frequencies. If you specify more than one form of damping, Mechanical APDL calculates an effective
damping ratio at each frequency.
Note
If no damping is specified in a PSD analysis, a default DMPRAT of 1 percent is used.
Note
Material-dependent damping ratio [MP,DMPR] is also available but only if specified in
the modal analysis where an effective damping ratio is calculated based on the elements’
strain energies.
- Alpha (Mass) Damping
Command(s):ALPHAD
GUI: Main Menu> Solution> Load Step Opts> Time/Frequenc> Damping
- Beta (Stiffness) Damping
Command(s):BETAD
GUI: Main Menu> Solution> Load Step Opts> Time/Frequenc> Damping
- Constant Damping Ratio
Command(s):DMPRAT
GUI: Main Menu> Solution> Load Step Opts> Time/Frequenc> Damping
- Frequency-Dependent Damping Ratio
Command(s):MDAMP
GUI: Main Menu> Solution> Load Step Opts> Time/Frequenc> Damping
- Residual Vector [RESVEC]
The residual vectors reduce the error caused when the higher modes are neglected in the analysis.
The remaining steps are specific to a random vibration analysis:
- Apply the PSD excitation.
- For base excitation, use the UX,UY,UZ labels and the ROTX,ROTY,ROTZ labels on the D (or DK, or
DL, or DA) command. A value of 0.0 (or blank) can be used to remove a specification. Values other
than 1.0 scale the participation factors.
- For uniform base motion using the SED command, specify SEDX,SEDY, or SEDZ. A value of 0.0 (or
blank) removes a specification.
- For nodal excitation, use the FX,FY,FZ labels on the F (or FK) command. A value of 0.0 (or blank)
can be used to remove a specification. Values other than 1.0 scale the participation factors.
Release 15.0 - © SAS IP, Inc. All rights reserved. - Contains proprietary and confidential information
Performing a Random Vibration (PSD) Analysis
