@article{MehtaEhrenwirthMissalletal.2021, author = {Mehta, Kedar and Ehrenwirth, Mathias and Missall, Siegmund and Degembaeva, Nadira and Akmatov, Kuban and Z{\"o}rner, Wilfried}, title = {Energy Profiling of a High-Altitude Kyrgyz Community: Challenges and Motivations to Preserve Floodplain Ecosystems Based on Household Survey}, volume = {13}, pages = {13086}, journal = {Sustainability}, number = {23}, publisher = {MDPI}, address = {Basel}, issn = {2071-1050}, doi = {https://doi.org/10.3390/su132313086}, year = {2021}, abstract = {The floodplain areas along the Naryn River in Kyrgyzstan are essential as they hold the riparian (local) ecosystems because they provide firewood, pastureland, and areas for recreation and protection against erosion. Due to limited access to adequate, reliable, and sustainable energy services, the rural population usually derived their energy needs from multiple natural energy resources (i.e., firewood, charcoal, agricultural residues, animal dung, and wood branches). This is considered a common and predominant practice in rural Kyrgyzstan. This situation leads to a negative impact on local ecosystem services. In addition to that, the reliance on solid fuels contributes to indoor and outdoor air pollution, which is partially threatening the local ecosystem services. By contrast, the employment of renewable-based energy supply systems would substantially reduce the burden on the environment, which is mainly untapped. To integrate renewable energies, it is important to understand the energy behavior of floodplain communities. In that response, the presented article is the first attempt to capture the energy identity of the floodplain community of Kyrgyzstan based on a quantitative energy-based (on-site) household survey. Furthermore, the present research article synthesizes the driving factors that have a (direct or indirect) impact on the energy and local ecosystem services. In addition, the present article proposes a brief pathway for the sustainable energy transition. The article records the recommendation to integrate renewable energies to preserve the local ecosystems of Kyrgyzstan.}, language = {en} } @article{MehtaEhrenwirthTrinkletal.2021, author = {Mehta, Kedar and Ehrenwirth, Mathias and Trinkl, Christoph and Z{\"o}rner, Wilfried and Greenough, Richard}, title = {The energy situation in Central Asia}, volume = {14}, pages = {2805}, journal = {Energies}, subtitle = {a comprehensive energy review focusing on rural areas}, number = {10}, publisher = {MDPI}, address = {Basel}, issn = {1996-1073}, doi = {https://doi.org/10.3390/en14102805}, year = {2021}, abstract = {The northern part of the globe is dominated by industrialisation and is well-developed. For many years, the southern part of the world (South Asia, Africa etc.) has been a target of research concentrating on access to energy (mainly electricity) in rural regions. However, the Central Asian region has not been a focus of energy research compared to South East Asia and Africa. Despite plentiful domestically available energy resources, the energy supply in Central Asia is very unevenly distributed between urban and rural areas. Almost half of the total population of Central Asia lives in rural areas and there is a lack of access to modern energy services to meet primary needs. To analyse the energy situation (i.e., electricity, heating, hot water consumption, cooking, etc.) in rural Central Asia, this paper reviews residential energy consumption trends in rural Central Asian regions as compared to urban areas. Furthermore, the paper illustrates the potential of renewable energies in Central Asia. To perform the study, a qualitative comparative analysis was conducted based on a literature review, data, and statistical information. In summary, the presented article discusses the rural energy situation analytically and provides in-depth insights of Central Asian energy infrastructure.}, language = {en} } @article{VannahmeEhrenwirthSchrag2021, author = {Vannahme, Anna and Ehrenwirth, Mathias and Schrag, Tobias}, title = {Enhancement of a district heating substation as part of a low-investment optimization strategy for district heating systems}, volume = {10}, pages = {53}, journal = {Resources}, number = {5}, publisher = {MDPI}, address = {Basel}, issn = {2079-9276}, doi = {https://doi.org/10.3390/resources10050053}, year = {2021}, abstract = {In an ongoing project, low-investment measures for the optimization of district heating systems are analyzed. The optimization strategies are collected in a catalog, which is the core of a guideline. The application of this guideline is demonstrated using two concrete district heating networks as examples. In this study, the improvement of an analog controlled district heating substation by an electronic controller is investigated. High supply temperatures and heat losses are often a challenge in district heating networks. The district heating substations have a major influence on the network return temperatures. The comparison of the two substation setups with analog and electronic controllers is carried out by laboratory measurement. It can be shown that the return temperatures can be reduced by an average of 20 K in winter and transition, as well as 16 K in summer. The district heating network losses are calculated for one of both specific district heating networks. They are calculated from the ratio of network losses to generated energy. The generated energy is the sum of network losses and consumer demand. The thermal losses of the network can be reduced by 3\%. The volume flow in the heating network can be reduced to a quarter. Therefore, the pumping energy requirement drops sharply since these changes cubically affect the volume flow}, language = {en} } @article{SchmittGottwaltWinkleretal.2021, author = {Schmitt, Matthias and Gottwalt, Albin and Winkler, Jakob and Tobie, Thomas and Schlick, Georg and Stahl, Karsten and Tetzlaff, Ulrich and Schlip, Johannes and Reinhart, Gunther}, title = {Carbon Particle In-Situ Alloying of the Case-Hardening Steel 16MnCr5 in Laser Powder Bed Fusion}, volume = {11}, pages = {11060896}, journal = {Metals}, number = {6}, publisher = {MDPI}, address = {Basel}, issn = {2075-4701}, doi = {https://doi.org/10.3390/met11060896}, year = {2021}, abstract = {The carbon content of steel affects many of its essential properties, e.g., hardness and mechanical strength. In the powder bed fusion process of metals using a laser beam (PBF-LB/M), usually, pre-alloyed metal powder is solidified layer-by-layer using a laser beam to create parts. A reduction of the carbon content in steels is observed during this process. This study examines adding carbon particles to the metal powder and in situ alloying in the PBF-LB/M process as a countermeasure. Suitable carbon particles are selected and their effect on the particle size distribution and homogeneity of the mixtures is analysed. The workability in PBF-LB is then shown. This is followed by an evaluation of the resulting mechanical properties (hardness and mechanical strength) and microstructure in the as-built state and the state after heat treatment. Furthermore, potential use cases like multi-material or functionally graded parts are discussed.}, language = {en} } @article{HandwerkerKesslerMarzbani2021, author = {Handwerker, Michael and Kessler, J{\"o}rg and Marzbani, Hormoz}, title = {Comparison of hydrogen powertrains with the battery powered electric vehicle and investigation of small-scale local hydrogen production using renewable energy}, volume = {2}, journal = {Hydrogen}, number = {1}, publisher = {MDPI}, address = {Basel}, issn = {2673-4141}, doi = {https://doi.org/10.3390/hydrogen2010005}, pages = {76 -- 100}, year = {2021}, abstract = {Climate change is one of the major problems that people face in this century, with fossil fuel combustion engines being huge contributors. Currently, the battery powered electric vehicle is considered the predecessor, while hydrogen vehicles only have an insignificant market share. To evaluate if this is justified, different hydrogen power train technologies are analyzed and compared to the battery powered electric vehicle. Even though most research focuses on the hydrogen fuel cells, it is shown that, despite the lower efficiency, the often-neglected hydrogen combustion engine could be the right solution for transitioning away from fossil fuels. This is mainly due to the lower costs and possibility of the use of existing manufacturing infrastructure. To achieve a similar level of refueling comfort as with the battery powered electric vehicle, the economic and technological aspects of the local small-scale hydrogen production are being investigated. Due to the low efficiency and high prices for the required components, this domestically produced hydrogen cannot compete with hydrogen produced from fossil fuels on a larger scale.}, language = {en} } @article{BugajeEhrenwirthTrinkletal.2021, author = {Bugaje, Aminu and Ehrenwirth, Mathias and Trinkl, Christoph and Z{\"o}rner, Wilfried}, title = {Electric two-wheeler vehicle integration into rural off-grid photovoltaic system in Kenya}, volume = {14}, pages = {7956}, journal = {Energies}, number = {23}, publisher = {MDPI}, address = {Basel}, issn = {1996-1073}, doi = {https://doi.org/10.3390/en14237956}, year = {2021}, abstract = {In both rural and urban areas, two-wheeler vehicles are the most common means of transportation, contributing to local air pollution and greenhouse gas emissions (GHG). Transitioning to electric two-wheeler vehicles can help reduce GHG emissions while also increasing the socioeconomic status of people in rural Kenya. Renewable energy systems can play a significant role in charging electric two-wheeled vehicles, resulting in lower carbon emissions and increased renewable energy penetration in rural Kenya. As a result, using the Conventional and Renewable Energy Optimization (CARNOT) Toolbox in the MATLAB/Simulink environment, this paper focuses on integrating and modeling electric two-wheeled vehicles (e-bikes) into an off-grid photovoltaic Water-Energy Hub located in the Lake Victoria Region of Western Kenya. Electricity demand data obtained from the Water-Energy Hub was investigated and analyzed. Potential solar energy surplus was identified and the surplus was used to incorporate the electric two-wheeler vehicles. The energy consumption of the electric two-wheeler vehicles was also measured in the field based on the rider's driving behavior. The modeling results revealed an annual power consumption of 27,267 kWh, a photovoltaic (PV) electricity production of 37,785 kWh, and an electricity deficit of 370 kWh. The annual results show that PV generation exceeds power consumption, implying that there should be no electricity deficit. The results, however, do not represent the results in hourly resolution, ignoring the impact of weather fluctuation on PV production. As a result, in order to comprehend the electricity deficit, hourly resolution results are shown. A load optimization method was designed to efficiently integrate the electric 2-wheeler vehicle into the Water-Energy Hub in order to alleviate the electricity deficit. The yearly electricity deficit was decreased to 1 kWh and the annual electricity consumption was raised by 11\% (i.e., 30,767 kWh), which is enough to charge four more electric two-wheeler batteries daily using the load optimization technique.}, language = {en} } @article{AxmannHambergerLiegl2019, author = {Axmann, Bernhard and Hamberger, Werner and Liegl, Thomas}, title = {Digitalisierung der Fabrik - Datenqualit{\"a}t als Schl{\"u}ssel zum Erfolg}, volume = {114}, journal = {Zeitschrift f{\"u}r wirtschaftlichen Fabrikbetrieb}, subtitle = {Welchen Wert haben Daten?}, number = {5}, publisher = {Hanser}, address = {M{\"u}nchen}, issn = {2511-0896}, doi = {https://doi.org/10.3139/104.112083}, pages = {302 -- 305}, year = {2019}, language = {de} } @article{ContiSaidiGoldbrunner2020, author = {Conti, Fosca and Saidi, Abdessamad and Goldbrunner, Markus}, title = {Evaluation Criteria and Benefit Analysis of Mixing Process in Anaerobic Digesters of Biogas Plants}, volume = {24}, journal = {Environmental and Climate Technologies}, number = {3}, publisher = {De Gruyter Poland}, address = {Warsaw}, issn = {2255-8837}, doi = {https://doi.org/10.2478/rtuect-2020-0105}, pages = {305 -- 317}, year = {2020}, abstract = {A valid method to evaluate decisions of a project proposal is the so-called cost-benefit analysis. Criteria are selected and properly weighted to determine if the project is effective and feasible. The present research study is focused on methodical selection of design parameters to install two propeller mixers inside anaerobic digesters of biogas plants. A cylindrical tank of 1400 m3 was considered. For the model-based optimisation, the substrate was considered as a non-Newtonian fluid with a density of 1090 kg/m3. The Oswald-de Waele power-law model was selected to account for the rheological behaviour of the fluid. Installation parameters of the mixers were rotational angles and heights of the shafts of the two propellers. A computational model was developed to simulate the fluid dynamics depending on the mixing process inside the tank. Several configurations were analysed according to evaluating criteria such as the value of the fluid velocity, its distribution along the three spatial dimensions, and the power consumption to rotate the mixers. The maximum fluid velocity and minimum power consumption were observed when the propellers are located at intermediate height inside the tank and with the shafts perpendicular to the tank radius. With this configuration, the fluid reaches a maximum velocity of 0.28 m/s. According to the investigation, it is evident that mixing systems with propeller shafts deep-seated and parallel to the tank radius should be avoided, both in term of efficiency of the fluid mixing distribution and in term of power consumption.}, language = {en} } @article{ContiSaidiGoldbrunner2020, author = {Conti, Fosca and Saidi, Abdessamad and Goldbrunner, Markus}, title = {Numeric Simulation-Based Analysis of the Mixing Process in Anaerobic Digesters of Biogas Plants}, volume = {43}, journal = {Chemical Engineering \& Technology}, number = {8}, publisher = {Wiley}, address = {Weinheim}, issn = {1521-4125}, doi = {https://doi.org/10.1002/ceat.201900650}, pages = {1522 -- 1529}, year = {2020}, abstract = {Stirring systems with two rotational three-bladed propellers were analyzed using computational fluid dynamics. The propellers are located at three heights and seven angles in a tank with 9 m radius. The fluid was characterized by non-Newtonian rheology and simulated by applying the k-ε turbulence model and the standard k-ω model. Reynolds numbers were estimated. High fluid speeds were obtained with the propellers located at a height of 2 m and oriented at 90° with respect to the tank radius. In the top regions of the tank, the fluid velocity was generally less intense and less affected by the angle setting. The configurations identified as good mixing systems showed power consumptions broadly distributed around 30 kW.}, language = {en} } @article{BaerWagenederSolkaetal.2020, author = {B{\"a}r, Katharina and Wageneder, Stefanie and Solka, Felix and Saidi, Abdessamad and Z{\"o}rner, Wilfried}, title = {Flexibility Potential of Photovoltaic Power Plant and Biogas Plant Hybrid Systems in the Distribution Grid}, volume = {43}, journal = {Chemical Engineering \& Technology}, number = {8}, publisher = {Wiley}, address = {Weinheim}, issn = {1521-4125}, doi = {https://doi.org/10.1002/ceat.202000025}, pages = {1571 -- 1577}, year = {2020}, abstract = {The potential of combining biogas and photovoltaic (PV) power plants in hybrid systems in the German distribution grid is analyzed. The focus of the present research is on balancing the intermittent power supply from PV power plants with the controllable power production of combined heat and power (CHP) units of biogas plants within a period of seconds. To achieve an increase of the total energy feed-in of biogas and PV power plants to the electricity grid, a biogas plant energy management system is described. System parameters, such as the variable feed-in of PV power plants or power ramps of the start-up process of controllable biogas plant CHP unit, are described and adapted to the global installed capacity of PV power plant and biogas plants in the German distribution grid.}, language = {en} } @article{DotzauerPfeifferLaueretal.2018, author = {Dotzauer, Martin and Pfeiffer, Diana and Lauer, Markus and Pohl, Marcel and Mauky, Eric and B{\"a}r, Katharina and Sonnleitner, Matthias and Z{\"o}rner, Wilfried and Hudde, Jessica and Schwarz, Bj{\"o}rn and Faßauer, Burkhardt and Dahmen, Markus and Rieke, Christian and Herbert, Johannes and Thr{\"a}n, Daniela}, title = {How to measure flexibility - Performance indicators for demand driven power generation from biogas plants}, volume = {2019}, journal = {Renewable Energy}, number = {134}, publisher = {Elsevier}, address = {Amsterdam}, issn = {1879-0682}, doi = {https://doi.org/10.1016/j.renene.2018.10.021}, pages = {135 -- 146}, year = {2018}, abstract = {Flexible power provision from biogas can significantly contribute to energy systems with high shares of renewables. However, the characteristics and demands for this flexibility are not clearly defined or measured. In this paper eight indicators are defined to shape "flexibility" and perform a downstream investigation of eight research projects focusing on flexible energy provision of biogas plants. The indicators are structured in three dimensions (1) velocity (ramps) by which the system can be modulated, (2) power range (bandwidth) and (3) duration for specific load conditions. Based on these indicators bottlenecks for the flexibility potential were identified. One crucial result shows that short-term flexibility of biogas plants is mainly driven by properties of the combined heat and power unit (velocity and bandwidth). The long-term flexibility depends mainly on gas storage, mode of operation and ability for modulation of the target gas production.}, language = {en} } @article{GrafTetzlaffBiscaiadeSouzaetal.2018, author = {Graf, Karin and Tetzlaff, Ulrich and Biscaia de Souza, Gelson and Scheid, Adriano}, title = {Effect of Dilution on the Microstructure and Properties of CoCrMoSi alloy Coatings Processed on High-Carbon Substrate}, volume = {22}, pages = {e20180502}, journal = {Materials Research: Revista Ibero-Americana de Materiais}, number = {1}, publisher = {Associa{\c{c}}{\~a}o Brasileira de Metalurgia e Materiais (ABM); Associa{\c{c}}{\~a}o Brasileira de Cer{\^a}mica (ABC); Associa{\c{c}}{\~a}o Brasileira de Pol{\´i}meros (ABPol)}, address = {S{\~a}o Carlos}, issn = {1980-5373}, doi = {https://doi.org/10.1590/1980-5373-MR-2018-0502}, year = {2018}, abstract = {The Laves phase reinforced CoCrMoSi alloy system has emerged as a candidate material to protect the surface of components to withstand harsh environments under wear and/or corrosion. However, previous reports have raised some concerns and restricted a wider selection of iron-based substrates to be coated, especially limiting the carbon content. This work aims to outline the Laves - Carbides phases in the microstructure and its effect on the properties of T400 alloy deposited on GGG40 ductile iron. Dilution of 26 \% ensured Laves formation either as primary or secondary, due to high-silicon substrate selected. Departing from 41 \% dilution, the alloy changed to a completely carbide strengthened system. Therefore, for the lowest dilution the coatings hardness is dictated by Laves phase whereas, for higher ones, carbides are the most influent phases.}, language = {en} } @article{SchlingensiepenMehmoodNemtanu2015, author = {Schlingensiepen, J{\"o}rn and Mehmood, Rashid and Nemtanu, Florin Codrut}, title = {Framework for an Autonomic Transport System in Smart Cities}, volume = {15}, journal = {Cybernetics and information technologies}, number = {5}, publisher = {De Gruyter}, address = {Berlin}, issn = {1314-4081}, doi = {https://doi.org/10.1515/cait-2015-0016}, pages = {50 -- 62}, year = {2015}, abstract = {Today the concept of smart cities is discussed in scientific society and politics. A core function of smart cities is transportation. This paper gives a short overview on the concepts for Intelligent Transport Systems (ITS) for smart cities and proposes a framework for the design of an autonomic transportation system that provides personalized mobility services to its users in a smart city setting. The transportation poses extreme environment for ICT systems due to fast moving vehicles and users, requiring real-time acquisition and high performance processing of large scale data, and rapidly changing communication networks topologies and node densities. The aim of this paper is to propose a framework that will act as a reference for the design of future transportation systems that are able to cope with the ever rising system complexities and users' demands. Therefore, a backbone system providing information at different levels was designed following the principles of a corporative ICT that were proposed in [1]. The framework fulfills the main requirement providing suitable information about the local decision engines in vehicles and infrastructure interacting in smart cities traffic systems.}, language = {en} } @article{HandwerkerKesslerMarzbani2021, author = {Handwerker, Michael and Kessler, J{\"o}rg and Marzbani, Hormoz}, title = {Review of mechanical properties of and optimisation methods for continuous fibre‑reinforced thermoplastic parts manufactured by fused deposition modelling}, volume = {6}, journal = {Progress in Additive Manufacturing}, number = {4}, publisher = {Springer Nature}, address = {Cham}, issn = {2363-9520}, doi = {https://doi.org/10.1007/s40964-021-00187-1}, pages = {663 -- 677}, year = {2021}, abstract = {A new way of manufacturing continuous fibre-reinforced plastics is the embedding of fibres in the filament of a 3D printer. This method could be used in manufacturing composite materials with a thermoplastic matrix containing glass, Kevlar and carbon fibres. This paper provides an overview of research on the mechanical and physical properties of these parts as well as optimisation approaches of additively manufactured thermoplastics. Furthermore, applicable testing and analysis methods and their corresponding standards are included. Several studies, which represent the current state of the art, are reviewed in detail for the analysis of the mechanical performance of different fibre reinforcements. In addition, an overview of different optimisation approaches is given. The ultimate tensile strength of Kevlar and glass fibre-reinforced parts are similar to those of common Aluminium alloys whereas the carbon fibre reinforced parts outperform their aluminium counterparts. Major performance limitations include a poor adhesion between layers as well as a high air void ratio.}, language = {en} } @article{AgricolaPalmJaegleetal.2025, author = {Agricola, Barbara and Palm, Frank and J{\"a}gle, Eric A. and Kerschenlohr, Annegret}, title = {Influence of alloying elements on precipitation formation and mechanical properties of Al-Cr-Mo-Sc-Zr alloys during laser powder bed fusion at room and elevated temperatures}, volume = {2025}, journal = {Journal of Materials Research and Technology}, number = {36}, publisher = {Elsevier}, address = {Rio de Janeiro}, issn = {2238-7854}, doi = {https://doi.org/10.1016/j.jmrt.2025.04.255}, pages = {6632 -- 6645}, year = {2025}, abstract = {Most of the high-strength aluminium alloys for Laser Powder Bed Fusion (L-PBF) in research are based on conventional hardenable Al-Cu, Al-Mg-Si and Al-Zn-Mg alloys that have issues with hot-cracking during the L-PBF process. This study investigates the effect of alloying elements on two novel Al-Cr-Mo-Sc-Zr alloys (Scancromal® variants) with a good, crack-free processability and strength-ductility combination. A layer thickness of 100 μm was used, highlighting the high productivity and good processability of Al-Cr alloys. Heat treatments and hardness measurements were conducted to investigate peak age heat treatment and revealed a relation between Sc/Zr-ratio and peak aged temperature. SEM observations of small precipitates at grain boundaries and fracture surfaces contributed to understanding the changing fracture mechanism from less ductile (2.4-10.2\% elongation) to very ductile (14.1-19\% elongation). Tensile tests at elevated temperatures and creep tests showed a positive effect of Cr and Mo on high temperature strength. High-temperature properties, especially creep results of Al-Cr alloys and Scalmalloy® (Al-Mg-Mn-Sc-Zr) are presented for the first time and emphasize the increased heat-resistance by Cr and Mo. The threshold stress, below which theoretically no creep should occur, of the presented Scancromal® variants is at least 5 times higher (142-189 MPa) compared to Scalmalloy® (28 MPa). A comprehensive comparison of the results to literature values of AlSi10Mg, other Al-Cr alloys and high temperature Al alloys gives valuable insight on how the aging response, microstructure, ductility and high-temperature strength of this type of alloy is influenced by its alloying elements.}, language = {en} } @article{GottwaltKubaschinskiWaltzetal.2025, author = {Gottwalt, Albin and Kubaschinski, Paul and Waltz, Manuela and Tetzlaff, Ulrich}, title = {Influence of shear cutting parameters on the edge properties and the fatigue behavior of non-oriented electrical steel sheets}, volume = {56}, journal = {Materials Science \& Engineering Technology}, number = {4}, publisher = {Wiley}, address = {Weinheim}, issn = {0933-5137}, doi = {https://doi.org/10.1002/mawe.202400094}, pages = {537 -- 548}, year = {2025}, abstract = {The fatigue behavior of a fully processed, non-oriented electrical steel sheet is investigated for different shear cutting parameters. Therefore, three cutting clearances (15 μm, 35 μm and 50 μm) in combination with two different punching tool wear states (sharp and worn) are compared regarding their mechanical properties. For this purpose, surface measurements, nanoindentation tests and stress-controlled fatigue tests with a positive load ratio are performed for all six parameter sets. During shear cutting the material gets locally strain-hardened and a deformed surface with micro-notches is created. Compared to a polished reference condition, the fatigue strength of the shear-cut sheets is severely deteriorated. However, the intensity of deterioration varies depending on the shear cutting parameters. For small cutting clearances, the highest fatigue life is observed for a sharp cutting tool. In contrast, for medium and high cutting clearances, samples that are cut with a worn tool achieve higher fatigue lives. Surface characteristics in the fracture zone, which act as a failure-critical crack location, are considered as the main influencing factor.}, language = {en} } @article{SalamatElsbacher2022, author = {Salamat, Babak and Elsbacher, Gerhard}, title = {Centralized Control in Networks of Underactuated Nonidentical Euler-Lagrange Systems Using a Generalised Multicoordinates Transformation}, volume = {10}, journal = {IEEE Access}, publisher = {IEEE}, address = {New York}, issn = {2169-3536}, doi = {https://doi.org/10.1109/ACCESS.2022.3178606}, pages = {58311 -- 58319}, year = {2022}, abstract = {Controlling the network of underactuated Euler-Lagrange (EL) systems is challenging because of their coupled inertia matrices and time-variant control input matrices. We present generalized multi-coordinates transformation that renders the network of underactuated Euler-Lagrange dynamics in particular forms, whose mechanical properties should be preserved. The network of N nonidentical Euler-Lagrange EL-systems is modeled as a weighted interconnection graph where each EL-system is a node, and the control action at each node is a function of its state and the states of its neighbors. Second, we propose an online optimally centralized control mechanism with the prime objective of energy efficiency. The result is applied to the network of underactuated vertical takeoff and landing aircraft with strong input coupling, including the effect of the weight of the rotors into the dynamical system models. In this regard, we obtain very simple and powerful state-feedback solutions.}, language = {en} } @article{ReumSchmittSummetal.2024, author = {Reum, Tobias and Schmitt, David and Summ, Thorsten and Trinkl, Christoph and Ochs, Fabian and Schrag, Tobias}, title = {Experimental analysis of parallel operation of two heat sources in a dual-source heat pump incorporating two compressors}, volume = {2025}, journal = {International Journal of Refrigeration}, number = {171}, publisher = {Elsevier}, address = {Amsterdam}, issn = {1879-2081}, doi = {https://doi.org/10.1016/j.ijrefrig.2024.12.013}, pages = {124 -- 138}, year = {2024}, abstract = {Dual-source heat pumps have the potential to improve heating efficiency and / or the space required for heat sources. Parallel operation of two heat sources using two compressors can increase these benefits but poses technological challenges - specifically in the increased refrigerant cycle interconnection complexity, refrigerant and compressor oil management. These benefits and challenges have yet to be thoroughly investigated which is the primary objective of this research paper. An experimental analysis was conducted on a dual-source heat pump that utilized both an air heat source and a ground heat source. It included both individual and parallel operation modes of the heat sources. A prototype with a novel two-compressor interconnection was designed, manufactured, and tested in laboratory conditions. Analysis of the energetic benefit included efficiency evaluation at different ambient conditions and the corresponding loads on the ground source heat exchanger. Energetically, the single source operation showed comparable results in the coefficient of performance to conventional heat pumps despite the increased interconnection complexity. Parallel operation could efficiently cover heating loads at reduced load on the individual heat sources (at -7 °C, a reduction to 41 \% on the ground-source and 58 \% on the air-source heat exchanger). Technological challenges were highlighted in refrigerant and compressor oil shifts. While a control-based solution for the refrigerant shift was demonstrated, the oil shift requires further analysis of oil conditions in failing compressors.}, language = {en} } @article{KiehlScheidGrafetal.2022, author = {Kiehl, Maximilian and Scheid, Adriano and Graf, Karin and Ernst, Benedikt and Tetzlaff, Ulrich}, title = {Coaxial Laser Cladding of Cobalt-Base Alloy Stellite™ 6 on Grey Cast Iron Analysis of the Microstructural and Mechanical Properties Depending on the Laser Power}, volume = {32}, journal = {Journal of Materials Engineering and Performance}, number = {8}, publisher = {Springer}, address = {New York}, issn = {1544-1024}, doi = {https://doi.org/10.1007/s11665-022-07358-3}, pages = {3821 -- 3838}, year = {2022}, abstract = {A high-power diode laser was used to generate single- and multi-bead coatings of Stellite™ 6 by coaxial laser cladding over flat grey cast iron (EN-GJLP-200) as a preliminary study to develop a wear and corrosion resistant coating for brake disks on a cost-effective substrate. In this article, we have focused on a detailed quantitative analysis of the effect of different laser powers (1.5, 2.0, 2.5, 3.0, 3.5, and 4.0 kW) on the bead geometry, dilution, microstructure, and hardness. Coatings dilution or composition depends directly on the laser power as well as bead geometry. The typical microstructure of the coatings comprises a solid solution of α (hcp)- and β (fcc)-Co with a dendritic structure as a metal matrix and an interdendritic lamellar eutectic, which contains predominantly β-Co, chromium carbides Cr7C3 and Cr23C6 as well as blocky tungsten carbide W2C. Coating hardness depends on the chemical composition and microstructure that is modified by the deposition parameters. Low laser power results in high carbide fraction and most refined microstructures, accounting for harder coatings.}, language = {en} } @article{GueldaliDeRoseMittagetal.2025, author = {G{\"u}ldali, Derya and De Rose, Angela and Mittag, Max and Gr{\"u}bel, Benjamin and Neuhaus, Holger and Tetzlaff, Ulrich}, title = {Interconnection of low-temperature metallization on silicon solar cells - The role of silver in tin-bismuth-based solder alloys}, volume = {2025}, pages = {113488}, journal = {Solar Energy Materials and Solar Cells}, number = {285}, publisher = {Elsevier}, address = {Amsterdam}, issn = {1879-3398}, doi = {https://doi.org/10.1016/j.solmat.2025.113488}, year = {2025}, abstract = {This study investigates the potential of tin-bismuth (SnBi) alloys micro-alloyed with silver (Ag) to enhance low-temperature (LT) soldering for photovoltaic (PV) modules. The primary focus is on addressing challenges such as intermetallic compound (IMC) formation, which can compromise mechanical strength and durability under thermal cycling, thereby improving the long-term stability of solder joints. A systematic investigation of the influence of the Ag amount is being conducted with the intention to find the optimal alloy composition for SnBi solder joints on LT metallization contacts. The objective is to provide a cost-effective, lead-free alternative for the interconnection of temperature-sensitive solar cells like silicon heterojunction (SHJ) cells. The findings illustrate that the addition of 0.4 \%wt. Ag notably enhances the wettability and initial mechanical strength of the solder. An increase in the Ag content to 1.0 \%wt. results in an excessive growth of IMC, which in turn leads to increased brittleness and potential long-term stability issues of the solder joint. Thermal cycling tests demonstrate that modules soldered with SnBiAg0.4 exhibited less than -5 \% loss in power. This composition represents an optimal balance between performance and cost. These findings show the potential of SnBiAg0.4 as a suitable solder alloy regarding long-term stability and electrical performance for interconnection of LT metallization contacts of solar cells in PV module manufacturing.}, language = {en} } @article{MehtaZoerner2025, author = {Mehta, Kedar and Z{\"o}rner, Wilfried}, title = {Optimizing Agri-PV System: Systematic Methodology to Assess Key Design Parameters}, volume = {18}, pages = {3877}, journal = {Energies}, number = {14}, publisher = {MDPI}, address = {Basel}, issn = {1996-1073}, doi = {https://doi.org/10.3390/en18143877}, year = {2025}, abstract = {Agrivoltaic (Agri-PV) systems face the critical challenge of balancing photovoltaic energy generation with crop productivity, yet systematic approaches to quantifying the trade-offs between these objectives remain scarce. In this study, we identify nine essential design indicators: panel tilt angle, elevation, photovoltaic coverage ratio, shading factor, land equivalent ratio, photosynthetically active radiation (PAR) utilization, crop yield stability index, water use efficiency, and return on investment. We introduce a novel dual matrix Analytic Hierarchy Process (AHP) to evaluate their relative significance. An international panel of eighteen Agri-PV experts, encompassing academia, industry, and policy, provided pairwise comparisons of these indicators under two objectives: maximizing annual energy yield and sustaining crop output. The high consistency observed in expert responses allowed for the derivation of normalized weight vectors, which form the basis of two Weighted Influence Matrices. Analysis of Total Weighted Influence scores from these matrices reveal distinct priority sets: panel tilt, coverage ratio, and elevation are most influential for energy optimization, while PAR utilization, yield stability, and elevation are prioritized for crop productivity. This methodology translates qualitative expert knowledge into quantitative, actionable guidance, clearly delineating both synergies, such as the mutual benefit of increased elevation for energy and crop outcomes, and trade-offs, exemplified by the negative impact of high photovoltaic coverage on crop yield despite gains in energy output. By offering a transparent, expert-driven decision-support tool, this framework enables practitioners to customize Agri-PV system configurations according to local climatic, agronomic, and economic contexts. Ultimately, this approach advances the optimization of the food energy nexus and supports integrated sustainability outcomes in Agri-PV deployment.}, language = {en} } @article{RieglGaullBeitelschmidt2023, author = {Riegl, Peter and Gaull, Andreas and Beitelschmidt, Michael}, title = {Simulation-Based Testing and Performance Evaluation of Vehicle Safety Functions}, volume = {7}, pages = {12-07-01-0006}, journal = {SAE International Journal of Connected and Automated Vehicles}, number = {1}, publisher = {SAE International}, address = {Warrendale}, issn = {2574-0741}, doi = {https://doi.org/10.4271/12-07-01-0006}, pages = {69 -- 93}, year = {2023}, language = {en} } @article{VolpatodeSouzaPintoPereiraLemosetal.2023, author = {Volpato, Guilherme and de Souza Pinto Pereira, Adriano and Lemos, Georges and Schmitt, Matthias and Glatzel, Uwe and Pyczak, Florian and Tetzlaff, Ulrich and Fredel, M{\´a}rcio Celso}, title = {Out-of-Equilibrium Formation of Ni3Ti η-Phase in Inconel X-750 Produced via Laser Powder Bed Fusion and Spark Plasma Sintering}, volume = {54}, journal = {Metallurgical and Materials Transactions A: Physical metallurgy and materials science}, number = {5}, publisher = {Springer}, address = {Boston}, issn = {1073-5623}, doi = {https://doi.org/10.1007/s11661-022-06946-1}, pages = {1924 -- 1936}, year = {2023}, language = {en} } @article{VolpatodeSouzaPintoPereiraFredeletal.2024, author = {Volpato, Guilherme and de Souza Pinto Pereira, Adriano and Fredel, M{\´a}rcio Celso and Tetzlaff, Ulrich}, title = {On the Development of a Heat Treatment for Inconel Alloy X-750 Produced Using Laser Powder Bed Fusion}, volume = {55}, journal = {Metallurgical and Materials Transactions A: Physical metallurgy and materials science}, number = {11}, publisher = {Springer}, address = {Boston}, issn = {1073-5623}, doi = {https://doi.org/10.1007/s11661-024-07589-0}, pages = {4585 -- 4599}, year = {2024}, language = {en} } @article{AmaralFiorentinGoellinger2020, author = {Amaral, Jana{\´i}na R. and Fiorentin, Thiago Antonio and G{\"o}llinger, Harald}, title = {Improvement of vehicle stability using a controller based on reinforcement learning}, volume = {14}, journal = {International Journal of Vehicle Systems Modelling and Testing (IJVSMT)}, number = {2-3}, publisher = {Inderscience}, address = {Genf}, issn = {1745-6436}, doi = {https://doi.org/10.1504/IJVSMT.2020.111677}, pages = {97 -- 112}, year = {2020}, language = {en} } @article{MehtaWrightBrownetal.2025, author = {Mehta, Kedar and Wright, Andrew and Brown, Neil and Z{\"o}rner, Wilfried}, title = {Transitioning to Low-Carbon Heating: Decision-Making Approach for Cold Communities}, volume = {9}, pages = {zkaf010}, journal = {Clean Energy}, number = {4}, publisher = {Oxford University Press}, address = {Oxford}, issn = {2515-396X}, doi = {https://doi.org/10.1093/ce/zkaf010}, year = {2025}, abstract = {Selecting a sustainable heat energy supply system for high-altitude, cold-climatic communities in developing countries is essential for both decision-makers and the scientific community. However, no comprehensive guide or framework exists to address this issue and decarbonize cold communities sustainably. This research aims to fill that gap by identifying and developing a methodology for selecting a suitable heat energy supply system, using Kyrgyzstan as a case study. The approach takes into account renewable energy sources, local conditions, and specific criteria necessary for designing a sustainable energy supply. The paper introduces a decision-making framework based on 17 criteria, covering geographical, environmental, economic, technical, and social aspects, derived from the opinions of over 20 experts. This framework serves as a guide for selecting and designing an appropriate heat energy supply system. Five heat supply options are analyzed in Kyrgyzstan's high-altitude, cold rural setting to demonstrate the framework's potential. The analysis reveals that centralized district heating is the most suitable solution, scoring 79\% for system selection. This methodology is partially or fully transferable to regions or countries with similar climates and local circumstances, offering a valuable resource for the development of sustainable heat energy solutions in cold, high-altitude communities.}, language = {en} } @article{DriesWallmerspergerKessler2023, author = {Dries, Fabian W. and Wallmersperger, Thomas and Kessler, J{\"o}rg}, title = {Homogenization of plane ring mesh under static loading}, volume = {23}, pages = {e202300021}, journal = {Proceedings in applied mathematics and mechanics: PAMM}, number = {2}, publisher = {Wiley}, address = {Weinheim}, issn = {1617-7061}, doi = {https://doi.org/10.1002/pamm.202300021}, year = {2023}, abstract = {Plane ring meshes can be produced in large dimensions for various applications, for example, in architecture or protective systems. The numerical simulation of all individual rings of ring meshes is very costly, which is why methods to abstract the structure have been sought in the past. In this paper, a method for determining the strain parameters of a representative ring mesh section under in-plane tensile loads is presented. Methods of rigid body analysis and representative volume elements with periodic boundary conditions are used. Green Lagrangian strain tensors are determined for both an exemplary representative ring mesh section under different tensile load cases and an experimental ring mesh under one load case. The comparison of the Green Lagrangian strain tensors of the ring meshes between numerical simulations and experiments shows a very good agreement.}, language = {en} } @article{HuberDiel2022, author = {Huber, Otto and Diel, Sergej}, title = {Design f{\"u}r Leichtbau und Nachhaltigkeit}, volume = {2022}, journal = {Technik in Bayern: Nachrichten aus Technik, Naturwissenschaft und Wirtschaft: das Regionalmagazin f{\"u}r VDI und VDE}, number = {1}, publisher = {MuP Verlag GmbH}, address = {M{\"u}nchen}, issn = {1610-6563}, url = {https://www.technik-in-bayern.de/mehr-technik/ingenieurskunst/design-fuer-leichtbau-und-nachhaltigkeit}, pages = {14 -- 15}, year = {2022}, language = {de} } @article{BaerSaidiHackletal.2019, author = {B{\"a}r, Katharina and Saidi, Abdessamad and Hackl, Christoph and Z{\"o}rner, Wilfried}, title = {Combined operation of photovoltaic and biogas plants for optimal transformer loading}, volume = {2019}, journal = {Chemical Engineering Transactions}, number = {76}, publisher = {AIDIC The Italian Association of Chemical Engineering}, address = {Milano}, issn = {2283-9216}, doi = {https://doi.org/10.3303/CET1976101}, pages = {601 -- 606}, year = {2019}, language = {en} } @article{StarkContiSaidietal.2019, author = {Stark, Matthias and Conti, Fosca and Saidi, Abdessamad and Z{\"o}rner, Wilfried and Greenough, Richard}, title = {Steam storage systems for flexible biomass CHP plants}, volume = {2019}, pages = {105321}, journal = {Biomass and Bioenergy}, subtitle = {evaluation and initial model based calculation}, number = {128}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0961-9534}, doi = {https://doi.org/10.1016/j.biombioe.2019.105321}, year = {2019}, language = {en} } @article{StarkPhilippSaidietal.2019, author = {Stark, Matthias and Philipp, Matthias and Saidi, Abdessamad and Trinkl, Christoph and Z{\"o}rner, Wilfried and Greenough, Richard}, title = {Design parameters of steam accumulators for the utilization in industrial solid biomass-fuelled CHP plants}, volume = {2019}, journal = {Chemical Engineering Transactions}, number = {76}, publisher = {AIDIC The Italian Association of Chemical Engineering}, address = {Milano}, issn = {2283-9216}, doi = {https://doi.org/10.3303/CET1976137}, pages = {817 -- 822}, year = {2019}, language = {en} } @article{WernerEhrenwirthMuschiketal.2021, author = {Werner, Melanie and Ehrenwirth, Mathias and Muschik, Sebastian and Trinkl, Christoph and Schrag, Tobias}, title = {Operational experiences with a temperature-variable district heating network for a rural community}, volume = {46}, journal = {Chemical Engineering \& Technology}, number = {3}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {0930-7516}, doi = {https://doi.org/10.1002/ceat.202100114}, pages = {482 -- 490}, year = {2021}, abstract = {The potential of utilizing temperature-variable district heating systems in rural areas was investigated. A local district heating system in Germany and the related project NATAR are briefly described; measurement data is evaluated. Operational experiences with a seasonal temperature reduction and consequent advantages for different heat generation systems and heat storages are discussed. The analysis of measurement data reveals a high optimization potential for solar thermal systems in case of an integration both into a low- and a high-temperature storage. Furthermore, a combined heat-and-power plant in combination with a CO2 heat pump promises sector-coupling potential and high electricity self-consumption.}, language = {en} } @article{SlonskiSchrag2019, author = {Slonski, Matthias and Schrag, Tobias}, title = {Linear optimisation of a settlement towards the energy-plus house standard}, volume = {12}, pages = {210}, journal = {Energies}, number = {2}, publisher = {MDPI}, address = {Basel}, issn = {1996-1073}, doi = {https://doi.org/10.3390/en12020210}, year = {2019}, abstract = {Future buildings will use technologies that are either well-known, innovative, or a combination thereof in order to be environmentally friendly and feasible at the same time. To evaluate and compare such systems through simulation, adaptive tools need to be available. This paper describes a conceived method for planning quarters and settlements. The novelty of this work emerges from the combination of a building simulation with a linear economic optimisation of the energy system, to achieve the energy-plus house standard for a settlement. Furthermore, the tools applied are adaptive or open source. In this article, a hypothetical basic example is given for a predefined idealised settlement, which consists of 132 single-family houses of one building type. The hourly demand for electrical energy and heat is established for three energy-efficiency classes for the building type with a dynamic simulation in MATLAB/SIMULINK using the CARNOT toolbox. This toolbox is also used to calculate the specific electrical energy production by photovoltaics. The components for the energy system of the settlement are implemented in the open source linear optimisation tool URBS. An economic optimum for the energy system of the settlement is found for each of the energy efficiency classes for an accumulated energy demand of the buildings. In this way, a lossless energy hub between the buildings is assumed. The results of the conducted simulations indicate that the optimal ratio of air/water to ground/water heat pumps shifts towards air/water heat pumps with more energy efficient houses. This is due to the lower specific investment costs, which outweigh the operational costs when less energy is required. The lowest costs for the entire energy system are for the one with the most energy efficient settlement. This is the case, as the costs for the higher energy standard of the buildings are not considered in the calculations. The behaviour of the optimisation is tested and discussed through a sensitivity analysis for one efficiency class. By presenting this simple, comprehensible example, an impression of the possible applications for this methodology is conveyed.}, language = {en} } @article{GottwaltKubaschinskiWaltzetal.2022, author = {Gottwalt, Albin and Kubaschinski, Paul and Waltz, Manuela and Glatzel, Uwe and Tetzlaff, Ulrich}, title = {An experimental setup for fatigue testing of thin electrical steel sheets}, volume = {2022}, pages = {106987}, journal = {International Journal of Fatigue}, number = {162}, publisher = {Elsevier}, address = {Oxford}, issn = {0142-1123}, doi = {https://doi.org/10.1016/j.ijfatigue.2022.106987}, year = {2022}, abstract = {In this study, the fatigue behavior of thin electrical steel sheets under cyclic loading is investigated. Results from strain-controlled and stress-controlled fatigue tests with different specimen geometries and different test setups are presented and compared with conventional testing methods. The results imply that conventional testing methods should be adjusted for testing thin electrical steel sheets because the fatigue life depends significantly on the test setup as well as the specimen geometry. Therefore, this study proposes an improved specimen geometry and test setup for stress- and strain-controlled fatigue tests of thin electrical steel sheets depending on the desired testing parameters.}, language = {en} } @article{MehtaMingalevaZoerneretal.2022, author = {Mehta, Kedar and Mingaleva, Ekaterina and Z{\"o}rner, Wilfried and Degembaeva, Nadira and Baibagyshov, Ermek}, title = {Comprehensive analysis of the energy legislative framework of Kyrgyzstan}, volume = {2022}, pages = {100013}, journal = {Cleaner Energy Systems}, subtitle = {Investigation to develop a roadmap of Kyrgyz renewable energy sector}, number = {2}, publisher = {Elsevier}, address = {Amsterdam}, issn = {2772-7831}, doi = {https://doi.org/10.1016/j.cles.2022.100013}, year = {2022}, abstract = {Kyrgyzstan - a Central Asian country - faces a high degree of energy insecurity. Especially the Kyrgyz power sector suffers from outdated infrastructure and is not capable of fulfilling the growing and fluctuating inter-seasonal energy demand. On the contrary, the country is endowed with an abundant amount of renewable energies, which can significantly contribute to bringing stability to the energy sector. The current energy policy is considered as one of the key barriers to the developing the renewable energy sector in Kyrgyzstan. Hence, there is an immediate need to evaluate the formulated energy policy to investigate gaps and uncertainties. In response to that, the presented study is the first attempt that provides an in-depth assessment of Kyrgyzstan's current energy legislative framework. It determines the primary mechanisms for the operation and conduction of renewable energy sources in terms of legal and economic aspects. Furthermore, it provides detailed insight into the current Feed-in tariff calculation methodology and scrutinizes the special provisions for private investors. Based on the in-depth assessment, the article recapitulates the shortfall in the existing energy policies. The article found that there is huge potential available for the renewable energy market. To unlock that, the presented article emahsised on synergestic policy making approach to overcome barriers and expand the Kyrgyz renewable energy sector. The article further showcased how the improvements in the regulatory framework would raise the interest of the private investors / local energy players to promote the installation of renewable energy technologies over the county.}, language = {en} } @article{MehtaEhrenwirthTrinkletal.2022, author = {Mehta, Kedar and Ehrenwirth, Mathias and Trinkl, Christoph and Z{\"o}rner, Wilfried}, title = {Mapping Potential for Improving Rural Energy Services in Kyrgyzstan: Factors for Achieving Sustainable Development Goals in the Community Context}, volume = {3}, journal = {World}, number = {3}, publisher = {MDPI}, address = {Basel}, issn = {2673-4060}, doi = {https://doi.org/10.3390/world3030032}, pages = {586 -- 606}, year = {2022}, abstract = {Energy is a pivotal element for overall development. Therefore, affordable and clean energy for all (Sustainable Development Goal 7) is one of the important elements. Despite a suitable approach, Kyrgyzstan lags behind to achieve its Sustainable Development Goals by 2030. Improving access to energy can significantly impact the progress of many other sustainable development targets. However, access to reliable, sustainable, and adequate energy is a crucial task in rural Kyrgyzstan. Taking into consideration the energy situation and the importance of the availability of energy services, the overarching aim of the presented article is to map the potential of improving rural energy services to foster overall sustainable development goals. The article presents the most relevant information about rural energy usage behaviour based on three primary pillars: energy demand, energy carrier, and energy sources. In addition, the presented research article synthesises the key driving factors which have a direct or indirect impact on the energy services in rural areas. The summarised data displays a deep insight into a variety of complex and dynamic household energy consumption patterns. The article provides a potential solution nexus to foster improved energy services in rural Kyrgyzstan and therefore to foster the overall sustainable development in Kyrgyzstan. The findings of the article help to formulate a strategy to design rural energy services for policy makers and stockholders.}, language = {en} } @article{ThambiSchiesslWaltzetal.2017, author = {Thambi, Joel Luther and Schiessl, Andreas and Waltz, Manuela and Lang, Klaus-Dieter and Tetzlaff, Ulrich}, title = {Modified Constitutive Creep Laws With Micromechanical Modeling of Pb-Free Solder Alloys}, volume = {139}, pages = {031002}, journal = {Journal of Electronic Packaging}, number = {3}, publisher = {The American Society of Mechanical Engineers}, address = {New York}, issn = {1528-9044}, doi = {https://doi.org/10.1115/1.4035850}, year = {2017}, language = {en} } @article{ThambiTetzlaffSchiessletal.2016, author = {Thambi, Joel Luther and Tetzlaff, Ulrich and Schiessl, Andreas and Lang, Klaus-Dieter and Waltz, Manuela}, title = {High cycle fatigue behaviour and generalized fatigue model development of lead-free solder alloy based on local stress approach}, journal = {Microelectronics Reliability}, number = {66}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0026-2714}, doi = {https://doi.org/10.1016/j.microrel.2016.10.004}, pages = {98 -- 105}, year = {2016}, language = {en} } @article{SalamatElsbacher2022, author = {Salamat, Babak and Elsbacher, Gerhard}, title = {Steering a Swarm of Large-Scale Underactuated Mechanical Systems Using a Generalized Coordinates Transformation}, volume = {9}, pages = {702}, journal = {Aerospace}, number = {11}, publisher = {MDPI}, address = {Basel}, issn = {2226-4310}, doi = {https://doi.org/10.3390/aerospace9110702}, year = {2022}, abstract = {Steering large-scale particle or robot systems is challenging because of their high dimensionality. We use a centralized stochastic approach that allows for optimal control at the cost of a central element instead of a decentralized approach. Previous works are often restricted to the assumption of fully actuated robots. Here we propose an approach for underactuated robots that allows for energy-efficient control of the robot system. We consider a simple task of gathering the robots (minimizing positional variance) and steering them towards a goal point within a bounded area without obstacles. We make two main contributions. First, we present a generalized coordinate transformation for underactuated robots, whose physical properties should be considered. We choose Euler-Lagrange systems that describe a large class of robot systems. Second, we propose an optimal control mechanism with the prime objective of energy efficiency. We show the feasibility of our approach in robot simulations.}, language = {en} } @article{ChandraMaederBienertetal.2022, author = {Chandra, Sourav and Maeder, Marcus and Bienert, J{\"o}rg and Beinersdorf, H. and Jiang, W. and Matsagar, Vasant and Marburg, S.}, title = {Identification of temperature-dependent elastic and damping parameters of carbon-epoxy composite plates based on experimental modal data}, volume = {2023}, pages = {109945}, journal = {Mechanical Systems and Signal Processing}, number = {187}, publisher = {Elsevier}, issn = {0888-3270}, doi = {https://doi.org/10.1016/j.ymssp.2022.109945}, year = {2022}, language = {en} } @article{MehtaZoernerGreenough2022, author = {Mehta, Kedar and Z{\"o}rner, Wilfried and Greenough, Richard}, title = {Residential Building Construction Techniques and the Potential for Energy Efficiency in Central Asia: Example from High-Altitude Rural Settlement in Kyrgyzstan}, volume = {15}, pages = {8869}, journal = {Energies}, number = {23}, publisher = {MDPI}, address = {Basel}, issn = {1996-1073}, doi = {https://doi.org/10.3390/en15238869}, year = {2022}, abstract = {Building construction in rural Kyrgyzstan is heavily dominated by earthen buildings. Old and inappropriate residential building structures contribute significantly to high domestic space heating energy consumption. Therefore, it is necessary to understand the relevant building construction techniques. However, the scant information on Kyrgyz building techniques, especially for high-altitude rural settlements, was the prime motivation to perform the presented study. The key objective of the study is to investigate residential building construction techniques in high-altitude rural Kyrgyzstan, and this was to be achieved by house visits during field trips, literature review, and pilot interviews with local people. The analysis enabled the detailed identification of individual building envelopes as well as predominant building materials to be recorded. Based on the assessment, a housing profile was created that represents the typical characteristics of traditional rural Kyrgyz houses. Furthermore, the study demonstrates the potential for energy savings in rural Kyrgyz houses of 50-70\%. However, local conditions prevent people from making improvements to all domestic energy efficiency parameters simultaneously. Therefore, the study developed a 'sequential roadmap' to reduce domestic space heating demand in different phases based on simulation studies. Existing low-income rural Kyrgyz habitations can use the presented roadmap to reduce domestic space heating demand sequentially to overcome financial barriers and, therefore, contribute to establishing sustainable buildings in Kyrgyzstan. These results may be partially replicated in other Central Asian rural communities depending on their location and building characteristics.}, language = {en} } @article{StarkTrinklZoerneretal.2018, author = {Stark, Matthias and Trinkl, Christoph and Z{\"o}rner, Wilfried and Greenough, Richard}, title = {Methodological Evaluation of Storage Systems for Flexible Power Generation from Solid Biomass}, volume = {41}, journal = {Chemical Engineering \& Technology}, number = {11}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1521-4125}, doi = {https://doi.org/10.1002/ceat.201800099}, pages = {2168 -- 2176}, year = {2018}, language = {en} } @article{FunkDrechslerFiorentinGoellinger2021, author = {Funk Drechsler, Maikol and Fiorentin, Thiago Antonio and G{\"o}llinger, Harald}, title = {Actor-Critic Traction Control Based on Reinforcement Learning with Open-Loop Training}, volume = {2021}, pages = {4641450}, journal = {Modelling and Simulation in Engineering}, publisher = {Hindawi}, address = {New York}, issn = {1687-5605}, doi = {https://doi.org/10.1155/2021/4641450}, year = {2021}, abstract = {The use of actor-critic algorithms can improve the controllers currently implemented in automotive applications. This method combines reinforcement learning (RL) and neural networks to achieve the possibility of controlling nonlinear systems with real-time capabilities. Actor-critic algorithms were already applied with success in different controllers including autonomous driving, antilock braking system (ABS), and electronic stability control (ESC). However, in the current researches, virtual environments are implemented for the training process instead of using real plants to obtain the datasets. This limitation is given by trial and error methods implemented for the training process, which generates considerable risks in case the controller directly acts on the real plant. In this way, the present research proposes and evaluates an open-loop training process, which permits the data acquisition without the control interaction and an open-loop training of the neural networks. The performance of the trained controllers is evaluated by a design of experiments (DOE) to understand how it is affected by the generated dataset. The results present a successful application of open-loop training architecture. The controller can maintain the slip ratio under adequate levels during maneuvers on different floors, including grounds that are not applied during the training process. The actor neural network is also able to identify the different floors and change the acceleration profile according to the characteristics of each ground.}, language = {en} } @article{SelleneitStoecklHolzhammer2020, author = {Selleneit, Volker and St{\"o}ckl, Martin and Holzhammer, Uwe}, title = {System efficiency: methodology for rating of industrial utilities in electricity grids with a high share of variable renewable energies}, volume = {2020}, pages = {109969}, journal = {Renewable and Sustainable Energy Reviews}, subtitle = {a first approach}, number = {130}, publisher = {Elsevier}, address = {Amsterdam}, issn = {1364-0321}, doi = {https://doi.org/10.1016/j.rser.2020.109969}, year = {2020}, language = {en} } @article{SelleneitStoecklPhilippetal.2019, author = {Selleneit, Volker and St{\"o}ckl, Martin and Philipp, Matthias and Mast, Tanja and Holzhammer, Uwe and Schlosser, Florian}, title = {System efficiency rating of industrial utilities in electricity grids with a high share of variable renewable energies}, volume = {2019}, journal = {Chemical Engineering Transactions}, number = {76}, publisher = {AIDIC}, address = {Mailand}, issn = {2283-9216}, doi = {https://doi.org/10.3303/CET1976163}, pages = {973 -- 978}, year = {2019}, language = {en} } @article{StoecklSelleneitPhilippetal.2019, author = {St{\"o}ckl, Martin and Selleneit, Volker and Philipp, Matthias and Holzhammer, Uwe}, title = {An approach to calculate electricity costs for the german industry for a system efficient design by combining energy efficiency and demand response}, volume = {2019}, journal = {Chemical Engineering Transactions}, number = {76}, publisher = {AIDIC}, address = {Mailand}, issn = {2283-9216}, doi = {https://doi.org/10.3303/CET1976191}, pages = {1141 -- 1146}, year = {2019}, language = {en} } @article{PhilippSchummSchlosseretal.2017, author = {Philipp, Matthias and Schumm, Gregor and Schlosser, Florian and Peesel, Ron-Hendrick and Holzhammer, Uwe}, title = {Grundsatzfragen der Abw{\"a}rmenutzung}, volume = {69}, journal = {BWK - Das Energie-Fachmagazin}, number = {4}, publisher = {VDI Fachmedien}, address = {D{\"u}sseldorf}, issn = {1618-193X}, url = {https://www.ingenieur.de/fachmedien/bwk/energieversorgung/grundsatzfragen-der-abwaermenutzung/}, pages = {36 -- 39}, year = {2017}, language = {de} } @article{CorreadaSilvaVolpatoFredeletal.2019, author = {Corr{\^e}a da Silva, Cau{\^e} and Volpato, Guilherme and Fredel, M{\´a}rcio Celso and Tetzlaff, Ulrich}, title = {Low-pressure processing and microstructural evaluation of unidirectional carbon fiber-reinforced aluminum-nickel matrix composites}, volume = {2019}, journal = {Journal of Materials Processing Technology}, number = {269}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0924-0136}, doi = {https://doi.org/10.1016/j.jmatprotec.2019.01.032}, pages = {10 -- 15}, year = {2019}, language = {en} } @article{LemosFredelPyczaketal.2019, author = {Lemos, Georges and Fredel, M{\´a}rcio Celso and Pyczak, Florian and Tetzlaff, Ulrich}, title = {Influence of distinct manufacturing processes on the microstructure of Ni-based metal matrix composites submitted to long thermal exposure}, volume = {2019}, journal = {Key Engineering Materials}, number = {809}, publisher = {Trans Tech Publications}, address = {Baech}, issn = {1662-9795}, doi = {https://doi.org/10.4028/www.scientific.net/KEM.809.79}, pages = {79 -- 86}, year = {2019}, language = {en} } @article{BaderBrandmayrTrinkletal.2014, author = {Bader, Tobias and Brandmayr, Sebastian and Trinkl, Christoph and Z{\"o}rner, Wilfried and Hanby, Victor Ian}, title = {Climate Specific Design and Effectiveness of Solar DEC-systems}, volume = {2014}, journal = {Energy Procedia}, subtitle = {a Methodological Zoning Approach}, number = {48}, publisher = {Elsevier}, address = {Amsterdam}, issn = {1876-6102}, doi = {https://doi.org/10.1016/j.egypro.2014.02.090}, pages = {778 -- 789}, year = {2014}, abstract = {The climate specific effectiveness of solar DEC-systems and relevant preferable adaptions of the system design have been so far predominantly analysed based on individual simulation for selected sites. In order to systematically deduce design-specific outline data for the application of the solar DEC-technology at climatically different sites a methodological zoning approach was further developed. A subsequent meteorological analysis for 17 sites mapping the world climate creates a transparent understanding on the activity of the specific system components. This results in a comprehension on the site-specific effectiveness of solar DEC-systems and provides insights on principally relevant and efficient system configurations.}, language = {en} } @article{ReiterBrandmayrTrinkletal.2014, author = {Reiter, Christoph and Brandmayr, Sebastian and Trinkl, Christoph and Z{\"o}rner, Wilfried and Hanby, Victor Ian}, title = {Performance Optimisation of Polymeric Collectors by Means of Dynamic Simulation and Sensitivity Analysis}, volume = {2014}, journal = {Energy Procedia}, number = {48}, publisher = {Elsevier}, address = {Amsterdam}, issn = {1876-6102}, doi = {https://doi.org/10.1016/j.egypro.2014.02.023}, pages = {181 -- 191}, year = {2014}, abstract = {A dynamic flat-plate collector model for parametric sensitivity studies on polymer-based collector designs was developed. Validation using experimental results of conventional flat-plate collectors showed satisfying results especially regarding the calculation of individual part temperatures of a collector. The model was used to predict system efficiency as well as individual part temperatures in order to analyse a polymeric collector approach in comparison to a conventional collector. The simulation results showed that the fractional energy savings of systems with conventional flat-plate collectors cannot be reached with the analysed polymeric collector approach. Also the stagnation temperatures of more efficient approaches are too high for low-cost polymeric materials. The exemplary analysis of annual temperature loads of the backside insulation for different approaches proved the necessity of careful collector design aiming at temperature reduction for all individual collector parts.}, language = {en} }