Generalized Burgers equations and Euler–Painlevé transcendents. III

Abstract

It was proposed earlier [P. L. Sachdev, K. R. C. Nair, and V. G. Tikekar, J. Math. Phys. 27, 1506 (1986); P. L. Sachdev and K. R. C. Nair, ibid. 28, 977 (1987)] that the Euler–Painlevé equations y(d²y/dη²)+a(dy/dη)²+f(η)y(dy/dη)+g(η)y²+b(dy/dη)+c=0 represent generalized Burgers equations (GBE's) in the same way as Painlevé equations represent the Korteweg–de Vries type of equations. The earlier studies were carried out in the context of GBE's with damping and those with spherical and cylindrical symmetry. In the present paper, GBE's with variable coefficients of viscosity and those with inhomogeneous terms are considered for their possible connection to Euler–Painleve equations. It is found that the Euler–Painlevé equation, which represents the GBE u_t+u^βu_x=(δ/2)g(t)u_xx, g(t)=(1+t)ⁿ, β>0, has solutions, which either decay or oscillate at η=±∞, only when -1<n<1. The solutions are shocklike when η=1. On the other hand, they oscillate over the whole real line when n=-1. Furthermore, the solutions monotonically decay both at η=+∞ and η=-∞, that is, they have a single hump form if β≥β_n=(1-n)/(1+n). For β<β_n, the solutions have an oscillatory behavior either at η=+∞ or at η=-∞, or at η=+∞ and η=-∞. For β=β_n, there exists a single parameter family of exact single hump solutions, similar to those found for the nonplanar Burgers equations in Paper II. Thus the parametric value β=β_n seems to bifurcate the families of solutions, which remain bounded at η=±∞. Other GBE's considered here are also found to be reducible to Euler–Painlevé equations.The scope of these equations is broadened by relating them to a large number of nonlinear DE's selected from the compendia of Kamke [Differential Gleichungen : Lô sungsmethoden und Lô sungen (Akademische Verlagsgesellschaft, Leipzig, 1943)] and Murphy [Ordinary Differential Equations and their Solutions (Van Nostrand, Princeton, NJ, 1960)]. These latter equations arise from a wide range of physical applications and are of some historical interest as well. They are all special cases of a slightly generalized form of the Euler–painleve equation.