04 Fakultät Energie-, Verfahrens- und Biotechnik
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/5
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Item Open Access Assessing fatigue life cycles of material X10CrMoVNb9-1 through a combination of experimental and finite element analysis(2023) Rahim, Mohammad Ridzwan Bin Abd; Schmauder, Siegfried; Manurung, Yupiter H. P.; Binkele, Peter; Dusza, Ján; Csanádi, Tamás; Ahmad, Meor Iqram Meor; Mat, Muhd Faiz; Dogahe, Kiarash JamaliThis paper uses a two-scale material modeling approach to investigate fatigue crack initiation and propagation of the material X10CrMoVNb9-1 (P91) under cyclic loading at room temperature. The Voronoi tessellation method was implemented to generate an artificial microstructure model at the microstructure level, and then, the finite element (FE) method was applied to identify different stress distributions. The stress distributions for multiple artificial microstructures was analyzed by using the physically based Tanaka-Mura model to estimate the number of cycles for crack initiation. Considering the prediction of macro-scale and long-term crack formation, the Paris law was utilized in this research. Experimental work on fatigue life with this material was performed, and good agreement was found with the results obtained in FE modeling. The number of cycles for fatigue crack propagation attains up to a maximum of 40% of the final fatigue lifetime with a typical value of 15% in many cases. This physically based two-scale technique significantly advances fatigue research, particularly in power plants, and paves the way for rapid and low-cost virtual material analysis and fatigue resistance analysis in the context of environmental fatigue applications.Item Open Access The natural breakup length of a steady capillary jet : application to serial femtosecond crystallography(2021) Gañán-Calvo, Alfonso M.; Chapman, Henry N.; Heymann, Michael; Wiedorn, Max O.; Knoska, Juraj; Gañán-Riesco, Braulio; López-Herrera, José M.; Cruz-Mazo, Francisco; Herrada, Miguel A.; Montanero, José M.; Bajt, SašaOne of the most successful ways to introduce samples in Serial Femtosecond Crystallography has been the use of microscopic capillary liquid jets produced by gas flow focusing, whose length-to-diameter ratio and velocity are essential to fulfill the requirements of the high pulse rates of current XFELs. In this work, we demonstrate the validity of a classical scaling law with two universal constants to calculate that length as a function of the liquid properties and operating conditions. These constants are determined by fitting the scaling law to a large set of experimental and numerical measurements, including previously published data. Both the experimental and numerical jet lengths conform remarkably well to the proposed scaling law. We show that, while a capillary jet is a globally unstable system to linear perturbations above a critical length, its actual and shorter long-term average intact length is determined by the nonlinear perturbations coming from the jet breakup itself. Therefore, this length is determined solely by the properties of the liquid, the average velocity of the liquid and the flow rate expelled. This confirms the very early observations from Smith and Moss 1917, Proc R Soc Lond A Math Phys Eng, 93, 373, to McCarthy and Molloy 1974, Chem Eng J, 7, 1, among others, while it contrasts with the classical conception of temporal stability that attributes the natural breakup length to the jet birth conditions in the ejector or small interactions with the environment.Item Open Access Optimizing aerosol-based sample delivery for single particle imaging at X-ray Free-Electron Lasers : pushing the limits: boosting data collection, minimizing background noise, and expanding sample compatibility(2024) Rafie-Zinedine, Safi; Heymann, Michael (Jun.Prof. Dr.)One of the most promising applications of X-ray Free Electron Lasers (XFELs) is the imaging of isolated particles, such as proteins, using single-particle X-ray diffractive imaging (SPI). This technique can provide high-resolution structural information on individual particles and facilitate the study of dynamic processes at the nanoscale. SPI, employing gas phase injection through an aerodynamic lens stack (ALS), has attracted significant attention due to its low background scattering and suitability for high-rate data collection. Despite these advantages, these SPI experiments encounter several challenges, especially with smaller and lighter biomolecule particles. These include low signal strength, limited collected datasets, high background scattering, and issues with sample compatibility in delivery system. In this doctoral thesis, I address the latter three challenges by developing and optimizing traditional electrospray-based gas phase sample delivery systems for SPI at XFELs. My research aims to enhance particle transmission efficiency, reduce background scattering, and expand the conductivity range of these systems to enable high-resolution imaging of smaller biological particles. I have developed three modified electrospray systems based on the traditional system to improve SPI at XFELs: enhanced electrospray, helium electrospray (He-ES), and coaxial helium electrospray (CHeES). The enhanced electrospray, upgraded from the traditional system by exploring different neutralizers and geometries, achieves an eightfold increase in particle transmission efficiency by employing a VUV neutralizer and optimizing the counter electrode's orifice size. This enhanced system achieves over 40% particle transmission from solution to the X-ray interaction region. The He-ES system uses a 3D-printed nozzle to reduce N2 and CO2 usage compared to traditional electrospray while ensuring stable sample delivery. It enhances particle delivery efficiency tenfold for 26 nm-sized biological particles and decreases gas load in the interaction chamber by 80%. Lastly, the CHeES system uses a coaxial 3D-printed nozzle to accommodate a broader conductivity range up to 40 000 µS/cm-eight times higher than traditional systems, and to lower background noise using He-ES technique. In tests at the European XFEL, the CHeES system notably lowered background noise by more than threefold in helium mode. My findings indicate improvements in transmission efficiency, background noise reduction, and sample versatility in SPI experiments, potentially enhancing both data quality and quantity. These advancements could yield higher-resolution structures and expand the scope for studying diverse biological and material science samples. My research has broader implications for structural biology, as obtaining higher-resolution structures is crucial for understanding the atomic structure of proteins and other biomolecules.Item Open Access Investigation of tungsten exposed to fusion relevant intense H/He particle fluxes and thermal loads(2016) Lemahieu, Nathan; Tovar, Günter (Prof. Dr.)Item Open Access Experimental and numerical study of turbulence in fusion plasmas using reflectometry synthetic diagnostics(2018) Zadvitskiy, Georgiy; Tovar, Günter (Prof. Dr.)Anomalous energy and particle transport is closely related to micro-turbulence. Therefore plasma turbulence studies are essential for successful operation of magnetic confinement fusion devices. This thesis deals with the development of interpretative models for Ultra-Fast Swept Reflectometry (USFR), a diagnostic used for the measurement of turbulence radial wave-number spectra in fusion devices. While the interpretation of reflectometry data is quite straightforward for small levels of turbulence, it becomes much trickier for larger levels as the reflectometer answer is no longer linear with the turbulence level. It has been shown for instance that resonances due to probing field trapping can appear in turbulent plasma and produce jumps of the signal phase. In the plasma edge region the turbulence level is usually high and can lead to a non-linear regime of the reflectometer response. The loss of probing beam coherency and beam widening when the probing beam crosses the edge turbulence layer can affect USFR core measurements. Edge turbulence with a long correlation length leads to small beam widening and strong distortion of the probing wave phase. However backscattering effects from turbulence with short correlation lengths are also able to cause reflectometer signal change. To study turbulence wave-number spectra as well as reflectometer signal phase variations, signal amplitude variations can be analized. Unlike signal phase variation, amplitude does not suffer from resonant jumps, and can give more clear qualitative evaluation of turbulence structure. In the case when the turbulence amplitude peaked in the edge region, it can be detected as spectral peak near local Bragg resonance wave-number. USFR with a set of receiving antennas arranged poloidally was proposed to obtain more information on the edge turbulence properties. A displacement of the spectral peak appears when the receiving antenna is misaligned with the emitting one. Peak displacement measurements could provide additional information on probing beam shaping and turbulence properties and help in coherent mode observation as well. A 2D full wave code was applied as a synthetic diagnostic to Gysela gyro-kinetic code data to study Tore-Supra tokamak core turbulence. Radial correlation lengths computed from the amplitude of multi-channel fixed frequency reflectometry signals 5have shown good agreement with the turbulence correlation length directly computed from the simulation. The synthetic diagnostic was then applied to analyse the correlation length and wave-number spectra obtained by USFR in the ASDEX-Upgrade tokamak. A comparison between 1D and 2D results have shown different behaviour. However correlation lengths measured with UFSR signals are in the same order with turbulence ones.Item Open Access A consistent and implicit Rhie-Chow interpolation for drag forces in coupled multiphase solvers(2021) Hanimann, Lucian; Mangani, Luca; Darwish, Marwan; Casartelli, Ernesto; Vogt, Damian M.The use of coupled algorithms for single fluid flow simulation has proven its superiority as opposed to segregated algorithms, especially in terms of robustness and performance. In this paper, the coupled approach is extended for the simulation of multi-fluid flows, using a collocated and pressure-based finite volume discretization technique with a Eulerian-Eulerian model. In this context a key ingredient in this method is extending the Rhie-Chow interpolation technique to account for the unique flow coupling that arises from inter-phase drag. The treatment of this inter-fluid coupling and the fashion in which it interacts with the velocity-pressure solution algorithm is presented in detail and its effect on robustness and accuracy is demonstrated using 2D dilute gas-solid flow test case. The results achieved with this technique show substantial improvement in accuracy and performance when compared to a leading commercial code for a transonic nozzle configuration.