@article{Vetter, author = {Vetter, Mark}, title = {Simulating water temperatures and stratification of a pre-alpine lake with a hydrodynamic model}, series = {Hydrological Processes}, volume = {28}, journal = {Hydrological Processes}, number = {3}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:863-opus-20702}, pages = {1450 -- 1464}, abstract = {We report on the calibration of the one-dimensional hydrodynamic lake model Dynamic Reservoir Simulation Model to simulate the water temperature conditions of the pre-alpine Lake Ammersee (southeast Germany) that is a representative of deep and large lakes in this region. Special focus is given to the calibration in order to reproduce the correct thermal distribution and stratification including the time of onset and duration of summer stratification. To ensure the application of the model to investigate the impact of climate change on lakes, an analysis of the model sensitivity under stepwise modification of meteorological input parameters (air temperature, wind speed, precipitation, global radiation, cloud cover, vapour pressure and tributary water temperature) was conducted. The total mean error of the calibration results is -0.23 °C, the root mean square error amounts to 1.012 °C. All characteristics of the annual stratification cycle were reproduced accurately by the model. Additionally, the simulated deviations for all applied modifications of the input parameters for the sensitivity analysis can be differentiated in the high temporal resolution of monthly values for each specific depth. The smallest applied alteration to each modified input parameter caused a maximum deviation in the simulation results of at least 0.26 °C. The most sensitive reactions of the model can be observed through modifications of the input parameters air temperature and wind speed. Hence, the results show that further investigations at Lake Ammersee, such as coupling the hydrodynamic model with chemo-dynamic models to assess the impact of changing climate on biochemical conditions within lakes, can be carried out using Dynamic Reservoir Simulation Model.}, language = {en} } @article{Vetter, author = {Vetter, Mark}, title = {Using the General Lake Model (GLM) to simulate water temperatures and ice cover of a medium-sized lake}, series = {Environmental Earth Sciences}, volume = {76}, journal = {Environmental Earth Sciences}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:863-opus-20710}, abstract = {Thermal dynamics of lakes has a key role in chemical and biological processes in lakes including nutrient distributions and phytoplankton growth. Applications of hydrodynamic models to lakes can provide insights into possible future alterations in thermal dynamics induced by climate change. In this study we present the calibration and validation of the newest version of the open-source hydrodynamic model GLM (General Lake Model) to the dimictic Lake Ammersee, located in south-east Germany. The simulation of lake water temperatures for the calibration period revealed an overall root mean square error of 0.65 °C and a mean error of 0.08 °C. The seasonal stratification pattern and the annual thermal structure of this dimictic lake were reproduced by the model. The model simulated the presence of winter ice cover for the only year out of eight years simulated, when ice cover was observed. Elevated lake water temperatures were also reproduced in model simulations during a period in 2003 of unusually high air temperatures. Statistical analysis of the model calibration results for Lake Ammersee indicates a fit comparable to, or better than most other well-established hydrodynamic models and provides an opportunity for continuous simulations through periods of ice cover. Our results indicate a major improvement of GLM compared with earlier model versions and demonstrate the applicability of GLM for limnophysical studies, particularly for altered forcing conditions such as climate change.}, language = {en} } @article{Vetter, author = {Vetter, Mark}, title = {Future alterations of thermal characteristics in a medium-sized lake simulated by coupling a regional climate model with a lake model}, series = {Climate Dynamics}, volume = {44}, journal = {Climate Dynamics}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:863-opus-20723}, pages = {371 -- 384}, abstract = {Regional climate models (RCM) provide site-specific meteorological data at a suitable spatial resolution for the estimation of future climate-driven changes in aquatic ecosystems. In this study, we used meteorological data from the RCM weather-situation-based regionalization method (WETTREG), available for Germany, to force a one-dimensional hydrodynamic lake model to simulate climate-induced changes on the summer thermal stratification of Lake Ammersee in southern Germany. In comparison to the period of 2002-2010, an extension by 22 days of the summer stratification period was simulated for 2042-2050. Further, a vertical shift in the position of metalimnion and thermocline within the lake was not detected, but a slight increase in the metalimnion thickness during mid-summer of 1 m was simulated. Along with these changes in stratification patterns, warming for the epilimnion water temperatures during summer stratification and for the entire water body in winter were simulated for the future. By contrast the hypolimnion temperatures are simulated to decrease during the summer stratification. In addition to simulating future limno-physical aspects, the investigation demonstrates that the RCM data of the WETTREG projection are suitable for conducting climate change impact studies.}, language = {en} } @article{HoefflinSauerSchiffleretal., author = {H{\"o}fflin, Dennis and Sauer, Christian and Schiffler, Andreas and Hartmann, J{\"u}rgen}, title = {Process Monitoring Using Synchronized Path Infrared Thermography in PBF-LB/M}, series = {Sensors}, volume = {22}, journal = {Sensors}, number = {16}, publisher = {MDPI}, doi = {10.3390/s22165943}, pages = {5943}, abstract = {Additive manufacturing processes, particularly Laser-Based Powder Bed Fusion of Metals (PBF-LB/M), enable the development of new application possibilities due to their manufacturing-specific freedom of design. These new fields of application require a high degree of component quality, especially in safety-relevant areas. This is currently ensured primarily via a considerable amount of downstream quality control. Suitable process monitoring systems promise to reduce this effort drastically. This paper introduces a novel monitoring method in order to gain process-specific thermal information during the manufacturing process. The Synchronized Path Infrared Thermography (SPIT) method is based on two synchronized galvanometer scanners allowing high-speed and high-resolution observations of the melt pool in the SWIR range. One scanner is used to steer the laser over the building platform, while the second scanner guides the field of view of an IR camera. With this setup, the melting process is observed at different laser powers, scan speeds and at different locations with respect to the laser position, in order to demonstrate the positioning accuracy of the system and to initially gain thermal process data of the melt pool and the heat-affected zone. Therefore, the SPIT system shows a speed independent overall accuracy of ±2 Pixel within the evaluated range. The system further allows detailed thermal observation of the melt pool and the surrounding heat-affected zone.}, language = {en} } @article{KnoppShandyManaraetal., author = {Knopp, Kevin and Shandy, Amir and Manara, Jochen and Vidi, Stephan and Hartmann, J{\"u}rgen}, title = {Metrologische Apparaturen zur Messung thermophysikalischer Materialeigenschaften bei sehr hohen Temperaturen im EU-Projekt Hi-TRACE}, series = {FHWS Science Journal}, volume = {5}, journal = {FHWS Science Journal}, number = {2}, issn = {2196-6095}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:863-opus-20046}, pages = {83 -- 92}, abstract = {Industriezweige wie die Glas-Industrie, die Kraftwerkstechnik sowie die Luft- und Raumfahrttechnik m{\"u}ssen kontinuierlich neue Methoden entwickeln, sowie bestehende Verfahren optimieren, um in ihren Bereichen wettbewerbsf{\"a}hig zu sein bzw. neue Anforderungen an Umwelt- und Klimaschutz zu erf{\"u}llen. Dies beinhaltet oft die Entwicklung neuer Materialien, die leichter zu fabrizieren sind und sowohl mechanisch als auch thermisch h{\"o}heren Belastungen standhalten. F{\"u}r die genannten Industriezweige sind Prozesse mit hohen Betriebstemperaturen bis zu 3.000 °C kennzeichnend und damit ist die Kenntnis von Materialeigenschaften bei diesen extremen Temperaturen von großer Bedeutung. Auch wenn es bereits einige Messapparaturen f{\"u}r die Bestimmung von thermophysikalischen Materialdaten bei hohen Temperaturen gibt, muss die R{\"u}ckf{\"u}hrung dieser auf die SI Basiseinheiten gew{\"a}hrleistet werden, um die Zuverl{\"a}ssigkeit der gemessenen Daten f{\"u}r die Anforderung der genannten Branchen sicherzustellen. Diese Aufgabe ist das Ziel des EMPIR-(European Metrology Programme for Innovation and Research) Projektes Hi-TRACE [1]. Hi-TRACE zielt darauf ab, Referenzapparaturen und neue Methoden f{\"u}r die Messung von thermophysikalischen Materialeigenschaften, (thermische Diffusivit{\"a}t, spezifische W{\"a}rme, Emissionsgrad und Schmelztemperatur) sowie der Haftung von Schichten {\"u}ber 1.000 °C zu bestimmen.}, language = {de} } @article{OchsWehnertKnoppetal., author = {Ochs, Dennis and Wehnert, Kira-Kristin and Knopp, Kevin and Hartmann, J{\"u}rgen and Versch, Alexander and Schiffler, Andreas}, title = {Untersuchungen zur Temperaturleitf{\"a}higkeit additiv gefertigter Stahlproben in Abh{\"a}ngigkeit der relativen Dichte}, series = {FHWS Science Journal}, volume = {5}, journal = {FHWS Science Journal}, number = {2}, issn = {2196-6095}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:863-opus-19986}, pages = {75 -- 82}, abstract = {Das direkte Metall-Laser-Schmelzen (DMLS) aus der Familie der Additiven Fertigungsverfahren (AM) erm{\"o}glicht die schichtweise Erzeugung komplexer dreidimensionaler Geometrien mit hoher relativer Dichte unter Verwendung von Metallpulver als Ausgangsmaterial [1]. Die Technologie wird zunehmend eingesetzt, um innovative Bauteile material- und gewichtssparend herzustellen oder komplexe Produkte ohne zus{\"a}tzliche Werkzeuge oder Spannvorrichtungen zu fertigen. Dar{\"u}ber hinaus sind Funktionsintegrationen, zum Beispiel Gussformen mit eingepr{\"a}gten K{\"u}hlkan{\"a}len, m{\"o}glich. Da einzelne Metallpulverschichten auf vorhergehende Schichten aufgeschmolzen werden, entstehen w{\"a}hrend der Herstellung des Bauteils komplexe, zeitabh{\"a}ngige Temperaturprofile [2]. Durch den Einsatz hoher Laserintensit{\"a}ten und Scangeschwindigkeiten, bei denen die Belichtungszeit der Laserbestrahlung im Bereich von Millisekunden liegt, werden zudem extrem hohe Aufheiz- und Abk{\"u}hlraten induziert, die zu einzigartigen Mikrostrukturen und Materialeigenschaften f{\"u}hren [3]. Diese extremen Prozessbedingungen k{\"o}nnen sich jedoch auch negativ auf den Fertigungsprozess auswirken. Bei komplexen Bauteilen bleibt die Prozessstabilit{\"a}t und Qualit{\"a}tssicherung Umfragen zufolge weiterhin die wichtigste technologische Barriere f{\"u}r den Einsatz additiv gefertigter Bauteile in hochbelasteten oder sicherheitsrelevanten Bereichen [4]. Daher verspricht der Zusammenhang zwischen Temperaturprofil w{\"a}hrend der Fertigung, relativer Dichte der Bauteile, sowie thermophysikalischer Eigenschaften additiv gefertigter Proben wichtige Erkenntnisse, insbesondere im Hinblick auf eine zerst{\"o}rungsfreie Qualit{\"a}tssicherung, sowie neue Anwendungsm{\"o}glichkeiten.}, language = {de} } @article{JuergenArduiniManaraetal., author = {J{\"u}rgen, Hartmann and Arduini, Mariacarla and Manara, Jochen and Stark, Thomas and Ebert, Hans-Peter}, title = {Development and Evaluation of an Improved Apparatus for Measuring the Emissivity at High Temperatures}, series = {Sensors}, volume = {21}, journal = {Sensors}, number = {18}, issn = {1424-8220}, doi = {10.3390/s21186252}, abstract = {An improved apparatus for measuring the spectral directional emissivity in the wavelength range between 1 µm and 20 µm at temperatures up to 2400 K is presented in this paper. As a heating unit an inductor is used to warm up the specimen, as well as the blackbody reference to the specified temperatures. The heating unit is placed in a double-walled vacuum vessel. A defined temperature, as well as a homogenous temperature distribution of the whole surrounding is ensured by a heat transfer fluid flowing through the gap of the double-walled vessel. Additionally, the surrounding is coated with a high-emitting paint and serves as blackbody-like surrounding to ensure defined boundary conditions. For measuring the spectral directional emissivity at different emission angles, a movable mirror is installed in front of the specimen, which can be adjusted by a rotatable arrangement guiding the emitted radiation into the attached FTIR-spectrometer. The setup of the emissivity measurement apparatus (EMMA) and the measurement procedure are introduced, and the derived measurement results are presented. For evaluating the apparatus, measurements were performed on different materials. The determined emissivities agree well with values published in literature within the derived relative uncertainties below 4\% for most wavelengths.}, language = {en} } @article{WehnertOchsSchmittetal., author = {Wehnert, Kira-Kristin and Ochs, Dennis and Schmitt, Jan and Hartmann, J{\"u}rgen and Schiffler, Andreas}, title = {Reducing Lifecycle Costs due to Profile Scanning of the Powder Bed in Metal Printing}, series = {Procedia CIRP 98}, volume = {98}, journal = {Procedia CIRP 98}, publisher = {Elsevir}, pages = {684 -- 689}, abstract = {First time right is one major goal in powder based 3D metal printing. Reaching this goal is driven by reducing life cycle costs for quality measures, to minimize scrap rate and to increase productivity under optimal resource efficiency. Therefore, monitoring the state of the powder bed for each printed layer is state of the art in selective laser melting. In the most modern approaches the quality monitoring is done by computer vision systems working with an interference on trained neural networks with images taken after exposure and after recoating. There are two drawbacks of this monitoring method: First, the sensor signals - the image of the powder bed - give no direct height information. Second, the application of this method needs to be trained and labeled with reference images for several cases. The novel approach presented in this paper uses a laser line scanner attached to the recoating machine. With this new concept, a direct threshold measure can be applied during the recoating process to detect deviations in height level without prior knowledge. The evaluation can be done online during recoating and feedback to the controller to monitor each individual layer. Hence, in case of deviations the location in the printing plane is an inherent measurement and will be used to decide which severity of error is reported. The signal is used to control the process, either by starting the recoating process again or stopping the printing process. With this approach, the sources of error for each layer can be evaluated with deep information to evaluate the cause of the error. This allows a reduction of failure in the future, which saves material costs, reduces running time of the machine life cycle phase in serial production and results in less rework for manufactured parts. Also a shorter throughput time per print job results, which means that the employee can spent more time to other print jobs and making efficient use of the employee's work force. In summary, this novel approach will not only reduce material costs but also operating costs and thus optimize the entire life cycle cost structure. The paper presents a first feasibility and application of the described approach for test workpieces in comparison to conventional monitoring systems on an EOS M290 machine.}, language = {en} } @article{GielingerBohnDeinzeretal., author = {Gielinger, Sebastian and Bohn, Gunther and Deinzer, Frank and Linke, Andreas}, title = {Investigation of an inline inspection method for the examination of cylinder-like specular surfaces using deflectometry}, series = {applied sciences}, volume = {12}, journal = {applied sciences}, number = {13}, issn = {2076-3417}, abstract = {An optical measuring method is presented, with which it is possible to measure and evaluate reflective cylindrical surfaces using a combination of deflectometry and subsequent reconstruction of the surface. The system is set up and tested on rolling elements of cylindrical roller bearings. However, it is not limited to this use case and can be applied to other cylindrical specular surfaces. The system distinguishes itself from existing test methods through the combination of high-resolution three-dimensional defect measurement with a very short recording time, and offers the possibility of introducing tolerance limits in the production of cylindrical specular surfaces. With this method, it is possible to record a defect with the dimensions of 1.3 mm by 1.8 mm within 5 s and to reconstruct the absolute depth. The resolution of the system is below 10 μm in both X- and Y-direction, and is therefore sufficiently accurate to detect typical surface defects such as scratches, dents, or deformations. To validate the measured values of the system, the results of an artificially generated 10.35 μm deep defect location were compared with those of a highly accurate mechanical stylus measurement.}, language = {en} }