I am trying to simulate one rotation of a crank so that the arm and piston follow it.
I have set up a NLT analysis with some basic constraints. I have also added PIN constraints between piston and arm as well as arm and crank (yellow in the screenshot).
I can't seem to be able to correctly apply loading or transient table to simulate one full rotation of crank and see what happens to rest of part.
How does one go about setting this up?
Any hint is appreciated.
I have attached the model files to this post.
Solved! Go to Solution.
Solved by John_Holtz. Go to Solution.
Hi @ghadyani
A nonlinear transient response analysis in Nastran either cannot perform this analysis, or it is very difficult to get it to do what you want. The main reason is this (assuming you are duplicating the setup from Simulation Mechanical): you want an enforced motion to indicate that the crank rotates X degrees in T seconds. A nonlinear transient analysis does not support enforced motion loads.
A "Rotational Force" is a centrifugal load. It tries to stretch the model in the radial direction based on the speed (RPM or equivalent units) and rotation axis. This is not the type of load that you want for this analysis.
The other problems with your setup is that Pin constraints that you applied to the "joints" between the linkages are constraints that connect the model to the ground. You need to create a connection between parts that allows rotation. As far as I know, the only way to do that in Inventor Nastran (Nastran In-CAD) is the method described in this post: Pin and universal joint between bodies . The other thing that is required for a large displacement analysis is to change the rigid connectors to bar elements, as described in this post: Pinned connection in Autodesk Nastran .
If such an analysis can be performed in Nastran, it would require using the explicit solver (which was released as a preview in version 2020.1). I do not know if the explicit solver has all of the capabilities that would be necessary:
Perhaps another reader knows that answer offhand. Otherwise, a test model would be required to test out the concepts (such as your piston model 😊).
Hi @ghadyani
I am pleased to report that the explicit dynamics analysis can handle the piston analysis, with one minor difference than what I was describing before. Here is what you can do:
In my model, I worked my way up from rotating just the crank to rotating the crank and arm. See the attached model "explicit dynamics (version 2020.2).zip" and animation "piston animation.zip". I was using version 2020.2 of Inventor Nastran.
Hi John,
Thanks for your reply and all useful links.
I won't be able to open your model since I am on 2019, but I will try your suggestions and report back.
EDIT: As you said your solution is only applicable to 2020.1
Hi John,
Thanks to your post and links, I have learned a lot when it comes to this kind of simulation.
I just wanted to verify that everything I am doing is done correctly before moving to a full assembly. So I just analyzed the crank part only under a 45-degree rotation. However, I ran into two issues:
Hi @ghadyani . You are making progress 🙂.
Note: the constraint that is named "Necessary?" is not necessary. The rigid connectors prevent the nodes on the inside of the hole from moving the Z direction.
@John_HoltzThanks for explanations, this clarifies the issues.
In spirit of replicating tutorials for Simulation Mechanical, I'm going to post another question on how to have actuators (hydraulic/pneumatic) in Nastran.
Can you please check this still works in 2021.0.0.401?
I get a message saying cross section not available (for beam idealization) for explicit...
(as per your recommondations & the pin guide)
And when I run the examples I don't get the animation outcome...
Hi @eggheadkhan
The explicit analysis type is different in many ways, so some instructions in the articles do not apply directly.
There are three options for defining the beam cross-section properties. You have tried 1 and learned that that does not work for the explicit analysis. You only have two more options to try! (Hint: use the "Property Input".)
hi @John_Holtz , thanks for your reply.
to be honest, I played a lot of whack-a-mole over the weekend, and for the project on my desk, I hired someone to do it for me.
I learnt that the explicit solver only likes to use 1x Xeon 8168 when 2 are available, and doesn't like AMD 7742 (at least on win10), plus a few other things 🙂
but what I'd like to learn is how to replicate that animation of yours somehow... is your attachment above ready to go for inventor nastran 2021.0.0.401? (the crank and the arm moved a little, but even increasing the duration 10x, seemed to just bend the crank beyond that point)
Hi @eggheadkhan
Regarding AMD processors, please see this forum post: https://forums.autodesk.com/t5/inventor-nastran-forum/inventor-nastran-explicit-solver-will-not-work...
The 2020.2 model that I provided runs the same in 2021.0. You may need to do these items:
If extending the duration, be sure to extend the "Transient Table Data" for the enforced motion load. Otherwise, the crank will get to 0.1 seconds and stop (which is the end of my load curve). The explicit analysis does not appear to extrapolate the load curve table. I ran the analysis for 2 full revolutions of the crank arm. A nice little out-of-plane vibration starts to occur on the second revolution, so it will be interesting to see what happens after 10 full revolutions.
it didn't quite make all 10, the first one is useful, then we go to a "explicit" 🙂 dance...
thanks for the reply.
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