Table of Contents
Shell elements
Semi-loof elements, which model thin shells, can be used for all problem types except materially nonlinear problems.
Each element is described in the name.i1 file using one EL batch:
EL T 61 E IE N IN$_1$ IN$_2$ $\dots$ IN$_\mathtt{NNE}$ G NG H $h_1$ $h_2$ $\dots$ $h_\mathtt{NNE}$
The T group can be omitted if $\mathtt{ITE}={}$$\mathtt{ITED}$${}=61$.
| $\mathtt{IE}$ | The element number. | |
|---|---|---|
| $\mathtt{IN}_j$ | The node numbers of the element in the prescribed order, see the Reference Manual. Midside nodes must not be omitted. | |
| $j$ | The local number of the element node, $1\le j\le\mathtt{NNE}$. | |
| $\mathtt{NNE}$ | The number of nodes in the element. | |
| $\mathtt{NG}$ | The order of numerical integration for the element, $2\le\mathtt{NG}\le4$. If the G group is missing, the value $\mathtt{NGD}$ applies. Usually $\mathtt{NG}=\mathtt{NGD}=3$. | |
| $h_j$ | The nodal thicknesses of the element. If only one value is specified, it applies to all nodes of the element. If the H group is missing, the value $\mathtt{THDEF}$ applies to all nodes of the element. The thicknesses are automatically multiplied by the $\mathtt{SCALE}$ scale factor; for example, the value $\mathtt{SCALE}=0.001$ means that all thicknesses are given in millimeters. | |
Note
The EL batch can have any number of continuation lines. Data are written from column 3 to column 72 (the first two columns are generally reserved for two-letter batch names), see the Reference Manual.
Example
Let us consider a triangular shell element. The global node numbers follow from the specific numbering of the mesh.
According to the Reference Manual, the node numbers can be written in three ways:
22 24 77 23 44 43 24 77 22 44 43 23 77 22 24 43 23 44
in which case the $\zeta$ axis will point upward as in the figure, or in three further ways:
22 77 24 43 44 23 77 24 22 44 23 43 24 22 77 23 43 44
in which case the $\zeta$ axis will point downward.
A typical form of the EL batch, corresponding to the orientation of the coordinate system $\xi,\eta,\zeta$ and the order of the edges shown in the figure, will be:
EL T 61 E 211 N 22 24 77 23 44 43
The order of numerical integration and the thickness of the element will be given by the default values $\mathtt{NGD}$ and $\mathtt{THDEF}$. If only shell elements occurred in the mesh, the notation could be simplified by specifying $\mathtt{ITED}=61$, and the T 61 group would be omitted.
Stiffeners
A semi-loof element can be stiffened along one or more edges, see the Reference Manual.
Each stiffener is described by one pair of S and R groups, which are appended to the end of the corresponding EL batch:
EL $\dots$ S IH R $I_\eta$ $I_\zeta$ $A$ $\alpha_v$ $h_T$ $h_v$
| $\mathtt{IH}$ | The local number of the edge of the shell element. |
|---|---|
| $I_\eta$ | The second moment of area about the local axis $\eta_v$ $[\text{m}^4]$. |
| $I_\zeta$ | The second moment of area about the local axis $\zeta_v$ $[\text{m}^4]$. |
| $A$ | The cross-sectional area $[\text{m}^2]$. |
| $\alpha_v$ | The angle between the local axis $\eta_v$ and the tangent plane $[^\circ]$. |
| $h_T$ | The distance of the centroid from the surface $[\text{m}]$ (entered as negative if the stiffener is attached to the bottom of the surface). |
| $h_v$ | The height $[\text{m}]$ (entered as negative if the stiffener is attached to the bottom of the surface). |
Example
Let us consider a triangular shell element. The local edge numbers follow from the specific numbering of the mesh. Let us assume that edge 24–44–77 is to be longitudinally stiffened by a rib attached to the bottom.
A typical form of the EL batch will be:
EL T 61 E 211 N 22 24 77 23 44 43 ␣␣S 2 R <Ieta> <Izeta> <A> <αᵥ> -<hᴛ> -<hᵥ>
where the corresponding values of the stiffener’s geometric properties are written in place of the expressions <…>.
The heights $h_T$ and $h_v$ will be entered as negative.