{"id":360083,"date":"2024-04-02T16:09:03","date_gmt":"2024-04-02T16:09:03","guid":{"rendered":"\/forum\/forums\/reply\/360083\/"},"modified":"2024-04-02T16:09:03","modified_gmt":"2024-04-02T16:09:03","slug":"360083","status":"publish","type":"reply","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/reply\/360083\/","title":{"rendered":"Reply To: Negative stiffness in x-position between PM and steel stator"},"content":{"rendered":"

<p>I’m not sure this is exactly what you’re asking for, but I found this old MAPDL input file that uses two spring elements (COMBIN14 and COMBIN39) to posit nonlinear negative stiffness between two nodes (to mimic net magnetic force versus separation):<\/p><div>fini<\/div><div>\/cle<\/div><div> <\/div><div>\/sys,del test_neg_K_05*.png<\/div><div>\/fil,test_neg_K_05<\/div><div> <\/div><div>\/pnu,node,1<\/div><div>\/pnu,type,1<\/div><div>\/tri,lbot<\/div><div>\/esha,1<\/div><div>\/ics,1,5<\/div><div>\/pbc,u,1<\/div><div> <\/div><div> <\/div><div>C***********************************<\/div><div>C*** MODEL<\/div><div>C***********************************<\/div><div>\/prep7<\/div><div> <\/div><div>n,1,,1 ! NODES<\/div><div>n,2<\/div><div>n,3,,2<\/div><div> <\/div><div>et,1,39,0,0,2 ! NONLINEAR SPRING (COMBIN39) ATTRIBUTES<\/div><div>r,1, -0.5,10-1.25, -0.4,5-1.25, -0.3,3-1.25<\/div><div>rmore, -0.2,2-1.25, -0.1,1.5-1.25, 0,1.25-1.25<\/div><div>rmore,  0.1,1.10-1.25, 0.2,1.05-1.25, 0.3,1.03-1.25<\/div><div>rmore,  0.4,1.02-1.25, 0.5,1.015-1.25<\/div><div> <\/div><div>et,2,14,,,2 ! LINEAR SPRING (COMBIN14) ATTRIBUTES<\/div><div>r,2,1.25\/50<\/div><div> <\/div><div>type,1 ! SINGLE NONLINEAR COMBIN39 ELEMENT<\/div><div>real,1<\/div><div>e,2,1<\/div><div> <\/div><div>type,2 ! SINGLE LINEAR COMBIN14 ELEMENT<\/div><div>real,2<\/div><div>e,3,2<\/div><div> <\/div><div>d,1,uy ! BOUNDARY CONDITIONS<\/div><div>d,3,uy,50<\/div><div> <\/div><div> <\/div><div>fini<\/div><div> <\/div><div>\/solu ! SOLVE<\/div><div>auto,off<\/div><div>outr,all,all<\/div><div> <\/div><div>nsub,1<\/div><div>d,2,uy,-0.5<\/div><div>solv<\/div><div> <\/div><div>nsub,10<\/div><div>d,2,uy,0.5<\/div><div>solv<\/div><div>fini<\/div><div> <\/div><div>eplo<\/div><div>\/sho,png $eplo $\/sho,close $\/wait,2<\/div><div> <\/div><div>\/post26 ! VERIFY FORCE-DEFLECTION<\/div><div>nsol,2,2,uy<\/div><div>xvar,2<\/div><div>rfor,3,2,fy<\/div><div>\/axl,x,Node 2 UY Displacement<\/div><div>\/axl,y,Reaction Force @ Node 2<\/div><div>!\/yra,0,10<\/div><div>plva,3<\/div><div>\/sho,png $plva,3 $\/sho,close $\/wait,2<\/div><p>Note that as node 2 at the bottom of the two element model is moved upward, the reaction force becomes increasingly negative (the springs are pulling upward on node 2 with increasing force as node 2 gets closer to node 3).<\/p><p><\/p><p><\/p><p> <\/p><p>In Mechanical, you would have to include commands like these in a command object, maybe written in such a way that the springs are attached to remote point nodes scoped to surfaces.<\/p><p> <\/p><p>–Bill<\/p><\/p>\n","protected":false},"template":"","class_list":["post-360083","reply","type-reply","status-publish","hentry"],"aioseo_notices":[],"acf":[],"_links":{"self":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/replies\/360083","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/replies"}],"about":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/types\/reply"}],"version-history":[{"count":0,"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/replies\/360083\/revisions"}],"wp:attachment":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/media?parent=360083"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}