RBE3 - Part 2

RBE3 works by creating CEs (constraint equations) to distribute force and moment. As John Swanson tells, the RBE3 command in ANSYS was added to duplicate the same command in NASTRAN.

Let's consider an example which demonstrates applying a torque load to the inside of the cylinder:


! internal radius
RAD1=0.8
! external radius
RAD2=1.0
! number of nodes
N=40
! moment applied
MOMENT=1000.0
! nodal force calculated
! this force is distributed to each slave node of RBE3 structure
FORCE=MOMENT/(N*RAD1)


Now we should generate geometry of the problem, and generate FE mesh


/PREP7
! select proper element types
ET,1,PLANE42
ET,2,MASS21
! set mass in X direction for MASS21
R,2,1.0
! Elastic modulus = 10000
MP,EX,1,1E4
! create geometry
CYL4,,,RAD1,,RAD2
LESIZE,ALL,,,N/4
! select PLANE42 for cylinder meshing and mesh
TYPE,1
AMESH,ALL
! create master node in the center of the cylinder
N,100,0,0,0
! set point mass onto this node
TYPE,2
REAL,2
E,100
! select cylindrical CS for operations
CSYS,1
! select internal nodes
NSEL,,LOC,X,RAD1
! link central master node with slave nodes
! on the internal surface of the cylinder
RBE3,100,ROTZ,ALL
! let's show generated CEs
CELIST
FINISH


We should get the following result:



Now apply boundary conditions and solve


/SOLUTION
! constraint nodes on the external surface
! disable radial movement and circular rotation
NSEL,,LOC,X,RAD2
D,ALL,,0.0,,,,UX,UY
NSEL,ALL
! constraint central (master) node
! disable all DOFs except ROTZ
D,100,,0.0,,,,UX,UY,UZ,ROTX,ROTY
! apply MZ moment
F,100,MZ,MOMENT
! and solve
SOLVE
FINISH


Now postprocess results:


/POST1
! show results in cylindrical CS
RSYS,1
! consider only internal nodes
NSEL,,LOC,X,RAD1
! It is emphasized that FY is equal to FORCE parameter
! This shows us how RBE3 distributes moment
PRNLD,FY


We should get the following picture:




! now let's consider again all nodes
NSEL,ALL
! plot circumferential displacement (theta)
! as expected, maximum in on the internal surface nodes
PLNS,U,Y


We should get the following:



THE END!