[TSC]

Hello all,

I am trying to simulate a boat (2 DOVs) with flat water conditions. Therefore I use the DFBI Rot+Trans Model in combination with a DFBI Morpher.
First I generate two blocks, one around the ship, the other reflects the computational domain. An interface connects both blocks.
Now the block around the ship uses the DFBI Rot+Trans model, as the computaional domain gets the DFBI Morpher. After the release time ends and ramping begins I get the error:
"Warning: 5 cells in region Subtract have zero or negative volume. This may be due to an invalid imported mesh or to errors initializing an interface. Repair the mesh before proceeding."
This means the inner block (ship) starts to move while the outer block (domain) is fixed and there are intersection resulting zero volume cells (pic: http://s7.directupload.net/images/130501/lnhfjrht.png).

Why both blocks aren't connected? I initialized the interface before running and check the mesh for any errors. Maybe the resulting moments are too big for the DFBI Morpher?

[abdullahkarimi]

Make sure that you choose 'floating' method for Morpher for the interface boundary which is not moving.
I was getting this problem and after using 'floating', the problem got resolved.

[lyly0309]

Originally Posted by abdullahkarimi

Make sure that you choose 'floating' method for Morpher for the interface boundary which is not moving.
I was getting this problem and after using 'floating', the problem got resolved.

You said using "floating" for the static interface boundary, but in fact when these two DFBI modules combined, the interface boundary should move as the DFBI Rot and Trans moves. So do you know what kind of morphing boundary should be set for these moving interface boundaries ? Thank you very much!

[falak]

Dear I have a cylinder when i apply DFBI translation and rot on this my whole domain starts moving. Do I need to apply morphing ?

[ggulgulia]

Hello TSC,

The issue might be probably due to a local cell set becoming invalid in addition to what you mentioned. This issue is majorly due to cell quality becoming progressively poor as the morpher proceeds to deform the domain on interest. This is the same reason morpher is not recommended for large displacements.

Secondly, you might want to make sure that the displacement in one time step should not be greater than the smallest cell size anywhere in the domain. Ofcourse this stems from the courant number conformality requirement in CFD.

If your displacement is large, I suggest go for overset mesh. Or else you can have a macro run the simulation which will remesh the computational domain once the cell quality due to morpher displacement falls below desired limit.

[lyly0309]

Originally Posted by ggulgulia

Hello TSC,

The issue might be probably due to a local cell set becoming invalid in addition to what you mentioned. This issue is majorly due to cell quality becoming progressively poor as the morpher proceeds to deform the domain on interest. This is the same reason morpher is not recommended for large displacements.

Secondly, you might want to make sure that the displacement in one time step should not be greater than the smallest cell size anywhere in the domain. Ofcourse this stems from the courant number conformality requirement in CFD.

If your displacement is large, I suggest go for overset mesh. Or else you can have a macro run the simulation which will remesh the computational domain once the cell quality due to morpher displacement falls below desired limit.

Dear ggulgulia :

You said that we can remesh the computational domain. But when the domain are remeshed , the domain also returns to the original state. That is to say displacement returns to zero again. Do you mean that there is a another method to remesh domain while keep the morpher displacement unchanged? And How to remesh the domain to improve the mesh quality? Thank You !

[Frikha]

Hi , ihave the same problem does any one has a solutioN??

"1747 cells in region Domaine fluide supérieur have zero or negative volume. This may be due to an invalid imported mesh or to errors initializing an interface. Repair the mesh before proceeding."

[me3840]

The solution to this issue is very case-dependent. You will not get a "click this button and it works" answer.

This thread is already 4 years old. Considering how different the issues are between your case and the original for this thread, please make a new one and describe your problem in detail.

[Frikha]

Originally Posted by me3840

The solution to this issue is very case-dependent. You will not get a "click this button and it works" answer.

This thread is already 4 years old. Considering how different the issues are between your case and the original for this thread, please make a new one and describe your problem in detail.

for sure , i have search , my case was a mving piston inside a chamber , which is in compresion and expansion state ,and i think before posting any issues here , i need to learn often about mesh motion and morphing .

[Islam Abdelghafar]

Originally Posted by abdullahkarimi

Make sure that you choose 'floating' method for Morpher for the interface boundary which is not moving.
I was getting this problem and after using 'floating', the problem got resolved.

When you use 'Floating' it will not be rigid anymore and the boundary wall will move or morph and for sure you need it to be fixed not moving or morphing.

I have tried to set the 'Six DOF Morpher Specification' of the fixed boundary wall to 'Constraint', then choose 'Initial Boundary' for the 'Morpher Constraint Specification, however, remeshing will be needed as some point.