## FEA Boundary Conditions

## FEA Boundary Conditions

(OP)

Hello everyone,

I have got a basic question with regards to the boundary conditions of a FEA model. It's a simple made of rectangular beams frame, supported with wheels bolted on to each of the four corners. I am looking at stresses and displacements in the frame.

I would like to get your opinion on the boundary conditions one would use in such set-up. I have blocked all displacements (x,y & z) on one of the supporting corners and blocked only the vertical displacements (z)on the other three corners. With regards to rotations, I have kept the model unconstrained for rotations around all three axes. A crude sketch of the frame is attached

Any ideas/suggestions are welcome

Best Regards

I have got a basic question with regards to the boundary conditions of a FEA model. It's a simple made of rectangular beams frame, supported with wheels bolted on to each of the four corners. I am looking at stresses and displacements in the frame.

I would like to get your opinion on the boundary conditions one would use in such set-up. I have blocked all displacements (x,y & z) on one of the supporting corners and blocked only the vertical displacements (z)on the other three corners. With regards to rotations, I have kept the model unconstrained for rotations around all three axes. A crude sketch of the frame is attached

Any ideas/suggestions are welcome

Best Regards

## RE: FEA Boundary Conditions

"Hoffen wir mal, dass alles gut geht !"

General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

## RE: FEA Boundary Conditions

If your frame is unconstrained in X and Y in the real world, there is no way to impose side loads on it. Don't analyze for them.

Is your frame symmetric about X and Y. Analyze one quarter of it. I think this will let you constrain everything for vertical loads (only).

--

JHG

## RE: FEA Boundary Conditions

personally not a fan of symmetric models ... which also requires symmetric loads.

"Hoffen wir mal, dass alles gut geht !"

General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

## RE: FEA Boundary Conditions

If your unspecified FEA software can handle this, fine (but theoretically incorrect). If it cannot, then you need

eitherto apply a ZZ constraint to a nodeorto apply an appropriately located X or Y constraint to one of your three Z=0 nodes._{ —————————————————————————————————}^{Engineering mathematician/analyst. See my profile for more details.}## RE: FEA Boundary Conditions

## RE: FEA Boundary Conditions

yes, you need another X or Y to create a couple about Z. Check that the X and Y constraint forces are zero and the Z constraints add to your applied load.

"Hoffen wir mal, dass alles gut geht !"

General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

## RE: FEA Boundary Conditions

## RE: FEA Boundary Conditions

This overconstraining is probably why rb1957 was initially "beguiled by the 6 constraints". I was briefly similarly beguiled.

_{ —————————————————————————————————}^{Engineering mathematician/analyst. See my profile for more details.}## RE: FEA Boundary Conditions

But still,

~~remembering this is the student forum,~~it is a good exercise to run with a variety of Z stiffness (from infinite (hard constraint) to 1E4 or less) to see the difference.I don't think it matters much on this simple frame, but it is an opportunity to learn and to stick something in the ol' toolbox.

"Hoffen wir mal, dass alles gut geht !"

General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

## RE: FEA Boundary Conditions

General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.