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Pressure Vessel Hexahedral Meshing Error

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Re: Pressure Vessel Hexahedral Meshing Error

Posted by Dharmit Thakore at March 05. 2013

Another view of Geometry

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Pressure Vessel Hexahedral Meshing Error

Posted by Dharmit Thakore at March 05. 2013

Hi,

This is my first post  pardon any ignorance on my part.

I am using CaeLinux with Salome 6.3.0.

I am trying to model a nozzle on a Pressure vessel section and meshing it but I am having errors.

To keep it simple, I modelled 4 cylinders

1. Radius 1500, Height 1500

2. Radius 1490, Height 1510

3. Radius 150, Height 1700

4. Radius 140, Height 1710

Cylinders 3 and 4 have been rotated 90 degrees and translated 750mm.

Cylinders 1 and 3 were fused (Fuse1).

Cylinders 2 and 4 were fused (Fuse2).

Fuse2 was cut from Fuse1 to get the geometry in Geometry1.png file

Plane1 was created to get edges for Submesh.

Partition1 was created from Cut1 and Plane1.

Edges from thickness of shell as well as nozzle were grouped into Group_1.

 

Meshing

Automatic Hexahedral meshing hypothesis was used with 50 equispaced elements.

Submesh with 5 equidistance elements was added.

When I press Compute, I am getting following error (Mesh2.png)

Can someone please tell me where is the mistake?

Your help is much appreciated.

Following to this I will post another thread for Stress Classification Line for ASME Section VIII Division 2 Part 5 design and how to get about getting stress values, but first problem first.

Cheers

Dharmit

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Re: Pressure Vessel Hexahedral Meshing Error

Posted by Dharmit Thakore at March 05. 2013

This is how mesh looks

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Re: Pressure Vessel Hexahedral Meshing Error

Posted by Dharmit Thakore at March 05. 2013

This is the error message

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Re: Pressure Vessel Hexahedral Meshing Error

Posted by Saint Michael at March 05. 2013

Hi Dharmit

Though the geometry is really not complex but only from a human point of view :). It's a rather complex geometry for free meshing algorithms available in SALOME.

The simplest solution in your case is to use "Pipe T-Shape" function of GEOM module (located somewhere in "New Entity" menu) to model your geometry. This function creates a shape ready for hexahedral meshing.

St.Michael

Re: Pressure Vessel Hexahedral Meshing Error

Posted by Dharmit Thakore at March 05. 2013

Hi St.Michael,

Thanks for replying to my post.

When I am trying to use PipeTShape as you described, I am getting error "Edge 1 Could not be Built".  I have attached a screenshot for the same.

Any guesses?

Cheers

Dharmit

Previously Saint Michael wrote:

Hi Dharmit

Though the geometry is really not complex but only from a human point of view :). It's a rather complex geometry for free meshing algorithms available in SALOME.

The simplest solution in your case is to use "Pipe T-Shape" function of GEOM module (located somewhere in "New Entity" menu) to model your geometry. This function creates a shape ready for hexahedral meshing.

St.Michael

 

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Re: Pressure Vessel Hexahedral Meshing Error

Posted by Saint Michael at March 06. 2013

I see this bug in 6.6.0 as well.

Even if "Pipe T-Shape" fails with your parameters, you can create a t-pipe with default parameters to learn at least how to split your tube to make it meshable with hexahedra.

St.Michael

Re: Pressure Vessel Hexahedral Meshing Error

Posted by Dharmit Thakore at March 06. 2013

Hi St Michael,

I am not able to understand your statement.  Do you mean that I should create the model by just cylinders and then try to mesh it?  I have already tried to mesh it with no success (thus my first post), if I have mis-understood your statement, I apologise for it.

As an Update to my yesterday's try, I tried to partition the mesh with planes around the smaller nozzle on four sides and one plane made from the outside surface of the nozzle cutting the tank.

When I tried to mesh it, I am getting error, but a different type of error.

Please see attached Mesh view from the inside of the tank.

Error message will be shown in next post.

Cheers

Dharmit

 

Previously Saint Michael wrote:

I see this bug in 6.6.0 as well.

Even if "Pipe T-Shape" fails with your parameters, you can create a t-pipe with default parameters to learn at least how to split your tube to make it meshable with hexahedra.

St.Michael

 

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Re: Pressure Vessel Hexahedral Meshing Error

Posted by Dharmit Thakore at March 06. 2013

This is the error message that I am getting.

As can be seen from the mesh, Salome is having trouble meshing around the cylinder to cylinder junction.

Any Ideas on how to do this type of Hexahedral meshing?

Any help would be much appreciated.

Cheers

Dharmit

Previously Dharmit Thakore wrote:

Hi St Michael,

I am not able to understand your statement.  Do you mean that I should create the model by just cylinders and then try to mesh it?  I have already tried to mesh it with no success (thus my first post), if I have mis-understood your statement, I apologise for it.

As an Update to my yesterday's try, I tried to partition the mesh with planes around the smaller nozzle on four sides and one plane made from the outside surface of the nozzle cutting the tank.

When I tried to mesh it, I am getting error, but a different type of error.

Please see attached Mesh view from the inside of the tank.

Error message will be shown in next post.

Cheers

Dharmit

 

Previously Saint Michael wrote:

I see this bug in 6.6.0 as well.

Even if "Pipe T-Shape" fails with your parameters, you can create a t-pipe with default parameters to learn at least how to split your tube to make it meshable with hexahedra.

St.Michael

 

 

Attachments

Re: Pressure Vessel Hexahedral Meshing Error

Posted by Saint Michael at March 06. 2013

Previously Dharmit Thakore wrote:

Hi St Michael,

I am not able to understand your statement.  Do you mean that I should create the model by just cylinders and then try to mesh it?  I have already tried to mesh it with no success (thus my first post), if I have mis-understood your statement, I apologise for it.

Previously Saint Michael wrote:

Even if "Pipe T-Shape" fails with your parameters, you can create a t-pipe with default parameters to learn at least how to split your tube to make it meshable with hexahedra.

 

Hi Dharmit

To be able to generate hexahedral mesh, you are to Partition your geometry into solids each being a logical box of 6 sides. You get your new portion of errors because some of solids you get after Partition are not of such kind.

So my advice is still in force. I mean that you can use "Pipe T-Shape" to understand how to Partition you geometry. Pipe T-Shape fails if you try to enter size of the pipe you want to mesh. Fine, so don't modify default values in the "Pipe T-Shape" dialog, as it should work with the default values. As soon as Pipe T-Shape" produces an OK shape, you can study it to learn how it is Partitioned so that MESH module is able to generated a hexahedral mesh on it. This makes sense because the shape you try to mesh and that created by "Pipe T-Shape" are geometrically similar.

St.Michael

Re: Pressure Vessel Hexahedral Meshing Error

Posted by Dharmit Thakore at March 08. 2013

I finally found a way to Hexa mesh a cylinder to cylinder junction.

Attached is the final mesh.

Cheers

Dharmit

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Re: Pressure Vessel Hexahedral Meshing Error

Posted by Dharmit Thakore at March 08. 2013

Another view of the mesh upclose.

In this type of meshing any size intersecting cylinder can be meshed.

I will write up how I did it sometime later as it is getting late.

Cheers

Dharmit

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Re: Pressure Vessel Hexahedral Meshing Error

Posted by Dharmit Thakore at April 16. 2013

Hi,

I am writing a report on

1. How to model Pressure Vessel with a Nozzle (Half cylinder) in Salome

2. How to partition it for meshing

3. How to mesh it with Haxahedral mesh

4. What Boundary Conditions to apply

5. Post Processing in Salome

I will post it out soon.

Thanks

Dharmit

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