http://hdl.handle.net/10993/90 Search this channel search https://orbilu.uni.lu/simple-search http://hdl.handle.net/10993/43867 Title: Microstructure-based multiscale modeling of mechanical response for materials with complex microstructures <br/> <br/>Author, co-author: Kabore, Brice Wendlassida <br/> <br/>Abstract: Complex microstructures are found in several material especially in biological tissues, geotechnical materials and many manufactured materials including composites. These materials are difficult to handle by classical numerical analysis tools and the need to incorporate more details on the microstructure have been observed. This thesis focuses on the microstructure-based multi-scale modeling of the mechanical response of materials with complex microstructures and whose mechanical properties are inherently dependent on their internal structure. The conditions of interest are large displacements and high-rate deformation. This work contributes to the understanding of the relevance of microstructure informations on the macroscopic response. A primary application of this research is the investigation and modeling of snow behavior, it has been extended to modeling the impact response in concrete and composite. In the first part, a discrete approach for fine-scale modeling is applied to study the behavior of snow under the conditions mentioned above. Also, application of the this modeling approach to concrete and composite can be found in the appendices. The fine-scale approach presented herein is based on the coupling of Discrete Element Method and aspects of beam theory. This fine-scale approach has proven to be successful in modeling micro-scale processes found in snow. The micro-scale processes are mainly intergranular friction, intergranular bond fracture, creep, sintering, cohesion, and grain rearrangement. These processes not only influence the overall response of the material but also induce permanent changes in its internal structure. Therefore, the initial geometry considered during numerical analysis should be updated after each time or loading increment before further loading. Moreover, when the material matrix is partially granular and continuum, the influence of fluctuating grains micro-inertia caused by debonding, cracking and contact have a significant effect on the macroscopic response especially under dynamic loading. Consequently, the overall rate and history dependent behavior of the material is more easily captured by discrete models. Discrete modeling has proven to be efficient approach for acquiring profound scientific insight into deformation and failure processes of many materials. While important details can be obtained using the discrete models, computational cost and intensive calibration process is required for a good prediction material behavior in the real case scenarios. Therefore, in order to extend the abovementioned fine-scale model to real engineering cases a coarse-scale continuum model based have been developed using an upscaling approach. This upscaled model is based on the macroscopic response of the material with a special regard to the microstructure information of the material. Different strategies are presented for incorporating the microstructure information in the model. Micro-scale related dissipation mechanisms have been incorporated in the coarse-scale model through viscoplasticity and fracture in finite strain formulation. The thesis is divided into nine chapters, where each is an independent paper published or submitted as a refereed journal article. Fri, 17 Jul 2020 13:17:11 GMT http://hdl.handle.net/10993/43830 Title: Point Collocation Methods for Linear Elasticity Problems <br/> <br/>Author, co-author: Jacquemin, Thibault Augustin Marie <br/> <br/>Abstract: Point collocation is the oldest way to solve partial differential equations. Methods based on collocation have been studied since decades and many variations have been proposed over the years. More recently, those methods have shown a greater interest thanks to the advances in computing hardware. The collocation methods offer a great flexibility with regards to the discretization of a defined domain and the approximation of the field derivatives. This presentation will introduce the bases of the collocation methods and of the generalized finite difference method. The importance of the selection of the nodes involved in the approximation of the field derivatives will then be presented. Finally two aspects for which the method is particularly attractive will be detailed: the solution of a PDE from a given geometry with minimum discretization effort and the adaptivity of a model based on a posteriori error estimation. Mon, 13 Jul 2020 10:01:40 GMT http://hdl.handle.net/10993/43776 Title: Numerical determination and experimental verification of the optimum autofrettage pressure for a complex aluminium high-pressure valve to foster crack closure <br/> <br/>Author, co-author: Repplinger, Christian; Sellen, Stephan; Kedziora, Slawomir; Zürbes, Arno; Cao, Thanh Binh; Maas, Stefan Wed, 08 Jul 2020 07:48:55 GMT http://hdl.handle.net/10993/43510 Title: Surface Energy Modification of Filter Media to achieve optimal Performance Characteristics in select Applications <br/> <br/>Author, co-author: Staudt, Johannes <br/> <br/>Abstract: The surface modification of modern filter media is examined from the perspective of the energetic properties and how they influence select filtration applications. In contrast to the known mechanical filtration mechanisms, which are mainly applicable to the solid-liquid separations, new findings strongly suggest that direct interaction forces between the filter and the functional fluids must be taken into account in order to achieve sufficient efficiencies. Separation processes of liquid phases such as liquidliquid coalescence (LLC) or the treatment of process gases with liquid-gas coalescence (LGC) require special properties of filter media with regard to the degree of interaction with these phases. These include but are not limited to surface energy, wettability, chemical resistance, etc. The focus falls increasingly on eliminating the undesired interactions of modern filters with the fluid to be filtered. Filtration with modern fine filter media can result in undesired additive removal (ADDREM), particularly of those additives that are not fully dissolved in carrier fluid. Specifically this refers to the removal of antifoamants from gear oils, which lead to serious consequential damage of those systems. The interfacial interactions between the filter media and the functional fluids are also responsible for other effects such as the highly undesirable phenomenon of electrostatic charging/discharging (ESC/ESD) during the filtration of low-conductivity oils. In this work, the effect of the surface energy modification, in particular, is examined in greater detail. Ultimately, the surface energy of modern filter media is characterized and modified in order to optimize their performance in select applications. The work also presents some examples that illustrate the importance of surface energy in highly challenging filtration applications. Tue, 16 Jun 2020 08:20:19 GMT http://hdl.handle.net/10993/43469 Title: Finite deformations govern the anisotropic shear-induced area reduction of soft elastic contacts <br/> <br/>Author, co-author: Lengiewicz, Jakub; de Souza, Mariana; Lahmar, Mohamed A.; Courbon, Cédric; Dalmas, Davy; Stupkiewicz, Stanislaw; Scheibert, Julien <br/> <br/>Abstract: Solid contacts involving soft materials are important in mechanical engineering or biomechanics. Experimentally, such contacts have been shown to shrink significantly under shear, an effect which is usually explained using adhesion models. Here we show that quantitative agreement with recent high-load experiments can be obtained, with no adjustable parameter, using a non-adhesive model, provided that finite deformations are taken into account. Analysis of the model uncovers the basic mechanisms underlying anisotropic shear-induced area reduction, local contact lifting being the dominant one. We confirm experimentally the relevance of all those mechanisms, by tracking the shear-induced evolution of tracers inserted close to the surface of a smooth elastomer sphere in contact with a smooth glass plate. Our results suggest that finite deformations are an alternative to adhesion, when interpreting a variety of sheared contact experiments involving soft materials. Wed, 10 Jun 2020 13:48:39 GMT http://hdl.handle.net/10993/43036 Title: Influence of pubic symphysis stiffness on pelvic load distribution during single leg stance <br/> <br/>Author, co-author: Ricci, Pierre-Louis; Maas, Stefan; Gerich, Torsten; Kelm, Jens <br/> <br/>Abstract: This study focuses on the influence of the softening and stiffening of pubic symphysis on the load distribution within the bones of the pelvic ring under the physiological loadings of the single leg stance. Muscle forces and joint reaction forces were first determined by inverse dynamics and applied to a linear finite element model of the pelvis. With normal pubic symphysis stiffness, high Von Mises stresses are located on the anterior surface to the sacrum around the sacroiliac joint and on the superior ramus, both on the side of the weightbearing leg. Softening of the pubic symphysis redirects the load backward, decreases the stresses at the anterior pelvis, and increases them at the posterior pelvis. A stiffening of the pubic symphysis redirects the load forward, increases the load on the posterior pelvis, and decreases them at the anterior pelvis. This investigation highlights the significance of the pubic symphysis on the load distribution of the pelvis and in maintaining the integrity of the structures. Its role should not be neglected when analyzing the pelvis. Thu, 30 Apr 2020 13:29:25 GMT http://hdl.handle.net/10993/43032 Title: La Fabrication Additive Robotisée: Perspective et Recherche autour d'Impression 3D de Pièces Métalliques de Grandes Dimensions pour l'Industrie Aéronautique <br/> <br/>Author, co-author: Mbodj, Natago Guilé; Plapper, Peter Tue, 28 Apr 2020 15:22:37 GMT http://hdl.handle.net/10993/42977 Title: UNTERSUCHUNG DER METALLURGISCHEN PHASENBILDUNG UND DEREN EINFLUSS AUF DIE VERBINDUNGSEIGENSCHAFTEN SOWIE AUF DIE VERSAGENSURSACHEN VON LASERGESCHWEIßTEN HARTMETALL-STAHL-VERBUNDEN <br/> <br/>Author, co-author: Schiry, Marc <br/> <br/>Abstract: Laser beam welding of hard metal to steel offers multiple advantages regarding resource saving, mechanical strength of the joint and automation capability. The present work focuses on the fundamental research and development of the laser based welding process of tungsten carbide-cobalt hard metals with a tempering steel. Metallurgical analysis of the welding process showed that the formation of intermetallic and/or intermediate phases has a significant influence on the properties and mechanical strength of the dissimilar joint. The amount of molten hard metal in the steel melt bath plays a key role for the formation of the different phases. Therefore, a new parameter dy was defined, which correlates with the hard metal content in the melt pool. It is shown that for hard metals with 12 wt.% of cobalt binder, the phase transformation in the weld seam starts with a relative hard metal content of 10 vol.%. This threshold is dependent on the relative cobalt concentration in the hard metal. The tungsten carbide grain size has a low influence on the phase transformation in the weld seam. Steel melt pools with hard metal content lower than 10 vol.% show under metallographic observation a martensitic/bainitic microstructure. Simulation of the stress formation in the joint showed that due to the volume expansion of martensite during the transformation, tensile stress in the hard metal part was formed. Under shear load, these tensile stresses compensate with the induced compressive stresses and results an almost stress free interface. High shear strengths of the dissimilar joints are possible. A higher percentage of hard metal melting during the welding process increases the carbon and tungsten content in the melt bath. Consequently, the martensite start temperature decreases significantly. When the initiating temperature for martensite transformation falls under room temperature, the weld seam transforms into an austenitic microstructure. Because of the missing volume expansion during cooling of the weld seam volume, low stresses in the hard metal are generated. Under shear load of the joint area, high tensile stresses appear in the sintered part. These stress concentration decreases the shear strength of the weld and lead to premature failure. For the industrial use case, high mechanical strength and a robust manufacturing process is needed. Therefore, the laser welding process of hard metal to steel was optimized. The joint properties strongly depend on the weld bead geometry. Weld seams with x- or v-shaped profiles enable local concentrated metallurgical bonding of the sintered part to the steel sheet. Reduction of the horizontal focal distance of the laser beam to the interface increases the bonding ratio, but also intensifies the melting of the hard metal part and lead to the metallurgical transformation. By tilting a v-shape weld seam, it was possible to optimize the bonding behavior and to minimize the amount of liquefied hard metal in the melt bath. Hard metal with low amounts of binder showed a high temperature sensitivity. After laser welding of these grades, hot cracks were found in the sinter material. These cracks were formed due to the high stresses, which are generate during cooling of the dissimilar joint. Therefore, a laser based heat treatment process was developed and applied. With a defined pre- and post-heating of the joint area, the cooling rate was reduced significantly and the stresses in the hard metal part minimized. High shear strengths were the result. Wed, 15 Apr 2020 17:18:04 GMT http://hdl.handle.net/10993/42814 Title: Designing an early failure indicator channel for an in-tank hydrogen valve via a fatigue-based approach <br/> <br/>Author, co-author: Cao, Thanh Binh; Kedziora, Slawomir; Sellen, Stephan; Maas, Stefan; Repplinger, Christian <br/> <br/>Abstract: This study introduced a fatigue-based approach to design and implement an indicator channel into an in-tank hydrogen valve. It was aimed at providing a mean to point out multiple early valve’s damages. To achieve the goal, the study was proposed to handle via three main phases. They included (i) the risk point determinations, (ii) the new valve design and the crack nucleation life estimations, as well as (iii) the simplified crack growth analyses. The obtained results firstly highlighted the construction of the test channel (TC), whose branches were located close to the predicted damage’s sites. The damages could be identified either when a crack reaches the TC (then forms a leakage) or indirectly via the crack propagations’ correlation. The results also pointed out that the TC-implemented valve could perform as similarly as the non-TC one in the non-treated condition. More importantly, this new structure was proved to have a capacity of satisfying the required minimal life of 1.5E5 cycles, depending on the combined uses of the specific material and the pre-treatment, among those considered. In addition, the results emphasized the complexity of the TC that could not be formed by the traditional manufacturing process. Hence, direct metal laser sintering was proposed for the associated prototype and the final TC was issued based on the fundamental requirements of the technique. Finally, it was suggested that practical experiments should essentially be carried out to yield more evidence to support the demonstrated results. Fri, 20 Mar 2020 11:28:12 GMT http://hdl.handle.net/10993/42775 Title: The Buckling and Post-Buckling of Steel C-Columns in Elevated Temperature <br/> <br/>Author, co-author: Czechowski, Leszek; Kedziora, Slawomir; Kolakowsk, Zbigniew <br/> <br/>Abstract: This work deals with the investigation of a steel thin-walled C-column subjected to compression due to temperature increase. These experimental studies of the compressed columns in post-buckling state were conducted to determine their load-carrying capacity. To ensure appropriate supports and keeping of columns, plates with grooves were constructed. The tests of the columns' compression for different preloads were carried out. By comparing the experiment results, numerical calculations based on the finite element method (FEM) and the semi-analytical method (SAM) of solution were performed. The computations were executed with the use of full material characteristics with consideration of large strains and deflections. Furthermore, while observing the deformation of columns, a non-contact Digital Correlation ARAMIS\textregistered system was employed whose calculated results of deformations are very close to the results of the numerical method. The paper revealed that maximum recorded loads under temperature rise are comparable regardless of a value of initial load. A good correlation in results between used methods was achieved. The main goal of the present work was to assess of behavior of thin-walled compressed steel columns in a temperature-controlled environment till their full damage Tue, 10 Mar 2020 04:30:05 GMT http://hdl.handle.net/10993/42680 Title: Practical aspects of the Bank-Weiser estimator implementation and Biomechanics applications. <br/> <br/>Author, co-author: Bulle, Raphaël; Bordas, Stéphane; Chouly, Franz; Lozinski, Alexei; Hale, Jack Sun, 01 Mar 2020 04:30:07 GMT http://hdl.handle.net/10993/42672 Title: Materials, valves and sealing gaskets for high pressure applications <br/> <br/>Author, co-author: Repplinger, Christian; Sellen, Stephan; Kedziora, Slawomir; Zürbes, Arno; Maas, Stefan Fri, 28 Feb 2020 15:04:59 GMT http://hdl.handle.net/10993/42671 Title: Determination of the optimum autofrettage pressure for a complex aluminum valve body <br/> <br/>Author, co-author: Repplinger, Christian; Sellen, Stephan; Kedziora, Slawomir; Zürbes, Arno; Cao, Thanh Binh; Maas, Stefan Fri, 28 Feb 2020 14:57:32 GMT http://hdl.handle.net/10993/42653 Title: Experimentelle Untersuchungen und analytischen Modellierung von adiabaten Siedevorgängen in Naturumlaufsystemen <br/> <br/>Author, co-author: Haag, Michel <br/> <br/>Abstract: Moderne Nuklearreaktoren setzen vermehrt auf den Einsatz passiver Sicherheitssysteme, damit die Integrität des Sicherheitsbehälters im Falle eines Unfalls sichergestellt werden kann. Um eine passive Wärmeabfuhr aus dem Sicherheitsbehälter an die Umgebung zu ermöglichen, werden Naturumlaufsysteme verwendet. Diese haben den Nachteil, dass Instabilitäten auftreten, sobald es zu Verdampfungen im Naturumlauf kommt. Diese Arbeit beschäftigt sich mit der Untersuchung von Instabilitäten in einem zweiphasigen Naturumlaufsystem. Nach einer detaillierten Literaturrecherche über bestehende Versuchsanlagen, wurden während des ersten Teils dieser Arbeit experimentelle Untersuchungen zum Stabilitätsverhalten von Naturumlaufsystemen durchgeführt. Hierfür wurde die Versuchsanlage INTRAVIT designt und an der Universität Luxemburg errichtet. INTRAVIT bietet zum einen ein hohes Maß an Flexibilität für die Auslegung der Rohrleitungen und zum anderen den Vorteil der direkten, elektrisch steuerbaren Wärmezufuhr. Es wurden zwei Messkampagnen durchgeführt. In der ersten Messkampagne wurde, bei konstanter Steigrohrlänge, der Einfluss des Heizrohrneigungswinkels auf die Instabilitäten untersucht. Für die zweite Messkampagne wurde, bei konstantem Neigungswinkel des Heizrohrs, zum einen der Einfluss der Steigrohrlänge und zum anderen der Einfluss des Strömungswiderstands im Fallrohr auf die Instabilitäten untersucht. Für die Untersuchungen wurden die Temperaturen, der Massenstrom und die Verteilung des Dampfgehalts im Steigrohr analysiert. Zudem wurde der Druckverlauf während der Instabilitäten gemessen, um die Druckstöße während den Kondensationsschläge zu untersuchen. In einem zweiten Teil dieser Arbeit wurde ein analytisches Modell zur Beschreibung von Verdampfungsvorgängen in adiabaten Rohren hergeleitet. Das Modell besteht aus mehreren Teilmodellen, die die Phasenoberflächendichte und die Verdampfungsrate in Abhängigkeit der Strömungsform berechnen. Das Einsetzen der Verdampfung wird hierbei über ein integriertes Keimbildungsmodell berechnet. Das hergeleitete Modell wurde in den Systemcode ATHLET implementiert. Die Versuche aus den INTRAVIT-Messkampagnen wurden mit dem neuen Verdampfungsmodell und dem Standard-Verdampfungsmodell modelliert. Anschließend wurden die Ergebnisse mit den Messdaten verglichen. Mit der Realisierung der INTRAVIT-Anlage legt diese Arbeit einen Grundstein für weiterführende Untersuchungen an Instabilitäten in Naturumlaufsystemen. Zudem wurde ein Verdampfungsmodell hergeleitet, das durch Anpassen einzelner Teilmodelle beliebig weiterentwickelt werden kann.; Modern nuclear reactors increasingly use passive safety systems to ensure the integrity of the containment in the event of an accident. Natural circulation systems allow passive heat removal from the containment to the environment. One of their disadvantages is that instabilities develop as soon as evaporation occurs in the system. This thesis investigates instabilities in two-phase natural circulation systems. After comprehensive literature review on existing test facilities, the first part of this work presents experimental investigations on the stability behaviour of natural circulation systems. To conduct these investigations, the INTRAVIT test facility was designed and constructed at the University of Luxembourg. INTRAVIT offers both a high degree of flexibility in the design of the pipelines and the advantage of a direct, electrically controllable heat supply. Two measurement campaigns were carried out. During the first campaign, the influence of the heating tube inclination angle on the instabilities was investigated at constant riser pipe length. During the second measurement campaign, the influence of the riser pipe length and the influence of the flow resistance in the downcomer pipe were investigated at a constant inclination angle of the heating tube. For these investigations, temperatures, mass flow and the distribution of void in the riser pipe were analysed. In addition, pressure response during the instabilities was measured to investigate the pressure shocks caused by water hammering. The second part of this work develops an analytical model to decribe evaporation processes in adiabatic pipes. The model consists of several sub models that calculate the interfacial surface density and the evaporation rate as a function of the flow pattern. An integrated nucleation model calculates the onset of the evaporation. The derived model was implemented in the system code ATHLET. Experiments from the INTRAVIT measurement campaigns were then modelled using the new evaporation model as well as the standard evaporation model. Both were compared with the measurement data. The design and construction of the INTRAVIT test facility is a foundation for future research on instabilities in natural circulation systems. Moreover, a new evaporation model is presented, which can easily be adapted and refined by modifying individual sub models. Thu, 27 Feb 2020 18:29:11 GMT http://hdl.handle.net/10993/42616 Title: Metallographic Studies of Dissimilar Al-Cu Laser-Welded Joints Using Various Etchants <br/> <br/>Author, co-author: Schmalen, Pascal Guy; Mathivanan, Karthik; Plapper, Peter <br/> <br/>Abstract: The welding of Al and Cu is considered as difficult due to the formation of intermetallic compounds, which cause a brittle joint with increased electrical resistance. This paper investigates etching techniques that were used to contrast the intermetallic compounds for optical microscope analysis. A 0.5 mm AA-1050 sheet was welded to a 0.5 mm SF-Cu sheet in overlap configuration. The cross sections were etched by using 17 different reagents, including common Al-grade 2xxx etchants, Al-bronze etchants, and specific IMC etchants. A complete microstructural characterization, including the formation of intermetallic compounds, is presented. The experimental result showed that a clear distinction of metallurgic structures is possible, thus enabling a more detailed analysis of Al-Cu welds. It was found that etchants #09, #14, and #16 revealed best the four different intermetallic compounds θ-Al2Cu, η-AlCu, ζ-Al3Cu4, and γ-Al4Cu9. Mon, 24 Feb 2020 10:21:13 GMT http://hdl.handle.net/10993/42453 Title: Optimum Autofrettage Pressure of Hydrogen Valve Using Finite Element and Fatigue Analysis <br/> <br/>Author, co-author: Kedziora, Slawomir; Cao, Thanh Binh <br/> <br/>Abstract: The presented article shows an estimation method of optimum autofrettage pressure taking into consideration subsequent cyclic loading. An autofrettage process is used in pressure vessel applications for strength improvement. The process relies on applying massive pressure that causes internal portions of the part to yield plastically, resulting in internal compressive residual stresses when pressure is released. Later applied working pressure (much lower than autofrettage pressure) creates stress reduced by the residual compressive stress improving the structural performance of the pressure vessels. The optimum autofrettage pressure is a load that maximizes the fatigue life of the structure at the working load. The estimation method of that pressure of a hydrogen valve is the subject of the presented work. Finite element and fatigue analyses were employed to investigate the presented problem. An automated model was developed to analyze the design for various autofrettage pressures. As the results of the procedure, the optimum autofrettage pressure is determined. The research has shown that the developed method can profitably investigate the complex parts giving the autofrettage load that maximizes the fatigue life. The findings suggest that the technique can be applied to a large group of products subjected to the autofrettage process. Sat, 08 Feb 2020 08:55:47 GMT http://hdl.handle.net/10993/42437 Title: Optimization assisted redesigning a structure of a hydrogen valve: the redesign process and numerical evaluations <br/> <br/>Author, co-author: Cao, Thanh Binh; Kedziora, Slawomir; Sellen, Stephan; Repplinger, Christian <br/> <br/>Abstract: This study introduced the redesign process of an automotive hydrogen valve. The process relied on the structural optimization approach, which used to build up the new valves having promising stiffness and the lowest possible weights. To achieve the goals, the study was proposed to be taken place via the three main stages. These stages included topology optimization, lattice optimization, as well as numerical evaluations. The achieved results firstly indicated that the two newly designed valves possessed longer life and lower mass than the original valve. Especially, the topology optimized one could withstand more than 5E4 working cycles in the pre-treated condition before the first crack would be nucleated. The results also pointed out the influences of the pre-treatment pressure on the fatigue performance of the hydrogen valve. Within the examined ranges of the pressure, increasing the pressure’s magnitudes tended to shorten the fatigue life of the topology optimized valve. Additionally, the results highlighted the impact of the employed materials on the estimated fatigue life of such a non-treated structure. In the highlights, the considered steel valves could function normally far beyond 1.5E5 working cycles while the aluminum valves would have an initial crack formation prior to reaching 3E3 cycles. The results also suggested that further practical evidence is needed to not only confirm whether the selected printed aluminum is among the promising candidate materials of the hydrogen valve but also to support the described evaluations. Thu, 06 Feb 2020 17:06:57 GMT http://hdl.handle.net/10993/42349 Title: Modelling of Passive Heat Removal Systems: A Review with Reference to the Framatome BWR Reactor KERENA: Part II <br/> <br/>Author, co-author: Manthey, René; Viereckl, Frances; Moonesi Shabestary, Amirhosein; Zhang, Yu; Ding, Wei; Lucas, Dirk; Schuster, Christoph; Leyer, Stephan; Hurtado, Antonio; Hampel, Uwe <br/> <br/>Abstract: Passive safety systems are an important feature of currently designed and constructed nuclear power plants. They operate independent of external power supply and manual interventions and are solely driven by thermal gradients and gravitational force. This brings up new needs for performance and reliably assessment. This paper provides a review on fundamental approaches to model and analyze the performance of passive heat removal systems exemplified for the passive heat removal chain of the KERENA boiling water reactor concept developed by Framatome. We discuss modeling concepts for one-dimensional system codes such as ATHLET, RELAP and TRACE and furthermore for computational fluid dynamics codes. Part I dealt with numerical and experimental methods for modeling of condensation inside the emergency condenser and on the containment cooling condenser. This second part deals with boiling and two-phase flow instabilities. Wed, 29 Jan 2020 19:54:05 GMT http://hdl.handle.net/10993/42329 Title: Prevention of Electrostatic Charge Generation in Filtration of Low-Conductivity Oils by Surface Modification of Modern Filter Media <br/> <br/>Author, co-author: Staudt, Johannes; Duchowski, Johan; Leyer, Stephan <br/> <br/>Abstract: The electrostatic charging behavior of filter elements operating in various hydraulic and lubricating fluids has been re-examined from the perspective of fundamental material properties of the two materials participating in the event. In contrast to the previously proposed mechanisms that focused predominantly on fluid and material conductivities, new evidence strongly suggests that the relative placement of the substrates in the triboelectric series must be taken into account. The positions occupied in the triboelectric series account for the donor/acceptor tendencies exhibited by the materials when brought close together in close proximity ( 10 nm). Nevertheless, this behavior is only an outward manifestation of the deeper underlying characteristics that include material surface energies and, looking even deeper, the associated electron work functions of the interacting materials. Herein we provide several examples of the enhanced understanding of the electrostatic charging/discharging (ESC/ESD) phenomena as they occur in the course of filtration of hydraulic and lubricating fluids through modern filter elements constructed of synthetic glass fiber and polymer materials. Wed, 29 Jan 2020 05:31:07 GMT http://hdl.handle.net/10993/42255 Title: CFD Simulations of Adiabatic Boiling in Different Riser Geometries <br/> <br/>Author, co-author: Haag, M; Leyer, Stephan Mon, 27 Jan 2020 15:09:20 GMT