how Rayleigh Damping Command consider damping ratio for structural modes?

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eftekhar
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Joined: Fri Apr 30, 2021 6:08 am

how Rayleigh Damping Command consider damping ratio for structural modes?

Post by eftekhar » Fri Oct 01, 2021 3:00 pm

Hi
I had a questiones about the operation of the Riley damping command in Opensees.
First, how does the Rayleigh Damping Command affect the damping in any structural mode?
Second, can the Rayleigh Damping Command be set to affect only certain modes of the structure?
Any help is greatly appreciated
I wish you all the best

fmk
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Location: UC Berkeley
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Re: how Rayleigh Damping Command consider damping ratio for structural modes?

Post by fmk » Mon Nov 01, 2021 10:16 pm

1. I suggest you refer to a text book or google "rayleigh damping":

https://www.orcina.com/webhelp/OrcaFlex ... idance.htm
https://www.usbr.gov/ssle/damsafety/Tec ... -07-03.pdf

2. It cannot, from reading the text book or above links you should understand why.

eftekhar
Posts: 13
Joined: Fri Apr 30, 2021 6:08 am

Re: how Rayleigh Damping Command consider damping ratio for structural modes?

Post by eftekhar » Sun Dec 05, 2021 2:35 pm

thank you so much i found a code for rayleigh damping in tcl editor,

"
set xDamp 0.02; # 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 1; # 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

"
is this right?
if yes, why cant i set I & J based on number of modes i want to consider them for damping?

mhscott
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Location: Corvallis, Oregon USA
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Re: how Rayleigh Damping Command consider damping ratio for structural modes?

Post by mhscott » Mon Dec 06, 2021 7:56 am

You need to give a number of modes to the eigen command. You are passing nEigenJ, which is 1, so you only get one mode.

eftekhar
Posts: 13
Joined: Fri Apr 30, 2021 6:08 am

Re: how Rayleigh Damping Command consider damping ratio for structural modes?

Post by eftekhar » Mon Dec 06, 2021 3:27 pm

deer prof scott i did that in my code but when i ran the model i face this error

"
ArpackSolver::Error with _saupd info = -9999
Could not build an Arnoldi factorization.IPARAM(5) the size of the current Arnoldi factorization: is 3factorization. The user is advised to check thatenough workspace and array storage has been allocated.
WARNING StaticAnalysis::eigen() - EigenSOE failed in solve()
missing function argument at _@_
in expression "pow(_@_,0.5)"
(parsing expression "pow(,0.5)")
invoked from within
"expr pow($lambdaI,0.5)"
invoked from within
"set omegaI [expr pow($lambdaI,0.5)]"
(file "analysis.tcl" line 14)
invoked from within
"source analysis.tcl "
(file "D:\desktop n\01.Master\uni Ms\governingequationone\coding\one story assymetry structure\0.5 s period\model 0.5-0.5-0.1\own model\main.tcl" line 8)

"
thank you truly for heloing me.

mhscott
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Joined: Tue Jul 06, 2004 3:38 pm
Location: Corvallis, Oregon USA
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Re: how Rayleigh Damping Command consider damping ratio for structural modes?

Post by mhscott » Tue Dec 07, 2021 5:55 am

The default eigenvalue solver doesn't always work when you ask for number of modes that is close to the number of dynamic DOFs in your model.

You can try using the fullGenLapack option

eigen fullGenLapack $Nmodes

eftekhar
Posts: 13
Joined: Fri Apr 30, 2021 6:08 am

Re: how Rayleigh Damping Command consider damping ratio for structural modes?

Post by eftekhar » Tue Dec 07, 2021 8:02 am

thanks fmk and prof scott

i Awared that we can only use two modes parameters for Rayleigh Damping because of it's coding on opensees and also because of it's definition.

wish you best.

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