The goal of this paper is to construct explicitly the global attractors of quasilinear parabolic equations when solution can also grow-up, and hence the attractor is unbounded and induces a flow at infinity. In particular, we construct heteroclinic connections between bounded and/or unbounded hyperbolic equilibria when the diffusion is asymptotically linear.Keywords: quasilinear parabolic equations, infinite dimensional dynamical systems, grow-up, unbounded global attractor, Sturm attractor.
Main resultsConsider the scalar quasilinear parabolic differential equation. We suppose that 2α + β > 1 so that solutions are at least C 1 ([0, π]). The appropriate functional setting is described in Section 2.1.We are interested in the asymptotic behaviour of solutions of (1.1) when grow-up can occur, namely, when solutions grows unboundedly as t → ∞. Sufficient conditions for grow-up to occur is when b > 0, as we will prove later in Lemma 2.1. This class of asymptotics is also known as slowly non-dissipative. In this setting, there does not exist a global attractor in the usual sense, namely a maximal compact invariant set that attracts all bounded sets. Emitting the compactness condition, there is an unbounded global attractor A ⊆ X α , defined as the minimal invariant non-empty set in X α attracting all bounded sets, firstly introduced by Chepyzhov and Goritskii [7]. The goal of this paper is to decompose A into smaller invariant sets, describe them and show how they are related. This geometric description of the attractor A in the semilinear dissipative case was carried out by Brunovský and Fiedler [5] for f (u), by Fiedler and Rocha [10] for f (x, u, u x ), for periodic boundary conditions by Fiedler, Rocha and Wolfrum [11], and for quasilinear equations by Lappicy [15]. Such attractors are known as Sturm attractors. When solutions can grow-up, the semilinear case was previously studied by Hell [13] in order to give an understanding of the structure at infinity, Ben-Gal [4] for f (u), Pimentel and Rocha [22] for f (x, u, u x ). The case of periodic boundary condition was treated separately in Pimentel [21]. Such attractors are known as unbounded Sturm attractors.Despite non-dissipativity, there still exist a Lyapunov function constructed by Matano [19]. Hence, the following dichotomy hold: either solutions converge to a bounded equilibrium as t → ∞, or it is a grow-up solution.