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WARNING: CTestEnergyIncr::test() - failed to converge
after: 50 iterations

This mean that your model failed to meet the test criteria.
The rest of the message says the same, only you used an "adaptative" solution so once once criteria fails, it try another one and so forth.

This is your test command : test $testTypeDynamic $TolDynamic $maxNumIterDynamic
this is your adaptative solution
if {$ok != 0} { ; # if analysis was not successful.
# change some analysis parameters to achieve convergence
# performance is slower inside this loop
# Time-controlled analysis
set ok 0;
set controlTime [getTime];
while {$controlTime < $TmaxAnalysis && $ok == 0} {
set ok [analyze 1 $DtAnalysis]
set controlTime [getTime]
set ok [analyze 1 $DtAnalysis]
if {$ok != 0} {
puts "Trying Newton with Initial Tangent .."
test NormDispIncr $TolDynamic 100 0
algorithm Newton -initial
set ok [analyze 1 $DtAnalysis]
test $testTypeDynamic $TolDynamic $maxNumIterDynamic 0
algorithm $algorithmTypeDynamic
}
if {$ok != 0} {
puts "Trying Broyden .."
algorithm Broyden 8
set ok [analyze 1 $DtAnalysis]
algorithm $algorithmTypeDynamic
}
if {$ok != 0} {
puts "Trying NewtonWithLineSearch .."
algorithm NewtonLineSearch .8
set ok [analyze 1 $DtAnalysis]
algorithm $algorithmTypeDynamic
}
}
}; # end if ok !0

I guess for someone who's pretty new to OpenSees as you say, you should start with a rather simpler model. Check the simple example using elastic model on the OS wiki and try understand before you use a more complex model. Good Luck !

Assuming that you observe the reduction during the free oscillating phase of the loading, since you used the equivalent of the viscous damper but applied to acceleration, is it not normal that you observe this reduction in movement?

No idea. One simple way thought to check if it comes from your material is to use another already built in material, like a elastic one.
If you get no damping using this alternative material, you know it comes from your code.
If you do get damping using this other material, you know it does not necessary comes from your code.
Hope it helps,
GL

When you select the newmark method, you specify gamma and beta. If you use gamma>0.5, you induce numerical damping equivalent to gamma-0.5.
Beta should then be selected as 1/4*(gamma+1/2).
If you used gamma = 0.5 and Beta as 1/4, I don't think you did induce numerical damping.

Did you impose numerical damping?

Check your model against proposed example and you will eventually find the problem. I would suggest you use simpler element for a start (don't start with a complex fluid-coupled model as it introduce more difficulty.. you can add it later when you have a solid model).
GL

Shall I just model it as a column to see the natural frequencies? -- I would tend to say it depend on why you want to model this soil deposit.

You say you want to " do the eigen value analysis ". If this is your only objectif, use the relation 4H/(Vs*(2n-1)) to obtain the n-th periods value.
If you want to conduct a wave passage analysis then you can sure do it with a soil column. Just use consisten lateral boundary (equalDOF). You should then cross-check your result using proShake.

May I ask what type of soil you are modelling? It's very hard to say anything without carefully looking the code.
In any cases, did you check the OS example of a soil column analysis? http://opensees.berkeley.edu/wiki/index ... _Analysis) and http://opensees.berkeley.edu/wiki/index ... oil_Column
Hope it helps, GL

Are you doing your analysis in the elastic or inelastic phase of the PDMY material?
Also make sure you have correct effective stress and correct small strain G and K.
If you still get discrepancy, perhaps you should try with a 1D column using elastic isotropic material first to get the 4H/Vs value.

Consider à Variable Transient analysis? http://opensees.berkeley.edu/wiki/index ... is_Command

Did you empty the memory after the analysis was complete (wipe command or close the OS programs)?

Thk for the input; I did not know about this !

IT happens when an impossible command is issued.
Use a print screen (quick) when the windows fade off. If you time it right, you will see a error command displayed in the OS windows. Might take several attemps to time it right (put a "gets stdin" before the closing of the windows in your script so you can time it right).

set f11 [open input.txt r]
set f1 [read $f11]
Now the data are stored in var f1

I am afraid not. See the discussion here about the same question and solution. In your case, keeping track of your variable in a list then using a loop with unset would appears the best approach.
http://computer-programming-forum.com/5 ... 071742.htm
GL