Koval’chuk, P.S. and Kubenko, V.D. (2001) “Application of the Averaging Method to the Investigation of Nonlinear Wave Processes in Elastic Systems with Circular Symmetry”, Ukrains’kyi Matematychnyi Zhurnal, 53(10), pp. 1358–1367. Available at: https://umj.imath.kiev.ua/index.php/umj/article/view/4355 (Accessed: 6 December 2025).