  \Omega\,, \\[0mm]  \displaystyle \frac{\partial \phi'}{\partial z} = 0 \quad \text{on}\quad \Omega_x \times \partial \Omega_z \,, \qquad \displaystyle \phi' = 0 \quad \text{on} \quad \partial \Omega_x \times \Omega_z\,, \\[0mm]  \displaystyle  \overline{ \phi'}= 0\,, \quad \text{in} \quad \Omega_x\,. \end{array} \right.$$ 