Quasi static equilibrium result in a Radioss analysis
This scenario has likely happened to you.
You created a Radioss model with the boundary conditions and all the information to simulate your structure.
The analysis finishes as you expected.
But in the end , due to the nature of the explicit simulation, there is vibration on the structure that may prevent you to compare the output with a test result (that is in equilibrium) , or another type of result.
And the more flexible the structure, the larger is the amplitude of variation and the period of oscillation.
In this case we need to come up with a way to reduce the kinetic energy of the system.
Some of the ways are using either by /DAMP that is Rayleigh mass and stiffness damping coefficients or using /DYREL, dynamic relaxation.
(You can refer to the help documentation for more details)
These options are well suitable but there is the complex phase of calculating the parameters for the damping, and it may lead to some reruns until reach the proper final condition.
Another way that is possible to do the kinetic energy reduction is using /KEREL, kinetic energy relaxation.
But this option is not really practical as it reduces energy based on the max values.
We may be missing important results depending on the energy level.
One neat option that was added on solver, since version 2019.1, is the keyword /ADYREL, adaptive dynamic relaxation.
It is based on /DYREL but the period to be damped is automatically calculated and varies during the simulation.
Given a great deal of help when dealing with the oscillation.
And in the version 2020 it was added the option to set Tstart and Tstop.
More details in the documentation: https://2020.help.altair.com/2020/hwsolvers/rad/topics/solvers/rad/adyrel_engine_r.htm
Attached you can find a simple example, mass+spring, that show case the usage of /ADYREL.
I hope this option helps you as well.
Regards
Comments
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really nice example, very easy to catch the idea! tks for sharing!
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