These are the double integration method, Macaulay's method, the principle of superposition, the moment-area method, and Castigliano's theorem, which is based on strain energy.

Jorge Martín-Morales, Antonio M. Oller-Marcén, Computing Volumes of Solids of Revolution with Double Integrals, The College Mathematics Journal, Vol. 45, No. 3 (May 2014), pp. 219-221 ...