Contact Penetration Problem

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  • Last Post 22 May 2020
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mskr posted this 20 May 2020

I have a valve of elastic material and testing the closing behavior by applying a force like this:

I have set up a contact on the two faces where the leaflets are expected to touch:

This contact has a large pinball radius, but I testet many sizes as well as automatic. I also tested manual Penetration Tolerance and different Update Stiffness frequencies, but the penetration problem persists.

In my mesh, I made sure to have more than 1 element through the thickness, while keeping it coarse for quicker testing:

Simulating until 50 ms with time step 10 ms, I notice that the leaflets are overlapping/penetrating:

Gif: https://imgur.com/a/RyTLUik

It looks like there is no response to collision happening at all, which could mean either the collision is not detected or it is not deemed necessary to resolve it. Not sure what exactly is happening here.

I already tried finer mesh and smaller time steps, but it did not seem to help, at least to the extent of my testing, which was bound by time.

After all this trial and error I am interested in real understanding. What could be an approach to fix this?

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Aniket posted this 20 May 2020

Just be sure, can you insert a contact tool in the solution and evaluate for penetration results?

Also, what is the result scale that is being used here?

Are there any other BCs being applied on these two surfaces?

Just two cents: more than one element in the thickness should not affect the contact detection (meaning you can try with a coarser mesh), you can try to split the problem in two load steps, first load step will bring them near each other quickly, and when they have a minimal gap between them, use very small timesteps, also pinball radius seems a bit excessive to me.

-Aniket

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mskr posted this 20 May 2020

Thanks for the suggestions.

The contact tool reports zero penetration and I am currently trying to understand this by reading the users guide.

What do you mean with result scale? My geometry is fairly small, the mesh element sizing is 0.5 mm.

As BCs, there is only the shown fixed support on the outer faces and the force acting towards negative x.

I will try your other suggestions and report back.

 

EDIT: After reading the guide, I just have to accept, that there is no penetration detected. I think there is no troubleshooting that applies to my problem. 

I have already reduced time step, so that the thin leavelet overlap seems to be resolved, at least just by looking at the total deformation animation, but I will double check that. 

Chinmay posted this 20 May 2020

Hi, I work with similar designs. Instead of closing, I test for locking of elastic materials. Firstly I think you should just try to solve it using auto meshing because it gives quick results and also the mesh size wont really affect the penetration. The contact and target must be properly assigned with appropriate pinball radius. The radius you used is too big considering the overall size of the part. Also I used static structural to find all the results. If you could share the ansys file, maybe I will be able to help easily.

Chinmay

mskr posted this 20 May 2020

Thanks Chinmay, I uploaded my workbench project. I have now set pinball radius to program controlled and contact type to frictionless. There is still the same penetration happening. Eager to see what you come up with.

https://drive.google.com/file/d/1tadkzJG-kYO6kiq3l4542Z69CPmDgIv_/view?usp=sharing

I also did a static analysis now, as you suggested. It solved almost instantly which is great for trying out things (in transient I had to wait at least 20 minutes per solve). The result looks as it should be:

Large deflection must be on to avoid an error.

Pinball radius had to be set manually to 10 mm to have both contact faces included (partly is enough), to avoid an error:

This is with program controlled time stepping. I think, in transient analysis, I (just) have to find the right time step size to make it work, but not sure how exactly.

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mskr posted this 20 May 2020

Here is a working case:

Contact settings:

Analysis settings:

Set force x component to function expression "-time".

Result:

Setting result deformation scale to 1:

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Aniket posted this 20 May 2020

Chinmay, good tips and even better to see users contributing! mskr, I believe the only question that is unanswered now is what I meant by the result scale, so if you click on a result on the top toolbar you can see a drop-down for deformation scale that is shown in the graphics window. If it is set to auto-scale (rather than true scale), it can be more than a true scale (exaggerated rather) and can show some weird results.

If you feel the question is answered, please mark appropriate reply as solution!

-Aniket

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mskr posted this 20 May 2020

Thanks I added the result with true scale to my post above and marked it as answer.

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Chinmay posted this 21 May 2020

Thank you Aniket for your kind words. I am new to Ansys and most people helped me here with my difficulties, I am just trying to do my part and help as much as I can. I do have a question, I have done a certified Ansys course but I still feel its insufficient for the work I do in an Industry. Can you please suggest me a course or a person which or who might help me with the same. I wish to be an expert at operating Ansys to its potential and become a Simulation Engineer. Thank you.

Chinmay

Aniket posted this 22 May 2020

Chinmay, Have you already tried the :

https://www.ansys.com/blog/engineering-simulations-course

https://confluence.cornell.edu/display/SIMULATION/ANSYS+Learning+Modules

-Aniket

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