600 Technik, Medizin, angewandte Wissenschaften
Refine
Year of publication
Document Type
- Article (65)
- Master's Thesis (16)
- Part of a Book (14)
- Bachelor Thesis (10)
- Report (8)
- Other (6)
- Book (3)
- Study Thesis (3)
- Working Paper (1)
Has Fulltext
- yes (126)
Keywords
- Biogas (5)
- Diabetes mellitus Typ 1 (4)
- GIS (4)
- Sonnenenergie (4)
- Erneuerbare Energien (3)
- HIV (3)
- Informationsverhalten (3)
- Optimization (3)
- Simulation (3)
- Smart Energy (3)
Faculty
- Fakultät 12 / Institut für Technologie und Ressourcenmanagement in den Tropen und Subtropen (19)
- Fakultät 09 / Institut für Rettungsingenieurwesen und Gefahrenabwehr (18)
- Fakultät 09 / Cologne Institute for Renewable Energy (16)
- Fakultät 09 / Institut für Produktentwicklung und Konstruktionstechnik (10)
- Angewandte Naturwissenschaften (F11) (9)
- Fakultät 10 / Institut Allgemeiner Maschinenbau (9)
- Fakultät 03 / Institut für Informationswissenschaft (6)
- Fakultät 09 / Institut Anlagen und Verfahrenstechnik (6)
- Fakultät 10 / :metabolon Institut (5)
- Fakultät 07 / Institut für Nachrichtentechnik (4)
Since the beginning of 2021, CEN/TS 19100 Design of Glass Structures has been available in its first three parts. The fourth part is expected soon. This Technical Specification of the European standards organisation CEN is as a pre-standard of a corresponding future Eurocode. These documents constitute the first ever comprehensive design code for the entire structural glass engineering field on the European market for the first time. In addition to a clear outline, the Technical Specification has been drafted to be compatible with EN 1990 “Basis of Design” and to address glass-specific design matters, particularly related to robustness and redundancy. Although the standard still has the status of a CEN/TS, thereby allowing the European nations the option of whether to introduce it, either in full or in parts, it already contains national openings through which the European countries can adapt the design results to their own safety level by National Determined Parameters (NDPs). Such an approach already anticipates the future Eurocode, which is expected to be published as EN 19100—Design of Glass Structures. This article provides some context on the history and concept behind the new documents and gives an overview of the design rules and the corresponding technical background of the different parts of CEN/TS 19100.
The crosslink density of elastomers is the essential property that determines many other but especially the mechanical product properties. Different raw materials, especially recycled and bio-based materials, influence the vulcanization and may change the crosslink density when they are used as a substitute to conventional raw materials. Aim of this study is to develop a procedure that allows the reliable determination of the crosslink density in highly filled EPDM compounds as basis for future investigations focussed on substitution with sustainable materials in this compound. Unfortunately, experiences with other rubber compounds like tire treads cannot be directly applied here because of the use of other filler types and amounts as well as the differences in the polymer with regard to active sites (available double bonds). Equilibrium swelling, Flory-stress-strain-measurements, freezing point depression and temperature-scanning-stress-relaxation are applied to a model EPDM compound with high filler and softener amount as typically used for sealings. For sensitivity investigation the amount of the crosslink agent sulfur was varied. Furthermore, the influence of different accelerators was investigated. All methods are able to determine the crosslink density but with different standard deviations due to measurement errors. Partially, they can be optimized for this use case. Based on the results a combination of Flory-stress-strain-measurements and freezing point depression was chosen to be used in the future.
Kenya experiences massive urban growth, also into natural hazard-prone areas, exposing settlements and the natural environment to riverine and pluvial floods and other natural hazards. While Nairobi as the capital and principal city has been extensively analysed regarding urban growth and flood hazard in some central parts, awareness of growing peri-urban areas has not been studied as much. The results are of interest to other locations in Kenya and worldwide, too, since the current research and disaster risk practice focus is still too much on megacities and city centres. Therefore, the study compares urban growth into hazard areas in urban rims of Nairobi and Nyeri, Kenya. A change assessment from 1948 to 2020 is conducted by aerial images, declassified satellite images, and recent data. Urban growth rates are 10- to 26-fold, while growth into flood exposed areas ranges from 2- to 100-fold. This study reveals unused opportunities for expanding existing land-use change analysis back to the 1940s in data-scarce environments.
The paper focuses on the analytical analysis of the propagation of a normal shock wave in an adiabatic gas flow with nanoparticles. A modified Rankine–Hugoniot model was used for this purpose. A solution is obtained for the Rankine–Hugoniot conditions in a gas flow with different nanoparticle concentrations, which makes it possible to analyze the dynamics of variation of the parameters of this type of flow under a shock wave. The variation of velocity, pressure and entropy production of the adiabatic gas flow during a direct shock wave depending on the concentration of nanoparticles in the gas was depicted graphically. It was revealed that increasing the nanoparticle concentration to φ ~ 0.1 weakens the effect of the shock wave, and then, after passing the zone of minimum parameters, the intensity of the shock wave increases.
Purpose Langevin transducers are ultrasonic transducers that convert electrical into mechanical energy through the piezoelectric effect. This class of transducers achieves the highest efficiency in their mechanical resonance. Studies have shown that the resonant frequency changes with temperature. The aim of this contribution is to reproduce this temperature-dependence resonance frequency as accurately as possible with FEM simulations. Methods Therefore, the temperature-dependent resonance behavior of Langevin transducers is examined experimentally. A FEM model is created on the basis of temperature-dependent measured material coefficients. Using parameter correlations and optimization algorithms, the FEM model is fitted and validated by experimental results. Six variants of Langevin transducers are examined in the range from 30 °C to 80 °C with resonance frequencies between 34 and 38 kHz. They differ in three geometries and two materials. Results The experimental results show that the resonance frequencies decrease with increasing temperatures by 5.0–19.4 Hz/°C, depending on the material and geometry. As decisive parameters for the model fitting of the FEM results, three function-dependent stiffness coefficients of the piezoelectric material PZT8 and the Young’s moduli of the metallic materials are determined by parameter correlation. Conclusion Through the targeted fitting of these function-dependent parameters, the calculation of the resonance frequencies of Langevin transducers can be qualitatively and quantitatively improved, independent of shape and material.
Ni–Ti alloys are used as functional materials in numerous sectors such as aerospace, automotive engineering, medical technology, and consumer goods. Their properties in terms of shape memory effect and superelasticity offer a great potential for innovative smart products. However, forming and machining of these alloys into concrete products is challenging. Assembling plain structures by laser welding to complex product shapes offers an economical alternative in many cases, but can be associated with negative effects, such as reduction of strength, development of brittle intermetallic compounds, alteration of transformation temperatures, and modification of shape memory effects and superelastic behavior. Against this background, investigations on laser welding of Ni55/Ti45 foil with a thickness of 125 µ m by a fiber laser were conducted. Supported by methods of design of experiments, optimal parameters were determined with respect to laser power, welding speed, focus position, and beam oscillation, and the welding results were analyzed concerning the microstructure and mechanical characteristics of the welded joints. The effect of laser beam oscillation was investigated for the first time for the welding of this alloy. Due to the very low thickness, the preparation of the foils for the microstructure characterization is quite demanding. Best results were obtained by ion milling. Fracture surfaces and the influence of the welding were also investigated.
Three-dimensional printing is ideally suited to produce unique and complex shapes. In this study, the material properties of polysiloxanes, commonly named silicones, produced additively by two different methods, namely, multi-jet fusion (MJF) and material extrusion (ME) with liquid printing heads, are investigated. The chemical composition was compared via Fourier-transform infrared spectroscopy, evolved gas analysis mass spectrometry, pyrolysis gas chromatography coupled to mass spectrometry, and thermogravimetry (TGA). Density and low-temperature flexibility, mechanical properties and crosslink distance via freezing point depression were measured before and after post-treatment at elevated temperatures. The results show significant differences in the chemical composition, material properties, as well as surface quality of the tested products produced by the two manufacturing routes. Chemical analysis indicates that the investigated MJF materials contain acrylate moieties, possibly isobornyl acrylate linking branches. The hardness of the MJF samples is associated with crosslinking density. In the ashes after TGA, traces of phosphorus were found, which could originate from initiators or catalysts of the curing process. The ME materials contain fillers, most probably silica, that differ in their amount. It is possible that silica also plays a role in the processing to stabilize the extrusion strand. For the harder material, a higher crosslink density was found, which was supported also by the other tested properties. The MJF samples have smooth surfaces, while the ME samples show grooved surface structures typical for the material extrusion process. Post-treatment did not improve the material properties. In the MJF samples, significant color changes were observed.
Previous studies have shown that partially coating electrode surfaces with patterns of ‘islands’ of hydrophobic tetrafluoroethylene (PTFE; Teflon) may lead to more energy efficient gas generation. This occurred because the gas bubbles formed preferentially on the PTFE, thereby freeing up the catalytically active metallic surfaces to produce the gas more efficiently. This work examined electrochemically induced hydrogen bubble formation on a nickel electrode surface that had been coated with linear patterns of PTFE. The impact of the PTFE line size (width) and degree of coverage was examined and analyzed. No improvement in electrical energy efficiency was observed up to 15 mA/cm 2 when comparing the PTFE-coated electrodes with the control bare uncoated electrode. However, increasing PTFE coverage up to 15% generally improved electrolysis performance. Moreover, samples with 50% wider lines performed better (at the equivalent PTFE coverage), yielding an overpotential decline of up to 3.9% depending on the PTFE coverage. A ‘bubble-scavenging’ phenomenon was also observed, wherein bubbles present on the PTFE lines rapidly shrunk until they disappeared.
The significant expansion of renewable energies has led to an increased importance of storage systems. Decentralized storage solutions, including Home Battery Energy Storage Systems (HBESSs) and District Battery Energy Storage Systems (DBESSs), play a crucial role in this context. This study compares individual HBESSs with a community-used DBESS regarding the grade of autarky and self-consumption, specifically focusing on a planned residential area consisting of 36 single-family houses. A simulation tool was developed to conduct load flow simulations based on household electricity consumption, wallbox profiles for electric vehicle charging, and photovoltaic generation data across various battery capacities and system boundaries. The results demonstrate that the DBESS, compared to individual HBESSs with equivalent cumulative battery capacities, can achieve a maximum increase in the grade of autarky of up to 11.6%, alongside an 8.0% increase in the grade of self-consumption for the given use case. In terms of capacity, the DBESS allows for a saving of up to 68% compared to HBESS to achieve similar results for the studied neighborhood.
Der anthropogene Klimawandel erfordert drastische Maßnahmen zur Reduzierung von Treib-hausgasemissionen, insbesondere im Verkehrssektor. Alternative Antriebe wie batterieelektri-sche Fahrzeuge sind vielversprechend, auch für den Rettungsdienst, der derzeit überwiegend Fahrzeuge mit Verbrennungsmotoren nutzt. Ein Hindernis für die Einführung von batterie-elektrischen Rettungswagen ist die begrenzte Reichweite. Ziel dieser Arbeit ist die Entwicklung einer Methodik zur Ermittlung, ob und welche konventionell betriebenen Rettungswagen unter welchen ladeinfrastrukturellen Voraussetzungen durch batterieelektrische Rettungswagen er-setzt werden können. Konkret wird untersucht, welche der neun im Ilm-Kreis stationierten Ret-tungswagen durch das Modell „WAS 500 E-Ambulanz“ ersetzt werden können und welche Ladeinfrastruktur dafür notwendig ist.
Die Analyse basiert auf Einsatzfahrtdaten der Rettungswagen im Ilm-Kreis aus dem Jahr 2022. Fehlende Daten wurden durch Imputation ergänzt. Die Methodik umfasst die Entwicklung ma-thematisch-physikalischer Modelle zur Simulation des Ladezustands der batterieelektrischen Rettungswagen unter den zwei Szenarien: „Ladeinfrastruktur nur an Rettungswachen“ und „Ladeinfrastruktur an Rettungswachen und Krankenhäusern“. Herausforderungen bestehen in den Datenlücken und der Qualität der vorhandenen Daten. Die Modellierung weist Einschrän-kungen aufgrund der Datenqualität und Vereinfachungen realer Bedingungen auf. Eine Mo-dellvalidierung war nur grundlegend möglich. Die Methodik kann auf andere Untersuchungs-gebiete übertragen werden, sofern die Parameter angepasst werden und eine ausreichende Datenqualität gewährleistet ist. Zielgruppe sind Entscheidungsträger im Rettungsdienst und bei der Fahrzeugbeschaffung.
Die Simulation zeigt, dass keiner der Rettungswagen im Ilm-Kreis einschränkungslos ersetzt werden kann. Hauptursachen sind aufeinanderfolgende Einsatzfahrten ohne ausreichende Zwischenladung und Einsätze mit Gesamtverbräuchen über der maximalen Batteriekapazität. Im Szenario „Ladeinfrastruktur nur an Rettungswachen“ liegt die Ausfallrate zwischen 1,71 % und 4,9 %, während sie im Szenario „Ladeinfrastruktur an Rettungswachen und Krankenhäu-sern“ auf 0,14 % bis 0,91 % sinkt. Unter der Voraussetzung der Einhaltung bestimmter Ein-schränkungen ist es möglich, im Rahmen des Szenarios „Ladeinfrastruktur an Rettungswa-chen und Krankenhäusern“ vier Rettungswagen durch batterieelektrische Rettungswagen zu ersetzen. Die Einschränkungen umfassen eine Anpassung der Dispositionsstrategie sowie die fortlaufende Vorhaltung konventioneller Rettungswagen an anderen Standorten. Weitere For-schung ist notwendig, um die Modellgenauigkeit zu verbessern und die genauen Auswirkun-gen angepasster Dispositionsstrategien zu untersuchen. Zukünftige Praxistests und Wirt-schaftlichkeitsanalysen sind erforderlich, um die umfassende Eignung von batterieelektrischen Rettungswagen sicherzustellen.