KOVAL’CHUK, P. S.; KUBENKO, V. D. Application of the Averaging Method to the Investigation of Nonlinear Wave Processes in Elastic Systems with Circular Symmetry. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 53, n. 10, p. 1358–1367, 2001. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/4355. Acesso em: 6 dec. 2025.