05 Fakultät Informatik, Elektrotechnik und Informationstechnik

Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/6

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Open Access
Alte und neue Sprachkonzepte: Einstufung und Bewertung
(1990) Ludewig, Jochen
Die "4th Generation Languages" entsprechen dem Katalog einer Fertighausfabrik. Lösungen können aus vorhandenen Komponenten schnell und billig zusammengesetzt werden - oder sie sind nicht möglich. Die Stärken liegen also in Geschwindigkeit und Kosten von Standardlösungen, die Schwächen in der mangelnden Flexibilität bei speziellen Problemen, insbesondere auch bei der Erweiterung vorhandener Software-Systeme.
Open Access
Analysis of the influence of static and dynamic eccentricity on back EMF of a permanent magnet synchronous motor
(2017) Fischer, Manuel; Roth-Stielow, Jörg
In this paper the measurement results that represent the back electromotive force (EMF) of a small drive permanent magnet synchronous machine (PMSM) are proposed. The focus is on the comparison between three mechanical configurations: the original one and a setup with static and dynamic eccentricity. Additionally, the influence of compensating currents is considered due to the circuitry of the windings belonging to one phase. This leads to quite similar gradients of back EMF in all three mechanical configurations.
Open Access
Are suggestions of coupled file changes interesting?
(2016) Ramadani, Jasmin; Wagner, Stefan
Software repositories include information which can be made available for bug fixing or maintenance using repository mining. The identification of coupled changes have been proposed several times. Yet, existing studies focus on the found couplings and ignore feedback from developers. We investigate three development projects and their repositories to find files that frequently change together to support the software developers. We complement the coupled files information with details from the issue tracking system and the project documentation. We contrast our findings with feedback from the developers about how interesting our findings are for them. We found that the small size of the repositories made an insightful analysis difficult. The response to coupled changes both from experienced and inexperienced developers was mostly neutral. They accepted most of the additional attributes we presented. Furthermore, developers also suggested other additional issues to be relevant, e.g. the context of the coupled changes and the way they are presented, which we did not cover in this study. Therefore, coupled change analysis research will need to take the presentation and context information into account.
Open Access
Assessing iterative practical software engineering courses with play money
(2016) Mindermann, Kai; Ostberg, Jan-Peter; Wagner, Stefan
Changing our practical software engineering course from the previous waterfall model to a more agile and iterative approach created more severe assessment challenges. To cope with them we added an assessment concept based on play money. The concept not only includes weekly expenses to simulate real running costs but also investments, which correspond to assessment results of the submissions. This concept simulates a startup-like working environment and its financing in an university course. Our early evaluation shows that the combination of the iterative approach and the play money investments is motivating for many students. At this point we think that the combined approach has advantages from both the supervising and the students point of view. We planned more evaluations to better understand all its effects.
Open Access
Assessment of overload capabilities of power transformers by thermal modelling
(2011) Schmidt, Nicolas; Tenbohlen, Stefan; Skrzypek, Raimund; Dolata, Bartek
This contribution presents an approach to determine the overload capabilities of oil-cooled power transformers depending on the ambient temperature. For this purpose the investigated method introduces a simplified, empirical based thermal model that predicts changes in oil temperature with high accuracy. This model considers the entire transformer as a single, homogenous tempered body with a certain thermal capacity. All electrical losses are perceived as an input of equally distributed heat and assumed to be the sum of the load and no-load losses given by the transformer design. In contrary to earlier approaches the heat exchange with the ambience is modelled as a complex function depending first of all on the temperature difference between the transformer and its surroundings. Furthermore, the loading rate, material properties, levels of temperatures and emerging temperature gradients are taken into account as influencing factors determining the heat exchange. To display the behaviour of a specific transformer, the model employs several empirical factors. For determination of these empirical factors an evaluation time of two to four representative weeks of transformer operation is found to be sufficient. To validate the created model and test its operational reliability, measuring data from several ONAN- and ONAF-transformers are consulted. These data sets comprise the top oil and ambient temperature as well as the loading rate and the status of the cooling system. Furthermore, the corresponding name plate data is integrated. Subsequently to the calculation of the top oil temperature, the maximum constant loading rate resulting in a hot-spot temperature below critical level is determined based upon the remarks of IEC 60076 - 7 [1]. Finally, a characteristic linear function for each investigated transformer displaying the maximum loading rate depending solely on the ambient temperature is derived. In case of the investigated ONAN- and ONAF-transformers within a power range of 31.5 - 63 MVA, significant overload potentials could be disclosed.
Open Access
CASE - eine kritische Übersicht
(1989) Ludewig, Jochen
CASE ist aus dem Bedürfnis entstanden, den Prozeß der Software-Entwicklung durch Werkzeuge so zu unterstützen, daß die Produktivität gesteigert und die Qualität erhöht wird. Solche Werkzeuge sind auf der Basis moderner Rechner und Betriebssysteme möglich. Für die Interessenten ist es allerdings nicht leicht, die seriösen Produktinformationen von den überzogenen Werbesprüchen zu unterscheiden. Der Beitrag zielt zunächst darauf ab, das Wort CASE mit einem klaren Begriff zu verbinden. Der Zusammenhang zwischen Werkzeugen und Methoden wird ausführlich diskutiert. Weitere Schwerpunkte sind eine Übersicht der Werkzeuge, die unter den Begriff CASE fallen, eine Zusammenstellung der wichtigsten Anforderungen, eine Klassifikation von Werkzeugausstattungen und eine Diskussion ungelöster Probleme heutiger Werkzeuge. Einige Prognosen für die zukünftige Entwicklung des Software Engineerings schließen den Vortrag ab.
Open Access
A case study on artefact-based RE improvement in practice
(2015) Méndez Fernández, Daniel; Wagner, Stefan
Background: Most requirements engineering (RE) process improvement approaches are solution-driven and activity-based. They focus on the assessment of the RE of a company against an external norm of best practices. A consequence is that practitioners often have to rely on an improvement approach that skips a profound problem analysis and that results in an RE approach that might be alien to the organisational needs. Objective: In recent years, we have developed an RE improvement approach (called ArtREPI ) that guides a holistic RE improvement against individual goals of a company putting primary attention to the quality of the artefacts. In this paper, we aim at exploring ArtREPI’s benefits and limitations. Method: We contribute an industrial evaluation of ArtREPI by relying on a case study research. Results: Our results suggest that ArtREPI is well-suited for the establishment of an RE that reflects a specific organisational culture but to some extent at the cost of efficiency resulting from intensive discussions on a terminology that suits all involved stakeholders. Conclusions: Our results reveal first benefits and limitations, but we can also conclude the need of longitudinal and independent investigations for which we herewith lay the foundation.
Open Access
Cervical muscle reflexes during lateral accelerations
(2023) Millard, Matthew; Hunger, Susanne; Broß, Lisa; Fehr, Jörg; Holzapfel, Christian; Stutzig, Norman; Siebert, Tobias
Autonomous vehicles will allow a variety of seating orientations that may change the risk of neck injury during an accident. Having a rotated head at the time of a rear-end collision in a conventional vehicle is associated with a higher risk of acute and chronic whiplash. The change in posture affects both the movement of the head and the response of the muscles. We are studying the reflexes of the muscles of the neck so that we can validate the responses of digital human body models that are used in crash simulations. The neck movements and muscle activity of 21 participants (11 female) were recorded at the Stuttgart FKFS mechanical driving simulator. During the maneuver we recorded the acceleration of the seat and electromyographic (EMG) signals from the sternocleidomastoid (STR) muscles using a Biopac MP 160 system (USA). As intuition would suggest, the reflexes of the muscles of the neck are sensitive to posture and the direction of the acceleration.
Open Access
Characterization of automotive high voltage networks for EMI measurements
(2010) Reuter, Martin; Tenbohlen, Stefan; Köhler, Wolfgang
This paper deals with a method of determining the high-frequency impedances of automotive HV power networks (300 kHz - 200 MHz). A Vector Network Analyzer (VNA) is used to measure Scattering-Parameters of different HV power cables. Matrix conversions allow calculating an impedance network, which is able to represent automotive HV networks.
Open Access
Clone detection in automotive model-based development
(2008) Deißenböck, Florian; Hummel, Benjamin; Juergens, Elmar; Schätz, Bernhard; Wagner, Stefan; Girard, Jean-François; Teuchert, Stefan
Model-based development is becoming an increasingly common development methodology. In important domains like embedded systems already major parts of the code are generated from models specified with domain-specific modelling languages. Hence, such models are nowadays an integral part of the software development and maintenance process and therefore have a major economic and strategic value for the software-developing organisations. Nevertheless almost no work has been done on a quality defect that is known to seriously hamper maintenance productivity in classic code-based development: Cloning. This paper presents an approach for the automatic detection of clones in large models as they are used in model-based development of control systems. The approach is based on graph theory and hence can be applied to most graphical data-flow languages. An industrial case study demonstrates the applicability of our approach for the detection of clones in Matlab/Simulink models that are widely used in model-based development of embedded systems in the automotive domain.
Open Access
Comparison of rotor arrangements of Transverse Flux Machines for a robotic direct drive optimized by genetic algorithm and Regression Tree Method
(2023) Kaiser, Benedikt; Schmid, Martin; Parspour, Nejila
Articulated robotics applications typically have a demand for high torque at low speed. However, conventional electrical machines cannot generate a reasonable amount of torque directly by electro-magnetics. Therefore, gearboxes are used to convert speed and torque, accepting loss of mechanical power due to additional friction. Although geared solutions for robotic drive trains already offer exceedingly high torque densities, they are limited by the drawbacks of high reduction gears, such as non-linearities in friction, complex flexibility effects, and limited service life of mechanics in contrary to direct drive solutions. The Transverse Flux Machine with the high gravimetric torque density may be a solution for reducing or eliminating the need for a gearbox. Using a genetic algorithm, the proposed Transverse Flux Machines are optimized. To enhance the optimization’s speed, the machines’ calculations done by Finite-Element-Analysis of selected generations are replaced by a Regression Tree Model whose results are verified after a defined expired model service life with a subsequent adjustment of the model. The eligibility of different arrangements the Transverse Flux Machines’ rotor are compared regarding the application as low-speed direct drive in robotics, also compared to similar Radial Flux Machines. The optimized Transverse Flux Machines have a higher efficiency due to lower copper loss and a higher active gravimetric torque density. However, the Radial Flux Machines have higher total torques and power factors.
Open Access
Comprehensive comparison of a SiC MOSFET and Si IGBT based inverter
(2019) Nitzsche, Maximilian; Cheshire, Christoph; Fischer, Manuel; Ruthardt, Johannes; Roth-Stielow, Jörg
The investment which is necessary to replace Si IGBTs with SiC MOSFETs in medium to high power DC-AC inverters needs to be balanced carefully against the advantages SiC offers. This paper compares a 20 kW Si IGBT inverter with a 20 kW SiC MOSFET inverter. The power semiconductor components are operated identically in a modular half bridge module to ensure comparability. Thereby the measurement of the switching losses is explicitly not the focus but the overall efficiency while taking volume, current ripple, switching frequency and inductance into account. The limits of reasonable operating range shall be evaluated and an overview on the benefits of SiC on system level will be given.
Open Access
A comprehensive safety engineering approach for software-intensive systems based on STPA
(2015) Abdulkhaleq, Asim; Wagner, Stefan; Leveson, Nancy
Formal verification and testing are complementary approaches which are used in the development process to verify the functional correctness of software. However, the correctness of software cannot ensure the safe operation of safety-critical software systems. The software must be verified against its safety requirements which are identified by safety analysis, to ensure that potential hazardous causes cannot occur. The complexity of software makes defining appropriate software safety requirements with traditional safety analysis techniques difficult. STPA (Systems-Theoretic Processes Analysis) is a unique safety analysis approach that has been developed to identify system hazards, including the software-related hazards. This paper presents a comprehensive safety engineering approach based on STPA, including software testing and model checking approaches for the purpose of developing safe software. The proposed approach can be embedded within a defined software engineering process or applied to existing software systems, allow software and safety engineers integrate the analysis of software risks with their verification. The application of the proposed approach is illustrated with an automotive software controller.
Open Access
Computer-aided safety analysis of computer-controlled systems : a case example
(2000) Biegert, Uwe
Computer controlled systems consist of a complex interaction between technical process, human task and software. For the development of safety critical systems new method are required, which not only consider one of these parts of a computer-controlled system. In this paper a qualitative modeling method is presented. The method is called SQMA, Situationbased Qualitative Modeling and Analysis and it origin goes back to Qualitative Reasoning. First, all parts of a system are modeled separated and then combined to a unique model of a computer-controlled system. With this qualitative model a computer supported hazard analysis can be realised.
Open Access
A controlled experiment for the empirical evaluation of safety analysis techniques for safety-critical software
(2015) Abdulkhaleq, Asim; Wagner, Stefan
Context: Today's safety critical systems are increasingly reliant on software. Software becomes responsible for most of the critical functions of systems. Many different safety analysis techniques have been developed to identify hazards of systems. FTA and FMEA are most commonly used by safety analysts. Recently, STPA has been proposed with the goal to better cope with complex systems including software. Objective: This research aimed at comparing quantitatively these three safety analysis techniques with regard to their effectiveness, applicability, understandability, ease of use and efficiency in identifying software safety requirements at the system level. Method: We conducted a controlled experiment with 21 master and bachelor students applying these three techniques to three safety-critical systems: train door control, anti-lock braking and traffic collision and avoidance. Results: The results showed that there is no statistically significant difference between these techniques in terms of applicability, understandability and ease of use, but a significant difference in terms of effectiveness and efficiency is obtained. Conclusion: We conclude that STPA seems to be an effective method to identify software safety requirements at the system level. In particular, STPA addresses more different software safety requirements than the traditional techniques FTA and FMEA, but STPA needs more time to carry out by safety analysts with little or no prior experience.
Open Access
CorefAnnotator : a new annotation tool for entity references
(2018) Reiter, Nils
Open Access
Designing for noticeability: understanding the impact of visual importance on desktop notifications
(2022) Müller, Philipp; Staal, Sander; Bâce, Mihai; Bulling, Andreas
Desktop notifications should be noticeable but are also subject to a number of design choices, e.g. concerning their size, placement, or opacity. It is currently unknown, however, how these choices interact with the desktop background and their influence on noticeability. To address this limitation, we introduce a software tool to automatically synthesize realistically looking desktop images for major operating systems and applications. Using these images, we present a user study (N=34) to investigate the noticeability of notifications during a primary task. We are first to show that visual importance of the background at the notification location significantly impacts whether users detect notifications. We analyse the utility of visual importance to compensate for suboptimal design choices with respect to noticeability, e.g. small notification size. Finally, we introduce noticeability maps - 2D maps encoding the predicted noticeability across the desktop and inform designers how to trade-off notification design and noticeability.
Open Access
Detecting protagonists in German plays around 1800 as a classification task
(2018) Reiter, Nils; Krautter, Benjamin; Pagel, Janis; Willand, Marcus
In this paper, we aim at identifying protagonists in plays automatically. To this end, we train a classifier using various features and investigate the importance of each feature. A challenging aspect here is that the number of spoken words for a character is a very strong baseline. We can show, however, that a) the stage presence of characters and b) topics used in their speech can help to detect protagonists even above the baseline.
Open Access
Does outside-in teaching improve the learning of object-oriented programming?
(2015) Janke, Erica; Brune, Philipp; Wagner, Stefan
Object-oriented programming (OOP) is widely used in the software industry and university introductory courses today. Following the structure of most textbooks, such courses frequently are organised starting with the concepts of imperative and structured programming and only later introducing OOP. An alternative approach is to begin directly with OOP following the Outside-In teaching method as proposed by Meyer. Empirical results for the effects of Outside-In teaching on students and lecturers are sparse, however. We describe the conceptual design and empirical evaluation of two OOP introductory courses from different universities based on Outside-In teaching. The evaluation results are compared to those from a third course serving as the control group, which was taught OOP the "traditional" way. We evaluate the initial motivation and knowledge of the participants and the learning outcomes. In addition, we analyse results of the end- term exams and qualitatively analyse the results of interviews with the lecturers and tutors. Regarding the learning outcomes, the results show no signif- icant differences between the Outside-In and the “traditional” teaching method. In general, students found it harder to solve and implement algorithmic problems than to understand object oriented (OO) concepts. Students taught OOP by the Outside-In method, however, were less afraid that they would not pass the exam at the end of term and understood the OO paradigm more quickly. Therefore, the Outside-In method is no silver bullet for teaching OOP regarding the learning outcomes but has positive effects on motivation and interest.
Open Access
Dynamic ontology supported user interface for personalized decision support
(2012) Bosch, Harald; Thom, Dennis; Heinze, Geoffrey-Alexeij; Wokusch, Stefan; Ertl, Thomas
European citizens are increasingly aware of the influence of air quality and weather on their health and quality of life. At the same time, more environmental information is freely available through a plethora of websites, dedicated portals, and web services. In order to exploit these data for personal decisions one has to identify, retrieve, and combine the information that is relevant to one's personal situation, planned activity, and information need. Often, this task is hindered by different data formats, display styles and data resolutions. The PESCaDO system is a web-based decision support system addressing this issue. The inquiry to the system, as well as the system's result, can cover a broad range of environmental aspects and personal situations and is therefore quite complex. In this work we present a novel approach on how the system can actively assist users in all steps of the decision making process, especially by enhancing the user interaction. This approach combines an intelligent dialog steering method based on analyzing the domain ontology with flexible, dynamic data visualizations for a situation depending orchestration of data sources. Both aspects have been evaluated in on-line user studies, as well as with an expert evaluation of the whole system.