arXiv subjects

Songsong Lu

Publications and source records attributed to Songsong Lu.

3 recordsLinked to original sources

arXiv2022

Strongly Compact Strong Trajectory Attractors for Evolutionary Systems and their Applications

We show that for any fixed accuracy and time length $T$, a {\it finite} number of $T$-time length pieces of the complete trajectories on the global attractor are capable of uniformly approximating all trajectories within the accuracy in the natural strong metric after sufficiently large time when the observed dissipative system is asymptotically compact. Moreover, we obtain the strong equicontinuity of all the complete trajectories on the global attractor. These results follow by proving the existence of a strongly compact strong trajectory attractor. The notion of a trajectory attractor was previously constructed for a family of auxiliary systems including the originally considered one without uniqueness. Recently, Cheskidov and the author developed a new framework called evolutionary system, with which a (weak) trajectory attractor can be actually defined for the original system. In this paper, the theory of trajectory attractors is further developed in the natural strong metric for our purpose. We then apply it to both the 2D and the 3D Navier-Stokes equations and a general nonautonomous reaction-diffusion system.

math.DS↗

arXiv2022

Evolutionary system, global attractor, trajectory attractor and applications to the nonautonomous reaction-diffusion systems

In [Adv. Math., 267(2014), 277-306], Cheskidov and Lu develop a new framework of the evolutionary system that deals directly with the notion of a uniform global attractor due to Haraux, and by which a trajectory attractor is able to be defined for the original system under consideration. The notion of a trajectory attractor was previously established for a system without uniqueness by considering a family of auxiliary systems including the original one. In this paper, we further prove the existence of a notion of a strongly compact strong trajectory attractor if the system is asymptotically compact. As a consequence, we obtain the strong equicontinuity of all complete trajectories on global attractor and the finite strong uniform tracking property. Then we apply the theory to a general nonautonomous reaction-diffusion systems. In particular, we obtain the structure of uniform global attractors without any additional condition on nonlinearity other than those guarantee the existence of a uniform absorbing set. Finally, we construct some interesting examples of such nonlinearities. It is not known whether they can be handled by previous frameworks.

math.DS↗

arXiv2014

Uniform global attractors for the nonautonomous 3D Navier-Stokes equations

We obtain the existence and the structure of the weak uniform (with respect to the initial time) global attractor and construct a trajectory attractor for the 3D Navier-Stokes equations (NSE) with a fixed time-dependent force satisfying a translation boundedness condition. Moreover, we show that if the force is normal and every complete bounded solution is strongly continuous, then the uniform global attractor is strong, strongly compact, and solutions converge strongly toward the trajectory attractor. Our method is based on taking a closure of the autonomous evolutionary system without uniqueness, whose trajectories are solutions to the nonautonomous 3D NSE. The established framework is general and can also be applied to other nonautonomous dissipative partial differential equations for which the uniqueness of solutions might not hold. It is not known whether previous frameworks can also be applied in such cases as we indicate in open problems related to the question of uniqueness of the Leray-Hopf weak solutions.

math.DS↗