Thnx

I am going to start my career in the CAE field with the software ANSYS. But the problem i am facing is how to decide the mesh element size for a particular geometry.
Sir, can you please suggest me about how to decide mesh element size (max face size of element, mini element size and max element size.)
Thank You

I wonder if anybody has done detailed comparison between finite volume method and finite element method with the same mesh containing non-orthogonality, skewness, non-uniformity. To my understanding (with some level of experience with the finite element method on hex-quad meshes), the finite element method is quite robust (or insensitive) with high aspect ratio meshes and large element-to-element size ratios (nonuniformity). But finite volume method, based on central difference or so, will theoretically lose accuracy on nonuniform meshes. Am I correct?

Hi,

I’m interested in benchmark studies comparing hexa with tetra meshes… What would you recommend for reading (articles, books,…)?

Point # 2 : As we increase the no of faces (hexa, polygonal) in a cell, we can have more information from neighbouring cells. Since tet cells have less neighbouring cells therefore it needs more dense mesh in those critical regions. This is what we learned in our CFD classes.

Take an example of backward facing step validation case. You can easily observe HEX meshes have clear advantages.

However for quick design iterations for complex geometries, it is better to go for tet type meshes, which easily adopt the themselves to geometry.

Can we use tet mesh for transition predictions? separation dominated flows? LES simulations?

How we are going to estimate uncertainty with tet mesh to the time needed for hex mesh generation? Which one is more important? Doubts on results from tet meshes or time consumed in Hex mesh?

thank you for your input.
1. as an experienced user, you probably seldom rely on these automatic tools. However, for most not-so-experienced users, automation tools are valuable.

2. actually, my point is hex mesh are seldom necessary. Mesh quality, not mesh type, is the key.

Regarding Point # 4. I have two observations:

1. There are many meshers in market which are able to make mesh with minimum user input. But still they need manual work for fine tuning the mesh in important regions which software does not know at all. Moreover for hexa mesh, automatic meshers will find hard time for complicated models. But I would always go for good tet mesh than the bad Hexa mesh.

2. Author has emphasized importance of experienced users and Hexa mesh. Which implies if you have option to create Hexa mesh you should go for it. Which is really a contradiction!!!

But there are many situations in which it is not possible to create hexa mesh or the problem is not highly dependent on mesh.

Last but not the least, you always need a good Hexa mesh if you want to have good results and your model shall be used for different design points simulation e.g. aircraft, missile, turbine, compressor CFD simulation etc.

Thank you for your comments and inputs, Sanjay.

1. For structural incompressible problems, Hex and Quads give better results than Tets and Tri. Even with the addition of bubble functions and incompatible modes to satisfy the LBB conditions, the Tets and Tris do not reach the same level of accuracy. In the fluids problems, the flow direction can lead to numerical diffusion if not aligned (so Physics based meshing is a must but that can be judiciously combined with Hexs and Quads to give better results than Tets and Tris).

2. Instead of FEA and CFD, please say Structural and CFD since finite elements have been extensively used for CFD as well.