410
J. Murawski and J. Woge Nielsen
the analysis to oil in the surface layer. Oil that is mixed down in the water column
is solely driven by currents. It is usually not buoyant enough to rise to the surface again, especially at later stages of the spill development when up to 75 % of
oil have been taken up by emulsification and volatile components have evaporated
completely.
Both wind and waves play an important role, to some extent complementary to
each other, in the drift and fate of oil spills. The oil parcels that reach the shoreline
first have normally travelled at the surface all the time and have been exposed to
the wind forces for the duration of the travel time. Although oil moves fastest at the
surface due to the wind, at the same time oil parcels at the surface are continuously
exposed to the impact of waves that successively mix them down into the water
column. The fastest-propagating oil parcels thus reflect a delicate balance of the
impact of wind and waves.
The performed analysis of oil drift patterns provides the basis for the critical
evaluation of the existing ship routes. Monte Carlo techniques have been used to
analyse seasonal and annual drift patterns and to generate season-specific optimum
fairways. A key development is the evidence that greatly different seasons such
as winter and summer may require the same fairway design whereas a drastically
different design fits much better for both transitional seasons, spring and autumn.
The combined summer and winter designs have the best overall performance in
terms of path integrals of the cost function along fairways and therefore at best
represent the average patterns of joint propagation of oil owing to sea currents and
winds.
As each design represents a set of seasons, it is crucial for the overall estimation
to compare the cross-seasonal performance. Summer-winter designs perform just a
little worse in spring and autumn. By contrast, spring and autumn designs perform
much better in their season, but much worse outside their season. The drawbacks of
seasonal designs can be to some extent compensated by using annual mean designs.
Such combined designs represent neither maxima nor minima of the seasonal configurations, they are universal and for that reason performance all-rounders. It is not
surprising that such designs have something of everything and that they combine
a good annual mean performance with a small cross-seasonal performance drop.
The true value of combined design becomes apparent when one compares all three
designs to each other.
The choice of the final design depends on the long-term strategy of maritime
management and policies, and environmental as well as economical performance.
If much focus is put on the all-season, climatologically valid performance, then
combined designs are preferable, but also summer-winter designs are worthwile to
look at. Spring-autumn designs might be disregarded, because of a substantial drop
in their performance in summer and winter. Combined designs seem to be a good
option, because their economical performance in terms of travel time, speed and
fuel consumption is in the range of optimized economical designs of the existing
ship routing software packages.
Cost efficient navigation in coastal waters depends on direct, short distance
courses. It should also account for the particular water depth to avoid resistance
J. Murawski and J. Woge Nielsen
the analysis to oil in the surface layer. Oil that is mixed down in the water column
is solely driven by currents. It is usually not buoyant enough to rise to the surface again, especially at later stages of the spill development when up to 75 % of
oil have been taken up by emulsification and volatile components have evaporated
completely.
Both wind and waves play an important role, to some extent complementary to
each other, in the drift and fate of oil spills. The oil parcels that reach the shoreline
first have normally travelled at the surface all the time and have been exposed to
the wind forces for the duration of the travel time. Although oil moves fastest at the
surface due to the wind, at the same time oil parcels at the surface are continuously
exposed to the impact of waves that successively mix them down into the water
column. The fastest-propagating oil parcels thus reflect a delicate balance of the
impact of wind and waves.
The performed analysis of oil drift patterns provides the basis for the critical
evaluation of the existing ship routes. Monte Carlo techniques have been used to
analyse seasonal and annual drift patterns and to generate season-specific optimum
fairways. A key development is the evidence that greatly different seasons such
as winter and summer may require the same fairway design whereas a drastically
different design fits much better for both transitional seasons, spring and autumn.
The combined summer and winter designs have the best overall performance in
terms of path integrals of the cost function along fairways and therefore at best
represent the average patterns of joint propagation of oil owing to sea currents and
winds.
As each design represents a set of seasons, it is crucial for the overall estimation
to compare the cross-seasonal performance. Summer-winter designs perform just a
little worse in spring and autumn. By contrast, spring and autumn designs perform
much better in their season, but much worse outside their season. The drawbacks of
seasonal designs can be to some extent compensated by using annual mean designs.
Such combined designs represent neither maxima nor minima of the seasonal configurations, they are universal and for that reason performance all-rounders. It is not
surprising that such designs have something of everything and that they combine
a good annual mean performance with a small cross-seasonal performance drop.
The true value of combined design becomes apparent when one compares all three
designs to each other.
The choice of the final design depends on the long-term strategy of maritime
management and policies, and environmental as well as economical performance.
If much focus is put on the all-season, climatologically valid performance, then
combined designs are preferable, but also summer-winter designs are worthwile to
look at. Spring-autumn designs might be disregarded, because of a substantial drop
in their performance in summer and winter. Combined designs seem to be a good
option, because their economical performance in terms of travel time, speed and
fuel consumption is in the range of optimized economical designs of the existing
ship routing software packages.
Cost efficient navigation in coastal waters depends on direct, short distance
courses. It should also account for the particular water depth to avoid resistance