06 Fakultät Luft- und Raumfahrttechnik und Geodäsie
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/7
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Item Open Access Messungen im Bereich eines Windparks mit Fokus auf tief- und niederfrequente Schallemissionen und -immissionen(2022) Blumendeller, Esther; Gaßner, Laura; Müller, Florian; Wigger, Maayen; Berlinger, Philipp; Cheng, Po WenDie Nutzung von Windenergie wird einen entscheidenden Anteil am erneuerbaren Energiemix der Zukunft haben. Während der Stromgewinnung geben Windenergieanlagen (WEA) Schall und Erschütterungen (seismische Wellen) in die Umgebung ab, vor allem im tieffrequenten Bereich. Im Zuge des interdisziplinären Verbundprojektes Inter-Wind werden akustische Messungen zur Unterstützung psychologischer Fragebögen, kombiniert mit seismischen und meteorologischen Messungen an Windparks auf der Schwäbischen Alb durchgeführt. Ziel des Projektes ist es, die Gründe für Belästigung der Anwohner in Zusammenhang mit den Immissionen der WEA zu verstehen. Hierbei liegt der Fokus auf dem tieffrequenten (20-200 Hz) und niederfrequenten (1-20 Hz) Bereich. Akustische und seismische Messungen wurden an einem Windpark auf der Schwäbischen Alb, mit drei WEA des Typs GE 2.75-120 durchgeführt. Parallel dazu konnten Anwohner Belästigungszeiträume über eine Geräuschmelde-App dokumentieren. In diesem Beitrag wird die Umsetzung einer interdisziplinären Messkampagne im Bereich des Tegelberg Windparks und eines Wohngebäudes in Tallage in ca. 1 km Entfernung zum Windpark beschrieben. Schließlich werden erste Ergebnisse der akustischen Messungen und interdisziplinären Untersuchung vorgestellt und diskutiert.Item Open Access Rheology, dispersion, and cure kinetics of epoxy filled with amine‐ and non‐functionalized reduced graphene oxide for composite manufacturing(2021) Ackermann, Annika C.; Carosella, Stefan; Rettenmayr, Markus; Fox, Bronwyn L.; Middendorf, PeterThis study evaluates the effect of plasma surface functionalization of reduced graphene oxide particles on the processing characteristics and homogeneity of dispersion of a bisphenol A‐(epichlorhydrin) epoxy matrix and amine‐based hardener with varying weight fractions from 0.00 to 1.50 wt%. It was observed that amine‐functionalized reduced graphene oxide leads to a more drastic viscosity increase of up to 18‐fold of the uncured suspensions and that its presence influences the conversion rates of the curing reaction. Optical microscopy of thin sections and transmission electron microscopy analysis showed that a more homogeneous dispersion of the particles could be achieved especially at higher weight fractions by using an appropriate surface functionalization. This knowledge can be used to define suitable processing conditions for epoxies with amine‐based hardeners depending on the loading and functionalization of graphene‐related particles.Item Open Access IEA Wind Task 32: Wind Lidar : identifying and mitigating barriers to the adoption of wind lidar(2018) Clifton, Andrew; Clive, Peter; Gottschall, Julia; Schlipf, David; Simley, Eric; Simmons, Luke; Stein, Detlef; Trabucchi, Davide; Vasiljevic, Nikola; Würth, InesIEA Wind Task 32 exists to identify and mitigate barriers to the adoption of lidar for wind energy applications. It leverages ongoing international research and development activities in academia and industry to investigate site assessment, power performance testing, controls and loads, and complex flows. Since its initiation in 2011, Task 32 has been responsible for several recommended practices and expert reports that have contributed to the adoption of ground-based, nacelle-based, and floating lidar by the wind industry. Future challenges include the development of lidar uncertainty models, best practices for data management, and developing community-based tools for data analysis, planning of lidar measurements and lidar configuration. This paper describes the barriers that Task 32 identified to the deployment of wind lidar in each of these application areas, and the steps that have been taken to confirm or mitigate the barriers. Task 32 will continue to be a meeting point for the international wind lidar community until at least 2020 and welcomes old and new participants.Item Open Access Maintenance strategies for large offshore wind farms(2012) Scheu, MattiWhich equipment is needed and how shall tasks be scheduled in order to implement the economically most efficient operation and maintenance strategy for large offshore wind farms? This is the question motivating this research project. Considering production losses due to turbine downtime as well as local geographical and weather conditions, an efficient operation and maintenance (O&M) solution shall be achieved for two reference sites at the UK east coast. For this purpose, a Matlab-based tool has been developed, consisting of the following five main modules: Weather, Failures, Resources, Strategy and Cost. The "Weather" module is able to generate future sea states and wind speeds based on historical data. It uses a finite state Markov chain in discrete time to model significant wave heights. Wind speeds are then generated according to their conditional probability distribution at the corresponding wave height. In order to validate the weather module, several time series were generated and compared with existing data. For comparison, the mean values, standard errors, linear correlations and cumulative distribution functions for persistence of operational weather windows were chosen, both for synthetic and observed wind speed and wave height time series. Both reference sites in the UK North Sea were considered for validation. Failure rates are the basis for the "Failure" module. As an input, data gathered from onshore reliability investigations are used, which can be updated once more detailed data is available for offshore turbines. The outcomes of this module are turbine-failures occurring at a certain time. Within the “Resources” module, it is defined which equipment and personnel is available for O&M activities. The equipment is specified by its technical characteristics, e.g., the maximum transportable personnel and the operational wave height boundary. Another key parameter is the "Strategy". The main goal of this module is to take the decision whether to perform an operation or not. Within this thesis, one specific strategy has been used, but references are made to possible modifications in the according paragraphs. The measurement of economic performance is done in the "Cost" module. Here, production losses are quantified by combining the wind speed during a failure with the linearized power curve of the turbine and the local buyback price system. Therefore, the worth of additional or better maintenance equipment can be seen directly as an increase in availability and a decrease of production losses. Results show how sensitive availability and therefore production losses change with respect to changes in the maintenance fleet, reliability characteristics of components and distance to shore. Major improvements of availability were achieved by applying maintenance vessels with a higher operational wave height boundary. An increase of this constraint from one to 1.8 m significant wave height raised the availability by up to 30 percent, leading to a much better economic performance. The influence of the weather forecast accuracy on the number of maintenance vessel and crane deployments is also stated, showing a significant increase of deployments if the weather forecast is only accurate for short times. An improvement of component-reliability, modeled as a 50% decreased annual failure rate, could save up to 440 k€ of yearly production losses for each modeled wind turbine. Higher transit times, due to a greater distance to shore, strongly decrease the wind park availability.Item Open Access Using GRACE data to study the impact of snow and rainfall on terrestrial water storage in Northeast China(2020) Qian, An; Yi, Shuang; Chang, Le; Sun, Guangtong; Liu, XiaoyangWater resources are important for agricultural, industrial, and urban development. In this paper, we analyzed the influence of rainfall and snowfall on variations in terrestrial water storage (TWS) in Northeast China from Gravity Recovery and Climate Experiment (GRACE) gravity satellite data, GlobSnow snow water equivalent product, and ERA5-land monthly total precipitation, snowfall, and snow depth data. This study revealed the main composition and variation characteristics of TWS in Northeast China. We found that GRACE provided an effective method for monitoring large areas of stable seasonal snow cover and variations in TWS in Northeast China at both seasonal and interannual scales. On the seasonal scale, although summer rainfall was 10 times greater than winter snowfall, the terrestrial water storage in Northeast China peaked in winter, and summer rainfall brought about only a sub-peak, 1 month later than the maximum rainfall. On the interannual scale, TWS in Northeast China was controlled by rainfall. The correlation analysis results revealed that the annual fluctuations of TWS and rainfall in Northeast China appear to be influenced by ENSO (EI Niño-Southern Oscillation) events with a lag of 2-3 years. In addition, this study proposed a reconstruction model for the interannual variation in TWS in Northeast China from 2003 to 2016 on the basis of the contemporary terrestrial water storage and rainfall data.Item Open Access Acoustic and seismic emissions from wind turbines(2017) Calarco, Francesca; Cheng, Po Wen; Zieger, Toni; Ritter, JoachimWith regards to the interdisciplinary “TremAc” Project funded by the German Federal Ministry for Economic Affairs and Energy, this paper examines acoustic and seismic emissions generated by wind turbines with the aim of identifying a better understanding of their interaction. Measurement campaigns will be carried out in the field around a single wind turbine plant and results in terms of acoustic and seismic signals will be correlated and then evaluated in relation to environmental factors such as wind speed, wind direction and temperature as well as to data related to the wind turbines-specifications (e.g. rotation speed).Item Open Access Validation of the safety requirements of the landing gear using fault tree analysis(2022) Iven, Leander; Zaidi, YaseenWe analyze the functionality of the landing system of a regional aircraft in the extension and cruise flight modes and validate safety requirements through the fault tree analysis. The main landing gear system is captured in the electromechanical-fluidic domain and system behavior is abstracted in an elementary hydraulic circuit. The functional representation is then constructed into a fault tree which allows analysis of the failure propagation originating at different branch terminals, for instance, at the main landing gear actuator which extends the gear and holds it retracted during the cruise, door actuator, door uplocks, and hydraulic power supply. Each component is assigned a failure probability. Each failure mode is abstracted as a top-level event having a probability of failure and through Boolean combinations of component failures in the lower branches. Two reliability aspects considered are the availability to fully lower the landing gear and the integrity of inadvertent gear or door extension while cruising. Architectural changes through undercarriage system reconfiguration and component redundancy have been exploited to improve system failure rates. The analysis determines the overall system failure rate against the flight cycles. The process is agile to accommodate design changes with the evolution of architecture during the systems engineering lifecycle.Item Open Access Simulating asteroid impacts and meteor events by high-power lasers : from the laboratory to spaceborne missions(2023) Ferus, Martin; Knížek, Antonín; Cassone, Giuseppe; Rimmer, Paul B.; Changela, Hitesh; Chatzitheodoridis, Elias; Uwarova, Inna; Žabka, Ján; Kabáth, Petr; Saija, Franz; Saeidfirozeh, Homa; Lenža, Libor; Krůs, Miroslav; Petera, Lukáš; Nejdl, Lukáš; Kubelík, Petr; Křivková, Anna; Černý, David; Divoký, Martin; Pisařík, Michael; Kohout, Tomáš; Palamakumbure, Lakshika; Drtinová, Barbora; Hlouchová, Klára; Schmidt, Nikola; Martins, Zita; Yáñez, Jorge; Civiš, Svatopoluk; Pořízka, Pavel; Mocek, Tomáš; Petri, Jona; Klinkner, SabineMeteor plasmas and impact events are complex, dynamic natural phenomena. Simulating these processes in the laboratory is, however, a challenge. The technique of laser induced dielectric breakdown was first used for this purpose almost 50 years ago. Since then, laser-based experiments have helped to simulate high energy processes in the Tunguska and Chicxulub impact events, heavy bombardment on the early Earth, prebiotic chemical evolution, space weathering of celestial bodies and meteor plasma. This review summarizes the current level of knowledge and outlines possible paths of future development.Item Open Access Numerical study on the aerodynamic characteristics of the NACA 0018 airfoil at low Reynolds number for Darrieus wind turbines using the Transition SST model(2021) Rogowski, Krzysztof; Królak, Grzegorz; Bangga, GalihA symmetrical NACA 0018 airfoil is often used in such applications as small-to-medium scale vertical-axis wind turbines and aerial vehicles. A review of the literature indicates a large gap in experimental studies of this airfoil at low and moderate Reynolds numbers in the previous century. This gap has limited the potential development of classical turbulence models, which in this range of Reynolds numbers predict the lift coefficients with insufficiently accurate results in comparison to contemporary experimental studies. Therefore, this paper validates the aerodynamic performance of the NACA 0018 airfoil and the characteristics of the laminar separation bubble formed on its suction side using the standard uncalibrated four-equation Transition SST turbulence model and the unsteady Reynolds-averaged Navier-Stokes (URANS) equations. A numerical study was conducted for the chord Reynolds number of 160,000, angles of attack between 0 and 11 degrees, as well as for the free-stream turbulence intensity of 0.05%. The calculated lift and drag coefficients, aerodynamic derivatives, as well as the location and length of the laminar bubble quite well agree with the results of experimental measurements taken from the literature for validation. A sensitivity study of the numerical model was performed in this paper to examine the effects of the time-step size, geometrical parameters and mesh distribution around the airfoil on the simulation results. The airfoil data sets obtained in this work using the Transition SST and the k-ω SST turbulence models were used in the improved double multiple streamtube (IDMS) to calculate aerodynamic blade loads of a vertical-axis wind turbine. The characteristics of the normal component of the aerodynamic blade load obtained by the Transition SST approach are much better suited to the experimental data compared to the k-ω SST turbulence model.Item Open Access Uncertainty quantification for full-flight data based engine fault detection with neural networks(2022) Weiss, Matthias; Staudacher, Stephan; Mathes, Jürgen; Becchio, Duilio; Keller, ChristianCurrent state-of-the-art engine condition monitoring is based on a minimum of one steady-state data point per flight. Due to the scarcity of available data points, there are difficulties distinguishing between random scatter and an underlying fault introducing a detection latency of several flights. Today’s increased availability of data acquisition hardware in modern aircraft provides continuously sampled in-flight measurements, so-called full-flight data. These full-flight data give access to sufficient data points to detect faults within a single flight, significantly improving the availability and safety of aircraft. Artificial neural networks are considered well suited for the timely analysis of an extensive amount of incoming data. This article proposes uncertainty quantification for artificial neural networks, leading to more reliable and robust fault detection. An existing approach for approximating the aleatoric uncertainty was extended by an Out-of-Distribution Detection in order to take the epistemic uncertainty into account. The method was statistically evaluated, and a grid search was performed to evaluate optimal parameter combinations maximizing the true positive detection rates. All test cases were derived based on in-flight measurements of a commercially operated regional jet. Especially when requiring low false positive detection rates, the true positive detections could be improved 2.8 times while improving response times by approximately 6.9 compared to methods only accounting for the aleatoric uncertainty.