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# Asymptotic behavior of solutions for the time-delayed equations of Benjamin-Bona-Mahony’s type

*Boundary Value Problems*
**volume 2015**, Article number: 129 (2015)

## Abstract

In this paper, we investigate the asymptotic behavior of the solutions for the equations of Benjamin-Bona-Mahony’s type with a time delay. We prove the global existence of solutions and energy decay. By using the Liapunov function method, we shall show that the solution is exponentially decay if the delay parameter *τ* is sufficiently small.

## 1 Introduction

In this paper, we consider a family of dispersive equations of Benjamin-Bona-Mahony’s type under the effect of dissipation, and we will investigate the asymptotic behavior of the solutions. Our model can be written in the abstract form

where \(x\in\mathbb{R}^{1}\), \(t>0\), \(-\tau\leq s\leq0\), \(\alpha>0\), and we set \(\Omega=(0,1)\). The operators *M* and *L* can be differential operators or pseudo-differential operators, and the orders of pseudo-differential operators *M* and *L* are *μ* and *s* with \(s\geq\mu\geq2\).

In the simplest case, when *M* and *L* are the differential operators \(M=I-\frac{\partial}{\partial x^{2}}\), \(L=-\frac{\partial}{\partial x^{2}}\), (1.1) is the well-known Benjamin-Bona-Mahony model [1]:

which describes the unidirectional propagation of weakly nonlinear dispersive long waves where Burger’s type dissipation is considered. The existence of global solutions and asymptotic behavior in time have been studied by several authors. The asymptotic behavior of solutions to the generalized Korteweg-de Vries-Burgers and Benjamin-Bona-Mahony-Burgers equations in one space dimension was studied by Amick, Bona and Schonbek in [2], by Wang and Yang in [3], and by Bona and Luo in [4]. These results were generalized by Zhang [5] to multiple spatial dimensions. In [6–8] the authors considered a family of equations of KdV and BBM’s type described by pseudo-differential operators, and studied the asymptotic behavior in one space dimension. In [9] study the Cauchy problem for a class of nonlinear dissipative equations of Benjamin-Bona-Mahony’s type and discuss the existence of a global attractor and estimate its Hausdorff and fractal dimensions. But few of the equations involving delay.

To explain our motivation of introducing a time delay into Benjamin-Bona-Mahony equation, we consider the rate of change of *u*, which we denote by \(\frac{Du}{Dt}\), is

where \(x(t)\) is understood to change with time at \(u=\frac{dx}{dt}\). However, we might have a delay *τ* to *u*. In this case the rate of change of *u* with the delay *τ* should be

This clearly shows how we obtain the time-delay term \(u(x,t-\tau)u_{x}(x,t)\) in Benjamin-Bona-Mahony equation (1.4). There is literature about delay reaction-diffusion equations [10–12], on which our work is based. Recently, the asymptotic behavior of solutions of time-delayed Burgers equation was studied by Liu in [13]. Subsequently, exponentially decay rate of solutions for Benjamin-Bona-Mahony equation (1.4) with a time decay was studied in [14], and in [15] author have obtained the exponentially decay rate of solutions for the time-Delayed Kuramoto-Sivashinsky equation. Here, by using the Liapunov function method, we shall show that the solution of problems (1.1)-(1.3) is exponentially decay if the delay parameter *τ* is sufficiently small.

We shall use standard notation. By \(L^{p}(\Omega)\) we shall denote the space of functions in Ω whose *p*th power is integrable, with the norm \(\|g\| _{L^{p}}^{p}=\int_{\Omega}|g(x)|^{p}\,dx\), \(1\leq p<+\infty\). The norm in \(L^{2}(\Omega)\) we will denote by \(\|\cdot\|_{L^{2}}=\|\cdot\|\). By \(L^{\infty}(\Omega)\) we denote the space of measurable essentially bounded functions in Ω with the norm

For each \(\sigma\in\mathbb{R}\) we shall denote by \(H^{\sigma}(\Omega)\) the usual Sobolev space of order *σ*. By \(H_{\mathrm{per}}^{\sigma}(\Omega)\), \(\sigma\geq0\) we shall indicate the space of functions periodic in the sense of (1.2). If \(g\in H_{\mathrm{per}}^{\sigma}(\Omega)\) then *g* has an expansion in a Fourier series,

The norm of *g* in \(H_{\mathrm{per}}^{\sigma}(\Omega)\) will be denoted by

which is equivalent to \(H^{\sigma}(\Omega)\) norm, \(\sigma\geq0\), according to Temam [16]. We shall denote by \(\dot{L}^{2}(\Omega)\) and \(\dot{H}^{\sigma}(\Omega)\) the space of functions \(g\in L^{2}(\Omega)\) or \(H^{\sigma}(\Omega)\) such that

The space \(\dot{H}^{\sigma}(\Omega)\), \(\sigma\in\mathbb{R}_{+}\), is the space of functions \(g\in L^{2}(\Omega)\)) such that *g* satisfies (1.5) and

In \(\dot{H}_{\mathrm{per}}^{1}(\Omega)\) the Poincaré inequality holds, that is, if \(g\in\dot{H}_{\mathrm{per}}^{1}(\Omega)\) then

The inequality (1.6) shows that \(\dot{H}_{\mathrm{per}}^{1}(\Omega)\) is a Hilbert space with scalar product of \(H_{0}^{1}(\Omega)\), and \(\|u\| _{H^{1}}=(u,u)_{H^{1}}^{1/2}\) is a norm on this space equivalent to that induced by \(H^{1}(\Omega)\).

The operators *M* and *L* of (1.1) are pseudo-differential operators of orders *μ* and *s*, respectively, with

and

where *m* and *l* are the principal symbols of the operators *M* and *L*, respectively. We assume from now on that the symbols *m* and *l* are even functions of *k* that satisfy the growth conditions:

(i) There exist constants \(c_{1}, c_{2}>0\) such that

(ii) There exist constants \(c_{3}, c_{4}>0\) such that

The domains of operators *M* and *L* are given by

Let *X* be a Banach space and \(a< b\). We denote by \(C^{n}([a,b];X)\) the space of *n* times continuously differentiable functions defined on \([a,b]\) with values in *X* with the supremum norm and we write \(C([a,b];X)\) for \(C^{0}([a,b];X)\).

The main result of this paper is stated as follows.

### Theorem 1.1

*For any initial condition*
\(u_{0}=u_{0}(x,s)\in C([-\tau,0], \dot{H}_{\mathrm{per}}^{\frac{\mu}{2}}(\Omega))\), \(\mu\geq2\), \(s\geq 0\), *and suppose*
*M*
*and*
*L*
*satisfy the assumptions* (1.7), (1.8). *Then problem* (1.1)-(1.3) *has a unique global mild solution*
*u*
*on*
\([-\tau, \infty)\)
*with*

### Theorem 1.2

*Under the assumption of Theorem *
1.1, *if*
\(\mu=s\), *there are*
\(\tau_{0}, \omega, K>0\)
*such that*, *for*
\(\tau<\tau_{0}\), *the solution of* (1.1)-(1.3) *satisfies*

This paper is organized as follows. In next section, we prove the existence of the solution. Furthermore, we show that the solution is exponentially decay by using the Liapunov function method.

## 2 Exponential decay estimates

Firstly, we briefly show that problem (1.1)-(1.3) is well posed. To conveniences, we denote \(\|u\|\leq\lambda_{1}\|L^{\frac{1}{2}}u\|\), \(\|u_{x}\|\leq\lambda_{2}\|L^{\frac{1}{2}}u\|\), \(\|u\|\leq\lambda_{3}\|M^{\frac{1}{2}}u\|\), \(\|u_{x}\|\leq\lambda_{4}\| M^{\frac{1}{2}}u\|\), \(\|M^{\frac{1}{2}}u\|\leq\lambda_{5}\|L^{\frac{1}{2}}u\|\).

### Proof of Theorem 1.1

By the standard methods as in [9], it is easy to prove that for every initial value \(u_{0}=u_{0}(x,s)\in C([-\tau,0], \dot{H}_{\mathrm{per}}^{\frac{\mu}{2}}(\Omega))\), there exists a \(T=T(u_{0})>0\) such that problem (1.1)-(1.3) has a unique mild solution *u* on \([-\tau, T]\) with

Furthermore, for any \(\tau>0\), the solution of (1.1)-(1.3) does not blow up in finite time. Indeed, multiplying (1.1) by *u*, integrating by parts, we obtain, for \(0\leq t\leq\tau\),

By the Young inequality, we get

which implies that

where \(K_{1}(\|u_{0}\|_{C([-\tau,0], \dot{H}_{\mathrm{per}}^{\frac{\mu}{2}}(\Omega ))})\) is a positive constant depending on \(\|u_{0}\|_{C([-\tau,0], \dot{H}_{\mathrm{per}}^{\frac{\mu}{2}}(\Omega ))}\). Repeating the above procedure, we can prove that, for \(n\tau\leq t\leq(n+1)\tau\) (\(n=1,2,\ldots\)),

In summary, we have proved Theorem 1.1. □

Secondly, we prove that our main result about the exponential stability. To this end, we introduce the following notations. For a given initial condition \(u_{0}=u_{0}(x,s)\in C([-\tau,0], \dot{H}_{\mathrm{per}}^{\frac{\mu}{2}}(\Omega))\), denote

Set

and let \(\tau_{0}\) be small enough, such that for any *τ*, \(0\leq\tau <\tau_{0}\leq\sigma\),

### Proof of Theorem 1.2

Let

Since

and \(\|M^{1/2}u(t)\|\) is continuous, we have \(T_{0}>0\). We shall prove that \(T_{0}=+\infty\). For this, we argue by *contradiction*. If \(T_{0}<+\infty\), then we have

and

Multiplying (1.1) by *u*, then integrating on Ω with respect to *x*, we obtain

Since \(\int_{0}^{1} u^{2}(t)u_{x}(t)\,dx=0\), we have

where

We now majorize Φ in the right hand side of (2.7). Firstly, since

we have

Let

we have

and

We now want to estimate Ψ. To this end, multiplying (1.1) by \(u_{t}\), then integrating on Ω with respect to *x*, we obtain

Integrating on \([t-\tau, t]\), \(0\leq t\leq T_{0}\), we obtain

where

which implies that

We now majorize *H*:

with \(0<\varepsilon<2\lambda_{3}^{-2}\). Thus by (2.10)-(2.11), we have

furthermore, by (2.9), we get

Then (2.8) and (2.13) implies that

Thus, by (2.7) and (2.14), we obtain

furthermore,

where *ω* is defined by (2.3). Solving the above inequality gives

Hence

which is in contradiction with (2.6). Therefore, we have proved that \(T_{0}=+\infty\) and then (1.9) follows from (2.16). Thus we have completed the proof of Theorem 1.2. □

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## Acknowledgements

This work was supported by the Postdoctor Research Fund of Chongqing (No. YuXM201102006), the National Natural Science Foundation of China (No. 61273020), and the Fundamental Research Funds for the Central Universities (No. XDJK2009C070).

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### Authors’ contributions

FW gave access to information, PZ formulated the outline and ZC wrote the essay. All authors read and approved the final manuscript.

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Wei, F., Zhilin, P. & Chaosheng, Z. Asymptotic behavior of solutions for the time-delayed equations of Benjamin-Bona-Mahony’s type.
*Bound Value Probl* **2015**, 129 (2015). https://doi.org/10.1186/s13661-015-0388-3

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DOI: https://doi.org/10.1186/s13661-015-0388-3