- Generate frictional sliding force via the CMROTATE command. The contact stiffness matrix is based
only on the initial contact status. - Specify the QR damped or unsymmetric mode extraction method (MODOPT,QRDAMP or UNSYM).
- If you are planning to perform multiple solutions and want to reuse the Block Lanczos eigensolution
from the previous load steps, issue QRDOPT,ON (QRDAMP only). - Issue the SOLVE command.
- To perform friction sensitivity studies by reusing the normal modes from the Block Lanczos solution
(QRDAMP only), just change the friction coefficients and issue the SOLVE command.
- Expand the modes and postprocess the results from Jobname.RST.
The following example illustrat es the linear non-prestressed modal analysis method for brake squeal
analysis:
/prep7
!
! Create the brake model
!
finish
!
/solu
!
! Perform a linear modal analysis
!
antype,modal
nropt,unsym! unsymmetric stiffness matrix
!
! Create an element component (for example, BrakeCM) consisting of brake
! rotor and contact/target elements.
!
cmrotate,BrakeCM,ROTATX,ROTATY,ROTATZ
!
! Use QR damped or UNSYM eigensolver
!
qrdopt,on! Generate Jobname.MODESYM
modopt,qrdamp,...! (or) modopt,unsym
mxpand,...
solve
!
mp,mu,cid,0.3! Change freiction coefficient
solve
finish3.7.4. Reuse of Jobname.MODESYM in QRDAMP eigensolver
This section describes the reuse of Jobname.MODESYM in QRDAMP eigensolver. Reuse is activated by
the reuse flag (ReuseKey) in the QRDOPT command. A typical example of the reuse of Jobname.MOD-
ESYM would be for determining instability predictions in brake squeal analysis (Brake Squeal (Prestressed
Modal) Analysis (p. 53)).
To reuse Jobname.MODESYM in QRDAMP eigensolver, turn on the ReuseKey reuse flag in the QRDOPT
command. The following solution steps occur:
- In the first load step, if Jobname.MODESYM does not exist, the block Lanczos eigensolution is performed
to create the Jobname.MODESYM mode file. This file contains symmetric normal modes of the eigen-
problem, given by:
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