Deals with requesting Modal Participation for a Modal Frequency Response analysis using
OptiStruct.
Modal Participation represents the complex contribution of a structure or a fluid mode to a
response at a particular frequency. Modal Participation is useful to diagnose low frequency
NVH problems, when the modes are well separated, that is, the modal density is low.Figure 1. Simplified Vehicle Model
Model Files
Before you begin, copy the file(s) used in this example to
your working directory.
The model used is a simplified car model with an acoustic cavity as shown in Figure 1. The model is already setup for a modal frequency
response run. The response point for Modal Participation is the node which approximates the
location of the Driver Ear in the acoustic cavity. The source of excitation is a unit load
in the Global Z direction at the Engine Block. When diagnosing NVH problems, user is
interested in peaks which in magnitude are above a certain pre-defined target level. So
instead of outputting Modal Participation at all solution frequencies, it is much more
efficient to request for data at frequencies for which the peak magnitudes violate
pre-defined NVH targets. This is accomplished by using PFMODE (output
request for Modal Participation) with PEAKOUT (request output data for
‘n’ number of peaks, where ‘n’ can be changed by you).
FE Model
Element Types
CHEXA
CPENTA
CTETRA
CQUAD4
CTRIA3
CBUSH
CBAR
RBE2
The linear material properties are:
MAT1
For Steel
For Glass
For Seats
MAT10
For Acoustic Cavity
Results
The Modal/Panel Participation utility in HyperView is used to
post-process the results. You can choose the frequency at which the NVH issue is happening
and look at the Structure/Fluid modes contributing the most to it.Figure 2. Top Contributors at a Particular Frequency in Bar Plot
Format