The RSYS command seems to have no effect on the older element
formulations in a large deformation (NLGEOM,ON) analysis. Why?
This behavior is documented in Section 5.5.1 "Rotating Results to a Different Coordinate System" in the ANSYS 8.1 Basic Analysis Procedures Guide with the following note: Note In a large deformation analysis (for example, if you have issued the NLGEOM ,ON command and the element has large deflection capability), the element coordinate system is first rotated by the amount of rigid body rotation of the element. Therefore the component stresses and strains and other derived element data include the effect of the rigid body rotation. The coordinate system used to display these results is the specified results coordinate system rotated by the amount of rigid body rotation. The exceptions to this are HYPER56, HYPER58, HYPER74, HYPER84, HYPER86, and HYPER158. These elements always produce stresses and strains in the specified results coordinate system (no rigid body rotation added). This is also true for elements that contain hyperelastic material properties (TB,HYPER), such as, SHELL181, PLANE182, PLANE183, SOLID185, SOLID186, SOLID187, SHELL208, and SHELL209. For these elements, when a hyperelastic material component is defined, the element component result is always in the initial global coordinate system, regardless of the coordinate system specified. For other (non-hyperelastic) material properties, the output of the element component results is in the initial global coordinate system (This is the default.). All component result transformations to other coordinate systems will be relative to the initial global system. The primary data (for example, displacements) in a large deformation analysis do not include the rigid body rotation effect, because the nodal coordinate systems are not rotated by the amount of rigid body rotation. The note above is best explained by an example. The ANSYS 8.1 input below compares the old generation elements (SOLID45 and SHELL43) to the new generation elements (SOLID185 and SHELL181) for large deformation (NLGEOM,ON) analyses. For RSYS,SOLU, both the old and new generation elements give the stress and strain results in terms of the updated, local element coordinate system, as one would expect. However, the element behavior is different for RSYS,0. For the old generation elements, the global Cartesian coordinate system rotates (rigid body motion) along with the element, such that the results are NOT in terms of the original global Cartesian system, but rather a "new" global Cartesian system. If ESYS is not used for these old elements, RSYS,0 and RSYS,SOLU will give the same results, so there is no point to even requesting RSYS,0 results. Conversely, the new generation elements are superior in that they give RSYS,0 results in terms of the ORIGINAL global Cartesian coordinate system, not some rotated system. Incidentally, if NLGEOM,ON is NOT used, the old and new elements behave the same for RSYS,0 results, since there is no update of the global Cartesian coordinate system. The differences are only for large deformation analyses. fini /clear /eshape,1 /view,,1,2,3 /plopts,info,1 /title, RSYS,0 Stress Results with NLGEOM,ON /prep7 et,1,SOLID45 r,1 et,2,SOLID185,,2 ! enhanced strain formulation r,2 et,3,SHELL43 r,3,0.1 et,4,SHELL181 r,4,0.1 mp,ex,1,30.0e6 mp,nuxy,1,0.30 mp,dens,1,0.00074 tb,biso,1 tbdata,1,60.0e3 tbdata,2,30.0e4 mat,1 esize,0.5 /dev,vect,1 /psym,esys,1 block,0,1,0,20,-0.05,0.05 type,1 real,1 lsel,u,loc,y,1,19 lesize,all,,,2 vmesh,1 ! 1st structure = SOLID45 (old generation brick) block,2,3,0,20,-0.05,0.05 type,2 real,2 lsel,u,loc,y,1,19 lesize,all,,,2 vmesh,2 ! 2nd structure = SOLID185 (new generation brick) rect,4,5,0,20 type,3 real,3 amesh,13 ! 3rd structure = SHELL43 (old generation shell) rect,6,7,0,20 type,4 real,4 amesh,14 ! 4th structure = SHELL181 (new generation shell) lsel,all eplot fini /solu antype,static nlgeom,on nsubst,10,1000,10 outres,all,all nsel,s,loc,y,0.0 d,all,all,0.0 nsel,all acel,0.0,0.0,386.4e2 ! 100 g load ... eplot solve save fini /post1 set,last /edge,,1 /dscale,,1 /dev,vect,0 plnsol,u,sum,2 rsys,0 nsel,s,loc,y,0.0,3.0 nsel,r,loc,z,0.0,0.1 ! top layer of brick elements ... esln,s,1 /graph,full ! PowerGraphics does not support RSYS=SOLU shell,top ! since PowerGraphics is not being used ... /show,png rsys,0 /title, RSYS=0 SY results plnsol,s,y rsys,solu /title, RSYS=SOLU SY results plnsol,s,y rsys,0 /title, RSYS=0 SZ results plnsol,s,z rsys,solu /title, RSYS=SOLU SZ results plnsol,s,z /show,close /eof . |
||
|