u⁡(r⁢ⅇⅈ⁢θ)=12⁢π⁢∫02⁢π(R2-r2)⁢h⁡(R⁢ⅇⅈ⁢ϕ)⁢ⅆ⁡ϕR2-2⁢R⁢r⁢cos⁡(ϕ-θ)+r2