Explicit Analysis

[Anonymous]

Hi everybody,

talking about the last release of Inventor Nastran 2020, which is the difference between Explicit Dynamics and Explicit Quasi-Static? When using the first and when the latter?

Tutorials A6 and A7 only explain how to set the analysis.

Then I have found this link, but it gives only few details:

https://knowledge.autodesk.com/support/inventor-nastran/learn-explore/caas/CloudHelp/cloudhelp/2020/...

thx

luca

[Anonymous]

up

[John_Holtz]

Hi @Anonymous 

Both analysis types use the same solver.

• Explicit Dynamics solves the analysis using dynamics. The loads cause the parts to move, and the solution is the result of that dynamic motion.
• Explicit Quasi-Static attempts to approach a static solution by using the dynamic solver but applying the loads as slowly as possible. For example, a duration of 0.1 seconds may be too fast (the kinetic energy is high), but 1 second may be close to approximating a static solution (because the kinetic energy is low.) During the process of determining "how slow approximates a static solution", the analysis is performed multiple times (so it can take longer to run). [Those times of 0.1 and 1 second are just made up. Since the time step is often on the order of 1E-6 to 1E-9, trying to reach a duration of 1 second with a time step size of 1E-9 would be a very long runtime! But I think from testing that even a "short" duration event often has a relatively low kinetic energy and therefore is a good approximation to a static solution.)

[Roelof.Feijen]

Hi @Anonymous ,

The image below was taken from a youtube presentation about other FEA software. Hopefully this will bring even more clarity to when using implicit and when using explicit analysis.

[Anonymous]

Thx John and thx Roelof,

the table is clear; so it's matter of strain rate.

Now I'm wondering which is the difference between applying a Quasi-static analysis instead of a Non-Linear Static Analysis. Both analysis calculate strain and I should use them when I can think to my problem approximately as Static.

The solver is different the solution is calculated with different process but ideally are these two analysis similar?

I can't figure out when I should apply the first or the latter; yes, the strain rate of the Quasi-Static should be higher than the Non-Linear Static (as I understood) but it's a very thin line, no? 

Since this post has been created to understand the meaning of these new analysis it would be good having some guidelines. 

p.s.: I created an explicit analysis of a bullet but I'm having some problems so I'll create a specific post for it.

thx 

luca