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Exact traveling wave solutions for system of nonlinear evolution equations
SpringerPlus volume 5, Article number: 663 (2016)
Abstract
In this work, recently deduced generalized Kudryashov method is applied to the variant Boussinesq equations, and the (2 + 1)dimensional breaking soliton equations. As a result a range of qualitative explicit exact traveling wave solutions are deduced for these equations, which motivates us to develop, in the near future, a new approach to obtain unsteady solutions of autonomous nonlinear evolution equations those arise in mathematical physics and engineering fields. It is uncomplicated to extend this method to higherorder nonlinear evolution equations in mathematical physics. And it should be possible to apply the same method to nonlinear evolution equations having more general forms of nonlinearities by utilizing the traveling wave hypothesis.
Background
The study of autonomous nonlinear evolution equations has a rich and long history, which has continued to attract attention in more recent years. The exact solutions to nonlinear evolution equations are the key tool to understand the various physical phenomena that govern the real world today. Hence searching for exact traveling wave solutions to nonlinear evolution equations plays an important role in the study of nonlinear physical phenomena in many fields such as fluid dynamics, water wave mechanics, meteorology, electromagnetic theory, plasma physics and nonlinear optics.
In the past several decades, there has been significant progress in the development of various methods for finding exact traveling wave solutions to nonlinear evolution equations, such as the Bäcklund transformation (Wahlquist and Estabrook 1973; Luo 2011), the Fexpansion method (Liu and Yang 2004; Islam et al. 2014), the tanh method (Wazwaz 2004), the expfunction method (Yusufoglu 2008; Khan and Akbar 2014a), the (G′/G)expansion method (Wang et al. 2008; Zayed and AlJoudi 2010; Kim and Sakthivel 2012; Khan and Akbar 2014b; Islam et al. 2013), the functional variable method (Zerarka et al. 2010; Khan and Akbar 2014c; Zayed et al. 2013a), the exp(−Φ(ξ))expansion method (Khan and Akbar 2014d, 2015), the modified simple equation method (Jawad et al. 2010; Khan and Akbar 2013, 2014e; Ahmed et al. 2013), the homotopy perturbation method (MohiudDin 2007; MohyudDin and Noor 2009), the Kudryashov method (Kudryashov 2012; Lee and Sakthivel 2013), and the Riccati equation mapping method (Zayed and Arnous 2013a, b).
The aim of this work is to demonstrate the efficiency of the generalized Kudryashov method for finding exact traveling wave solutions transmutable to the solitary wave solutions for system of nonlinear evolution equations. For this purpose, we consider the one dimensional variant Boussinesq equations, and the (2 + 1)dimensional breaking soliton equations.
Algorithm of the generalized Kudryashov method
Let us consider the nonlinear evolution equation in two independent variables x and t:
where \( u = u(x,t) \) is an unknown function, \( x \) is the spatial variable and \( t \) is the time variable, \( P \) is a polynomial in \( u \) and its various partial derivatives, in which the highest order derivatives and nonlinear terms are involved.
The main steps of generalized Kudryashov method are as follows (Demiray et al. 2014a, b; Baskonus and Bulut 2015):
Step 1:
The traveling wave variable \( \xi = x  \omega \,t \) transforms Eq. (1) into an ordinary differential equation of the form:
where the prime indicates differentiation with respect to \( \xi \), and ω ∊ ℝ\{0} is the velocity of the relative wave mode.
Equation (2) may be successively integrated as many times as possible. Remaining to the boundary conditions \( u(\xi ) \to 0 \) and \( \frac{{d^{m} u(\xi )}}{{d\xi^{m} }} \to 0\,(m = 1,\,2,\,3,\, \ldots ) \) for \( \xi \to \pm \infty \), \( \xi = x  \omega \,t \), the constants of integration, if any, should be set to zero (Malfliet and Hereman 1996; Wazwaz 2009).
Step 2:
Suppose that the solution of Eq. (2) has the following form:
where \( a_{i} (i = 0,\,1,\,2, \ldots ,N) \) and \( b_{j} (j = 0,\,1,\,2, \ldots ,M) \) are constants to be determined afterward such that \( a_{N} \ne 0 \) and \( b_{M} \ne 0 \), and \( Q = Q(\xi ) \) satisfies the following ordinary differential equation:
The solution of Eq. (4) is as follows:
where A is a constant of integration.
Step 3:
The positive integers N and M appearing in Eq. (3) can be determined by considering the homogeneous balance between the highest order derivatives and the nonlinear terms come out in Eq. (1) or Eq. (2). Moreover precisely, we define the degree of \( u(\xi ) \) as \( D(u(\xi )) = N  M \) which gives rise to the degree of other expression as follows:
where \( p,\,q,\,s \) are integer numbers.
Therefore, we can find the value of N and M in Eq. (3).
Step 4:
Substituting Eqs. (3) and (4) into Eq. (2), we obtain a polynomial in \( Q^{i  j} \), (\( i,j = 0,\,1,\,2, \ldots \)). In this polynomial equating the coefficients of all terms of the same powers of Q to zero, we obtain a system of algebraic equations which can be solved by using Maple or Mathematica to get the unknown parameters \( a_{i} (i = 0,\,1,\,2, \ldots ,N) \), \( b_{j} (j = 0,\,1,\,2, \ldots ,M) \), and \( \omega \). Consequently, we obtain the exact solutions of Eq. (1).
Applications
In this section, we will apply the generalized Kudryashov method to construct the exact traveling wave solutions transmutable to the solitary wave solutions for the following two nonlinear evolution equations:
Example 1. The variant Boussinesq equations:
In this subsection, we will apply the generalized Kudryashov method to find the exact solutions and then the solitary wave solutions to the variant Boussinesq equations (Wang et al. 2008; Khan and Akbar 2013, 2014b) in the form,
which was derived by Sachs in the year 1988 (Sachs 1988) as a model for water waves (Guo et al. 2015), where \( u(x,t) \) is the velocity, \( H(x,t) \) is the total bottom depth of the region occupied by the fluid and the subscripts denote the partial derivatives. The Boussinesq equation is a celebrated model of long water wave of moderate amplitude, which describes one dimensional, and weakly nonlinear internal wave which develops at the boundary between two immiscible fluids. Besides, the equation is a simplified model of the atmospheric movement equation which is applicable to mesoscale and quasiincompressible fluid movement, which means important physical applications in hydrodynamics. The Boussinesq equation also is of considerable mathematic interests because of its rich mathematical structures (Guo et al. 2015).
The traveling wave transformation is defined by,
Using traveling wave Eqs. (7), (6) transform into the following ordinary differential equations:
Integrating Eqs. (8) and (9) with respect to ξ, choosing the constant of integration as zero (under the boundary conditions described in “Algorithm of the generalized Kudryashov method” section (Step 1) and using similar boundary conditions for H(ξ)), we obtain the following ordinary differential equations respectively:
From Eq. (10), we get
Substituting Eq. (12) into Eq. (11), we obtain
Now balancing the highest order derivative \( u^{{\prime \prime }} \) and nonlinear term \( u^{3} \), we get \( 3N  3M = N  M + 2 \) or equivalent to \( N = M + 1 \).
Setting \( M = 1 \), we obtain \( N = 2 \). Therefore, Eq. (3) reduces to
Substituting Eq. (14) along with Eq. (4) into Eq. (13), we get a polynomial of \( Q^{k} \), (\( k = 0,\,1,\,2, \ldots \)). Equating the coefficients of this polynomial of the same powers of Q to zero, we obtain a system of algebraic equations. This system of equations yields the values for \( \omega ,a_{0} ,a_{1} ,a_{2} ,b_{0} \) and \( b_{1} \).
Set 1 corresponds to the following solutions for the variant Boussinesq equations:
Set 2 corresponds to the following solutions for the variant Boussinesq equations:
Set 3 corresponds to the following solutions for the variant Boussinesq equations:
Set 4 corresponds to the following solutions for the variant Boussinesq equations:
Set 5 corresponds to the following solutions for the variant Boussinesq equations:
Set 6 corresponds to the following solutions for the variant Boussinesq equations:
Remark
The bottom depth H(x,t) must be a nonnegative and real physical quantity. Solutions (17)–(22) of the variant Boussinesq equations are significant both mathematically and physically for their positive sign for H(x, t). Besides solutions (15) and (23) are valid mathematically and physically for their positive and negative signs for u(x, t) but their corresponding solutions (16) and (24) are valid only mathematically. Solutions (25) and (26) are complex solutions, therefore although they are logically true but they have no physical significance (Figs. 1, 2).
We can obtain some traveling wave solutions since A is an arbitrary constant of integration, for example.
If we put A = 1 into Eqs. (19) and (20) and considering u(x, t) > 0 as well as a wave moving to the right, i.e., in the positive direction of xaxis, we obtain
Example 2: The (2 + 1)dimensional breaking soliton equations:
Now, we will investigate explicit exact traveling wave solutions of the following (2 + 1)dimensional breaking soliton equations (Zayed et al. 2013b):
where α is a nonzero constant. Equations (29) and (30) describe the (2 + 1)dimensional interaction of a Riemann wave propagation along the yaxis with a long wave propagated along the xaxis.
Applying the traveling wave variable \( \xi = x + y  \omega \,t \) and proceeding as before, we obtain
Integrating Eq. (32), we obtain
choosing constant of integration as zero under the boundary conditions elucidated in “Algorithm of the generalized Kudryashov method” section (Step 1) and similar boundary conditions for v(ξ).
Substituting Eq. (33) into Eq. (31) and integrating, we get
choosing constant of integration to zero under the boundary conditions mentioned in “Algorithm of the generalized Kudryashov method” section (Step 1).
Considering the homogeneous balance between \( u^{{\prime \prime }} \) and \( u^{2} \) in Eq. (34), we obtain \( N = M + 2 \).
Setting \( M = 1 \), we obtain \( N = 3 \). Therefore, Eq. (3) takes the form
Substituting Eq. (35) along with Eq. (4) into Eq. (34), we get a polynomial of \( Q^{k} \), (\( k = 0,\,1,\,2, \ldots \)). Equating the coefficients of the polynomial of the same powers of Q to zero, we obtain a system of algebraic equations. This system of equations yields the values for \( \omega ,a_{0} ,a_{1} ,a_{2} ,b_{0} \) and \( b_{1} \).
Set 1 corresponds to the following solutions for the breaking soliton equations:
If we set A = 1, then Eq. (36) transforms to
Again, if we set A = −1, then Eq. (36) becomes
Set 2 corresponds to the following solutions for the breaking soliton equations:
If we set A = 1, then Eq. (39) becomes
Again, if we set A = −1, then Eq. (39) becomes (Fig. 3)
Comparisons

1.
Khan and Akbar (2013) studied the variant Boussinesq equations by means of the modified simple equation method and found only four solutions (see “Appendix 1”). On the other hand, by using the generalized Kudryashov method we have found twelve solutions. Moreover, if we put A = 1 into our solutions Eqs. (19) and (20), then these solutions coincide with the solutions (42) and (44) obtained by Khan and Akbar (2013) for the value of \( \omega =  1 \) and \( \omega = 1 \) (see “Appendix 1”). Similarly, if we put A = −1, then our solutions Eqs. (19) and (20) coincide with the solutions (43) and (45) for the values of \( \omega =  1 \) and \( \omega = 1 \) obtained by Khan and Akbar (2013).
The remaining solutions of Khan and Akbar (2013) given in “Appendix 1” are obtained changing ξ by −ξ in our Eq. (19). Note that all the solutions obtained here are also valid when one replaces the traveling wave variable ξ by −ξ.

2.
Zayed et al. (2013b) investigated exact traveling wave solutions to the (2 + 1)dimensional breaking soliton equation by means of the functional variable method and found only one solution (see “Appendix 2”). On the other hand, by using the generalized Kudryashov method we found four solutions from which one of our solutions coincides with the solution of Zayed et al. If we set \( c = \alpha \) into the solution (46) (see “Appendix 2”) obtained by Zayed et al. (2013b), then our solution (41) coincides with that solution.
From the above discussion, we conclude that the generalized Kudryashov method is a more reliable technique, in principle, than the modified simple equation method and the functional variable method.
Conclusions
In this article, we have successfully presented a mathematical tool named the generalized Kudryashov method for finding exact traveling wave solutions to the variant Boussinesq equations, and the (2 + 1)dimensional breaking soliton equations. The obtained results will serve as a very important milestone in the study of plasma physics and water waves phenomena. We also have demonstrated that the generalized Kudryashov method is an effective tool for obtaining exact analytical solutions for large classes of system of nonlinear evolution equations.
References
Ahmed MT, Khan K, Akbar MA (2013) Study of nonlinear evolution equations to construct traveling wave solutions via modified simple equation method. Phys Rev Res Int 3(4):490–503
Baskonus HM, Bulut H (2015) New hyperbolic function solutions for some nonlinear partial differential equation arising in mathematical physics. Entropy 17:4255–4270. doi:10.3390/e17064255
Demiray ST, Pandir Y, Bulut H (2014a) The investigation of exact solutions of nonlinear timefractional Klein–Gordon equation by using generalized Kudryashov method. AIP Conf Proc 1637:283. doi:10.1063/1.4904590
Demiray ST, Pandir Y, Bulut H (2014b) Generalized Kudryashov method for timefractional differential equations. In: Abstract and applied analysis, vol 2014, Article ID 901540
Guo P, Wu X, Wang LB (2015) Multiple soliton solutions for the variant Boussinesq equations. Adv Differ Equ. doi:10.1186/s1366201503714
Islam ME, Khan K, Akbar MA, Islam R (2013) Traveling wave solutions of nonlinear evolution equation via enhanced (G’/G)expansion method. GANIT J Bangladesh Math Soc 33:83–92. doi:10.3329/ganit.v33i0.17662
Islam MS, Khan K, Akbar M, Mastroberardino A (2014) A note on improved Fexpansion method combined with Riccati equation applied to nonlinear evolution equations. R Soc Open Sci 1:140038. doi:10.1098/rsos.140038
Jawad AJM, Petkovic MD, Biswas A (2010) Modified simple equation method for nonlinear evolution equations. Appl Math Comput 217:869–877
Khan K, Akbar MA (2013) Traveling wave solutions of some coupled nonlinear evolution equations. ISRN Math Phys, Volume 2013, Article ID 685736 doi:10.1155/2013/685736
Khan K, Akbar MA (2014a) Traveling wave solutions of the (2 + 1)dimensional Zoomeron equation and Burgers equation via the MSE method and the Expfunction method. Ain Shams Eng J 5:247–256. doi:10.1016/j.asej.2013.07.007
Khan K, Akbar MA (2014b) Study of analytical method to seek for exact solutions of variant Boussinesq equations. SpringerPlus. 3:324. doi:10.1186/219318013324
Khan K, Akbar MA (2014c) Study of functional variable method for finding exact solutions of nonlinear evolution equations. Walailak J Sci Tech 12:1031–1042
Khan K, Akbar MA (2014d) The exp(−Φ(ξ))expansion method for finding traveling wave solutions of VakhnenkoParkes equation. Int J Dyn Syst Differ Equ 5(1):72–83
Khan K, Akbar MA (2014e) Exact solutions of the (2 + 1)dimensional cubic Klein–Gordon equation and the (3 + 1)dimensional Zakharov–Kuznetsov equation using the modified simple equation method. J Assoc Arab Univ Basic Appl Sci 15:74–81. doi:10.1016/j.jaubas.2013.05.001
Khan K, Akbar MA (2015) Exact traveling wave solutions of Kadomtsev–Petviashvili equation. J Egypt Math Soc 23(2):278–281. doi:10.1016/j.joems.2014.03.010
Kim H, Sakthivel R (2012) New exact travelling wave solutions of some nonlinear higher dimensional physical models. Rep Math Phys 70:39–50
Kudryashov NA (2012) On one method for finding exact solutions of nonlinear differential equations. Commun Nonlinear Sci Numer Simul 17(6):2248–2253
Lee J, Sakthivel R (2013) Exact travelling wave solutions for some important nonlinear physical models. Pramana J Phys 80(5):757–769
Liu JB, Yang KQ (2004) The extended Fexpansion method and exact solutions of nonlinear PDEs. Chaos Solitons Fractals 22:111–121
Luo L (2011) New exact solutions and Bäcklund transformation for Boiti–Leon–Manna–Pempinelli equation. Phys Lett A 375:1059–1063
Malfliet W, Hereman W (1996) The tanh method: I. Exact solutions of nonlinear evolution and wave equations. Phys Scr 54:563–568. doi:10.1016/S03784754(02)001829
MohiudDin ST (2007) Homotopy perturbation method for solving fourthorder boundary value problems. Math Prob Eng, vol 2007, Article ID 98602:115. doi:10.1155/2007/98602
MohyudDin ST, Noor MA (2009) Homotopy perturbation method for solving partial differential equations. Z Naturforsch A 64a:157–170
Sachs RL (1988) On the integrable variant of the Boussinesq system: Painlevé property, rational solutions, a related manybody system, and equivalence with the AKNS hierarchy. Phys D 30:1–27
Wahlquist HD, Estabrook FB (1973) Bäcklund transformation for solutions of the Kortewegde Vries equation. Phys Rev Lett 31:1386–1390
Wang M, Li X, Zhang J (2008) The (G′/G)expansion method and travelling wave solutions of nonlinear evolution equations in mathematical physics. Phys Lett A 372:417–423
Wazwaz AM (2004) The tanh method for traveling wave solutions of nonlinear equations. Appl Math Comput 154(3):713–723. doi:10.1016/S00963003(03)007458
Wazwaz AM (2009) Partial differential equations and solitary waves theory. Higher Education Press and SpringerVerlag, Berlin Heidelberg, Beijing
Yusufoglu E (2008) New solitary solutions for the MBBM equations using Expfunction method. Phys Lett A 372:442–446
Zayed EME, AlJoudi S (2010) Applications of an extended (G′/G)expansion method to find exact solutions of nonlinear PDEs in mathematical physics. Math Prob Eng 2010:19. doi:10.1155/2010/768573
Zayed EME, Arnous AH (2013a) Many exact solutions for nonlinear dynamics of DNA model using the generalized Riccati equation mapping method. Sci Res Essays 8(8):340–346. doi:10.5897/SRE12.704
Zayed EME, Arnous AH (2013b) Many families of exact solutions for nonlinear system of partial differential equations describing the dynamics of DNA. J Part Differ Equ 26(4):373–384. doi:10.4208/jpde.v26.n4.5
Zayed EME, Amer YA, Arnous AH (2013a) Functional variable method and its applications for finding exact solutions of nonlinear PDEs in mathematical physics. Sci Res Essays 8(42):2068–2074. doi:10.5897/SRE2013.5725
Zayed EME, Ibrahim SAH, Arnous AH (2013b) Applications of the functional variable method for finding the exact solutions of nonlinear evolution equations in mathematical physics. AIP Conf Proc 1558:1951. doi:10.1063/1.4825916
Zerarka A, Uamane SO, Attaf A (2010) On the functional variable method for finding exact solutions to a class of wave equations. Appl Math Comput 217:2897
Authors’ contributions
This work was carried out in collaboration among the authors. KK, MAA and AHA have a good contribution to design the study, and to perform the analysis of this research work. All authors read and approved the final manuscript.
Acknowledgements
Authors are thankful to the respected reviewers for their valuable suggestions to improve the quality of this article. Authors would like to thank to Professor Dr. AbdulMajid Wazwaz, Department of Mathematics, Saint Xavier University, Chicago, IL 60655, USA, who has expanded his helping hands for developing this article. Besides no study sponsor is involved with this work.
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The authors declare that they have no competing interests.
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Appendices
Appendix 1
Khan and Akbar (2013) found the following exact traveling wave solutions of the variant Boussinesq equations by using the modified simple equation method:
Appendix 2
Zayed et al. (2013b) found the following exact traveling wave solution to the (2 + 1)dimensional Breaking Soliton Equation by means of functional variable method:
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Khan, K., Akbar, M.A. & Arnous, A.H. Exact traveling wave solutions for system of nonlinear evolution equations. SpringerPlus 5, 663 (2016). https://doi.org/10.1186/s4006401622190
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DOI: https://doi.org/10.1186/s4006401622190
Keywords
 Generalized Kudryashov method
 Nonlinear evolution equation
 Variant Boussinesq equation
 Breaking soliton equations
 Exact traveling wave solutions
Mathematics Subject Classification
 35K99
 35P05
 35P99