## General Mechanical

#### How to model bearing with springs on a shaft

• luanhanming
Subscriber

Hello ANSYS experts,

I am working on a project regarding the deflection calculation of a shaft supported by two tapered roller bearings, and I am just trying a simple test model to figure out how to set up bearing configuration and boundary conditions in Workbench.

I have the following questions that I am struggling with for months, and I sincerely look for your inputs to guide me through the problems.

Problem Description:

Material Property of Test Shaft

Bearing Properties:

Bearing stiffess: K11=K22=5E5 N/mm

Question 1:

How to set up boundary conditions for longitudinal springs if I use them to represent bearings in Workbench? How to setup the six DOFs in remote displacement for the spring mobile end connected to the vertex on shaft?

PS: My shaft was created in a line body in Design Modular and these two bearing locations are just represented by two vertices. I want to set up each bearing in the way of ANSYS bearing connection but with preload and just two 90-degree spacing springs.

I created each spring with one end grounded and another end to the same remote point scoped to the vertex which represents the bearing location on this shaft.

Question 2: Can you explain how overall the six DOFs of the shaft rigid body are constrained in the scenario considering bearing stiffness?

PS: The bearing stiffness effect on shaft deflection is my study of interest. I don’t want to just fix both UY and UZ at the two bearing locations (plus fixing UX at one shaft end and fixing ROTX at one bearing location for static solver).

I’ve tried to set the Y direction spring’s mobile end only movable along Y axis (Only UY is free, all other DOFs are fixed and I believe that is how a longitudinal spring is supposed to work- only moves along one axis). The same applies to Z direction spring. However, the solver still says my model has been set to fully constraint rigid body motion and can’t give proper computing result for deflection.

Question 3: I wonder if ANSYS Workbench allows people to configure bearing support in the way I used?

PS: As I am interested in seeing the shaft deflection at its hangover tip and these two bearing locations, I setup a Y direction and a Z direction spring to represent a bearing’s stiffness along Y and Z axis. In this test model, the shaft is just subjected to a Y direction 1000 N force. So, I am thinking only using a Y direction spring at both of the two bearing locations is sufficient.

However, in my real project, the shaft hangover tip is also subjected to Z direction force. I don’t want to setup the model separately (Y axis spring one time and Z axis spring one time) for analyzing the Y and Z deflection impact of the forces from different direction. Can you guide me to setup my model to do both tasks at once?

Question 5: If I model the bearing supports with springs which constraint bearing’s deflection along UY and UZ instead of directly set UY=UZ=0, will the solver essentially give me warning said “you model has not enough constraints and might cause rigid body motion”?

PS: Does this warning pop-up always mean the model is not set properly and results are wrong?

Question 6: What is the length of the spring I should set? Is the length equal to 0.5*(Bearing housing bore Diameter- Shaft Diameter)?

I have read all Peter’s comments on this forum and still have no clue on my project. I also attached a link below of my ANSYS workbench project file for people to help me edit bearing setup and boundary conditions.

Best Regards,

Mito

• Erik Kostson
Ansys Employee

See if this helps (it shows how to model bearing in ansys via the bearing object which is under connections inside mechanical):
https://forum-legacy.ansys.com/discussion/comment/16022#Comment_16022

• luanhanming
Subscriber
Hi Erik, I read that before butI still don't know how to setup my model properly after reading the discussion provided. I hope someone can download my model and edit it so that it is easier for me to understand.

I had already read this discussion and nearly all the discussion regarding bearing setup on the forum including Peter's comments but still strugling with my problem. That's the reason why I summary my problem and sincerely seek for help.

Regards,

Mito
• luanhanming
Subscriber
Hello everyone,

Can anyone guide me through this problem? My study of interest is find the deflection on shaft hangover tip and deflection at the two bearing locations. I really don't know how to set up the bearings with springs and make proper bondary conditions.

I really appreciate and need your help.

Sincerely,

Mito
• peteroznewman
Subscriber

Hello Mito,

I opened your model and deleted all the objects that were not essential.  What you are left with is a Y and Z spring to ground at each bearing. That takes away 4 DOF. The X displacement and X rotation on one vertex takes away 2 more DOF to fully constrain the 6 DOF needed for a Static Solution. Ignore the warning that "Not enough constraints appear to be applied..." becuase it is not true.

• peteroznewman
Subscriber
I put a copy of my ANSYS 2021 R2 archive here at this URL:  jumpshare.com/v/zvFmQLuMjlw3xptW8atm
• Hedzer Tillema
Subscriber

Recently, SKF launched a dedicated App to model rolling bearings in Ansys Mechanical. Perhaps this could help you: https://catalog.ansys.com/product/63497ec83c6398b6fea1184a/skf-bearing