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  • 1
    Publication Date: 2009-06-01
    Print ISSN: 0262-4079
    Topics: Natural Sciences in General
    Published by Elsevier
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  • 2
    Publication Date: 2009-03-01
    Print ISSN: 1076-2787
    Electronic ISSN: 1099-0526
    Topics: Computer Science , Mathematics
    Published by Hindawi
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  • 3
    Publication Date: 2019-06-28
    Description: General multilevel nonlinear optimization problems arise in design of complex systems and can be used as a means of regularization for multi-criteria optimization problems. Here, for clarity in displaying our ideas, we restrict ourselves to general bi-level optimization problems, and we present two solution approaches. Both approaches use a trust-region globalization strategy, and they can be easily extended to handle the general multilevel problem. We make no convexity assumptions, but we do assume that the problem has a nondegenerate feasible set. We consider necessary optimality conditions for the bi-level problem formulations and discuss results that can be extended to obtain multilevel optimization formulations with constraints at each level.
    Keywords: NUMERICAL ANALYSIS
    Type: NASA-CR-194980 , NAS 1.26:194980 , ICASE-94-77
    Format: application/pdf
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  • 4
    Publication Date: 2019-06-28
    Description: Multidisciplinary design optimization (MDO) gives rise to nonlinear optimization problems characterized by a large number of constraints that naturally occur in blocks. We propose a class of multilevel optimization methods motivated by the structure and number of constraints and by the expense of the derivative computations for MDO. The algorithms are an extension to the nonlinear programming problem of the successful class of local Brown-Brent algorithms for nonlinear equations. Our extensions allow the user to partition constraints into arbitrary blocks to fit the application, and they separately process each block and the objective function, restricted to certain subspaces. The methods use trust regions as a globalization strategy, and they have been shown to be globally convergent under reasonable assumptions. The multilevel algorithms can be applied to all classes of MDO formulations. Multilevel algorithms for solving nonlinear systems of equations are a special case of the multilevel optimization methods. In this case, they can be viewed as a trust-region globalization of the Brown-Brent class.
    Keywords: NUMERICAL ANALYSIS
    Type: AD-A284318 , NASA-CR-194940 , NAS 1.26:194940 , ICASE-94-53
    Format: application/pdf
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  • 5
    Publication Date: 2019-07-13
    Description: We discuss criteria by which one can classify, analyze, and evaluate approaches to solving multidisciplinary design optimization (MDO) problems. Central to our discussion is the often overlooked distinction between questions of formulating MDO problems and solving the resulting computational problem. We illustrate our general remarks by comparing several approaches to MDO that have been proposed.
    Keywords: Aircraft Design, Testing and Performance
    Type: First ASMO UK/ISSMO CONFERENCE on Engineering Design Optimization; Jul 08, 1999 - Jul 09, 1999; Unknown
    Format: application/pdf
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  • 6
    Publication Date: 2019-07-13
    Description: The complexity of the present system for managing air traffic has led to "discreteness" in approaches to creating new concepts: new concepts are created as point designs, based on experience, expertise, and creativity of the proposer. Discrete point designs may be highly successful but they are difficult to substantiate in the face of equally strong substantiation of competing concepts, as well as the state of the art in concept evaluation via simulations. Hybrid concepts may present a compromise - the golden middle. Yet a hybrid of sometimes in principle incompatible concepts forms another point design that faces the challenge of substantiation and validation. We are faced with the need to re-design the air transportation system ab initio. This is a daunting task, especially considering the problem of transitioning from the present system to any fundamentally new system. However, design from scratch is also an opportunity to reconsider approaches to new concept development. In this position paper we propose an approach, Optimized Parametric Functional Design, for systematic development of concepts for management and control of airspace systems, based on optimization formulations in terms of required system functions and states. This reasoning framework, realizable in the context of ab initio system design, offers an approach to deriving substantiated airspace management and control concepts. With growing computational power, we hope that the approach will also yield a methodology for actual dynamic control of airspace
    Keywords: Air Transportation and Safety; Systems Analysis and Operations Research
    Type: AIAA Paper 2013-4419 , NF1676L-16964 , AIAA Aviation Technology, Integration, and Operations (ATIO) Conference; Aug 12, 2013 - Aug 14, 2013; Los Angeles, CA; United States
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  • 7
    Publication Date: 2019-07-13
    Description: The Air Traffic Monotonic Lagrangian Grid (ATMLG) is used to simulate a 24 hour period of air traffic flow in the National Airspace System (NAS). During this time period, there are 41,594 flights over the United States, and the flight plan information (departure and arrival airports and times, and waypoints along the way) are obtained from an Federal Aviation Administration (FAA) Enhanced Traffic Management System (ETMS) dataset. Two simulation procedures are tested and compared: one based on the Monotonic Lagrangian Grid (MLG), and the other based on the stationary Latitude-Longitude (Lat- Long) grid. Simulating one full day of air traffic over the United States required the following amounts of CPU time on a single processor of an SGI Altix: 88 s for the MLG method, and 163 s for the Lat-Long grid method. We present a discussion of the amount of CPU time required for each of the simulation processes (updating aircraft trajectories, sorting, conflict detection and resolution, etc.), and show that the main advantage of the MLG method is that it is a general sorting algorithm that can sort on multiple properties. We discuss how many MLG neighbors must be considered in the separation assurance procedure in order to ensure a five-mile separation buffer between aircraft, and we investigate the effect of removing waypoints from aircraft trajectories. When aircraft choose their own trajectory, there are more flights with shorter duration times and fewer CD&R maneuvers, resulting in significant fuel savings.
    Keywords: Aircraft Stability and Control
    Type: AIAA Paper 2011-6887 , NF1676L-12217 , 11th AIAA Aviation Technology, Integration, and Operations (ATIO) Conference; Sep 20, 2011 - Sep 22, 2011; Virginia Beach, VA; United States
    Format: application/pdf
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  • 8
    Publication Date: 2019-07-12
    Description: Main Message: National and Global Needs - Develop scalable airspace operations management system to accommodate increased mobility needs, emerging airspace uses, mix, future demand. Be affordable and economically viable. Sense of Urgency. Saturation (delays), emerging airspace uses, proactive development. Autonomy is Needed for Airspace Operations to Meet Future Needs. Costs, time critical decisions, mobility, scalability, limits of cognitive workload. AutoMax to Accommodate National and Global Needs. Auto: Automation, autonomy, autonomicity for airspace operations. Max: Maximizing performance of the National Airspace System. Interesting Challenges and Path Forward.
    Keywords: Air Transportation and Safety
    Type: ARC-E-DAA-TN11498
    Format: application/pdf
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  • 9
    Publication Date: 2019-07-20
    Description: Current rapidly-exploring random tree (RRT) algorithms rely on proximity query packages that often include collision checkers, tolerance verification, and distance computation algorithms for the generation of safe paths. In this paper, we broaden the information available to the path-planning algorithm by incorporating silhouette information of nearby obstacles in conflict. A silhouette-informed tree (SIT) is generated through the flight-safe region of a wire maze for a single unmanned aerial system (UAS). The silhouette is used to extract local geometric information of nearby obstacles and provide path alternatives around these obstacles. Thus, focusing the search for the generation of new tree branches near these obstacles, and decreasing the number of samples required to explore the narrow corridors within the wire maze. The SIT is then processed to extract a path that connects the initial location of the UAS with the goal, reduce the number of line segments in this path if possible, and smooth the resulting path using Pythagorean Hodograph Bezier curves. To ensure that the smoothed path remains in the flight-safe region of the configuration space, a tolerance verification algorithm for Bezier curves and convex polytopes in three dimensions is proposed. Lastly, temporal specifications are imposed on the smoothed path in the shape of an arbitrary speed profile.
    Keywords: Cybernetics, Artificial Intelligence and Robotics
    Type: NF1676L-28796 , AIAA Aviation and Aeronautics Forum (Aviation 2018); Jun 25, 2018 - Jun 29, 2018; Atlanta, GA; United States
    Format: application/pdf
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  • 10
    Publication Date: 2019-07-10
    Description: Opportunities for breakthroughs in the large-scale computational simulation and design of aerospace vehicles are presented. Computational fluid dynamics tools to be used within multidisciplinary analysis and design methods are emphasized. The opportunities stem from speedups and robustness improvements in the underlying unit operations associated with simulation (geometry modeling, grid generation, physical modeling, analysis, etc.). Further, an improved programming environment can synergistically integrate these unit operations to leverage the gains. The speedups result from reducing the problem setup time through geometry modeling and grid generation operations, and reducing the solution time through the operation counts associated with solving the discretized equations to a sufficient accuracy. The opportunities are addressed only at a general level here, but an extensive list of references containing further details is included. The opportunities discussed are being addressed through the Fast Adaptive Aerospace Tools (FAAST) element of the Advanced Systems Concept to Test (ASCoT) and the third Generation Reusable Launch Vehicles (RLV) projects at NASA Langley Research Center. The overall goal is to enable greater inroads into the design process with large-scale simulations.
    Keywords: Aerodynamics
    Type: NASA/TM-2002-211747 , L-18196 , NAS 1.15:211747
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