Select Boundary Mode from the Boundary menu or click the button. Then select a boundary or multiple boundaries for which you are specifying the conditions. Note that no if you do not select any boundaries, then the specified conditions apply to all boundaries.
To select a single boundary, click it using the left mouse button.
To select several boundaries and to deselect them, use Shift+click (or click using the middle mouse button).
To select all boundaries, use the Select All option from the Edit menu.
Select Specify Boundary Conditions from the Boundary menu.
Specify Boundary Conditions opens a dialog box where you can specify the boundary condition for the selected boundary segments. There are three different condition types:
Generalized Neumann conditions, where the boundary
condition is determined by the coefficients
to the following equation:
In the system cases,
q is a 2-by-2 matrix
g is a 2-by-1 vector.
Dirichlet conditions: u is specified on the boundary. The boundary condition equation is hu = r, where h is a weight factor that can be applied (normally 1).
In the system cases,
h is a 2-by-2 matrix
r is a 2-by-1 vector.
Mixed boundary conditions (system cases only), which
is a mix of Dirichlet and Neumann conditions.
a 2-by-2 matrix,
g is a 2-by-1 vector,
a 1-by-2 vector, and
r is a scalar.
The following figure shows the dialog box for the generic system PDE (Options > Application > Generic System).
For boundary condition entries you can use the following variables in a valid MATLAB® expression:
The 2-D coordinates
A boundary segment parameter
proportional to arc length.
s is 0 at the start
of the boundary segment and increases to 1 along the boundary segment
in the direction indicated by the arrow.
The outward normal vector components
If you need the tangential vector, it can be expressed using
ny since tx = –ny and ty = nx.
If the boundary condition is a function of the solution
u, you must
use the nonlinear solver. If the boundary condition is a function of the time
t, you must choose a parabolic or hyperbolic PDE.
In the nongeneric application modes, the Description column contains descriptions of the physical interpretation of the boundary condition parameters.