Mechanical APDL Structural Analysis Guide

EXPASS,ON! Expansion pass

EXPSOL,...! Expand a single solution

HREXP,...! Phase angle for expanded solution

SOLVE

FINISH

! Review the Results of the Expanded Solution

/POST1

SET,...! Read results for desired frequency

PLDISP,...! Deformed shape

PLNSOL,...! Contour plot of nodal results

---

FINISH

See the Command Reference for a discussion of the ANTYPE,MODOPT,HROPT,HROUT,LVSCALE,F,
HARFRQ,DMPRAT,DMPSTR,MDAMP,NSUBST,KBC,FILE,NSOL,PLCPLX,PLVAR,EXPASS,EXPSOL,
HREXP,SET, and PLNSOL commands.

4.9. Additional Harmonic Analysis Details

4.9.1. Prestressed Harmonic Analysis

A prestressed harmonic analysis calculates the dynamic response of a prestressed structure, such as a
violin string. The prestress influences the stiffness of the structure through the stress-stiffening (or
possibly a nonlinear tangent) matrix contribution. Response to harmonically varying loads is computed
using this effective stiffness of the structure. The output stresses, therefore, will reflect the prestress
effect on the structure.

The linear perturbation full harmonic procedure is the preferred method for performing a prestressed
harmonic analysis. Because the linear perturbation analysis accommodates both linearly and nonlinearly
prestressed cases, the prestressed effects of the structure from the previous linear or nonlinear, static
or full transient analysis are included. For more information, see Full Harmonic Analysis Based on Linear
Perturbation in the Mechanical APDL Theory Reference.

As alternatives to the linear perturbation full harmonic procedure, several other procedures for performing
a prestressed harmonic analysis are described below.

4.9.1.1. Prestressed Full Harmonic Analysis

The procedure described here for doing a prestressed full harmonic analysis is essentially the same as
that for any other full harmonic analysis except that you first need to prestress the structure by doing
a static analysis:

1. Build the model and obtain a static solution with prestress effects turned on (PSTRES,ON). The pro-
   cedure to obtain the static solution is explained in Structural Static Analysis (p. 9).


2. Reenter SOLUTION and obtain the full harmonic solution, also with prestress effects turned on (reissue
   PSTRES,ON). Files Jobname.EMAT and Jobname.ESAV from the static analysis must be available.
   Hence, if another analysis is performed between the static and prestressed harmonic analyses, the
   static analysis will need to be rerun.

Because only linear behavior is valid in a harmonic analysis, nonlinear elements (if any) will be

treated as linear elements. If you include contact elements, for example, their stiffnesses are

calculated based on their initial status and are never changed. For a prestressed harmonic

analysis, the program assumes that the initial status of the contact elements is the status at the

completion of the static prestress analysis. (Note that the linear perturbation full harmonic

Release 15.0 - © SAS IP, Inc. All rights reserved. - Contains proprietary and confidential information

Harmonic Analysis