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Modeling of Suspension with 1D-Elements

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Hello,

 

I want to model a suspension using 1D-Elements. CROD are used to model the rods from the chassis to the wheel carrier. They are connected to the chassis using RBE3 with dof123 constrained to allow for free rotation. The problem is with the connection to and modeling of the wheel carrier. The rods need to be able to rotate freely around the connection points to the wheel carrier as well. I know about BEAM-Elements but as far as I know they only allow for free rotation around 1 axis. ROD- elements shouldnt constrain the rotations either, but they added stiffness to the model compared to the last option, a simple RBE2 with dof 123 from the end points of the rod to the wheel center as a central node. This setup with an RBE2 with dof123 as a wheelcarrier works good in analysis, but in freeesize I randomly get the error

" *** ERROR # 153 ***
 Exactly zero pivoting encountered during Numerical Factorization;
 the model may have rigid body mode. "

 

- My question are as follows: Why dont rods work as intended? They shouldnt constrain rotation as far as i know

- Why does the rbe2 lead to that error? in analysis the flow of force makes sense and no anomalies appear, sometime the freesize even completes without any problem at all.

- do you know of any way to model freely rotatable 1D-elements aside from the options above?

 

Below is a picture of the model:

image.png.d5101e130edcd2db0fc41861a6307979.png

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Hi Pranav,

I know CROD support only tension and compression. However, since the 1D-Elements are (in theory) connected freely rotatable only forces along the rod should be transmitted. This is similar to a rod with a swivel head in real life. Im just confused as to why the CRODs as the wheel carrier (in the picture in place of the RBE2) add unnatural stiffness to the model when compared to a RBE2 with dofs123. Do CRODs constrain rotational movement while not transmitting torque - effectively "erasing" said torque?

The document linked above dind't help me understand whats up here - can you help me understand what I'm missing here?

And I've seen the post you linked above already, but sadly the suggested solution of using a ball joint from the joint tool of hypermesh doesn't work at all.

Interestingly the forces transmitted along the CRODs seem to be correct when using an RBE2 as a wheel carrier.

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Hello Prakash,

thank you for your answer!

 

The file is attached, on top of that i added the .hm in case you need it.

 

    Regarding my problem with CRODS i think i found my mistake:

I played around with the CRODs and the RBEs today and double checked the resulting forces on the rods with the manually calculated ones. Using RBE2s my results were similar to what was calculated by hand. I think my mistake was directly applying the force to the wheel carrier out of CRODs. Since the forces are applied in an angle to at least 2 of the rods, some of the force is simply translated as lateral force on a CROD and therefore not transmitted further.

0911_front_opti.out

 

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