3,604 research outputs found
Satellite downlink scheduling problem: A case study
The synthetic aperture radar (SAR) technology enables satellites to
efficiently acquire high quality images of the Earth surface. This generates
significant communication traffic from the satellite to the ground stations,
and, thus, image downlinking often becomes the bottleneck in the efficiency of
the whole system. In this paper we address the downlink scheduling problem for
Canada's Earth observing SAR satellite, RADARSAT-2. Being an applied problem,
downlink scheduling is characterised with a number of constraints that make it
difficult not only to optimise the schedule but even to produce a feasible
solution. We propose a fast schedule generation procedure that abstracts the
problem specific constraints and provides a simple interface to optimisation
algorithms. By comparing empirically several standard meta-heuristics applied
to the problem, we select the most suitable one and show that it is clearly
superior to the approach currently in use.Comment: 23 page
Insight into High-quality Aerodynamic Design Spaces through Multi-objective Optimization
An approach to support the computational aerodynamic design process is presented
and demonstrated through the application of a novel multi-objective variant of
the Tabu Search optimization algorithm for continuous problems to the
aerodynamic design optimization of turbomachinery blades. The aim is to improve
the performance of a specific stage and ultimately of the whole engine. The
integrated system developed for this purpose is described. This combines the
optimizer with an existing geometry parameterization scheme and a well-
established CFD package. The system’s performance is illustrated through case
studies – one two-dimensional, one three-dimensional – in which flow
characteristics important to the overall performance of turbomachinery blades
are optimized. By showing the designer the trade-off surfaces between the
competing objectives, this approach provides considerable insight into the
design space under consideration and presents the designer with a range of
different Pareto-optimal designs for further consideration. Special emphasis is
given to the dimensionality in objective function space of the optimization
problem, which seeks designs that perform well for a range of flow performance
metrics. The resulting compressor blades achieve their high performance by
exploiting complicated physical mechanisms successfully identified through the
design process. The system can readily be run on parallel computers,
substantially reducing wall-clock run times – a significant benefit when
tackling computationally demanding design problems. Overall optimal performance
is offered by compromise designs on the Pareto trade-off surface revealed
through a true multi-objective design optimization test case. Bearing in mind
the continuing rapid advances in computing power and the benefits discussed,
this approach brings the adoption of such techniques in real-world engineering
design practice a ste
Free Search of real value or how to make computers think
This book introduces in detail Free Search - a novel advanced method for search and optimisation. It also deals with some essential questions that have been raised in a strong debate following the publication of this method in
journal and conference papers. In the light of this debate, Free Search deserves serious attention, as it appears to be superior to other competitive methods in the context of the experimental results obtained. This superiority is not only
quantitative in terms of the actual optimal value found but also qualitative in terms of independence from initial conditions and adaptation capabilities in an unknown environment
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