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JOURNALS // Journal of Computational and Engineering Mathematics // Archive

J. Comp. Eng. Math., 2025 Volume 12, Issue 4, Pages 3–10 (Mi jcem289)

Computational Mathematics

On a problem in the theory of relaxation oscillations

B. G. Grebenshchikov, E. A. Derkunova

South Ural State University, Chelyabinsk, Russian Federation

Abstract: We consider a model of a braking device described by a differential equation relating the brake shoe rotation angle and its relative angular velocity. The dry friction torque depends on the rotation angle and angular velocity as a piecewise function, while the moment of inertia of the brake shoe device under consideration is a small quantity. From a mathematical standpoint, this equation reduces to a system of two differential equations, one of which contains a small parameter at the highest derivative, a so-called Tikhonov system. The system under consideration has a single equilibrium state, but it is unstable. It is self-excited, and relaxation self-oscillations will set in. Our goal was to provide an example of such a right-hand side of the equation of motion for which experimental phenomena are sufficiently accurately explained, and to obtain an asymptotic expansion of the solution as a function of time. To find the asymptotic expansion of an arbitrary-order solution to our problem, we used the method of constructing boundary functions. The justification of the asymptotic expansion can be carried out as in classical theory.

Keywords: singularly perturbed equations, degenerate equation, asymptotic expansion, boundary function method, relaxation oscillations.

UDC: 517.9

MSC: 34D15, 34E10

Received: 15.10.2025

Language: English

DOI: 10.14529/jcem250401



© Steklov Math. Inst. of RAS, 2026