I have contributed quite a bit to the FEniCS project, and the incompressible Navier-Stokes solver Oasis has been developed within the FEniCS framework. The solver has been developed for
efficiency, with MPI, and it is written entirely in Python. The Oasis solver is documented in the
Computer Physics Communications paper, where we
show that it may run as fast and accurate as the low-level finite volume
C++ solvers OpenFOAM and CDP (Stanford).
The Oasis solver has been used in a range of master theses (see Teaching).
For one of my master students, Per Thomas Haga, the thesis led to a journal paper on injecting
drugs in the Cerebrospinal fluid (CSF) . The animation on the right
shows how an injected drug moves up and down inside the CSF channel. It can also
be sen that, due to the very low diffusivity of the scalar drug, we modelled the
scalar transport using Lagrangian particle tracking.
I have been working quite a bit together with Kristian Valen-Sendstad at Simula, on different aspects of biomedical
flows. Our simulations on intracranial aneurysms
, actually reached the headlines of Norway's larges
newspaper (VG) 1, when we found a correlation between transition
to turbulence and the risk of aneurysm rupture (more famously known as stroke).
For this work I performed most of the simulations when still at FFI.
Figure 1: Headlines in norwegian newspaper VG, 5/11-2011.
More recently we have been studying transition and
mesh sensitivity in the FDA nozzle benchmark. In 
we use both regular CFD and linear stability analysis to show that care must be
taken when designing a CFD benchmark. Transition to turbulence can only
come from a seed, or perturbation, and an ideal case like the FDA
benchmark should not transtition at all unless some noise is added to the
system. Figure 2 is showing an unstable eigenmode in the FDA
bechmark, showing that transition should in deed occur at the Reynolds
number=3500. Here I have conducted the stability simulations using the
dog linear stability
analysis software package.
Figure 2: Linear stability analysis of the FDA benchmark. Showing the most unstable eigenmode.
M. Mortensen, K.-A. Mardal and H. P. Langtangen.
Simulation of Transitional Flows,
Automated Solution of Differential Equations by the Finite Element Method: The FEniCS Book,
edited by A. Logg, K.-A. Mardal and G. Wells,
pp. pp. 421-440,
P. T. Haga, G. Pizzichelli, M. Mortensen, M. Kuchta, S. H. Pahlavian, E. Sinibaldi, B. A. Martin and K.-A. Mardal.
A Numerical Investigation of Intrathecal Isobaric Drug Dispersion Within the Cervical Subarachnoid Space,
A. Bergersen, M. Mortensen and K. Valen-Sendstad.
The FDA Nozzle Benchmark: in Theory There Is No Difference Between Theory and Practice, But in Practice There Is,
Accepted for publication in International Journal for Numerical Methods in Biomedical Engineering,