一般来说, 大多数非线性方程都是关于时间
$ \begin{equation} \begin{aligned} u_{tt}+(c_1+c_2)&u_{xt}+c_1c_2u_{xx}+\Big((\alpha_1+\alpha_2) \frac{\partial}{\partial t}+(\alpha_1c_2+\alpha _2 c_1) \frac{\partial}{\partial x}\Big)uu_x\\ &+\Big( (\beta_1+\beta_2)\frac{\partial}{\partial t}+(\beta_1c_2+\beta_2c_1)\frac{\partial}{\partial x}\Big) u_{xxx} = 0. \end{aligned} \end{equation} $ | (0.1) |
其中:
经过特殊的变换, 并令
$ \begin{equation} \begin{aligned} s = \frac{1}{2}(c_1-c_2), \quad \alpha = \frac{\alpha_1-\alpha_2}{\alpha_1+\alpha_2}, \quad \beta = \frac{\beta_1-\beta_2}{\beta_1+\beta_2}, \quad -1 \leqslant \alpha, \, \beta \leqslant 1. \end{aligned} \end{equation} $ | (0.2) |
方程(0.1)可以约化为
$ \begin{equation} \begin{aligned} u_{tt}-s^2u_{xx}+\Big( \frac{\partial}{\partial t}-\alpha s\frac{\partial}{\partial x}\Big) uu_x +\Big( \frac{\partial}{\partial t}-\beta s\frac{\partial}{\partial x}\Big) u_{xxx} = 0. \end{aligned} \end{equation} $ | (0.3) |
可以看出, 当
本文结构安排如下:第1节, 根据Korsunsky在文献[1]中提出的方法, 构造新的双模耦合KdV (nTMcKdV)方程; 第2节, 利用简化的双线性方法[23-27], 得到nTMcKdV方程的多孤子解存在的条件; 第3节, 利用不同的函数展开法, 如tanh/coth和tan/cot方法找到方程的其他精确解.此外, 本节中还得到了nTMcKdV方程的Jacobi椭圆函数解; 在第4节中给出结论.
1 新的双模耦合KdV方程本文主要研究一个新的双模耦合KdV方程. Yu在文献[28]中通过Kronecker内积构造了一个新的非线性可积耦合KdV族.他们得到了耦合KdV方程
$ \begin{equation} \left\{ \begin{aligned} &u_t+\dfrac{1}{4}u_{xxx}+\dfrac{3}{2}uu_x = 0, \\ &v_t+\dfrac{1}{4}v_{xxx}+2vv_x+\dfrac{3}{2}(uv)_x = 0. \end{aligned} \right. \end{equation} $ | (1.1) |
文献[28]研究了方程(1.1)的延拓结构.根据Korsunsky在文献[1]中提出的方法, 我们构造出新的双模耦合KdV (nTMcKdV)方程
$ \begin{equation} \left\{ \begin{aligned} u_{tt}&+(c_1+c_2)u_{xt}+c_1c_2u_{xx}+\Big( (\alpha_1+\alpha_2)\frac{\partial}{\partial t}+(\alpha_1c_2+\alpha _2 c_1)\frac{\partial}{\partial x} \Big) \frac{3}{2}uu_x\\ &+\Big( (\beta_1+\beta_2)\frac{\partial}{\partial t}+(\beta_1c_2+\beta_2c_1) \frac{\partial}{\partial x}\Big) \frac{1}{4}u_{xxx} = 0, \\ v_{tt}&+(c_1+c_2)v_{xt}+c_1c_2v_{xx}+\Big( (\alpha_1+\alpha_2)\frac{\partial}{\partial t}+(\alpha_1c_2+\alpha _2 c_1) \frac{\partial}{\partial x} \Big)\Big(2vv_x+\frac{3}{2}(uv)_x\Big)\\ &+\Big( (\beta_1+\beta_2)\frac{\partial}{\partial t}+(\beta_1c_2+\beta_2c_1)\frac{\partial}{\partial x}\Big) \frac{1}{4}v_{xxx} = 0. \end{aligned} \right. \end{equation} $ | (1.2) |
经过变换(0.2), 方程(1.2)就可约化为
$ \begin{equation} \left\{ \begin{aligned} u_{tt}&-s^2u_{xx}+\Big( \frac{\partial}{\partial t}-\alpha s\frac{\partial}{\partial x}\Big) \frac{3}{2}uu_x +\Big( \frac{\partial}{\partial t}-\beta s\frac{\partial}{\partial x}\Big) \frac{1}{4}u_{xxx} = 0, \\ v_{tt}&-s^2v_{xx}+\Big( \frac{\partial}{\partial t}-\alpha s\frac{\partial}{\partial x}\Big) \Big(2vv_x+\frac{3}{2}(uv)_x \Big) +\Big( \frac{\partial}{\partial t}-\beta s\frac{\partial}{\partial x}\Big) \frac{1}{4}v_{xxx} = 0. \end{aligned} \right. \end{equation} $ | (1.3) |
可以看到当
在本节中, 将利用简化的双线性方法研究双模耦合KdV(nTMcKdV)方程的多孤子解.把方程
$ \begin{equation} \left\{ \begin{aligned} u(x, t)& = {\rm e}^{\theta_i} = {\rm e}^{k_i x-c_i t}, \\ v(x, t)& = {\rm e}^{\theta_i} = {\rm e}^{k_i x-c_i t}, \quad i = 1, 2, 3, \cdots, n. \end{aligned} \right. \end{equation} $ | (2.1) |
代入方程(1.3)中并比较线性项与非线性项, 得到耗散关系
$ \begin{equation} \begin{aligned} c_i = \frac{k_i^3\pm k_i\sqrt{k_i^4+16\beta sk_i^2+64s^2}}{8}. \end{aligned} \end{equation} $ | (2.2) |
因此
$ \begin{equation} \theta_i = k_i x-\frac{k_i^3\pm k_i\sqrt{k_i^4+16\beta sk_i^2+64s^2}}{8}t. \end{equation} $ | (2.3) |
利用Cole-Hopf变换, 假定方程(1.3)存在多孤子解
$ \begin{equation} \left\{ \begin{aligned} u(x, t)& = R_1(\ln f(x, t))_{xx}, \\ v(x, t)& = R_2(\ln f(x, t))_{xx}, \end{aligned} \right. \end{equation} $ | (2.4) |
其中
$ \begin{equation} f(x, t) = 1+{\rm e}^{\theta_1} = 1+{\rm e}^{k_1 x-\frac{k_1^3\pm k_1\sqrt{k_1^4+16\beta sk_1^2+64s^2}}{8}t}. \end{equation} $ | (2.5) |
把方程(2.4)、(2.5)代入nTMcKdV方程(1.3)并求解
$ \begin{equation} \beta = \alpha, \quad R_1 = 2, \quad R_2 = -\frac{3}{2} \end{equation} $ | (2.6) |
时, 单孤子解存在.
把式(2.5)与式(2.6)代入方程(2.4), 可得到nTMcKdV方程(1.3)的单孤子解为
$ \begin{equation*} \left\{ \begin{aligned} u(x, t)& = \frac{2k_1^2{\rm e}^{k_1 x-\frac{k_1^3\pm k_1\sqrt{k_1^4+16\beta sk_1^2+64s^2}} {8}t}}{\Big( 1+{\rm e}^{k_1 x-\frac{k_1^3\pm k_1\sqrt{k_1^4 +16\beta sk_1^2+64s^2}}{8}t}\Big) ^2}, \\ v(x, t)& = -\frac{3}{2}\cdot\frac{k_1^2{\rm e}^{k_1 x-\frac{k_1^3\pm k_1\sqrt{k_1^4+16\beta sk_1^2+64s^2}}{8}t}}{\Big( 1+{\rm e}^{k_1 x-\frac{k_1^3\pm k_1\sqrt{k_1^4+16\beta sk_1^2+64s^2}}{8}t}\Big) ^2}. \end{aligned} \right. \end{equation*} $ |
对于二孤子解, 令
$ \begin{equation} \begin{aligned} &f(x, t) = 1+{\rm e}^{\theta_1}+{\rm e}^{\theta_2}+a_{12}{\rm e}^{\theta_1+\theta_2}\\ &\; \; \; \; \; \; \; \; \; \; \; = 1+{\rm e}^{k_1 x-\frac{k_1^3\pm k_1\sqrt{k_1^4+16\beta sk_1^2+64s^2}}{8}t}+{\rm e}^{k_2 x-\frac{k_2^3\pm k_2\sqrt{k_2^4+16\beta sk_2^2+64s^2}}{8}t}\\ &\; \; \; \; \; \; \; \; \; \; \; \, \; \; \; +a_{12}{\rm e}^{k_1 x+k_2 x-\frac{k_1^3\pm k_1\sqrt{k_1^4+16\beta sk_1^2+64s^2}}{8}t-\frac{k_2^3\pm k_2\sqrt{k_2^4+16\beta sk_2^2+64s^2}}{8}t}. \end{aligned} \end{equation} $ | (2.7) |
把方程(2.4)、(2.7)代入nTMcKdV方程(1.3)并求解
$ \begin{equation} a_{ij} = \frac{(k_i-k_j)^2}{(k_i+k_j)^2}, \quad 1\leqslant i<j \leqslant 3. \end{equation} $ | (2.8) |
因此二孤子解为
$ \begin{equation*} \label{e2.9} \left\{ \begin{aligned} u(x, t)& = 2\; \frac{k_1^2{\rm e}^{\theta_1}+k_2^2{\rm e}^{\theta_2}+2(k_1-k_2)^2{\rm e}^{\theta_1+\theta_2}+a_{12}(k_2^2{\rm e}^{2\theta_1+\theta_2}+k_1^2{\rm e}^{\theta_1+2\theta_2}) }{(1+{\rm e}^{\theta_1}+{\rm e}^{\theta_2}+a_{12}{\rm e}^{\theta_1+\theta_2})^2}, \\ v(x, t)& = -\frac{3}{2}\cdot\frac{k_1^2{\rm e}^{\theta_1}+k_2^2{\rm e}^{\theta_2}+2(k_1-k_2)^2{\rm e}^{\theta_1+\theta_2}+a_{12}(k_2^2{\rm e}^{2\theta_1+\theta_2}+k_1^2{\rm e}^{\theta_1+2\theta_2}) }{(1+{\rm e}^{\theta_1}+{\rm e}^{\theta_2}+a_{12}{\rm e}^{\theta_1+\theta_2})^2}. \end{aligned} \right. \end{equation*} $ |
为了得到三孤子解, 令
$ \begin{equation} f(x, t) = 1+{\rm e}^{\theta_1}+{\rm e}^{\theta_2}+{\rm e}^{\theta_3}+a_{12}{\rm e}^{\theta_1+\theta_2}+a_{13}{\rm e}^{\theta_1+\theta_3} +a_{23}{\rm e}^{\theta_2+\theta_3}+a_{123}{\rm e}^{\theta_1+\theta_2+\theta_3}, \end{equation} $ | (2.9) |
其中
注 与耦合KdV方程(1.1)不同, nTMcKdV方程(1.3)的孤子解存在只是针对特殊的
在本节中, 我们将会利用tanh/coth方法[29-31]来求nTMcKdV方程的精确解.设
$ \begin{equation} \left\{ \begin{aligned} u(x, t)& = a_0+a_1{\rm tanh}^{m_1}(kx-ct), \\ v(x, t)& = b_0+b_1{\rm tanh}^{m_2}(kx-ct). \end{aligned} \right. \end{equation} $ | (3.1) |
将方程(3.1)代入方程(1.3), 在所得方程中平衡非线性项与耗散项可得
$ \begin{equation} \left\{ \begin{aligned} u(x, t)& = a_0+a_1{\rm tanh}^2(kx-ct), \\ v(x, t)& = b_0+b_1{\rm tanh}^2(kx-ct). \end{aligned} \right. \end{equation} $ | (3.2) |
把方程(3.2)代入nTMcKdV方程(1.3)并比较所得方程中
$ \begin{equation} \left\{ \begin{aligned} &a_1 = a, \quad b_0 = b, \\ &b_1 = -\frac{3}{4}a, \quad c = -\frac{sk(2\beta k^2+a\alpha)}{2k^2+a}, \\ &a_0 = -\frac{2}{3}a-\frac{s(2k^2+a)}{3k^2(\alpha-\beta)}+\frac{s(2\beta k^2+a\alpha)^2}{3k^2(\alpha-\beta)(2k^2+a)}, \end{aligned} \right. \end{equation} $ | (3.3) |
这里
由式(3.2)与式(3.3), 可求得解
$ \begin{equation} \left\{ \begin{aligned} u(x, t)& = -\frac{2}{3}a-\frac{s(2k^2+a)}{3k^2(\alpha-\beta)}+\frac{s(2\beta k^2+a\alpha)^2}{3k^2(\alpha-\beta)(2k^2+a)}\\ &\quad+a\; {\rm tanh}^2\Big( kx+\frac{sk(2\beta k^2+a\alpha)}{2k^2+a}t\Big), \\ v(x, t)& = b-\frac{3a}{4}{\rm tanh}^2\Big( kx+\frac{sk(2\beta k^2+a\alpha)}{2k^2+a}t\Big). \end{aligned} \right. \end{equation} $ | (3.4) |
若设
$ \begin{equation} \left\{ \begin{aligned} u(x, t)& = a_0+a_1{\rm coth}^2(kx-ct), \\ v(x, t)& = b_0+b_1{\rm coth}^2(kx-ct). \end{aligned} \right. \end{equation} $ | (3.5) |
与
$ \begin{equation} \left\{ \begin{aligned} u(x, t)& = -\frac{2}{3}a-\frac{s(2k^2+a)}{3k^2(\alpha-\beta)}+\frac{s(2\beta k^2+a\alpha)^2}{3k^2(\alpha-\beta)(2k^2+a)}\\ &\quad+a\; {\rm coth}^2\Big( kx+\frac{sk(2\beta k^2+a\alpha)}{2k^2+a}t\Big), \\ v(x, t)& = b-\frac{3a}{4}{\rm coth}^2\Big( kx+\frac{sk(2\beta k^2+a\alpha)}{2k^2+a}t\Big). \end{aligned} \right. \end{equation} $ | (3.6) |
把方程(3.2)代入nTMcKdV方程(1.3)并令
$ \begin{equation} \left\{ \begin{aligned} &a_0 = a, \quad b_0 = b, \\ &a_1 = -2k^2, \quad b_1 = \frac{3}{2}k^2, \\ &c = -k^3+\frac{3}{4}ak\pm \frac{1}{4}k\sqrt{16k^4-8k^2(3a+4\alpha s)+9a^2+8s(3a\alpha+2s)}, \end{aligned} \right. \end{equation} $ | (3.7) |
这里
由式(3.2)与式(3.7)可求得解为
$ \begin{equation} \left\{ \begin{aligned} &u(x, t) = a-2k^2{\rm tanh}^2\Big[ kx- \Big( -k^3+\frac{3}{4}ak\\ &\qquad\qquad\pm \frac{1}{4}k\sqrt{16k^4-8k^2(3a+4\alpha s)+9a^2+8s(3a\alpha+2s)}\Big) t\Big], \\ &v(x, t) = b+\frac{3}{2}k^2{\rm tanh}^2\Big[ kx-\Big( -k^3+\frac{3}{4}ak\\ &\qquad\qquad\pm \frac{1}{4}k\sqrt{16k^4-8k^2(3a+4\alpha s)+9a^2+8s(3a\alpha+2s)}\Big) t\Big]. \end{aligned} \right. \end{equation} $ | (3.8) |
若设
$ \begin{equation} \left\{ \begin{aligned} u(x, t)& = a_0+a_1{\rm coth}^2(kx-ct), \\ v(x, t)& = b_0+b_1{\rm coth}^2(kx-ct). \end{aligned} \right. \end{equation} $ | (3.9) |
与
$ \begin{equation} \left\{ \begin{aligned} &u(x, t) = a-2k^2{\rm coth}^2\Big[ kx- \Big( -k^3+\frac{3}{4}ak\\ &\qquad\qquad\pm \frac{1}{4}k\sqrt{16k^4-8k^2(3a+4\alpha s)+9a^2+8s(3a\alpha+2s)}\Big) t\Big], \\ &v(x, t) = b+\frac{3}{2}k^2{\rm coth}^2\Big[ kx-\Big( -k^3+\frac{3}{4}ak\\ &\qquad\qquad\pm \frac{1}{4}k\sqrt{16k^4-8k^2(3a+4\alpha s)+9a^2+8s(3a\alpha+2s)}\Big) t\Big]. \end{aligned} \right. \end{equation} $ | (3.10) |
在本节中, 对于一般的非线性参数与耗散参数值, 将利用tan/cot方法来求{nTMcKdV}方程的周期解.设
$ \begin{equation} \left\{ \begin{aligned} u(x, t)& = a_0+a_1{\rm tan}^{m_3}(kx-ct), \\ v(x, t)& = b_0+b_1{\rm tan}^{m_4}(kx-ct). \end{aligned} \right. \end{equation} $ | (3.11) |
把式(3.11)代入方程(1.3), 在所得方程中平衡非线性项与耗散项可得
$ \begin{equation} \left\{ \begin{aligned} u(x, t)& = a_0+a_1{\rm tan}^2(kx-ct), \\ v(x, t)& = b_0+b_1{\rm tan}^2(kx-ct). \end{aligned} \right. \end{equation} $ | (3.12) |
事实上, 由于
$ \begin{equation} \left\{ \begin{aligned} u(x, t)& = \frac{2}{3}a-\frac{s(2k^2+a)}{3k^2(\alpha-\beta)}+\frac{s(2\beta k^2+a\alpha)^2}{3k^2(\alpha-\beta)(2k^2+a)}\\ &\quad+a\; {\rm tan}^2\Big( kx+\frac{sk(2\beta k^2+a\alpha)}{2k^2+a}t\Big), \\ v(x, t)& = b-\frac{3a}{4}{\rm tan}^2\Big( kx+\frac{sk(2\beta k^2+a\alpha)}{2k^2+a}t\Big). \end{aligned} \right. \end{equation} $ | (3.13) |
若设
$ \begin{equation} \left\{ \begin{aligned} u(x, t)& = a_0+a_1{\rm cot}^2(kx-ct), \\ v(x, t)& = b_0+b_1{\rm cot}^2(kx-ct). \end{aligned} \right. \end{equation} $ | (3.14) |
与
$ \begin{equation} \left\{ \begin{aligned} u(x, t)& = \frac{2}{3}a-\frac{s(2k^2+a)}{3k^2(\alpha-\beta)}+\frac{s(2\beta k^2+a\alpha)^2}{3k^2(\alpha-\beta)(2k^2+a)}\\ &\quad+a\; {\rm cot}^2\Big( kx+\frac{sk(2\beta k^2+a\alpha)}{2k^2+a}t\Big), \\ v(x, t)& = b-\frac{3a}{4}{\rm cot}^2\Big( kx+\frac{sk(2\beta k^2+a\alpha)}{2k^2+a}t\Big). \end{aligned} \right. \end{equation} $ | (3.15) |
令
$ \begin{equation} \left\{ \begin{aligned} &u(x, t) = a-2k^2{\rm tan}^2\Big[ kx- \Big( k^3+\frac{3}{4}ak\\ &\qquad\qquad\pm \frac{1}{4}k\sqrt{16k^4+8k^2(3a+4\alpha s)+9a^2+8s(3a\alpha+2s)}\Big) t\Big], \\ &v(x, t) = b+\frac{3}{2}k^2{\rm tan}^2\Big[ kx-\Big( k^3+\frac{3}{4}ak\\ &\qquad\qquad\pm \frac{1}{4}k\sqrt{16k^4+8k^2(3a+4\alpha s)+9a^2+8s(3a\alpha+2s)}\Big) t\Big]. \end{aligned} \right. \end{equation} $ | (3.16) |
若设
$ \begin{equation} \left\{ \begin{aligned} u(x, t)& = a_0+a_1{\rm cot}^2(kx-ct), \\ v(x, t)& = b_0+b_1{\rm cot}^2(kx-ct). \end{aligned} \right. \end{equation} $ | (3.17) |
与
$ \begin{equation} \left\{ \begin{aligned} &u(x, t) = a-2k^2{\rm cot}^2\Big[ kx- \Big( k^3+\frac{3}{4}ak\\ &\qquad\qquad\pm \frac{1}{4}k\sqrt{16k^4+8k^2(3a+4\alpha s)+9a^2+8s(3a\alpha+2s)}\Big) t\Big], \\ &v(x, t) = b+\frac{3}{2}k^2{\rm cot}^2\Big[ kx-\Big( k^3+\frac{3}{4}ak\\ &\qquad\qquad\pm \frac{1}{4}k\sqrt{16k^4+8k^2(3a+4\alpha s)+9a^2+8s(3a\alpha+2s)}\Big) t\Big]. \end{aligned} \right. \end{equation} $ | (3.18) |
在研究nTMcKdV方程(1.3)的Jacobi椭圆函数解之前, 我们先介绍一些基本关系式[12, 32]
$ \begin{equation} \left\{ \begin{aligned} &{\rm sn}(\zeta, 1) = {\rm tanh}(\zeta), \quad{\rm cn}(\zeta, 1) = {\rm sech}(\zeta), \\ &{\rm sn}^2(\zeta, m)+{\rm cn}^2(\zeta, m) = 1, \quad m^2{\rm sn}^2(\zeta, m)+{\rm dn}^2(\zeta, m) = 1, \; m \in (0, 1]. \end{aligned} \right. \end{equation} $ | (3.19) |
设
$ \begin{equation} \left\{ \begin{aligned} -\frac{3}{2}&(\lambda+\alpha s)u'^2+(\lambda^2-s^2)u''-\frac{3}{2}(\lambda+\alpha s)uu''-\frac{1}{4}k^2(\lambda+\beta s)u'''' = 0, \\ -\frac{3}{2}&(\lambda+\alpha s)u''v-3(\lambda+\alpha s)u'v'-2(\lambda+\alpha s)v'^2+(\lambda^2-s^2)v''-2(\lambda+\alpha s)vv''\\ &-\frac{3}{2}(\lambda+\alpha s)uv''-\frac{1}{4}k^2(\lambda+\beta s)v'''' = 0. \end{aligned} \right. \end{equation} $ | (3.20) |
设
$u(\xi ) = \sum\limits_{i = 0}^M {{a_i}} {\mkern 1mu} {\rm{s}}{{\rm{n}}^i}(\xi ,m),\quad v(\xi ) = \sum\limits_{i = 0}^N {{b_i}} {\mkern 1mu} {\rm{s}}{{\rm{n}}^i}(\xi ,m). $ | (3.21) |
把式(3.21)代入方程(3.20)并比较非线性项与耗散项, 可得到
$ \begin{equation} \left\{ \begin{aligned} u(\xi)& = a_0+a_1 \, {\rm sn}(\xi, m)+a_2 \, {\rm sn}^2(\xi, m), \\ v(\xi)& = b_0+b_1 \, {\rm sn}(\xi, m)+b_2 \, {\rm sn}^2(\xi, m). \end{aligned} \right. \end{equation} $ | (3.22) |
将方程(3.22)代入方程(3.20)并利用关系式(3.19), 在所得方程中令
$ \begin{equation} \left\{ \begin{aligned} &a_1 = 0, \; b_1 = 0, \; b_0 = b, \\ &a_0 = \frac{2}{3}\cdot\frac{\beta k^2m^2s+k^2\lambda m^2+\beta k^2s+k^2\lambda+\lambda^2-s^2}{\alpha s+\lambda}, \\ &a_2 = -\frac{2k^2m^2(\beta s+\lambda)}{\alpha s+\lambda}, \quad b_2 = \frac{3}{2}\cdot\frac{k^2m^2(\beta s+\lambda)}{\alpha s+\lambda}, \end{aligned} \right. \end{equation} $ | (3.23) |
这里
$ \begin{equation} \left\{ \begin{aligned} u(x, t) = &\, \frac{2}{3(\alpha s+\lambda)} [ k^2(1+m^2)(\beta s+\lambda)+\lambda^2-s^2\\ &-3k^2m^2(\beta s+\lambda){\rm sn}^2\big(k(x-\lambda t), m\big)], \\ v(x, t) = &\, b+\frac{3}{2}\cdot\frac{k^2m^2(\beta s+\lambda)}{\alpha s+\lambda}{\rm sn}^2\big(k(x-\lambda t), m\big). \end{aligned} \right. \end{equation} $ | (3.24) |
若式(3.24)中
$ \begin{equation} \left\{ \begin{aligned} u(x, t) = &\, \frac{2}{3(\alpha s+\lambda)} [ 2k^2(\beta s+\lambda)+\lambda^2-s^2-3k^2(\beta s+\lambda){\rm tanh}^2\big(k(x-\lambda t)\big)], \\ v(x, t) = &\, b+\frac{3}{2}\cdot\frac{k^2(\beta s+\lambda)}{\alpha s+\lambda}{\rm tanh}^2\big(k(x-\lambda t)\big). \end{aligned} \right. \end{equation} $ | (3.25) |
可以看出这组解即为利用tanh方法得到的解(3.4)或(3.8).
3.3.2 Jacobi椭圆余弦函数解在式(3.21)中用
$ \begin{equation} \left\{ \begin{aligned} u(\xi)& = a_0+a_1 \, {\rm cn}(\xi, m)+a_2 \, {\rm cn}^2(\xi, m), \\ v(\xi)& = b_0+b_1 \, {\rm cn}(\xi, m)+b_2 \, {\rm cn}^2(\xi, m). \end{aligned} \right. \end{equation} $ | (3.26) |
将式(3.26)代入方程(3.20)并利用关系式(3.19), 在所得方程中令
$ \begin{equation} \left\{ \begin{aligned} &a_1 = 0, \; b_1 = 0, \; b_0 = b, \\ &a_0 = -\frac{2}{3}\cdot\frac{2\beta k^2m^2s+2k^2\lambda m^2-\beta k^2s-k^2\lambda-\lambda^2+s^2}{\alpha s+\lambda}, \\ &a_2 = \frac{2k^2m^2(\beta s+\lambda)}{\alpha s+\lambda}, \quad b_2 = -\frac{3}{2}\cdot\frac{k^2m^2(\beta s+\lambda)}{\alpha s+\lambda}, \end{aligned} \right. \end{equation} $ | (3.27) |
这里
$ \begin{equation} \left\{ \begin{aligned} u(x, t)& = -\frac{2}{3(\alpha s+\lambda)} [ k^2(2m^2-1)(\beta s+\lambda)-\lambda^2+s^2\\ &\quad-3k^2m^2(\beta s+\lambda){\rm cn}^2\big(k(x-\lambda t), m\big) ], \\[-1mm] v(x, t)& = b-\frac{3}{2}\cdot\frac{k^2m^2(\beta s+\lambda)}{\alpha s+\lambda}{\rm cn}^2\big(k(x-\lambda t), m\big) . \end{aligned} \right. \end{equation} $ | (3.28) |
注 由式(3.27)中
若在解(3.28)中取
$ \begin{equation*} \label{e3.31} \left\{ \begin{aligned} u(x, t)& = -\frac{2}{3(\alpha s+\lambda)} [ k^2(\beta s+\lambda)-\lambda^2+ s^2-3k^2(\beta s+\lambda){\rm sech}^2\big(k(x-\lambda t)\big)], \\[-1mm] v(x, t)& = b-\frac{3}{2}\cdot\frac{k^2(\beta s+\lambda)}{\alpha s+\lambda}{\rm sech}^2\big(k(x-\lambda t)\big). \end{aligned} \right. \end{equation*} $ |
与求
$ \begin{equation*} \label{e3.32} \left\{ \begin{aligned} u(x, t)& = \frac{2}{3(\alpha s+\lambda)} [ k^2(m^2-2)(\beta s+\lambda)+\lambda^2-s^2\\[-1mm] &\; \; \; +3k^2(\beta s+\lambda){\rm dn}^2\big(k(x-\lambda t), m\big)], \\[-1mm] v(x, t)& = b-\frac{3}{2}\cdot\frac{k^2(\beta s+\lambda)}{\alpha s+\lambda}{\rm dn}^2(k(x-\lambda t), m). \end{aligned} \right. \end{equation*} $ |
由于
$ \begin{equation*} \left\{ \begin{aligned} u(x, t)& = \frac{2}{3(\alpha s+\lambda)} [ -2\kappa^2(\beta s+\lambda)+ \lambda^2-s^2-3\kappa^2(\beta s+\lambda){\rm tan}^2(\kappa(x-\lambda t))], \\[-1mm] v(x, t)& = b+\frac{3}{2}\cdot\frac{\kappa^2(\beta s+\lambda)}{\alpha s+\lambda}{\rm tan}^2\big(\kappa(x-\lambda t)\big). \end{aligned} \right. \end{equation*} $ |
可以看出这组解即为利用tan方法得到的解(3.13)或(3.16).
4 结论在本文中, 我们构造了一个新的双模耦合KdV方程.一方面, 通过简化的Hirota方法和Cole-Hopf变换, 对于特殊的
[1] |
KORSUNSKY S V. Soliton solutions for a second-order KdV equation[J]. Phys Lett A, 1994, 185: 174-176. DOI:10.1016/0375-9601(94)90842-7 |
[2] |
LEE C T, LIU J L, LEE C C, et al. The second-order KdV equation and its soliton-like solution[J]. Modern Physics Letters B, 2009, 23: 1771-1780. |
[3] |
LEE C C, LEE C T, LIU J L, et al. Quasi-solitons of the two-mode Korteweg-de Vries equation[J]. Eur Phys J Appl Phys, 2010, 52: 11301. DOI:10.1051/epjap/2010132 |
[4] |
LEE C T. Some notes on a two-mode Korteweg-de Vries equation[J]. Phys Scr, 2010, 81: 065006. DOI:10.1088/0031-8949/81/06/065006 |
[5] |
LEE C T, LIU J L. A Hamiltonian model and soliton phenomenon for a two-mode KdV equation[J]. Rocky Mt J Math, 2011, 41: 1273-1289. DOI:10.1216/RMJ-2011-41-4-1273 |
[6] |
LEE C T, LEE C C. On wave solutions of a weakly nonlinear and weakly dispersive two-mode wave system[J]. Waves in Random and Complex Media, 2013, 23: 56-76. DOI:10.1080/17455030.2013.770585 |
[7] |
LEE C T, LEE C C. Analysis of solitonic phenomenon for a two-mode KdV equation[J]. Physics of Wave Phenomena, 2014, 22: 69-80. DOI:10.3103/S1541308X14010130 |
[8] |
LEE C T, LEE C C. On the study of a nonlinear higher order dispersive wave equation:Its mathematical physical structure and anomaly soliton phenomena[J]. Waves in Random and Complex Media, 2015, 25: 197-222. DOI:10.1080/17455030.2014.1002441 |
[9] |
LEE C T, LEE C C. Symbolic computation on a second-order KdV equation[J]. Journal of Symbolic Computation, 2016, 74: 70-95. DOI:10.1016/j.jsc.2015.06.006 |
[10] |
WAZWAZ A M. Multiple soliton solutions and other exact solutions for a two-mode KdV equation[J]. Math Methods Appl Sci, 2017, 40: 2277-2283. |
[11] |
LEE C T, LEE C C, LIU M L. Double-soliton and conservation law structures for a higher-order type of Korteweg-de Vries equation[J]. Physics Essays, 2015, 28: 633-638. DOI:10.4006/0836-1398-28.4.633 |
[12] |
ALQURAN M, JARRAH A. Jacobi elliptic function solutions for a two-mode KdV equation[J/OL]. Journal of King Saud University-Science, (2017-07-03)[2018-06-28]. http://dx.doi.org/10.1016/j.jksus.2017.06.010.
|
[13] |
XIAO Z J, TIAN B, ZHEN H L, et al. Multi-soliton solutions and Bäcklund transformation for a two-mode KdV equation in a fluid[J]. Waves in Random and Complex Media, 2017, 27: 1-14. DOI:10.1080/17455030.2016.1185193 |
[14] |
WAZWAZ A M. A two-mode modified KdV equation with multiple soliton solutions[J]. Appl Math Lett, 2017, 70: 1-6. DOI:10.1016/j.aml.2017.02.015 |
[15] |
WAZWAZ A M. A two-mode Burgers equation of weak shock waves in a fluid:Multiple kink solutions and other exact solutions[J]. Int J Appl Comput Math, 2017, 3: 3977-3985. DOI:10.1007/s40819-016-0302-4 |
[16] |
WAZWAZ A M. A study on a two-wave mode Kadomtsev-Petviashvili equation:Conditions for multiple soliton solutions to exist[J]. Math Methods Appl Sci, 2017, 40: 4128-4133. DOI:10.1002/mma.v40.11 |
[17] |
JARADAT H M, SYAM M, ALQURAN M. A two-mode coupled Korteweg-de Vries:Multiple-soliton solutions and other exact solutions[J]. Nonlinear Dyn, 2017, 90: 371-377. DOI:10.1007/s11071-017-3668-x |
[18] |
WAZWAZ A M. Two-mode fifth-order KdV equations:Necessary conditions for multiple-soliton solutions to exist[J]. Nonlinear Dyn, 2017, 87: 1685-1691. DOI:10.1007/s11071-016-3144-z |
[19] |
WAZWAZ A M. Two-mode Sharma-Tasso-Olver equation and two-mode fourth-order Burgers equation:Multiple kink solutions[J]. Alexandria Eng J, 2018, 57: 1971-1976. DOI:10.1016/j.aej.2017.04.003 |
[20] |
JARDAT H M. Two-mode coupled Burgers equation:Multiple-kink solutions and other exact solutions[J]. Alexandria Eng J, 2018, 57: 2151-2155. DOI:10.1016/j.aej.2017.06.014 |
[21] |
SYAM M, JARADAT H M, ALQURAN M. A study on the two-mode coupled modified Korteweg-de Vries using the simplified bilinear and the trigonometric-function methods[J]. Nonlinear Dyn, 2017, 90: 1363-1371. DOI:10.1007/s11071-017-3732-6 |
[22] |
WAZWAZ A M. Two wave mode higher-order modified KdV equations:Essential conditions for multiple soliton solutions to exist[J]. International Journal of Numerical Methods for Heat and Fluid Flow, 2017, 27: 2223-2230. DOI:10.1108/HFF-10-2016-0413 |
[23] |
HEREMAN W, NUSEIR A. Symbolic methods to construct exact solutions of nonlinear partial differential equations[J]. Mathematics and Computers in Simulation, 1997, 43: 13-27. DOI:10.1016/S0378-4754(96)00053-5 |
[24] |
WAZWAZ A M. Single and multiple-soliton solutions for the (2+1)-dimensional KdV equation[J]. Appl Math Comput, 2008, 204: 20-26. |
[25] |
ZUO J M, ZHANG Y M. The Hirota bilinear method for the coupled Burgers equation and the high-order Boussinesq-Burgers equation[J]. Chin Phy B, 2011, 20: 010205. DOI:10.1088/1674-1056/20/1/010205 |
[26] |
WAZWAZ A M. Multiple soliton solutions for the integrable couplings of the KdV and the KP equations[J]. Open Physics, 2013, 11: 291-295. |
[27] |
WAZWAZ A M. Multiple kink solutions for two coupled integrable (2+1)-dimensional systems[J]. Appl Math Lett, 2016, 58: 1-6. DOI:10.1016/j.aml.2016.01.019 |
[28] |
YU F J. Prolongation structure for nonlinear integrable couplings of a KdV soliton hierarchy[J]. Chin Phys B, 2012, 21: 010201. DOI:10.1088/1674-1056/21/1/010201 |
[29] |
MALFLIET W, HEREMAN W. The tanh method:I. Exact solutions of nonlinear evolution and wave equations[J]. Phys Scr, 1996, 54: 563-568. DOI:10.1088/0031-8949/54/6/003 |
[30] |
FAN E, HONA Y C. Generalized tanh method extended to special types of nonlinear equations[J]. Zeitschrift für Naturforschung A, 2002, 57: 692-700. |
[31] |
WAZWAZ A M. The tanh method for traveling wave solutions of nonlinear equations[J]. Appl Math and Comput, 2004, 154: 713-723. |
[32] |
LIU S, FU Z, LIU S, et al. Jacobi elliptic function expansion method and periodic wave solutions of nonlinear wave equations[J]. Phys Lett A, 2001, 289: 69-74. DOI:10.1016/S0375-9601(01)00580-1 |