1. Discretization

1.1. Degrees of freedom

For three-dimensional shell modeling, the degrees of freedom of discretization are, at each node of the support mesh, the six displacement components (three translations and three rotations) at the vertices and midpoints nodes on the sides of the support mesh. At the central node of the support mesh, the degrees of freedom are reduced to only rotations. These knots belong to the middle leaf of the shell.

Modeling	Degrees of freedom (at each node)
COQUE_3D	DX DY DZ DRX DRY DRZ DRX DRY DRZ only at the central node

1.2. Support mesh for stiffness, mass matrices, etc.

The finite element support cells, in displacement formulation, can be triangles with 7 knots or quadrangles with 9 knots. These meshes are not supposed to be plane; they are created from meshes in TRIA6 and QUAD8 by the CREA_MAILLAGE command (see [U4.23.02]).

Modeling	Mesh	Finished Element
COQUE_3D	TRIA7 QUAD9	MEC3TR7H MEC3QU9H

1.3. Cargo support mesh

All the loads applicable to the facets of the shell elements are treated by direct discretization on the support mesh of the element in displacement formulation.

No load support mesh is therefore necessary for the faces of the shell elements.

For loads applicable to the edges of the shell elements, a SEG3 support mesh can be used:

Modeling	Mesh	Finished Element
COQUE_3D	SEG3	MEBOCQ3