Palmero, Matheus S. [UNESP]Díaz, Gabriel I.McClintock, Peter V. E.Leonel, Edson D. [UNESP]2020-12-122020-12-122020-01-01Chaos, v. 30, n. 1, 2020.1054-1500http://hdl.handle.net/11449/198429We show that, in strongly chaotic dynamical systems, the average particle velocity can be calculated analytically by consideration of Brownian dynamics in a phase space, the method of images, and the use of the classical diffusion equation. The method is demonstrated on the simplified Fermi-Ulam accelerator model, which has a mixed phase space with chaotic seas, invariant tori, and Kolmogorov-Arnold-Moser islands. The calculated average velocities agree well with numerical simulations and with an earlier empirical theory.engArtigo10.1063/1.51006072-s2.0-85078254841