No force in ViscousDamper Material

[GiuseppeDelGobbo]

Hello, I am trying to model a SDOF system with a Maxwell model material in order to reproduce the results from (http://opensees.berkeley.edu/wiki/index ... r_Material). I am trying to run a displacement time history analysis. The script would produce an error message "could not invert flexibility" and not run unless I added a second elastic element. With the elastic element, I am finding that there is no force in the damper material. I have tried applying the viscousdamper material to a zerolength element, a two node link, and a nonlinear beam column element. What am I doing incorrectly? Thank you for the help.

model BasicBuilder -ndm 2 -ndf 3

node 1 0.0 0.0
node 2 7000.0 0.0 -mass 100.0 100.0 0.0

fix 1 1 1 0
fix 2 0 1 0

set transfTag 1
geomTransf Linear $transfTag
element elasticBeamColumn 2 1 2 1 1 1 $transfTag

uniaxialMaterial ViscousDamper 2 30000000 2803000 0.3
element twoNodeLink 4 1 2 -mat 2 -dir 1

recorder Element -file Force.txt -time -ele 4 localForce;
recorder Element -file Diplacement.txt -time -ele 4 deformation
recorder Node -file NodeDiplacement.txt -time -node 2 -dof 1 2 disp

recorder Element -file eForce.txt -time -ele 1 localForce;
recorder Element -file eDiplacement.txt -time -ele 1 deformation


set GMSineDispAmpl 12
set freq 0.5
set TPeriodSine [expr 1/$freq]

set DtAnalysis 0.001
set DurationSine $TPeriodSine

timeSeries Trig 13 0 $TPeriodSine $TPeriodSine -factor $GMSineDispAmpl

pattern MultipleSupport 2 {
groundMotion 66 Plain -disp 13
imposedMotion 2 1 66
}

wipeAnalysis
test EnergyIncr 1.0e-8 100
algorithm Newton
system UmfPack
numberer RCM
constraints Transformation
integrator Newmark 0.5 0.25
analysis Transient
set Nsteps [expr int($DurationSine/$DtAnalysis)];
analyze $Nsteps $DtAnalysis

puts "done"
wipe

[emjac]

Did you try running the example file here? http://opensees.berkeley.edu/wiki/index ... us_Dampers

When I run it the damper just gives zero... so maybe it is not your problem.

[GiuseppeDelGobbo]

Thanks, I did try that example.

I think I may now understand the problem. I believe that the viscousdamper material model does not actually introduce a stiffness into the OpenSees model. Rather, it only outputs forces considering K and C values.