The present work investigates the turbulent jet flow mixing of downward impinging jets within a staggered rod bundle based on previous experimental work. The two inlet jets had Reynold's numbers of 11,160 and 6,250 and were chosen to coincide with the available data. Steady state simulations were initially carried out on a semi-structured polyhedral mesh of roughly 13.2 million cells following a sensitivity study over six different discretized meshes. Very large eddy simulations were carried out over the most refined mesh and continuous 1D wavelet transforms were used to analyze the dominant instabilities and how they propagate through the system in an effort to provide some insight into potential problems relating to structural vibrations due to turbulent instabilities. The presence of strong standing horseshoe vorticies near the base of each cylinder adjacent to an inlet jet was noted and is of potential importance in the abrasion wear of the graphite support columns of the VHTR if sufficient wear particles are present in the gas flow.

In der vorliegenden Arbeit wird eine simulationsbasierte Methodik zur Energie- und Kostenoptimierung der Kühlung von Rechenzentren mit Kalt-/Warmluft-Separation vorgestellt. Dabei wird die spezifische Charakteristik der Luftseparation für einen wesentlich einfacheren und schnelleren Simulationsansatz genutzt, als das mit herkömmlichen, strömungsmechanischen Methoden möglich ist. Außerdem wird der Energiebedarf des Lufttransports – einschließlich der IT-Ventilatoren – in der Optimierung berücksichtigt. Beispielhaft entwickelte Komponentenmodelle umfassen die IT-Systeme und alle für die Kühlung relevanten Anlagen in einer dem aktuellen Stand der Technik entsprechenden Ausführung. Die besonders wichtigen Aspekte Freikühlbetrieb und Verdunstungskühlung werden berücksichtigt. Anhand verschiedener Konfigurationen eines Modellrechenzentrums wird beispielhaft die Minimierung der jährlichen verbrauchsgebunden Kosten durch Anpassung von Temperatursoll- werten und anderen Parametern der Regelung demonstriert; bestehendes Einsparpotenzial wird quantifiziert. Da die Kalt-/Warmluft-Separation in modernen Installationen mit hoher Leistungsdichte auch Auswirkungen auf bauliche Anforderungen hat, wird ein für diesen Anwendungsfall optimiertes Gebäudekonzept vorgeschlagen und praktisch untersucht, das sich insbesondere durch Vorteile hinsichtlich Energieeffizienz, Flexibilität und Betriebssicherheit auszeichnet.:1 Einleitung 1.1 Motivation 1.2 Kategorisierung von Rechenzentren 1.3 Effizienzmetriken für Rechenzentren 1.4 Wissenschaftlicher Beitrag und Abgrenzung 2 Luftgekühlte IT-Systeme: Anforderungen und Trends 2.1 Anforderungen an das Raumklima 2.1.1 Lufttemperatur 2.1.2 Luftfeuchte 2.1.3 Luftzustand im Warmgang 2.1.4 Schalldruckpegel und Schadgase 2.1.5 Betriebsabläufe und Personal 2.2 Kühllasten 2.2.1 Leistungsbedarf der IT-Systeme 2.2.2 Lastgänge und Teillastbetrieb der IT-Systeme 2.2.3 Flächenspezifische Kühllasten 2.3 Leckströme 2.4 Entwicklungstendenzen 3 Rechenzentrumskühlung: Übliche Lösungen und Optimierungskonzepte 3.1 Anlagenkonzepte zur Entwärmung von Rechenzentren 3.1.1 Freie Kühlung 3.1.2 Maschinelle Kälteerzeugung 3.1.3 Umluftkühlung von Rechnerräumen 3.2 Umluftkühlung mit Separation von Kalt- und Warmluft 3.2.1 Konzept 3.2.2 Umsetzung 3.2.3 Regelung der Umluftkühlgeräte 3.2.4 Effizienzoptimierung durch Anhebung der Lufttemperatur 3.2.5 Betriebssicherheit 3.3 Modellbasierte Untersuchungen in der Literatur 3.4 Zwischenfazit 4 Modellbildung 4.1 Struktur des Modells und Ablauf der Simulation 4.2 Annahmen und Randbedingungen 4.3 Modellierung der IT-Systeme 4.3.1 Testsysteme und -software 4.3.2 Testaufbau und Messung der relevanten physikalischen Größen 4.3.3 Drehzahl der internen Ventilatoren 4.3.4 Leistungsaufnahme der internen Ventilatoren 4.3.5 Luftvolumenstrom 4.3.6 Leistungsaufnahme der IT-Systeme ohne Lüfter 4.3.7 Ausblastemperatur 4.4 Modellierung der Kühlsysteme 4.4.1 Pumpen, Rohrnetz und Ventilatoren 4.4.2 Wärmeübertrager 4.4.3 Umluftkühlgeräte 4.4.4 Pufferspeicher 4.4.5 Kältemaschinen 4.4.6 Rückkühlwerke 4.4.7 Freie Kühlung 4.5 Regelstrategien, Sollwertvorgaben und Lastprofile 4.5.1 Kaltluft 4.5.2 Kaltwasser 4.5.3 Kühlwasser 4.5.4 Kälteerzeuger 4.5.5 Lastprofil der IT-Systeme 4.5.6 Wetterdaten 4.5.7 Standortspezifische Kosten für sonstige Betriebsstoffe 4.6 Validierung der Simulationsumgebung 4.6.1 Stichprobenartige experimentelle Prüfung der ULKG-Modellierung 4.6.2 Stichprobenartige experimentelle Prüfung der Modellierung der Kälteerzeugung 4.6.3 Plausibilitätskontrolle und Modellgrenzen 4.7 Zwischenfazit 5 Variantenuntersuchungen und Ableitung von Empfehlungen 5.1 Konfiguration und ausgewählte Betriebspunkte des Modellrechenzentrums 5.2 Optimierung des Jahresenergiebedarfs mit konstanten Kühlmedientemperaturen 5.2.1 Jahresenergiebedarf des Modell-RZs und Optimierung nach Best Practices 5.2.2 Bestimmung der optimalen (konstanten) ULKG-Ausblastemperatur 5.2.3 Einfluss von Last und Typ der IT-Systeme 5.2.4 Einfluss von Standortfaktoren 5.2.5 Einsparpotenzial Pumpenenergie 5.3 Optimierung mit variablen Kühlmedientemperaturen, RKW trocken 5.3.1 Dynamische Sollwertschiebung der Luft- und Kaltwassertemperaturen 5.3.2 Sollwertschiebung der Kühlwassertemperaturen im Kältemaschinenbetrieb 5.3.3 Kombination der Optimierungen und Übertragung auf andere Standorte 5.4 Optimierung mit variablen Kühlmedientemperaturen, RKW benetzt 5.4.1 Dynamische Sollwertschiebung der Luft- und Kaltwassertemperaturen 5.4.2 Optimierung eines modifizierten Modells ohne Kältemaschinen 5.4.3 Betriebssicherheit der Konfiguration ohne Kältemaschinen 5.4.4 Optimierung der Betriebssicherheit durch Eisspeicher 5.5 Zwischenfazit 6 Vorstellung und Diskussion eines neuen Gebäudekonzepts für Rechenzentren 6.1 Gebäudekonzepte und Anforderungen an Sicherheit, Effizienz und Flexibilität 6.1.1 Limitierungen klassischer Konstruktionsprinzipien 6.1.2 Alternative Konzepte für Umluftkühlung in Rechenzentren 6.1.3 Rechenzentren mit Installationsgeschoss statt Doppelboden 6.2 Plenum statt Doppelboden: Konzept und Umsetzung 6.2.1 Aufgabenstellung und konzeptionelle Anforderungen 6.2.2 Lösung mit dem Plenums-Konzept 6.2.3 Anforderungen an die Regelung der Umluftkühlgeräte 6.3 Experimentelle Leistungsbestimmung und Optimierung 6.3.1 Testaufbau und Messung der relevanten physikalischen Größen 6.3.2 Regelung von Luftvolumenstrom und -Temperatur bei konstanter Last 6.3.3 Optimierung der Kaskadenschaltung der Umluftkühlgeräte bei Lastwechseln 6.3.4 Optimierung der Betriebssicherheit der Umluftkühlung bei Stromausfällen 6.3.5 Ermittlung der Leistungsgrenzen 6.4 Zwischenfazit und weiteres Optimierungspotenzial 7 Zusammenfassung und Ausblick

Please read the abstract in the section, 00front, of this document / Dissertation (M Mus (Performing Art))--University of Pretoria, 2008. / Music / MMus / unrestricted

Thesis is bend on design of intake manifold for car Formula SAE. For driving of this car is used engine Yamaha YZF R6 (2005). Design of intake tract is processed so that agrees with rules and specifications for cars Formula SAE. For restriction of engine performance is in intake tract installed restrictor. For filling efficiency uplift of engine is used the resonance effect in intake pipes. Analysis of flow is carry out on simulation software for analyses of one dimensional flow.

The aim of this diploma thesis is to create a thermodynamic computational model of a single cylinder IC engine for the Formula SAE car. The single cylinder SI engine KTM 500 EXC is considered as a powertrain unit. The intake manifold of the serial enduro motorcycle is modified according to the Formula SAE 2014 rules. Analysis of the one dimensional flow is performed by using Lotus engine simulation software.

Der vorliegende Beitrag beleuchtet als Teil eines Blended-Learning Ansatzes vorrangig den Einsatz von Live-Umfragen (ARS – Audience Responce Systems) im Vorlesungsrahmen. Gerade naturwissenschaftlich geprägte Studiengänge (hier die Fachrichtung Physik) sind häufig durch Frontalunterricht geprägt. Das maßgebliche Ziel des Projektes war es, das Format durch gezielte Einbindung der Studierenden aufzulockern und die Diskussionskultur in der Lehrveranstaltung zu stärken. Einhergehend mit der Aktivierung erhalten die Lernenden eine unmittelbare Rückmeldung zu ihrem Wissensstand und die/ der Lehrende ein Feedback zu möglichen Wissenslücken. Die Live-Umfragen fanden über die Online- Plattform invote.de in Form von Single-Choice-Fragen statt. Erweitert wurde dieser Ansatz, indem diese Inhalte ebenfalls für eine asynchrone Wissensvermittlung im Lernmanagement-System (LMS) Moodle implementiert und mit Feedback flankiert wurden. Dies führte im Vergleich zu früheren Iterationen der Lehrveranstaltung zu einem höheren Aktivitätslevel des Plenums und fachlich fundierten Diskussionen. In Evaluationen zum Ende des Semesters sowie in persönlichen Gesprächen mit den Studierenden, wurde der Einsatz der Fragen in synchroner sowie asynchroner Form explizit als Zugewinn für die Qualität der Lehrveranstaltung herausgestellt.

<p>Severe accidents in a Light Water Reactor (LWR) have been a subject of the research for the last three decades. The research in this area aims to further understanding of the inherent physical phenomena and reduce the uncertainties surrounding their quantification, with the ultimate goal of developing models that can be applied to safety analysis of nuclear reactors. The research is also focusing on evaluation of the proposed accident management schemes for mitigating the consequences of such accidents.</p><p>During a hypothetical severe accident, whatever the scenario, there is likelihood that the core material will be relocated and accumulated in the lower plenum in the form of a debris bed or a melt pool. Physical phenomena involved in a severe accident progression are complex. The interactions of core debris or melt with the reactor structures depend very much on the debris bed or melt pool thermal hydraulics. That is why predictions of heat transfer during melt pool formation in the reactor lower head are important for the safety assessment.</p><p>The main purpose of the present study is to advance a method for describing turbulent natural convection heat transfer of a melt pool, and to develop a computational platform for cost-effective, sufficiently-accurate numerical simulations and analyses of Core Melt-Structure-Water Interactions in the LWR lower head during a postulated severe core-melting accident.</p><p>Given the insights gained from Computational Fluid Dynamics (CFD) simulations, a physics-based model and computationally-efficient tools are developed for multi-dimensional simulations of transient thermal-hydraulic phenomena in the lower plenum of a Boiling Water Reactor (BWR) during the late phase of an in-vessel core melt progression. A model is developed for the core debris bed heat up and formation of a melt pool in the lower head of the reactor vessel, and implemented in a commercial CFD code. To describe the natural convection heat transfer inside the volumetrically decay-heated melt pool, we advanced the Effective Convectivity Conductivity Model (ECCM), which was previously developed and implemented in the MVITA code. In the present study, natural convection heat transfer is accounted for by only the Effective Convectivity Model (ECM). The heat transport and interactions are represented through an energy-conservation formulation. The ECM then enables simulations of heat transfer of a high Rayleigh melt pool in 3D large dimension geometry.</p><p>In order to describe the phase-change heat transfer associated with core debris, a temperature-based enthalpy formulation is employed in the ECM (the phase-change ECM or so called the PECM). The PECM is capable to represent possible convection heat transfer in a mushy zone. The simple approach of the PECM method allows implementing different models of the fluid velocity in a mushy zone for a non-eutectic mixture. The developed models are validated by a dual approach, i.e., against the existing experimental data and the CFD simulation results.</p><p>The ECM and PECM methods are applied to predict thermal loads to the vessel wall and Control Rod Guide Tubes (CRGTs) during core debris heat up and melting in the BWR lower plenum. Applying the ECM and PECM to simulations of reactor-scale melt pool heat transfer, the results of the ECM and PECM calculations show an apparent effectiveness of the developed methods that enables simulations of long term accident transients. It is also found that during severe accident progression, the cooling by water flowing inside the CRGTs plays a very important role in reducing the thermal load on the reactor vessel wall. The results of the CFD, ECM and PECM simulations suggest a potential of the CRGT cooling as an effective mitigative measure during a severe accident progression.</p>

Severe accidents in a Light Water Reactor (LWR) have been a subject of intense research for the last three decades. The research in this area aims to reach understanding of the inherent physical phenomena and reduce the uncertainties in their quantification, with the ultimate goal of developing models that can be applied to safety analysis of nuclear reactors, and to evaluation of the proposed accident management schemes for mitigating the consequences of severe accidents.  In a hypothetical severe accident there is likelihood that the core materials will be relocated to the lower plenum and form a decay-heated debris bed (debris cake) or a melt pool. Interactions of core debris or melt with the reactor structures depend to a large extent on the debris bed or melt pool thermal hydraulics. In case of inadequate cooling, the excessive heat would drive the structures' overheating and ablation, and hence govern the vessel failure mode and timing. In turn, threats to containment integrity associated with potential ex-vessel steam explosions and ex-vessel debris uncoolability depend on the composition, superheat, and amount of molten corium available for discharge upon the vessel failure. That is why predictions of transient melt pool heat transfer in the reactor lower head, subsequent vessel failure modes and melt characteristics upon the discharge are of paramount importance for plant safety assessment.  The main purpose of the present study is to develop a method for reliable prediction of melt pool thermal hydraulics, namely to establish a computational platform for cost-effective, sufficiently-accurate numerical simulations and analyses of core Melt-Structure-Water Interactions in the LWR lower head during a postulated severe core-melting accident. To achieve the goal, an approach to efficient use of Computational Fluid Dynamics (CFD) has been proposed to guide and support the development of models suitable for accident analysis.   The CFD method, on the one hand, is indispensable for scrutinizing flow physics, on the other hand, the validated CFD method can be used to generate necessary data for validation of the accident analysis models. Given the insights gained from the CFD study, physics-based models and computationally-efficient tools are developed for multi-dimensional simulations of transient thermal-hydraulic phenomena in the lower plenum of a LWR during the late phase of an in-vessel core melt progression. To describe natural convection heat transfer in an internally heated volume, and molten metal layer heated from below and cooled from the top (and side) walls, the Effective Convectivity Models (ECM) are developed and implemented in a commercial CFD code. The ECM uses directional heat transfer characteristic velocities to transport the heat to cooled boundaries. The heat transport and interactions are represented through an energy-conservation formulation. The ECM then enables 3D heat transfer simulations of a homogeneous (and stratified) melt pool formed in the LWR lower head. In order to describe phase-change heat transfer associated with core debris or binary mixture (e.g. in a molten metal layer), a temperature-based enthalpy formulation is employed in the Phase-change ECM (so called the PECM). The PECM is capable to represent natural convection heat transfer in a mushy zone. Simple formulation of the PECM method allows implementing different models of mushy zone heat transfer for non-eutectic mixtures. For a non-eutectic binary mixture, compositional convection associated with concentration gradients can be taken into account. The developed models are validated against both existing experimental data and the CFD-generated data. ECM and PECM simulations show a superior computational efficiency compared to the CFD simulation method. The ECM and PECM methods are applied to predict thermal loads imposed on the vessel wall and Control Rod Guide Tubes (CRGTs) during core debris heatup and melting in a Boiling Water Reactor (BWR) lower plenum. It is found that during the accident progression, the CRGT cooling plays a very important role in reducing the thermal loads on the reactor vessel wall. Results of the ECM and PECM simulations suggest a high potential of the CRGT cooling to be an effective measure for severe accident management in BWRs. / <p>QC 20100812</p>

Severe accidents in a Light Water Reactor (LWR) have been a subject of the research for the last three decades. The research in this area aims to further understanding of the inherent physical phenomena and reduce the uncertainties surrounding their quantification, with the ultimate goal of developing models that can be applied to safety analysis of nuclear reactors. The research is also focusing on evaluation of the proposed accident management schemes for mitigating the consequences of such accidents. During a hypothetical severe accident, whatever the scenario, there is likelihood that the core material will be relocated and accumulated in the lower plenum in the form of a debris bed or a melt pool. Physical phenomena involved in a severe accident progression are complex. The interactions of core debris or melt with the reactor structures depend very much on the debris bed or melt pool thermal hydraulics. That is why predictions of heat transfer during melt pool formation in the reactor lower head are important for the safety assessment. The main purpose of the present study is to advance a method for describing turbulent natural convection heat transfer of a melt pool, and to develop a computational platform for cost-effective, sufficiently-accurate numerical simulations and analyses of Core Melt-Structure-Water Interactions in the LWR lower head during a postulated severe core-melting accident. Given the insights gained from Computational Fluid Dynamics (CFD) simulations, a physics-based model and computationally-efficient tools are developed for multi-dimensional simulations of transient thermal-hydraulic phenomena in the lower plenum of a Boiling Water Reactor (BWR) during the late phase of an in-vessel core melt progression. A model is developed for the core debris bed heat up and formation of a melt pool in the lower head of the reactor vessel, and implemented in a commercial CFD code. To describe the natural convection heat transfer inside the volumetrically decay-heated melt pool, we advanced the Effective Convectivity Conductivity Model (ECCM), which was previously developed and implemented in the MVITA code. In the present study, natural convection heat transfer is accounted for by only the Effective Convectivity Model (ECM). The heat transport and interactions are represented through an energy-conservation formulation. The ECM then enables simulations of heat transfer of a high Rayleigh melt pool in 3D large dimension geometry. In order to describe the phase-change heat transfer associated with core debris, a temperature-based enthalpy formulation is employed in the ECM (the phase-change ECM or so called the PECM). The PECM is capable to represent possible convection heat transfer in a mushy zone. The simple approach of the PECM method allows implementing different models of the fluid velocity in a mushy zone for a non-eutectic mixture. The developed models are validated by a dual approach, i.e., against the existing experimental data and the CFD simulation results. The ECM and PECM methods are applied to predict thermal loads to the vessel wall and Control Rod Guide Tubes (CRGTs) during core debris heat up and melting in the BWR lower plenum. Applying the ECM and PECM to simulations of reactor-scale melt pool heat transfer, the results of the ECM and PECM calculations show an apparent effectiveness of the developed methods that enables simulations of long term accident transients. It is also found that during severe accident progression, the cooling by water flowing inside the CRGTs plays a very important role in reducing the thermal load on the reactor vessel wall. The results of the CFD, ECM and PECM simulations suggest a potential of the CRGT cooling as an effective mitigative measure during a severe accident progression. / QC 20101119

Dunovský M. The Situation in the Political District of Strakonice in the Period between May 1946 and February 1948. Key Words: Strakonice, parliamentary elections in May 1946, renewed ONV Strakonice, renewed MNV Strakonice, the council of ONV Strakonice, the council of MNV Strakonice, plenum of MNV Strakonice, confiscations of private possessions, February 1948, people's militia, OAV-NF Strakonice, public purification. This thesis focuses primarily on the description of the political conditions in the area of the former political district of Strakonice between May 1946 and February 1948. Hence, the main focus lies on the topics such as the activity and agenda of ONV Strakonice and MNV Strakonice with regard to the personal and political structure of these authorities following the parliamentary elections in the spring of 1946 and the radical changes after the political coup on February 25th 1948. In this respect the thesis tracks the alterations in the distribution of political power in the region and offers a clear view of the transition from the unstable post- war democracy to the communistic dictatorship. Confiscations of private possessions based on the decisions of the responsible authorities are among other issues addressed in the thesis. In this respect the thesis covers the entire area of...