How to use the proteus.BoundaryConditions.constantBC function in proteus

def setFreeSlip(self):
        """
        sets free slip conditions at the boundary
        """
        self.reset()
        self.BC_type = 'FreeSlip'
        self.p_advective = constantBC(0.)
        self.u_advective = constantBC(0.)
        self.v_advective = constantBC(0.)
        self.w_advective = constantBC(0.)
        self.vof_advective = constantBC(0.)
        self.k_dirichlet = constantBC(0.)
        self.u_diffusive = constantBC(0.)
        self.v_diffusive = constantBC(0.)
        self.w_diffusive = constantBC(0.)
        self.dissipation_diffusive = constantBC(0.)

def setFreeSlip(self):
        """
        sets free slip conditions at the boundary
        """
        self.reset()
        self.BC_type = 'FreeSlip'
        self.p_advective = constantBC(0.)
        self.u_advective = constantBC(0.)
        self.v_advective = constantBC(0.)
        self.w_advective = constantBC(0.)
        self.vof_advective = constantBC(0.)
        self.k_dirichlet = constantBC(0.)
        self.u_diffusive = constantBC(0.)
        self.v_diffusive = constantBC(0.)
        self.w_diffusive = constantBC(0.)
        self.dissipation_diffusive = constantBC(0.)

def setTank(self):
        b_or = self._b_or[self._b_i]
        if b_or[0] == 1 or b_or[0] == -1:
            self.hx_dirichlet = constantBC(0.)
            self.u_stress = None
        elif b_or[1] == 1 or b_or[1] == -1:
            self.hy_dirichlet = constantBC(0.)
            self.v_stress = None
        elif len(b_or) > 2 and (b_or[2] == 1 or b_or[2] == -1):
            self.hz_dirichlet = constantBC(0.)
            self.w_stress = None

a0 = pRef - rho*g[vert_axis]*refLevel
        a1 = rho*g[vert_axis]
        # This is the normal velocity, based on the boundary orientation

        def get_outlet_ux_dirichlet(i):
            def ux_dirichlet(x, t):
                b_or = self._b_or[self._b_i]
                if b_or[i] == 0:
                    return 0.
            return ux_dirichlet
        self.u_dirichlet = get_outlet_ux_dirichlet(0)
        self.v_dirichlet = get_outlet_ux_dirichlet(1)
        if len(g) == 3:
            self.w_dirichlet = get_outlet_ux_dirichlet(2)
        self.p_dirichlet = linearBC(a0, a1, vert_axis)
        self.vof_dirichlet = constantBC(vof)
        self.u_diffusive = constantBC(0.)
        self.v_diffusive = constantBC(0.)
        self.w_diffusive = constantBC(0.)

return constantBC(0.)

        if orientation is None and self._b_or[self._b_i] is not None:
            b_or = self._b_or[self._b_i]
        elif orientation is not None:
            b_or = orientation
        else:
            print('Boundary orientation needs to be defined')
        self.reset()
        self.p_dirichlet = constantBC(0.)
        self.u_dirichlet = get_ux_dirichlet(0)
        self.v_dirichlet = get_ux_dirichlet(1)
        if len(b_or) > 2:
            self.w_dirichlet = get_ux_dirichlet(2)
        self.vof_dirichlet = constantBC(1.)  # air
        self.u_diffusive = constantBC(0.)
        self.v_diffusive = constantBC(0.)
        self.w_diffusive = constantBC(0.)
        self.k_diffusive = constantBC(0.)
        self.dissipation_diffusive = constantBC(0.)

def setFreeSlip(self):
        """
        sets free slip conditions at the boundary
        """
        self.reset()
        self.BC_type = 'FreeSlip'
        self.p_advective = constantBC(0.)
        self.u_advective = constantBC(0.)
        self.v_advective = constantBC(0.)
        self.w_advective = constantBC(0.)
        self.vof_advective = constantBC(0.)
        self.k_dirichlet = constantBC(0.)
        self.u_diffusive = constantBC(0.)
        self.v_diffusive = constantBC(0.)
        self.w_diffusive = constantBC(0.)
        self.dissipation_diffusive = constantBC(0.)

def setFreeSlip(self):
        """
        sets free slip conditions at the boundary
        """
        self.reset()
        self.BC_type = 'FreeSlip'
        self.p_advective = constantBC(0.)
        self.u_advective = constantBC(0.)
        self.v_advective = constantBC(0.)
        self.w_advective = constantBC(0.)
        self.vof_advective = constantBC(0.)
        self.k_dirichlet = constantBC(0.)
        self.u_diffusive = constantBC(0.)
        self.v_diffusive = constantBC(0.)
        self.w_diffusive = constantBC(0.)
        self.dissipation_diffusive = constantBC(0.)

def get_ux_dirichlet(i):
            if b_or[i] == 1. or b_or[i] == -1.:
                return None
            else:
                return constantBC(0.)

def setFixedNodes(self):
        """
        For moving domains: fixes nodes/boundary
        """
        self.hx_dirichlet = constantBC(0.)
        self.hy_dirichlet = constantBC(0.)
        self.hz_dirichlet = constantBC(0.)
        self.u_stress = None
        self.v_stress = None
        self.w_stress = None