OS-E: 0300 Modal Participation

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, i.e. the modal density is low.

Figure 1. Simplified Vehicle Model

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

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