A Simple Adjustment to Fix a Contact Convergence Problem in Ansys Mechanical

By: Ted Harris
– June 4, 2020
Categories:

As I write this from home during the Covid-19 crisis, I want to assure you that PADT is conscious of many others working from home while using Ansys software as well.  We’re trying to help with those who may be struggling with certain types of models.  In this posting, I’ll talk about a contact convergence problem in Ansys Mechanical.  I’ll discuss steps we can take to identify the problem and overcome it, as well as a simple setting to make which dramatically helped in this case. 

The geometry in use here is a fairly simple assembly from an old training class.  It’s a wheel or roller held by a housing, which is in turn bolted to something to hold it in place.

A close up of a deviceDescription automatically generated

The materials used are linear properties for structural steel.  The loading consists of a bearing load representing a downward force applied by some kind of strap or belt looped over the wheel, along with displacement constraints on the back surfaces and around the bolt holes, as shown in the image below.  The flat faces on the back side have a frictionless support applied (allows in plane sliding only), while the circular faces where bolt heads and washers would be are fully constrained with fixed supports.

A close up of a logoDescription automatically generated

As is always the case in Ansys Mechanical, contact pairs are created wherever touching surfaces in the assembly are detected.  The default behavior for those contact pairs is bonded, meaning the touching surfaces can neither slide nor separate.  We will make a change to the default for the wheel on its shaft, though, changing the contact behavior from bonded to frictional.  The friction coefficient defined was 0.2.  This represents some resistance to sliding.  Unlike bonded contact in which the status of the contact pair cannot change during the analysis, frictional contact is truly nonlinear behavior, as the stiffness of the contact pair can change as deflection changes. 

This shows the basic contact settings for the frictional contact pair:

A screenshot of a cell phoneDescription automatically generated

At this point, we attempt a solve.  After a while, we get an error message stating, “An internal solution magnitude limit was exceeded,” as shown below.  What this means is that our contact elements are not working as expected, and part of our structure is trying to fly off into space.  Keep in mind in a static analysis there are no inertia effects, so an unconstrained body is truly unconstrained.

At this point, the user may be tempted to start turning multiple knobs to take care of the situation.  Typical things to adjust for contact convergence problems are adding more substeps, reducing contact stiffness, and possibly switching to the unsymmetric solver option when frictional contact is involved.  In this case, a simple adjustment is all it takes to get the solution to easily converge. 

Another thing we might do to help us is to insert a Contact Tool in the Connections branch and interrogate the initial contact status:

This shows us that our frictional contact region is actually not in initial contact but has a gap.  There are multiple techniques available for handling this situation, such as adding weak springs, running a transient solution (computationally expensive), starting with a displacement as a load and then switching to a force load, etc.  However, if we are confident that these parts actually SHOULD be initially touching but are not due to some slop in the CAD geometry, there is a very easy adjustment to handle this.

The Simple Adjustment That Gets This Model to Solve Successfully

Knowing that the parts should be initially in contact, one simple adjustment is all that is needed to close the initial gap and allow the simulation to successfully solve.  The adjustment is to set the Interface Treatment in the Contact Details for the contact region in question to Adjust to Touch:

This change automatically closes the initial gap and, in this case, allows the solution to successfully solve very quickly. 

For your models, if you are confident that parts should be in initial contact, you may also find that this adjustment is a great aid in closing gaps due to small problems in the CAD geometry.  We encourage you to test it out.

Categories

Certified Elite Channel Partner

Get Your Ansys Products & Support from the Engineers who Contribute to this Blog.

Product Development
Diamond Partner

Technical Expertise to Enable your Addictive Manufacturing Success.

PADT’s Pulse Newsletter

Keep up to date on what is going on at PADT by subscribing to our newsletter.


By submitting this form, you are consenting to receive marketing emails from: Phoenix Analysis and Design Technologies, 7755 S. Research Dr., Tempe, AZ, 85284, https://www.padtinc.com. You can revoke your consent to receive emails at any time by using the SafeUnsubscribe® link, found at the bottom of every email. Emails are serviced by Constant Contact

Share this post:

Share on twitter
Share on facebook
Share on linkedin
Share on pinterest

Upcoming Events

08/05/2022

Flagstaff Tech Tour, 2022

08/02/2022

2022 CEO Leadership Retreat

08/01/2022

2022 CEO Leadership Retreat

07/27/2022

Thermal Integrity Updates in Ansys 2022 R1 - Webinar

07/20/2022

Simulation Best Practices for the Pharmaceutical Industry - Webinar

07/14/2022

NCMS Technology Showcase: Corpus Christi Army Depot

07/13/2022

NCMS Technology Showcase: Corpus Christi Army Depot

07/13/2022

Additive & Structural Optimization Updates in Ansys 2022 R1 - Webinar

07/07/2022

Arizona AADM Conference, 2022

06/29/2022

LS-DYNA Updates & Advancements in Ansys 2022 R1 - Webinar

06/23/2022

Simulation Best Practices for Wind Turbine Design - Webinar

06/15/2022

MAPDL Updates & Advancements in Ansys 2022 R1 - Webinar

06/01/2022

Mechanical Updates in Ansys 2022 R1 - pt. 2 Webinar

05/26/2022

Modelling liquid cryogenic rocket engines in Flownex - Webinar

05/25/2022

SMR & Advanced Reactor 2022

05/25/2022

05/24/2022

SMR & Advanced Reactor 2022

05/19/2022

RAPID + tct 2022

05/19/2022

Venture Cafe Roundtable: AI & Healthcare

05/18/2022

Tucson after5 Tech Mixer: World View

05/18/2022

RAPID + tct 2022

More Info

05/18/2022

Signal & Power Integrity Updates in Ansys 2022 R1 - Webinar

05/18/2022

Simulation World 2022

05/17/2022

RAPID + tct 2022

05/11/2022

Experience Stratasys Manufacturing Virtual Event

05/04/2022

Mechanical Meshing Updates in Ansys 2022 R1 - Webinar

04/27/2022

04/22/2022

12TH ANNUAL TUCSON GOLF TOURNAMENT

04/21/2022

04/20/2022

Additional Fluids Updates in Ansys 2022 R1

04/20/2022

Experience Stratasys Tour – Tempe Arizona

04/18/2022

Experience Stratasys Tour - Flagstaff Arizona

04/14/2022

D&M West | MD&M West

04/13/2022

D&M West | MD&M West

04/13/2022

Experience Stratasys Tour - Albuquerque New Mexico

04/12/2022

D&M West | MD&M West

04/12/2022

Experience Stratasys Tour - Los Alamos New Mexico

04/12/2022

Optimizing Engineering Workflows f​​​​or Propulsion System Design

04/07/2022

Experience Stratasys Tour - Austin Texas

04/07/2022

37th Space Symposium - Arizona Space Industry

04/06/2022

Transforming Digital Engineering with Ansys Discovery 2022 R1

04/06/2022

37th Space Symposium - Arizona Space Industry

04/05/2022

37th Space Symposium - Arizona Space Industry

04/04/2022

37th Space Symposium - Arizona Space Industry

03/30/2022

Simulation Best Practices for Vehicle Engineering - Webinar

03/23/2022

03/23/2022

High & Low Frequency Electromagnetics Updates in Ansys 2022 R1

02/24/2022

Arizona Technology Council After 5 Tech Mixer "Pandemic Pivot Pizza Pa

02/23/2022

SciTech Festival: Spend an Hour with 3D Printing Experts

02/11/2022

Webinar: Mechanical overview for Ansys 2022 R1

More Info

02/09/2022

Webinar: Product Development 101 (FAKE)

02/08/2022

Webinar: Navigating the Additive Landscape

01/27/2022

Arizona Technology Council 1st Quarter VIP Tech Mixer

More Info

01/26/2022

Simulation Best Practices for Gas Turbine Design & Development - Webin

More Info

01/19/2022

Arizona Photonics Days

More Info

11/04/2021

ExperienceIT, New Mexico

More Info

11/03/2021

Additive Manufacturing & Structural Optimization in Ansys 2021 R2 - We

More Info

11/03/2021

Optics Valley Technical Series: The Future of Simulation in the Optics

More Info

11/02/2021

SBIR Liftoff AZTC Virtual Breakfast Series

More Info

10/10/2021

Stratasys Mobile Truck Stop - Tucson Arizona

More Info

Search in PADT site

Contact Us

Most of our customers receive their support over the phone or via email. Customers who are close by can also set up a face-to-face appointment with one of our engineers.

For most locations, simply contact us: