The Bhatnagar--Gross--Krook (BGK) equation is a relaxation model of the Boltzmann equation which is widely used in place of the Boltzmann equation for the simulation of various kinetic flow problems. In this work, we study the asymptotic stability of the BGK model when the initial data is not necessarily close to the global equilibrium pointwisely. Due to the highly nonlinear structure of the relaxation operator, the argument developed to derive the bootstrap estimate for the Boltzmann equation leads to a weaker estimate in the case of the BGK model, which does not exclude the possible blow-up of the perturbation. To overcome this issue, we carry out a refined analysis of the macroscopic fields to guarantee that the system transits from a highly nonlinear regime into a quadratic nonlinear regime after a long but finite time, in which the highly nonlinear perturbative term relaxes to essentially quadratic nonlinearity.

Publication:

SIAM JOURNAL ON MATHEMATICAL ANALYSIS

http://dx.doi.org/10.1137/25M1774537

Author:

GI-CHAN BAE

Research Institute of Mathematics, Seoul National University, Seoul 08826, Republic of Korea

gcbae02@snu.ac.kr

GYOUNGHUN KO

HCMS, Academy of Mathematics and Systems Science, Chinese Academy of Sciences, Beijing 100045, China

gyeonghungo@amss.ac.cn

DONGHYUN LEE

Department of Mathematics, Pohang University of Science and Technology, Pohang, South Korea

donglee@postech.ac.kr

SEOK-BAE YUN

Department of Mathematics, Sungkyunkwan University, Suwon 16419, Republic of Korea

sbyun01@skku.edu