A Sample 2D Stokes Problem

**FEM2D_STOKES_SPARSE_CAVITY** is a square region that is 1 unit wide and 1 unit
high. The tangential velocity is specified to be 1 along the
top boundary, with a zero normal component. On all other parts
of the boundary, the velocity is specified to be zero.

To run the problem directly, you only need the user-supplied routines
in **dirichlet_condition.m** and **rhs.m**, the node data in
**nodes6.txt**, and the element data in **triangles6.txt**.

You can run the program with the MATLAB command

fems2d_stokes_sparse ( 'nodes6.txt', 'triangles6.txt' )

The computer code and data files described and made available on this web page are distributed under the GNU LGPL license.

**FEM2D_STOKES_SPARSE_CAVITY** is available in
a MATLAB version.

FEM2D_STOKES_SPARSE,
a MATLAB program which
solves the steady (time independent) incompressible Stokes equations
on an arbitrary triangulated region,
using the finite element method and MATLAB's **sparse** facility.

Some of the files needed to run the problem include:

- dirichlet_condition.m, evaluates the right hand sides of the Dirichlet boundary conditions.
- rhs.m, evaluates the right hand sides (source terms) of the Stokes equations.
- cavity_output.txt, output from a run of the program;

The geometry is defined by sets of nodes and triangles. The velocities use the full set of nodes, and quadratic (6 node) triangles.

- nodes6.txt, a text file containing the velocity nodes;
- nodes6.png, a PNG image of the velocity nodes;
- triangles6.txt, the quadratic triangulation;
- triangles6.png, a PNG image of the order 6 triangulation;

The pressures are associated with a subset of the nodes called "pressure nodes", and linear (3 node) triangles. Note that, in the order 3 triangulation, the nodes are renumbered, and do NOT inherit the labels used in the order 6 triangulation.

- nodes3.txt, a text file containing the pressure nodes;
- nodes3.png, a PNG image of the pressure nodes;
- triangles3.txt, the linear triangulation;
- triangles3.png, a PNG image of the linear triangulation;

The pressures are a scalar quantity associated with the pressure nodes, the velocities are a vector quantity associated with the vector nodes.

- pressure3.txt, a text file containing the pressure P at each linear node;
- pressure3.png, a PNG image of a contour plot of the pressure, produced by TRIANGULATION_ORDER3_CONTOUR.
- velocity6.txt, a text file containing the velocity (U,V) at each velocity node;
- velocity6_dir.png, a PNG image of the velocity direction field, created by VECTOR_PLOT.
- velocity6_vec.png, a PNG image of the velocity field, created by VECTOR_PLOT.
- velocity6_arrows.png, a PNG image of the velocity field, created by VELOCITY_ARROWS.