Panel a): variation of the force f_dis,rot which is derived form the potential function Ψ_dis,rot versus coordinates θ and ϕ at the surface of accretors in model M1. Panel b): variation of the radial component of tidal forces which is derived from the potential function Ψ_tide at the surface of accretor versus coordinates θ and ϕ in model M1. Panel c): variation of the gravitational acceleration | g_eff | at the secondary star’s surface under coordinates θ and ϕ in Roche model. The radius is treated as the constant value. Panel d): variation of the gravitational acceleration | g_eff | at the secondary star’s surface under coordinates θ and ϕ in model M1. The effective gravitational acceleration can be derived from Eq. (1).