summary_coherence


Purpose

Calculates the weighted coherence for a given set of FRF and Coherence

Syntax

c = summary_coherence(f)
c = summary_coherence(f,freq_range,dof,'dof','freq','both','all','use_frf','silent')

Description

Summary coherence is used to assess overall frequency response function quality for a given set of response degrees of freedom over a specified frequency range.

F is an imat_fn containing FRF or Autospectra, and Coherence.

FREQ_RANGE is a 1x2 vector containing the frequency range of interest. If not supplied, SUMMARY_COHERENCE will use the entire frequency range.

DOF is an imat_ctrace containing a list of response degrees of freedom to be used. If not supplied, SUMMARY_COHERENCE will use all of the DOF in the coherence functions.

Passing in the string 'silent' suppresses output.

The following strings select the various summary coherence summation options:

'freq' Summary coherence for each test DOF over a range of frequencies. Gives an indication of sensor quality.
'dof' Summary coherence for each frequency over a set of test DOF. Gives an indication of overall FRF quality as a function of frequency.
'both' Summary coherence over a set of test DOF and over a set of frequencies gives a scalar value that can be used to assess overall test quality.
'all' Select all of the above options.

 

The optional input string causes SUMMARY_COHERENCE to estimate response DOF autospectra by assuming white noise input. If not supplied, SUMMARY_COHERENCE will use the response DOF Autospectra directly.

C is a structure containing the summary coherence output. It contains the following fields:

.matrix Coherence matrix (MxN) where M is number of frequencies and N is number of DOF.
.coherence imat_fn containing coherence functions.
.freq Vector of evaluation frequencies.
.dof imat_ctrace containing DOF evaluated.
.summary_freq 'freq' option only. Vector of length N containing summed coherences. Values are also stored in column N+1 of .matrix.
.summary_dof 'dof' option only. imat_fn containing summed coherences. Values are also stored in row M+1 of .matrix.
.summary_both 'both' option only. Scalar summed coherences. Value is also stored in location M+1,N+1 of .matrix.

 

Reference

Kevin L. Napolitano, Nathaniel C. Yoder, Ralph D. Brillhart, "A Comparison Of Multiple Impact Testing Methods", IMAC, 2012.

Examples

>> c = summary_coherence(f);

>> c = summary_coherence(f,[100 500],'all');

>> c = summary_coherence(f,ct,'freq','dof','silent','use_frf');