Structural Dynamics
Structural Dynamics
(OP)
Why can changing the dt= time step, effect the non-linear time history results for x-displacements?
I hope someone can provide insight.
Thanks,
tre
I hope someone can provide insight.
Thanks,
tre






RE: Structural Dynamics
Mike McCann
MMC Engineering
RE: Structural Dynamics
BA
RE: Structural Dynamics
RE: Structural Dynamics
Take a very basic example - suppose we have a structure which is vibrating with simple harmonic (sinusoidal) motion, with period of 1 second, and zero phase shift.
Sample the response function at 1 second intervals, starting at t = 0.0 seconds, and every time step will return a value of precisely "0". Sample it again at half-second intervals, and you will STILL get "0" at every sample. This might lead you to think (erroneously) that there is no response - after all, you've reduced your time interval, and the solution shows no more convergence!
Now sample at 1/4 second intervals - you will get a saw-tooth function, which is a much better fit to the true sinusoidal function, but still not very good. Sample at 1/100th or 1/1000th second intervals, and you will start to get a good approximation of the real behaviour.
Bottom line - your time step must be "small enough" to capture the time variability of the forcing function AND the response of the system. This typically means that your time step must be rather smaller than the period of the highest natural frequency which is "of interest".
Hope this helps!
RE: Structural Dynamics
Fe
RE: Structural Dynamics
I have to admit that this is one of the most amusing threads I've ever read around here.
RE: Structural Dynamics
RE: Structural Dynamics
BA
RE: Structural Dynamics
hahahahah... (im laughing at the big ears)
Fe
RE: Structural Dynamics
Fe
RE: Structural Dynamics
(no offense to the OP)
Fe
RE: Structural Dynamics
BA
RE: Structural Dynamics
Fe
RE: Structural Dynamics
RE: Structural Dynamics
RE: Structural Dynamics
RE: Structural Dynamics
RE: Structural Dynamics
Fe
RE: Structural Dynamics
BA
RE: Structural Dynamics
RE: Structural Dynamics
Hartog => too squishy
Inman => too hard
Rao => just right
I wonder if anyone padded their cover's....maybe the fluid mechanics text somehow acted as a water-bed type pillow?
{plz ignore me if im "on cr$ck", I just finished writing a shit load of code}
Fe