This paper investigates the spatial decay estimates for a coupled Moore-Gibson-Thompson (MGT) and Fourier heat system defined on a semi-infinite cylindrical domain in $\mathbb{R}^3$. Under homogeneous initial-boundary conditions and suitable decay assumptions at infinity, we derive a second-order differential inequality satisfied by the total energy functional. By transforming this inequality into a first-order form via operator factorization, we establish explicit exponential decay estimates of the energy along the axial direction. The result generalizes the classical Saint-Venant principle to higher-order coupled dissipative systems and provides a quantitative characterization of spatial decay for MGT-Fourier-type equations in unbounded domains. The findings contribute to the mathematical theory of thermoviscoelasticity and offer a foundation for further studies on structural stability and long-time behavior in such coupled systems.
Citation: Jincheng Shi, Zijun Cheng. Exponential spatial decay estimates for the MGT-Fourier system in semi-infinite cylindrical domains[J]. AIMS Mathematics, 2026, 11(7): 19921-19937. doi: 10.3934/math.2026808
This paper investigates the spatial decay estimates for a coupled Moore-Gibson-Thompson (MGT) and Fourier heat system defined on a semi-infinite cylindrical domain in $\mathbb{R}^3$. Under homogeneous initial-boundary conditions and suitable decay assumptions at infinity, we derive a second-order differential inequality satisfied by the total energy functional. By transforming this inequality into a first-order form via operator factorization, we establish explicit exponential decay estimates of the energy along the axial direction. The result generalizes the classical Saint-Venant principle to higher-order coupled dissipative systems and provides a quantitative characterization of spatial decay for MGT-Fourier-type equations in unbounded domains. The findings contribute to the mathematical theory of thermoviscoelasticity and offer a foundation for further studies on structural stability and long-time behavior in such coupled systems.
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