Global well‐posedness of the variable‐order fractional wave equation with variable exponent nonlinearity

Abstract In this paper, we conduct a comprehensive study of the global well‐posedness of solution for a class of nonlocal wave equations with variable‐order fractional Laplacian and variable exponent nonlinearity by constructing a suitable framework of the variational theory. We first prove the local‐in‐time existence of the weak solution via the Galerkin approximation technique and fixed point theory. Then by constructing the potential well theory, we classify the initial data leading to the global existence and finite time blowup of the solution for three different initial energy cases, that is, subcritical initial energy case, critical initial energy case, and supercritical initial energy case. For the subcritical and critical initial energy cases, we show that the solution exists globally in time when the initial data belong to the stable manifold and blows up in finite time when the initial data belong to the unstable manifold. For the supercritical initial energy case, we observe some initial conditions that enable the finite time blow‐up solution by an adapted concavity method, and the issue of global existence still remains unsolved. As a further study of finite time blowup, we estimate the upper and lower bounds of blow‐up time by using different strategies, that is, applying some first‐order differential inequality regardless of the different initial energy levels, to give a unified expression for the lower bound estimation for three initial energy levels. For the upper bound estimation, we utilize two second‐order differential inequalities influenced by the different energy levels to give the upper bound estimations of the blow‐up time at each initial energy level.