Time-Periodic Solution of the Weakly Dissipative Camassa-Holm Equation
Abstract
This paper is concerned with time-periodic solution of the weakly dissipative Camassa-Holm equation with a periodic boundary condition. The existence and uniqueness of a time periodic solution is presented.
1. Introduction
Since the equation was derived physically by Camassa and Holm [1, 2], many researchers have paid extensive attention to it. The Camassa-Holm equation is also a model for the propagation of axially symmetric waves in hyperelastic rods [3, 4]. It has a bi-Hamiltonian structure [5, 6] and is completely integrable [1, 2, 7–11]. It is a reexpression of geodesic flow on the diffeomorphism group of the circle [12] and on the Virasoro group [13]. Its solitary waves are peaked [7], and they are orbitally stable and interact like solitons [14–16]. The peakons capture a characteristic of the traveling waves of greatest height-exact traveling solutions of the governing equations for water waves with a peak at their crest [17–19].
It is worth pointing out that the advantage of the Camassa-Holm equation in comparison with the KdV equation lies in the fact that the Camassa-Holm equation has peaked solitons and models wave breaking [2, 20, 21].
In general, it is difficult to avoid energy dissipation mechanisms in a real world. Ott and Sudan [38] investigated how the KdV equation was modified by the presence of dissipation and the effect of such dissipation on the solitary solution of the KdV equation. Ghidaglia [39] investigated the long-time behavior of solutions to the weakly dissipative KdV equation as a finite-dimensional dynamical system.
The local well-posedness, global existence, and blow-up phenomena of the Cauchy problem of (1.4) on the line [40] and on the circle [41] were studied. A new global existence result and a new blow-up result for strong solutions to this equation with certain profiles are presented recently [42]. We found that the behaviors of (1.4) are similar to the Camassa-Holm equation in a finite interval of time, such as the local well-posedness and the blow-up phenomena, and that there are considerable differences between (1.4) and the Camassa-Holm equation in their long-time behaviors. The global solutions of (1.4) decay to zero as time goes to infinity provided the potential is of one sign (see [40, 41]). This long-time behavior is an important feature that the Camassa-Holm equation does not possess. It is well known that the Camassa-Holm equation has peaked traveling wave solutions. But the fact that any global solution of (1.4) decays to zero means that there are no traveling wave solutions of (1.4).
Equation (1.4) has the same blow-up rate as the Camassa-Holm equation does when the blow-up occurs [41]. This fact shows that the blow-up rate of the Camassa-Holm equation is not affected by the weakly dissipative term, but the occurrence of blow-up of (1.4) is affected by the dissipative parameter [40, 41].
Our paper is organized as follows. In Section 2, we give some notations and definition of some space used in this paper. In Section 3, we prove the existence of the approximate solution and give uniform a priori estimates needed where we prove the convergence of a sequence of the approximate solution. Section 4 is devoted to the study of the existence and uniqueness of time-periodic solution for (1.6)–(1.8).
2. Preliminaries
Before starting our work, it is appropriate to introduce some notations and inequalities that will be used in the paper.
Let X be a Banach space, we denote by Ck(ω; X) the set of ω-periodic X-valued measurable functions on ℝ1 with continuous derivatives up to order k. The norm in the space Ck(ω; X) is .
The space Wk,p(ω; X) denote the set of functions which belong to Lp(ω; X) together with their derivatives up to order k, and we write Wk,2(ω; X) = Hk(ω; X) in particular when X is a Hilbert space.
Lp(Ω) and Hm(Ω) are classical Sobolev spaces. For simplicity, we write by ∥·∥p as p ≠ 2 and by ∥·∥.
3. A Priori Estimates
In this section, we first prove that (1.6)–(1.8) have a sequence of approximate solutions , then give a prior, estimates about .
Lemma 3.1. If f ∈ C1(ω; H−1(Ω)), then
Proof. Multiplying (3.1) by ajn(t) and summing up over j from 1 to n, we obtain
Then, we can get
Notice that , .
From Young’s inequality, we have , where ε > 0 is a constant.
According to the above relations, we can derive from (3.4) that
Considering the time periodicity of un and integrating (3.5) over [0, ω], we get
Hence, there exists t* ∈ [0, ω) such that .
From (3.5), we have .
Integrating the above inequality with respect to t from t* to t ∈ [t*, t* + ω], we deduce that
Hence, we infer
From Lemma 3.1 and Leray-Schauder fixed point theorem, (3.1) has solution , which is also a sequence of approximate solutions of (1.6)–(1.8). In order to obtain the convergence of sequence , we need to give a priori estimates for the high-order derivers of .
Lemma 3.2. If f ∈ C1(ω; H−1(Ω)), then
Proof. Multiplying (3.1) by −λjajn(t) and summing up over j from 1 to n, we have
The above equation yields
From Young’s inequality, we have
From (2.2), (3.8), and Young’s inequality, we can deduce that
From (2.3), (3.8), Cauchy-Schwarz inequality, Young’s inequality, and Lemma 3.1, we get
Taking (3.11)–(3.15) into account, we can infer that
Integrating (3.16) about t from 0 to ω and considering the time periodicity of un, we get
Hence, there exists t* ∈ [0, ω) such that
From (3.16), we have
Then we can obtain
In the following, we continue to establish a priori estimates for high-order derivers of the approximate solution by an inductive argument.
Lemma 3.3. For any k ≥ 0, if f ∈ C1(ω; Hk−1(Ω)), then
Proof. By Lemma 3.2, we know the conclusion of Lemma 3.3 holds for k = 0.
Assume that for k ≤ m − 1(m ≥ 2) the conclusion of Lemma 3.3 holds, we want to prove that the same statement holds for k = m also.
Multiplying (3.1) by and summing up over j from 1 to n, we have
Follow the same methods discussed in Lemma 3.2, we have
From the conclusion of Lemma 3.3 for k ≤ m − 1, (2.2), (2.4) and Young’s inequality, we can deduce that
Similarly, we can also deduce that
From the conclusion of Lemma 3.3 for k ≤ m − 1, Young’s inequality and (2.3), we have
Combining (3.25) and the above inequality, we can get
Similarly,
Taking (3.22)–(3.24) and (3.27)-(3.28) into account, we can deduce that
From the above relation, we can infer
Integrating (3.30) about t from 0 to ω, there exists t* ∈ [0, ω) such that
From (3.30), we have
Integrating the above inequality from t* to t ∈ [t*, t* + ω] and with (3.31), we can easily obtain
The proof is completed.
Lemma 3.4. For any k ≥ 0, if f ∈ C1(ω; Hk+1(Ω)), then
Proof. We first prove the conclusion of Lemma 3.4 holds for k = 0. Multiplying (3.1) by and summing up over j from 1 to n, we have
By Lemma 3.3, if f ∈ C1(ω; H1(Ω)), then we have . Hence,
Therefore, from (3.35) and (3.36), it is easy to know that
Assume that the conclusion of Lemma 3.4 holds for k ≤ m(m ≥ 1), we want to prove that the conclusion of Lemma 3.4 also holds for k = m + 1.
Multiplying (3.1) by and summing up over j from 1 to n, we have
By Lemma 3.3, if f ∈ C1(ω; Hm+2(Ω)), then for k ≤ m + 5. Hence,
Taking (3.38) and (3.39) into account, it follows
This completes the proof of Lemma 3.4 by an inductive argument.
4. Existence and Uniqueness of Time-Periodic Solution
We have proved that (1.6)–(1.8) have a sequence of approximate solutions . In this section, we want to prove that the sequence converges and the limit is a solution of (1.6)–(1.8).
So we obtain that the existence of time periodic solution for (1.6)–(1.8), which is the following theorem.
Theorem 4.1. Given f ∈ C1(ω; Hk+1(Ω)), k ≥ 0, there exists a time periodic solution u(t, x) to (1.6)–(1.8), such that u(t, x) ∈ L∞(ω; Hk+4(Ω))∩W1,∞(ω; Hk(Ω)).
Under the assumption of Theorem 4.1, we are unable to prove the uniqueness of the solution for (1.6)–(1.8). But if we assume that M is sufficiently small, then the result can be obtained.
Theorem 4.2. Suppose that the assumption in Theorem 4.1 holds. If M is sufficiently small, then the time periodic solution of (1.6)–(1.8) in Theorem 4.1 is unique.
Proof. Let u and be any two time periodic solutions of (1.6)–(1.8). With , we can get from (1.6) that
Taking the inner product of (4.7) with v, we have
Since,
Hence, if M is sufficient small such that , , then it follows from (4.8)–(4.11), we get
Applying Gronwall’s inequality, we derive that
Since v is ω-periodic in t, then for any positive integer m we have
Then we can infer that
It follows from v(0) = vx(0) = 0 that , which completes the proof of Theorem 4.2.