[Vidit Sharma]

Hi All..

Sir,
I am trying to rotate a 2D box or a 2D cup structure in Fluent using smoothing and remeshing. I am using tri mesh and as mentioned in Fluent Manual I am using smoothing and remeshing and also set the remeshing parameters from mesh info tab given in the remeshing menu. But the problem is that when i start simulation and it goes to first time step Fluent display "Updating mesh at time level N..." and here it stops and it happened alot of time and even waiting after a whole day it didnt worked. I also tried time step size from 0.01 to 0.000001 but it still show this problem.

Can you plz help in this case?

Thank u in advance

[skyblue_mech]

Hi Enry,
I am interested about the UDF since I have started to work on my moving mesh problem for a project this semester.
I shall be glad if you share the same so I can have some idea how to start with and how to write the UDF in my case.

Debanjan Deep

[skyblue_mech]

Originally Posted by enry

I solved the problem. In case somebody is interested:
-UDF for the moving surface
-DEFORMING with re-meshing for fluid around moving surface
-DEFORMING with re-meshing for surface that is moving with fluid (i.e. re-meshing for surface that will be deformed because of moving surface)
-spring constant factor 0
-boundary node relaxation 1
-if there is a boundary layer, define a fluid-zone for the boundary layer, mesh it with map scheme, and in FLUENT define that fluid-zone as DEFORMING without re-meshing
-enable spring-on-all-shapes through the following command line: define models dynamic-mesh-controls smoothing-parameter spring-on-all-shapes yes

Bye.

Hi Enry,
I am interested about the UDF since I have started to work on my moving mesh problem for a project this semester.
I shall be glad if you share the same so I can have some idea how to start with and how to write the UDF in my case.

Debanjan Deep

[samcfd]

Hi,

I'm carrying out a 2D pitching airfoil simulation using dynamic meshing with a "O" Grid. The dynamic conditions i have given were
1) airfoil - rigid body with UDF with pitching over X=0.25
2)interior - deforming with the min and max length scale from zone scale info
3) fluid -deforming with the min and max length scale from zone scale info.

The spring constant i gave was 0.001 and
convergence tolerance 0.0001
No of iterations 150.

The time step tat i used is 0.001.

After running the iterations and after about 500 time steps i'm getting the following error

negative volume detected
dynamic mesh update failed.
i have worked around with the spring constant and also with the time step nothing worked.
could someone help me out rectify this issue..
thanks in advance,
sam

[meb]

Hello,
we can support your study with RBF Morph. I can help you with a test on your mesh if you want.

Originally Posted by samcfd

Hi,

I'm carrying out a 2D pitching airfoil simulation using dynamic meshing with a "O" Grid. The dynamic conditions i have given were
1) airfoil - rigid body with UDF with pitching over X=0.25
2)interior - deforming with the min and max length scale from zone scale info
3) fluid -deforming with the min and max length scale from zone scale info.

The spring constant i gave was 0.001 and
convergence tolerance 0.0001
No of iterations 150.

The time step tat i used is 0.001.

After running the iterations and after about 500 time steps i'm getting the following error

negative volume detected
dynamic mesh update failed.
i have worked around with the spring constant and also with the time step nothing worked.
could someone help me out rectify this issue..
thanks in advance,
sam

[samcfd]

Dear Meb,

yes i can support...what input parameters do u require.

Originally Posted by meb

Hello,
we can support your study with RBF Morph. I can help you with a test on your mesh if you want.

[meb]

If you can share the mesh and movement info (i.e. movement type and desired range), we can do the test and publish here what we get using RBF Morph.

Best.

Originally Posted by samcfd

Dear Meb,

yes i can support...what input parameters do u require.

[samcfd]

Could u pls send me ur maild id

Originally Posted by meb

If you can share the mesh and movement info (i.e. movement type and desired range), we can do the test and publish here what we get using RBF Morph.

Best.

[meb]

Sorry for the delay (so many ongoing activities!).
You can do the job using RBF Morph. We did it on a 3d mesh. 2d currently is not a standard feature of RBF Morph; we can deliver custom builds that support it.

[PNSK]

I think
1) Minimum length scale : 0.4 times average length scale
2) Maximum length scale: 1.4 time average length scale

i like to know how to rectify " Negative cell volume" error

[PNSK]

Thanks for your answer mrestrepo30 because of it i solved my problem

[mjthomp3]

Originally Posted by mahzironrazak

Hi All

I am trying to simulate 3D flapping wing using fluent and i keep getting negative volume when i run the mesh motion. I used smoothing and remeshing. I have reduce the time step and still it didnt work. I also changed the remeshing parameters but no go. I read that for dynamic mesh "the translation in one time step should not be more than half the cell size adjacent to the moving boundary". what does that means? How can i get the cell size adjacent to the moving boundary? By the way how do i determine the correct value for dynamic mesh parameters :


1) Minimum length scale
2) Maximum length scale
3) Adjacent zone cell height

I used the data from mesh scale info (button)

Will increasing the density of the grid reduces the possibility of getting negative volume.

cheers

hey what dynamic mesh method are you using??
I am also doing the same but am curious on the method your using.....

[mjthomp3]

Originally Posted by meb

Sorry for the delay (so many ongoing activities!).
You can do the job using RBF Morph. We did it on a 3d mesh. 2d currently is not a standard feature of RBF Morph; we can deliver custom builds that support it.

really neat video? Can you tell the steps to do it?
I was wondering, I have a 3D bumblbee MAV drone wing that i am doing research on. I was wondering how could I use the software you are mentioning in order to make it flap?

[mohamed samy]

I got the same problem here did u found a solution ?!

[meisam-mech]

that seems intersting

[meisam-mech]

Originally Posted by almostafa67

hi dear all...
i have this problem as you;i changed time step from 0.0001 to 0.00001 but again this message(update-dynamic-mesh failed. negative cell volume detected.) showed up,could u help me out plz?
thank u in advance for any help provided

Try chaning spring factor ( lower than defualt). I found that useful

[f.barikloo]

hello. how can I see domain mesh motion along with the body motion? consider a body in a domain, I have hooked the UDF to body, I see the body motion but I could not see the domain motion. what is the correct setting for viewing zone motion with body motion?
thanks a lot.

[arunraj]

Hello everyone,
I have some doubt regarding simulation using Fluent 13. Previously I used Fluent 16 to simulate the flapping wing. I got correct results by using Fluent 16. Then my supervisor asked to simulate the further simulations in Fluent 13 which is installed in the server. So I tried to simulate using the server. But the real problem is I am not able to get the same Cl AND Cd pattern with Fluent 13 for the same settings. I dont understand the error at all. I am loading the same mesh file (created using WORKBENCH 16) and following the exact same steps in FLUENT 13 which I followed in FLUENT 16 but I am not able to get the results. The trend of Cl and Cd curve is completely different. So could you tell what could be the reason. I used the following settings in both FLUENT 13 and 16. But in FLUENT 13, I am not getting the same result for same mesh file

Pressure based, Transient, absolute and planar
Laminar, air - 1.225 kg/m3 and viscosity 2.45e-4
Boundary condition: pressure outlet
Smoothing: spring based, 0. Boundary layer relaxation 1, convergence 0.0001, iterations: 10000
PISO scheme: skewness correction-1, neighbor correction-1, Lease square cell based, standard , first order upwind, first order implicit, under-relaxation, pressure:0.3, momentum: 0.5.

One more thing, in the global dynamic mesh settings , re-meshing tab the default max cell skewness value is 0.7 in case of Fluent 16 and when I use Fluent 13 for the same mesh file it shows default max cell skewness value is 0.66. I am little curious about this as I am using global settings for my deforming domain.

It would be a great help if you let me know the mistake or changes in settings.

[ravikr]

Hello Every1,


I want to simulate oscillating (sinnosodially) LPT blade in fluent for 10 degree amplitude. I came to know of dynamic meshing in the fluent. So inititially, just to learn the dynamic meshing, i simulate some 3D oblect with fully structred grid (Single Zone), but i was unable to give it motion. every time i got an error "-ve cell volume" because of very small distance near the surface (y plus=1) . After a lot of research on cfd online thread i came to know that remeshing works better for tri/tetra mesh (i think !). and to use multiple zone mesh.


So now I am simulating an elliptical blade with two mesh zones (Structre and tetra as shown in the figure (Mesh). the inner elliptical structured zone, i am moving it with the blade. But when i see display mesh motion only tetra element at interface of two mesh are streching rest of tetra zone is not adjusting itself although i made it deforming zone and after some time i get "-ve cell volume" error. i think remeshing is not happening in tetra zone.


I have gone through all the relevent thread and videos but they mostly on 2D geometry.


I am new to dynamic meshing and I have a few questions:

1. Is remeshing possible for 3D hybrid mesh ?

2. If yes then what remeshing method (cell, face, cutcell, region, 2.5D cylinder) would work for 3D hybrid mesh ?

3. What is the Dynamic mesh setting required?


4. What mesh zones setting required.

5. IS something wrong with the mesh parameters?


All the relevent images are attached. If any one require files/data related to the project i have no issue sharing it.


Thanks in advance

[arunraj]

Dear friend,
First of all, make sure you gave the UDF properly using euler's angle. Use the below link for sample UDF.

CG Motion Absolute coordinates

1. Is remeshing possible for 3D hybrid mesh ?
Yes, it is possible.

2. If yes then what remeshing method (cell, face, cutcell, region, 2.5D cylinder) would work for 3D hybrid mesh ?
you can use smoothing+remeshing or remeshing alone. cell and face remeshing. Spring based smoothing is easy to use.

3. Use spring factor 0. Minimum length scale = 0.001 *minimum mesh size. Maximum length scale = 0.001 *minimum mesh size. Skewness = 0.6 (usually). 0.001 is a typical value. you can further reduce or increase depending on your need. Use trial and error method.

4. Rigid body for blade.