The Membrane (mbrn) interface (
), found under the
Structural Mechanics branch (
) when adding a physics interface, is mainly used to model prestressed membranes, but can also be used to model a thin cladding on a solid. Membranes can be considered as plane stress elements on boundaries in 3D with a possibility to deform both in the in-plane and out-of-plane directions. There is also a version of the membrane interface for 2D axisymmetric problems. The membrane interface is then applicable to lines since that is what represents boundaries.
When this physics interface is added, these default nodes are also added to the Model Builder:
Linear Elastic Material,
Free (a condition where edges are free, with no loads or constraints), and
Initial Values. In the case if axial symmetry, an
Axial Symmetry node is also added. From the
Physics toolbar, you can then add other nodes that implement, for example, loads and constraints. You can also right-click
Membrane to select physics features from the context menu.
The Label is the default physics interface name.
The Name is used primarily as a scope prefix for variables defined by the physics interface. Refer to such physics interface variables in expressions using the pattern
<name>.<variable_name>. In order to distinguish between variables belonging to different physics interfaces, the
name string must be unique. Only letters, numbers, and underscores (_) are permitted in the
Name field. The first character must be a letter.
The default Name (for the first physics interface in the model) is
mbrn.
From the Structural transient behavior list, select
Include inertial terms (the default) or
Quasi-static. Use
Quasi-static to treat the elastic behavior as quasi-static (with no mass effects; that is, no second-order time derivatives). Selecting this option gives a more efficient solution for problems where the variation in time is slow when compared to the natural frequencies of the system.
Enter the default coordinates for the Reference point for moment computation xref. The resulting moments (applied or as reactions) are then computed relative to this reference point. During the results and analysis stage, the coordinates can be changed in the
Parameters section in the result nodes.
The dependent variable (field variable) is for the Displacement field u which has three components
(u,
v, and
w). The name can be changed but the names of fields and dependent variables must be unique within a model.
In the Membrane interface you can choose not only the order of the discretization, but also the type of shape functions: Lagrange or
serendipity. For highly distorted elements, Lagrange shape functions provide better accuracy than serendipity shape functions of the same order. The serendipity shape functions will however give significant reductions of the model size for a given mesh containing quadrilateral elements.
