[math]\displaystyle{
\Delta\phi^{\mathrm{D}} =0,\,\,-h\lt z\lt 0,
}[/math]
[math]\displaystyle{
\partial_{z}\phi^{\mathrm{D}} =0,\,\,z=-h,
}[/math]
[math]\displaystyle{
\partial_{z}\phi^{\mathrm{D}} =\alpha \phi^{\mathrm{D}},\,\,x\notin(-L,L),\,\,
z=0,
}[/math]
[math]\displaystyle{
\partial_{z}\phi^{\mathrm{D}} =0,\,\,x\in(-L,L),\,\,z=0.
}[/math]