Universität Stuttgart
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Item Open Access Effects of chemical modifications on the rheological and the expansion behavior of polylactide (PLA) in foam extrusion(2019) Standau, Tobias; Castellón, Svenja Murillo; Delavoie, Agathe; Bonten, Christian; Altstädt, VolkerIt is well known that polylactide (PLA) is difficult to foam due to its low melt strength. Thus, many ways were described in the literature to enhance the foamability. However, the melt strength was actually determined only in a limited number of publications. In this study, the addition of chemical modifiers was used to change the rheological behavior of PLA and thereby improve its foamability in foam extrusion process. For the first time the use of dicumyl peroxide modified PLA in foam extrusion is described. Both modifications lead to a distinct increase in melt strength. Here, the highest increase was shown for the PLA modified with dicumyl peroxide. Furthermore, strain hardening was observed for PLA modified with the peroxide. Low density foams were achieved for neat and modified PLA in foam extrusion. Neat PLA showed a density of 45 kg/m 3 , while the peroxide modified PLA showed the highest expansion with a density reduction down to 32 kg/m 3 . Both modifications result in a more uniform cell structure and an improved compression strength. Here, the foamed, peroxide modified PLA showed outstanding performance compared to neat PLA foam with twice the compression strength (151 Pa) even at a 30% lower density.Item Open Access IEA Wind Task 32: Wind Lidar : identifying and mitigating barriers to the adoption of wind lidar(2018) Clifton, Andrew; Clive, Peter; Gottschall, Julia; Schlipf, David; Simley, Eric; Simmons, Luke; Stein, Detlef; Trabucchi, Davide; Vasiljevic, Nikola; Würth, InesIEA Wind Task 32 exists to identify and mitigate barriers to the adoption of lidar for wind energy applications. It leverages ongoing international research and development activities in academia and industry to investigate site assessment, power performance testing, controls and loads, and complex flows. Since its initiation in 2011, Task 32 has been responsible for several recommended practices and expert reports that have contributed to the adoption of ground-based, nacelle-based, and floating lidar by the wind industry. Future challenges include the development of lidar uncertainty models, best practices for data management, and developing community-based tools for data analysis, planning of lidar measurements and lidar configuration. This paper describes the barriers that Task 32 identified to the deployment of wind lidar in each of these application areas, and the steps that have been taken to confirm or mitigate the barriers. Task 32 will continue to be a meeting point for the international wind lidar community until at least 2020 and welcomes old and new participants.Item Open Access Hochwasser – Staatsfeind Nr. 1(2002) Ehret, Uwe; Bárdossy, AndrásIn diesem Beitrag wird zusammen mit einer Erläuterung der Entstehung und der verschiedenen Arten von Hochwasser ein kurzer Überblick über die Arten des Hochwasserschutzes und der Hochwasservorhersage gegeben. Während sich die staatlichen Vorhersageinstitutionen momentan hauptsächlich auf große Flüsse wie Donau, Rhein und Neckar konzentrieren, wurde im Rahmen eines Forschungsprojekts am Institut für Wasserbau (IWS) ein Vorhersage- und Warnsystem für ein kleines Flusseinzugsgebiet, den Goldersbach bei Tübingen, entwickelt.Item Open Access Satelliten im Dienst der Geodäsie und Geoinformatik(2003) Kleusberg, AlfredAm 4. Oktober 1957 wurde vom Gebiet der damaligen UdSSR der erste künstliche Satellit der Erde in den Weltraum geschickt. Von den vielen Nachfolgemissionen der vergangenen 46 Jahre waren einige Satelliten speziell für Aufgaben der Geodäsie und Geoinformatik designiert; viele weitere, ursprünglich für andere Aufgaben in Betrieb genommene Satelliten erwiesen sich im Nachhinein als sehr gute Lieferanten von Daten zur Lösung geodätischer Probleme. Um diesen Beitrag der Satellitenmethoden im richtigen Licht zu sehen, ist es aufschlussreich, zuerst die Entwicklung der Geodäsie von ihren Ursprüngen bis zum Jahre 1957 nachzuvollziehen. Dies kann natürlich im Rahmen dieses Beitrags nur in Form von mehr oder weniger subjektiv herausgegriffenen Einzelereignissen der Geschichte erfolgen.Item Open Access Lidar-based wake tracking for closed-loop wind farm control(2017) Raach, Steffen; Schlipf, David; Cheng, Po WenThis work presents two advancements towards closed-loop wake redirection of a wind turbine. First, a model-based wake-tracking approach is presented, which uses a nacelle-based lidar system facing downwind to obtain information about the wake. The method uses a reduced-order wake model to track the wake. The wake tracking is demonstrated with lidar measurement data from an offshore campaign and with simulated lidar data from a simulation with the Simulator fOr Wind Farm Applications (SOWFA). Second, a controller for closed-loop wake steering is presented. It uses the wake-tracking information to set the yaw actuator of the wind turbine to redirect the wake to a desired position. Altogether, the two approaches enable a closed-loop wake redirection.Item Open Access Heat accumulation during pulsed laser materials processing(2014) Weber, Rudolf; Graf, Thomas; Berger, Peter; Onuseit, Volkher; Wiedenmann, Margit; Freitag, Chistian; Feuer, AnneLaser materials processing with ultra-short pulses allows very precise and high quality results with a minimum extent of the thermally affected zone. However, with increasing average laser power and repetition rates the so-called heat accumulation effect becomes a considerable issue.Item Open Access Beschreibung einer Vorrichtung zur Beförderung einer Flüssigkeit aus Unterdruckgefäßen in ein Medium mit Überdruck(2008) Suchov, Vladimir G.; Elin, I. I.; Berezovskij, N. E.; Akkerman, I. N.; Pertschi, Ottmar (Übersetzer)Patentbeschreibung einer Vorrichtung, mit der Flüssigkeiten aus Unterdruckgefäßen in ein Medium mit Überdruck befördert werden können und die darauf beruht, daß die in Reihe angeordneten Aufnahmegefäße einerseits im Vakuum, andererseits mit Normaldruck arbeitenItem Open Access Cooperative search by combining simulated and real robots in a swarm under the view of multibody system dynamics(2013) Tang, Qirong; Eberhard, PeterThis paper presents a new approach for cooperative search of a robot swarm. After modeling the robot, the mechanical Particle Swarm Optimization method is conducted based on physical robot properties. Benefiting from the effective localization and navigation by sensor data fusion, a mixed robot swarm which contains both simulated and real robots is then successfully used for searching a target cooperatively. With the promising results from experiments based on different scenarios, the feasibility, the interaction of real and simulated robots, the fault tolerance, and also the scalability of the proposed method are investigated.Item Open Access Development and validation of a novel setup for LEDs lifetime estimation on molded interconnect devices(2018) Soltani, Mahdi; Freyburger, Moritz; Kulkarni, Romit; Mohr, Rainer; Groezinger, Tobias; Zimmermann, AndréItem Open Access Modeling the chemoelectromechanical behavior of skeletal muscle using the parallel open-source software library OpenCMISS(2013) Heidlauf, Thomas; Röhrle, OliverAn extensible, flexible, multiscale and multiphysics model for non-isometric skeletal muscle behavior is presented. The skeletal muscle chemoelectromechanical model is based on a bottom-up approach modeling the entire excitation-contraction pathway by strongly coupling a detailed biophysical model of a half-sarcomere to the propagation of action potentials along skeletal muscle fibers, and linking cellular parameters to a transversely isotropic continuum-mechanical constitutive equation describing the overall mechanical behavior of skeletal muscle tissue. Since the multiscale model exhibits separable time scales, a special emphasis is placed on employing computationally efficient staggered solution schemes. Further, the implementation builds on the open-source software library OpenCMISS and uses state-ofthe-art parallelization techniques taking advantage of the unique anatomical fiber architecture of skeletal muscles. OpenCMISS utilizes standardized data structures for geometrical aspects (FieldML) and cellular models (CellML). Both standards are designed to allow for a maximum on flexibility, reproducibility, and extensibility. The results demonstrate the model´s capability of simulating different aspects of non-isometric muscle contraction and to efficiently simulate the chemoelectromechanical behavior in complex skeletal muscles such as the tibialis anterior muscle.