Currently employed at Para//ab, BCCS, where I mostly work
on projects related to ocean modeling, but also with parallel
computing and optimization of applications for supercomputing,
e.g. climate models or other projects where Para//ab participate.
The equations we try to solve, also called "the model",
is a system of partial differential equations that describes the
dynamics of the ocean. This system is very complex. To get anywhere we
do as most scientists; divide the problem into smaller subproblems
that we know how to deal with efficiently. A "numerical model" is a
result of such a process, it is a reformulation of the problem into a
form suitable for solution by computers.
One example is the
Bergen Ocean Model
that is developed and frequently used here in Bergen - look at
for graphical presentations of some of our results.
Doing lots of simplifications and assumptions comes at a cost; we
introduce error. Our primary concern is called numerical error, which
we try to identify and remove/minimise. The underlying physical model
has of course also weaknesses, and it is not always obvious if errors
are numerical or due to the model itself. On our way we utilize tools
from many fields of science and also try to pick up the essential
ideas. Examples of such fields are e.g. oceanography, linear algebra,
programming, visualisation and parallel computing.
Some of my recent activities are reflected in:
Thiem, Ø., Avlesen, H., Alendal, G. and Berntsen, J. (2005):
Internal waves and internal solitones shoaling and breaking along a
continental slope. Report No. 14, BCCS Technical report series,
University of Bergen, Norway.
- Øyvind Thiem, Helge Avlesen og Guttorm Alendal: Simulering av
strømforhold i og rundt Vatlestraumen. August 2005.
- Helge Avlesen. On the parallelization of a non hydrostatic, sigma
co-ordinate ocean model. NOTUR advanced user support project 2004.
- Avlesen, H. and Berntsen,J. (2004) A 60 day hindcast study of the
Norwegian Seas with focus on Ormen Lange using 20km and 4 km
resolution. Report No. 10, BCCS Technical report series, University of
- Avlesen, H. Berntsen,J. and Furnes,G. (2002) On the current
conditions along the Ormen Lange pipeline path during an extreme,
idealized storm passage. Report Nr. 238, Department of Informatics,
University of Bergen, Norway.
- Avlesen, H. and Berntsen,J. (2001) Flow over rough topography. A
preliminary study with high resolution topography at Ormen
Lange. Technical report No 209, The Nansen Environmental and Remote
- Avlesen, H., Berntsen, J. and Espelid, T.O. (2001) A convergence
study of two ocean models applied to a density driven flow.
International Journal for Numerical Methods in Fluids, 36:
- Avlesen, H. (2000) On the choice of numerical algorithms for ocean
modeling. Ph.D. thesis, Department of Informatics, University of
- Avlesen, H., Berntsen, J. (2000) A 2km resolution study of the Skagerak
circulation, with a comparison of three internal pressure schemes Report
Nr. 199, Department of Informatics, University of Bergen.
- Avlesen, H., Berntsen, J. and Espelid, T.O. (1998) A convergence
study of two prognostic, sigma co-ordinate ocean models on a density
driven flow in a quadratic basin. Report Nr. 157, Department of
Informatics, University of Bergen.
- Avlesen,H. (1998) A study of two new splitting methods for the
gravity part of the shallow water equations. Report Nr. 145,
Department of Informatics, University of Bergen.
I finished my studies for the Dr degree modeling the
Skagerak area, some animations can be found
Abstracts for work on the TODO list...
"On the applicability of implicit methods in regional scale
baroclinic ocean models"
In present ocean models both implicit and explicit methods are
commonly used to find the surface elevation. When applying implicit
methods in ocean modelling with Courant numbers greater than unity,
one will fail to represent short modes of the solution. If
these modes are of minor importance to the overall problem, implicit
methods may still be a cost effective way of propagating the
solution in time.
In the present paper the domain of validity of implicit methods for
solving the shallow water equations is investigated for a baroclinic
benchmark, using both implicit and explicit versions of a sigma
coordinate ocean model.
It is also demonstrated that the commonly used boundary conditions
for the water elevation in ocean models, using semi-implicit time
stepping methods, may not be in agreement with the thermal wind
equations for geostrophic flow.
We find that the implicit method performs well with high spatial
resolution, but on coarse grids the explicit method give much more
accurate results. We believe that the enhanced resolution improve
the results for the implicit method due to a better representation
of the surface gravity waves, and that it also reduce the above
mentioned problem with the boundary condition.