inventor nastran complex leafspring problem

[NielsVerkade]

hello everyone,

For my final thesis im engineering this leafspring, it makes a complex 180 degree bend, and the front part is supposed to rotate away from the back 120 degrees in the work axis. I have a non-linear staticI have constrained the backside, made a solid body rigid connection between the bottom of the front part and the rotation point. i put an enforced motion rotation on the rotation point...but its not working.

does anybody have any clue why its giving me error E5073 or not showing any movement at all? 

[John_Holtz]

Hi @NielsVerkade 

I am curious what your search finds for the error message. I used three different search engines, all of which lead to this article: "Fatal error E5073: Non-zero load vector required for nonlinear analysis" in Nastran analysis. The article says when using a nonlinear analysis with an enforced motion load, the error occurs because you do not have a constraint on the same geometry and in the same direction as the enforced motion.

What the article is trying to say is this: the enforced motion does not move the model. The enforced motion moves a constraint, and the constraint moves the model. Without a constraint, there is no load in the analysis, and that is the source of the E5073 error.

John

[NielsVerkade]

okay, that makes sense, but then how do i make the FEM functional? i feel like i've already tried everything i have knowledge of.

[John_Holtz]

Hi @NielsVerkade. I think this should be your workflow:

1. Apply a load to the model.
2. Get the analysis to run.
3. Review the results and determine if the analysis is giving the results you want (because the setup is correct) or not (because the setup is wrong).

Which step are you having a problem with?

(ETA = Edited To Add ....)

• Your original image shows a rigid connector from the spring to workpoint 2. The model you provided does not have the connector using work point 2. Is there a reason for that change?
• Your original image shows an enforced rotation about the X axis at workpoint 2. The model does not have any load applied. (Are you sure the rotation is about the X axis? I have doubts that you can rotate the spring 120 degrees in that direction. ETA Is the spring being rotated around the Z axis?)
• The constraint at the rigid connector needs to be Rx fixed. The enforced rotation about X rotates the constraint fixed in Rx. That causes the center of the connector to rotate which moves the spring. Other directions for the constraint should be fixed based on how the mechanism that creates the 120 degrees rotation moves the work point. (For example, are all other directions free? Is the X translation fixed by the mechanism?)
• The default behavior of rigid body connectors is they only support small displacement. 120 degrees rotation is huge displacement. You need to change the parameter RigidElemType from RBE to Bar. (Parameters are the second to last branch of the model tree.)
• 120 degrees rotation is huge. You should set the Nonlinear Setup to use at least 100 increments, maybe as many as 500 increments. (The default number of increments of blank rarely works very well.) Set the intermediate output to On so that you can see the results as they are being calculated.
• Your spring is very thin. Solid elements usually do not give accurate results for thin pieces (ETA when there is only 1 element through the thickness). Are you sure you do not want to use shell elements?

John

[John_Holtz]

Is this the setup and result that you want?

John

[NielsVerkade]

thanks for the knowledge and help sofar! being a noobie in FEM, especially non-linear stuff, im learning alot.

The rotation is about the x-axis. 
i have added a video of the behaviour i want to FEM.

is it possible for me to "simply" edit the FEM you have sent to rotate about the x-axis? or will the break the model?

[John_Holtz]

Thanks for the video. That is quite different than what you had setup.

The center point of the rigid connector, at the center of the circular device in the video, does not move in X,Y,Z translation or Y,Z rotation. The device only allows rotation about X. Therefore, the constraint on the rigid connector needs to be fixed in all directions so that the center of the connector does not move (other than the enforced rotation about X).

The rotation angle follows the right-hand rule. The video shows it rotating -120 degrees about X. You can edit my model, you can edit your model, you can create a new model. The software does not care how you create it. 🙂

John

[NielsVerkade]

ah okay! i think i have it pretty close now! if you look at the video you can see it working.

I do have one more question, how come the leafspring doesnt follow a certain curve? but instead seems to move in a linear motion to the end while turning? (picture for clarification)

[John_Holtz]

You are using the wrong command to create the animation. See Animation does not match the individual results of a Nastran analysis and create a Multiset Animation.

John

[NielsVerkade · Accepted solution]

Thank you so much for the help, and thanks for teaching me about non-linear and forced movements! i really appreciate it.