[sortik]

I think that I somehow don't understand how automatic contact region generation works and how it should be used.



I am facing several problems.


1) I always used DM with one part that was created from several parts trought function Form new parts to create conformal mesh. Even though my model was ok (there were no overlapping faces, no clearances no babd edges/faces) sometimes meshing module created contacts that made no sense (see image contact.jpg). There is no point in this contact to be created. I learned that this could indicade error in the model (either there is a clearance or overlapping or just a bad face). But I am 100% sure there is no problem.

Why is the contact created in the first place? Can I just delete the contact a continue with the simulation?


2) I tried to switch to SCDM but I have so many troubles with it. It looks like the SCDM isn't so precise and creating a model from scratch in SCDM produces so many bad edges, overlaping faces and clearances that a lot of time I am not even able to create a mesh because of bad edges that can't be removed. For example I have one stp model - If i import it to SCDM set shared topolgy to merge and open it in mesh module (CFX) I get a lot of automatic contact regions even though the value is set to 0.000001m.
If I open the same model in DM and create a form new part I get like 75% less automatic contact regions compared to DM.


I just don't get it
Could you please give me any advice? thank you

[Gweher]

Hi Sortik,

I suppose that you use "automatic contact" creation which is basically searching for contact pairs within a given tolerance. You can perfectly delete the contact pair and insert manual one if needed.

If you have several parts where you need conformal mesh at part interface you can simply select all the parts in DM > rmb > form new part (this will regroup them under the same part and impose conformal mesh during the meshing procedure and without requiring contact definition). In SC you need to select the bodies > form new component. Then under component properties select "share".

Have fun

[sortik]

Hi Gweher,


thank you for your fast response. Yes I am aware of that, but why is the automatic contact created in the first place when the topology is shared and the tolerance is really small? Can I consider it as a badly created contact?
I have no gaps between faces and still there are automaticaly created contacts and I am worried that is because my geomery has some errors even though I checked everything in SCDM.

[Gweher]

Hi Sortik,



It's a bit difficult to say without having a look at the model. Did you also check in SC (with the repair tools) that you didn't have any overlapping faces for instance ?

[Svetlana]

Contacts are created between bodies from different parts. If your bodies are all in one part, then why do you need a contact region?

[Gweher]

You're right, if its in the same part (multibody part) then you don't need contacts as they are imposed directly through conformal meshing at the parts interfaces.



Just need to be careful with SC as when you form a multibody part (rbm > form component) you need to change the behavior under properties > share.

[Svetlana]

A bit confused here, what is RBM and SC?

[Gweher]

RMB = right mouse button (typo with RBM)


SC = Spaceclaim (also a geometry editor from Ansys but a direct modeller compared to DesignModeller which is more a traditional history based CAD software).

[MIDHUN@CFD]

use form new part to create confornmal meshes if not dont use FNP .. with form new part there wont be contact regions. If your namings of bodies are same and you use FNM then in fluent all these bodies come as single domain.

[sortik]

thanks for your help. I didn't need contacts, however when I formed new part there were always some contacts created. I checked the model a few times and indeed found some errors like extra edges and overlapping faces and also som clearances. It is a bit crazy editing large assemblies in SC since somehow this kind of "errors" are created by SC without you knowing about it.

When I form new part and there is some contacts in mesher I know for sure my model has errors and also there is a high chance that there will be problem with a mesh

[Gweher]

When you form a part in Spaceclaim (i.e. component) you need to change the properties to "share" if you want to have the same behavior as in Design modeller with "form new part":



Have fun

[Manel]

Originally Posted by Gweher

You're right, if its in the same part (multibody part) then you don't need contacts as they are imposed directly through conformal meshing at the parts interfaces.



Just need to be careful with SC as when you form a multibody part (rbm > form component) you need to change the behavior under properties > share.

Hi Gweher,

Can you please tell me how can i change behaviour to share by using ansys design modeler and Ansys meshing ?

thanks you,

Best regards ,
Manel

[Manel]

Hi Gweher,

Can you please tell me how can i change behaviour to share by using Ansys Design modeler and Ansys meshing?

thanks you,

Best regards ,
Manel

[Khan_CFD]

Dear Gweher,

I have a doubt on similar lines.

When we create a single part from say 3 parts (and there are 3 bodies, say cuboids present side by side), the contact regions do not appear in the fluent boundary conditions, instead a 'wall' appears between two bodies. Whereas, when we allow 3 parts to remain, 2 contact regions are created. However, we can give the boundary conditions at walls or interface contact regions in both the cases.

The questions is, what is difference between creating a single part and letting different parts be as they are...?

Thanks.

[zaqureshi]

hello mr. khan,

i am facing the same issue of contact regions appearing in a single part - multibody geometry. the contact regions are not supposed to arise due to forming of one part. did you find a solution to this problem?

can you please let me know about it.

best regards,

zahid

[Khan_CFD]

Originally Posted by zaqureshi

hello mr. khan,

i am facing the same issue of contact regions appearing in a single part - multibody geometry. the contact regions are not supposed to arise due to forming of one part. did you find a solution to this problem?

can you please let me know about it.

best regards,

zahid

Hi,


My problem was a bit different than yours. My question was about difference between multi part body and single part body. I did not have the problem of contact regions appearing in single part body.


However, I guess you have not merged various parts into a single part in design modeler geometry. If you did so most likely that problem should not happen.


I came to know that single part helps in making conformal mesh between various body parts.


Regards.