@article{KosterScheidweilerTieves2016, author = {Koster, Arie and Scheidweiler, Robert and Tieves, Martin}, title = {A flow based pruning scheme for enumerative equitable coloring algorithms}, series = {A flow based pruning scheme for enumerative equitable coloring algorithms}, journal = {A flow based pruning scheme for enumerative equitable coloring algorithms}, doi = {10.48550/arXiv.1607.08754}, pages = {1 -- 30}, year = {2016}, abstract = {An equitable graph coloring is a proper vertex coloring of a graph G where the sizes of the color classes differ by at most one. The equitable chromatic number is the smallest number k such that G admits such equitable k-coloring. We focus on enumerative algorithms for the computation of the equitable coloring number and propose a general scheme to derive pruning rules for them: We show how the extendability of a partial coloring into an equitable coloring can be modeled via network flows. Thus, we obtain pruning rules which can be checked via flow algorithms. Computational experiments show that the search tree of enumerative algorithms can be significantly reduced in size by these rules and, in most instances, such naive approach even yields a faster algorithm. Moreover, the stability, i.e., the number of solved instances within a given time limit, is greatly improved. Since the execution of flow algorithms at each node of a search tree is time consuming, we derive arithmetic pruning rules (generalized Hall-conditions) from the network model. Adding these rules to an enumerative algorithm yields an even larger runtime improvement.}, language = {en} } @article{BeckenbachScheidweiler2016, author = {Beckenbach, Isabel and Scheidweiler, Robert}, title = {Perfect ƒ-Matchings and ƒ-Factors in Hypergraphs - A Combinatorial Approach}, series = {Discrete Mathematics}, volume = {240}, journal = {Discrete Mathematics}, number = {10}, publisher = {Elsevier}, address = {Amsterdam}, issn = {2192-7782}, doi = {10.1016/j.disc.2017.05.005}, pages = {2499 -- 2506}, year = {2016}, abstract = {We prove characterizations of the existence of perfect ƒ-matchings in uniform mengerian and perfect hypergraphs. Moreover, we investigate the ƒ-factor problem in balanced hypergraphs. For uniform balanced hypergraphs we prove two existence theorems with purely combinatorial arguments, whereas for non-uniform balanced hypergraphs we show that the ƒ-factor problem is NP-hard.}, language = {en} } @article{ScheidweilerTriesch2016, author = {Scheidweiler, Robert and Triesch, Eberhard}, title = {A note on the duality between matchings and vertex covers in balanced hypergraphs}, series = {Journal of Combinatorial Optimization}, volume = {32}, journal = {Journal of Combinatorial Optimization}, number = {2}, publisher = {Springer}, address = {Berlin}, issn = {1573-2886}, doi = {10.1007/s10878-015-9887-5}, pages = {639 -- 644}, year = {2016}, abstract = {We present a new Min-Max theorem for an optimization problem closely connected to matchings and vertex covers in balanced hypergraphs. The result generalizes Kőnig's Theorem (Berge and Las Vergnas in Ann N Y Acad Sci 175:32-40, 1970; Fulkerson et al. in Math Progr Study 1:120-132, 1974) and Hall's Theorem (Conforti et al. in Combinatorica 16:325-329, 1996) for balanced hypergraphs.}, language = {en} } @article{KilicRaatschenKoerfgenetal.2017, author = {Kilic, S. A. and Raatschen, Hans-J{\"u}rgen and K{\"o}rfgen, B. and Apaydin, N. M. and Astaneh-Asl, A.}, title = {FE Model of the Fatih Sultan Mehmet Suspension Bridge Using Thin Shell Finite Elements}, series = {Arabian Journal for Science and Engineering}, volume = {42}, journal = {Arabian Journal for Science and Engineering}, number = {3}, publisher = {Springer Nature}, issn = {2191-4281}, doi = {10.1007/s13369-016-2316-y}, pages = {1103 -- 1116}, year = {2017}, abstract = {This paper presents the results of an eigenvalue analysis of the Fatih Sultan Mehmet Bridge. A high-resolution finite element model was created directly from the available design documents. All physical properties of the structural components were included in detail, so no calibration to the measured data was necessary. The deck and towers were modeled with shell elements. A nonlinear static analysis was performed before the eigenvalue calculation. The calculated natural frequencies and corresponding mode shapes showed good agreement with the available measured ambient vibration data. The calculation of the effective modal mass showed that nine modes had single contributions higher than 5 \% of the total mass. They were in a frequency range up to 1.2 Hz. The comparison of the results for the torsional modes especially demonstrated the advantage of using thin shell finite elements over the beam modeling approach.}, language = {en} } @article{RieperGebhardtStucker2016, author = {Rieper, Harald and Gebhardt, Andreas and Stucker, Brent}, title = {Selective Laser Melting of the Eutectic Silver-Copper Alloy Ag 28 wt \% Cu}, series = {RTejournal - Forum f{\"u}r Rapid Technologie}, volume = {13}, journal = {RTejournal - Forum f{\"u}r Rapid Technologie}, issn = {1614-0923}, url = {http://nbn-resolving.de/nbn:de:0009-2-44141}, year = {2016}, abstract = {The aim of this work was to perform a detailed investigation of the use of Selective Laser Melting (SLM) technology to process eutectic silver-copper alloy Ag 28 wt. \% Cu (also called AgCu28). The processing occurred with a Realizer SLM 50 desktop machine. The powder analysis (SEM-topography, EDX, particle distribution) was reported as well as the absorption rates for the near-infrared (NIR) spectrum. Microscope imaging showed the surface topography of the manufactured parts. Furthermore, microsections were conducted for the analysis of porosity. The Design of Experiments approach used the response surface method in order to model the statistical relationship between laser power, spot distance and pulse time.}, language = {en} } @book{Gebhardt2016, author = {Gebhardt, Andreas}, title = {Additive Fertigungsverfahren : Additive Manufacturing und 3D-Drucken f{\"u}r Prototyping - Tooling - Produktion}, edition = {5. aktualisierte und erweiterte Auflage}, publisher = {Hanser}, address = {M{\"u}nchen}, isbn = {978-3-446-44401-0 ; 978-3-446-44539-0}, doi = {10.3139/9783446445390}, pages = {XXIV, 711 S. : zahlr. Ill. u. graph. Darst.}, year = {2016}, language = {de} } @article{HaagZontarSchleupenetal.2014, author = {Haag, S. and Zontar, D. and Schleupen, Josef and M{\"u}ller, T. and Brecher, C.}, title = {Chain of refined perception in self-optimizing assembly of micro-optical systems}, series = {Journal of sensors and sensor systems}, volume = {3}, journal = {Journal of sensors and sensor systems}, number = {1}, publisher = {Copernicus Publ.}, address = {G{\"o}ttingen}, issn = {2194-878X}, doi = {10.5194/jsss-3-87-2014}, pages = {87 -- 95}, year = {2014}, abstract = {Today, the assembly of laser systems requires a large share of manual operations due to its complexity regarding the optimal alignment of optics. Although the feasibility of automated alignment of laser optics has been shown in research labs, the development effort for the automation of assembly does not meet economic requirements - especially for low-volume laser production. This paper presents a model-based and sensor-integrated assembly execution approach for flexible assembly cells consisting of a macro-positioner covering a large workspace and a compact micromanipulator with camera attached to the positioner. In order to make full use of available models from computer-aided design (CAD) and optical simulation, sensor systems at different levels of accuracy are used for matching perceived information with model data. This approach is named "chain of refined perception", and it allows for automated planning of complex assembly tasks along all major phases of assembly such as collision-free path planning, part feeding, and active and passive alignment. The focus of the paper is put on the in-process image-based metrology and information extraction used for identifying and calibrating local coordinate systems as well as the exploitation of that information for a part feeding process for micro-optics. Results will be presented regarding the processes of automated calibration of the robot camera as well as the local coordinate systems of part feeding area and robot base.}, language = {en} } @book{Feuerriegel2016, author = {Feuerriegel, Uwe}, title = {Verfahrenstechnik mit EXCEL: Verfahrenstechnische Berechnungen effektiv durchf{\"u}hren und professionell dokumentieren}, publisher = {Springer Fachmedien}, address = {Wiesbaden}, isbn = {978-3-658-02902-9}, doi = {10.1007/978-3-658-02903-6}, pages = {XVII, 381 Seiten}, year = {2016}, language = {de} } @inproceedings{KesslerBalcGebhardt2016, author = {Kessler, Julia and Balc, Nicolae and Gebhardt, Andreas}, title = {Basic research on lattice structures focused on the strut shape and welding beads}, series = {Physics Procedia}, volume = {Vol. 83}, booktitle = {Physics Procedia}, issn = {1875-3884}, doi = {10.1016/j.phpro.2016.08.086}, pages = {833 -- 838}, year = {2016}, language = {en} } @inproceedings{BagheriSchleupenDahmannetal.2016, author = {Bagheri, Mohsen and Schleupen, Josef and Dahmann, Peter and Kallweit, Stephan}, title = {Kletternde Wartungsplattform f{\"u}r die wetterunabh{\"a}ngige Instandhaltung von Rotorbl{\"a}ttern an Windenergieanlagen - SMART}, series = {AKIDA 2016 Aachener Kolloquium f{\"u}r Instandhaltung, Diagnose und Anlagen{\"u}berwachung (AKIDA) am 15. und 16.11.2016, Technologiezentrum Aachen}, booktitle = {AKIDA 2016 Aachener Kolloquium f{\"u}r Instandhaltung, Diagnose und Anlagen{\"u}berwachung (AKIDA) am 15. und 16.11.2016, Technologiezentrum Aachen}, pages = {21 Folien}, year = {2016}, abstract = {In Deutschland liegt der Anteil der Windkraft an der Gesamtstromerzeugung bei 13,3\% mit mehr als 25.000 installierten Windenergieanlagen (WEA). Weltweit erf{\"a}hrt die Windbranche ein rasantes Wachstum. Indien und China berichten eine j{\"a}hrliche Wachstumsrate an Neuinstallationen von 45\%. Die Technologie zur Erzeugung elektrischer Energie aus Windkraft ist noch vergleichsweise jung. Durch die weltweit steigende Anzahl an Windenergieanlagen w{\"a}chst zunehmend der Bedarf an innovativen Wartungsl{\"o}sungen. Komponenten wie Generator oder Getriebe sind inzwischen weitestgehend ausgereift. Der Fokus richtet sich zunehmend auf die wesentliche Kernkomponente - die Rotorbl{\"a}tter. Industriekletterer inspizieren die Rotorbl{\"a}tter oder T{\"u}rme i.d.R. in einem zwei Jahres Rhythmus. Sie werden zunehmend durch Seilarbeitsb{\"u}hnen unterst{\"u}tzt. F{\"u}r gr{\"o}ßere Reparaturen kommen Kr{\"a}ne zum Einsatz, mit denen das Rotorblatt f{\"u}r die Instandhaltung demontiert wird. Die Standardinspektion besteht aus Sicht- und Klopfpr{\"u}fung der Rotorblattoberfl{\"a}che und ist nur bei sehr ruhiger Wetterlage durchf{\"u}hrbar. Seit September 2014 wird das Forschungsprojekt SMART (Scanning, Monitoring, Analysis, Repair and Transportation), Entwicklung einer Wartungsplattform f{\"u}r WEA, vom BMWi gef{\"o}rdert. Das Konsortium besteht aus zwei Firmen und der Fachhochschule Aachen. Die SMART-Anlage klettert reibschl{\"u}ssig am Turm der WEA mittels speziellen Kettenfahrwerken (Abbildung) auf- und abw{\"a}rts. Ein ringf{\"o}rmiges Spannsystems, basierend auf dem Konzept der „N{\"u}rnberger"-Schere, erzeugt die erforderliche Anpresskraft f{\"u}r den Kletterprozess. Wettergesch{\"u}tzte Arbeitskabinen erm{\"o}glichen die ganzj{\"a}hrige Instandhaltung von Rotorbl{\"a}ttern und ebenso T{\"u}rmen. Dadurch k{\"o}nnen Wartungsarbeiten auf 24 Stunden am Tag ausgeweitet werden. Der kombinierte Einsatz (Sensorfusion) bildgebender Messtechnik wie Thermografie, Ultraschall, und Terahertz in der Arbeitskabine kann die Dokumentation, Effizienz und Qualit{\"a}t der Instandhaltungsarbeiten erheblich verbessern. Langfristiges Ziel von SMART ist ein Condition Monitoring f{\"u}r Rotorbl{\"a}tter und T{\"u}rme auf Basis digitalisierter dreidimensionaler Volumenscans. Der kooperative Einsatz mit UAVs erweitert die Instandhaltungsstrategie. UAVs erm{\"o}glichen die schnelle, kosteng{\"u}nstige globale optische Inspektion von Rotorblattoberfl{\"a}chen zur Detektion potentieller Fehlstellen. Der „Proof-of-Concept" Meilenstein wurde mit der Demonstration eines funktionsf{\"a}higen Modells im Dezember 2015 erfolgreich abgeschlossen.}, language = {de} }