A stabilised nodal spectral element method for fully nonlinear water waves

Allan Peter Engsig-Karup, C. Eskilsson, Daniele Bigoni

Research output: Contribution to journalJournal articleResearchpeer-review

Abstract

We present an arbitrary-order spectral element method for general-purpose simulation of non-overturning water waves, described by fully nonlinear potential theory. The method can be viewed as a high-order extension of the classical finite element method proposed by Cai et al. (1998) [5], although the numerical implementation differs greatly. Features of the proposed spectral element method include: nodal Lagrange basis functions, a general quadrature-free approach and gradient recovery using global L2 projections. The quartic nonlinear terms present in the Zakharov form of the free surface conditions can cause severe aliasing problems and consequently numerical instability for marginally resolved or very steep waves. We show how the scheme can be stabilised through a combination of over-integration of the Galerkin projections and a mild spectral filtering on a per element basis. This effectively removes any aliasing driven instabilities while retaining the high-order accuracy of the numerical scheme. The additional computational cost of the over-integration is found insignificant compared to the cost of solving the Laplace problem. The model is applied to several benchmark cases in two dimensions. The results confirm the high order accuracy of the model (exponential convergence), and demonstrate the potential for accuracy and speedup. The results of numerical experiments are in excellent agreement with both analytical and experimental results for strongly nonlinear and irregular dispersive wave propagation. The benefit of using a high-order – possibly adapted – spatial discretisation for accurate water wave propagation over long times and distances is particularly attractive for marine hydrodynamics applications.
Original languageEnglish
JournalJournal of Computational Physics
Volume318
Pages (from-to)1-21
ISSN0021-9991
DOIs
Publication statusPublished - 2016

Keywords

  • Nonlinear and dispersive free surface waves
  • Hydrodynamics
  • Spectral element method
  • Unstructured mesh
  • Finite element methods
  • High-order discretisation

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