- Perform a QR damped or unsymmetric modal analysis (second phase of the linear perturbation analysis):
- Specify the QR damped or unsymmetric mode extraction method (MODOPT,QRDAMP or UNSYM).
- Issue the SOLVE command.
The eigensolver uses the unsymmetric stiffness matrix generat ed in the contact elements, and it
may lead to complex eigenfrequencies.- Expand the modes and postprocess the results from the Jobname.RSTP file.
The following example illustrat es the full nonlinear perturbed modal analysis method for brake squeal
analysis:
/prep7
!
! Create the brake model and apply force normal to the contact surface to
! simulate contact pressure between brake pad and disc.
!
!
finish
!
/solu
!
! Non-linear prestress static analysis
!
antype,static
nlgeom,on! include large-deflection effects (optional)
nropt,unsym! unsymmetric stiffness matrix
rescontrol,define! specify restart files needed for multiframe restart
!
! Create an element component (for example, BrakeCM) consisting of brake
! rotor and contact/target element.
solve
!
! Pseudo rotation of disc and contact elements
! (this step generates the unsymmetric [K] in contact elements)
!
cmrotate,BrakeCM,ROTATX,ROTATY,ROTATZ
nsubst,1
solve
finish
!
/solu
antype,static,restart,,,perturb! restart from last load step and substep
! of previous static solution to perform perperbuation analysis
perturb,modal! perform perturbed modal solve
solve,elform! regenerate element matrices
!
! Use QR damped or UNSYM eigensolver
!
modopt,qrdamp
mxpand,...
solve
finish3.7.3.2. Partial Nonlinear Perturbed Modal Analysis
When large deflection and/or stress stiffening effects play an important role in the final eigensolution,
you can perform a partial prestressed modal analysis as described here.
- Perform a static contact analysis to establish contact conditions:
- Activate large deflection effects (NLGEOM,ON); optional.
Release 15.0 - © SAS IP, Inc. All rights reserved. - Contains proprietary and confidential informationModal Analysis Examples