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High-temperature calibration methods in additive manufacturing involve the use of advanced techniques to accurately measure and control the temperature of the build material during the additive manufacturing process. Infrared cameras, blackbody radiation sources and non-linear optimization algorithms are used to correlate the temperature of the material with its emitted thermal radiation. This is essential for ensuring the quality and repeatability of the final product. This paper presents the calibration procedure of an imaging system for in-situ measurement of absolute temperatures and temperature gradients during powder bed fusion of metal with laser beam (PBF-LB/M) in the temperature range of 500 K–1500 K. It describes the design of the optical setup to meet specific requirements in this application area as well as the procedure for accounting the various factors influencing the temperature measurement. These include camera-specific effects such as varying spectral sensitivities of the individual pixels of the sensor as well as influences of the exposure time and the exposed sensor area. Furthermore, influences caused by the complex optical path, such as inhomogeneous transmission properties of the galvanometer scanner as well as angle-dependent transmission properties of the f-theta lens were considered. A two-step fitting algorithm based on Planck's law of radiation was applied to best represent the correlation. With the presented procedure the calibrated thermography system provides the ability to measure absolute temperatures under real process conditions with high accuracy.
In this paper the applicability of different optical measurement techniques for species and temperature detection in internal combustion engines is discussed, especially for hydrogen combustion. The presented techniques cover the flame luminosity, the laser-induced fluorescence, laser Rayleigh scattering, spontaneous Raman scattering and non-linear Raman measurement techniques like coherent anti-Stokes Raman scattering. The potential of the 2-dimensional detection of hydrogen via spontaneous Raman scattering is discussed.
Planar laser-induced fluorescence (PLIF) has been successfully used for the investigation of the mixture formation process in hydrogen engines for passenger cars. Detailed information has been obtained about process development (qualitative measurement) and on fuel/air-ratio (quantitative measurement) inside the combustion chamber. These results can be used for further optimization of mixture formation and combustion process concerning emissions and fuel consumption. The measurement technique used is not only limited to hydrogen or to passenger car engines, but can also be applied to other fuel gases like natural gas or to other engine sizes like bus engines. The main topic of this paper is the experimental verification of the procedure which was executed by simultaneous PLIF and Raman scattering measurements. By Raman scattering the fuel/air-ratio can directly be determined from direct concentration measurements of the different gas species. The fuel/air-ratios determined by PLIF and Raman measurements are in good agreement indicating that a quantitative fuel/air-ratio measurement during the mixture formation process of gas and hydrogen engines is possible by PLIF. This fact is also confirmed by other measurements, e.g., global fuel/air-ratio calculated from measured intake air and fuel gas flow.
Verbrauchsfern erzeugter Strom aus regenerativen Energien kann über große Distanzen am wirtschaftlichsten mittels der Hochspannungsgleichstromübertragung (HGÜ) transportiert werden. Die HGÜ führt zu einer veränderten elektrischen Belastung der Hochspannungskomponenten. Transiente Übergangsvorgänge bestimmen die elektrischen Feldverteilungen. Bei der Berechnung elektrischer Feldverteilungen in Isoliersystemen für die Hochspannungsgleichstromübertragung (HGÜ) mit Hilfe der Finiten-Elemente-Methode (FEM) wurden die dielektrischen Eigenschaften bisher in Form von Permittivitäten und parameterabhängigen Leitfähigkeiten berücksichtigt. Langsame Polarisationsvorgänge werden dabei nicht berücksichtigt. Für die Berechnung komplexer Isoliersysteme durch die FEM ist deshalb die Beschreibung der langsamen Polarisationsvorgänge im Isolierstoff durch Differentialgleichungen wünschenswert, die direkt in die FEM einbezogen werden und mit denen je nach Bedarf sowohl einzelne Polarisationsmechanismen als auch ihre Überlagerungen berücksichtigt werden können. In dieser Arbeit werden hierfür auf Basis des bekannten Debye-Ansatzes, und in Analogie zum Netzwerkmodell, zusätzlich zu den Gleichungen, die Verschiebungs- und Leitungsströme beschreiben, weitere Differentialgleichungen direkt in die FEM einbezogen, welche die feld- und temperaturabhängigen Polarisationsströme individuell abbilden. Die Materialfunktionen und ihre Parameter werden durch Messung von Polarisations- und Depolarisationsströmen (PDC) ermittelt. Durch die Implementierung von beliebigen Polarisationsmechanismen in einem FEM-Programm wurde eine Lücke der Berechnungsmöglichkeiten von komplexen, auch dreidimensionalen Isoliersystemen geschlossen, in denen oftmals stationäre oder transiente Temperaturgradienten vorliegen und in denen sich transiente elektrische Feldverteilungen ausbilden. Zur Verifizierung des beschriebenen Berechnungsverfahrens werden transiente Potentialverläufe an den Steuerbelägen von entsprechend modifizierten Hochspannungsdurchführungen unter Gleich- und Umpolspannungen sowie unter thermischen Gradienten gemessen. Dabei kann eine bisher nicht erreichte Übereinstimmung der transienten und stationären Potentialverläufe zwischen FEM-Simulation und Messung erzielt werden. Auswirkungen auf Prüf- und Belastungsszenarien werden anhand von Simulationen diskutiert.
Nowadays, cable systems are often preferred when deciding on the type of new transmission lines even in the high and extra high voltage range. One of the main reasons is the better public acceptance. In addition, the power to be transmitted in the grid is increasing leading to increased ohmic losses and thus, to higher thermal stress on the materials. The investigations in this contribution focus on cable joints, which represent important and decisive components of cable systems. In order to optimize the design and to ensure reliable operation over the entire service life, the temperature profile within these components is of special interest. For their detailed investigation, a test circuit was set up consisting of a cable section and sections with build-up stages of a cable joint. A large number of measuring points were defined also at points where no measurement is possible in normal operation. With a thermographic camera the surface temperature distributions were observed. With the laboratory setup temperature profiles under various load conditions were recorded. A detailed FEM model was built and verified with help of these measurements. The model permits the investigation of specific questions of cable systems such as the comparison of temperature loads resulting from normal operating conditions and of test procedures according to the relevant standards. Besides others the effect of stressing the insulation and sealing system by heating the inner conductor vs. heating from outside by surrounding water is discussed.
Bei der Berechnung elektrischer Feldverteilungen in Isoliersystemen für die Hochspannungsgleichstromübertragung (HGÜ) mit Hilfe der Finiten Elemente Methode (FEM) werden die dielektrischen Eigenschaften bisher meist in Form von Permittivitäten und Leitfähigkeiten berücksichtigt. Da die transienten Verläufe nicht ausreichend genau abgebildet werden, ist Stand der Technik die Polarisationsvorgänge exakter durch Netzwerkmodelle nachzubilden. Durch Implementierung von Polarisationsmechanismen in einem FEM-Programm wurde diese Lücke geschlossen und es können nun elektrische Feldverteilungen vor allem im transienten Zustand wesentlich präziser berechnet werden. In Analogie zum RC-Netzwerkmodell werden hierfür zusätzlich zu den Gleichungen, die die feldabhängigen Verschiebungs- und Leitungsströme beschreiben, weitere Differentialgleichungen eingesetzt, welche die ebenfalls feldabhängigen Polarisationsströme abbilden. Die Materialfunktionen und ihre Parameter werden durch Messung von Polarisations- und Depolarisationsströmen (PDC) ermittelt. Diese Gleichungen werden sowohl für die RC-Netzwerkmodelle als auch für die Aufstellung der Differentialgleichungen für die FEM benötigt. Sie können unmittelbar auf die am jeweiligen Ort im Isoliersystem herrschende Temperatur umgerechnet werden. Somit sind transiente elektrische Feldberechnungen auch für komplexe Isoliersysteme möglich, die sich nur durch mehrdimensionale FEM-Modelle abbilden lassen und in denen oftmals stationäre oder transiente Temperaturgradienten vorliegen. Das beschriebene Berechnungsverfahren wird durch die rückwirkungsfreie Messung transienter Potentialverläufe an den Steuerbelägen von entsprechend modifizierten kondensatorgesteuerten Hochspannungsdurchführungen verifiziert. Dabei kann eine höhere Übereinstimmung der transienten und stationären Potentialverläufe zwischen Simulation und Messung erzielt werden.
Measurements and calculations of critical thermal and electrical stress conditions for HVDC bushings
(2017)
Powder Bed Monitoring Using Semantic Image Segmentation to Detect Failures during 3D Metal Printing
(2023)
Monitoring the metal Additive Manufacturing (AM) process is an important task within the scope of quality assurance. This article presents a method to gain insights into process quality by comparing the actual and target layers. Images of the powder bed were captured and segmented using an Xception–style neural network to predict the powder and part areas. The segmentation result of every layer is compared to the reference layer regarding the area, centroids, and normalized area difference of each part. To evaluate the method, a print job with three parts was chosen where one of them broke off and another one had thermal deformations. The calculated metrics are useful for detecting if a part is damaged or for identifying thermal distortions. The method introduced by this work can be used to monitor the metal AM process for quality assurance. Due to the limited camera resolutions and inconsistent lighting conditions, the approach has some limitations, which are discussed at the end.
Versatile model order reduction techniques for the reduction of dynamic systems have been presented in the last decades. Krylov subspace based methods are considered as efficient in terms of computational effort and reduction order and can be used in order to match the transfer function locally. However, they lack of a simple and efficient automatisation and error estimation. On the other hand, modal reduction is popular because it leads to exactly matching eigenfrequencies. The static behaviour and the overall accuracy of the frequency response, though, are poor. In this paper, a combination of both methods is presented and discussed.
In order to characterise a method for the reduction of mechanical models for the simulation of machine tools and similar mechatronic systems, first, the requirements on the model reduction method are derived. Criteria for the relative error of the frequency response function, the transmission zeros, and the poles are defined and the idea of defining a frequency range of interest is established.
Subsequently, a combination of Krylov and modal subspaces for the reduction of dynamic systems with second-order structure and proportional damping is presented. It is shown that the combination of the bases of the two methods leads to a combination of the advantages and an elimination of the drawbacks of them both. Moreover, an estimation for the upper bound of the defined error criteria is developed and verified with numerical results.
The result of this paper is an a priori parametrisable and numerically efficient model reduction method, which leads to reduced systems of low order with a definable error limit within a definable frequency range.
Einfluss der absorbierenden akustischen Leistung auf die Eigenschaften von Resonanzfrequenzen
(2021)
A main research topic in acoustics is the reduction of indoor noise, which has increasingly received attention in recent years. A commonly used solution to solve these problems is reducing noise using damping structures, which absorb sound. This work aims at the numerical optimization of damping structures in interior problems, following three goals. First, the optimal damping structure for the required frequency range has to be determined. Second, the optimal position of the damping material has to be found. Third, we are focusing on lightweight design, which means that the amount of damping material used, has to be kept to a minimum. We present the implementation of a genetic algorithm into our open source code, which we use to optimize the damping behaviour and in consequence, the sound propagation for interior problems. We show an example of the application of this code.
Transfer path analysis (TPA) is a proven method for identifying critical structure-borne and airborne sound paths. The basic idea is to divide the overall system into an exciting active component (source) and a passive component, e.g. the mechanical structure to be investigated, with their respective measurement points. By separating them, two independent systems are created, whereby on one hand, the excitation behaviour can be characterised and on the other hand, the transmission behaviour can be assessed. Finally, both systems are validated by comparing them to each other and deciding whether changes to source or structure are required or not. The advantage is the simple description of the source as a black box without complex modelling. In this contribution, this systematic is applied to window regulator systems as they are found in vehicles. The focus is on a hybrid approach between experimental and numerical transfer path analysis. For this purpose, the basic workflow of suitable TPA methods is discussed. This includes the operational measurement of different exciting electric motors variants, the determination of the transfer functions of the structure, the calculation of the contact forces and the analysis of the individual transfer paths.