def __init__(self, type_, name, faces=[]):
        """ initialize boundary
        type_ is type keyword (wall, patch, empty, ..)
        name is nave of boundary emelment
        faces is faces which are applied with this boundary conditions
        """
        self.type_ = type_
        self.name = name
        self.faces = faces
def __init__ ( self , type_ , name , faces = [ ] ) : self . type_ = type_ self . name = name self . faces = faces
initialize boundary
        type_ is type keyword (wall, patch, empty, ..)
        name is nave of boundary emelment
        faces is faces which are applied with this boundary conditions