Spring Mass Nastran Analysis

[Anonymous]

Hi I am trying to simulate a simple mass spring system to determine the frequency response of the mass. I cant seem to get it to work and there is very little resource material on this area which I found it quite surprising. im trying to work out the relation ship between the rigid body connector and the spring connector.

My understanding is you first set up the rigid body connector first selecting the face and then selecting the point where the spring will be placed on that face. Then you create the spring connector between the two points. Am I correct in thinking this?  Its just my results have been anything but what I would expect using hookes law.

Thank you.

[John_Holtz]

Hi @Anonymous . Welcome to the Inventor Nastran forum.

I have some questions to understand what you are trying to model.

1. What version of Inventor are you using?
2. What analysis type are you using?
3. When you write that you "create the spring connector between the two points", what two points are you referring to? The center of the rigid connector and ?
4. What values did you enter for the 6 stiffness values for the spring? (You may need to review this article on the Autodesk Knowledge Network: How to enter spring stiffness in Nastran.)
5. What constraints did you apply to the model and where?

An image of your model and setup may be helpful to describe what you have done.

[Anonymous]

Hi @John_Holtz thanks for the fast reply! im using Inventor professional 2020, and I am using modal frequency response. I am using two bodies and one is fixed (see attached screenshot), so the other point is the centre of the rigid connector on the opposite face. I entered 280 for the k3 value as the mass is moving parallel to  my z plane and 1 for all other values. I have a fixed constraint on the top face of the supporting mass to simulate the mass being suspended from the bottom of a beam (see attached).

[John_Holtz · Accepted solution]

Good. It looks like the model is setup properly regarding the spring and masses. Depending on what you are trying to simulate, you might want a Tx and Ty constraint on the moving mass so that the side-to-side vibration is not an issue.

Beyond that, what problem are you having with the results? My guess is that you are doing a "sine sweep" to create a transmissibility curve (like this image from Wikipedia).

[Anonymous]

Thank you for confirming I had constrained the problem correctly, I since changed to a Tx and Ty and got results that matched the theory.