On the Melnikov method for fractional-order systems

TL;DR

This paper clarifies and correctly applies the Melnikov method to fractional-order systems, addressing previous issues with perturbation calculations and providing a globally closed-form criterion verified by numerical methods.

Contribution

It redefines the application of Melnikov method in fractional dynamics, deriving a globally closed-form criterion and clarifying the handling of perturbations with fractional calculus.

Findings

Derived a globally closed-form Melnikov criterion for fractional systems

Clarified the correct application of perturbation calculations in fractional Melnikov analysis

Validated the criterion through numerical simulations

Abstract

This paper is dedicated to clarifying and introducing the correct application of Melnikov method in fractional dynamics. Attention to the complex dynamics of hyperbolic orbits and to fractional calculus can be, respectively, traced back to Poincar\'es attack on the three-body problem a century ago and to the early days of calculus three centuries ago. Nowadays, fractional calculus has been widely applied in modeling dynamic problems across various fields due to its advantages in describing problems with non-locality. Some of these models have also been confirmed to exhibit hyperbolic orbit dynamics, and recently, they have been extensively studied based on Melnikov method, an analytical approach for homoclinic and heteroclinic orbit dynamics. Despite its decade-long application in fractional dynamics, there is a universal problem in these applications that remains to be clarified, i.e., defining fractional-order systems within finite memory boundaries leads to the neglect of perturbation calculation for parts of the stable and unstable manifolds in Melnikov analysis. After clarifying and redefining the problem, a rigorous analytical case is provided for reference. Unlike existing results, the Melnikov criterion here is derived in a globally closed form, which was previously considered unobtainable due to difficulties in the analysis of fractional-order perturbations characterized by convolution integrals with power-law type singular kernels. Finally, numerical methods are employed to verify the derived Melnikov criterion. Overall, the clarification for the problem and the presented case are expected to provide insights for future research in this topic.