Error in applying initial velocity to a SDOF

[baozaizhang]

Hi, All:

I am trying to apply a initial velocity to a SDOF system. What I did was I built a SDOF system with a linear zero-length spring. Then I applied imposed motion with initial velocity and initial displacement (0) to the mass point by MultipleSupport input.
OpenSees gave me error "FATAL FullGenLinSOE::getX - vectX == 0" for both eigen analysis and time history analysis. But if I delete the MultipleSupport input, the eigen analysis ran as expected. Would you please tell me if there is a way to solve this?

The reason why I want to use multiple support input to impose initial velocity to the SDOF is I wanted to impose an initial velocity to one mass point of a two-degree-of-freedom system, but I think I can only apply the initial velocity to one mass point of a MDOF system by using the multipleSupport command. Before I do it, I just want to check the SDOF system with a classical solution to see if I used MultipleSupport command correctly.

Thank you very much for your help.

Please see my codes in the following:

wipe
wipe Analysis
logFile errorFile on;
model BasicBuilder -ndm 1 -ndf 1
uniaxialMaterial Elastic 1 100
node 1 0.0
node 2 0.0
mass 2 1.0
fix 1 1
fix 2 0
element zeroLength 1 1 2 -mat 1 -dir 1;

set Initial_Vel2 2; # initial velocity for node 2
set GMfatt 1
set InputVeloFile AppliedVelocity2.txt; # set variable holding new filename (PEER files have .at2/dt2 extension)
set InputDispFile AppliedDisp.txt; # set variable holding new filename (PEER files have .at2/dt2 extension)
set VelocitySeries "Series -dt $dT -filePath $InputVeloFile -factor $GMfatt"; # time series information
set DispSeries "Series -dt $dT -filePath $InputDispFile -factor $GMfatt"; # time series information
# multiple-support excitation: displacement input at individual nodes
pattern MultipleSupport 400 { # groundMotion $gmTag Plain <-accel $tsTag> <-vel $tsTag> <-disp $tsTag> <-int (IntegratorType intArgs)> <-fact $cFactor>
groundMotion $Initial_Vel2 Plain -vel $VelocitySeries -disp $DispSeries
# imposedMotion $nodeTag $dirn $gMotionTag
imposedMotion 2 1 $Initial_Vel2
}

system FullGeneral
numberer Plain
constraints Transformation
integrator Newmark 0.5 0.25
test RelativeNormDispIncr 1.0e-12 50 0
algorithm Newton
# Create the analysis object
analysis Transient

eigen -fullGenLapack 1;

[fmk]

you have 0 unknown dof when you use the transformation method .. you might try the Penalty method