“…We assume the following separation of variables for the incremental fields [37] falsefalse{u˙r(r,θ),S˙rr(r,θ),ϕ˙(r,θ),D˙r(r,θ)falsefalse} 1em=falsefalse{Ur(r),Σrr(r),Φ(r),Δr(r)falsefalse}Pmfalse(cosθfalse),and2em falsefalse{u˙θ(r,θ),S˙rθ(r,θ)falsefalse}={Uθfalse(rfalse)...…”