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 Andrew February 18, 2003 23:19

Difference between structured & unstructured mesh

Hello everybody

What's the difference between structured mesh and unstructred mesh? Thanks.

Andrew

 derrek February 23, 2003 22:12

Re: Difference between structured & unstructured m

Andrew:

Typically a structured mesh is comprised of hex (brick)elements (quads in 2D) that follow a unifrom pattern. An unstructured mesh does not follow a unifrom pattern, usually comprised of tet elements (tris in 2D).

derrek

 Robin February 24, 2003 10:39

Re: Difference between structured & unstructured m

Hi Andrew,

A single block structured mesh may comprise of square elements (2D) or hexahedral elements (3D) which are orthogonal in i, j space (2D) or i, j, k space (3D). Although is is also possible to have wedges (3D), triangles (2D) and pyramids (3D) in a structured mesh.

Looking at a 2D example, for simplicity, every node in a 2D structured mesh has a corresponding integer i and j index value which is unique. The physical locations of the nodes are stored in a table or are functionally related to the mesh space (ie (x,y)= f(i,j)). It is also implied then that the neigbours of node (i,j) are (i-1,j), (i+1,j), (i,j-1), (i,j+1), (i-1,j-1), and (i+1,j+1). If you are writing a CFD code, a structured mesh makes it very easy to loop through neighbours and can be efficient with memory.

A structured mesh has many coding advantages, but it may be difficult to conform a single block to a complicated shape. Code developers have got around this by allowing multiple blocks (multiblock unstructured), but this can make the internal memory strucutres more inefficient. Another way to make the mesh generation simpler, and improve code performance in other ways is to throw away the block structure and replace indices with node numbers and a connectivity table. This is known as an unstructured mesh, because it lacks the i,j,k structure.

A common misperception is that a hex mesh is strucutred and a tet mesh is unstructured. It is accurate to say that a tet mesh is unstructured, however a hex mesh can also be unstructred. The difference between a structured hex mesh and an ustructured hex mesh is simply in how the data is stored.

Regards, Robin

 derrek February 27, 2003 21:38

Re: Difference between structured & unstructured m

Robin:

Thanks for the thorough explanation. I should have used the word "typically" a little more forcefully. I didn't mean to imply a definition of structured & unstructured.

derrek

 Jaiganesh S January 3, 2012 02:44

Structured HexaMesh and Unstructured Hexamesh Different

1.What is the main different between in structured hexa and unstructured hexa?

 ghorrocks January 8, 2012 20:30

Structured hex meshes are in a grid, so an element can be identified by and ijk coordinate. Unstructured hex meshes are, well, unstructured.

 heidar February 2, 2012 17:34

good news

hey guys
In fact a mesh is said to be structured if one can found a primitive motif which is regular in space. This implies that for instance node connectivities has a fixed pattern. But the geometry may be not constant, for instance your mesh can be deformed from place to place (for instance to match a specific boundary). The only thing you know for sure when the mesh is regular is that the node (or elements) connectivty is always the same. This may be useful for algorithm design since you always have the same pattern.
However unstructured mesh are generally more flexible, since the connectivity pattern is not fixed, at the cost of having to store the connectivity. There is no generic answer to your last question, since it depends strongly upon the application you have in mind.

Could you please explain it more?

regards

 ghorrocks April 2, 2014 18:20

This topic is covered in any CFD text book. I do not fancy retyping text books into forums.

 Abhya March 21, 2016 12:16

Quote:
 Originally Posted by ghorrocks (Post 483534) This topic is covered in any CFD text book. I do not fancy retyping text books into forums.
I hope you realize we dont want a retyped Text explanation...:confused:
Something like this (quoted below - post by Robin) is much better than that..I'd call that condensed understanding ... and that's what guys mean while asking such questions .. they wish to save some time and effort by learning from a well learned fellow..!
Quote:
 Originally Posted by Robin ;65829 Hi Andrew, A single block structured mesh may comprise of square elements (2D) or hexahedral elements (3D) which are orthogonal in i, j space (2D) or i, j, k space (3D). Although is is also possible to have wedges (3D), triangles (2D) and pyramids (3D) in a structured mesh. Looking at a 2D example, for simplicity, every node in a 2D structured mesh has a corresponding integer i and j index value which is unique. The physical locations of the nodes are stored in a table or are functionally related to the mesh space (ie (x,y)= f(i,j)). It is also implied then that the neigbours of node (i,j) are (i-1,j), (i+1,j), (i,j-1), (i,j+1), (i-1,j-1), and (i+1,j+1). If you are writing a CFD code, a structured mesh makes it very easy to loop through neighbours and can be efficient with memory. A structured mesh has many coding advantages, but it may be difficult to conform a single block to a complicated shape. Code developers have got around this by allowing multiple blocks (multiblock unstructured), but this can make the internal memory strucutres more inefficient. Another way to make the mesh generation simpler, and improve code performance in other ways is to throw away the block structure and replace indices with node numbers and a connectivity table. This is known as an unstructured mesh, because it lacks the i,j,k structure. A common misperception is that a hex mesh is strucutred and a tet mesh is unstructured. It is accurate to say that a tet mesh is unstructured, however a hex mesh can also be unstructred. The difference between a structured hex mesh and an ustructured hex mesh is simply in how the data is stored. Regards, Robin

Super clear explanation btw Robin :)

 ghorrocks March 21, 2016 18:07

Yes, Robin's answer was good and he should be commended for that. But vague questions like "Could you please explain it more?" really don't encourage people to write thoughtful answers as there was little thought put into the question. You will find that to get good answers you need to ask good questions - which means clearly stating what bit you don't understand and explaining what background reading/knowledge you have in the topic.

 majid fahim August 10, 2017 08:49

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