How to measure reactions in a rigid body ?

[misha2002miller]

Whether it is possible to know the reactions in the node where the rigid body is used ?

When trying to know the forces through SPC Summation all at zero. At least on the hard connector, the output is given on the side.

In the analysis settings, I ticked all the boxes.

[John_Holtz]

Hi @misha2002miller . Welcome to the Inventor Nastran forum.

The results in the rigid connectors is under "MPC". The SPC Summation dialog only sums the results "SPC" which come from the constraints. Thus, the SPC Summation dialog will not work for your purposes.

Also, the sum of the forces in the rigid connector are equal and opposite. If you could sum the forces around the face where the ends of the connector are located, the sum would be zero (or whatever force is applied to the center point of the connector). You already know the load at the center of the connector, so summing the results is not necessary.

Perhaps what you want to know is the force in the individual "spokes". You can see that by viewing the contour results "Reaction Force > MPC Force Along -Axis".

Let us know if you have any questions.

John

[misha2002miller]

Hi thanks I understand. I wanted to try to replace the bearing in the assembly with a rigid body connector and learn the ratio for the bearing. Is there any way to simulate the bearing in the assembly so that you can measure the forces that will act on it? I use Inventor Nastran 2022

[John_Holtz]

A bearing is attached to two pieces in real life, and that needs to be true in the model also. 

1. The outer diameter of the bearing usually fits in some type of groove or pocket in a housing.
2. The inner diameter of the bearing usually fits over a shaft. 🙂

In your original image showing the rigid body connector, what (if anything) is applied at the center of the rigid connector at work point <1>? What is the rigid connector attached to at face <7> and point <1>. (Point <1> may be a mistake. Usually the "ends of the spokes" of a rigid connector are attached to faces or edges of the CAD model. Is it unusual to attach the connector to faces and a point unless you are connecting separate beams together.)

For example, face <7> could be the outside of the shaft and the centerpoint work point <1> represents the connection of the bearing to the housing.

• If the housing is not in the model, then a constraint at work point <1> simulates the housing holding up the shaft, and the SPC summation (Reaction in newer versions of Inventor Nastran) gives the forces transmitted from the shaft to the housing.
• If the housing is modeled, the center of the connector attached to a point on the housing.

Now that I think of it, my original post that said the sum of the MPC forces are zero is not entirely correct. The MPC force sum would equal the force that is applied at the center of the rigid connector (which could be a reaction force from a constraint or another piece of the model).

• If you applied a force or constraint at the center of the connector, there is no need to sum the MPC forces because you know what the force is (because you applied it or can get the reaction force).
• If the center of the connector is attached to a part of the model, then you need to sum the MPC force to find the "reaction" between the model and rigid connector. You can use FNO Reader to do that.
• If there is nothing at the center of the rigid connector, then there is 0 force at the center. In this special case, the sum of the MPC force would be 0.

John