Neumann Boundary Conditions

Neumann conditions prescribe fluxes of mass or heat crossing boundary surfaces. A special case of Neumann boundary conditions is “no flux,” which in the integral finite difference framework is handled simply by not specifying any flow connections across the boundary. More general flux conditions are prescribed by introducing sinks or sources of appropriate strength into the elements adjacent to the boundary. Time-dependent Neumann conditions can be specified by making sink and source rates time dependent.