twonodelink, damping

[dangdang]

Hi guys
i just make SDOF spring model.
I used 'twonodelink' command and i have some questions.

1. damping
I want to put 0.05 damping in this model, but eigen didn't work.( "eigen -fullGenLankpack 1 " didn't work too)
So i used sqrt(k/m) to get omega and put damping. Is it right?

2. equivalent damping
If 1 daming is right, can you guys give me some advice to put some equivalent damping?

Thanks for your command.

This is my script.
-----------------------------------------------------------------------------------
# units: kg, mm, sec, N
wipe all

# Define Acc file
source model.tcl
set Accfile "$acc.acc"
set outputfile "$output-non(1)"
set dt $dt_acc
set Nsteps $Nsteps_acc

# Define Save
file mkdir $outputfile

# Define model
model BasicBuilder -ndm 2 -ndf 3

set h 3500
set m 5.908
set g 9800
node 1 0.0 0.0
node 2 0.0 $h -mass $m 1e-9 0.0

fix 1 1 1 1
fix 2 0 1 1

set Tn 1; # sec (Natural period)
set pi [expr acos(-1.0)];

# Columns and Beam Properties
set K [expr pow(2*$pi/$Tn,2)*$m]; # KN/mm
set damp 0.05

set Fy 0.764
set E $K
set b 0

# Define Material
set materialTag 1
uniaxialMaterial Steel01 $materialTag $Fy $E $b

# Define Element
set elementTag 1
element twoNodeLink $elementTag 1 2 -mat $materialTag -dir 2 -doRayleigh;

puts "Model Built"

# Define timeSeries
timeSeries Path 1001 -dt $dt -filePath $Accfile -factor 1;

# Define RECORDERS
recorder Node -file $outputfile/Aabs.out -timeSeries 1001 -time -node 2 -dof 1 accel;
recorder Node -file $outputfile/Afree.out -time -time -node 2 -dof 1 accel;
recorder Element -file $outputfile/Deform.out -time -ele 1 deformations ;
recorder Element -file $outputfile/Force.out -time -ele 1 globalForce ;

# Define Damping
set omega [expr sqrt($K/$m)]
set period [expr 2*($pi/$omega)]
set freq [expr 1/$period]
set damp 0.05;
rayleigh 0 0 0 [expr 2.*$damp/($omega)]

#pattern UniformExcitation $patternTag $dir -accel $tsTag <-vel0 $ver0>
pattern UniformExcitation 1 1 -accel 1001; # define where and how (pattern tag, dof) acceleration is applied

# create the analysis
#wipeAnalysis; # clear previously-define analysis parameters
constraints Transformation; # how it handles boundary conditions
numberer Plain; # renumber dof's to minimize band-width (optimization), if you want to
system SparseGeneral -piv; # how to store and solve the system of equations in the analysis (large model: try UmfPack)
test EnergyIncr 1.0e-8 100 0; # test Eneregy incerment
algorithm ModifiedNewton; # use Kyrlow-Newton algorithm
integrator Newmark 0.5 0.25 ; # determine the next time step for an analysis
analysis Transient; # define type of analysis: time-dependent
analyze $Nsteps $dt; # apply 10*4096 steps for 0.001-sec time steps in analysis
wipe

puts "Done!"

[selimgunay]

Yes, computing omega as (k/m)^0.5 and using mass proportional damping is sufficient. What do you mean by equivalent damping? You are already using the nonlinear response explicitly with a bilinear material.