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Methods to Model and approximate damping in FEA (for impact sim.)

Methods to Model and approximate damping in FEA (for impact sim.)

Methods to Model and approximate damping in FEA (for impact sim.)

(OP)
SHORT VERSION
Is there a procedure/method for approximating the damping properties (Rayleigh coefficients for example) of a structure when you have no data on the damping [and you cannot run experiments to determine the damping properties]?



LONG VERSION
I was wondering if there is a way I could quickly 'determine' the damping properties of a skid landing gear, without actually going out and running experimental tests.

Basically I'm running a hard-landing FEA simulation of a rotorcraft skid landing gear. To get meaningful results, the input data needs to make sense. Inertia and mass properties are known, and the stiffness properties are obtained implicitly from defining the material and geometry. So, I'm wondering what the common practice is for damping, when you have no actual data. I have to 2 sloppy ideas so far.


IDEA 1
Can I just enter no data on damping (effectively setting damping coefficients to zero, aside from plasticity and friction which would indirectly damp out energy)? This seems like a sloppy solution. Damping would still be included by the plastic limit of the material as well as friction at the skid-ground interface. However, I feel it's common practice to include other types of damping, and this seems incomplete. If the material stays within its plastic limit, that leaves friction as the ONLY damping mechanism. Hence, the damping shown in the model cannot be very accurate.


IDEA 2
Should I model damping by including Rayleigh (proportional) damping? Is there some sort of standard procedure to estimate the alpha, beta coefficients [again, without having any experimental data]? In my experience, Rayleigh damping is a non-physical model used to "force" your results to match known data and thus the (rayleigh) damping coefficients are obtained backwards. In other words, without any physical data, I do not think a Rayleigh damping model is any use to me. I could be wrong though.

Do you guys have any better ideas? Basically, if I add some sort of damping coefficent (Rayleigh or something similar) to my model, it would either need to be physically accurate OR justifiable (cited and obtained from an accepted procedure, methodology)??


Thanks

RE: Methods to Model and approximate damping in FEA (for impact sim.)

With no test data it's going to be difficult to create any damping coefficient from my experience. You can use a frequency analysis to calculate the natural frequency and hen use this as a conservative guess of the damping required.

I used this method in an extremely different situation in my paper presented at Abaqus's conference the Simulia Customer Conference in 2010. I have attached the original paper to this post. An article was also written and is located here http://www.3ds.com/customer-stories/single/bausch-...

I hope this helps.

Rob Stupplebeen
www.optimaldevice.com
https://sites.google.com/site/robertkstupplebeen/

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