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Lie Symmetries and Conservation Laws of the Generalised Foam-Drainage Equation

  • Zhi-Yong Zhang EMAIL logo and Kai-Hua Ma
Published/Copyright: January 11, 2017

Abstract

We perform a complete Lie point symmetry classification of the generalised foam-drainage equation and then construct an optimal system of one-dimensional subalgebra of the admitted symmetry operators and use them to reduce the equations under study. A power series solution of the reduced equation is constructed. Moreover, we find all multipliers of the equations and apply them to construct conservation laws.

Acknowledgements

This paper is supported by the National Natural Science Foundation of China (Nos. 11671014, 11301012), Scientic Research Project of Beijing Educational Committee, the Youth Talent Program (No. XN071009) and College Student’s Sci-tech Activities of North China University of Technology.

Appendix

In this section, we show the convergence of the power solution (22). From (24), we get

(A-1)|cn+2|M[|cn|+k=0n|ck||cn+1k|+k=0nj=0k|cnk||cj+1||ck+1j|+k=1nj=0k|cn+2k||cjckj|],

whereM=max{|1λc02|,2c02}.

Assuming another power series

(A-2)μ=P(z)=n=0Pnzn,

where

Pn+2=M[Pn+k=0nPkPn+1k+k=0nj=0kPnkPj+1Pk+1j+k=1nj=0kPn+2kPjPkj]

and P0=|c0|,P1=|c1|,P2=|(12λc12+2λc1)/(2λc0)|. Obviously, we find

|cn|Pn   n=0,1,2,

Therefore, the series (A-2) is the majorant series of (22), so we have

μ=P(z)=P0+P1z+P2z2+n=1Pn+2zn+2=P0+P1z+P2z2+M[n=1Pnzn+2+n=1k=0nPkPn+1kzn+2+n=1k=0nj=0kPnkPj+1Pk+1jzn+2+n=1k=1nj=0kPn+2kPjPkjzn+2]=P0+P1z+P2z2+M[P(z)z2+P(z)z(P(z)P0P1z)+(P(z)P0)3+P(z)(P(z)P0)(P(z)P0P1z)].

Let

Θ(z,μ)=μP0P1zP2z2M[μz2+μz(μP0P1z)+(μP0)3+μ(μP0)(μP0P1z)]=0.

It is easy to find that Θ(z, μ) is the analytic implicit in the real plane, Θ(0, P0)=0 and Θμ(0,P0)=1. According to the implicit function theorem, we conclude μ=P(z) is analytic in a neighbourhood of the point (0, P0) of the plane with a positive radius. This implies the power series (22) converges in a neighbourhood of the plane.

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Received: 2016-9-3
Accepted: 2016-11-18
Published Online: 2017-1-11
Published in Print: 2017-3-1

©2017 Walter de Gruyter GmbH, Berlin/Boston

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