torsional vibration problem
torsional vibration problem
(OP)
Hi All,
I am moddelling the drive of an aluminium mill, using mass elements (rotary inertia) and torsional springs between them, much like a conventional torsional vibration calculation. However, instead of steady-state conditions, i want to calculate the response to the torque that is created when the aluminium enters the rolls, which creates a sudden load change in a very brief moment. We measured an increase from zero to 10 kNm in 0.02 seconds, after which the installation shows resonance and the vibation dies out due to the damping present in the system.
Does anyone have an idea how to model the sudden load change? How do i define the load? how do i define the time spectrum?
Any ideas are welcome.





RE: torsional vibration problem
This behaviour seems due to milling operation starting: this load change could be simulated with an impulsive load change. The load can be a step like force applied on one end of your torsional beam.
With a calculation by hand you could stimate the first torsional frequency and dumping value and relaxation time.
I hope this could be of some help.
RE: torsional vibration problem
1/ run a time history (and hence transient analysis) on this model to obtain the response or
2/ run the job in the frequency domain (FFT your data to produce a spectrum and then run an harmonic analysis using the FFTd data).
If it is a shock load (load applied over very short time span) I would try inputting a small time history and run a transient analysis (make sure the time integration is switched on to capture inertia effects and that rotary inertia is active in the mass elements). This would be a reasonably inexpensive analysis since you would have only a small DOF in the model. How to define the load/spectrum depends on the FE package you use, but is usually very easy to do.
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RE: torsional vibration problem
RE: torsional vibration problem
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See FAQ569-1083 for details on how to make best use of Eng-Tips.com
RE: torsional vibration problem