13,082 research outputs found
Pencil-Beam Surveys for Trans-Neptunian Objects: Novel Methods for Optimization and Characterization
Digital co-addition of astronomical images is a common technique for
increasing signal-to-noise and image depth. A modification of this simple
technique has been applied to the detection of minor bodies in the Solar
System: first stationary objects are removed through the subtraction of a
high-SN template image, then the sky motion of the Solar System bodies of
interest is predicted and compensated for by shifting pixels in software prior
to the co-addition step. This "shift-and-stack" approach has been applied with
great success in directed surveys for minor Solar System bodies. In these
surveys, the shifts have been parameterized in a variety of ways. However,
these parameterizations have not been optimized and in most cases cannot be
effectively applied to data sets with long observation arcs due to objects'
real trajectories diverging from linear tracks on the sky. This paper presents
two novel probabilistic approaches for determining a near-optimum set of
shift-vectors to apply to any image set given a desired region of orbital space
to search. The first method is designed for short observational arcs, and the
second for observational arcs long enough to require non-linear shift-vectors.
Using these techniques and other optimizations, we derive optimized grids for
previous surveys that have used "shift-and-stack" approaches to illustrate the
improvements that can be made with our method, and at the same time derive new
limits on the range of orbital parameters these surveys searched. We conclude
with a simulation of a future applications for this approach with LSST, and
show that combining multiple nights of data from such next-generation
facilities is within the realm of computational feasibility.Comment: Accepted for publication in PASP March 1, 2010
Search-based 3D Planning and Trajectory Optimization for Safe Micro Aerial Vehicle Flight Under Sensor Visibility Constraints
Safe navigation of Micro Aerial Vehicles (MAVs) requires not only
obstacle-free flight paths according to a static environment map, but also the
perception of and reaction to previously unknown and dynamic objects. This
implies that the onboard sensors cover the current flight direction. Due to the
limited payload of MAVs, full sensor coverage of the environment has to be
traded off with flight time. Thus, often only a part of the environment is
covered.
We present a combined allocentric complete planning and trajectory
optimization approach taking these sensor visibility constraints into account.
The optimized trajectories yield flight paths within the apex angle of a
Velodyne Puck Lite 3D laser scanner enabling low-level collision avoidance to
perceive obstacles in the flight direction. Furthermore, the optimized
trajectories take the flight dynamics into account and contain the velocities
and accelerations along the path.
We evaluate our approach with a DJI Matrice 600 MAV and in simulation
employing hardware-in-the-loop.Comment: In Proceedings of IEEE International Conference on Robotics and
Automation (ICRA), Montreal, Canada, May 201
Shape optimization of three-dimensional stamped and solid automotive components
The shape optimization of realistic, 3-D automotive components is discussed. The integration of the major parts of the total process: modeling, mesh generation, finite element and sensitivity analysis, and optimization are stressed. Stamped components and solid components are treated separately. For stamped parts a highly automated capability was developed. The problem description is based upon a parameterized boundary design element concept for the definition of the geometry. Automatic triangulation and adaptive mesh refinement are used to provide an automated analysis capability which requires only boundary data and takes into account sensitivity of the solution accuracy to boundary shape. For solid components a general extension of the 2-D boundary design element concept has not been achieved. In this case, the parameterized surface shape is provided using a generic modeling concept based upon isoparametric mapping patches which also serves as the mesh generator. Emphasis is placed upon the coupling of optimization with a commercially available finite element program. To do this it is necessary to modularize the program architecture and obtain shape design sensitivities using the material derivative approach so that only boundary solution data is needed
Dagstuhl Reports : Volume 1, Issue 2, February 2011
Online Privacy: Towards Informational Self-Determination on the Internet (Dagstuhl Perspectives Workshop 11061) : Simone Fischer-HĂŒbner, Chris Hoofnagle, Kai Rannenberg, Michael Waidner, Ioannis Krontiris and Michael Marhöfer Self-Repairing Programs (Dagstuhl Seminar 11062) : Mauro PezzĂ©, Martin C. Rinard, Westley Weimer and Andreas Zeller Theory and Applications of Graph Searching Problems (Dagstuhl Seminar 11071) : Fedor V. Fomin, Pierre Fraigniaud, Stephan Kreutzer and Dimitrios M. Thilikos Combinatorial and Algorithmic Aspects of Sequence Processing (Dagstuhl Seminar 11081) : Maxime Crochemore, Lila Kari, Mehryar Mohri and Dirk Nowotka Packing and Scheduling Algorithms for Information and Communication Services (Dagstuhl Seminar 11091) Klaus Jansen, Claire Mathieu, Hadas Shachnai and Neal E. Youn
Offshore Wind Farm Electrical Cable Layout Optimization
This is the author accepted manuscript. The final version is available from Taylor & Francis via the DOI in this record.This article explores an automated approach for the efficient placement of substations and the design of an inter-array electrical collection network for an offshore wind farm through the minimization of the cost. To accomplish this, the problem is represented as a number of sub-problems that are solved in series using a combination of heuristic algorithms. The overall problem is first solved by clustering the turbines to generate valid substation positions. From this, a navigational mesh pathfinding algorithm based on Delaunay triangulation is applied to identify valid cable paths, which are then used in a mixed-integer linear programming problem to solve for a constrained capacitated minimum spanning tree considering all realistic constraints. The final tree that is produced represents the solution to the inter-array cable problem. This method is applied to a planned wind farm to illustrate the suitability of the approach and the resulting layout that is generated
Aerodynamics of a rigid curved kite wing
A preliminary numerical study on the aerodynamics of a kite wing for high
altitude wind power generators is proposed. Tethered kites are a key element of
an innovative wind energy technology, which aims to capture energy from the
wind at higher altitudes than conventional wind towers. We present the results
obtained from three-dimensional finite volume numerical simulations of the
steady air flow past a three-dimensional curved rectangular kite wing (aspect
ratio equal to 3.2, Reynolds number equal to 3x10^6). Two angles of incidence
-- a standard incidence for the flight of a tethered airfoil (6{\deg}) and an
incidence close to the stall (18{\deg}) -- were considered. The simulations
were performed by solving the Reynolds Averaged Navier-Stokes flow model using
the industrial STAR-CCM+ code. The overall aerodynamic characteristics of the
kite wing were determined and compared to the aerodynamic characteristics of
the flat rectangular non twisted wing with an identical aspect ratio and
section (Clark Y profile). The boundary layer of both the curved and the flat
wings was considered to be turbulent throughout. It was observed that the
curvature induces only a mild deterioration of the aerodynamics properties.
Pressure distributions around different sections along the span are also
presented, together with isolines of the average pressure and kinetic energy
fields at a few sections across the wing and the wake. Our results indicate
that the curvature induces a slower spatial decay of the vorticity in the wake,
and in particular, inside the wing tip vortices.Comment: 13 pages, 13 figures. Submitted to "Renewable Energy
29 W High power CW supercontinuum source.
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