Research Article | Open Access
Qi Wei, Rongjun Cheng, "The Improved Moving Least-Square Ritz Method for the One-Dimensional Sine-Gordon Equation", Mathematical Problems in Engineering, vol. 2014, Article ID 383219, 10 pages, 2014. https://doi.org/10.1155/2014/383219
The Improved Moving Least-Square Ritz Method for the One-Dimensional Sine-Gordon Equation
Abstract
Analysis of the one-dimensional sine-Gordon equation is performed using the improved moving least-square Ritz method (IMLS-Ritz method). The improved moving least-square approximation is employed to approximate the 1D displacement field. A system of discrete equations is obtained by application of the Ritz minimization procedure. The effectiveness and accuracy of the IMLS-Ritz method for the sine-Gordon equation are investigated by numerical examples in this paper.
1. Introduction
It is well known that many physical phenomena in one or higher-dimensional space can be described by a soliton model. Many of these models are based on simple integrable models such as Korteweg-de Vries equation and the nonlinear Schrdinger equation. Solitons have found to model among others shallow-water waves, optical fibres, Josephson-junction oscillators, and so forth. Equations which also lead to solitary waves are the sine-Gordon. The sine-Gordon equation arises in extended rectangular Josephson junctions, which consist of two layers of super conducting materials separated by an isolating barrier. A typical arrangement is a layer of lead and a layer of niobium separated by a layer of niobium oxide. A quantum particle has a nonzero significant probability of being able to penetrate to the other side of a potential barrier that would be impenetrable to the corresponding classical particle. This phenomenon is usually referred to as quantum tunneling [1–3].
A numerical study for sine-Gordon equation has been proposed including the finite difference schemes [4–6], the finite element methods [7, 8], the modified Adomian decomposition method [9], the boundary integral equation approach [10], radius basis function (RBF) [11], the meshless local Petrov-Galerkin (MLPG) [12], the discrete singular convolution [13], meshless local boundary integral equation method (LBIE) [14], the dual reciprocity boundary element method (DRBEM) [15], and the mesh-free kp-Ritz method [16].
The meshless method is a new and interesting numerical technique. Important meshless methods have been developed and proposed, such as smooth particle hydrodynamics methods (SPH) [17], radial basis function (RBF) [18], element free Galerkin method (EFG) [19], meshless local Petrov-Galerkin method (MLPG) [20], reproducing kernel particle method (RKPM) [21–23], the boundary element free method (BEFM) [24–27], the complex variable meshless method [28–36], improved element free Galerkin method (IEFG) [37–41], and the improved meshless local Petrov-Galerkin method [42–46].
The moving least-square (MLS) technique was originally used for data fitting. Nowadays, the MLS technique has been employed as the shape functions of the meshless method or element-free Galerkin (EFG) method [47]. Though EFG method is now a very popular numerical computational method, a disadvantage of the method is that the final algebraic equations system is sometimes ill-conditioned. Sometimes a poor solution will be obtained due to the ill-conditioned system. The improved moving least-square (IMLS) approximation has been proposed [48–52] to overcome this disadvantage. In the IMLS, the orthogonal function system with a weight function is chosen to be the basis functions. The algebraic equations system in the IMLS approximation will be no more ill-conditioned.
The Ritz [53] approximation technique is a generalization of the Rayleigh [54] method and it has been widely used in computational mechanics. The element-free kp-Ritz method is firstly developed and implemented for the free vibration analysis of rotating cylindrical panels by Liew et al. [55]. The kp-Ritz method was widely applied and used in many kinds of problems, such as free vibration of two-side simply-supported laminated cylindrical panels [56], nonlinear analysis of laminated composite plates [57], Sine-Gordon equation [16], 3D wave equation [58], and biological population problem [59].
A new numerical method which is named the IMLS-Ritz method for the sine-Gordon equation is presented in this paper. In this paper, the unknown function is approximated by these IMLS approximations; a system of nonlinear discrete equations is obtained by the Ritz minimization procedure, and the boundary conditions are enforced by the penalty method.
2. IMLS-Ritz Formulation for the Sine-Gordon Equation
Consider the following one-dimensional sine-Gordon equation: with initial conditions and boundary conditions where denotes the domain of , denotes the boundaries, and and are wave modes or kinks and velocity, respectively. Parameter is the so-called dissipative term, assumed to be a real number with .
The weighted integral form of (1a) is obtained as follows:
The weak form of (2) is
The energy functional can be written as
In the improved moving least-square approximation [19], define a local approximation by
This defines the quadratic form
Equation (6) can be rewritten in the vector form
To find the coefficients , we obtain the extremum of by which results in the equation system
If the functions satisfy the conditions then is called a weighted orthogonal function set with a weight function about points . The weighted orthogonal basis function set can be formed with the Schmidt method [39–41], Equation (9) can be rewritten as The coefficients can be directly obtained as follows: that is, where
From (12), the approximation function can be rewritten as where is the shape function and
Taking derivatives of (17), we can obtain the first derivatives of shape function
Imposing boundary conditions by penalty method, the total energy functional for this problem will be obtained:
By (16), we can derive the approximation function Substituting (20) into (19) and applying the Ritz minimization procedure to the energy function , we obtain In the matrix form, the results can be expressed as where
Making time discretization of (22) by the center difference method, we get where
The numerical solution of the one-dimensional sine-Gordon equation will be obtained by solving the above iteration equation.
3. Numerical Examples and Analysis
To verify the efficiency and accuracy of the proposed IMLS-Ritz method for the sine-Gordon equation, two examples are studied and the numerical results are presented. The weight function is chosen to be cubic spline and the bases are chosen to be linear in all examples.
Example 1. Consider the sine-Gordon Equation (1a)–(1d) without nonlinear term over the region with initial conditions
with boundary conditions
The exact solution is
The IMLS-Ritz method is applied to solve the above equation with penalty factor and time step length , . In Figure 1, the numerical solution and exact solution are plotted at times 0.1, 0.2, 0.3, and 0.4, respectively. In Figures 2, 3, and 4, the graphs of error function are plotted at times 0.1, 0.2, and 0.3, respectively, where is the exact solution and numerical solution is obtained by using the IMLS-Ritz method. Table 1 shows the comparison of exact solutions and numerical solutions by IMLS-Ritz method and EFG method. From the results of Table 1, we can draw the conclusion that IMLS-Ritz method has higher accuracy than the EFG method. The surfaces of the numerical solution with the IMLS-Ritz method and exact solutions are plotted in Figures 5 and 6.
|






Example 2. Consider the case in (1a)–(1d) over the rectangular region and initial condition which derives the analytic solution and the boundary conditions can be obtained from (30).
The IMLS-Ritz method is applied to solve the above equation with penalty factor and time step length , . Figure 7 depicts the numerical and exact solution when 1, 5, 10, 20, and 30, respectively. In Figures 8, 9, and 10, the graphs of error function are plotted at times 1, 5, and 10, respectively, where is the exact solution and numerical solution is obtained by using the IMLS-Ritz method. Table 2 shows the comparison of exact solutions and numerical solutions by IMLS-Ritz method and EFG method. From the results of Table 2, it is shown that IMLS-Ritz method has higher accuracy than the EFG method. The surfaces of the numerical solution with the IMLS-Ritz method and exact solution are plotted in Figures 11 and 12.
|






Example 3. Consider the case in (1a)–(1d) over the rectangular region and initial condition and the boundary conditions can be derived from the following exact solitary wave solution: where and is the velocity of solitary wave.
The IMLS-Ritz method is applied to solve the above equation with penalty factor and time step length , , . Table 3 shows the comparison of exact solutions and numerical solutions by IMLS-Ritz method and EFG method. From the results of Table 3, it is shown that IMLS-Ritz method has higher accuracy than the EFG method. The surfaces of the numerical solution with the IMLS-Ritz method and exact solution are plotted in Figures 13 and 14. In Figure 15, the graph of error function is plotted at time , where is the exact solution and the numerical solution is obtained by using the IMLS-Ritz method.
|



From these figures, it is shown that numerical results obtained by the IMLS-Ritz method are in good agreement with the exact solutions.
4. Conclusion
This paper presents a numerical method, named the IMLS-Ritz method, for the one-dimensional sine-Gordon equation. The IMLS approximation is employed to approximate the 1D displacement field. A system of discrete equations is obtained through application of the Ritz minimization. In the IMLS approximation, the basis function is chosen as the orthogonal function system with a weight function. The IMLS approximation has greater computational efficiency and precision than the MLS approximation, and it does not lead to an ill-conditioned system of equations. The numerical results show that the technique is accurate and efficient.
Conflict of Interests
The authors declare that there is no conflict of interests regarding the publication of this paper.
Acknowledgments
This work was supported by the National Natural Science Foundation of Ningbo City (Grant nos. 2013A610067, 2102A610023, and 2013A610103), the Natural Science Foundation of Zhejiang Province of China (Grant no. Y6110007), and the National Natural Science of China (Grant no. 41305016).
References
- R. K. Dodd, J. C. Eilbeck, J. D. Gibbon, and H. C. Morris, Solitons and Nonlinear Wave Equations, Academic Press, London, UK, 1982. View at: MathSciNet
- A. Barone, F. Esposito, C. J. Magee, and A. C. Scott, “Theory and applications of the sine-gordon equation,” La Rivista del Nuovo Cimento, vol. 1, no. 2, pp. 227–267, 1971. View at: Publisher Site | Google Scholar
- M. Dehghan and A. Shokri, “A numerical method for one-dimensional nonlinear sine-Gordon equation using collocation and radial basis functions,” Numerical Methods Partial Differential Equations, vol. 79, no. 3, pp. 700–715, 2008. View at: Google Scholar
- M. Cui, “Fourth-order compact scheme for the one-dimensional Sine-Gordon equation,” Numerical Methods for Partial Differential Equations, vol. 25, no. 3, pp. 685–711, 2009. View at: Publisher Site | Google Scholar | Zentralblatt MATH | MathSciNet
- A. Q. M. Khaliq, B. Abukhodair, Q. Sheng, and M. S. Ismail, “A predictor-corrector scheme for the sine-Gordon equation,” Numerical Methods for Partial Differential Equations, vol. 16, no. 2, pp. 133–146, 2000. View at: Publisher Site | Google Scholar | Zentralblatt MATH | MathSciNet
- J. I. Ramos, “The sine-Gordon equation in the finite line,” Applied Mathematics and Computation, vol. 124, no. 1, pp. 45–93, 2001. View at: Publisher Site | Google Scholar | Zentralblatt MATH | MathSciNet
- J. Argyris and M. Haase, “An engineer's guide to soliton phenomena: application of the finite element method,” Computer Methods in Applied Mechanics and Engineering, vol. 61, no. 1, pp. 71–122, 1987. View at: Publisher Site | Google Scholar | Zentralblatt MATH | MathSciNet
- J. Argyris, M. Haase, and J. C. Heinrich, “Finite element approximation to two-dimensional sine-Gordon solitons,” Computer Methods in Applied Mechanics and Engineering, vol. 86, no. 1, pp. 1–26, 1991. View at: Publisher Site | Google Scholar | Zentralblatt MATH | MathSciNet
- D. Kaya, “A numerical solution of the sine-Gordon equation using the modified decomposition method,” Applied Mathematics and Computation, vol. 143, no. 2-3, pp. 309–317, 2003. View at: Publisher Site | Google Scholar | Zentralblatt MATH | MathSciNet
- M. Dehghan and D. Mirzaei, “The boundary integral equation approach for numerical solution of the one-dimensional sine-Gordon equation,” Numerical Methods for Partial Differential Equations, vol. 24, no. 6, pp. 1405–1415, 2008. View at: Publisher Site | Google Scholar | Zentralblatt MATH | MathSciNet
- M. Dehghan and A. Shokri, “A numerical method for solution of the two-dimensional sine-Gordon equation using the radial basis functions,” Mathematics and Computers in Simulation, vol. 79, no. 3, pp. 700–715, 2008. View at: Publisher Site | Google Scholar | Zentralblatt MATH | MathSciNet
- D. Mirzaei and M. Dehghan, “Meshless local Petrov-Galerkin (MLPG) approximation to the two dimensional sine-Gordon equation,” Journal of Computational and Applied Mathematics, vol. 233, no. 10, pp. 2737–2754, 2010. View at: Publisher Site | Google Scholar | Zentralblatt MATH | MathSciNet
- G. W. Wei, “Discrete singular convolution for the sine-Gordon equation,” Physica D, vol. 137, no. 3-4, pp. 247–259, 2000. View at: Publisher Site | Google Scholar | Zentralblatt MATH | MathSciNet
- D. Mirzaei and M. Dehghan, “Implementation of meshless LBIE method to the 2D non-linear SG problem,” International Journal for Numerical Methods in Engineering, vol. 79, no. 13, pp. 1662–1682, 2009. View at: Publisher Site | Google Scholar | MathSciNet
- M. Dehghan and D. Mirzaei, “The dual reciprocity boundary element method (DRBEM) for two-dimensional sine-Gordon equation,” Computer Methods in Applied Mechanics and Engineering, vol. 197, no. 6-8, pp. 476–486, 2008. View at: Publisher Site | Google Scholar | Zentralblatt MATH | MathSciNet
- R. J. Cheng and K. M. Liew, “Analyzing two-dimensional sine-Gordon equation with the mesh-free reproducing kernel particle Ritz method,” Computer Methods in Applied Mechanics and Engineering, vol. 245/246, pp. 132–143, 2012. View at: Publisher Site | Google Scholar | MathSciNet
- J. J. Monaghan, “An introduction to SPH,” Computer Physics Communications, vol. 48, no. 1, pp. 89–96, 1988. View at: Google Scholar
- W. Chen, Meshfree Methods for Partial Differential Equations, Springer, 2003.
- T. Belytschko, Y. Y. Lu, and L. Gu, “Element-free Galerkin methods,” International Journal for Numerical Methods in Engineering, vol. 37, no. 2, pp. 229–256, 1994. View at: Publisher Site | Google Scholar | Zentralblatt MATH | MathSciNet
- S. N. Atluri and T. Zhu, “A new meshless local Petrov-Galerkin (MLPG) approach in computational mechanics,” Computational Mechanics, vol. 22, no. 8-9, pp. 117–127, 1998. View at: Publisher Site | Google Scholar | Zentralblatt MATH | MathSciNet
- Y. X. Qin and Y. M. Cheng, “Reproducing kernel particle boundary element-free method for potential problems,” Chinese Journal of Theoretical and Applied Mechanics, vol. 41, no. 6, pp. 898–905, 2009. View at: Google Scholar | MathSciNet
- R. Cheng and K. M. Liew, “The reproducing kernel particle method for two-dimensional unsteady heat conduction problems,” Computational Mechanics, vol. 45, no. 2, pp. 1–10, 2009. View at: Publisher Site | Google Scholar | Zentralblatt MATH | MathSciNet
- R. J. Cheng and K. M. Liew, “A meshless analysis of three-dimensional transient heat conduction problems,” Engineering Analysis with Boundary Elements, vol. 36, no. 2, pp. 203–210, 2012. View at: Publisher Site | Google Scholar | Zentralblatt MATH | MathSciNet
- Y. Cheng and M. Peng, “Boundary element-free method for elastodynamics,” Science in China G, vol. 48, no. 6, pp. 641–657, 2005. View at: Publisher Site | Google Scholar
- M. Peng and Y. Cheng, “A boundary element-free method (BEFM) for two-dimensional potential problems,” Engineering Analysis with Boundary Elements, vol. 33, no. 1, pp. 77–82, 2009. View at: Publisher Site | Google Scholar | Zentralblatt MATH | MathSciNet
- J. Wang, J. Wang, F. Sun, and Y. Cheng, “An interpolating boundary element-free method with nonsingular weight function for two-dimensional potential problems,” International Journal of Computational Methods, vol. 10, no. 6, Article ID 1350043, 2013. View at: Publisher Site | Google Scholar | MathSciNet
- K. M. Liew, Y. Cheng, and S. Kitipornchai, “Analyzing the 2D fracture problems via the enriched boundary element-free method,” International Journal of Solids and Structures, vol. 44, no. 11-12, pp. 4220–4233, 2007. View at: Publisher Site | Google Scholar
- Y. Cheng and J. Li, “Complex variable meshless method for fracture problems,” Science in China G, vol. 49, no. 1, pp. 46–59, 2006. View at: Publisher Site | Google Scholar
- M. Peng, P. Liu, and Y. Cheng, “The complex variable element-free Galerkin (CVEFG) method for two-dimensional elasticity problems,” International Journal of Applied Mechanics, vol. 1, no. 2, pp. 367–385, 2009. View at: Publisher Site | Google Scholar
- L. Chen and Y. M. Cheng, “The complex variable reproducing kernel particle method for elasto-plasticity problems,” Science China, vol. 53, no. 5, pp. 954–965, 2010. View at: Publisher Site | Google Scholar
- M. Peng, D. Li, and Y. Cheng, “The complex variable element-free Galerkin (CVEFG) method for elasto-plasticity problems,” Engineering Structures, vol. 33, no. 1, pp. 127–135, 2011. View at: Publisher Site | Google Scholar
- Y. M. Cheng, R. X. Li, and M. J. Peng, “Complex variable element-free Galerkin (CVEFG) method for viscoelasticity problems,” Chinese Physics B, vol. 21, no. 9, Article ID 090205, 2012. View at: Google Scholar
- J. F. Wang and Y. M. Cheng, “A new complex variable meshless method for transient heat conduction problems,” Chinese Physics B, vol. 21, no. 12, Article ID 120206, 2012. View at: Google Scholar
- Y. M. Cheng, J. F. Wang, and R. X. Li, “The complex variable element-free Galerkin (CVEFG) method for two-dimensional elastodynamics problems,” International Journal of Applied Mechanics, vol. 4, no. 4, Article ID 1250042, 2012. View at: Google Scholar
- J. F. Wang and Y. M. Cheng, “A new complex variable meshless method for advection-diffusion problems,” Chinese Physics B, vol. 22, no. 3, Article ID 130208, 2013. View at: Google Scholar
- L. Chen, H. P. Ma, and Y. M. Cheng, “Combining the complex variable reproducing kernel particle method and the finite element method for solving transient heat conduction problems,” Chinese Physics B, vol. 22, no. 5, Article ID 130202, 2013. View at: Google Scholar
- H. P. Ren and Y. M. Cheng, “The interpolating element-free Galerkin (IEFG) method for two-dimensional elasticity problems,” International Journal of Applied Mechanics, vol. 3, no. 4, pp. 735–758, 2011. View at: Publisher Site | Google Scholar
- J. F. Wang, F. X. Sun, and Y. M. Cheng, “An improved interpolating element-free Galerkin method with nonsingular weight function for two-dimensional potential problems,” Chinese Physics B, vol. 21, no. 9, Article ID 090204, 2012. View at: Google Scholar
- R. J. Cheng and Q. Wei, “Analysis of the generalized Camassa and Holm equation with the improved element-free Galerkin method,” Chinese Physics B, vol. 22, no. 6, Article ID 060209, 2013. View at: Google Scholar
- R. J. Cheng and H. X. Ge, “Analyzing the equal width wave (EW) equation with the mesh-free kp-Ritz method,” Chinese Physics B, vol. 21, no. 10, Article ID 100209, 2012. View at: Google Scholar
- R.-J. Cheng and H.-X. Ge, “The element-free Galerkin method of numerically solving a regularized long-wave equation,” Chinese Physics B, vol. 21, no. 4, Article ID 040203, 2012. View at: Publisher Site | Google Scholar
- B.-J. Zheng and B.-D. Dai, “Improved meshless local Petrov-Galerkin method for two-dimensional potential problems,” Acta Physica Sinica, vol. 59, no. 8, pp. 5182–5189, 2010. View at: Google Scholar
- L. X. Guo and B. D. Dai, “A moving Kriging interpolation-based boundary node ethod for two-dimensional potential problems,” Chinese Physics B, vol. 12, no. 6, Article ID 120202, 2010. View at: Google Scholar
- B. Zheng and B. Dai, “A meshless local moving Kriging method for two-dimensional solids,” Applied Mathematics and Computation, vol. 218, no. 2, pp. 563–573, 2011. View at: Publisher Site | Google Scholar | Zentralblatt MATH | MathSciNet
- B. Dai, B. Zheng, Q. Liang, and L. Wang, “Numerical solution of transient heat conduction problems using improved meshless local Petrov-Galerkin method,” Applied Mathematics and Computation, vol. 219, no. 19, pp. 10044–10052, 2013. View at: Publisher Site | Google Scholar | MathSciNet
- B. Dai and Y. Cheng, “An improved local boundary integral equation method for two-dimensional potential problems,” International Journal of Applied Mechanics, vol. 2, no. 2, pp. 421–436, 2010. View at: Publisher Site | Google Scholar
- T. Belytschko, Y. Krongauz, D. Organ, M. Fleming, and P. Krysl, “Meshless methods: an overview and recent developments,” Computer Methods in Applied Mechanics and Engineering, vol. 139, no. 1–4, pp. 3–47, 1996. View at: Google Scholar
- Z. Zhang, K. M. Liew, and Y. Cheng, “Coupling of the improved element-free Galerkin and boundary element methods for two-dimensional elasticity problems,” Engineering Analysis with Boundary Elements, vol. 32, no. 2, pp. 100–107, 2008. View at: Publisher Site | Google Scholar
- Z. Zhang, K. M. Liew, Y. Cheng, and Y. Y. Lee, “Analyzing 2D fracture problems with the improved element-free Galerkin method,” Engineering Analysis with Boundary Elements, vol. 32, no. 3, pp. 241–250, 2008. View at: Publisher Site | Google Scholar
- Z. Zhang, J. F. Wang, Y. M. Cheng, and K. M. Liew, “The improved element-free Galerkin method for three-dimensional transient heat conduction problems,” Science China Physics, Mechanics & Astronomy, vol. 56, no. 8, pp. 1568–1580, 2013. View at: Google Scholar
- Z. Zhang, S. Y. Hao, K. M. Liew, and Y. M. Cheng, “The improved element-free Galerkin method for two-dimensional elastodynamics problems,” Engineering Analysis with Boundary Elements, vol. 37, no. 12, pp. 1576–1584, 2013. View at: Publisher Site | Google Scholar | MathSciNet
- Z. Zhang, D.-M. Li, Y.-M. Cheng, and K. M. Liew, “The improved element-free Galerkin method for three-dimensional wave equation,” Acta Mechanica Sinica, vol. 28, no. 3, pp. 808–818, 2012. View at: Publisher Site | Google Scholar | MathSciNet
- W. Ritz, “Uber eine neue methode zur losung gewisser variationsprobleme der mathematischen physic,” Journal fur Reine und Angewandte Mathematik, vol. 135, no. 2, pp. 1–61, 1909. View at: Google Scholar
- B. J. W. S. Rayleigh, The Theory of Sound, vol. 1, Macmillan, New York, NY, USA, 1877, reprinted by Dover Publications in 1945. View at: MathSciNet
- K. M. Liew, X. Zhao, and T. Y. Ng, “The element-free kp-Ritz method for vibration of laminated rotating cylindrical panels,” International Journal of Structural Stability and Dynamics, vol. 2, no. 4, pp. 523–558, 2002. View at: Publisher Site | Google Scholar
- X. Zhao, T. Y. Ng, and K. M. Liew, “Free vibration of two-side simply-supported laminated cylindrical panels via the mesh-free kp-Ritz method,” International Journal of Mechanical Sciences, vol. 46, no. 1, pp. 123–142, 2004. View at: Publisher Site | Google Scholar
- K. M. Liew, J. Wang, M. J. Tan, and S. Rajendran, “Nonlinear analysis of laminated composite plates using the mesh-free kp-Ritz method based on FSDT,” Computer Methods in Applied Mechanics and Engineering, vol. 193, no. 45–47, pp. 4763–4779, 2004. View at: Publisher Site | Google Scholar
- K. M. Liew and R. J. Cheng, “Numerical study of the three-dimensional wave equation using the mesh-free kp-Ritz method,” Engineering Analysis with Boundary Elements, vol. 37, no. 7-8, pp. 977–989, 2013. View at: Google Scholar
- R. J. Cheng, L. W. Zhang, and K. M. Liew, “Modeling of biological population problems using the element-free kp-Ritz method,” Applied Mathematics and Computation, vol. 227, pp. 274–290, 2014. View at: Publisher Site | Google Scholar | MathSciNet
Copyright
Copyright © 2014 Qi Wei and Rongjun Cheng. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.