Open-Access-Journals @ Otto-von-Guericke-Universität Magdeburg
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On the Stability of Direct Spring-Operated Pressure Relief Valves: Impact of Frozen Mixture Flow and Lift Restriction
No full textThe current work explores the effect of (frozen) mixture flow and lift restriction on the stability of direct spring-operated pressure relief valves. First, we study the effect of frozen mixture (constant mass fraction) flow through a pressure relief valve with upstream piping. DIER\u27s technique is employed to cope with the mixture parameters, notably sonic velocity and choked/non-choked flow through the nozzle. By means of one-dimensional simulation, we show that the change in sonic velocity plays a fundamental role in both the valve opening time and its stability. Due to the extremely low sonic velocities in certain range of water-air mass fraction, such valves will have a poor response time (slow opening) and chatter even for short inlet pipings. Next, we investigate the possibility of improving the dynamical performance of the safety valve by using a larger valve (i.e., a larger orifice) with a restricted lift option while keeping the vented mass flow rate through the valve constant. Our numerical investigations reveal that the additional restoring force emerging from the valve restriction at the upper stopper improves the stability behaviour in the case of gas applications but can hardly have any influence in the case of liquid service
Genug bezahlbarer und zukunftsfähiger Wohnraum für alle: Suffizienzansätze für das Bauen und Wohnen
No full textSuffizienz zielt im Handlungsfeld Bauen und Wohnen darauf ab, die Bedürfnisse der Menschen nach attraktivem und bezahlbarem Wohnen unter Einhaltung lokaler und globaler ökologischer Grenzen zu befriedigen und damit neue Wege für die Bau- und Wohnwende aufzuzeigen. Neben der Bestandsentwicklung vor Neubau sind die Reduktion der Pro-Kopf-Wohnfläche, die Anpassbarkeit, Lowtech und einfaches Bauen sowie das energie- und ressourcensparende Nutzungsverhalten weitere Schwerpunktthemen für die Umsetzung von Gebäudesuffizienz. Im Anschluss an die Diskussion dieser Maßnahmen werden in einem Ausblick acht politische Handlungsfelder benannt, in denen Suffizienz im Gebäudebereich durch die Bundesebene unterstützt werden kann.In the field of action of building and housing, sufficiency aims at satisfying people\u27s needs for attractive and affordable housing while respecting local and global ecological limits and to show new ways for the transformation of building and housing. In addition to the development of existing buildings before new construction, the reduction of per-capita living space, adaptability, low-tech and simple construction, as well as energy- and resource-saving user behavior are further key issues for the implementation of building sufficiency. After discussing these measures, the outlook names eight political fields of action in which sufficiency in the building sector can be supported by the federal level
Challenges of initial TVET teacher training in Indonesia: Empirical Analysis of Skills Deficit of Mechanical Engineering Teachers
No full textThe fulfillment of competent secondary vocational school (SMK) teachers needs in accordance with the requirements and standards of teacher competence in Indonesia has not yet been carried out according to expectations. This research seeks to find out more about what skills deficit are possessed by prospective vocational teachers who have just graduated from university and to find out more deeply what are the factors that influence these skills deficit. Prospective vocational teachers who will serve in secondary vocational schools (SMKs) at this time need a long adaptation process before being able to teach at each level of competence according to their competence. Based on the research question, "what kind of skills deficit and its factors influence, owned by prospective mechanical engineering teachers related to the school needs for competent teachers inWest Java?" the implementation of the teaching internship program for prospective vocational teachers as well as the learning process carried out at the TVET faculty will be the starting point for this research. Problem-Centred Interviews (PCI) have been conducted with the supervisor teachers in the teaching internship program (n=10) and lecturers who teach practical courses at the TVET faculty (n=10) with an approach to the process carried out on teaching internship program activities for prospective vocational teachers in SMKs and an approach to the practical learning process carried out at the TVET faculty in order to prepare prospective vocational teachers according to the needs of SMKs. These interviews have been evaluated using the methods of inductive category formation, the forms of analysis of qualitative content analysis about kind of skills deficit and its factors influence reconstructed, interpreted and summarized in a catalogue of criteria. From the result of the analysis, it is found out that the prospective teachers ready to teach in basic competence subjects at schools are not yet ready for advanced levels of competence in respective subjects. The interview results also show that there is no systematic approach to assure the quality of the graduates based on the standard until now since there is no third-party assessment for university students. For that reason there is no assurance that the prospective teachers have enough competence for becoming a TVET teacher in SMKs
Artificial Intelligence and Fuzzy Logic in modern Human Resource Management
No full textThe corporate environment is always characterized by a high degree of volatility, uncertainty, complexity and ambiguity. These aspects influence Human Resource Management (HRM) just like other areas of the company. In the context of decision problems, especially in HRM, it is not always possible to specify all the considered variables precisely. A suitable instrument to deal with such fuzzy conditions is Fuzzy Logic (FL). This paper aims to give insights into this field and its possible applications in HRM. For this purpose, selected theoretical foundations from the areas of HRM, FL and Artificial Intelligence (AI) are presented first. Based on this, situations in HRM are shown in which it can be useful to include FL in decision calculations. These concern e.g. problems of personnel allocation or considerations on the segmentation of labor forces. The paper is aimed at both practitioners and scholars
Closed-form series solutions to peridynamic rod equations: Influence of kernel function
No full textPeridynamics is a generalized continuum theory that takes into account long range internal force/moment interactions.The aim of this paper is to derive closed form analytical solutions for peridynamic rod equations with fixed-fixed and fixed-freeboundary conditions. A family of kernel functions is introduced to analyze the influence on the results for rods under distributedstatic load and free vibrations for different initial conditions. To validate the derived solutions, nonlocal results are comparedagainst classical results for different boundary conditions and horizon sizes. One can observe that when the horizon size approacheszero, the results according the non-local and local theories converge to each other. Introduced kernels indeed play different roles inboth statics and dynamics. In particular, the Gauss type kernel function gives the results which are closest to the classical solutions
Defuzzification in Scenario Management: A theoretical and practical Guide
No full textIt is virtually a truism that companies should respond to situations of high complexity, dynamics and contingency with strategic management measures. Not least in turbulent VUCA-type environments, the company is well advised to use alternative scenarios for environmental forecasting. The so-called scenario technique is used for this purpose. Human modes of thought, judgment and action are often ambiguous and rarely univocal. Here, so-called expert (control) systems based on fuzzy control offer valuable help. Their core is rule inference resulting in fuzzy rule output. In many cases, however, managers are interested in receiving concrete recommendations for action that are as unambiguous as possible. To do so, they need to defuzzify the fuzzy output set. In this paper, we consider selected defuzzification procedures in the area of scenario management
Virtuelle Kraftwerke im Verteilnetz: Systemstützender Betrieb im wirtschaftlichen Kontext : eine gesamtheitliche Betrachtung Virtueller Kraftwerke
No full textMit der Zunahme von dezentralen, volatilen erneuerbaren Energien steigt auch die Schwierigkeit zur Stabilisierung des Energiesystems Strom. Insbesondere durch den Wegfall von konventionellen Kraftwerken ist es notwendig, geeignete Steuerungskonzep-te zu őnden und Systemdienstleistungen auch aus erneuerbaren Energien bereitzustellen, um ein zuverlässiges und stabiles System zu gewährleisten. Die vorliegende Dissertation liefert mit dem Konzept des Virtuellen Kraftwerks einen Ansatz zur Bündelung von kleinen, dezentralen, erneuerbaren Energien-Anlagen der Mittel- und Niederspannung. Mit dem hier vorgestellten Virtuellen Kraftwerk wird der große Nutzen von gepoolten Anlagen in den Prozessen der Netzbetreiber aufgezeigt und das Gesamtverständnis des techno-ökonomischen Stromsystems erweitert. Darüber hinaus liefert diese Dissertation die Least-Squares-Kombiprognose zur Verbesserung der PV- und Wind-Einspeiseprognose. Den Kernbeitrag stellt die Entwicklung und algorithmische Umsetzung von netzdienlichen Betriebsführungskonzepten für das Virtuelle Kraftwerk dar. Diese zielen auf die Maximierung der Bereitstellung von Regelleistung, Redispatchvermögen und auf die Einhaltung des Day-Ahead-Fahrplans ab. Zudem werden wirtschaftliche Betriebskonzepte umgesetzt, die als ökonomischer Maßstab zur Bewertung der netzdienlichen Konzepte herangezogen werden. Anhand eines exemplarischen Virtuellen Kraftwerks werden die Algorithmen getestet und der große Nutzen der Betriebskonzepte sowie eine Wirtschaftlichkeit (auch ohne EEG-Förderung) nachgewiesen. Abschließend liefern die Analysen Anhand eines Mittelspannungstestnetzes eine Einordnung des Virtuellen Kraftwerkbetriebs in die Netzbetriebsführung. Zu diesem Zweck wird das Cigré-Benchmarknetz rein mit erneuerbaren Energien und Lasten auf Basis von statistischen Werten von EE-dominierten Verteilnetzbetreibern parametrisiert
Farbsortierroboter für Socken
No full textDas Seminarprojekt der Fakultät für Elektrotechnik und Informationstechnik der Otto-von-Guericke-Universität Mag-deburg findet im Wintersemester eines jeden Studienjahres statt. An diesem Projekt müssen Studierende teilnehmen, die jeweils eine Projektgruppe aus zwei Studierenden wählen. Jede Gruppe findet ihr eigenes Projekt und muss dieses vor den Dozenten und anderen Studenten präsentieren. Mein Team wird an einem Projekt zur Farbkorrektur der Farben Rot, Gelb und Blau mit Hilfe eines LEGO-MINDSTORMS-EV3 arbeiten
Addressing wind comfort in an urban area using an immersed boundary framework
No full textConsidering wind, air and heat comfort in designing new urban areas is still a challenge for city planners. Urban heat islands, or the phenomena of locally increased temperatures in urban areas compared to their rural surroundings, are becoming increasingly problematic with global warming and the rise of urbanization. Therefore, new areas must be planned considering appropriate ventilation to mitigate these high-temperature regions and cooling strategies, such as green infrastructures, must be considered. Typically, most of the comfort criteria are evaluated and assessed in the final stages of urban planning when further strategic interventions are no longer possible. Here, a numerical framework is tested that urban planners can use as a future tool to analyze complex fluid dynamics and heat transfer in the early stages of urban planning. The framework solves the RANS equations using an immersed boundary approach to discretize the complex urban topography in a cartesian octree grid. The grid is automatically generated, eliminating the complex pre-processing of urban topographies and making the framework accessible to all users. The results are validated against experimental data from wind tunnel measurements of wind-driven ventilation in street canyons. After validation, we will apply the numerical framework to estimate the wind comfort in an idealized urban area. Finally, guidelines will be provided on the choice of minimum grid sizes required to capture the relevant flow structures inside a canyon accurately
Performance of hybrid turbulence models in OpenFOAM for numerical simulations of a confined backward-facing step flow at low Prandtl number
No full text/To date, numerical simulation of complex turbulent flows with separation remains challenging. On the one hand,turbulence models in Reynolds-averaged Navier-Stokes (RANS) equations struggle with correctly representing turbulent momentum transfer in such flows, whereas turbulence-resolving techniques such as large-eddy simulations (LES) carry high computational cost on the other hand. Alternatively, hybrid RANS–LES turbulence models promise to deliver scale-resolving accuracy at acceptable computational cost, yet their accuracy remains highly dependent on simulation setup and flow conditions. Here, we investigate hybrid turbulence models readily available in OpenFOAM, and benchmark their performance to Reynolds-averaged approaches and turbulence-resolving high-fidelity reference data for a confined backward-facing step flow at low Prandtl number and relatively low Reynolds number. Although temperature is generally well predicted by all considered setups, a comparison between RANS and LES shows that turbulence resolution can increase the accuracy for the considered flow case. Results show that scale-adaptive simulation techniques do not produce resolved turbulence and fail to outperform the baseline Reynolds-averaged simulations for the considered case. In contrast, detached-eddy variants do resolve turbulence in the separated shear layer, yet some configurations suffer from modeled-stress depletion due to late development of resolved turbulence. A grid coarsening study compares the degradation of accuracy for each approach, showcasing robustness of the standard RANS approach and the good performance of full LES even at surprisingly coarse resolutions. For each grid, the best-performing setup was either a RANS or an LES approach, but never a hybrid turbulence model setup. Finally, a Reynolds-number sensitivity is presented, indicating that resolved turbulence development is promoted at higher Reynolds numbers, thus leading to setups more amenable to hybrid turbulence models.