Generalized separation of variables and exact solutions of nonlinear equations

We consider a generalized procedure of separation of variables in nonlinear hyperbolic-type equations and Korteweg–de-Vries-type equations. We construct a broad class of exact solutions of these equations that cannot be obtained by the Lie method and method of conditional symmetries.     

一类强阻尼非线性波动方程的广义解

用Galerkin方法研究了一类非线性波动方程的初边值问题,证明其在一定条件下强解的存在性.     

A note on separation of variables solutions of generalized nonlinear diffusion equations

In this letter we show how more cases of the generalized nonlinear diffusion equation that contain separable solutions to those found by Zhang et al. (2002, 2003) via the generalized conditional symmetries method, can be found. Importantly we demonstrate with an example that can be used to describe water flow in unsaturated soil, and which can provide new insights when plant-root uptake is affected by water speed.     

Matrix differential equations with separation of variables

We consider matrix differential equations with separation of variables and homogeneous equations reducible to them. For the mentioned equations we obtain sufficient conditions for the solvability in quadratures.     

Exact solitary wave solutions of nonlinear wave equations

The hyperbolic function method for nonlinear wave equations is presented. In support of a computer algebra system, many exact solitary wave solutions of a class of nonlinear wave equations are obtained via the method. The method is based on the fact that the solitary wave solutions are essentially of a localized nature. Writing the solitary wave solutions of a nonlinear wave equation as the polynomials of hyperbolic functions, the nonlinear wave equation can be changed into a nonlinear system of algebraic equations. The system can be solved via Wu Elimination or Gr?bner base method. The exact solitary wave solutions of the nonlinear wave equation are obtained including many new exact solitary wave solutions.     

Statistical mechanics of nonlinear wave equations

The recurrences of initial states for nonlinear wave equations of the form with odd f are studied. The main result refines and generalizes the investigations of Friedlander and is related to the Poincaré theorem for finite dimensional Hamiltonian systems. Bibliography: 7 titles. Published inZapiski Nauchnykh Seminarov POMI, Vol. 235, 1900, pp. 287–294.     

Blowup of solutions of nonlinear equations and systems of nonlinear equations in wave theory

We consider the phenomenon of solution blowup for the system of equations describing surface water waves and also for the acoustic wave equation in viscous medium using the test-function method developed by Galactionov, Pokhozhaev, and Mitidieri.     

Time periodic solutions of nonlinear wave equations

Existence and regularity of solutions of $$(1)u_{tt} - u_{xx} = \varepsilon K(x,t,u,u_t )0< x< \pi ,0 \leqslant t \leqslant 2\pi $$ together with the periodicity and boundary conditions $$(2)u(x,t + 2\pi ) = u(x,t),u(0,t) = 0 = u(\pi ,t)$$ is studied both with an without the dissipation u_t. A solution is a pair (χ, u). A main feature of interest here is an infinite dimensional biofurcation problem. Under appropriate conditions on K, global existence results are obtained by a combination of analytical and topological methods.     

Discrete Dubrovin equations and separation of variables for discrete systems

A universal system of difference equations associated with a hyperelliptic curve is derived constituting the discrete analogue of the Dubrovin equations arising in the theory of finite-gap integration. The parametrisation of the solutions in terms of Abelian functions of Kleinian type (i.e. the higher-genus analogues of the Weierstrass elliptic functions) is discussed as well as the connections with the method of separation of variables.     

Lagrangian for nonlinear perturbed heat and wave equations

The perturbed heat and wave equations [A.H. Bokhari, A.G. Johnpillai, F.M. Mahomed, F.D. Zaman, Approximate conservation laws of nonlinear perturbed heat and wave equations, Nonlinear Analysis. Real World Applications 13 (2012) 2823–2829] are studied, which were considered to admit no standard Lagrangian. By the semi-inverse method, however, an exact Lagrangian is obtained and its proof is given.     

Multidimensional nonlinear wave equations with multivalued solutions

We present the theory of breaking waves in nonlinear systems whose dynamics and spatial structure are described by multidimensional nonlinear hyperbolic wave equations. We obtain a general relation between systems of first-order quasilinear equations and nonlinear hyperbolic equations of higher orders, which, in particular, describe electromagnetic waves in a medium with nonlinear polarization of an arbitrary form. We use this approach to construct exact multivalued solutions of such equations and to study their spatial structure and dynamics. The results are generalized to a wide class of multidimensional equations such as d’Alembert equations, nonlinear Klein-Gordon equations, and nonlinear telegraph equations.