Learning Forum

[przemyslaw.ochyra]

Hi everyone,

I'm trying to better understand the differences between the three Interface Treatment options in Ansys Workbench contact settings:

• Add Offset
• Offset Only
• Offset Only, Ignore Initial Status

I’ve read the documentation, but I’d really appreciate a clear explanation — especially in the context of a practical example.

Let’s say I have a shaft press-fitted into a hole, and due to meshing imperfections, the shaft surface has a small local indentation of 0.01 mm. The overall geometry shows a penetration of 0.05 mm, and I apply an offset of 0.02 mm.

Here’s how I currently understand the behavior of each option:

• Add Offset: Adds the offset to the existing geometry. So in most areas, I get 0.07 mm penetration, and in the indented region, 0.06 mm.
• Offset Only: Replaces the geometric condition with the offset. So I get 0.02 mm penetration in most areas, and 0.01 mm in the indented region.
• Offset Only, Ignore Initial Status: Ignores the geometry entirely and applies a uniform 0.02 mm penetration everywhere — even in the indented region.

Is this interpretation correct?
Also, in which situations would you recommend using each option — especially for modeling interference fits with imperfect meshes?

Thanks in advance for your help!

Best regards,
Przemysław

[Himanshu]

Practical Use-Cases:

Option	When to Use
Add Offset	When you want to account for both real geometric penetrations and additional offset due to modeling assumptions (e.g., to ensure contact). Ideal if you trust your mesh but want to add a safety margin to contact penetrations.
Offset Only	Use when you want to replace unreliable or noisy geometric penetrations (e.g., due to mesh imperfections) with a controlled offset, but still respect local variations. Good for interference fits where you suspect local imperfections but want a consistent "offset" contact initiation.
Offset Only, Ignore Initial Status	Use when geometry penetrations are very unreliable or irrelevant, and you want a clean, uniform initial penetration. Useful for idealized interference fits or when mesh artifacts distort the contact surfaces heavily.

 

[Himanshu]

Summary for your shaft press-fit with imperfect mesh:

• If you trust the geometry but want to ensure contact despite mesh imperfections, Add Offset might be best.

• If your mesh imperfections create unrealistic penetration spikes, and you want a controlled uniform penetration while still respecting local shape, Offset Only is a safer bet.

• If mesh quality is poor or you want to enforce a strict, uniform interference fit ignoring local irregularities, Offset Only, Ignore Initial Status gives you a clean slate.