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BY 4.0 license Open Access Published by De Gruyter June 22, 2018

An effective technique for the conformable space-time fractional EW and modified EW equations

  • K. Hosseini EMAIL logo , A. Bekir and F. Rabiei
From the journal Nonlinear Engineering

Abstract

The current work deals with the fractional forms of EW and modified EW equations in the conformable sense and their exact solutions. In this respect, by utilizing a traveling wave transformation, the governing space-time fractional models are converted to the nonlinear ordinary differential equations (NLODEs); and then, the resulting NLODEs are solved through an effective method called the exp(−ϕ(ϵ))-expansion method. As a consequence, a number of exact solutions to the fractional forms of EW and modified EW equations are generated.

1 Introduction

These days, the fractional differential equations (FDEs) have been the subject of a lot of research, owing to their frequent appearance in various areas from physics and chemistry to biology and engineering. A variety of useful methods, such as sub-equation method [1,2,3,4], modified trial equation method [5,6,7,8], (G′/G)-expansion method [9,10,11,12], exp-function method [13,14,15,16], Kudryashov method [17,18,19,20], and first integral method [21,22,23,24] have been applied to find the exact solutions of FDEs. One capable technique which has newly gained special interest is the exp(−ϕ(ϵ)) method. For instance, Hosseini et al. [25] exerted the exp(−ϕ(ϵ)) method to produce the exact solutions of the density-dependent conformable fractional diffusion-reaction equation and Raza et al. [26] adopted the exp(−ϕ(ϵ)) method to extract the explicit solutions of higher dimensional equations with fractional temporal evolution. For more articles, see [27,28,29,30,31,32,33,34,35,36,37,38,39,40]. In this paper, the exact solutions of the fractional forms of EW and modified EW equations in the conformable sense are achieved by means of the exp(−ϕ(ϵ)) method. The mathematical modelings of these fractional differential equations are presented below:

  • The fractional EW equation [41]

    Dtαu(x,t)+σDxαu2(x,t)δDxxt3αu(x,t)=0,t>0,0<α1.(1)
  • The fractional modified EW equation [41]

    Dtαu(x,t)+σDxαu3(x,t)δDxxt3αu(x,t)=0,t>0,0<α1.(2)

The EW equations describe the propagation of the wave in nonlinear media [42]. Several schemes have already been exerted for studying the above models; for example, Kudryashov method [17], ansatz method [41], and Fan sub-equation method [43]. This paper is organized as below: In Section 2, we will introduce the conformable derivative and its properties. In Section 3, we will explain the ideas of the exp(−ϕ(ϵ)) method. In Section 4, we will employ the exp(−ϕ(ϵ)) method to solve the fractional forms of EW and modified EW equations; and at the end, we will provide the results.

2 Conformable fractional derivative

Recently, a new version of fractional derivatives “the conformable fractional derivative” was proposed in [44] which obeys some classical properties that cannot be satisfied by the other definitions [45]. The conformable fractional derivative of f of order α is defined as [44]

Tα(f)(t)=limτ0f(t+τt1α)f(t)τ,

where f : (0, ∞) → R, t > 0, and α ∈ (0, 1]. Some worthwhile features of the conformable derivative are as follows

  1. Tα(af+bg)=aTα(f)+bTα(g),a,bR.
  2. Tα(tμ)=μtμα,μR.
  3. Tα(fog)(t)=t1αg(t)f(g(t)).

3 Basic ideas of exp(−ϕ(ϵ))-expansion method

Let’s consider a nonlinear space-time FDE in the conformable sense as follows

F(u,Dtα1u,Dxα2u,Dt2α1u,Dtα1Dxα2u,Dx2α2u,)=0,0<α1,α2<1.(3)

By using the transformation

u(x,t)=f(ϵ),ϵ=kxα2α2ltα1α1,

Eq. (3) changes into an ODE of integer order as

G(f,f,f,)=0,(4)

where G is a function in the unknown function f and its derivatives.

Let present the solution of Eq. (4) as below

f(ϵ)=n=0Nan(exp(ϕ(ϵ)))n,(5)

where an, n = 0, 1, …, N (aN ≠ 0) are unknown constants and ϕ(ϵ) satisfies a nonlinear ordinary differential equation as

ϕ(ϵ)=exp(ϕ(ϵ))+μexp(ϕ(ϵ))+λ.

Now, various cases can be considered:

  1. If λ2 − 4μ > 0 and μ ≠ 0, then

    ϕ1(ϵ)=lnλ24μtanhλ24μ2(ϵ+C)λ2μ.
  2. If λ2 − 4μ > 0, μ = 0, and λ ≠ 0, then

    ϕ2(ϵ)=lnλcosh(λ(ϵ+C))+sinh(λ(ϵ+C))1.
  3. If λ2 − 4μ < 0 and μ ≠ 0, then

    ϕ3(ϵ)=ln4μλ2tan4μλ22(ϵ+C)λ2μ.

To procure the positive integer N in Eq. (5), we balance the terms in Eq. (4). Setting Eq. (5) in Eq. (4), results in

P(exp(ϕ(ϵ)))=0.(6)

Through equating all the coefficients in (6) to zero, we will attain an algebraic set, which can be easily solved for determining the unknowns. Substituting them into (5), finally yields the exact solutions of original Eq. (3).

4 Applications

Now, we adopt the exp(−ϕ(ϵ)) method to seek the exact solutions of the fractional forms of EW and modified EW equations in the conformable sense.

4.1 The conformable space-time fractional EW equation

By using the transformation

u(x,t)=f(ϵ),ϵ=kxααltαα,

Eq. (1) can be changed into the following ODE

lf+σk(f2)+δlk2f=0.(7)

Integrating (7) once with respect to ϵ, gives

lf+σkf2+δlk2f=0,(8)

where integrating constant is supposed to be zero.

4.1.1 Applying the exp(−ϕ(ϵ))-expansion method

By balancing f2 and f″ in Eq. (8), we obtain N = 2. Hence, Eq. (8) has the following formal solution

f(ϵ)=a0+a1exp(ϕ(ϵ))+a2exp(2ϕ(ϵ)).(9)

Through setting Eq. (9) in Eq. (8) and equating all the coefficients to zero, we will achieve an algebraic set in the form

la0+δlλμk2a1+2δlμ2k2a2+kσa02=0,(δlλ2k2+2δlμk2l)a1+6δlλμk2a2+2kσa0a1=0,3δlλk2a1+(4δlλ2k2+8δlμk2l)a2+kσa12+2kσa0a2=0,2δlk2a1+10δlλk2a2+2kσa1a2=0,6δlk2a2+δσa22=0.

Applying the symbolic computation package, results in

  1. a0=6lμδ(λ24μ)σ(λ24μ),a1=6δlλσδ(λ24μ),a2=6δlσδ(λ24μ),k=±1δ(λ24μ).

    Thus, the exact solutions to the fractional form of EW equation in the conformable sense can be constructed as follows

    For λ2 − 4μ > 0 and μ ≠ 0

    u1,2(x,t)=6lμδ(λ24μ)σ(λ24μ)±12δlλμσδ(λ24μ)λ24μtanh(λ24μ2(±1δ(λ24μ)xααltαα+C))+λ24δlμ2σδ(λ24μ)λ24μtanh(λ24μ2(±1δ(λ24μ)xααltαα+C))+λ2.

    For λ2 − 4μ > 0, μ = 0, and λ ≠ 0

    u3,4(x,t)=6δlλ2σδλ2coshλ±1δλ2xααltαα+C+sinhλ±1δλ2xααltαα+C16δlλ2σδλ2coshλ±1δλ2xααltαα+C+sinhλ±1δλ2xααltαα+C12.

    For λ2 − 4μ < 0 and μ ≠ 0

    u5,6(x,t)=6lμδ(λ24μ)σ(λ24μ)±12δlλμσδ(λ24μ)4μλ2tan4μλ22±1δ(λ24μ)xααltαα+C+λ24δlμ2σδ(λ24μ)4μλ2tan4μλ22±1δ(λ24μ)xααltαα+C+λ2.
  2. a0=±l(λ2+2μ)δ(λ24μ)σ(λ24μ),a1=6δlλσδ(λ24μ),a2=6δlσδ(λ24μ),k=±1δ(λ24μ).

Consequently, the exact solutions to the fractional form of EW equation in the conformable sense can be established as follows

For λ2 − 4μ > 0 and μ ≠ 0

u7,8(x,t)=±l(λ2+2μ)δ(λ24μ)σ(λ24μ)±12δlλμσδ(λ24μ)λ24μtanhλ24μ2±1δ(λ24μ)xααltαα+C+λ24δlμ2σδ(λ24μ)λ24μtanhλ24μ2±1δ(λ24μ)xααltαα+C+λ2.

For λ2 − 4μ > 0, μ = 0, and λ ≠ 0

u9,10(x,t)=±lδλ2σ6δlλ2σδλ2coshλ±1δλ2xααltαα+C+sinhλ±1δλ2xααltαα+C16δlλ2σδλ2coshλ±1δλ2xααltαα+C+sinhλ±1δλ2xααltαα+C12.

For λ2 − 4μ < 0 and μ ≠ 0

u11,12(x,t)=±l(λ2+2μ)δ(λ24μ)σ(λ24μ)±12δlλμσδ(λ24μ)4μλ2tan4μλ22±1δ(λ24μ)xααltαα+C+λ24δlμ2σδ(λ24μ)4μλ2tan4μλ22±1δ(λ24μ)xααltαα+C+λ2.

4.2 The conformable space-time fractional modified EW equation

By using the transformation

u(x,t)=f(ϵ),ϵ=kxααltαα,

Eq. (2) can be converted to an ODE as follows

lf+σk(f3)+δlk2f=0.(10)

Integrating (10) once with respect to ϵ, yields

lf+σkf3+δlk2f=0,(11)

where integrating constant is assumed to be zero.

4.2.1 Applying the exp(−ϕ(ϵ))-expansion method

By balancing f3 and f″ in Eq. (11), we take N =1. Consequently, Eq. (11) has the following formal solution

f(ϵ)=a0+a1exp(ϕ(ϵ)).(12)

By inserting Eq. (12) along with its necessary derivative in Eq. (11) and equating all the coefficients to zero, we will derive an algebraic set as

la0+δlλμk2a1+kσa03=0,(δlλ2k2+2δlμk2l)a1+3kσa02a1=0,3δlλk2a1+3kσa0a12=0,2δlk2a1+kσa13=0.

Using the symbolic computation package, we will find

a0=12λa1,k=±22δ(λ24μ),l=σa122δ(λ24μ)4δ.

Thus, the exact solutions to the fractional form of modified EW equation in the conformable sense can be constructed as follows

For λ2 − 4μ > 0 and μ ≠ 0

u1,2(x,t)=12λa12μa1λ24μtanhλ24μ2±22δ(λ24μ)xαα±σa122δ(λ24μ)4δtαα+C+λ.

For λ2 − 4μ > 0, μ = 0, and λ ≠ 0

u3,4(x,t)=12λa1+λa1coshλ±22δλ2xαα±σa122δλ24δtαα+C+sinhλ±22δλ2xαα±σa122δλ24δtαα+C1.

For λ2 − 4μ < 0 and μ ≠ 0

u5,6(x,t)=12λa12μa14μλ2tan4μλ22±22δ(λ24μ)xαα±σa122δ(λ24μ)4δtαα+C+λ.

5 Conclusion

In this investigation, the fractional forms of EW and modified EW equations in the conformable sense were studied, successfully. First, by adopting a traveling wave transformation, the governing space-time fractional models were converted to the nonlinear ordinary differential equations; and then, the resulting NLODEs were solved using an effective method called the exp(−ϕ(ϵ))-expansion method. As a consequence, a variety of exact solutions to the fractional forms of EW and modified EW equations were formally extracted; confirming the competence of the scheme.

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Received: 2017-02-12
Revised: 2018-03-17
Accepted: 2018-04-07
Published Online: 2018-06-22
Published in Print: 2019-01-28

© 2019 K. Hosseini et al., published by De Gruyter.

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

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