Numerical schemes for a fully nonlinear coagulation-fragmentation model coming from wave kinetic theory

This article introduces a novel numerical approach for studying fully nonlinear coagulation-fragmentation models, where both the coagulation and fragmentation components of the collision operator are nonlinear. The model approximates the $3-$wave kinetic equations, a pivotal framework in wave turbulence theory governing the time evolution of wave spectra in weakly nonlinear systems. An implicit finite volume scheme (FVS) is derived to solve this equation. To the best of our knowledge, this is the first numerical scheme capable of accurately capturing the long-term asymptotic behavior of solutions to a fully nonlinear coagulation-fragmentation model that includes both forward and backward energy cascades. The scheme is implemented on some test problems, demonstrating strong alignment with theoretical predictions of energy cascade rates. We further introduce a weighted FVS variant to ensure energy conservation across varying degrees of kernel homogeneity. Convergence and first-order consistency are established through theoretical analysis and verified by experimental convergence orders in test cases.