# How to Constraint rods passing through a bushing without contacts?

I have a series of rods passing thought a wall through bushings. my interest is what happens to the objects held at the end of the cage. Its one of these things:

So you have end plates holding 4 bars and in between you have a plate with 4 bushings. As you move or apply a force the rods should slide through the bushings and create reaction displacements of the end parts. I only care about the displacements at the end parts and would like to have the rods pass through the bushings without any friction.

So far, I’ve sectioned the part of the rod that passes through the bushing and created a node set that I then attach to a reference point through a rigid constraint. The reference point is then given a boundary condition constraining the xy to 0mm and leaving Z free.

This sort of works, but the rods don’t follow the bushing holes obviously. how can I constrain the same reference point to two node sets?

I’m going to try a few things, but welcome any input.

Why don’t you want to use contacts in this analysis ? Without them you will likely have to do some tricks with rigid body constraints and MPCs.

Once I introduced contacts into any of my analyses they they take too long to solve. But no other reason really

Indeed, contacts can be quite problematic and they may increase the analysis time significantly. But they are often unavoidable and I would use them here as well. With proper local mesh refinement, the simulation shouldn’t take that long.

would you have a recommendation for size of mesh to use? the rods are like 4mm diameter. I’m currently using 0.2mm size.

hi,

if i understand correctly, you need to simplified the contact condition to avoid penalty.

are the rods made by stainless steel and the cage from plastic? if it’s true, then your assumption and simplification may reasonable.

you can use multipoint constraint equation, but it’s hard to do it manually. CalculiX GraphiX (CGX) could help much in this task.

alternatively, you can use Tied contact type by adjusting parameter values for it’s tangential movement. i has been discussed at another threads.

best,

Interesting. I totally missed this part. I’m going to go try it.

Such a mesh might be too dense. For initial calculations use rather coarse global meshes with local refinements in critical regions (with high stress gradients) and then refine when needed (following a mesh convergence study).

This is what I found for the Tie contacts:

``````> ** Constraints +++++++++++++++++++++++++++++++++++++++++++++
> **
> *Rigid body, Nset=Node_set-1, Ref node=453562, Rot node=453563
> *Tie, Name=Merged-1_to_Merged-2, Position tolerance=0.01, Adjust=No
> Internal_Selection-1_Merged-1_to_Merged-2_Slave, Internal_Selection-1_Merged-1_to_Merged-2_Master
> *Tie, Name=Merged-3_to_Merged-4, Position tolerance=0.01, Adjust=No
> Internal_Selection-1_Merged-3_to_Merged-4_Slave, Internal_Selection-1_Merged-3_to_Merged-4_Master
> *Tie, Name=Merged-5_to_Merged-6, Position tolerance=0.01, Adjust=No
> Internal_Selection-1_Merged-5_to_Merged-6_Slave, Internal_Selection-1_Merged-5_to_Merged-6_Master
> *Tie, Name=Merged-7_to_Merged-8, Position tolerance=0.01, Adjust=No
> Internal_Selection-1_Merged-7_to_Merged-8_Slave, Internal_Selection-1_Merged-7_to_Merged-8_Master
``````

It doesn’t seem to have a tangential direction to free up. I’m going to take a look at the examples.

Those are tie constraints. Xyont was talking about tied contact. It can be enabled by proper surface behavior definition:

``````*Surface interaction, name=…
*Surface behavior, pressure-overclosure=tied
slope_value
*Friction
fric_coeff, stick_slope
``````

ohhhh… ahhhh. Okay looking into this. LOL just finished tie-ing stuff up.

you define Tie constraint not Tied contact type, please look at my screenshot at these threads