Is there any command for "acceleration" boundary?

[Rocky]

I want to apply acceleration on one node with mass or without mass.
Can I do it in OpenSees
Thanks

[silvia]

mmmm.... i think that currently you can only impose a displacement history. the program uses the trapezoidal rule to get the accelerations. You can do the same, take your acceleration and convert it to displacement -- typical groundmotion records have the displacement corresponding to the acceleration. you would use the imposed-support excitation command.-- you can find more about it in the manual.


Here is a script I use to impose displacement history at specified nodes:

# read a PEER strong motion database file, extracts dt from the header and converts the file
# to the format OpenSees expects for Unifform ground motions
set inFile $GMdir$GroundFile.dt2
set outFile $GMdir$GroundFile.dis; # set variable holding new filename
ReadSMDFile $inFile $outFile dt; # call procedure to convert the ground-motion file
set GMfatt [expr $cm*$GMfact]; # data in input file is in cm Unifts -- DISPLACEMENT TH
set dispSeries "Series -dt $dt -filePath $outFile -factor $GMfatt "; # time series information
pattern MultipleSupport $IDloadTagA {
set IDgm 100
groundMotion $IDgm Plain -disp $dispSeries
foreach SupNode $iSupNode {
imposedSupportMotion $SupNode $IDdofA $IDgm
}
}; # end pattern

[Rocky]

Thanks for your reply.

I tried "imposedMotion" command, but found the result still no change:
the velocity and acceleration are still zero. I don't know why?
is there anything wrong in my code:

model basic -ndm 2 -ndf 3
node 1 0.0 0.0
node 2 0.0 3.0
fix 1 1 1 1
mass 2 64.0 0.0 0.0
geomTransf Linear 1
element elasticBeamColumn 1 1 2 1.0 30000.0 3.0 1

set dispSeries "Series -time {0.01} -values {0.4} -factor 1.0"
pattern MultipleSupport 1 {
groundMotion 1 Plain -disp $dispSeries
imposedMotion 2 1 1
}

#set gaccel "Series -time {0.01} -values {12000.0} -factor 1.0"
#pattern UniformExcitation 2 1 -accel $gaccel

recorder Node -file NoInertia.txt -node 2 -dof 1 reaction
recorder Node -file Inertia.txt -node 2 -dof 1 reactionIncludingInertia

constraints Transformation
numberer RCM
system SparseGeneral -piv
test EnergyIncr 1.0e-12 100 3
algorithm Newton
integrator Newmark 0.5 0.25
analysis Transient
analyze 1 0.01

[silvia]

where are the recorders for the dof's??

[Rocky]

Sorry, I cannot understand your question.
The recorder has no effect on the analysis. In fact, I check
the result by "print".
If you run the code, please delete the two recorder lines.

Thank you very much.

[Rocky]

Hi, Silvia:
I think I have solved the problem.
Thank you for your suggestion.