Generating the PECS'02 logo with a numerical model
A numerical model for simulating estuarine and shelf sea dynamics
has been used for generating the
logo for the PECS'02 conference. The model is a finite-difference model
written in horizontal orthogonal curvilinear coordinates which can be fitted
to lateral boundaries. This enables the model to better
represent flows along bended coast lines. For the discretisation of
advective transports of momentum and tracers, high order advection schemes
have been implemented. They are based on a directional-split method
applying one-dimensional TVD (Total Variation Diminishing)
schemes alternately in all three spatial dimensions. In contrast to
simpler advection schemes, they
are monotone (not generating over- and undershoots)
and only little diffusive.
As model domain, a straight channel of 4100 m length, 300 m width
and 2 m depth was constructed. In the middle the channel was
smoothly constricted to a width of only 100 m.
This domain was discretised by means of
a curvilinear grid with 410 × 30 elements in the horizontal.
In the vertical, only one layer was used.
The model was forced by a surface elevation difference of 0.1 m between
the two open ends of the channel.
After a steady-state flow with a
balance of pressure gradient, bottom friction and momentum advection
was reached, a passive tracer concentration with the shape
of the PECS'02 logo (in Times New Roman discretised by hand into a
160 × 30 matrix) was pasted into the straight upstream
part of the channel. The background tracer value was set to
c=10
and the logo to c=20.
It was then advected downstream by using the so-called
Superbee limiter for the TVD scheme, which is specifically known for little
numerical diffusion.
When passing the constriction, the PECS'02 logo was distorted due to the
hydraulic jump and the subsequent flow acceleration. After the "P"
had just passed the constriction, a snapshot of the passive tracer was made.
The logo was then displayed by printing all grid boxes with a
concentration of c>13.
Logo and text by
Hans Burchard
and
Karsten Bolding
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