The Pre-Test Calculator employs the Driving-Point Frequency Response Function (DPFRF) method to identify the optimum location to place exciters. The method is based on the assumption that the optimum location of exciters is the one that ensures higher peaks in its Driving Point FRF, and it therefore enhances the resonance of the structure.
The algorithm has the following parameters:
SN={xn}N – Set of candidate nodes (the total number of candidate nodes after filtering).
{Φi} – Set of modes considered in the analysis. Only the modes that are checked in the Frequency Worksheet inside the Pre-Test Worksheet are employed.
NE – Maximum number of exciters.
For each node in SN, the method consists of computing the peaks of the Accelerance DPFRF in the local Z direction. That is, to project the displacement degree of freedom in the Z direction determined by the local coordinate system at the candidate node and to compute its Accelerance DPFRF. This FRF is computed with the same methodology described in FRF Calculation Method.
Particularizing for the case of real mode shapes with equal input and output DOFs, and taking into account that the peaks of the Accelerance DPFRF are approximately located at the modal frequencies, the peaks of the DPFRF for each node n are:
The modal damping ratio that is assumed for all modes is 2%.
Once all peaks are computed (for each candidate sensor, a peak is computed per normal mode
), a metric is computed for each candidate node. This metric consists of
calculating the maximum of the DPFRF peaks. This is an indicator of the maximum strength of
the response:
Finally, the candidate nodes are sorted according to this metric and the first NE nodes are considered the best exciters.