Ansys Learning Forum › Forums › Discuss Simulation › General Mechanical › Meshing advice – tetrahedron to hex › Reply To: Meshing advice – tetrahedron to hex
April 12, 2022 at 9:15 am
Vigneswaran Sridharan
Ansys Employee
Hey
Linear tetrahedral/triangular elements suffer from three issues:
ÔÇÉThey have one integration point and are constant strain elements ÔÇô so we need an extremely fine mesh to capture the strain gradient accurately.
ÔÇÉ It's difficult to distort the element without changing its volume so theyÔÇÖre prone to volumetric locking for nearly or fully incompressible materials and maybe overly stiff.
ÔÇÉIn the case of bending-dominated problems, linear elements are also prone to shear locking which introduces spurious shear stresses in the part and make it overly stiff regardless of how fine the mesh is created.
Linear hexahedral elements, or the 8-noded hex elements, do not suffer from the first two issues, so they seem like a good alternative to linear tetrahedral elements, hence the general recommendation!
While it is a valid suggestion, it's not always possible to generate a hexahedral mesh. The above limitations are resolved by introducing mid-side nodes which creates a 10-noded tet element that uses second-order polynomial for shape functions. If the geometry is a combination of sweepable and irregular shapes in such then the combination of brick, tetrahedral, pyramid, or wedge elements is used. Pyramid elements are used in the transition regions.
Look at this relevant video on "Understanding importance of 3D element shapes and order"
Vigneswaran
Ansys Help
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ÔÇÉThey have one integration point and are constant strain elements ÔÇô so we need an extremely fine mesh to capture the strain gradient accurately.
ÔÇÉ It's difficult to distort the element without changing its volume so theyÔÇÖre prone to volumetric locking for nearly or fully incompressible materials and maybe overly stiff.
ÔÇÉIn the case of bending-dominated problems, linear elements are also prone to shear locking which introduces spurious shear stresses in the part and make it overly stiff regardless of how fine the mesh is created.
Linear hexahedral elements, or the 8-noded hex elements, do not suffer from the first two issues, so they seem like a good alternative to linear tetrahedral elements, hence the general recommendation!
While it is a valid suggestion, it's not always possible to generate a hexahedral mesh. The above limitations are resolved by introducing mid-side nodes which creates a 10-noded tet element that uses second-order polynomial for shape functions. If the geometry is a combination of sweepable and irregular shapes in such then the combination of brick, tetrahedral, pyramid, or wedge elements is used. Pyramid elements are used in the transition regions.
Look at this relevant video on "Understanding importance of 3D element shapes and order"
Vigneswaran
Ansys Help
Rules & Guidelines ÔÇö Ansys Learning Forum
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