High-Order Soliton Solutions and Hybrid Behavior for the (2 + 1)-Dimensional Konopelchenko-Dubrovsky Equations ()
1. Introduction
As one of the three most attractive research directions in nonlinear science (soliton, chaos and fractal theory), soliton theory plays an important role in various fields of natural science. In recent decades, with the rapid development of computer software, the research results of nonlinear partial differential equations (NPDE) are more and more abundant, especially some new analytical structures and new solving methods emerge in endlessly, such as the Hirota bilinear method [1] [2], the Grammian determinant method [3], the Lie group method [4], the Darboux transformation method [5]-[7], and the backlund transformation [8] [9], etc. Meanwhile, some new analytical structures of NPDE, such as the breather, lump solution and rogue wave are widely investigated [10]-[14].
In the application field of solitons, the research on the solution of NPDE is no longer limited to the fluid field, and its applications in nonlinear optics, plasmas, condensed matter physics and other fields have also been continuously expanded. Very recently, we found that the analytic structure related to hybrid behavior has been reported in many nonlinear systems, hybrid behavior between lump solution and 1-solitons, hybrid behavior between lump solution and breathers, and hybrid behavior between different solitons.
In this paper, we focus on the N-soliton and hybrid behavior of a (2 + 1)-dimensional Konopelchenko-Dubrovsky equations (KD):
(1)
where
are some arbitrary constants, which reflects richer physical meaning in nonlinear shallow waves.
As a generalized (2 + 1)-dimensional model, the KD equation has received widespread attention from the scientific community since its derivation, and research results have been continuously enriched. KD equation is mainly used in the study of weak dispersion characterization in physics, but also has a wide range of applications in nonlinear optics and plasma physics. Many scholars have contributed to the field of atmospheric science by studying the behavior of nonlinear waves to further reveal subtle scattering effects and large-scale interactions in the troposphere in the tropics and mid-latitudes, and understanding their dynamic behavior is important for understanding weather patterns. In 2001, Lin and Lou gave its multi-soliton solution [15]; Zhi H obtained its traveling wave solution using the hyperbolic tangent function method [16]; Cao obtained the exact multi-parameter solution on the basis of Xu’s stability method [17]; by combining the lie symmetry group with the idea of homologous testing, Kang and others gave the non-traveling wave soliton hybrid behavior with arbitrary time function, soliton-like solution and elliptic periodic solitary wave hybrid behavior [18]-[20]. However, to our knowledge, the evolution behavior and interaction phenomenon of some higher-order soliton solutions of KD, including hybrid phenomenon between high-order lump solution and soliton, hybrid behavior between lump solution and N-soliton, have not been studied and discussed.
The outline of the paper is as follows: In Section 2, based on the bilinear form of KD Equation (1), we will study the evolution behavior of the N-soliton by employing the long wave limit method and the paired-complexification technique of parameters, including the emergence of lump solutions and breather solutions, the hybrid phenomenon of different soliton solutions, interaction of high-order lump solutions. In Section 3, we will study the interaction between the 1-order lump solution and the 1-soliton, 1-order lump solution and the 2-soliton, and the 1-order lump solution and 1-order breather solution. Finally, the conclusion is given in Section 4.
2. Evolution Behavior of N-Soliton Solution
In this section, the evolution behavior of the N-soliton solutions of the KD equation will be studied by employing the long wave limit technique, such as the emergence of T-order breather soliton and M-order lump solution. In order to facilitate subsequent discussions, we will initially simplify the above KD equation and make the following transformation:
(2)
Bringing the above changes into (1) yields:
(3)
Let’s make
and do the following transformation:
(4)
where f is the test function to be selected. Substituting (4) into (3), we get the bilinear of KD equation in the following form:
(5)
while the bilinear operator
represents the Hirota’s bilinear differential operator [2].
2.1. The N-Soliton Solutions
To obtain the N-soliton solution of (4), we apply the usual perturbation method to expand the test function f into the following power series:
(6)
where
is the small parameter. Substituting (6) into (4), and to merge similar terms according to the
th power, there are as follows:
(7)
When
, take
in (4), according to (4), then there is
(8)
where there is
, and
. Therefore, substituting the above expression into (4) yields the 1-soliton solution.
(9)
When
, take
in (4), we can get
(10)
The following relationships are established:
(11)
Substituting (10) and (11) into (4), we can get the 2-soliton solution,
(12)
When
, take
in (4), then we can obtain that
(13)
and
(14)
Similarly, substituting the above expression into (4), the 3-soliton solution can be solved.
Based on the Hirota’s bilinear Equation (3), the N-order soliton solutions of KD Equation (1) can be obtained
(15)
where the
represents summation over all possible combinations of
, and the
is over all possible combinations of the N elements with the specific condition
. By combining (3) and (4), we get the parameter relationship as
(16)
where
and
are some free parameters. Substituting (4) with (5) into (2), we can obtain the N-soliton solutions of KD Equation (1).
In order to better show the evolution behavior of the N-soliton solution with the increase of the soliton number N, we give the spatial structure evolution diagram in Figure 1, with different parameter values as
1):
,
2):
,
3):
.
Figure 1. Spatial evolution images of N-soliton solutions u and v at
: (a)
; (b)
; (c)
.
2.2. From N-Soliton to T-Order Breather Soliton
The purpose of this section is to construct high-order breather soliton of KD. Since
contains free parameters
and
, we cannot get the breather soliton of KD Equation (1) when these parameters take some different values. However, the paired-complexification of parameters
can yield smooth breather soliton of KD on a zero background.
Based on the idea of the paired-complexification of parameters, we take the following parameter relations in (17),
(17)
where I means imaginary units. By combining (4), (5), (15) and (17), we can obtain the T-order breather soliton of KD equation.
For example, to construct the 1-order breather soliton, we take
in (4), then,
(18)
According to (18) and taking
,
,
,
in (16), we get
where
(19)
and the parameters
are some arbitrary real numbers.
Then, the 1-order breather solution can be obtained via inserting
into transformation (4),
(20)
The 1-order breather solution (20) contains some free parameters, and we can get some 1-order breather solution with different spatial structures by selecting different parameter values.
Similarly, taking
, we can get the 2-order breather solution of KD Equation (1). In order to better show the evolution behavior of the T-order breather soliton, we give the spatial structure evolution diagram in Figure 2, with different parameter values as
1):
,
2):
,
3):
,
Figure 2. Spatial evolution images of T-breather solutions u and v at
: (a) and (b):
; (c) and (d):
.
4):
.
By further analysis, we can see that the position of the 1-order breather solution on the
plane is determined by
and
. When
and
, 1-order breather solution is perpendicular to the Y-axis; when
and
, 1-order breather solution is parallel to the Y-axis; when
, the slope of 1-order breather solution in the
plane is
. Similar to 1-order breather solution, the position of 2-order breather solution on the plane
is determined by
,
,
and
. When
, 2-order breather solution is perpendicular to the Y-axis; when
and
, 2-order breather solution is parallel to the Y-axis; when
, the cross structure of the solution of 2-order breather in the
plane can be obtained.
2.3. From N-Soliton to M-Order Lump Solution
According to the long wave limit technique, we take
and let
tend to 0 in (21) and (4). Therefore, we get
(21)
with
(22)
Since u and v is given by transformation (2), we have therefore deduced the following rational solutions,
(23)
where
denotes the summation over all possible combinations of
, which are taken different values from these numbers
. Choosing
in (24), and substituting it into (2), we can get the N-order rational solution of KD Equation (1).
To obtain M-order lump solution for KD Equation (1), select
and
,
,
,
in Equations (1) and (2), where I represents the imaginary unit and
indicates that the complex number is conjugated taking.
For example, when
, take
,
in
, By simple calculations, we can obtain
(24)
where
(25)
Substituting (15) into (3) gives the 1-order lump solution solution of the Equation (1) (see Figure 3(a) and Figure 3(b)):
(26)
When
, we have
(27)
Similar to the calculation of
, when
,
, taking
,
, in (24), we can get 2-order lump solution (see Figure 3(c) and Figure 3(d)). The values of related parameters in Figure 3 are shown as follows:
1):
;
2):
;
3) and 4):
.
Figure 3. Spatial evolution images of M-order lump solutions u and v at t = 0: (a) and (b) M = 1; (c) and (d) M = 2.
Moreover, when
, taking
in (24), we can obtain the M-order lump solution of the KD equation.
In fact, we can note that when
, the period of the 1-order breather solution approaches infinity, and the smooth breather solution is transformed into the 1-order lump solution. Conversely, higher order lump solutions can also be derived from higher order breather solutions.
3. From N-Soliton to L-Order Hybrid Solution
In this section, we mainly study the high-order hybrid solution of KD (1) by combining the long wave limit technique and the paired-complexification of parameters, including the hybrid solution between the 1-order lump solution and 1-soliton solution, the hybrid solution between the 1-order lump solution and 2-soliton solution, the hybrid solution between the 1-order lump solution and 1-order breather solution.
3.1. A Hybrid Solution between the 1-Order Lump Solution and 1-Soliton
In order to construct the hybrid solution consisting of 1-order lump solution and 1-soliton solution, taking
,
in (4) and
can be written as follows:
(28)
where
(29)
By combining
and simplifying, we can obtain
(30)
letting
, we get
(31)
and
(32)
Taking
in (31) and (32), and substituting it into (2), we get a hybrid solution between the 1-order lump solution and the 1-soliton (see Figure 4). In Figure 4, we give the spatial structure evolution diagram of the hybrid solution with time t, where the values of the parameters are
Figure 4. Evolution structure diagram of the hybrid solutions u and v between 1-order lump solution and 1-soliton at different times: (a)
; (b)
; (c)
; (d)
; (e)
; (f)
.
From Figure 4, we find that the lump solution and 1-soliton solution do not affect each other’s motion during the interaction process, such as the motion speed and amplitude of the lump solution, the shape of the soliton solution, etc. This phenomenon is also known as the complete elastic collision [21].
3.2. A Hybrid Solution between the 1-Order Lump Solution and 2-Soliton
To obtain the hybrid solution consisting of 1-order lump solution and 2-soliton solution, taking
,
in (4) and letting
, we have
(33)
where
,
,
,
are given by (29), the
is determined by (5), and
(34)
Then, substituting (33) and (34) into (2), we get a hybrid solution between the 1-order lump solution and the 2-soliton (see Figure 5). In Figure 5, we give the spatial structure evolution diagram of the hybrid solution with time t, where the values of the parameters are
3.3. A Hybrid Solution between the 1-Order Lump Solution and 1-Order Breather Solution
Unlike the previous hybrid solution of 1-order lump and 2-soliton, here we make the following transformation to obtain a new hybrid solution between the 1-order lump solution and 1-order breather solution:
Figure 5. Evolution structure diagram of the hybrid solutions u and v between 1-order lump solution and 2-soliton at different times: (a)
; (b)
; (c)
; (d)
; (e)
; (f)
.
(35)
We substitute
in (22) and
in (34), combined with (35), into the following equation:
(36)
Next, in the same situation as before, we substitute (36) into (4) and take the relevant parameters to obtain the hybrid solution between the 1-order lump solution and 1-order breather solution. In order to better demonstrate its spatial structure, we provide a demonstration diagram in Figure 6, with the relevant parameters as follows:
From Figure 6, we can see that over time, the lump solution and breather solution interact with each other, and their shapes remain unchanged before and after each other, which indicates that this is an elastic collision.
Figure 6. Evolution structure diagram of the hybrid solutions u and v between 1-order lump solution and 1-order breather solution at different times: (a)
; (b)
; (c)
; (d)
; (e)
; (f)
.
4. Conclusion
This article is mainly divided into two parts. One part is to use the long wave limit method to obtain a series of solutions to the KD equation. Starting from the N-soliton solution of the KD equation, the first step is to perform parameter complexation to obtain the breather solution of the KD equation. Then, by limiting the parameter
, the lump solution of the KD equation is obtained; the other part is based on the series of solutions, selecting different test functions to obtain hybrid solutions of the KD equation, such as the 1-order lump with 1-soliton, 2-soliton and 1-order breather solution. By analyzing the spatial evolution diagram of the hybrid solutions, we found that the three types of hybrid solutions mentioned above are all elastic collisions, and before and after the interaction, the velocity and shape of the waves do not change. The KD equation is a relatively classic class of nonlinear equations, and this article analyzes its different types of solutions, hoping to provide valuable information for the study of mathematical physics.
Acknowledgements
This work was partially supported by the Natural Science Foundation of Hunan Province (No. 2021JJ40434), and the Scientific Research Project of the Hunan Education Department (No. 21B0510).