3.1.9: Mesh to Shell

The “MeshToShell”-component takes a triangle or quad mesh and turns it into a group of shell or membrane elements (see fig. 3.1.9.1). Quads get automatically decomposed to triangles. Shell patches are rigidly connected when some of their nodes have the same index.

Colors can be attached to shells via the “Color”-input. In order to enable the display of shell element colors, activate “Elements” in submenu “Colors” of the “ModelView”-component. In addition “Cross section” needs to be selected in the submenu “Render Settings” of the “ShellView”-component.

Each patch of shells can be given an identifier via input “Id” for later reference when attaching custom material or cross section properties. By default shells have a thickness of $1cm$ and steel as their material. Use the “CroSec”-input to change that. Clicking on the “Options” submenu header further unfolds the component: The “Pts”- and “LDist”-input serve the same purpose as in the “LineToBeam”-component – see section 3.1.6. Additionally mesh faces with an area smaller than $LDist^2 \cdot 0.1$ get automatically removed.

Fig. 3.1.9.1: The “MeshToShell”-component turns meshes into shells

The shell elements used in Karamba3D resemble the TRIC-element devised by Argyris and coworkers (see [1], [2] for details). They are faceted (i.e. flat) elements. Karamba3D neglects transverse shear deformation in case of shell elements.

Shells and Membranes

In case of very thin shells the bending-stiffness can be neglected with respect to the in-plane stiffness. Thus one arrives at membrane elements with three translational degrees of freedom (dofs) per node. If "t" stands for the shell thickness then its bending stiffness is proportional to t³ whereas the in-plane stiffness varies with t. This leads to hugely different magnitues of entries in the element stiffness matrices and causes numerical problems in the solution procedure. Membrane elements result from the MeshToShell-component when the input-plug "Bending" is set to false. Flat assemblies of membrane elements have kinematic modes in transverse direction unless stabilized via positive $N^{II}$-values.