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Dr.-Ing. Raju M. Rohde , Dorsch Consult Wasser und Umwelt GmbH, München mit 32 Folien (S. 103-134). Beitrag zum 1. Aachener Softwaretag in der Wasserwirtschaft <1, 2007, Aachen>. Das System BaSYS.L.E.O. Ganglinien-Volumen-Methode Hydrodynamische Kanalnetzberechnung Hydraulische Objekte Hydrodynamische Schmutzfrachtberechnung
Flow separation is a phenomenon that occurs in all kinds of supersonic nozzles sometimes during run-up and shut-down operations. Especially in expansion nozzles of rocket engines with large area ratio, flow separation can trigger strong side loads that can damage the structure of the nozzle. The investigation presented in this paper seeks to establish measures that may be applied to alter the point of flow separation. In order to achieve this, a supersonic nozzle was placed at the exit plane of the conical nozzle. This resulted in the generation of cross flow surrounding the core jet flow from the conical nozzle. Due to the entrainment of the gas stream from the conical nozzle the pressure in its exit plane was found to be lower than that of the ambient. A Cold gas instead of hot combustion gases was used as the working fluid. A mathematical simulation of the concept was validated by experiment. Measurements confirmed the simulation results that due to the introduction of a second nozzle the pressure in the separated region of the conical nozzle was significantly reduced. It was also established that the boundary layer separation inside the conical nozzle was delayed thus allowing an increased degree of overexpansion. The condition established by the pressure measurements was also demonstrated qualitatively using transparent nozzle configurations.
Interplanetary trajectories for low-thrust spacecraft are often characterized by multiple revolutions around the sun. Unfortunately, the convergence of traditional trajectory optimizers that are based on numerical optimal control methods depends strongly on an adequate initial guess for the control function (if a direct method is used) or for the starting values of the adjoint vector (if an indirect method is used). Especially when many revolutions around the sun are re-
quired, trajectory optimization becomes a very difficult and time-consuming task that involves a lot of experience and expert knowledge in astrodynamics and optimal control theory, because an adequate initial guess is extremely hard to find. Evolutionary neurocontrol (ENC) was proposed as a smart method for low-thrust trajectory optimization that fuses artificial neural networks and evolutionary algorithms to so-called evolutionary neurocontrollers (ENCs) [1]. Inspired by natural archetypes, ENC attacks the trajectoryoptimization problem from the perspective of artificial intelligence and machine learning, a perspective that is quite different from that of optimal control theory. Within the context of ENC, a trajectory is regarded as the result of a spacecraft steering strategy that maps permanently the actual spacecraft state and the actual target state onto the actual spacecraft control vector. This way, the problem of searching the optimal spacecraft trajectory is equivalent to the problem of searching (or "learning") the optimal spacecraft steering strategy. An artificial neural network is used to implement such a spacecraft steering strategy. It can be regarded as a parameterized function (the network function) that is defined by the internal network parameters. Therefore, each distinct set of network parameters defines a different network function and thus a different steering strategy. The problem of searching the optimal steering strategy is now equivalent to the problem of searching the optimal set of network parameters. Evolutionary algorithms that work on a population of (artificial) chromosomes are used to find the optimal network parameters, because the parameters can be easily mapped onto a chromosome. The trajectory optimization problem is solved when the optimal chromosome is found. A comparison of solar sail trajectories that have been published by others [2, 3, 4, 5] with ENC-trajectories has shown that ENCs can be successfully applied for near-globally optimal spacecraft control [1, 6] and that they are able to find trajectories that are closer to the (unknown) global optimum, because they explore the trajectory search space more exhaustively than a human expert can do. The obtained trajectories are fairly accurate with respect to the terminal constraint. If a more accurate trajectory is required, the ENC-solution can be used as an initial guess for a local trajectory optimization method. Using ENC, low-thrust trajectories can be optimized without an initial guess and without expert attendance.
Here, new results for nuclear electric spacecraft and for solar sail spacecraft are presented and it will be shown that ENCs find very good trajectories even for very difficult problems. Trajectory optimization results are presented for 1. NASA's Solar Polar Imager Mission, a mission to attain a highly inclined close solar orbit with a solar sail [7] 2. a mission to de ect asteroid Apophis with a solar sail from a retrograde orbit with a very-high velocity impact [8, 9] 3. JPL's \2nd Global Trajectory Optimization Competition", a grand tour to visit four asteroids from different classes with a NEP spacecraft
Dipl.-Ing. Ralf Engels - DHI Wasser und Umwelt GmbH, Syke. 24 S. (S. 70-93) Beitrag zum 1. Aachener Softwaretag in der Wasserwirtschaft <1,2007, Aachen> Einleitung [des Autors] Die hydrodynamische Kanalnetzmodellierung ist ein Standardwerkzeug für die Bemessung von Kanalnetzen. Neben der Berechnung der hydrologischen und hydraulischen Gegebenheiten in einem städtischen Einzugsgebiet gehören auch weiterführende Technologien mittlerweile zum Standard. So können alle steuerbaren Elemente eines Kanalnetzes dynamisch so optimiert werden, dass die Leistungsfähigkeit des Kanalnetzes zusätzlich gesteigert werden kann. Automatische Werkzeuge zur dynamischen hydraulischen Schmutzfrachtberechnung ermöglichen die Erweiterung der Steuerung – insbesondere von Entlastungsanlagen – im Hinblick auf die entlasteten Schmutzfrachten und geben darüber hinaus detaillierte Informationen für den Betrieb der Kläranlage. Weiterführende biologische Prozessmodellierungen ergänzen dieses Themenfeld. GIS Werkzeuge können bei der räumlich differenzierten Modellierung von Kanalnetzen wertvolle Dienste leisten. Die detaillierte Betrachtung einzelner Haltungsflächen in ihrem räumlichen Zusammenhang ist damit ebenso möglich wie eine komplette Verwaltung aller für die Kanalnetzmodellierung notwendigen Daten in einem übersichtlichen grafischen Menü. Die Grenzen der Kanalnetzmodellierung lagen in früheren Zeiten an dessen Rand. Detaillierte Informationen über die Wege des Wassers auf der Geländeoberfläche, an der Schnittstelle zu Vorflutern und in der Interaktion mit Grundwasser waren bisher nicht modelltechnisch bewertbar. Eine dynamische Kopplung verschiedener Modelle zur Darstellung aller relevanten hydraulischen Prozesse ermöglicht eine integrative Betrachtung aller möglichen Wege, die das Wasser in der Stadt nehmen kann (Mark & Djordjevic, 2006). Dieser Beitrag präsentiert den Stand der Technik für die integrierte Modellierung städtischer Überschwemmungen mit Hilfe der Modellkopplung von Oberflächenmodellen und Kanalnetzmodellen.