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Soliton solutions for some nonlinear models in mathematical physics via conservation laws

  • In this paper, we derive the soliton solutions from conserved quantities for the Benjamin-Bona-Mahoney equation with dual-power law nonlinearity (BBM), modified regularized long wave (MRLW) equation, modified nonlinearly dispersive KdV equations 2K(2, 2, 1) and 3K(3, 2, 2) equation, which are constructed by the multiplier approach (variational derivative method). Finally, we give the numerical simulations to illustrate this method.

    Citation: F. A. Mohammed. Soliton solutions for some nonlinear models in mathematical physics via conservation laws[J]. AIMS Mathematics, 2022, 7(8): 15075-15093. doi: 10.3934/math.2022826

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  • In this paper, we derive the soliton solutions from conserved quantities for the Benjamin-Bona-Mahoney equation with dual-power law nonlinearity (BBM), modified regularized long wave (MRLW) equation, modified nonlinearly dispersive KdV equations 2K(2, 2, 1) and 3K(3, 2, 2) equation, which are constructed by the multiplier approach (variational derivative method). Finally, we give the numerical simulations to illustrate this method.



    In all areas of physics, conservation laws [1,2] are essential and important since they allow us to draw conclusions of a physical system under study in an efficient way. Knowledge of conservation laws are important for numerical integration of partial differential equations (PDEs). The existence of a large number of conservation laws for a nonlinear partial differential equation (system) is a strong indication of its integrability. Many powerful methods have been developed for the construction of conservation laws, such as the Noethers theorem [3] for variational problems, Laplaces Direct method [4], characteristic form introduced by Stuedel [5], multiplier approach [6,7], Kara and Mahomed [8] symmetry condition, partial Noether approach [9,10,11] and Cheviakov [12] developed powerful software packages to compute conservation laws for partial differential equations.

    The multiplier approach (also known as the variational derivative method) was successfully applied to the construction of conservation laws for nonlinear partial differential equations [13,14,15,16].

    Soliton solutions for nonlinear partial differential equations (PDEs) are play a significant role in soliton theory [17]

    In [18] the authors obtained the novel exact solutions in form of dark, bright, combined dark-bright, combined singular and other soliton solutions solitons for the meta materials model having third and fourth order dispersions, the authors in [19] obtained investigation for the optical solitons solution for the nonlinear Schr¨odinger equation in magneto-optic waveguides with anti-cubic nonlinearity and in [20] the author obtained the new exact soliton solutions for the two deformed nonlinear Schr¨odinger (NLS) type equations.

    Based on He's variational approach [21,22], which depends on the Lagrange function and the finding of conservation laws of system of differential equations (DEs), which is often the first step towards finding the solution the variational formula from the conserved quantities for Benjamin-Bona-Mahoney equation with dual-power law nonlinearity (BBM), modified regularized long wave (MRLW) equation and modified nonlinearly dispersive KdV equations 2K(2, 2, 1) and 3K(3, 2, 2) equation and new kinds of solitary wave solutions for these models and numerical simulations were obtained in Sections 3–6. in Section 5. This method helps to explore the new soliton solutions for new phenomena of nonlinear evolution equations. So we proposed a new method to derive the functional from conserved quantities since it depends on the Lagrange function and its derivatives [23] and then find the soliton solutions by Ritz method [24].

    The Benjamin-Bona-Mahoney equation with dual-power law nonlinearity (BBM) equation describes the dynamics of shallow water waves in the presence of advection, the modified regularized long wave (MRLW) equation was first introduced by Peregrine [25] to describe the development of an undular bore, the modified nonlinearly dispersive KdV equations 2K(2, 2, 1) equation and the modified nonlinearly dispersive KdV equations 3K(3, 2, 2) equation are derived from the well-known KdV equation which describes the mathematical modeling of traveling wave solutions, known as solitary water waves (also called solitons) in a shallow water domain.

    The proposed method derived the soliton solutions from the conserved quantities for the models while the existing method derived the soliton solutions from the Lagrangian for the models. In [26], He's variational iteration method was applied to obtain the numerical solution for various kinds of Newell-Whitehead-Segel nonlinear diffusion equation. This paper is organized as follows: In Section 2, we give brief definitions related to the multiplier approach and main steps for deriving the soliton solutions. In Sections 3–6, we apply this method to Benjamin-Bona-Mahoney equation with dual-power law nonlinearity (BBM), modified regularized long wave (MRLW) equation and modified nonlinearly dispersive KdV equations 2K(2, 2, 1) and 3K(3, 2, 2) equation and give the soliton solutions by using a proposed method and the figures for each models to illustrate the properties of these solitons solutions. Finally, results are summarized in Section 7.

    For giving an independent variable t,x and dependent variable u

    (1) The total derivative operator D with respect to t,x are

    Dt=t+utu+uttut+utxux+utxxuxx+......Dx=x+uxu+uxxux+uxtut+uxxtuxt+...... (2.1)

    (2) The Euler operator is defined

    δδu=uDtutDxux+D2tutt+D2xuxx+DxDtuxtD3tuttt..... (2.2)

    Consider a mth-order partial differential equation of t,x

    E(t,x,u,ut,ux,utt,utx,uxx,......)=0. (2.3)

    (3) A vector T=(T1,T2) such that

    DtT1+DxT2=0, (2.4)

    holds for all solutions of (2.3) is known as the conserved vector of (2.3).

    (4) The multiplier Λ for (2.3) has the property

    DtT1+DxT2=ΛE, (2.5)

    for arbitrary function u(x,t) [5,6]

    (5) The determining equations for multiplier are obtained by taking the variational derivative of (2.5) [6]

    δδu(ΛE)=0. (2.6)

    Equation (2.6) holds for arbitrary function u(x,t) not only for solutions of (2.3). We can derive the conserved vectors using (2.5) after computing the multiplier from (2.6)

    The main steps of the proposed method are given as follows:

    For giving a nonlinear equation

    Step 1. By using the wave transformation u(x,t)=u(ζ), ζ=kxωt+ζ0, we can convert Eq (2.3) into an ordinary differential equation (ODE)

    H(u,ωuζ,kuζ,ω2uζζ,kωuζζ,k2uζζ,.....)=0. (2.7)

    Step 2. Equation (2.4) can be converted into

    DζTζ=0, (2.8)

    Step 3. The multiplier Λ for (2.7) has the property

    DζTζ=Λ(ζ,u(ζ))H, (2.9)

    for arbitrary function U(ζ).

    Step 4. The determining equations for multiplier are obtained by taking the variational derivative of (2.9)

    δδu(Λ(ζ,u(ζ))H)=0. (2.10)

    Equation (2.10) holds for arbitrary function u(ζ) not only for solutions of (2.7). We can derive the conserved vectors using (2.9) after computing the multiplier from (2.10)

    Step 5. We construct the following functional

    J=0Tζdζ,orJ=Tζdζ, (2.11)

    where Tζ is the conserved quantity for the Eq (2.7).

    Step 6. By a Ritz method [24], we can obtain solitary wave solutions, such as u(ζ)=Asech(ζ),u(ζ)=Asech(ζ)2, where A is a constant to be determined.

    Substituting u(ζ)=Asech(ζ),u(ζ)=Asech(ζ)2 into Eq (2.11) and making J stationary with respect to A we obtain

    JA=0. (2.12)

    Solving Eq (2.12) we obtain the constant A. Hence the solitary wave solution is well determined.

    We consider the Benjamin-Bona-Mahoney equation with dual-power law nonlinearity (BBM) equation [27]

    ut+aux+(bun+cu2n)ux+luxxx=0. (3.1)

    The first term represents the evolution term while b and c represent the coefficients of dual-power law nonlinearity. Then a and l are the coefficients of dispersion terms. The parameter n is the power law parameter while u is the wave profile. The independent variables x and t represent spatial and temporal variables respectively.

    The two conserved vectors [28]

    Tt1=u22,Tx1=a2u2+bn+2un+2+c2(n+1)u2(n+1)+luuxxl2u2x,Tt2=u,Tx2=au+bn+1un+1+c2n+1u2n+1+luxx. (3.2)

    Using the wave variable transformation u(x,t)=u(ζ), ζ=kxωt+ζ0 to convert Eq (3.1) into ODE

    (kaω)u+k(bun+cu2n)u+k3lu=0. (3.3)

    The determining equation for multiplier Λ(ζ,u(ζ)), from (2.10), is

    Λu((kaω)u+k(bun+cu2n)u+k3lu)+k(nbun1+2ncu2n1)uΛDζ((kaω)+k(bun+cu2n))Λk3lD3ζΛ=0. (3.4)

    Equation (3.4) is separated according to different combinations of derivatives of u and and an overdetermined system of equations for multiplier Λ is obtained which gives

    Λ(ζ,u)=c1u+c2. (3.5)

    From (2.9) and (3.5), we obtain the conserved quantities

    Tζ=(akω)(12c1u(ζ)2+c2u(ζ))+bc2ku(ζ)n+1n+1+bc1ku(ζ)n+2n+2+c2du(ζ)2n+12n+1+c1du(ζ)2n+22n+2+c2k3lu(ζ)+c1k3l(u(ζ)u(ζ)12u(ζ)2). (3.6)

    We can construct the following functional

    J=0((akω)(12c1u(ζ)2+c2u(ζ))+bc2ku(ζ)n+1n+1+bc1ku(ζ)n+2n+2+c2du(ζ)2n+12n+1+c1du(ζ)2n+22n+2+c2k3lu(ζ)+c1k3l(u(ζ)u(ζ)12u(ζ)2))dζ. (3.7)

    According to the Ritz-like method, we look for a solitary wave solution in the form

    u(ζ)=Asech(ζ). (3.8)

    Substituting Eq (3.8) into Eq (3.7), we have for n=1

    J=112A(Ac1(6ak+2A2d+πAbk6(k3l+ω))+c2(6πak+πA2d+6Abk6πω)). (3.9)

    To find the constant A, we solve the following equation

    JA=14c2(2πak+πA2d+4Abk2πω)+c1(A(ak+k3(l)ω)+2A3d3+14πA2bk)=0. (3.10)

    From (3.10), we get

    A={3πbk3(3π2b2k2128adk+128dk3l+128dω)16d,c1=1,c2=0,2(2b2k2π2adk+π2dω)2bkπd,c1=0,c2=1. (3.11)

    Therefore, the solitary wave solutions for the BBM equation with dual-power law nonlinearity are

    u(x,t)={3πbk3(3π2b2k2128adk+128dk3l+128dω)16dsech(kxωt+ζ0),c1=1,c2=0,2(2b2k2π2adk+π2dω)2bkπdsech(kxωt+ζ0),c1=0,c2=1. (3.12)

    The 3D graphs in Figures 1 and 2 illustrate the trough propagating to the right, while 2D graphs show the movement of the wave along x-direction as time increases for Eq (3.12), a contour plot could also be useful for describing the movement of the solitons.

    Figure 1.  Shows the soliton solution of Eq (3.12) for c1=1,c2=0.
    Figure 2.  Shows the soliton solution of Eq (3.12) for c1=0,c2=1.

    For another soliton solution in the form [29]

    u(ζ)=Fsech2(ζ). (3.13)

    where F is a constant to be determined. Substituting Eq (3.13) into Eq (3.9), we obtain

    J=F315(Fc1(21(5ak12k3l5ω)+36F2d+56Fbk))+F315(7c2(45ak+8F2d+15Fbk45ω))). (3.14)

    To find the constant F, we solve the following equation

    JF=1105(2Fc1(35ak+24F2d+28Fbk84k3l35ω))+1105(7c2(15ak+8F2d+10Fbk15ω)))=0. (3.15)

    From Eq (3.15), we have

    F={7bk7(72dk3l30adk+7b2k2+30dω)12d,c1=1,c2=0,5bk5(5b2k224adk+24dω)8d,c1=0,c2=1. (3.16)

    Therefore, the solitary wave solutions for the BBM equation with dual-power law nonlinearity are as follows:

    u(x,t)={7bk7(72dk3l30adk+7b2k2+30dω)12dsech2(kxωt+ζ0),c1=1,c2=0,5bk5(5b2k224adk+24dω)8dsech2(kxωt+ζ0),c1=0,c2=1. (3.17)

    The 3D graphs in Figures 3 and 4 describe nonlinear wave propagation of soliton solutions, while 2D graphs depict the movement of the solitons obtained from Eq (3.17) for different times and a contour plot describes the movement of the solitons.

    Figure 3.  Shows the soliton solution of Eq (3.17) for c1=1,c2=0.
    Figure 4.  Shows the soliton solution of Eq (3.17) for c1=0,c2=1.

    We consider the modified regularized long wave (MRLW) equation [30]

    ut+ux+6u2uxμuxxt=0, (4.1)

    where μ is a positive constants, was originally introduced to describe the behavior of the undular bore by Peregrine [31], and later by Benjamin et al. [32]. This equation is very important in physics media since it describes a phenomenon with weak nonlinearity and dispersion waves, including nonlinear transverse waves in shallow water, ion-acoustic and magneto hydrodynamic waves in plasma and phonon packets in nonlinear crystals.

    The two conserved vectors [28]

    Tt1=u22μ(uuxx12u2x),Tx1=12u2+μuxut+32u4,Tt2=u,Tx2=u+2u3. (4.2)

    To find the soliton solutions, we convert Eq (4.1) into an ODE

    (kω)u+6ku2u+μk2ωu=0. (4.3)

    The multiplier Λ(ζ,u(ζ)), can be obtained as follows

    Λu((kω)u+6ku2u+μk2ωu)+12kuuΛDζ((kω)+6ku2)Λμωk2D3ζΛ=0. (4.4)

    Solving Eq (4.4) for multiplier Λ, we obtain

    Λ(ζ,u)=c1u+c2. (4.5)

    From (2.9) and (4.5), we obtain the conserved quantities

    Tζ=k2μω(c2u(ζ)+c1(u(ζ)u(ζ)12u(ζ)2))+12(kω)u(ζ)(c1u(ζ)+2c2)+32ku(ζ)3(c1u(ζ)+4c23). (4.6)

    From (4.6), we can obtain the functional

    J=0(k2μω(c2u(ζ)+c1(u(ζ)u(ζ)12u(ζ)2))+12(kω)u(ζ)(c1u(ζ)+2c2)+32ku(ζ)3(c1u(ζ)+4c23))dζ. (4.7)

    According to the Ritz-like method, we search a solitary wave solution in the form

    u(ζ)=Asech(ζ). (4.8)

    Substituting Eq (4.8) into Eq (4.7), we have

    J=12A(Ac1(2A2k+k2μω+kω)+πc2(A2k+kω)). (4.9)

    To find the constant A, we solve the following equation

    JA=12(2Ac1(4A2k+k2μω+kω)+πc2(3A2k+kω))=0. (4.10)

    From (4.10), we obtain

    A={ωkμωk24k,c1=1,c2=0,ωk3k,c1=0,c2=1. (4.11)

    Therefore, the solitary wave solutions for the MRLW equation are

    u(x,t)={ωkμωk24ksech(kxωt+ζ0),c1=1,c2=0,ωk3ksech(kxωt+ζ0),c1=0,c2=1. (4.12)

    The 3D graphs in Figures 5 and 6 describe the shape of solitons for waves u(x,t), while 2D graphs depict the movement of the soliton waves along x-direction as time increases for Eq (4.12), a contour plot can also be useful for deseribing the movement of the solitons for (4.12).

    Figure 5.  Shows the soliton solution of Eq (4.12) for c1=1,c2=0.
    Figure 6.  Shows the soliton solution of Eq (4.12) for c1=0,c2=1.

    For another soliton solution (3.13), we obtain

    J=1105F(Fc1((72F2+35)k+84k2μω35ω)+7c2((16F2+15)k15ω)). (4.13)

    Solving the following equation to find F

    JF=2105Fc1((144F2+35)k+84k2μω35ω)+15c2((16F2+5)k5ω)=0. (4.14)

    From Eq (4.14), we have

    F={1127(5ω12k2μω5k)k,c1=1,c2=0,145(ωk)k,c1=0,c2=1. (4.15)

    Therefore, the solitary wave solutions for the MRLW equation are as follows

    u(x,t)={1127(5ω12k2μω5k)ksech2(kxωt+ζ0),c1=1,c2=0,145(ωk)ksech2(kxωt+ζ0),c1=0,c2=1. (4.16)

    The 3D graphs in Figures 7 and 8 describe nonlinear wave propagation of soliton solutions to the right, while 2D graphs depict the movement of the solitons obtained from Eq (4.16) for different times and a contour plot describes the movement of the solitons.

    Figure 7.  Shows the soliton solution of Eq (4.16) for c1=1,c2=0.
    Figure 8.  Shows the soliton solution of Eq (4.16) for c1=0,c2=1.

    The modified nonlinearly dispersive KdV equations 2K(2, 2, 1) equation [33] takes the form

    uut+a(u2)x+buxxx=0, (5.1)

    where a and b are constants.

    The three conserved vectors [28]

    Tt1=u22(tx2a),Tx1=u2(atx2)+uxx(btx2)+12aux,Tt2=u33,Tx2=23au3b2(ux)2+buuxx,Tt3=u22,Tx3=au2+buxx. (5.2)

    By converting Eq (5.1) into an ODE

    (2akω)uu+bk3u=0. (5.3)

    The multiplier Λ(ζ,u(ζ)), can be obtained as follows

    Λu((2akω)uu+bk3u)+(2akω)(uΛDζ(uΛ))bk3D3ζΛ=0. (5.4)

    Solving Eq (5.4) for multiplier Λ, we obtain

    Λ(ζ,u)=c1u+c2. (5.5)

    From (2.9) and (5.5), we obtain the conserved quantities

    Tζ=16u(ζ)2(2akω)(2c1u(ζ)+3c2)+bk3(c2u(ζ)+c1(u(ζ)u(ζ)12u(ζ)2)). (5.6)

    From (5.6), we can obtain the functional

    J=0(16u(ζ)2(2akω)(2c1u(ζ)+3c2)+bk3(c2u(ζ)+c1(u(ζ)u(ζ)12u(ζ)2)))dζ. (5.7)

    According to the Ritz-like method, we search a solitary wave solution in the form

    u(ζ)=Asech(ζ). (5.8)

    Substituting Eq (5.8) into Eq (5.7), we have

    J=112A2(c1(πA(ω2ak)6bk3)+6c2(2akω)). (5.9)

    To find the constant A, we solve the following equation

    JA=14A(c1(πA(ω2ak)4bk3)+4c2(2akω))=0. (5.10)

    From (5.10), we obtain

    A={4bk3π(2akω),c1=1,c2=0,4(2ak+bk3+ω)π(2akω),c1=1,c2=1. (5.11)

    Therefore, the solitary wave solutions for the 2K(2, 2, 1) equation are

    u(x,t)={4bk3π(2akω)sech(kxωt+ζ0),c1=1,c2=0,4(2ak+bk3+ω)π(2akω)sech(kxωt+ζ0),c1=1,c2=1. (5.12)

    The 3D graphs in Figures 9 and 10 describe the shape of solitons for waves u(x,t), while 2D graphs depict the movement of the soliton waves along x-direction as time increases for Eq (5.12), a contour plot can also be useful for describing the movement of the solitons for (5.12).

    Figure 9.  Shows the soliton solution of Eq (5.12) for c1=1,c2=0.
    Figure 10.  Shows the soliton solution of Eq (5.12) for c1=1,c2=1.

    For another soliton solution (3.13), we obtain

    J=145F2(4c1(4aFk2Fω9bk3)+15c2(2akω)). (5.13)

    Solving the following equation to find F

    JF=215F(4c1(2aFkFω3bk3)+5c2(2akω))=0. (5.14)

    From Eq (5.14), we have

    F={3bk32akω,c1=1,c2=0,10ak+12bk3+5ω4(2akω),c1=1,c2=1. (5.15)

    Therefore, the solitary wave solutions for the 2K(2, 2, 1) equation are as follows:

    u(x,t)={3bk32akωsech2(kxωt+ζ0),c1=1,c2=0,10ak+12bk3+5ω4(2akω)sech2(kxωt+ζ0),c1=1,c2=1. (5.16)

    The 3D graphs in Figures 11 and 12 describe nonlinear wave propagation of soliton solutions to the right, while 2D graphs depict the movement of the solitons obtained from Eq (5.16) for different times and a contour plot describes the movement of the solitons.

    Figure 11.  Shows the soliton solution of Eq (5.16) for c1=1,c2=0.
    Figure 12.  Shows the soliton solution of Eq (5.16) for c1=1,c2=1.

    The modified nonlinearly dispersive KdV equations 3K(3, 2, 2) equation [33] take the form

    u2ut+a(u2)x+b(u2)xxx=0, (6.1)

    where a and b are constants.

    The four conserved vectors [28]

    Tt1=u55,Tx1=a2u4+bu2(u2)xx2bu2u2x,Tt2=au2,Tx2=au2+2(uuxx+u2x),Tt3=13u3sin(abx),Tx3=b(2(uuxx+u2x)sin(abx)2abuuxcos(abx)),Tt4=13u3cos(abx),Tx4=b(2(uuxx+u2x)cos(abx)+2abuuxsin(abx)). (6.2)

    By converting Eq (6.1) into an ODE

    (2akωu)uu+2k3(uu+3uu)=0. (6.3)

    The multiplier Λ(ζ,u(ζ)), can be obtained as follows

    Λu((2akωu)uu+2k3(uu+3uu))+((2ak2ωu)u+2k3u)ΛDζ((2akωu)u+6k3u)Λ)2k3D3ζ(uΛ)=0. (6.4)

    Solving Eq (6.4) for multiplier Λ, we obtain

    Λ(ζ,u)=c1+c2u2. (6.5)

    From (2.9) and (6.5), we obtain the conserved quantities

    Tζ=12aku(ζ)2(c2u(ζ)2+2c1)+2k3(c2u(ζ)3u(ζ)+32c1u(ζ)2+c1(u(ζ)u(ζ)12u(ζ)2))115ωu(ζ)3(3c2u(ζ)2+5c1). (6.6)

    From (6.6), we can get the functional

    J=0(12aku(ζ)2(c2u(ζ)2+2c1)+2k3(c2u(ζ)3u(ζ)+32c1u(ζ)2+c1(u(ζ)u(ζ)12u(ζ)2))115ωu(ζ)3(3c2u(ζ)2+5c1))dζ. (6.7)

    According to the Ritz-like method, we search a solitary wave solution in the form

    u(ζ)=Asech(ζ). (6.8)

    Substituting Eq (6.8) into Eq (6.7), we have

    J=c1(aA2k112πA3ω)1240A4c2(80ak+9πAω+192k3). (6.9)

    To find the constant A, we solve the following equation

    JA=1240A3c2(320ak+45πAω+768k3)14Ac1(πAω8ak)=0. (6.10)

    From (6.10), we obtain

    A={8akπω,c1=1,c2=0,64(5ak12k3)45πω,c1=0,c2=1. (6.11)

    Therefore, the solitary wave solutions for the 3K(3, 2, 2) equation are

    u(x,t)={8akπωsech(kxωt+ζ0),c1=1,c2=0,64(5ak12k3)45πωsech(kxωt+ζ0),c1=0,c2=1. (6.12)

    The 3D graphs in Figures 13 and 14 describe the shape of solitons for waves u(x,t), while 2D graphs depict the movement of the soliton waves along x-direction as time increases for Eq (6.12), a contour plot can also be useful for describing the properties of the solitary waves for (6.12).

    Figure 13.  Shows the soliton solution of Eq (6.12) for c1=1,c2=0.
    Figure 14.  Shows the soliton solution of Eq (6.12) for c1=0,c2=1.

    For another soliton solution (3.13), we obtain

    J=2F2(35c1(15ak4Fω)4F2c2(45ak+16Fω+240k3))1575. (6.13)

    Solving the following equation to find F

    JF=4315A(21c1(5ak2Aω)8A2c2(9ak+4Aω+48k3))=0. (6.14)

    From Eq (6.14), we have

    F={5ak2ω,c1=1,c2=0,3(3ak16k3)4ω,c1=0,c2=1. (6.15)

    Therefore, the solitary wave solutions for the 3K(3, 2, 2) equation are as follows:

    u(x,t)={5ak2ωsech2(kxωt+ζ0),c1=1,c2=0,3(3ak16k3)4ωsech2(kxωt+ζ0),c1=0,c2=1. (6.16)

    The 3D graphs in Figures 15 and 16 describe nonlinear wave propagation of soliton solutions, while 2D graphs depict the movement of the solitons obtained from Eq (6.16) for different times and a contour plot describes the movement of the solitons.

    Figure 15.  Shows the soliton solution of Eq (6.16) for c1=1,c2=0.
    Figure 16.  Shows the soliton solution of Eq (6.16) for c1=0,c2=1.

    In this paper we derive the soliton solutions directly from the conserved quantities for Benjamin-Bona-Mahoney equation with dual-power law nonlinearity (BBM), modified regularized long wave (MRLW) equation and modified nonlinearly dispersive KdV equations 2K(2, 2, 1) and 3K(3, 2, 2) equation, which are constructed by multiplier approach (variational derivative method). The multiplier approach on Benjamin-Bona-Mahoney equation with dual-power law nonlinearity (BBM) and modified regularized long wave (MRLW) equation gave two multipliers of Λ(x,t,u), and thus two conserved vectors obtained for each case. For the modified nonlinearly dispersive KdV equations 2K(2, 2, 1) equation, the multiplier approach yielded three multipliers and thus three conserved vectors were obtained. For the modified nonlinearly dispersive KdV equations 3K(3, 2, 2) equation, the multiplier approach yielded four multipliers and thus four conserved vectors were obtained. So, we can say that the proposed method is effective and an alternative mathematical tool for generating soliton solutions. The main results is derived the functional (2.11) using the conserved quantities and then the soliton solutions for the models. This is another method for deriving the variational principles for the nonlinear evolution equations and we can easily extend this work to all soliton equations in future works. Finally, we give the numerical simulations for these solutions.

    The author declares no conflicts of interest in this paper.



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