Transcript

IJRRAS 18 (2) ● February 2014 www.arpapress.com/Volumes/Vol18Issue2/IJRRAS_18_2_04.pdf

132

NEW EXACT SOLUTIONS OF SOME NONLINEAR PARTIAL

DIFFERENTIAL EQUATIONS VIA THE IMPROVED EXP-FUNCTION

METHOD

M. F. El-Sabbagh, R. Zait and R. M. Abdelazeem

Mathematics Department, Faculty of Science, MiniaUniversity, Egypt.

Corresponding e-mail: [email protected]

ABSTRACT In this paper, we establish new exact solutions of some nonlinear partial differential equations (PDEs) of interest

such as the Kaup–Kupershmidt, the generalized shallow water, the Boussinesq equations via the improved Exp–

function method. Also the method is used to construct periodic and solitary wave solutions for the considered

equations as well.

Keywords: Nonlinear PDEs, Exact solutions, The improved Exp–function method.

1. INTRODUCTION The nonlinear evolution equations (NLEEs) are widely used as models to describe complex physical phenomena in

various field of science, particularly in fluid mechanics, solid state physics, plasma waves and chemical physics.

Nonlinear equations covers also the following subjects: surface wave in compressible fluid, hydro magnetic waves

in cold plasma, acoustic waves in un harmonic crystal, ect. . The wide applicability of these equations is the main

reason for they have attracted so much attention from mathematicians in the last decades. The investigation of the

exact solutions of non linear partial differential equations (PDEs) plays an important role in the study of non-linear

physical phenomena. When we want to understand the physical mechanism of phenomena in nature, described by

non linear PDEs, exact solutions have to be explored. The study of nonlinear PDEs becomes one of the most

important topics in mathematical physics. Recently there are many new methods to obtain exact solutions of

nonlinear PDEs such as sine-cosine function method [1-5], tanh function method [6-8], (𝐺/

𝐺 )-expansion method

[9-13 ], extended Jacobi elliptic function method [14, 15]. He and Wu [16], proposed a straightforward and concise

method, called Exp-function method [17-24], to obtain generalized solitary wave solutions of nonlinear PDEs. Ali

[25] improved this method and obtained new exp-function solutions and periodic solutions as well.

In this paper, we use the improved Exp-function method [25, 26 ] to search for new solitary wave solutions,

compact like solutions and periodic solutions of some nonlinear PDEs, such as the Kaup–Kupershmidt equation

[27-35], the generalized shallow water equation [36, 37], and the Boussinesq equation [38-42].

2. THE IMPROVED EXP-FUNCTION METHOD:

We present the improved Exp-function method [25] in the following steps:

1- Consider the following nonlinear PDE with two independent variables π‘₯, 𝑑 and dependant variable 𝑒:

𝑁(𝑒,𝑒𝑑 ,𝑒π‘₯ ,𝑒π‘₯π‘₯ ,𝑒π‘₯𝑑 ,𝑒𝑑𝑑 ,… ) = 0 (1),

where 𝑁 is in general a polynomial function of its argument and the subscripts denote the partial derivatives.

2- We seek a traveling wave solution of Eq. (1) in the form

𝑒 π‘₯, 𝑑 = 𝑒 πœ‰ , πœ‰ = π‘˜π‘₯ + πœ”π‘‘ 2 ,

where π‘˜ and πœ” are constants to be determined

3- Using the transformation (2), Eq. (1) can be reduced to an ordinary differential equation (ODE):

𝐺 𝑒,𝑒′,𝑒′′,… = 0 3 ,

where 𝐺 is a polynomial of 𝑒 and its derivatives.

4- Through this method, we express the solution of the nonlinear PDE (1) in the form:

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𝑒 πœ‚ = 𝐴𝑗𝑒π‘₯𝑝(π‘—πœ‰)π‘š

𝑗=0

𝐡𝑖𝑒π‘₯𝑝(π‘–πœ‰)𝑛𝑖=0

4 ,

where π‘š and 𝑛 are positive integers that could be freely chosen.

5- To determine 𝑒 π‘₯, 𝑑 explicitly, one may apply the following producer:

(i) Substitute Eq. (4) into Eq. (3), then the lift hand side of Eq. (3) is converted into a polynomial in

𝑒π‘₯𝑝(πœ‰). Setting all coefficients of 𝑒π‘₯𝑝(πœ‰) to zero yield a system of algebraic equations for

𝐴0,𝐴1 ,𝐴2,… .π΄π‘š , 𝐡0 ,𝐡1 ,𝐡2 ,… .𝐡𝑛 , π‘˜ π‘Žπ‘›π‘‘ πœ”.

(ii) Solve these algebraic equations to obtain A0, A1, A2,… , Am , 𝐡0 ,𝐡1 ,𝐡2 ,… ,𝐡𝑛 , π‘˜ π‘Žπ‘›π‘‘ πœ”.

3. APPLICATIONS In order to illustrate the effectiveness of the above method, examples of mathematical and physical interests are

chosen as follows:

3.1The Kaup–Kupershmidt equation [27-35]

The Kaup–Kupershmidt equation is the nonlinear fifth-order partial differential equation; It is the first equation in a

hierarchy of integrable equations with Lax operator πœ•3

πœ•π‘₯3 + 2π‘’πœ•

πœ•π‘₯+

πœ•π‘’

πœ•π‘₯. It has properties similar (but not identical) to

those of the better known KdV hierarchy in which the Lax operator has order two.

In the present paper we introduce new exact solutions of the Kaup–Kupershmidt equation via the improved Exp-

function method as follows:

Consider the Kaup–Kupershmidt equation is given as:

𝑒𝑑 = 𝑒π‘₯π‘₯π‘₯π‘₯π‘₯ βˆ’ 20𝑒𝑒π‘₯π‘₯π‘₯ βˆ’ 50𝑒π‘₯𝑒π‘₯π‘₯ + 80𝑒2𝑒π‘₯ (5)

Using the transformation:

𝑒 = 𝑒 πœ‚ , πœ‚ = π‘₯ βˆ’ 𝑐𝑑 6 ,

where 𝑐 is a constant to be determined later. Substituting Eq. (6) into Eq. (5) we get

𝑐𝑒′ βˆ’ 𝑒′′′′′ + 20𝑒𝑒′′′ + 50𝑒′𝑒′′ βˆ’ 80𝑒2𝑒′ = 0 7 ,

where primes denote derivatives with respect to πœ‚. Now we study the following cases:

π‘ͺ𝒂𝒔𝒆 𝟏: π’Ž = 𝟐,𝒏 = 𝟐:

According to the improved Exp-function method, the travelling wave solution of Eq. (5) in this case can be written

as:

𝑒 π‘₯, 𝑑 = 𝐴0 + 𝐴1𝑒π‘₯𝑝(πœ‚) + 𝐴2𝑒π‘₯𝑝(2πœ‚)

𝐡0 + 𝐡1𝑒π‘₯𝑝(πœ‚) + 𝐡2𝑒π‘₯𝑝(2πœ‚) (8)

In case 𝐡2 β‰  0, Eq. (8) can be simplified as:

𝑒 π‘₯, 𝑑 = 𝐴0 + 𝐴1𝑒π‘₯𝑝(πœ‚) + 𝐴2𝑒π‘₯𝑝(2πœ‚)

𝐡0 + 𝐡1𝑒π‘₯𝑝(πœ‚) + 𝑒π‘₯𝑝(2πœ‚) (9)

Substituting Eq. (9) into Eq. (7), and using the Maple, equating to zero the coefficients of all powers of

𝑒π‘₯𝑝(πœ‚)yields a set of algebraic equations for 𝐴0, 𝐴1, 𝐴2, 𝐡0 ,𝐡1 and c. Solving these system of algebraic equations,

with the aid of Maple, we obtain families of solutions as the following:

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π‘­π’‚π’Žπ’Šπ’π’š 𝟏:

𝐡0 = 1,𝐴1 = βˆ’5,𝐴0 =1

2, 𝑐 = βˆ’11,𝐴2 =

1

2,𝐡1 = 2.

Thus the following solution is

𝑒1 π‘₯, 𝑑 =

12βˆ’ 5𝑒π‘₯𝑝(π‘₯ + 11𝑑) +

12𝑒π‘₯𝑝(2π‘₯ + 22𝑑)

1 + 2𝑒π‘₯𝑝(π‘₯ + 11𝑑) + 𝑒π‘₯𝑝(2π‘₯ + 22𝑑) (10)

π‘­π’Šπ’ˆπ’–π’“π’† 𝟏. π‘»π’“π’‚π’—π’†π’π’Šπ’π’ˆ π’˜π’‚π’—π’† π’”π’π’π’–π’•π’Šπ’π’ 𝒐𝒇 𝑬𝒒. πŸ“ 𝒇𝒐𝒓 π’”π’π’π’–π’•π’Šπ’π’ 𝟏𝟎 .

π‘­π’‚π’Žπ’Šπ’π’š 𝟐:

𝐡0 = 1,𝐴1 =βˆ’5

8,𝐴0 =

1

16, 𝑐 =

βˆ’1

16,𝐴2 =

1

16,𝐡1 = 2.

Thus the following solution is

𝑒2 π‘₯, 𝑑 =

116

βˆ’58𝑒π‘₯𝑝(π‘₯ +

𝑑16

) +1

16𝑒π‘₯𝑝(2π‘₯ +

𝑑8

)

1 + 2𝑒π‘₯𝑝(π‘₯ +𝑑

16) + 𝑒π‘₯𝑝(2π‘₯ +

𝑑8

) (11)

π‘­π’Šπ’ˆπ’–π’“π’† 𝟐. π‘»π’“π’‚π’—π’†π’π’Šπ’π’ˆ π’˜π’‚π’—π’† π’”π’π’π’–π’•π’Šπ’π’ 𝒐𝒇 𝑬𝒒. πŸ“ 𝒇𝒐𝒓 π’”π’π’π’–π’•π’Šπ’π’ 𝟏𝟏 .

π‘ͺ𝒂𝒔𝒆 𝟐: π’Ž = πŸ‘,𝒏 = πŸ‘:

According to the improved Exp-function method, the travelling wave solution of Eq. (5) in this case can be written

as:

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𝑒 π‘₯, 𝑑 = 𝐴0 + 𝐴1𝑒π‘₯𝑝(πœ‚) + 𝐴2𝑒π‘₯𝑝(2πœ‚) + 𝐴3𝑒π‘₯𝑝(3πœ‚)

𝐡0 + 𝐡1𝑒π‘₯𝑝(πœ‚) + 𝐡2𝑒π‘₯𝑝(2πœ‚) + 𝐡3𝑒π‘₯𝑝(3πœ‚) (12)

In case 𝐡3 β‰  0, Eq. (12) can be simplified as:

𝑒 π‘₯, 𝑑 = 𝐴0 + 𝐴1𝑒π‘₯𝑝(πœ‚) + 𝐴2𝑒π‘₯𝑝(2πœ‚) + 𝐴3𝑒π‘₯𝑝(3πœ‚)

𝐡0 + 𝐡1𝑒π‘₯𝑝(πœ‚) + 𝐡2𝑒π‘₯𝑝(2πœ‚) + 𝑒π‘₯𝑝(3πœ‚) 13

Substituting Eq. (13) into Eq. (7), and using the Maple, equating to zero the coefficients of all powers of

𝑒π‘₯ 𝑝 πœ‚ yields a set of algebraic equations for 𝐴0, 𝐴1, 𝐴2, 𝐴3, 𝐡0, 𝐡1 ,𝐡2 and c. Solving the system of algebraic

equations given above, with the aid of Maple, we obtain:

π‘­π’‚π’Žπ’Šπ’π’š 𝟏:

𝐴0 = 0,𝐴1 =1

8𝐡2

2 ,𝐴2 =βˆ’5

2𝐡2 ,𝐴3 =

1

2,𝐡0 = 0,𝐡1 =

1

4𝐡2

2 ,𝐡2 = 𝐡2 , 𝑐 = βˆ’11.

Thus the following solution is

𝑒5 π‘₯, 𝑑 =

14𝐡2

2𝑒π‘₯𝑝(π‘₯ + 11𝑑) βˆ’ 5𝐡2𝑒π‘₯𝑝(2π‘₯ + 22𝑑) + 𝑒π‘₯𝑝(3π‘₯ + 33𝑑)

12𝐡2

2𝑒π‘₯𝑝(π‘₯ + 11𝑑) + 2𝐡2𝑒π‘₯𝑝(2π‘₯ + 22𝑑) + 2𝑒π‘₯𝑝(3π‘₯ + 33𝑑) (14)

If 𝐡2 = 1, then

𝑒5 π‘₯, 𝑑 =

14𝑒π‘₯𝑝(π‘₯ + 11𝑑) βˆ’ 5𝑒π‘₯𝑝(2π‘₯ + 22𝑑) + 𝑒π‘₯𝑝(3π‘₯ + 33𝑑)

12𝑒π‘₯𝑝(π‘₯ + 11𝑑) + 2𝑒π‘₯𝑝(2π‘₯ + 22𝑑) + 2𝑒π‘₯𝑝(3π‘₯ + 33𝑑)

(15)

π‘­π’Šπ’ˆπ’–π’“π’† πŸ‘. π‘»π’“π’‚π’—π’†π’π’Šπ’π’ˆ π’˜π’‚π’—π’† π’”π’π’π’–π’•π’Šπ’π’ 𝒐𝒇 𝑬𝒒. πŸ“ 𝒇𝒐𝒓 π’”π’π’π’–π’•π’Šπ’π’ πŸπŸ“ ,π‘©πŸ = 𝟏.

π‘­π’‚π’Žπ’Šπ’π’š 𝟐:

𝐴0 = 0,𝐴1 =1

64𝐡2

2 ,𝐴2 =βˆ’5

16𝐡2 ,𝐴3 =

1

16,𝐡0 = 0,𝐡1 =

1

4𝐡2

2 ,𝐡2 = 𝐡2 , 𝑐 = βˆ’1

16.

Thus the following solution is

𝑒6 π‘₯, 𝑑 =

14𝐡2

2𝑒π‘₯𝑝(π‘₯ +𝑑

16) βˆ’ 5𝐡2𝑒π‘₯𝑝(2π‘₯ +

𝑑8

) + 𝑒π‘₯𝑝(3π‘₯ +3𝑑16

)

4(𝐡22𝑒π‘₯𝑝(π‘₯ +

𝑑16

) + 4𝐡2𝑒π‘₯𝑝(2π‘₯ +𝑑8

) + 4𝑒π‘₯𝑝(3π‘₯ +3𝑑16

)) (16)

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If 𝐡2 = 1, then

𝑒6 π‘₯, 𝑑 =

14𝑒π‘₯𝑝(π‘₯ +

𝑑16

) βˆ’ 5𝑒π‘₯𝑝(2π‘₯ +𝑑8

) + 𝑒π‘₯𝑝(3π‘₯ +3𝑑16

)

4(𝑒π‘₯ 𝑝 π‘₯ +𝑑

16 + 4𝑒π‘₯ 𝑝 2π‘₯ +

𝑑8 + 4𝑒π‘₯ 𝑝 3π‘₯ +

3𝑑16

) (17)

π‘­π’Šπ’ˆπ’–π’“π’† πŸ’. π‘»π’“π’‚π’—π’†π’π’Šπ’π’ˆ π’˜π’‚π’—π’† π’”π’π’π’–π’•π’Šπ’π’ 𝒐𝒇 𝑬𝒒. πŸ“ 𝒇𝒐𝒓 π’”π’π’π’–π’•π’Šπ’π’ πŸπŸ• ,π‘©πŸ = 𝟏.

3.2 The generalized shallow water equation: [36, 37]

The shallow water wave equations describe the evolution of incompressible flow, neglecting density change along

the depth. The shallow water wave equations are applicable to cases where the horizontal scale of the flow is much

bigger than the depth of fluid. The shallow water equations have been extensively used for a wide variety of coastal

phenomena, such as tide-currents, pollutant- dispersion storm-surges, tsunami-wave propagation, etc..

In the present paper we introduce new exact solutions of the generalized shallow water equation via the improved

Exp-function Method as follows:

Consider the generalized shallow water equation:

𝑒π‘₯π‘₯π‘₯𝑑 + 𝛼𝑒π‘₯𝑒π‘₯𝑑 + 𝛽𝑒𝑑𝑒π‘₯π‘₯ βˆ’ 𝑒π‘₯𝑑 βˆ’ 𝑒π‘₯π‘₯ = 0 18 ,

where 𝛼 and 𝛽 are arbitrary nonzero constants.

Using the transformation:

𝑒 = 𝑒 πœ‚ , πœ‚ = π‘₯ βˆ’ 𝑐𝑑 19 ,

where 𝑐 is a constant to be determined later. Substituting Eq. (19) into Eq. (18) we get

βˆ’π‘π‘’β€²β€²β€²β€² βˆ’ 𝑐𝛼𝑒′𝑒′′ βˆ’ 𝑐𝛽𝑒′𝑒′′ βˆ’ 𝑐𝑒′′ βˆ’ 𝑒′′ = 0 (20),

where the prime denotes the differential with respect to πœ‚.

Now we study the following cases:

π‘ͺ𝒂𝒔𝒆 𝟏: π’Ž = 𝟐,𝒏 = 𝟐:

According to the improved Exp-function method, the travelling wave solution of Eq. (18) in this case can be written

as:

𝑒 π‘₯, 𝑑 = 𝐴0 + 𝐴1𝑒π‘₯𝑝(πœ‚) + 𝐴2𝑒π‘₯𝑝(2πœ‚)

𝐡0 + 𝐡1𝑒π‘₯𝑝(πœ‚) + 𝐡2𝑒π‘₯𝑝(2πœ‚) (21)

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In case 𝐡2 β‰  0, Eq.(21) can be simplified as:

𝑒 π‘₯, 𝑑 = 𝐴0 + 𝐴1𝑒π‘₯𝑝(πœ‚) + 𝐴2𝑒π‘₯𝑝(2πœ‚)

𝐡0 + 𝐡1𝑒π‘₯𝑝(πœ‚) + 𝑒π‘₯𝑝(2πœ‚) 22

Substituting Eq. (22) into Eq. (20), and using the Maple, equating to zero the coefficients of all powers of

𝑒π‘₯𝑝(πœ‚)yields a set of algebraic equations for 𝐴0, 𝐴1, 𝐴2,𝐡0, 𝐡1 and c. Solving the system of algebraic equation

given above, with the aid of Maple, we obtain:

𝐴0 =𝐡0(βˆ’24+𝐴2𝛽+𝐴2𝛼)

𝛼+𝛽,𝐴1 = 0,𝐴2 = 𝐴2,𝐡0 = 𝐡0 ,𝐡1 = 0, 𝑐 =

βˆ’1

3.

Thus the following solution is

𝑒1 π‘₯, 𝑑 =

𝐡0(βˆ’24 + 𝐴2𝛽 + 𝐴2𝛼)𝛼 + 𝛽

+ 𝐴2𝑒π‘₯𝑝(2π‘₯ +2𝑑3

)

𝐡0 + 𝑒π‘₯𝑝(2π‘₯ +2𝑑3

) (23)

If 𝐴2 = 𝐡0 = 1, 𝛼 = 𝛽 = 2, then

𝑒1 π‘₯, 𝑑 =βˆ’5 + 𝑒π‘₯𝑝(2π‘₯ +

2𝑑3

)

1 + 𝑒π‘₯𝑝(2π‘₯ +2𝑑3

) (24)

π‘­π’Šπ’ˆπ’–π’“π’† πŸ“. π‘»π’“π’‚π’—π’†π’π’Šπ’π’ˆ π’˜π’‚π’—π’† π’”π’π’π’–π’•π’Šπ’π’ 𝒐𝒇 𝑬𝒒. πŸπŸ– 𝒇𝒐𝒓 π’”π’π’π’–π’•π’Šπ’π’ 𝑬𝒒. πŸπŸ’ ,π‘¨πŸ = π‘©πŸŽ = 𝟏, 𝜢 = 𝜷 = 𝟐.

π‘ͺ𝒂𝒔𝒆 𝟐: π’Ž = πŸ‘,𝒏 = πŸ‘:

According to the improved Exp-function method, the travelling wave solution of Eq. (18) in this case can be written

as:

𝑒 π‘₯, 𝑑 = 𝐴0 + 𝐴1𝑒π‘₯𝑝(πœ‚) + 𝐴2𝑒π‘₯𝑝(2πœ‚) + 𝐴3𝑒π‘₯𝑝(3πœ‚)

𝐡0 + 𝐡1𝑒π‘₯𝑝(πœ‚) + 𝐡2𝑒π‘₯𝑝(2πœ‚) + 𝐡3𝑒π‘₯𝑝(3πœ‚) (25)

In case 𝐡3 β‰  0, Eq.(25) can be simplified as:

𝑒 π‘₯, 𝑑 = 𝐴0 + 𝐴1𝑒π‘₯𝑝(πœ‚) + 𝐴2𝑒π‘₯𝑝(2πœ‚) + 𝐴3𝑒π‘₯𝑝(3πœ‚)

𝐡0 + 𝐡1𝑒π‘₯𝑝(πœ‚) + 𝐡2𝑒π‘₯𝑝(2πœ‚) + 𝑒π‘₯𝑝(3πœ‚) 26

Substituting Eq. (26) into Eq. (20), and using the Maple, equating to zero the coefficients of all powers of 𝑒π‘₯𝑝(πœ‚)

yields a set of algebraic equations for𝐴0, 𝐴1, 𝐴2, 𝐴3, 𝐡0, 𝐡1 ,𝐡2 and c. Solving the system of algebraic equation

given above, with the aid of Maple, we obtain:

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138

π‘­π’‚π’Žπ’Šπ’π’š 𝟏:

𝐴0 = 0,𝐴1 =𝐡1(βˆ’24 + 𝐴3𝛽 + 𝐴3𝛼)

𝛼 + 𝛽,𝐴2 = 0,𝐴3 = 𝐴3,𝐡0 = 0,𝐡1 = 𝐡1 ,𝐡2 = 𝐡2 , 𝑐 =

βˆ’1

3

Thus the following solution is

𝑒2 π‘₯, 𝑑 =

𝐡1(βˆ’24 + 𝐴3𝛽 + 𝐴3𝛼)𝛼 + 𝛽

𝑒π‘₯𝑝(π‘₯ +𝑑3

) + 𝐴3𝑒π‘₯𝑝(3π‘₯ + 𝑑)

𝐡1𝑒π‘₯𝑝(π‘₯ +𝑑3

) + 𝑒π‘₯𝑝(3π‘₯ + 𝑑) (27)

If 𝐡1 = 𝐴3 = 2, 𝛼 = 𝛽 = 1, then

𝑒2 π‘₯, 𝑑 =βˆ’20𝑒π‘₯𝑝(π‘₯ +

𝑑3

) + 2𝑒π‘₯𝑝(3π‘₯ + 𝑑)

2𝑒π‘₯𝑝(π‘₯ +𝑑3

) + 𝑒π‘₯𝑝(3π‘₯ + 𝑑) (28)

π‘­π’Šπ’ˆπ’–π’“π’† πŸ”. π‘»π’“π’‚π’—π’†π’π’Šπ’π’ˆ π’˜π’‚π’—π’† π’”π’π’π’–π’•π’Šπ’π’ 𝒐𝒇 𝑬𝒒. πŸπŸ– 𝒇𝒐𝒓 π’”π’π’π’–π’•π’Šπ’π’ 𝑬𝒒. πŸπŸ– ,π‘¨πŸ‘ = π‘©πŸ = 𝟐, 𝜢 = 𝜷 = 𝟏.

π‘­π’‚π’Žπ’Šπ’π’š 𝟐:

𝐴0 =𝐡0(𝐴3𝛽 + 𝐴3𝛼 βˆ’ 36)

𝛼 + 𝛽,𝐴1 = 0,𝐴2 = 0,𝐴3 = 𝐴3,𝐡0 = 𝐡0 ,𝐡1 = 0,𝐡2 = 0, 𝑐 =

βˆ’1

8

Thus the following solution is

𝑒3 π‘₯, 𝑑 =

𝐡0(𝐴3𝛽 + 𝐴3𝛼 βˆ’ 36)𝛼 + 𝛽

+ 𝐴3𝑒π‘₯𝑝(3π‘₯ +3𝑑8

)

𝐡0 + 𝑒π‘₯𝑝(3π‘₯ +3𝑑8

) (29)

If 𝐡0 = 𝐴3 = 2, 𝛼 = 𝛽 = 1, then

𝑒3 π‘₯, 𝑑 =βˆ’32 + 2𝑒π‘₯𝑝(3π‘₯ +

3𝑑8

)

2 + 𝑒π‘₯𝑝(3π‘₯ +3𝑑8

) (30)

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139

π‘­π’Šπ’ˆπ’–π’“π’† πŸ•. π‘»π’“π’‚π’—π’†π’π’Šπ’π’ˆ π’˜π’‚π’—π’† π’”π’π’π’–π’•π’Šπ’π’ 𝒐𝒇 𝑬𝒒. πŸπŸ– 𝒇𝒐𝒓 π’”π’π’π’–π’•π’Šπ’π’ 𝑬𝒒. πŸ‘πŸŽ ,π‘¨πŸ‘ = π‘©πŸŽ = 𝟐,𝜢 = 𝜷 = 𝟏.

3.3 The Boussinesq equation: [38-42]

The Boussinesq-type equations, which include the lowest-order effects of nonlinearity and frequency dispersion as

additions to the simplest non-dispersive linear long wave theory, provide a sound and increasingly well-tested basis

for the simulation of wave propagation in coastal regions. The standard Boussinesq equations for variable water

depth were first derived by Peregrine (1967), who used depth-averaged velocity as a dependent variable.

In the present paper we introduce new exact solutions of the Boussinesq equation via the improved Exp-function

method as follows:

Consider the Boussinesq equation:

𝑒𝑑𝑑 βˆ’ 𝑒π‘₯π‘₯ βˆ’ 𝑒π‘₯π‘₯π‘₯π‘₯ βˆ’ 6(𝑒π‘₯)2 βˆ’ 6𝑒𝑒π‘₯π‘₯ = 0 (31)

Using the transformation:

𝑒 = 𝑒 πœ‚ , πœ‰ = π‘˜π‘₯ + πœ”π‘‘ 32 ,

where π‘˜,πœ” are constants to be determined later. Substituting Eq. (32) into Eq. (31) we get

πœ”2𝑒′′ βˆ’ π‘˜2𝑒′′ βˆ’ π‘˜4𝑒′′′′ βˆ’ 6π‘˜2(𝑒′)2 βˆ’ 6π‘˜2𝑒𝑒′′ = 0 33 ,

where the prime denotes the differential with respect to πœ‰. Now we study the following cases:

π‘ͺ𝒂𝒔𝒆 𝟏: π’Ž = 𝟐,𝒏 = πŸ‘:

According to the improved Exp-function method, the travelling wave solution of Eq. (31) in this case can be written

as:

𝑒 π‘₯, 𝑑 = 𝐴0 + 𝐴1𝑒π‘₯𝑝(πœ‰) + 𝐴2𝑒π‘₯𝑝(2πœ‰)

𝐡0 + 𝐡1𝑒π‘₯𝑝(πœ‰) + 𝐡2𝑒π‘₯𝑝(2πœ‰) + 𝐡3𝑒π‘₯𝑝(3πœ‰) (34)

In case 𝐡3 β‰  0, Eq.(34) can be simplified as:

𝑒 π‘₯, 𝑑 = 𝐴0 + 𝐴1𝑒π‘₯𝑝(πœ‰) + 𝐴2𝑒π‘₯𝑝(2πœ‰)

𝐡0 + 𝐡1𝑒π‘₯𝑝(πœ‰) + 𝐡2𝑒π‘₯𝑝(2πœ‰) + 𝑒π‘₯𝑝(3πœ‰) 35

Substituting Eq. (35) into Eq. (33), and using the Maple, equating to zero the coefficients of all powers of

𝑒π‘₯ 𝑝 πœ‰ yields a set of algebraic equations for 𝐴0, 𝐴1, 𝐴2, 𝐡0, 𝐡1 ,𝐡2 , π‘˜ π‘Žπ‘›π‘‘ πœ”. Solving the system of algebraic

equation given above, with the aid of Maple, we obtain:

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π‘­π’‚π’Žπ’Šπ’π’š 𝟏:

𝐴0 = 0,𝐴1 = 0,𝐴2 = π‘˜2𝐡2 ,𝐡0 = 0,𝐡1 =𝐡2

2

4,𝐡2 = 𝐡2 ,πœ” = π‘˜ 1 + π‘˜2

Thus the following solution is

𝑒1 π‘₯, 𝑑 =π‘˜2𝐡2𝑒π‘₯𝑝(2π‘˜π‘₯ + 2π‘˜π‘‘ 1 + π‘˜2)

𝐡22

4𝑒π‘₯𝑝(π‘˜π‘₯ + π‘˜π‘‘ 1 + π‘˜2) + 𝐡2𝑒π‘₯𝑝(2π‘˜π‘₯ + 2π‘˜π‘‘ 1 + π‘˜2) + 𝑒π‘₯𝑝(3π‘˜π‘₯ + 3π‘˜π‘‘ 1 + π‘˜2)

(36)

If π‘˜ = 1, 𝐡2 = 2, then

𝑒1 π‘₯, 𝑑 =2𝑒π‘₯𝑝(2π‘₯ + 2𝑑 2)

𝑒π‘₯𝑝(π‘₯ + 𝑑 2) + 2𝑒π‘₯𝑝(2π‘₯ + 2𝑑 2) + 𝑒π‘₯𝑝(3π‘₯ + 3𝑑 2) (37)

π‘­π’Šπ’ˆπ’–π’“π’† πŸ–. π‘»π’“π’‚π’—π’†π’π’Šπ’π’ˆ π’˜π’‚π’—π’† π’”π’π’π’–π’•π’Šπ’π’ 𝒐𝒇 𝑬𝒒. πŸ‘πŸ 𝒇𝒐𝒓 π’”π’π’π’–π’•π’Šπ’π’ 𝑬𝒒. πŸ‘πŸ• ,π‘©πŸ = 𝟐,π’Œ = 𝟏.

π‘­π’‚π’Žπ’Šπ’π’š 𝟐:

𝐴0 = 0,𝐴1 = 0,𝐴2 = π‘˜2𝐡2 ,𝐡0 = 0,𝐡1 =𝐡2

2

4,𝐡2 = 𝐡2 ,πœ” = βˆ’π‘˜ 1 + π‘˜2

Thus the following solution is

𝑒2 π‘₯, 𝑑 =π‘˜2𝐡2𝑒π‘₯𝑝(2π‘˜π‘₯ βˆ’ 2π‘˜π‘‘ 1 + π‘˜2)

𝐡22

4𝑒π‘₯𝑝(π‘˜π‘₯ βˆ’ π‘˜π‘‘ 1 + π‘˜2) + 𝐡2𝑒π‘₯𝑝(2π‘˜π‘₯ βˆ’ 2π‘˜π‘‘ 1 + π‘˜2) + 𝑒π‘₯𝑝(3π‘˜π‘₯ βˆ’ 3π‘˜π‘‘ 1 + π‘˜2)

(38)

If 𝐡2 = 2, π‘˜ = 1, then

𝑒2 π‘₯, 𝑑 =2𝑒π‘₯ 𝑝 2π‘₯ βˆ’ 2𝑑 2

𝑒π‘₯𝑝(π‘₯ βˆ’ 𝑑 2) + 2𝑒π‘₯𝑝(2π‘₯ βˆ’ 2𝑑 2) + 𝑒π‘₯𝑝(3π‘₯ βˆ’ 3𝑑 2) (39)

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141

π‘­π’Šπ’ˆπ’–π’“π’† πŸ—. π‘»π’“π’‚π’—π’†π’π’Šπ’π’ˆ π’˜π’‚π’—π’† π’”π’π’π’–π’•π’Šπ’π’ 𝒐𝒇 𝑬𝒒. πŸ‘πŸ 𝒇𝒐𝒓 π’”π’π’π’–π’•π’Šπ’π’ 𝑬𝒒. πŸ‘πŸ— ,π‘©πŸ = 𝟐,π’Œ = 𝟏.

π‘ͺ𝒂𝒔𝒆 𝟐: π’Ž = 𝟐,𝒏 = πŸ’:

According to the improved Exp-function method, the travelling wave solution of Eq. (31) in this case can be written

as:

𝑒 π‘₯, 𝑑 = 𝐴0 + 𝐴1𝑒π‘₯ 𝑝 πœ‰ + 𝐴2𝑒π‘₯ 𝑝 2πœ‰

𝐡0 + 𝐡1𝑒π‘₯ 𝑝 πœ‰ + 𝐡2𝑒π‘₯ 𝑝 2πœ‰ + 𝐡3𝑒π‘₯ 𝑝 3πœ‰ + 𝐡4𝑒π‘₯ 𝑝 4πœ‰ (40)

In case 𝐡4 β‰  0, Eq.(40) can be simplified as:

𝑒 π‘₯, 𝑑 = 𝐴0 + 𝐴1𝑒π‘₯ 𝑝 πœ‰ + 𝐴2𝑒π‘₯ 𝑝 2πœ‰

𝐡0 + 𝐡1𝑒π‘₯ 𝑝 πœ‰ + 𝐡2𝑒π‘₯ 𝑝 2πœ‰ + 𝐡3𝑒π‘₯ 𝑝 3πœ‰ + 𝑒π‘₯ 𝑝 4πœ‰ 41

Substituting Eq. (41) into Eq. (33), and using the Maple, equating to zero the coefficients of all powers of

𝑒π‘₯ 𝑝 πœ‰ yields a set of algebraic equations for 𝐴0, 𝐴1, 𝐴2, 𝐡0 , 𝐡1 ,𝐡2 ,𝐡3 , π‘˜ and πœ”. Solving the system of algebraic

equation given above, with the aid of Maple, we obtain:

π‘­π’‚π’Žπ’Šπ’π’š 𝟏:

𝐴0 = 0,𝐴1 = 0,𝐴2 = 𝐴2,𝐡0 =𝐴2

2

64π‘˜4,𝐡1 = 0,𝐡2 =

𝐴2

4π‘˜2,𝐡3 = 𝐡3 ,πœ” = π‘˜ 1 + 4π‘˜2

Thus the following solution is

𝑒3 π‘₯, 𝑑 =𝐴2𝑒π‘₯𝑝(2π‘˜π‘₯ + 2π‘˜π‘‘ 1 + 4π‘˜2)

𝐴22

64π‘˜4 +𝐴2

4π‘˜2 𝑒π‘₯𝑝(2π‘˜π‘₯ + 2π‘˜π‘‘ 1 + 4π‘˜2) + 𝑒π‘₯𝑝(4π‘˜π‘₯ + 4π‘˜π‘‘ 1 + 4π‘˜2)

(42)

If 𝐴2 = 2, π‘˜ = 1, then

𝑒3 π‘₯, 𝑑 =2𝑒π‘₯𝑝(2π‘₯ + 2𝑑 5)

116

+12𝑒π‘₯𝑝(2π‘₯ + 2𝑑 5) + 𝑒π‘₯𝑝(4π‘₯ + 4𝑑 5)

(43)

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142

π‘­π’Šπ’ˆπ’–π’“π’† 𝟏𝟎. π‘»π’“π’‚π’—π’†π’π’Šπ’π’ˆ π’˜π’‚π’—π’† π’”π’π’π’–π’•π’Šπ’π’ 𝒐𝒇 𝑬𝒒. πŸ‘πŸ 𝒇𝒐𝒓 π’”π’π’π’–π’•π’Šπ’π’ 𝑬𝒒. πŸ’πŸ‘ ,π‘¨πŸ = 𝟐,π’Œ = 𝟏.

π‘­π’‚π’Žπ’Šπ’π’š 𝟐:

𝐴0 == 0,𝐴1 = 0,𝐴2 = 𝐴2,𝐡0 =𝐴2

2

64π‘˜4,𝐡1 = 0,𝐡2 =

𝐴2

4π‘˜2,𝐡3 = 𝐡3 ,πœ” = βˆ’π‘˜ 1 + 4π‘˜2

Thus the following solution is

𝑒4 π‘₯, 𝑑 =𝐴2𝑒π‘₯𝑝(2π‘˜π‘₯ βˆ’ 2π‘˜π‘‘ 1 + 4π‘˜2)

𝐴22

64π‘˜4 +𝐴2

4π‘˜2 𝑒π‘₯𝑝(2π‘˜π‘₯ βˆ’ 2π‘˜π‘‘ 1 + 4π‘˜2) + 𝑒π‘₯𝑝(4π‘˜π‘₯ βˆ’ 4π‘˜π‘‘ 1 + 4π‘˜2)

(44)

If 𝐴2 = 2, π‘˜ = 1, then

𝑒4 π‘₯, 𝑑 =2𝑒π‘₯𝑝(2π‘₯ βˆ’ 2𝑑 5)

116

+12𝑒π‘₯𝑝(2π‘₯ βˆ’ 2𝑑 5) + 𝑒π‘₯𝑝(4π‘₯ βˆ’ 4𝑑 5)

(45)

π‘­π’Šπ’ˆπ’–π’“π’† 𝟏𝟏. π‘»π’“π’‚π’—π’†π’π’Šπ’π’ˆ π’˜π’‚π’—π’† π’”π’π’π’–π’•π’Šπ’π’ 𝒐𝒇 𝑬𝒒. πŸ‘πŸ‘ 𝒇𝒐𝒓 π’”π’π’π’–π’•π’Šπ’π’ 𝑬𝒒. πŸ’πŸ“ ,π‘¨πŸ = 𝟐,π’Œ = 𝟏.

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4. CONCULSION

In this paper, the improved Exp-function method has been successfully applied to obtain new solutions of three

nonlinear partial differential equations. Thus, the improved Exp-function method can be extended to solve the

problems of nonlinear partial differential equations which arising in the theory of solitons and other areas.

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