@inproceedings{GoemmelButenwegKob2007,
author = {G{\"o}mmel, A. and Butenweg, Christoph and Kob, M.},
title = {A fluid-structure interaction model of vocal fold oscillation},
series = {5th International Workshop on Models and Analysis of Vocal Emissions for Biomedical Applications, MAVEBA 2007},
booktitle = {5th International Workshop on Models and Analysis of Vocal Emissions for Biomedical Applications, MAVEBA 2007},
isbn = {978-888453674-7},
pages = {127 -- 128},
year = {2007},
abstract = {Since fluid-structure interaction within the finite-element method is state of the art in many engineering fields, this method is used in voice analysis. A quasi two-dimensional model of the vocal folds including the ventricular folds is presented. First results of self-sustained vocal fold oscillation are presented and possibilities as well as limitations are discussed.},
language = {en}
}
@inproceedings{WeissAbanteribaEsch2007,
author = {Weiss, Alexander and Abanteriba, Sylvester and Esch, Thomas},
title = {Investigation of Flow Separation Inside a Conical Rocket Nozzle With the Aid of an Annular Cross Flow},
series = {Proceedings of the ASME/JSME 2007 5th Joint Fluids Engineering Conference. Volume 1: Symposia, Parts A and B},
booktitle = {Proceedings of the ASME/JSME 2007 5th Joint Fluids Engineering Conference. Volume 1: Symposia, Parts A and B},
publisher = {American Society of Mechanical Engineers (ASME)},
address = {New York},
isbn = {0-7918-4288-6},
doi = {10.1115/FEDSM2007-37387},
pages = {1861 -- 1871},
year = {2007},
abstract = {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.},
language = {en}
}
@inproceedings{Dachwald2007,
author = {Dachwald, Bernd},
title = {Low-Thrust Mission Analysis and Global Trajectory Optimization Using Evolutionary Neurocontrol: New Results},
series = {European Workshop on Space Mission Analysis ESA/ESOC, Darmstadt, Germany 10 { 12 Dec 2007},
booktitle = {European Workshop on Space Mission Analysis ESA/ESOC, Darmstadt, Germany 10 { 12 Dec 2007},
year = {2007},
abstract = {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},
language = {en}
}
@inproceedings{DachwaldSeboldtLoebetal.2007,
author = {Dachwald, Bernd and Seboldt, Wolfgang and Loeb, Horst W. and Schartner, Karl-Heinz},
title = {A comparison of SEP and NEP for a main belt asteroid sample return mission},
series = {7th International Symposium on Launcher Technologies, Barcelona, Spain, 02-05 April 2007},
booktitle = {7th International Symposium on Launcher Technologies, Barcelona, Spain, 02-05 April 2007},
pages = {1 -- 10},
year = {2007},
abstract = {Innovative interplanetary deep space missions, like a main belt asteroid sample return mission, require ever larger velocity increments (∆V s) and thus ever more demanding propulsion capabilities. Providing much larger exhaust velocities than chemical high-thrust systems, electric low-thrust space-propulsion systems can significantly enhance or even enable such high-energy missions. In 1995, a European-Russian Joint Study Group (JSG) presented a study report on "Advanced Interplanetary Missions Using Nuclear-Electric Propulsion" (NEP). One of the investigated reference missions was a sample return (SR) from the main belt asteroid (19) Fortuna. The envisaged nuclear power plant, Topaz-25, however, could not be realized and also the worldwide developments in space reactor hardware stalled. In this paper, we investigate, whether such a mission is also feasible using a solar electric propulsion (SEP) system and compare our SEP results to corresponding NEP results.},
language = {en}
}
@inproceedings{DachwaldMengaliQuartaetal.2007,
author = {Dachwald, Bernd and Mengali, Giovanni and Quarta, Alessandro A and Macdonald, Malcolm and McInnes, Colin R},
title = {Optical solar sail degradation modelling},
series = {1st International Symposium on Solar Sailing},
booktitle = {1st International Symposium on Solar Sailing},
pages = {1 -- 27},
year = {2007},
abstract = {We propose a simple parametric OSSD model that describes the variation of the sail film's optical coefficients with time, depending on the sail film's environmental history, i.e., the radiation dose. The primary intention of our model is not to describe the exact behavior of specific film-coating combinations in the real space environment, but to provide a more general parametric framework for describing the general optical degradation behavior of solar sails.},
language = {en}
}
@inproceedings{LoebSchartnerDachwaldetal.2007,
author = {Loeb, Horst Wolfgang and Schartner, Karl-Heinz and Dachwald, Bernd and Seboldt, Wolfgang},
title = {SEP-Sample return from a main belt asteroid},
series = {30th International Electric Propulsion Conference},
booktitle = {30th International Electric Propulsion Conference},
pages = {1 -- 11},
year = {2007},
abstract = {By DLR-contact, sample return missions to the large main-belt asteroid "19, Fortuna" have been studied. The mission scenario has been based on three ion thrusters of the RIT-22 model, which is presently under space qualification, and on solar arrays equipped with triple-junction GaAs solar cells. After having designed the spacecraft, the orbit-to-orbit trajectories for both, a one-way SEP mission with a chemical sample return and an all-SEP return mission, have been optimized using a combination of artificial neural networks with evolutionary algorithms. Additionally, body-to-body trajectories have been investigated within a launch period between 2012 and 2015. For orbit-to-orbit calculation, the launch masses of the hybrid mission and of the all-SEP mission resulted in 2.05 tons and 1.56 tons, respectively, including a scientific payload of 246 kg. For the related transfer durations 4.14 yrs and 4.62 yrs were obtained. Finally, a comparison between the mission scenarios based on SEP and on NEP have been carried out favouring clearly SEP.},
language = {en}
}
@inproceedings{DachwaldKahleWie2007,
author = {Dachwald, Bernd and Kahle, Ralph and Wie, Bong},
title = {Head-on impact deflection of NEAs: a case study for 99942 Apophis},
series = {Planetary Defense Conference 2007},
booktitle = {Planetary Defense Conference 2007},
pages = {1 -- 12},
year = {2007},
abstract = {Near-Earth asteroid (NEA) 99942 Apophis provides a typical example for the evolution of asteroid orbits that lead to Earth-impacts after a close Earth-encounter that results in a resonant return. Apophis will have a close Earth-encounter in 2029 with potential very close subsequent Earth-encounters (or even an impact) in 2036 or later, depending on whether it passes through one of several less than 1 km-sized gravitational keyholes during its 2029-encounter. A pre-2029 kinetic impact is a very favorable option to nudge the asteroid out of a keyhole. The highest impact velocity and thus deflection can be achieved from a trajectory that is retrograde to Apophis orbit. With a chemical or electric propulsion system, however, many gravity assists and thus a long time is required to achieve this. We show in this paper that the solar sail might be the better propulsion system for such a mission: a solar sail Kinetic Energy Impactor (KEI) spacecraft could impact Apophis from a retrograde trajectory with a very high relative velocity (75-80 km/s) during one of its perihelion passages. The spacecraft consists of a 160 m × 160 m, 168 kg solar sail assembly and a 150 kg impactor. Although conventional spacecraft can also achieve the required minimum deflection of 1 km for this approx. 320 m-sized object from a prograde trajectory, our solar sail KEI concept also allows the deflection of larger objects. For a launch in 2020, we also show that, even after Apophis has flown through one of the gravitational keyholes in 2029, the solar sail KEI concept is still feasible to prevent Apophis from impacting the Earth, but many KEIs would be required for consecutive impacts to increase the total Earth-miss distance to a safe value},
language = {en}
}
@article{WallerBraunHojdisetal.2007,
author = {Waller, Mark P. and Braun, Heiko and Hojdis, Nils and B{\"u}hl, Michael},
title = {Geometries of Second-Row Transition-Metal Complexes from Density-Functional Theory},
series = {Journal of Chemical Theory and Computation},
volume = {3},
journal = {Journal of Chemical Theory and Computation},
number = {6},
issn = {1549-9626},
doi = {10.1021/ct700178y},
pages = {2234 -- 2242},
year = {2007},
language = {en}
}
@article{GoeddekeStrzodkaMohdYusofetal.2007,
author = {G{\"o}ddeke, Dominik and Strzodka, Robert and Mohd-Yusof, Jamaludin and McCormick, Patrick and Buijssen, Sven H.M. and Grajewski, Matthias and Turek, Stefan},
title = {Exploring weak scalability for FEM calculations on a GPU-enhanced cluster},
series = {Parallel Computing},
volume = {33},
journal = {Parallel Computing},
number = {10-11},
issn = {0167-8191},
doi = {10.1016/j.parco.2007.09.002},
pages = {685 -- 699},
year = {2007},
language = {en}
}
@inproceedings{Matcha2007,
author = {Matcha, Heike},
title = {Parametric possibilities: designing with parametric modelling},
series = {Predicting the Future [25th eCAADe Conference Proceedings]},
booktitle = {Predicting the Future [25th eCAADe Conference Proceedings]},
isbn = {978-0-9541183-6-5},
pages = {849 -- 856},
year = {2007},
language = {en}
}