Mesh in Hexpress of Numeca
 

Hi, i must generate a mesh in Hexpress of Numeca, but I have some diffucult because it is the first time that I use Hexpress. I'm working with a geometry created with a scanner 3D. I can send also the geometry in PARASOLID.

Well can you give more information about your case and your geometry ?
What kind of issues are you experiencing ?

The best to get used to Hexpress is to do the tutorials, which are quite simple and provide you with the basics.

Hi, i send you an image of the geometry.I haven't experience in Hexpress because i always use Gambit, but for this case i must use hexpress. I must create a mesh.Can you send me some tutorials or can you gime me a help?i have the problems ti define the domain!!!If you want i can send the geometry in parasolid for email.

Well first of all you might want to unite your three bodies. Then in the CAD menu, click on "export", you will be asked to define curves and surface resolution you want.
Once your domain is created you have to go through the steps that are shown in that picture :

http://www.numeca.be/uploads/pics/sp...m_small_01.gif

Initial Mesh generation
Adaptation to the geometry
Snapping to the geometry
Optimization
Viscous layer insertion.

It is very intuitive.

For tutorials you should check numeca's website.

when i do the check of domain, the check in invalid. The domain is formed by vertex. How can i resolve this problem?

I don't know, maybe you should decrease the size of the minimum captured vertex. Switch to the default values maybe.

I think Rombzh is right.
you may solve this problem by reducing the size of minimum length captured. as a rough estimate, you can decrease the default value by divide it to 100.

I don't resolve my problem! Can you help me? I can send the geometry in Parasolid. I'm working with this geometry in fluent but i have some problem to model the porous media. I want to use Numeca. I alway used Gambit to generate mesh. I have few days to di this.

Can you provide us a screenshot of the input you prescribe when trying to export the domain ?
I am sorry I really do not have time to take a look at your geometry.

Maybe you simply should contact Numeca's tech support.

can you export your parasolid model?
did you get a ".dom" file from parasolid model?
can you tell in which step of meshing you face with error?
i think you had better to explain us what you have done in HEXPRESS step by step.

I import the file parasolid in Hexpress. My geometry is divided in three volume: inlet,porous media and outlet.
I first of all export the volume if inlet and work on the it. I merge the faces. The domain check is valid. Then i do the "initial mesh". The problem is "adapt the geoemtry", hexpress don't adapt the mesh to geometry.

How have you defined your boundary conditions ?
In the adaptation menu, what are your inputs ?

When you say that the adaptation step is not done by Hexpress, what is actually happening ? Any error messages ?

The boundary condition for the entire model are:
velocity inlet;
outflow;
wall;
Besides i insert inlet and outlet in the porous media.

In the adaption menu i don't insert nothing input.What do I insert?

You need to specify the level of refinements you want for each wall boundary condition.

I specified the level of refinement but the mesh don't adapt to the geometry.

What does that mean ? you need to be more specific. Can you attach a picture of your adaptation menu, with the different boundary condition settings (level of refinement, target cell size, curvature, Aspect ratio) ?

I don't knows values that i must set in the mirror!!!Help me

Sorry the imeage is here

dear jack;
"adapt the geometry" is probably the most time consuming part of meshing in this method. so you should be patient enough. the following tips concerning to your case come to my mind. please check them and report the ruslts:
1- when exporting the body to domain, in "faceting settings" reduce the "maximum length" value. you can ,as a rough estimate, devide its default value by 100.
2- increase the x,y,z initial meshes as much as possible. sometimes this error is due to improper size of elements. so try different elemet numbers in x,y and z directions.it may be time consuming.
3- check your solid model. maybe you have some discontinuities inside your model. or you may have some sharp faces or very low angles which do not allow the meshes to attach to your boundaries. Hex meshes are more sensitive than Tet meshes to sharp faces and low angles of geometries.
if you can mesh your model in Gambit, that may be because of Gambit Tet meshes which are more flexible. try to make your model a rather simpler if 1 and 2 tips does not help.
regards

I want to make in hexpress because fluent don't resolve exactly the porous media. It's a diffult geometry for the first time that i use hexpress. Who do you help me to do mesh?My contact msn is: jackr84@hotmail.it

I have determinated my problem. I post a figure in that i show the problem. How can i eliminate this surface. For this motive i don't create the mesh.

You seem to have overlapping surfaces, in that case I think you need to fix the CAD first, as Hexpress won't be helpful for this matter.

I resolved the problem. Now I do the mesh of two volumes, but for the third volume when I try to do the optimization phase the process failed.I try to modificy the optimization level but the optimization don't finish.

Check in the log file what is happening. It should point an issue with a specific edge or face.

There are concave cells and negative cells. How can i reduce them?

check where exactly this is happening and create local refinements maybe.

I imported the mesh in Numeca,but when i set the boundary condition of inlet there is a problem:

Erros:Can't read "ith_bc(phys_var;min_value;StaticPressureExtrapola ted,24,1,6)":no such variable"

hi "jackr84".......first of all check the boundary conditions-in HEXPRESS refinement is done on only on those surfaces which are tagged as WALL. Check the things out like geometry is clean & valid....if not try to clean in 3matic(no need of it, as you are saying that u were having x_t file; in hexpress itself u can clean), define proper taget cell size-TCS (TCS=initial_size/2^(refinement_level)), & hexpress has an built in algorithm which has success rate of 99.98% removing concave cells through default optimization step.

Hexpress
 

Hi,

I'm new with hexpress. Are there any tutorials?

Thanks in advance

Hexpress view 41
 

Hello Everyone,
Am facing some difficulty with the configuration file (.conf)in
HEXPRESS VIEW41. Is there any one who is using the same software.
Being a beginner i couldn't get the solution for my problem :(:confused:.
Please do reply.

Regards,
DJ SANTOSH KIRAN.

Dear DJ Santosh Kiran,

Maybe you can describe your problem such that people with experience in HEXPRESS/View can help you?

Best regards,
Colinda.

Dear friends,

I am trying to carry out a grid independence study with 3 different mesh size using HEXPRESS. I want to set the grid refinement ratio(r) to 1.4.

My question is; should we apply this value(r) only for Initial Mesh step at the beginning and keep the other parameters same? However, when i applied this refinement ratio for only in Initial Mesh step, the difference between medium and fine grid counts is very small, i.e medium count is 2M and fine is 2.7M. Is it also necessary to change the refinement values ​​on the surfaces and curves? How can i ensure that the grid refinement ratio will strongly enforced in the x, y, z direction as we move from the coarse to the medium, or from medium to fine? Can you help me if you have any knowledge or experience about this issue?

Any help will be greatly appreciated.

Grid independence study
 

Hey Lazarus

As you might have read in the paper from Tokyo Workshop 2015 NUMECA recommends to perform grid dependence studies based on changing the initial cell sizes. This allows to refine the whole fluid volume and not only the areas right next to the solid. Hexpress defines the initial mesh as an integer number of divisions in each direction. That is why the refinement ratio 1.25 is ideal, because it allows to keep integer number of cells (6, 8, 10 for example).

In practice:
- Medium mesh: the initial mesh needs to have a number of cells in each direction that is multiple of 4. For example, 20 cells in X direction, 8 cells in Y direction, 8 cells in Z direction. Try to keep the initial mesh as isotropic as possible, the default proposed by Hexpress is isotropic.
- N coarse = 3/4*N medium, N fine = 5/4*N medium, where N is the initial number of cells in X, Y and Z directions. If you need more meshes just continue with the same ratio.
- The diffusion (Adapt to geometry > Global > Advanced > Refinement diffusion) needs to be 1 for coarse, 2 for medium and 3 for fine. This diffusion is a measure of how far from the solid surface the refinement propagates in number of initial cells. The reason to change the diffusion is to ensure the distance covered by refinement is the same in all meshes.
- All surface refinements need to be defined with a defined "Max nb of refinements" and "target cell size" = (0,0,0) --> this way the different initial meshes will lead to different mesh sizes.

Thanks

Dear guys;

I have some problems in using hexpress/hybrid for generating mesh inside a geometry with interior zero-thickness walls. could you please help me in this regard?

Bests,