Control damping

[kyungtae79]

Hi, all

I am working on a bridge modeling.

For a 5% damping ratio, I used 'region' command with parameters following.. for all elements.

# RAYLEIGH damping parameters,
# D=$alphaM*M + $betaKcurr*Kcurrent + $betaKcomm*KlastCommit + $beatKinit*$Kinitial
set xDamp 0.05; # damping ratio
set MpropSwitch 1.0;
set KcurrSwitch 0.0;
set KcommSwitch 1.0;
set KinitSwitch 0.0;
set nEigenI 1; # mode 1
set nEigenJ 3; # mode 3
set lambdaN [eigen [expr $nEigenJ]]; # eigenvalue analysis for nEigenJ modes
set lambdaI [lindex $lambdaN [expr $nEigenI-1]]; # eigenvalue mode i
set lambdaJ [lindex $lambdaN [expr $nEigenJ-1]]; # eigenvalue mode j
set omegaI [expr pow($lambdaI,0.5)];
set omegaJ [expr pow($lambdaJ,0.5)];
set alphaM [expr $MpropSwitch*$xDamp*(2*$omegaI*$omegaJ)/($omegaI+$omegaJ)]; # M-prop. damping; D = alphaM*M
set betaKcurr [expr $KcurrSwitch*2.*$xDamp/($omegaI+$omegaJ)]; # current-K; +beatKcurr*KCurrent
set betaKcomm [expr $KcommSwitch*2.*$xDamp/($omegaI+$omegaJ)]; # last-committed K; +betaKcomm*KlastCommitt
set betaKinit [expr $KinitSwitch*2.*$xDamp/($omegaI+$omegaJ)]; # initial-K; +beatKinit*Kini
rayleigh $alphaM $betaKcurr $betaKinit $betaKcomm; # RAYLEIGH damping


However, I would like to assign a different damping ratio, for example, of 2% to some of zerolength elements with keeping the 5% damping for other elements.

For this control, do I need to change only 'set xDamp 0.05' into 'set xDamp 0.02'?
Then, assign new parameters obtained the above into zerolength elements using 'region' command?

Is it a right way?

Otherwise, I will appreciate any suggestion on this work.

All the best,

[fmk]

it is the way to assign different damping factors to different elements .. the properties you calculate are based on the entire system, not individual element contributions .. you cannot say 5% damping for some elements and 2% for others .. the terms you calculate are 5% for the whole system and 2% for the whole system.