesting dynamic structural degrees offreedom, aswellastheelementfeatures, suchasarmature melting anddeformation, are material attributes ofthenon-armature components ofthe beyondthepresent capabilities ofexperiment tostudy modelareshifted tosimulate themotion. Itisthese otherduring arailgun shot. Codesimulations incontrast have non-armature components that movebutinthedirection thepotential togain this sorely needed insight and, infact, opposite totheactual armature motion. Themethod has represent essentially theonly meansavailable atpresent. beenverified forelectromagnetic velocity effects using several simple modified textbook cases ofclosed wire