# Exact solutions of Benjamin-Bona-Mahony-Burgers-type nonlinear pseudo-parabolic equations

- Ömer Faruk Gözükızıl
^{1}Email author and - Şamil Akçağıl
^{1}

**2012**:144

**DOI: **10.1186/1687-2770-2012-144

© Gözükızıl and Akçağıl; licensee Springer 2012

**Received: **16 August 2012

**Accepted: **22 November 2012

**Published: **10 December 2012

## Abstract

In this paper, we consider some nonlinear pseudo-parabolic Benjamin-Bona-Mahony-Burgers (BBMB) equations. These equations are of a class of nonlinear pseudo-parabolic or Sobolev-type equations ${u}_{t}-\mathrm{\Delta}{u}_{t}-\alpha \mathrm{\Delta}u=f(x,u,\mathrm{\nabla}u)$, *α* is a fixed positive constant, arising from the mathematical physics. The tanh method with the aid of symbolic computational system is employed to investigate exact solutions of BBMB-type equations and the exact solutions are found. The results obtained can be viewed as verification and improvement of the previously known data.

### Keywords

nonlinear pseudo-parabolic equation Benjamin-Bona-Mahony-Burgers (BBMB)-type equation Sobolev-type equation tanh method## 1 Introduction

arise in many areas of mathematics and physics, where $u=u(x,t)$, $x\in \mathrm{\Omega}\subset {\mathbb{R}}^{n}$, $t\ge 0$, *η* and *α* are non-negative constants, Δ denotes the Laplace operator acting on the space variables *x*. Equations of type (1) with only one time derivative appearing in the highest-order term are called pseudo-parabolic and they are a special case of Sobolev equations. They are characterized by derivatives of mixed type (*i.e.*, time and space derivatives together) appearing in the highest-order terms of the equation and were studied by Sobolev [1]. Sobolev equations have been used to describe many physical phenomena [2–8]. Equation (1) arises as a mathematical model for the unidirectional propagation of nonlinear, dispersive, long waves. In applications, *u* is typically the amplitude or velocity, *x* is proportional to the distance in the direction of propagation, and *t* is proportional to elapsed time [9].

The BBMB equation has been tackled and investigated by many authors. For more details, we refer the reader to [11–15] and the references therein.

has been considered and a set of new solitons, kinks, antikinks, compactons, and Wadati solitons have been derived using by the classical Lie method, where *α* is a positive constant, $\beta \in \mathbb{R}$, and $g(u)$ is a ${C}^{2}$-smooth nonlinear function. Equation (4) with the dissipative term $\alpha {u}_{xx}$ arises in the phenomena for both the bore propagation and the water waves.

Peregrine [17] and Benjamin, Bona, and Mahony [10] have proposed equation (4) with the parameters $g(u)=u{u}_{x}$, $\alpha =0$, and $\beta =1$. Furthermore, Benjamin, Bona, and Mahony proposed equation (4) as an alternative regularized long-wave equation with the same parameters.

Khaled, Momani, and Alawneh obtained explicit and numerical solutions of BBMB equation (4) by using the Adomian’s decomposition method [18] .

Tari and Ganji implemented variational iteration and homotopy perturbation methods obtaining approximate explicit solutions for (4) with $g(u)=\frac{{u}^{2}}{2}$ [19] and El-Wakil, Abdou, and Hendi used another method (the exp-function) to obtain the generalized solitary solutions and periodic solutions of this equation [20].

In addition, we consider $g(u)=\frac{{u}^{3}}{3}$ and obtain analytic solutions in a closed form.

The aim of this work is twofold. First, it is to obtain the exact solutions of the Benjamin-Bona-Mahony-Burgers (BBMB) equation and the generalized Benjamin-Bona-Mahony-Burgers equation with $g(u)=u{u}_{x}$, $g(u)=\frac{{u}^{2}}{2}$, $g(u)=\frac{{u}^{3}}{3}$; and second, it is to show that the tanh method can be applied to obtain the solutions of pseudo-parabolic equations.

## 2 Outline of the tanh method

- (i)First, consider a general form of the nonlinear equation$P(u,{u}_{t},{u}_{x},{u}_{xx},\dots )=0.$(5)
- (ii)To find the traveling wave solution of equation (5), the wave variable $\xi =x-Vt$ is introduced so that$u(x,t)=U(\mu \xi ).$(6)

- (iii)
If all terms of the resulting ODE contain derivatives in

*ξ*, then by integrating this equation and by considering the constant of integration to be zero, one obtains a simplified ODE. - (iv)A new independent variable$Y=tanh(\mu \xi )$(9)

- (v)The
*ansatz*of the form$U(\mu \xi )=S(Y)=\sum _{k=0}^{M}{a}_{k}{Y}^{k}+\sum _{k=1}^{M}{b}_{k}{Y}^{-k}$(11)

*M*is a positive integer, in most cases, that will be determined. If

*M*is not an integer, then a transformation formula is used to overcome this difficulty. Substituting (10) and (11) into ODE (8) yields an equation in powers of

*Y*.

- (vi)
To determine the parameter

*M*, the linear terms of highest order in the resulting equation with the highest-order nonlinear terms are balanced. With*M*determined, one collects all the coefficients of powers of*Y*in the resulting equation where these coefficients have to vanish. This will give a system of algebraic equations involving the ${a}_{k}$ and ${b}_{k}$ ($k=0,\dots ,M$),*V*, and*μ*. Having determined these parameters, knowing that*M*is a positive integer in most cases, and using (11), one obtains an analytic solution in a closed form.

Throughout the work, Mathematica or Maple is used to deal with the tedious algebraic operations.

## 3 The Benjamin-Bona-Mahony-Burgers (BBMB) equation

*α*is a positive constant. Using the wave variable $\xi =x-Vt$ carries (12) into the ODE

*Y*, and setting it equal to zero, we find the system of equations

## 4 The generalized Benjamin-Bona-Mahony-Burgers equation

where *α* is a positive constant and $\beta \in \mathbb{R}$.

Case 1. $g(u)=u{u}_{x}$.

*k*is left as a free parameter. These give the following solutions:

Case 2. $g(u)=\frac{{u}^{2}}{2}$.

Case 3. $g(u)=\frac{{u}^{3}}{3}$.

## 5 Conclusion

In summary, we implemented the tanh method to solve some nonlinear pseudo-parabolic Benjamin-Bona-Mahony-Burgers equations and obtained new solutions which could not be attained in the past. Besides, we have seen that the tanh method is easy to apply and reliable to solve the pseudo-parabolic and the Sobolev-type equations.

## Declarations

## Authors’ Affiliations

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