Joar Bagge

I obtained my PhD from KTH in 2023 under the supervision of professor Anna-Karin Tornberg, and then spent two years as a postdoctoral fellow at the Oden Institute, The University of Texas at Austin. Since January 2026 I am back at KTH as a postdoc working with Sara Zahedi.

My research focuses on numerical methods for solving partial differential equations, such as the Stokes equation, Helmholtz equation and Laplace/Poisson equation. Applications are found e.g. in fluid dynamics, acoustic scattering and electrostatics. Some of the methods that I am interested in are boundary integral methods and other boundary methods, quadrature methods for singular and near-singular integration, fast summation methods, skeletonization and proxy compression methods. More recently, I am working on cut finite element methods and stochastic surface PDEs.

Publications

Journal papers

• J. Bagge, A.-K. Tornberg, “Fast Ewald summation for Stokes flow with arbitrary periodicity”, Journal of Computational Physics, vol. 493 (2023), 112473. DOI:10.1016/j.jcp.2023.112473
• J. Bagge, T. Rosén, F. Lundell, A.-K. Tornberg, “Parabolic velocity profile causes shape-selective drift of inertial ellipsoids”, Journal of Fluid Mechanics, vol. 926 (2021), A24. DOI:10.1017/jfm.2021.716
• D. Saffar Shamshirgar, J. Bagge, A.-K. Tornberg, “Fast Ewald summation for electrostatic potentials with arbitrary periodicity”, Journal of Chemical Physics, vol. 154 (2021), 164109. DOI:10.1063/5.0044895
• J. Bagge, A.-K. Tornberg, “Highly accurate special quadrature methods for Stokesian particle suspensions in confined geometries”, International Journal for Numerical Methods in Fluids, vol. 93 (2021), pp. 2175–2224. DOI:10.1002/fld.4970

Conference papers

• J. Bagge, A.-K. Tornberg, “Accurate quadrature methods with application to Stokes flow with particles in confined geometries”. In D. J. Chappell, Proceedings of the Eleventh UK Conference on Boundary Integral Methods (UKBIM 11), Nottingham, UK, July 2017, pp. 15–24. [Available here]

Theses

• J. Bagge, Accurate quadrature and fast summation in boundary integral methods for Stokes flow, Ph.D. thesis, KTH, 2023. [Available here]
• J. Bagge, Numerical simulation of an inertial spheroidal particle in Stokes flow, M.Sc. thesis, KTH, 2015. [Available here]
• J. Bagge, A graphotactic language metric : A measure of language distance based on the ordering of letters, with applications to language identification, B.Sc. thesis, KTH, 2013. [Available here]