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BY 4.0 license Open Access Published by De Gruyter July 12, 2019

The expa function method and the conformable time-fractional KdV equations

  • Asim Zafar EMAIL logo
From the journal Nonlinear Engineering

Abstract

The nonlinear fractional differential equations (FDEs) are produced by mathematical modelling of some nonlinear physical systems. The study of such nonlinear physical models through wave solutions analysis corresponding to their FDEs, has a dynamic role in applied sciences. In this paper, we are going to explore the conformable time-fractional KdV equations using the expa function method. The way to reach explicit exact wave solutions is to transform the fractional order PDE into a nonlinear ODE of discrete order through travelling wave transforms. The subsequent equation has been explored by utilizing the exp a function approach. Consequently, some new explicit exact wave solutions of the said equations are effectively formulated and graphically conveyed with the help of numerical simulation.

1 Introduction

The Korteweg– de Vries (KdV) equations have been observed in a broad variety of material science phenomena as a model for the development and communication of nonlinear waves. The KdV equation was introduced by Korteweg and de Vries to describe shallow water waves of long wavelength with small amplitude. Subsequently the KdV equation has been merged into a number of other physical contexts as collision-free hydromagnetic waves, stratified internal waves, particle acoustic waves, plasma physics, and so on [1, 2, 3, 4, 5, 6, 7].

Various fields of science and engineering are influenced by Leibnitz’s work on fractional calculus and having substantially increasing impact on these sciences during last twenty years ostensibly [8, 9, 10]. From different minds for different applications, many definitions of fractional derivatives, Like Hilfer, Riemann-Liouville, Caputo form and so on, have been introduced in the literature [11, 12], but the most fascinating definition and the geometrical explanation for complex fractional transform and fractional derivative are given in [13, 14].

The explicit exact wave solutions have always been a particular importance among the researchers in many fields of nonlinear sciences. The availability of symbolic computation softwares is a direct help to minimize the manual labor for finding problematic solutions to nonlinear evolution equations. Various significant methods have been presented to explore exact solutions in different research articles, for example, the ansatz method, modified simple equation method, the extended trail equation, the first integral, the improved tan(ϕ(η)/2)-expansion, the exp-function and the exp(–ϕ(ϵ)) methods [15, 16, 17, 18, 19, 20, 21]. Also some other reliable techniques, like homotopy method [22, 23, 24, 25], generalized Kudryashov method [26, 27, 28, 29], modified Kudryashov and the sine-Gordon expansion approach [30, 31, 32, 33] have been done by different researchers. Furthermore, the auxiliary equation method, the extended tanh-function method, generalized projective Riccati equation method, functional variable method, and Jacobi elliptic function expansion method have been explored in [34, 35, 36, 37, 38, 39] for integral and fractional order as well. The expa function method is a new and an efficient technique which has been acknowledged by the scholars rapidly. In particular, Ali and Hassan, Hosseini et al., Zayed and Al-Nowehy all have utilized the expa function method in [40, 41, 42, 43] respectively.

The paper’s aim is to apply the expa function approach to nonlinear conformable time-fractional KdV equations. The investigation for exact solutions is as follow. The description of conformable derivative and expa function approach is provided in section 2. The section 3 represents the method utilization for extracting new exact solutions with their graphical representation. The conclusion is provided in the last section.

2 A new approach for fractional derivatives

A simple but a fascinating definition of the fractional derivative called conformable fractional derivative has been introduced by Khalil et al. [13]. The Liebniz rule and the chain rule both are obeyed by this derivative. Recall the definition of the conformable derivative and with some properties.

Definition 1

Suppose h : ℝ+ → ℝ be a function. Then, for all t > 0,

Dty(h(t))=limε0h(t+εt1y)h(t)ε

is known as the conformable fractional derivative of h of order y, 0 < y ≤ 1. Some useful properties are being listed as follows:

Dty(ah+bg)=aDty(h)+bDty(g), for all a, b ∈ ℝ

Dty(hg)=hDty(g)+gDty(h)

Let h : ℝ+ → ℝ be a differentiable and y-differentiable function, g be a differentiable function defined in the range of h.

Dty(hg(t))=t1yg(t)h(g(t)).

On the top of that, the following rules hold.

Dty(tp) = ptpy, for all p ∈ ℝ

Dty(λ) = 0, where λ is constant.

Dty(h/g)=gDty(h)hDty(g)g2.

Conjointly, if h is differentiable, then Dty(h(t))=t1ydh(t)dt.

2.1 A transitory explanation of expa function method

The present subsection provides a concise explanation for the expa [40, 42, 44] in generating new explicit exact solutions of nonlinear conformable time-fractional DE. For this purpose, suppose that we have a nonlinear conformable time-fractional DE that can be presented in the form

F(u,Dtyu,Dxu,Dt2yu,Dxxu,...)=0(1)

The FDE (1) can be changed into the following nonlinear ODE of integer order

P(U,U,U,...,)=0(2)

with the use of following transformation

u(x,t)=U(ξ),ξ=kxltyy,(3)

where k, l are nonzero arbitrary constants.

Let us try to search a non-trivial solution for the Eq. (2) in the following form

U(ξ)=a0+a1aξ+...+aNaNξb0+b1aξ+...+bNaNξ(4)

where ai and bi for (0 ≤ iN) are found later and N is a free positive integer.

Replacing the Eq.(4) in the nonlinear Eq.(2), yields

P(aξ)=q0+q1aξ+...+qτaτξ=0(5)

Setting li(0 ≤ iτ) in Eq.(4) to be zero, results in a set of nonlinear equations as below

qi=0,i=0,...,τ(6)

which by solving the generated set (6), we approach to non-trivial solutions of the nonlinear FDE (1).

3 Explicit exact wave solutions for time fractional KdV equations

In this section, the following time fractional KdV and modified KdV equations [7], are going to be considered for solution via expa method.

Dtyu+pu2ux+quxxx=0,0<y1,(7)

Using the transformation (3), integrating w.r.t. ξ and taking constant of integration is zero, we get

lu+13pku3+qk3u=0.(8)

Through balancing, we select N = 1, the nontrivial solution (4) reduces to:

U(ξ)=α1αξ+α0β1αξ+β0,α1(9)

By setting the above solution in reduced equation Eq. (8) and equating factors of each power of aξ in the resulting equation, we reach a nonlinear algebraic set as

α03kp3α0β02l=03α1β02k3qlog2(α)3α0β0β1k3qlog2(α)+3α02α1kp3α1β02l6α0β0β1l=03α0β12k3qlog2(α)3α1β0β1k3qlog2(α)+3α0α12kp3α0β12l6α1β0β1l=0α13kp3α1β12l=0

which its solution yields

α0=3q2pβ0klog(α),α1=±3q2pβ1klog(α),l=12k3qlog2(α)

Thus, the following new explicit exact solutions to the conformable time fractional third order modified KdV equation can be written as

U1,2(ξ)=ıklog(α)3q2p(β0±β1αξ)β0+β1αξ(10)

where ξ=kx+12k3qlog2(α)tyy.

Fig. 1 Solution profile of U1,2 corresponding to p = 3, q = 2, β0 = 1 = β1 and α = 3
Fig. 1

Solution profile of U1,2 corresponding to p = 3, q = 2, β0 = 1 = β1 and α = 3

We now consider the time fractional conformable KdV Equation as follows.

Dtyu+puux+quxxx=0,0<y1,(11)

Using the transformation (3), integrating w.r.t. ξ and taking constant of integration is zero, we get

lu+12pku2+qk3u=0.(12)

Through balancing the terms we select N = 2, the non-trivial solution (4) becomes

U(ξ)=α2α2ξ+α1αξ+α0β2α2ξ+β1αξ+β0,α1(13)

By setting the above non-trivial solution in reduced equation Eq. (12) and equating factors of each power of αξ in the resulting equation, we reach a nonlinear algebraic set as

α02β0kp2α0β02l=0,2α1β02k3qlog2(α)2α0β0β1k3qlog2(α)+2α0α1β0kp+α02β1kp2α1β02l4α0β0β1l=0,8α2β02k3qlog2(α)+2α0β12k3qlog2(α)2α1β0β1k3qlog2(α)8α0β0β2k3qlog2(α)+α12β0kp+2α0α2β0kp+2α0α1β1kp+α02β2kp2α2β02l2α0β12l4α1β0β1l4α0β0β2l=0,6α2β0β1k3qlog2(α)12α1β0β2k3qlog2(α)+6α0β1β2k3qlog2(α)+2α1α2β0kp+α12β1kp+2α0α2β1kp+2α0α1β2kp2α1β12l4α2β0β1l4α1β0β2l4α0β1β2l=0,2α2β12k3qlog2(α)+8α0β22k3qlog2(α)8α2β0β2k3qlog2(α)2α1β1β2k3qlog2(α)+α22β0kp+2α1α2β1kp+α12β2kp+2α0α2β2kp2α2β12l2α0β22l4α2β0β2l4α1β1β2l=0,2α1β22k3qlog2(α)2α2β1β2k3qlog2(α)+α22β1kp+2α1α2β2kp2α1β22l4α2β1β2l=0,α22β2kp2α2β22l=0.

which its solution yields

α0=2β0k2qlog2(α)p,α1=4β1k2qlog2(α)p,α2=β12k2qlog2(α)2β0p,β2=β124β0,l=k3qlog2(α),α0=0,α1=6β1k2qlog2(α)p,α2=0,β2=β124β0,l=k3qlog2(α)

Thus, the following new explicit exact solution to the conformable time fractional third order KdV equation can be written as

U1(ξ)=β12k2qlog2(α)2β0pα2ξ+4β1k2qlog2(α)pαξ2β0k2qlog2(α)pβ124β0α2ξ+β1αξ+β0(14)

where ξ=kx+k3qlog2(α)tyy.

U2(ξ)=6β1k2qlog2(α)pαξβ124β0α2ξ+β1αξ+β0(15)

where ξ=kxk3qlog2(α)tyy.

Fig. 2 Solution profile of U1 corresponding to p = 3, q = 2, β0 = 1 = β1 and α = 3
Fig. 2

Solution profile of U1 corresponding to p = 3, q = 2, β0 = 1 = β1 and α = 3

Fig. 3 Solution profile of U2 corresponding to p = 3, q = 2, β0 = 1 = β1 and α = 3
Fig. 3

Solution profile of U2 corresponding to p = 3, q = 2, β0 = 1 = β1 and α = 3

4 Conclusion

We have succeeded in exploring the explicit exact wave solutions of conformable time fractional KdV equations via expa function method. These solutions are given explicitly and verified by setting back in the reduced equations with the aid of Mathematica. Furthermore, the numerical simulation of some but different kind of solutions through MATLAB has been given for the reader to visualize the basic phenomena.

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Received: 2018-06-26
Revised: 2018-09-01
Accepted: 2018-11-06
Published Online: 2019-07-12
Published in Print: 2019-01-28

© 2019 Asim Zafar, published by De Gruyter

This work is licensed under the Creative Commons Attribution 4.0 Public License.

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