Spent four days in figuring out how to construct an OpenFOAM polyMesh manually, it is more complicated than I thought, the difficult part is how to construct a multi-block mesh. One of the annoying issues in a multi-block polymesh construction is how to handle its internal lines/surfaces, where two lines become one. And then the points indices and the face indices all have to change accordingly. There may be many approaches to address this, but I, after many days' thought, decided to use a brutal...