Elementary Boundary Conditions

Material LAW11 is used to specify the elementary variables at the boundary of the computational domain.

Option 0 specifies stagnation conditions for perfect gas (Bernoulli inlet).
Option 1 specifies stagnation conditions for a linear compressible material (Bernoulli inlet).
Option 2 imposes values (inlet/outlet).
Option 3 is for non-reflective frontiers (outlet).

For example, in the input deck, density and energy are imposed constant at the inlet. Non-reflective frontiers are imposed at the outlet. Then, the flux is injected at inlet through imposed velocities at nodal points.

Non-Reflective Frontiers (NRF)

Option 3 of Material LAW11 is used to prevent outgoing wave reflections on the boundaries of the domain.

Two possibilities are:

An average pressure is imposed via a function. A relaxation term is added to let the average pressure converge toward the imposed value. This is well suited for outlets.
An average pressure is calculated from the neighboring element pressure and the pressure converges toward this always changing value.

The impedance of the boundary is exactly the wave impedance of a monopole radiating at distance 2l_c from the boundary, where l_c is specified in the input data for this law.

This non-reflective frontiers (NRF) is not effective when velocities are imposed or when nodes are fixed.