05 Fakultät Informatik, Elektrotechnik und Informationstechnik
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/6
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Item Open Access Dynamic ontology supported user interface for personalized decision support(2012) Bosch, Harald; Thom, Dennis; Heinze, Geoffrey-Alexeij; Wokusch, Stefan; Ertl, ThomasEuropean 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.Item Open Access The Quamoco product quality modelling and assessment approach(2012) Wagner, Stefan; Lochmann, Klaus; Heinemann, Lars; Kläs, Michael; Trendowicz, Adam; Plösch, Reinhold; Seidl, Andreas; Goeb, Andreas; Streit, JonathanPublished software quality models either provide abstract quality attributes or concrete quality assessments. There are no models that seamlessly integrate both aspects. In the project Quamoco, we built a comprehensive approach with the aim to close this gap. For this, we developed in several iterations a meta quality model specifying general concepts, a quality base model covering the most important quality factors and a quality assessment approach. The meta model introduces the new concept of a product factor, which bridges the gap between concrete measurements and abstract quality aspects. Product factors have measures and instruments to operationalise quality by measurements from manual inspection and tool analysis. The base model uses the ISO 25010 quality attributes, which we refine by 200 factors and 600 measures for Java and C# systems. We found in several empirical validations that the assessment results fit to the expectations of experts for the corresponding systems. The empirical analyses also showed that several of the correlations are statistically significant and that the maintainability part of the base model has the highest correlation, which fits to the fact that this part is the most comprehensive. Although we still see room for extending and improving the base model, it shows a high correspondence with expert opinions and hence is able to form the basis for repeatable and understandable quality assessments in practice.Item Open Access Experiences with applying STPA to software-intensive systems in the automotive domain(2013) Abdulkhaleq, Asim; Wagner, StefanHazard analysis is one of the most important elements in developing safe-critical systems. STPA (Systems-Theoretic Process Analysis) is a modern technique based on the new accident causation model STAMP (System-Theoretic Accident Model and Process) for analyzing hazard and safety issues, which can be applied early in the design process of a system to achieve an acceptable risk level. We have applied STPA to a well-known example of safety-critical systems in the automotive industries: Adaptive Cruise Control (ACC). The results of the application of STPA to our case study and the limitations and difficulties of applying STPA are presented.Item Open Access The use of application scanners in software product quality assessment(2011) Wagner, StefanSoftware development needs continuous quality control for a timely detection and removal of quality problems. This includes frequent quality assessments, which need to be automated as far as possible to be feasible. One way of automation in assessing the security of software are application scanners that test an executing software for vulnerabilities. At present, common quality assessments do not integrate such scanners for giving an overall quality statement. This paper presents an integration of application scanners into a general quality assessment method based on explicit quality models and Bayesian nets. Its applicability and the detection capabilities of common scanners are investigated in a case study with two open-source web shops.Item Open Access Einfluss der Abschlussimpedanz von Hochvoltkabeln auf Funkstörgrößen in elektrisch angetriebenen Kraftfahrzeugen(2012) Reuter, Martin; Waible, Manuel; Tenbohlen, Stefan; Köhler, WolfgangIn diesem Beitrag wird die Frage untersucht, welche Auswirkung die Fehlanpassung von Kfz-Hochvoltkabeln auf EMV-Störgrößen in der Komponentenmessung nach CISPR 25 hat.Item Open Access Assessment of overload capabilities of power transformers by thermal modelling(2011) Schmidt, Nicolas; Tenbohlen, Stefan; Skrzypek, Raimund; Dolata, BartekThis 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.Item Open Access Suitability of ultra high frequency partial discharge measurement for quality assurance and testing of power transformers(2013) Tenbohlen, Stefan; Siegel, Martin; Beltle, Michael; Reuter, MartinWell known reasons for local failures in power transformers are caused by partial discharges (PD) in the electric insulation. Continuous deterioration over time increases the defect which finally can lead to a breakdown of the entire insulation. The importance of PD measurement is accommodated by standardized electrical measurement according to IEC 60270 [1] which is required for acceptance certificates at routine testing. Therefore, the apparent charge QIEC has become an important value for transformer quality. Since a couple of years, alternative measurement methods for PD are used. Originally developed for gas insulated systems [2], [3], ultra high frequency (UHF) measurement found its way into transformer diagnosis over the last years [4]. To become an accepted quality factor, UHF has to be proven a reliable testing method, which can bear up against electrical measurements. Therefore, the general physics of UHF PD has to be considered at first. Ultra-high-frequency antennas measure electromagnetic emissions of PD directly in-oil inside a transformer. It becomes apparent, that UHF measurement usually is advantageous concerning external disturbances. Compared to the electric measurement, the UHF method is robust against external signals [5], which makes it suitable for both, offsite measurement at routine testing under laboratory conditions with low ambient noise and onsite, e.g. after transportation and installation of transformers with usually high noise levels. These considerations make the UHF method interesting as supplement for transformer routine tests. Therefore, a sensor calibration or at least a validation of its sensitivity is required [6] comparable to the electrical measurement. To provide profound knowledge of the equipment, the antenna factor (AF) of the UHF sensor needs to be determined under inside-transformer conditions. This contribution shows the determination of the UHF sensor’s AF using a Gigahertz-Transversal-Electro-Magnetic Setup (GTEM cell). To meet inside-transformer conditions, an oil-filled GTEM cell is required for correct permittivity. Correction factors can then be introduced to minimize measurement errors and to establish better comparability of different UHF sensors. Hence, a standard test setup can be defined.Item Open Access Influence of termination impedance on conducted emissions in automotive high voltage networks(2012) Reuter, Martin; Tenbohlen, Stefan; Köhler, WolfgangThis contribution investigates the effect of changed network topologies within HV systems on component level EMC tests. Therefore the recent state of art in component level testing is presented and the differences of LV and HV network topologies are discussed. An adaption of the component level test setup for HV components is introduced and a minimized HV system investigated. Results of a case study on an inverter for a hybrid car are presented and the impact of the measurements in the design of HV systems will be discussed.Item Open Access Water saturation limits and moisture equilibrium curves of alternative insulation systems(2011) Tenbohlen, Stefan; Jovalekic, Mark; Bates, Lisa; Szewczyk, RadoslawA method developed for establishing moisture equilibrium curves for any combination of liquid and solid insulation is presented in this paper. Moisture saturation curves for natural and synthetic esters have been presented in the temperature range up to 140°C together with curve for mineral oil as a reference. Sorption isotherms have been established for cellulose based and aramid fiber based materials. Eventually, the moisture equilibrium diagrams have been created for given combinations of solids and liquids. Moisture equilibrium curves have been created for combinations of mineral oil and ester fluids with aramid fiber based papers and boards, as they are commonly used in alternative insulation systems. The new curves give information on moisture distribution within the alternative insulation systems and may be critical for setting the material choices, design rules and maintenance guidelines for equipment using these combinations. Only then the materials could be used optimally and their specific characteristics could bring full range of benefits to the equipment. Also the condition monitoring and diagnostics for the purpose of asset management will be more reliable when these new characteristics are used. It has been observed that insulation components made of aramid insulation may have lower water content comparing to cellulose based conventional materials at the same water content measured in dielectric liquid. As a result, the performance of aramid insulation components may be less sensitive to moisture in oil (aging processes, dielectric strength, partial discharge performance) comparing to conventional systems based on cellulose.Item Open Access Naming the pain in requirements engineering: design of a global family of surveys and first results from Germany(2013) Méndez Fernández, Daniel; Wagner, StefanContext: For many years, we have observed industry struggling in defining a high quality requirements engineering (RE) and researchers trying to understand industrial expectations and problems. Although we are investigating the discipline with a plethora of empirical studies, those studies either concentrate on validating specific methods or on single companies or countries. Therefore, they allow only for limited empirical generalisations. Objective: To lay an empirical and generalisable foundation about the state of the practice in RE, we aim at a series of open and reproducible surveys that allow us to steer future research in a problem-driven manner. Method: We designed a globally distributed family of surveys in joint collaborations with different researchers from different countries. The instrument is based on an initial theory inferred from available studies. As a long-term goal, the survey will be regularly replicated to manifest a clear understanding on the status quo and practical needs in RE. In this paper, we present the design of the family of surveys and first results of its start in Germany. Results: Our first results contain responses from 30 German companies. The results are not yet generalisable, but already indicate several trends and problems. For instance, a commonly stated problem respondents see in their company standards are artefacts being underrepresented, and important problems they experience in their projects are incomplete and inconsistent requirements. Conclusion: The results suggest that the survey design and instrument are well-suited to be replicated and, thereby, to create a generalisable empirical basis of RE in practice.