truss damping

[lolitapr]

Dear all,

Im trying to model a spring element and viscous element. I tried to implement two truss elements. One with elastic material and the other with viscous material. When I tried to compared the results with K*u for the elastic and C*Veloc for the viscous I get exact results for the elastic but smaller results for the viscous.

Then I tried to model only the elastic truss and include Rayleigh damping with the following script:

set xDamp 0.02
set KcurrSwitch 0 ;
set KcommSwitch 1;
set KinitSwitch 0;

set nEigenI 1; # mode 1
set lambdaN [eigen [expr $nEigenI]]; # eigenvalue analysis for nEigenJ modes
set lambdaI [lindex $lambdaN [expr $nEigenI-1]]; # eigenvalue mode i
puts "$lambdaN $lambdaI"

set omegaI [expr pow($lambdaI,0.5)];
set alphaM 0; # M-prop. damping; D = alphaM*M
set betaKcurr [expr $KcurrSwitch*2.*$xDamp/($omegaI)]; # K-proportional damping; +beatKcurr*KCurrent
set betaKcomm [expr $KcommSwitch*2.*$xDamp/($omegaI)]; # K-prop. damping parameter; +betaKcomm*KlastCommitt
set betaKinit [expr $KinitSwitch*2.*$xDamp/($omegaI)]; # initial-stiffness proportional damping +beatKinit*Kini

Then when I compared the results I get the same as C*veloc if output the Rayleigh forces from the element source code. But I have done some reading and there is not suppose, by default of the truss element, to be Rayleigh forces included (as I read on the Community posts).

Thanks for your help on this matter,
M.C.