Mechanical APDL Structural Analysis Guide

!

! Non-linear prestress static analysis

!

antype,static

nlgeom,on! include large-deflection effects (optional)

nropt,unsym! unsymmetric stiffness matrix

rescontrol,define! specify restart files for multifrome restart

solve

finish

!

/solu

antype,static,restart,,,perturb! restart from last load steop and substep

! of previous static solution to perform

! perturbation analysis

perturb,modal! perform perturbed modal analysis

!

! Pseudo rotation of disc and contact elements

! (this step generates the unsymmetric [K] in contact elements)

!

! Create an element component (for example, BrakeCM) consisting of brake

! rotor and contact/target element.

!

cmrotate,BrakeCM,ROTATX,ROTATY,ROTATZ

solve,elform! regenerate the element matrices

!

! Use QR damped or UNSYM eigensolver

!

qrdopt,on! Generate Jobname.MODESYM

modopt,qrdamp,...! (or) modopt,unsym

mxpand,...

solve

finish

!

/clear,nostart

!

/solu

antype,static,restart,,,perturb! restart from last load step and substep

! of previous static solution to perform perperbuation analysis

mp,mu,cid,0.3! Change coefficient of friction

perturb,modal! perform perturbed modal solve

solve,elform! regenerate element matrices

!

! Use QR damped or UNSYM eigensolver

!

qrdopt,on! Reuse Jobname.MODESYM

modopt,qrdamp

mxpand,...

solve

finish

For further information, see Linear Perturbation Analysis (p. 287).

3.7.3.3. Linear Non-prestressed Modal Analysis

The full nonlinear perturbed modal analysis method described above requires a nonlinear static stress
analysis. If large-deflection or stress-stiffening effects are not critical, you can use the linear non-
prestressed modal analysis method instead. This method involves a single linear QR damped or unsym-
metric eigensolution. Since it is a linear analysis, this method is less time consuming. The following
steps are required:

1. Perform a QR damped (QRDAMP) or unsymmetric (UNSYM) modal analysis using the linear modal analysis
   procedure:
   
   
   • Use the unsymmetric stiffness matrix option (NROPT,UNSYM) to generat e the unsymmetric stiffness
     matrix. (No Newton-Raphson iterations are performed.)
   
   
   
   

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Modal Analysis Examples