FEM best practices and examples: Difference between revisions
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===Mesh element/theory=== | ===Mesh element/theory=== | ||
The mesh element used with in plates in [[XFEM4U]] is a modified [https://en.wikipedia.org/wiki/Bending_of_plates Kirchhoff] element. It is extended in 2021 by [https://nl.wikipedia.org/wiki/Johan_Blaauwendraad | The mesh element used with in plates in [[XFEM4U]] is a modified [https://en.wikipedia.org/wiki/Bending_of_plates Kirchhoff] element. It is extended in 2021 by [https://nl.wikipedia.org/wiki/Johan_Blaauwendraad Professor Blaauwendraad]. Usually Kirchhoff is less precise regarding shear force distribution. In the modified hybrid element this is solved. Therefore it is a extremely robust mesh element with very reliable shear force distribution. | ||
===Mesher=== | ===Mesher=== | ||
The mesher is using 4-nodes quadrangle elements because they are more accurate than 3-nodes triangle elements. On a edge | The mesher is using 4-nodes quadrangle elements because they are more accurate than 3-nodes triangle elements. On a edge there at least 2 elements with an even number. | ||
===Mesh Size=== | |||
Below we describe a method how to find the right mesh size for your structure. If you make the mesh too dense, internal forces will be higher then reality mainly because of point loads, point and linear supports. In reality they have a curtain area. In the model they are points and therefore infinite stress can occur. | |||
First some basics: | |||
* Element size should '''never''' be '''smaller''' then the '''plate thickness'''. Otherwise the theory of Kirchhoff is not correct anymore. | |||
* Element size is at '''least''' '''the''' '''smallest span''' in the structure to expect a correct result. | |||
* '''Steel''' '''plate''' structures: If you make you mesh '''50% smaller''' the stress should not increase more then '''10-12%.''' | |||
Workflow to find the right mesh size within a steel structure. | |||
=== Plate on Grade === | |||
Plate Forces | |||
[[Plate stresses/forces]] | |||
Revision as of 07:37, 28 August 2022
FEM-solver
The FEM-solver is written completely in C# with. It is geometrically linear. So second order effects are not taken into account.
Mesh element/theory
The mesh element used with in plates in XFEM4U is a modified Kirchhoff element. It is extended in 2021 by Professor Blaauwendraad. Usually Kirchhoff is less precise regarding shear force distribution. In the modified hybrid element this is solved. Therefore it is a extremely robust mesh element with very reliable shear force distribution.
Mesher
The mesher is using 4-nodes quadrangle elements because they are more accurate than 3-nodes triangle elements. On a edge there at least 2 elements with an even number.
Mesh Size
Below we describe a method how to find the right mesh size for your structure. If you make the mesh too dense, internal forces will be higher then reality mainly because of point loads, point and linear supports. In reality they have a curtain area. In the model they are points and therefore infinite stress can occur.
First some basics:
- Element size should never be smaller then the plate thickness. Otherwise the theory of Kirchhoff is not correct anymore.
- Element size is at least the smallest span in the structure to expect a correct result.
- Steel plate structures: If you make you mesh 50% smaller the stress should not increase more then 10-12%.
Workflow to find the right mesh size within a steel structure.
Plate on Grade
Plate Forces