My problem is defined like that. I am trying to find radial and tangential field distribution on a surface of the rotor of a large airgap synchronous machine. To do that I start from the general scalar potential equation solution in polar coordinates of the form pot = (ar+b/r)sin(teta). I take the gradient of this equation and have equations for both tangential and radial fields. Where I am struggling is finding a and b coefficients. In order to do it I need proper boundary conditions. So I assume two cases during the short circuit there are no radial fiel d only tangential so I can solve it for coefficients. During no load operation there is no tangential field on the side of the stator and I know the airgap flux density so I am able to find the coefficients. Is this the right approach.