The partial null conditions and global smooth solutions of the nonlinear wave equations on Rd x T with d=2, 3

In this paper, we investigate the fully nonlinear wave equations on the product space R3 x T with quadratic nonlinearities and on R2 x T with cubic nonlinearities, respectively. It is shown that for the small initial data satisfying some space-decay rates at infinity, these nonlinear equations admit global smooth solutions when the corresponding partial null conditions hold and while have almost global smooth solutions when the partial null conditions are violated. Our proof relies on the Fourier mode decomposition of the solutions with respect to the periodic direction, the efficient combinations of time-decay estimates for the solutions to the linear wave equations and the linear Klein-Gordon equations, and the global weighted energy estimates. In addition, an interesting auxiliary energy is introduced. As a byproduct, our results can be applied to the 4D irrotational compressible Euler equations of polytropic gases or Chaplygin gases on R3 x T, the 3D relativistic membrane equation and the 3D nonlinear membrane equation on R2 x T. (c) 2023 Elsevier Inc. All rights reserved.