Characteristic Length
Characteristic length (also called characteristic dimension) is used to compute the time step that satisfies the Courant-Friedrichs-Lewy (CFL) condition for a given analysis setup. The CFL condition is of interest mostly in explicit dynamics and computational fluid dynamics analyses. It governs the maximum time step for which a solution will be stable.
The characteristic length is defined based on the element type.
For hexahedral elements:
where:
Lc = characteristic length of the hex element
V = volume of the hex element
A = area of the element face
For tetrahedral elements:
where:
Lc = characteristic length of the tet element
h = height of the tet element from a node to its opposite face.
For pyramid elements: (5-node solid element)
where:
Lc = characteristic length of the pyramid element
h = height of the apex node to the base of the pyramid. Here, the base quad face can be divided into 4 different triangles, the minimum height to these 4 triangles is used.
For Shell quad elements:
where:
Lc = characteristic length of the quad element
A = element area
L = element edge length
D = diagonal of the quad element
For Shell tri elements:
where:
Lc = characteristic length of the tri element
A = element area
L = element edge length