[SciPy-User] finite element packages

Young, Karl karl.young@ucsf....
Fri Nov 20 12:06:06 CST 2009


Hi David,

Thanks for the quick reply. I'm at a fairly early stage with this and so it's still fairly exploratory. That said I guess the main goal is to help my friend, who already has a working prtotype of a flexible flywheel, model and balance various parameter choices  like speed of the flywheel, deformation of the wheel based on parameters associated with various material choices,... 

I obtained my analytic model by appropriately modifying the force diagram from a paper on the "skipping rope" problem; I obtained a nonlinear differential equation for the form of the loops of the flywheel that had elliptic functions as solutions. To first order I'm hoping that I can do some useful static modeling, i.e. in the rotating frame, even with more realistic parameters for the loop material, i.e. I guess the answer to the question is that my initial interest is in steady-state models (though I guess at some point it would be nice to study spin up and spin down). 

Again, to first order I'm not that concerned about looking at stability-instability transitions or oscillatory mode amplification and damping because my friend has a working prototype that seems to be pretty deeply in a stable range, at least re. variation in rotation speeds. The hope is that I can model the system in a way such that small changes in things like material parameters won't effect the stability regime (the flexible flywheel, combined with a fancy gimbal system seems to have a sort of surprisingly large stability range, re. parameters like rotation speeds and loop radius). But I may need to eventually model oscillatory modes and stability transitions re. use of some materials for the loop. 

The first goal will be to compare the model/simulations with his prototype, i.e. experiment (e.g. we may take pictures as in some of the skipping rope papers).

Maybe my approach sounds silly; it's very preliminary and exploratory. Physicists (and particularly me) are probably too dumb to think about hard mechanical engineering problems !

-- Karl        

________________________________________
From: scipy-user-bounces@scipy.org [scipy-user-bounces@scipy.org] On Behalf Of David Goldsmith [d.l.goldsmith@gmail.com]
Sent: Friday, November 20, 2009 9:10 AM
To: SciPy Users List
Subject: Re: [SciPy-User] finite element packages

Forgive me if you provided this in the previous thread, but, for reference, what analytic model(s) (differential equations, presumably) are you using that led you to elliptical functions?  Also, are you interested in modeling transient (time-dependent) or steady-state (d/dt=0), stability-instability transitions, oscillatory mode amplification and damping, etc.?  Finally, are you comparing theory w/ experiment, i.e., do you also have experimental data you're modeling and/or using to tweak your analytic models' parameters?

DG

On Fri, Nov 20, 2009 at 8:48 AM, Young, Karl <karl.young@ucsf.edu<mailto:karl.young@ucsf.edu>> wrote:

I'm trying to model a flexible flywheel (hence my question about Wierstrass elliptic functions a couple of weeks ago - thanks again for the helpful replies). I'm now trying to consider realistic models with elastic materials that go beyond my abilities to model analytically and figured I need to look at finite element models.

I haven't used finite element packages and was wondering if anyone on the list had any recommendations, preferably scipythonic but I'm just curious generally about what people would consider using for a problem like this (i.e. a rotating flexible rope type problem). Thanks for any thoughts,

-- Karl
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