Dynamic analysis

[camefem]

Hello,

For a dynamic analysis on automobile component, i have the following inputs.

Accleration: 24 G and 30 ms(continuously).

Mesh: shell (40000 elements)

Material: Linear. But geometric nonlinearity presents as per static loading analysis.


Do i need mass scaling as mentioned in abaqus manuals for this problem. Howmuch time is needed for an analysis. Load data given is sufficient or do i need more.

Thanks for your help.

regards

 

[mtnengr]

As I understand your problem, an acceleration is applied for 30 ms and then drops off to zero. Since your model has 40000 elements, there are a great number of eigenvalues associated with this class of problem. I suggest that you consider using the Ritz method to reduce the number of active DOF.

The Ritz method has been applied to comparable DOF models. See: Application of Ritz Vectors for Dynamic Analysis of Large Structures, Computer and Structures Vol 21 No 3, pp 461-467, 1985

 

[cbrn]

Hi,
40000 elements are quite a small-size problem for nowadays computers, even if you request a dynamic response; with more than 1000 eigenvalues (using the mode superposition method), it becomes a medium-size problem. However, if in doubt about how many modes to use, there is the possibility to filter them in/out with the significance factor. At least, this is very easy to do with Ansys, so I believe Abaqus has something very similar.
However, the Ritz reduction is a valuable suggestion.

Regards

 

[camefem]

Thanks for your replies.

Sorry.I should have been more clear. I am interested only in stresses in certain (BC) areas due to this sudden loading. (not in eigenfreq or modes).

I received an abaqus report for the above mentioned analysis. Could you guide me how to evaluate dynamic analysis results.

What are the parameters to be considered to predict a performance of the part under dynamic loading. As we do in static analysis, is von mises plot enough?

Thanks for your help.

camefem

 

[gurmeet2003]

Camefem,

It appears you have done a dynamic forced analysis and have the results in terms of deflection, stress, strain etc. Evaluation of results for a dynamic analysis should be no different than that for a static analysis.

Depending on the type of material (ductile/brittle), you will use a failure criterion either Von Mises stress or principal stress and establish a factor of safety. Then decide if the same is acceptalbe or not. You will check for fatigue. Also you can check to ensure that deflection is not excessive. You can check to ensure that the vibration levles are acceptable for your class of machinery.

Gurmeet