Characteristic Length (LS-DYNA) (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.

Characteristic Length (LS-DYNA) has different definition for different element type.

For Tetrahedron elements,

where,

h is the height of a tetrahedron element from a node to its opposite face.

For Hex elements,

where,

V is the volume of the hex element

A is area of the element face

For Pyramid (5-node solid element), Explicit analysis does not use pyramid element and therefore no definition for this element type. To avoid graphic display issues for element summary, pyramid height is used for this element type.

where, h is the 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 elements and Quad elements,

where,

A is element area

L is element edge length

D is the diagonal of quad element.

For Tri element,

where,

A is element area

L is element edge length

For Beam element, the characteristic length is the linear length to the beam element.