Linking ghost penalty and aggregated unfitted methods

Santiago Badia, Eric Neiva, Francesc Verdugo

Research output: Contribution to journalArticleResearchpeer-review

19 Citations (Scopus)


In this work, we analyse the links between ghost penalty stabilisation and aggregation-based discrete extension operators for the numerical approximation of elliptic partial differential equations on unfitted meshes. We explore the behaviour of ghost penalty methods in the limit as the penalty parameter goes to infinity, which returns a strong version of these methods. We observe that these methods suffer locking in that limit. On the contrary, aggregated finite element spaces are locking-free because they can be expressed as an extension operator from well-posed to ill-posed degrees of freedom. Next, we propose novel ghost penalty methods that penalise the distance between the solution and its aggregation-based discrete extension. These methods are locking-free and converge to aggregated finite element methods in the infinite penalty parameter limit. We include an exhaustive set of numerical experiments in which we compare weak (ghost penalty) and strong (aggregated finite elements) schemes in terms of error quantities, condition numbers and sensitivity with respect to penalty coefficients on different geometries, intersection locations and mesh topologies.

Original languageEnglish
Article number114232
Number of pages23
JournalComputer Methods in Applied Mechanics and Engineering
Publication statusPublished - 1 Jan 2022


  • Aggregated finite elements
  • Embedded methods
  • Ghost penalty
  • Stabilisation techniques
  • Unfitted finite elements

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