Contents
SDOFDEMO
ModalTools script to demonstrate modal parameter estimation using the SDOFLINE command that uses a "line fit" to obtain poles and residues of one or more modes. In this example, a single FRF is curve fitted for several poles and residues, and a synthesized FRF produced and plotted overlaid by the measured.
% Copyright (c) 2003-2006, Axiom EduTech AB, Ljusterö, Sweden. All rights reserved. % URL: http://www.vibratools.com Email: info@vibratools.com
Load Data
load sdof_frf % Contains a driving point FRF
Convert FRF to Mobility
Hv=cvfrfa2v(Data,Xaxis);
Hv=Hv*sign(headrd(Header))*sign(headmd(Header)); % Take care of phase if sensors where pointing various ways.
Select Frequencies to Fit
semilogy(Xaxis,abs(Hv)) xlabel('Frequency, Hz') ylabel('Mobility, (m/s)/N') figtext(30,50,'Select resonance frequencies') figtext(30,30,'Press <RETURN> to continue...') [finit,dummy]=ginput; nfreqlines=5; [poles,residues] = sdofline(Hv,Xaxis,nfreqlines,finit); [fe,ze]=poles2fd(poles); fprintf('\nEstimated resonance freq.: %6.2f Hz, %4.2f%% damping\n',[fe ze]')
Estimated resonance freq.: 28.20 Hz, 2.72% damping Estimated resonance freq.: 40.22 Hz, 0.75% damping Estimated resonance freq.: 75.10 Hz, 0.68% damping Estimated resonance freq.: 83.76 Hz, 0.74% damping Estimated resonance freq.: 94.43 Hz, 1.56% damping Estimated resonance freq.: 99.70 Hz, 0.66% damping
Plot Result
Check results by overlaying measured and synthesized functions. NOTE: This fit does not contain residual terms and can, therefore, be misleading.
cmpplot(Xaxis,Hv,residues,poles,[],1,1);
