I am running a transient analysis with a time step of 0.0003 seconds and have an input excitation that has a time step of 0.02 seconds.
The overall trend of the acceleration record is very near what I expected, however when I zoom in and look at the finer detail, the output is not what I would have expected.
Between the timesteps intervals of 0.02 seconds, the acceleration records are not linear, but exhibit quadratic behavior??
If OpenSees does a linear interopalation between the input excitation, why is there such strange behavior in the output acceleration records in the timestep intervals???
Below is the analysis solver method used.
system UmfPack
constraints Plain
test NormDispIncr 1.0e-7 40 0;
algorithm Newton
numberer RCM
integrator Newmark 0.5 0.25;
analysis Transient
pattern UniformExcitation 2 1 -accel $accelSeries;
analyze $totaltimestep $inctimestep[/img]
Solver issues?
Moderators: silvia, selimgunay, Moderators
why are you expecting a linear result for the nodal accelerations? .. just because
the supports have a linear relation for those intermediate time steps at which
you have not specified an input acceleration, does not mean the response at the
nodes is linear in the interval as well .. think of a SDOF system with ramp-up excitation where i/p accel ramps from 0 to constant value after time t .. does resposne stay constant or does structure oscillate after t?
the supports have a linear relation for those intermediate time steps at which
you have not specified an input acceleration, does not mean the response at the
nodes is linear in the interval as well .. think of a SDOF system with ramp-up excitation where i/p accel ramps from 0 to constant value after time t .. does resposne stay constant or does structure oscillate after t?