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Error analysis in a high accuracy sampled-data velocity stabilising system using Volterra series
(2015)
This paper presents a new method of analysing the error of a sampled-data velocity stabilising system with a wide range of pulse width modulation. The analysis is based on multi-channel model obtained as a result of approximation of pulse-modulated signal at the output of a PWM converter. Approximation of piecewise-linear modulation characteristics of each channel has been obtained as a series expansion of Hermite polynomials where the expansion comprises two polynomials of the first and third orders. The transfer function of every channel and a closed-loop system has been obtained using multidimensional Z-transform. The analytical expression of an error under impact of a step input has been derived using a transfer function of the closed-loop system. A dc electric drive has been used as an example of high accuracy sample-data stabilising system to verify and demonstrate the proposed method.
This paper presents a new method of analysing the error of a sampled-data velocity stabilising system with a wide range of pulse width modulation. The analysis is based on multi-channel model obtained as a result of approximation of pulse-modulated signal at the output of a PWM converter. Approximation of piecewise-linear modulation characteristics of each channel has been obtained as a series expansion of Hermite polynomials where the expansion comprises two polynomials of the first and third orders. The transfer function of every channel and a closed-loop system has been obtained using multidimensional Z-transform. The analytical expression of an error under impact of a step input has been derived using a transfer function of the closed-loop system. A dc electric drive has been used as an example of high accuracy sample-data stabilising system to verify and demonstrate the proposed method.
Turbulent compressible flows are traditionally simulated using explicit Eulerian time integration applied to the Navier-Stokes equations. However, the associated Courant-Friedrichs-Lewy condition severely restricts the maximum time step size. Exploiting the Lagrangian nature of the Boltzmann equation's material derivative, we now introduce a feasible three-dimensional semi-Lagrangian lattice Boltzmann method (SLLBM), which elegantly circumvents this restriction. Previous lattice Boltzmann methods for compressible flows were mostly restricted to two dimensions due to the enormous number of discrete velocities needed in three dimensions. In contrast, this Rapid Communication demonstrates how cubature rules enhance the SLLBM to yield a three-dimensional velocity set with only 45 discrete velocities. Based on simulations of a compressible Taylor-Green vortex we show that the new method accurately captures shocks or shocklets as well as turbulence in 3D without utilizing additional filtering or stabilizing techniques, even when the time step sizes are up to two orders of magnitude larger compared to simulations in the literature. Our new method therefore enables researchers for the first time to study compressible turbulent flows by a fully explicit scheme, whose range of admissible time step sizes is only dictated by physics, while being decoupled from the spatial discretization.
This work thoroughly investigates a semi-Lagrangian lattice Boltzmann (SLLBM) solver for compressible flows. In contrast to other LBM for compressible flows, the vertices are organized in cells, and interpolation polynomials up to fourth order are used to attain the off-vertex distribution function values. Differing from the recently introduced Particles on Demand (PoD) method , the method operates in a static, non-moving reference frame. Yet the SLLBM in the present formulation grants supersonic flows and exhibits a high degree of Galilean invariance. The SLLBM solver allows for an independent time step size due to the integration along characteristics and for the use of unusual velocity sets, like the D2Q25, which is constructed by the roots of the fifth-order Hermite polynomial. The properties of the present model are shown in diverse example simulations of a two-dimensional Taylor-Green vortex, a Sod shock tube, a two-dimensional Riemann problem and a shock-vortex interaction. It is shown that the cell-based interpolation and the use of Gauss-Lobatto-Chebyshev support points allow for spatially high-order solutions and minimize the mass loss caused by the interpolation. Transformed grids in the shock-vortex interaction show the general applicability to non-uniform grids.
Off-lattice Boltzmann methods increase the flexibility and applicability of lattice Boltzmann methods by decoupling the discretizations of time, space, and particle velocities. However, the velocity sets that are mostly used in off-lattice Boltzmann simulations were originally tailored to on-lattice Boltzmann methods. In this contribution, we show how the accuracy and efficiency of weakly and fully compressible semi-Lagrangian off-lattice Boltzmann simulations is increased by velocity sets derived from cubature rules, i.e. multivariate quadratures, which have not been produced by the Gauss-product rule. In particular, simulations of 2D shock-vortex interactions indicate that the cubature-derived degree-nine D2Q19 velocity set is capable to replace the Gauss-product rule-derived D2Q25. Likewise, the degree-five velocity sets D3Q13 and D3Q21, as well as a degree-seven D3V27 velocity set were successfully tested for 3D Taylor-Green vortex flows to challenge and surpass the quality of the customary D3Q27 velocity set. In compressible 3D Taylor-Green vortex flows with Mach numbers Ma={0.5;1.0;1.5;2.0} on-lattice simulations with velocity sets D3Q103 and D3V107 showed only limited stability, while the off-lattice degree-nine D3Q45 velocity set accurately reproduced the kinetic energy provided by literature.
Bionik
(2020)
Wie machen die das… kann angesichts der erstaunlichen Fähigkeiten mancher Lebewesen gefragt werden. Die Bionik fragt noch weiter …und wie kann man das nachmachen? Hier liegt ein Schwerpunkt dieses Lehrbuches, das die Bionik nicht nur an zahlreichen Beispielen erklärt, sondern auch eine Vorgehensweise für die Identifizierung biologischer Lösungen und deren Übertragung auf technische Anwendungen vermittelt. Basisinformationen der Biologie und Grundlagen der Konstruktionstechnik gewährleisten einen leichten Zugang zum Stoff. Mit dem 3D-Druck als Schlüsseltechnologie und der Thematisierung der Nachhaltigkeit geht das Buch zudem auf aktuelle Entwicklungen ein. Dieser ganzheitliche Blick auf die Bionik soll den Leser zur Durchführung bionischer Projekte befähigen und motivieren. (Verlagsangaben)
The most important component of a closed-loop industrial control system is the communication unit located between a digital controller and the object being controlled. A pulse converter is usually used for this purpose in systems operating under pulse width modulation. However the dynamic characteristics of the converter bring a significant impact on the quality of the system regulation. This article discusses the design and implementation a closed-loop digital automatic control system for a zero-current switching quasi-resonant boost converter. It enables a high-speed transient process of the controlled object voltage having the advantages provided by pulse methods of electrical energy conversion. This paper also presents the simulation and experimental verification of the proposed approach.
Sensor systems for machine monitoring (energy monitoring, condition monitoring) can be built up from available low cost components. The Raspberry Pi, being a miniature PC, is well suited to collect and save data, to control a human machine interface and make the connection to the Web via Ethernet. Metering the energy of a 3 phase power line can be done by an energy metering sensor combined with an Arduino Uno microcontroller. The used sensor ADE7758 can do energy and power measurement with about 1% accuracy. Autonomous, wireless sensors working on energy harvesting principles complement the system by measuring additional physical quantities and building a sensor network distributed over the machine. The use of programmable sensors is necessary to analyze measured data and transmit only a few specific values, thus having a minimum number of transmitted bytes.
This paper provides a performance analysis of a wearable photovoltaic system mounted on the outer surface of a backpack. Three types of photovoltaic materials, commonly used for electricity generation, have been investigated under various conditions including sun irradiance, angle-of-incidence and sun inclination. The results of the investigation have shown that the system equipped with the rigid mono-Si panels performs 3.5 to 4.9 times better than the system equipped with a-Si flexible PV modules. The average power generated by the wearable photovoltaic system is about 30% of the maximum installed power for any photovoltaic type. This paper presents the test data resulting from the evaluation of the daily energy production of a wearable photovoltaic power supply.
This paper proposes a new artificial neural network-based maximum power point tracker for photovoltaic application. This tracker significantly improves efficiency of the photovoltaic system with series-connection of photovoltaic modules in non-uniform irradiance on photovoltaic array surfaces. The artificial neural network uses irradiance and temperature sensors to generate the maximum power point reference voltage and employ a classical perturb and observe searching algorithm. The structure of the artificial neural network was obtained by numerical modelling using Matlab/Simulink. The artificial neural network was trained using Bayesian regularisation back-propagation algorithms and demonstrated a good prediction of the maximum power point. Relative number of Vmpp prediction errors in range of ±0.2V is 0.05% based on validation data.
This paper proposes a new artificial neural network-based position controller for a full-electric injection moulding machine. Such a controller improves the dynamic characteristics of the positioning for hot runners, pin valve and the injection motors for varying moulding parameters. Practical experimental data and Matlab’s System Identification Toolbox have been used to identify the transfer functions of the motors. The structure of the artificial neural network, which used positioning error and speed of error, was obtained by numerical modelling in Matlab/Simulink. The artificial neural network was trained using back-propagation algorithms to provide control of the motor current thus ensuring the required position and velocity. The efficiency of the proposed ANN-based controller has been estimated and verified in Simulink using real velocity data and the position of the injection moulding machine and pin valve motors.
We present the development and evaluation of a basic building block for a future wireless sensor network for agriculture monitoring in Argentina. The module consists of a compact battery-powered wireless sensor node capable of monitoring the ambient air parameters of temperature, humidity, gas and air pressure in the agriculture industry of Argentina's Pampa region. Further in-and outputs allow the system to be extended flexibly by adding more sensors. Throughout the development, a simple, low-cost and open-source-based approach together with a lightweight communication protocol was pursued. The sensor nodes cover ranges of over 400 metres and can be operated on two AAA alkaline batteries for several years. Detailed current consumption values, range limits and battery life estimates are presented.
Cost efficient energy monitoring in existing large buildings demands for autonomous indoor sensors with low power consumption, high performance in multipath fading channels and economic implementation. Good performance in multipath fading channels can be achieved with noncoherent chaotic modulation schemes such as chaos on-off keying (COOK) or differential chaos shift keying (DCSK). While COOK stands out in the area of power consumption, DCSK excels when it comes to its performance in noisy and multipath fading channels. This paper evaluates a combination of both schemes for autonomous indoor sensors. The simulation results show 50% less power consumption than DCSK and more than 3dB SNR gain in Rayleigh fading channels at BER=10-3 as compared to COOK, making it a promising candidate for low power transmission in autonomous wireless indoor sensors. We further present an enhanced version of this scheme showing another 1 dB SNR improvement, but at 25% less power consumption than DCSK.
Die Erfindung betrifft eine elektrische Insektenabwehrvorrichtung (1) zur Abwehr kriechender Insekten (2) umfassend eine Spannungserzeugungseinrichtung (4a, 4b) zur Erzeugung einer Abwehrspannung sowie umfassend zumindest zwei nebeneinander angeordnete und beabstandet zueinander verlaufende blanke elektrische Leiter (5a, 5b, 5c, 5d), die derart mit der Spannungserzeugungseinrichtung (4a, 4b) verbunden sind, dass die Abwehrspannung zwischen ihnen liegt. Die elektrischen Leiter sind als flache Leiterbahnen (5a, 5b, 5c, 5d) auf oder in der Oberfläche eines gemeinsamen Trägers (12, 13, 50, 60) ausgebildet, so dass ein Insekt (2) bei einem Berühren der Leiterbahnen (5a, 5b, 5c, 5d) einen elektrischen Schlag erhält.
Im Rahmen eines Masterprojektes wurde das Schwingungsverhalten an einem Elektromotor, welcher stets nach längerem Dauerbetrieb ein lautes Geräusch entwickelt, untersucht. Als Ursache für die Geräuschentwicklung wurde die axiale Schwingung des Rotorpaketes in den Rillenkugellagern identifiziert. In dem untersuchten Motor werden die Rillenkugellager mit einer Federvorspannung verbaut, wodurch sich ein definierter Druckwinkel einstellt. Aufgrund von Erwärmung im Dauerbetrieb und disfunktionaler Ausgleichsmöglichkeiten nimmt die Vorspannung und damit der Druckwinkel mit der Laufzeit ab.
The paper discusses utilisation of the brute force methods for the task of towers distribution in wireless communication systems. The proposed algorithm allows to find an optimal allocation of a tower between the settlements. A simple wireless communication has been used as an example to investigate the functionality of the algorithm's software.
Wireless Network has become the critical part of the communication infrastructure in our environment. Nowadays, the using of mobile computing devices such as laptops and Wi-Fi enabled phones in the workplace is increasing. The design of wireless networks for enterprise environments remains a challenging task due to the problem of topological design. In this paper, we discuss the computational aspects of the task of calculation the various criteria of efficiency wireless networks' topology. These criteria determine the different characteristics of wireless networks - the access level of populations to network services, the level of the distributed signal and the level of signal accepted in the city. We use brute force algorithm for comparing the different criteria of efficiency the topology of wireless networks. The brute force algorithm has high computational complexity therefore in our experiments we use parallel computing to solve the problem. For illustration the results we use the task of optimization the Wireless network topology for fragment of Myanmar territory.
Wireless sensor networks are widely used in a variety of fields including industrial environments. In case of a clustered network the location of cluster head affects the reliability of the network operation. Finding of the optimum location of the cluster head, therefore, is critical for the design of a network. This paper discusses the optimisation approach, based on the brute force algorithm, in the context of topology optimisation of a cluster structure centralised wireless sensor network. Two examples are given to verify the approach that demonstrate the implementation of the brute force algorithm to find an optimum location of the cluster head.
Die im Folgenden dargestellten wichtigsten Ergebnisse des Teilprojektes 5 "Mathematische Beschreibung der relevanten physikalischen Prozesse und numerische Simulation von Wasseraufbereitung und -verteilung" beziehen sich auf die Arbeitspakete 2 "Daten und Methoden zum Modellaufbau, zur Zustandsschätzung, Prognose und Bewertung" und 3 "Physikalische Modelle und Numerische Verfahren".
In this paper an overview on modelling techniques and numerical methods applied to problems in water network simulation is given. The considered applications cover river alarm systems (Rentrop and Steinebach, Surv Math Ind 6:245–265, 1997), water level forecast methods (Steinebach and Wilke, J CIWEM 14(1):39–44, 2000) up to sewer and water supply networks (Steinebach et al., Mathematical Optimization of Water Networks Martin. Springer, Basel, 2012).
The hyperbolic modelling equations are derived from mass and momentum conservation laws. A typical example are the well known Saint-Venant equations. For their numerical solution a conservative semi-discretisation in space by finite differences is proposed. A new well-balanced space discretisation scheme is presented which improves the local Lax-Friedrichs approach applied so far. Higher order discretisations are achieved by WENO methods (Kurganov and Levy, SIAM J Sci Comput 22(4):1461–1488, 2000).
Together with appropriate boundary and coupling conditions this method of lines approach leads to an index-one DAE system. Efficient solution of the DAE system is the topic of Jax and Steinebach (ROW methods adapted to network simulation for fluid flow, in preparation).
Maximal covering location problems have efficiently been solved using evolutionary computation. The multi-stage placement of charging stations for electric cars is an instance of this problem which is addressed in this study. It is particularly challenging, because a final solution is constructed in multiple steps, stations cannot be relocated easily and intermediate solutions should be optimal with respect to certain objectives.
An evolving strategy for a multi-stage placement of charging stations for electrical cars is developed. Both an incremental as well as a decremental placement decomposition are evaluated on this Maximum Covering Location Problem. We show that an incremental Genetic Algorithm benefits from problem decomposition effects of having multiple stages and shows greedy behaviour.
This paper discusses an approach of the abnormal condition detection of whole blood using piezo-synthetic effects in blood under dynamic external pressure. Three groups of samples having verified chemical and biological conditions were analysed to prove reliable detection: saline, whole blood and whole blood with colorectal cancer as an example of abnormal conditions. The procedure of a discrete differentiation process for obtained experimental data has been proposed as preliminary processing. Three information parameters have been selected to describe experimental data. Fischer F-statistics were used to determine the information content of the proposed information parameters. It has been proved that the proposed information parameters react on changing state of object under test and therefore can be effectively used for the abnormal condition detection.
In 2011, the German Federal Ministry of Transport, Building and Urban Development laid the foundation of the Hans-Ertel Centre for Weather Research [Hans-Ertel-Zentrum für Wetterforschung (HErZ)] in order to better connect fundamental meteorological research and teaching at German universities and atmospheric research centers with the needs of the German national weather service Deutscher Wetterdienst (DWD). The concept for HErZ was developed by DWD and its scientific advisory board with input from the entire German meteorological community. It foresees core research funding of about €2,000,000 yr−1 over a 12-yr period, during which time permanent research groups must be established and DWD subjects strengthened in the university curriculum. Five priority research areas were identified: atmospheric dynamics and predictability, data assimilation, model development, climate monitoring and diagnostics, and the optimal use of information from weather forecasting and climate monitoring for the benefit of society. Following an open call, five groups were selected for funding for the first 4-yr phase by an international review panel. A dual project leadership with one leader employed by the academic institute and the other by DWD ensures that research and teaching in HErZ is attuned to DWD needs and priorities, fosters a close collaboration with DWD, and facilitates the transfer of fundamental research into operations. In this article, we describe the rationale behind HErZ and the road to its establishment, present some scientific highlights from the initial five research groups, and discuss the merits and future development of this new concept to better link academic research with the needs and challenges of a national weather service.
Medien spielen eine Schlüsselrolle für die öffentliche Meinung und Akzeptanz neuer Technologien. Mit einer qualitativen Inhaltsanalyse journalistischer Artikel zum Elektrofahrrad wurden Akteure und ihre Einstellungen und Handlungen in Bezug auf das Elektrofahrrad untersucht. In die Analyse flossen 444 Artikel ausgewählter deutscher Qualitätsmedien aus dem Jahr 2018 ein. Die Untersuchung zeigt den gesellschaftlich relevanten Diskurs über Elektrofahrräder auf und bietet Anknüpfungspunkte für die Förderung von Individualmobilität und der Entwicklung zukunftsfähiger Mobilitätskonzepte.
Aufgrund der weltweiten Bemühungen, den CO2- und Schadstoffausstoß zu reduzieren, sind die Automobilhersteller veranlasst, die Entwicklung effizienter Fahrzeuge verstärkt voranzutreiben. Die gestiegenen Anforderungen machen sich besonders an den Entwicklungstrends der letzten Jahre bemerkbar. Neben Maßnahmen, um den Kraftstoffverbrauch konventioneller Fahrzeuge zu reduzieren, wie z.B. Downsizing, Start/Stopp-Automatiken oder Disconnect-Systemen bei Allradfahrzeugen, gewannen elektrifizierte Fahrzeugkonzepte wie Hybrid- und Elektrofahrzeuge stark an Bedeutung.
In light of emobility, the development of efficiency improved drivetrain components will also have a high priority. Whereas for conventional vehicle propulsion systems (i.e. combustion type engines) the avoidance of CO2 penalty was in strong focus, for electrified vehicles it is the impact on vehicle range. For GKN Driveline as the world's leading supplier of driveline components and systems, the prediction of energy savings is of particular importance in order to quantify the benefit of efficiency optimizations on the energy consumption of the vehicles. This paper gives an introduction to a simplified and transparent method of modelling to provide a basic understanding of the impact of efficiency improvements. Hereby it is shown, that with the increasing electrification of the drivetrain, the optimization of the efficiency in the mechanical path of power transmission will become even more important.
Wo Laborexperimente zu aufwendig, zu teuer, zu langsam oder zu gefährlich oder Stoffeigenschaften gar nicht erst experimentell zugänglich sind, können Computersimulationen von Atomen und Molekülen diese ersetzen oder ergänzen. Sie ermöglichen dadurch Reduktion von Kosten, Entwicklungszeit und Materialeinsatz. Die für diese Simulationen benötigten Molekülmodelle beinhalten zahlreiche Parameter, die der Simulant einstellen oder auswählen muss. Eine passende Parametrierung ist nur bei entsprechenden Kenntnissen über die Auswirkungen der Parameter auf die zu berechnenden Größen und Eigenschaften möglich. Eine Gruppe von Standardparametern in molekularen Simulationen sind die Partialladungen der einzelnen Atome innerhalb eines Moleküls. Die räumliche Ladungsverteilung innerhalb des Moleküls wird durch Punktladungen auf den Atomzentren angenähert. Für diese Annäherung existieren diverse Ansätze für verschiedene Molekülklassen und Anwendungen. In diesem Teilprojekt des Promotionsvorhabens wurde systematisch der Einfluss der Wahl des Partialladungssatzes auf potentielle Energien und ausgewählte makroskopische Eigenschaften aus Molekulardynamik-Simulationen evaluiert. Es konnte gezeigt werden, dass insbesondere bei stark polaren Molekülen die Auswahl des geeigneten Partialladungssatzes entscheidenden Einfluss auf die Simulationsergebnisse hat und daher nicht naiv, sondern nur ganz gezielt getroffen werden darf.
Work in progress: Starter-project for first semester students to survey their engineering studies
(2015)
In this contribution we briefly recap the general concept of the BRSU Race Academy. We then concentrate on and demonstrate how practical projects can be set up and executed within this framework. We discuss what is needed to train the members of the Race Academy properly and how the faculty advisor could change his course of action during the projects. The feedback and the results of such projects have been extremely positive so far: The Race Academy members have been perceived as role models to their peers, and an efficient peer-group atmosphere could be set up that facilitated learning. With their experience, solid user knowledge and the close contact to several industrial partners, a productive, authentic and practical working atmosphere has been established. We will give examples of how to use our new teaching approach to surpass the qualities of classes held in the traditional way. Furthermore, it is shown that the technical understanding is improved, as well as the personal experience to work with and integrate into a professional team.
Formula Student is known worldwide as a design contest for engineering students, in which they train technical skills and engineering thinking by developing and manufacturing a single-seated race car every year. The efficient transfer of highly specialized and professional knowledge about physics and manufacturing has to be ensured every year, as the members turn into alumni. This requires much more than only technical skills.
In this contribution, we want to present how the Bonn-Rhine-Sieg University of Applied Sciences supports its Formula Student team in order to foster and exploit its great potentials with a systematic approach, under the supervision of its team faculty advisor. We show how senior students learn how to teach their fellow students in their highly specialized skills in a so called “Race Academy”. This aims at the evolution of teaching content, and the art of teaching itself, by systematically involving peers in the teaching process.
En el siguiente trabajo se presentan las diferentes alternativas tecnológicas que brindarán soporte para las comunicaciones en el Proyecto Campo Conectado, priorizando el bajo consumo y mantenimiento. Esta plataforma de transmisión proveerá la conectividad necesaria para la recolección y envío de los datos requeridos por los productores agropecuarios, con el fin de mejorar la gestión de los procesos productivos y comerciales. Se comenta además los orígenes del proyecto y los actores involucrados en el mismo, destacándose el trabajo interinstitucional e interdisciplinar que se lleva a cabo.
The classification of median filter hardware structure was proposed. Main differences, advantages and disadvantages of each class were described. Scalable and synthesizable Verilog-descriptions were designed for two fast hardware structures. HDL-descriptions were synthesized on Altera and Xilinx FPGA platforms, comparative analysis on the basis of resource utilization and clock rate was done.
Solar energy is one option to serve the rising global energy demand with low environmental impact. Building an energy system with a considerable share of solar power requires long-term investment and a careful investigation of potential sites. Therefore, understanding the impacts from varying regionally and locally determined meteorological conditions on solar energy production will influence energy yield projections.
Solar energy is one option to serve the rising global energy demand with low environmental Impact [1]. Building an energy system with a considerable share of solar power requires long-term investment and a careful investigation of potential sites. Therefore, understanding the impacts from varying regionally and locally determined meteorological conditions on solar energy production will influence energy yield projections. Clouds are moving on a short term timescale and have a high influence on the available solar radiation, as they absorb, reflect and scatter parts of the incoming light [2]. However, modeling photovoltaic (PV) power yields with a spectral resolution and local cloud information gives new insights on the atmospheric impact on solar energy.
This paper addresses long-term historical changes in solar irradiance in West Africa (3 to 20° N and 20° W to 16° E) and the implications for photovoltaic systems. Here, we use satellite irradiance (Surface Solar Radiation Data Set – Heliosat, Edition 2.1 – SARAH-2.1) and temperature data from a reanalysis (ERA5) to derive photovoltaic yields. Based on 35 years of data (1983–2017), the temporal and regional variability as well as long-term trends in global and direct horizontal irradiance are analyzed. Furthermore, a detailed time series analysis is undertaken at four locations. According to the high spatial resolution SARAH-2.1 data record (0.05°×0.05°), solar irradiance is largest (up to a 300 W m−2 daily average) in the Sahara and the Sahel zone with a positive trend (up to 5 W m−2 per decade) and a lower temporal variability (<75 W m−2 between 1983 and 2017 for daily averages). In contrast, the solar irradiance is lower in southern West Africa (between 200 W m−2 and 250 W m−2) with a negative trend (up to −5 W m−2 per decade) and a higher temporal variability (up to 150 W m−2). The positive trend in the north is mostly connected to the dry season, whereas the negative trend in the south occurs during the wet season. Both trends show 95 % significance. Photovoltaic (PV) yields show a strong meridional gradient with the lowest values of around 4 kWh kWp−1 in southern West Africa and values of more than 5.5 kWh kWp−1 in the Sahara and Sahel zone.
Atmospheric aerosols affect the power production of solar energy systems. Their impact depends on both the atmospheric conditions and the solar technology employed. By being a region with a lack in power production and prone to high solar insolation, West Africa shows high potential for the application of solar power systems. However, dust outbreaks, containing high aerosol loads, occur especially in the Sahel, located between the Saharan desert in the north and the Sudanian Savanna in the south. They might affect the whole region for several days with significant effects on power generation. This study investigates the impact of atmospheric aerosols on solar energy production for the example year 2006 making use of six well instrumented sites in West Africa. Two different solar power technologies, a photovoltaic (PV) and a parabolic through (PT) power plant, are considered. The daily reduction of solar power due to aerosols is determined over mostly clear-sky days in 2006 with a model chain combining radiative transfer and technology specific power generation. For mostly clear days the local daily reduction of PV power (at alternating current) (PVAC) and PT power (PTP) due to the presence of aerosols lies between 13 % and 22 % and between 22 % and 37 %, respectively. In March 2006 a major dust outbreak occurred, which serves as an example to investigate the impact of an aerosol extreme event on solar power. During the dust outbreak, daily reduction of PVAC and PTP of up to 79 % and 100 % occur with a mean reduction of 20 % to 40 % for PVAC and of 32 % to 71 % for PTP during the 12 days of the event.
Solar energy plants are one of the key options to serve the rising global energy need with low environmental impact. Aerosols reduce global solar radiation due to absorption and scattering and therewith solar energy yields. Depending on the aerosol composition and size distribution they reduce the direct component of the solar radiation and modify the direction of the diffuse component compared to standard atmospheric conditions without aerosols.
Impact of atmospheric aerosols on photovoltaic energy production - Scenario for the Sahel zone
(2017)
Photovoltaic (PV) energy is one option to serve the rising global energy need with low environmental impact. PV is of particular interest for local energy solutions in developing countries prone to high solar insolation. In order to assess the PV potential of prospective sites, combining knowledge of the atmospheric state modulating solar radiation and the PV performance is necessary. The present study discusses the PV power as function of atmospheric aerosols in the Sahel zone for clear-sky-days. Daily yields for a polycrystalline silicon PV module are reduced by up to 48 % depending on the climatologically-relevant aerosol abundances.
Die Produktsimulation blasgeformter Kunststoffhohlkörpern ist trotz ausgereifter Software nach wie vor mit Unsicherheiten verbunden. Der Grund dafür ist vor allem in der unzureichenden Materialbeschreibung von Polymer-Werkstoffen zu suchen. Das komplexe zeit- und temperaturabhängige Werkstoffverhalten erfordert oftmals eine Abkehr von einfachen linear elastischen Materialmodellen hin zu komplexeren nichtlinear viskoelastisch-plastischen Modellen. Darüber hinaus hat auch der Verarbeitungsprozess maßgeblichen Einfluss auf die mechanischen Eigenschaften des Endproduktes. Eine Konsequenz daraus ist, dass lokale Materialparameter nicht mehr als konstant, sondern vielmehr als Funktion bestimmter Prozessparameter anzusehen sind. Im Rahmen des bereits abgeschlossenen Forschungsprojektes MatRes gelang es erstmals das prozessspezifische Materialverhalten blasgeformter Kunststoffhohlkörper zu identifizieren und in die Produktsimulation einzubinden. Diese Materialbeschreibung konnte dann im aktuellen Forschungsvorhaben ReBauVES dahingehend erweitert werden, dass auch Betrag und Richtung der lokalen Verstreckungen, sowie die damit verbundene Orthotropie berücksichtigt werden. Zukünftig soll es gelingen, durch die Verwendung prozessabhängiger viskoelastisch-plastischer Materialmodelle sowohl das Langzeitverhalten als auch das dehnratenabhängige Kurzzeitverhalten blasgeformter Hohlkörper mit hinreichender Genauigkeit zu beschreiben.
Das sogenannte „Deutschlandstipendium“ ist 2010 ins Leben gerufen worden. Gemäß den gesetzlichen Vorgaben sollen die Stipendien nach Begabung und Leistung vergeben werden. Darüber hinaus sollen auch gesellschaftliches Engagement oder besondere soziale, familiäre oder persönliche Umstände berücksichtigt werden. Bei der Finanzierung sind die Hochschulen zunächst auf das Einwerben privater Fördermittel angewiesen, die von Bund und Land um denselben Betrag aufgestockt werden. Die privaten Mittelgeber können für die von ihnen anteilig finanzierten Stipendien festlegen, aus welchen Studiengängen ihre Stipendiaten ausgewählt werden sollen. Die Hochschulen haben jedoch darauf zu achten, dass ein Drittel aller zu vergebenden Stipendien ohne eine entsprechende Zweckbindung vergeben werden. Einen direkten Einfluss auf die Auswahl einzelner Kandidaten dürfen die Förderer nicht haben. Vor diesem Hintergrund sind die Hochschulen angehalten, Anreize für private Förderer zu schaffen und parallel Bewerbungs- und Auswahlverfahren zu konzipieren, die die genannten gesetzlichen Vorgaben einhalten. Dadurch entsteht bei den Hochschulen ein erheblicher Verwaltungsaufwand. Zu dessen Reduzierung wird in diesem Artikel ein transparenter, nachvollziehbarer, zeit- und kostensparender Prozess durch einen programmierten Workflow beschrieben.
Der Nutzen von Prozessmanagement für die Effizienz und Effektivität der Organisation von Unternehmen ist vielfach bestätigt. Eine Studie der gfo-Gesellschaft für Organisation stellt fest, dass der Umsetzungsgrad der Prozessorganisation in Unternehmen dennoch mangelhaft ist. Es fehlt die Unterstützung der Leitung, die selbst noch überwiegend funktional organisiert ist.
Solar energy is one option to serve the rising global energy demand with low environmental impact.1 Building an energy system with a considerable share of solar power requires long-term investment and a careful investigation of potential sites. Therefore, understanding the impacts from varying regionally and locally determined meteorological conditions on solar energy production will influence energy yield projections. Clouds are moving on a short term timescale and have a high influence on the available solar radiation, as they absorb, reflect and scatter parts of the incoming light.2 However, the impact of cloudiness on photovoltaic power yields (PV) and cloud induced deviations from average yields might vary depending on the technology, location and time scale under consideration.
Study Islands are a setting for collaborative learning and guided self-study at a university. Success factors are identified, leading to a multi-dimensional approach: A conceptual understanding in regard to space and time, competences of the staff, and interaction between students and staff is introduced. Stake holders in the guided learning process – students, tutors, and academic staff – and their goals are identified. Developing an understanding of students’ motivation to attend opens up possibilities to encourage student participation. Experiences from two study islands show that established place and time as well as face-to-face interaction between students and staff play a major role in founding a stable relationship and forming a basis for students’ success.
Tierexperimentell konnte nachgewiesen werden, dass spezifische Ionenkanäle (vor allem TRPA1) des nozizeptiven Systems nachhaltig durch die Exposition mit blauem Licht moduliert werden können. Durch Nachweis der Wirksamkeit von nicht-visuellen Effekten einer Lichtexposition auf Somatosensorik und Nozizeption beim Menschen könnte der Einsatz einer Lichttherapie bei Patienten mit Erkrankungen des somatosensorischen Systems, insbesondere neuropathischen Schmerzen, von großer Bedeutung sein.
The paper presents a new control strategy of management of transport companies operating in completive transport environment. It is aimed to optimise the headway of transport companies to provide the balance between costs and benefits of operation under competition. The model of transport system build using AnyLogic comprises agent-based and discrete-event techniques. The model combined two transport companies was investigated under condition of the competition between them. It was demonstrated that the control strategy can ensure the balance of interests of transport companies trying to find compromise between cost of operation and quality of service.
This paper demonstrates a possibilities of using brute force methods for evaluating the effectiveness of hierarchical management systems. Proposed model of hierarchy provides finding the optimal distribution of load between the executive elements at a predetermined structure. A simple hierarchical structure has been used as an example to investigate the functionality of the model and its software implementation.
Transition point prediction in a multicomponent lattice Boltzmann model: Forcing scheme dependencies
(2018)
Pseudopotential (PP)-basierte Lattice-Boltzmann-Methoden werden zunehmend für die Simulation von Mehrphasenströmungen eingesetzt. Da sie auf einem phänomenologischen Ansatz basieren, ist ihr Einsatz mit einem hohen Modellierungsaufwand verbunden. Zudem entstehen an den Phasengrenzen sogenannte Scheingeschwindigkeiten, welche Genauigkeit und numerische Stabilität beeinträchtigen. Daher werden PP-Modelle in dieser Arbeit um drei neue Aspekte erweitert. Erstens wird gezeigt, dass bei der Modellierung unterschiedlicher Kontaktwinkel mit gängigen Methoden in Kombination mit verbesserten Kräfteschemata Scheintröpfchen entstehen. Diese werden durch einen neuartigen Ansatz eliminiert, der auf zusätzlichen Randbedingungen für alle Wechselwirkungskräfte basiert. Diese Technik verhindert nicht nur das Auftreten der Scheintröpfchen, sondern erhöht auch die Stabilität in wandgebundenen Strömungen. Zweitens wird ein neuartiges Verfahren zur Reduktion von Scheingeschwindigkeiten eingeführt. Dabei wird die Diskretisierung der Interaktionskräfte erweitert und die zusätzlichen, freien Koeffizienten in Simulationen statischer Tropfen numerisch optimiert. Die resultierende Diskretisierung wurde in Simulationen stationärer und dynamischer Testfälle validiert, wobei Scheingeschwindigkeiten deutlich reduziert werden konnten. Drittens und letztens wurden die Diffusionseigenschaften in Mehrstoffsystemen detailliert untersucht, wobei eine kritische Abhängigkeit zwischen den makroskopischen Diffusionskoeffizienten und dem Kräfteschema aufgezeigt wird. Diese Analyse bildet die Grundlage für den Vergleich und die zukünftige Entwicklung neuer Potentialfunktionen (für Mehrstoffsysteme) und reduziert den Modellierungsaufwand.
Ionic liquids are highly relevant for industrial applications as they stand out due to their special chemical and physical features, e.g. low vapor pressure, low melting point or extraordinary solution properties. The goal of this work is to study the capability of the three ionic liquids [C2MIM][NTf2], [C12MIM][NTf2] and [C2MIM][EtSO4] to diffuse through a POPC membrane (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine). To achieve this, we used molecular simulation techniques, which on the one hand give insight into specific domains of the membrane and on the other hand compute partition coefficients and free energy profiles of solutes in lipid membranes, which cannot be measured by labor experiments. To be as accurate as possible we parameterized a new united atom force field for the ionic liquid of type 1-alkyl-3-methylimidazoliumethylsulfate [CnMIM][EtSO4] with n = 1,2,4,6,8. Like the other IL force field for [CnMIM][NTf2] (see Köddermann et al., ChemPhysChem 14, 3368–3374, 2013) used in this work, the new one was derived to reproduce experimental densities and self-diffusion coefficients. The new force field reproduces the experimental data extremely well. Using this force field, the influences of cation and anion exchanges as well as the variation of the chain length on the free energy could be analyzed. We performed umbrella-sampling to characterize the free energy profile of one ion pair, accompanied by a second one, in solution, at the membrane interface, and inside the membrane. In the outlook we present our intention to parameterize force fields in a systematic and user-friendly way. We will use the combination of two optimization toolkits, developed at SCAI: The global optimization toolkit CoSMoS and the local optimization techniques implemented in the software package GROW.
Automated parameterization of intermolecular pair potentials using global optimization techniques
(2014)
In this work, different global optimization techniques are assessed for the automated development of molecular force fields, as used in molecular dynamics and Monte Carlo simulations. The quest of finding suitable force field parameters is treated as a mathematical minimization problem. Intricate problem characteristics such as extremely costly and even abortive simulations, noisy simulation results, and especially multiple local minima naturally lead to the use of sophisticated global optimization algorithms. Five diverse algorithms (pure random search, recursive random search, CMA-ES, differential evolution, and taboo search) are compared to our own tailor-made solution named CoSMoS. CoSMoS is an automated workflow. It models the parameters’ influence on the simulation observables to detect a globally optimal set of parameters. It is shown how and why this approach is superior to other algorithms. Applied to suitable test functions and simulations for phosgene, CoSMoS effectively reduces the number of required simulations and real time for the optimization task.
Die akustischen Anforderungen an den PKW nehmen zu, da Nebengeräusche im Antriebsstrang bei Elektroantrieben zukünftig nicht mehr durch den Verbrennungsmotor maskiert werden. Antriebswellen werden üblicherweise so ausgelegt, dass die erste Biegeeigenfrequenz über 200Hz und damit oberhalb der Anregung der zweiten Ordnung eines Vierzylindermotors liegt. Längswellen zur Drehmomentübertragung im Allradfahrzeugen werden aufgrund ihrer Länge oft zwei- oder dreiteilig konstruiert und über Kardan- oder Gleichlaufgelenke miteinander verbunden und in Zwischenlagern gehalten, um Eigenfrequenzen unterhalb von 200 Hz zu vermeiden.
Differential-Algebraic Equations and Beyond: From Smooth to Nonsmooth Constrained Dynamical Systems
(2018)
