6.4: Initial-Boundary Value Problems
- Page ID
- 2159
Consider the initial-boundary value problem for \(c=c(x,t)\)
\begin{eqnarray}
\label{sol1}
c_t&=&D\triangle c\ \ \mbox{in}\ \Omega\times (0,\infty)\\
\label{sol2}
c(x,0)&=&c_0(x)\ \ x\in\overline{\Omega}\\
\label{sol3}
\frac{\partial c}{\partial n}&=& 0\ \ \mbox{on}\ \partial\Omega\times (0,\infty).
\end{eqnarray}
Here is \(\Omega\subset\mathbb{R}^n\), \(n\) the exterior unit normal at the smooth parts of \(\partial\Omega\), \(D\) a positive constant and \(c_0(x)\) a given function.
Remark. In application to diffusion problems, \(c(x,t)\) is the concentration of a substance in a solution, \(c_0(x)\) its initial concentration and \(D\) the coefficient of diffusion.
The first Fick's rule says that
\[w=D\partial c/\partial n,\]
where \(w\) is the flow of the substance through the boundary \(\partial\Omega\). Thus according to the Neumann boundary condition (\ref{sol3}), we assume that there is no flow through the boundary.
Contributors and Attributions
Integrated by Justin Marshall.