### Abstract

In this article we give a detailed asymptotic analysis of the near critical self-similar blowup solutions to the Generalised Korteweg–de Vries equation (GKdV). We compare this analysis to some careful numerical calculations. It has been known that for a nonlinearity that has a power larger than the critical value p=5, solitary waves of the GKdV can become unstable and become infinite in finite time, in other words they blow up. Numerical simulations presented in Klein and Peter (2015) indicate that if p>5 the solitary waves travel to the right with an increasing speed, and simultaneously, form a similarity structure as they approach the blow-up time. This structure breaks down at p=5. Based on these observations, we rescale the GKdV equation to give an equation that will be analysed by using asymptotic methods as p→5^{+}. By doing this we resolve the complete structure of these self-similar blow-up solutions and study the singular nature of the solutions in the critical limit. In both the numerics and the asymptotics, we find that the solution has sech-like behaviour near the peak. Moreover, it becomes asymmetric with slow algebraic decay to the left of the peak and much more rapid algebraic decay to the right. The asymptotic expressions agree to high accuracy with the numerical results, performed by adaptive high-order solvers based on collocation or finite difference methods.

Original language | English |
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Article number | 132179 |

Journal | Physica D: Nonlinear Phenomena |

Volume | 401 |

Early online date | 4 Sep 2019 |

DOIs | |

Publication status | Published - 1 Jan 2020 |

### Keywords

- Asymptotic analysis
- Blow-up solutions
- Generalised Korteweg–de Vries equation
- Numerical methods

### ASJC Scopus subject areas

- Statistical and Nonlinear Physics
- Mathematical Physics
- Condensed Matter Physics
- Applied Mathematics

## Profiles

### Chris Budd

- Department of Mathematical Sciences - Professor
- EPSRC Centre for Doctoral Training in Statistical Applied Mathematics (SAMBa)
- Probability Laboratory at Bath
- Centre for Doctoral Training in Decarbonisation of the Built Environment (dCarb)
- Centre for Mathematical Biology
- Institute for Mathematical Innovation (IMI)

Person: Research & Teaching

## Cite this

*Physica D: Nonlinear Phenomena*,

*401*, [132179]. https://doi.org/10.1016/j.physd.2019.132179