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Random Vibration Analysis
Posted 28 janv. 2015, 12:12 UTC−5 Structural Mechanics Version 5.0 3 Replies
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Hi -
I'm trying to perform a random vibration analysis on a component. I have acceleration spectral density levels for my input, but I am not sure how to apply it. Does anyone have any experience doing random vibration analysis in Comsol? I am working w/ version 5.0. Any help would be appreciated.
Thanks.
I'm trying to perform a random vibration analysis on a component. I have acceleration spectral density levels for my input, but I am not sure how to apply it. Does anyone have any experience doing random vibration analysis in Comsol? I am working w/ version 5.0. Any help would be appreciated.
Thanks.
3 Replies Last Post 6 mars 2015, 15:00 UTC−5
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Posted:
10 years ago
Hi
you can either apply a domain load F=rho*acceleration (in frequency mode if you have a spectrum), or you can accelerate the base with an imposed acceleration, but be aware ...
If you do shock analysis, a half sine shock acceleration on the base will leave your object at a constant speed, so you need to measure w.r.t. your moving base.
The classical "large mass" (attaching your object to a large mass and loading this mass) will work if you are a bit careful with the scaling
Indeed there is no ready functions to rapidly define a PSD and apply it in COMSOL, as for the modal approach, you cannot easily do algebra on the eigenmodes responses, nor even get the mass participation factors for the rotational directions (only the linear ones), something you are used to in all other FEM programmes.
So normally you need to do quite some extra Matlab or C work to get a classical shock and random vibration analysis done for aero/space norms, the main reason (I understand) by COMSOL seems to be that these approaches are all "engineering simplifications" and COMSOL is doing their best to be perfectly "physics correct", to ensure full compatibility with their multiple-physics approach.
Unfortunately for us end users, any custom programming work must also be re-validated for each new release, this means you need regularly a few good but "cheap students" to get the work done, and as I have none, we do subcontract all these analysis to a local NASTRAN programmer to be ESA norm compliant :(
But still it's fully feasible in COMSOL ...
--
Good luck
Ivar
you can either apply a domain load F=rho*acceleration (in frequency mode if you have a spectrum), or you can accelerate the base with an imposed acceleration, but be aware ...
If you do shock analysis, a half sine shock acceleration on the base will leave your object at a constant speed, so you need to measure w.r.t. your moving base.
The classical "large mass" (attaching your object to a large mass and loading this mass) will work if you are a bit careful with the scaling
Indeed there is no ready functions to rapidly define a PSD and apply it in COMSOL, as for the modal approach, you cannot easily do algebra on the eigenmodes responses, nor even get the mass participation factors for the rotational directions (only the linear ones), something you are used to in all other FEM programmes.
So normally you need to do quite some extra Matlab or C work to get a classical shock and random vibration analysis done for aero/space norms, the main reason (I understand) by COMSOL seems to be that these approaches are all "engineering simplifications" and COMSOL is doing their best to be perfectly "physics correct", to ensure full compatibility with their multiple-physics approach.
Unfortunately for us end users, any custom programming work must also be re-validated for each new release, this means you need regularly a few good but "cheap students" to get the work done, and as I have none, we do subcontract all these analysis to a local NASTRAN programmer to be ESA norm compliant :(
But still it's fully feasible in COMSOL ...
--
Good luck
Ivar
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Posted:
10 years ago
Thanks, Ivar!
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Posted:
10 years ago
Hi,
I've a moving dynamic load (random load) on pavement which is obtained using matlab and would like to put this moving load in COMSOl so as to analyze the pavement response (Stress-Strain analysis). How can i put this moving load in COMSOL? I'm new user in COMSOL.
Thanks,
I've a moving dynamic load (random load) on pavement which is obtained using matlab and would like to put this moving load in COMSOl so as to analyze the pavement response (Stress-Strain analysis). How can i put this moving load in COMSOL? I'm new user in COMSOL.
Thanks,