M.Ing. / Stochastic analysis of water distribution systems allow the performance of systems to be evaluated under more realistic conditions that involve both deterministic and probabilistic factors. A software package called Mocasim II has been developed to perform stochastic analysis on water supply systems. This allows the relationship between the reliability of the supply system and the capacity of its service reservoir(s) to be quantified using Monte Carlo analysis. In a Monte Carlo analysis the factors which influence the reliability of the system such as water demand, fires, and pipe failures are simulated stochastically over a long period of time. A reliability-capacity relationship is quantified by analysing the failure behaviour of different service reservoir sizes. A previous version of Mocasim used a simple mass balance model for calculating the flows in simple, linear distribution networks. Mocasim II extends the functionality of its predecessor by enabling the probabilistic modelling of more complex water distribution models. This was achieved by integrating the stochastic modelling technique into the Epanet hydraulic analysis software package. Mocasim II was designed using an object-oriented model which has various advantages such as ease of programme testing, upgrading and maintaining as well as minimum repetitive code and a logical structure. Additional capabilities of Mocasim II include the determination of probability distributions for network properties such as flow rate, pressure and water quality at any node in the network. This will assist in estimating the levels of service of a water supply system. This project focussed on developing sections of Mocasim II to be integrated with existing software such as Mocasim I, the Epanet hydraulic engine, OOTEN, and a random number generator. The software was tested thoroughly. This involved testing each class separately as well as applying it to a test case which is a simple network consisting of a source, reservoir and demand node. The theoretical background of the stochastic model has been investigated and various aspects discussed. Various case studies in Windhoek-Namibia, Mabeskraal-South Africa and an Epanet design example demonstrate the capabilities of the software and benefits of a stochastic analysis. A workbook to be used in addition to the software's help facility has been developed.

An investigation into the thermo-mechanical closure effect when a fluid leaks through a crack is presented here. The extended finite element method is the modelling scheme adopted for this, and the application of heat flux and pressure jump conditions along the crack is one of the novel contributions of this work. By modelling the fluid as one dimensional steady state and obtaining a heat transfer coefficient, it has been shown here that coupling the fluid with the structure is possible all within a single element. Convergence studies done with analytical models as a benchmark demonstrate the accuracy of the new method. Simulations are performed with the new element for conditions seen in both gas cooled and water cooled reactors. Significant crack closure is observed when the bulk fluid temperature is 20oC hotter than the structure. It was also found that the amount of closure due to crack wall heating varies depending on the external boundary conditions, this is quantified in the thesis.

Os conceitos de competência do escoamento e de capacidade de transporte foram desenvolvidos para escoamentos fluviais e acabam sendo transferidos para a modelagem de correntes de turbidez. No entanto, não é claro até que ponto o estabelecimento de analogias entre o ambiente fluvial e as correntes de turbidez pode ser realizado. Nesse contexto, o principal objetivo deste trabalho foi avaliar os conceitos de competência e de capacidade nas correntes de turbidez. O estudo foi desenvolvido experimentalmente, em um canal de inclinação variável de 4 m de comprimento, 40 cm de altura e 12 cm de largura. Um leito móvel foi construído em um trecho intermediário do canal utilizando sedimento - carvão mineral (ρ = 1405 kgm³) - com tamanho areia média. No total, 30 simulações de correntes de turbidez contínuas foram realizadas, utilizando o mesmo sedimento, porém com tamanho areia muito fina. Foram simuladas três declividades diferentes (6%, 0,3% e 0,015%), vazões de injeção entre 15 e 25 lmin, concentrações iniciais variando entre 0,03% e 5,5% e a duração dos ensaios ficou compreendida entre 3 e 30 min. O levantamento do perfil longitudinal do leito móvel, antes e após o ensaio, foi realizado e todo o sedimento foi coletado. Três quantidades distintas de sedimento foram quantificadas: a quantidade depositada antes do leito móvel, a quantidade depositada no leito móvel e a quantidade depositada depois do leito móvel. O cálculo da eficiência de transporte das correntes de turbidez no trecho do leito móvel, bem como das suas descargas sólidas, foi realizado. Também foram realizadas análises granulométricas do sedimento depositado antes e após do leito móvel. Por fim, parâmetros do fluxo foram obtidos (altura e velocidade) através de análises visuais e números adimensionais clássicos do transporte sólido em canais abertos foram avaliados. A partir da interpretação dos dados, conclui-se que os conceitos de competência do escoamento e de capacidade de transporte não foram capazes de refletir o diâmetro característico do sedimento transportado pelas correntes simuladas e a capacidade máxima de transporte desses fluxos, como normalmente ocorre em escoamentos fluviais. A relação entre a eficiência de transporte desses fluxos e a descarga sólida dos mesmos indicou que a partir de uma região a eficiência tornou-se invariante. Essa relação possui curvas com tendência logarítmica e as suas assíntotas ocorreram em valores de eficiência da ordem de 50% (inclinação de 6%) e de 40% (inclinações de 0,3% e 0,015%). A relação entre o diâmetro característico do sedimento depositado depois do leito e antes do leito indicou uma diminuição de cerca de 18% no tamanho dos grãos depositados a jusante. / The modeling of turbidity currents uses the concepts of competence and flow capacity that have been developed based on river hydraulics. However, the analogies between the fluvial environment and turbidity currents are not very clear. The main purpose of this study was to evaluate the competence and flow capacity of turbidity currents. The study was performed using an experimental channel 4 m long, 40 cm high, and 12 cm wide with variable slope. A mobile bed of medium sand-size - mineral coal (ρ=1405 kgm³) - was constructed in an intermediate area of the channel. In total, 30 simulations of continuous turbidity currents were performed and the sediment used in the turbidity currents was very fine sand-size mineral coal. The simulations were accomplished considering three different channel slopes (6%, 0.3% e 0.015%); injection discharge varied between 15 and 25 l/min, and initial volumetric concentrations varied between 0.03% and 5.5%. The simulations lasted between 3 and 30 minutes. The longitudinal profile of the mobile bed was analyzed before and after each simulation, and all the sediment was collected at the end. Three different amounts of sediment were quantified: the amount of sediment deposited before, on, and after the mobile bed. Based on this data, both the transport efficiency and solid discharge of the turbidity current on the mobile bed were determined. Particle-size distribution of the deposited sediment before and after the mobile bed was also carried out. Finally, flow parameters were obtained (high and velocity) considering visual evaluation and the classical dimensional numbers in sediment transport in open channel flows were analyzed. The data interpretation revealed that the competence and flow capacity parameters were not able to reflect the grain diameter transported by the simulated currents and a maximum flow capacity of these flows, as usually is observed in fluvial flows. The relation between the transport efficiency and solid discharge of these flows demonstrated that after a certain point, the efficiency became constant. This relation resulted in log trend curves with asymptotes located at efficiency values of approximately 50% (6% slope) and 40% (0.3% and 0.015% slopes). The characteristic diameter of the sediment deposited after the mobile bed presented a reduction of 18% when compared to the sediment deposited before the mobile bed.

Le couplage multiphysique devient important dans les domaines de l’ingénierie nucléaire et de l’informatique. La capacité d’obtenir des solutions précises pour des modèles réalistes est essentielle à la conception et l’autorisation des conceptions nouvelles de réacteurs nucléaires, surtout dans des situations d’accidents graves. Les modèles physiques qui décrivent le comportement des réacteurs nucléaires dans des conditions accidentelles sont : le transport des neutrons, la conduction/convection thermique, la thermomécanique du combustible et des structures de support, la stœchiométrie du combustible, et d’autres encore. Cependant cette thèse se concentre sur le couplage entre deux modèles, le transport des neutrons et la conduction/convection thermique.Le but de cette thèse est de développer un solveur multiphysique pour la simulation des accidents de réacteurs nucléaires. Le travail s’est focalisé à la fois sur l’environnement de simulation et sur le traitement des données pour de telles simulations.Ces travaux discutent le développement d’un solveur multiphysique basé sur la méthode Newton-Krylov sans la jacobienne (JFNK). Ce solveur inclut des solveurs linéaires et non-linéaires, accompagné des interfaces par le calcul des résidus aux codes existantes pour le transport des neutrons et la thermo hydraulique (APOLLO3 et MCTH respectivement). Une nouvelle formulation pour le résidu du transport de neutrons est explorée, qui réduit la taille de la solution et l’espace de recherche par un facteur important ; le résidu, au lieu d’être basé sur le flux angulaire, est basé sur la source de fission.La question de savoir si l’utilisation d’un flux fondamental pour l’homogénéisation des sections efficaces est suffisamment précise pendant les simulations transitoires rapides est aussi explorée. Il est montré que, dans le cas d’un milieu infini et homogène, l’utilisation des sections efficaces fabriquées avec un flux fondamental est significativement différente d’une solution de référence. Cette erreur est diminuée en utilisant un flux de pondération alternatif qui vient d’un calcul à dépendance temporelle ; soit avec un flux intégré en temps soit avec une solution asymptotique. Le flux intégré en temps vient d’une solution multiphysique sur un sous-domaine de l’accident et intégrée en temps. L’intégration en temps peut être réalisée sur plusieurs « morceaux » qui ont le même comportement temporel. La solution asymptotique vient d’un calcul de valeur propre alpha et emploie un ou plusieurs modes alpha comme flux de pondération. Entre les deux méthodes, la méthode avec un flux intégré en temps est plus précise, mais prend plus de temps.Le domaine d’application de ces nouvelles méthodes est étendu en étudiant les effets d’hétérogénéités spatiales et la discrétisation des macro-intervalles en temps. Premièrement, un cas avec des hétérogénéités spatiales et une perturbation locale est utilisé pour montrer que ces méthodes peuvent être utilisées pour l’homogénéisation au niveau des assemblages. Ces nouvelles méthodes fonctionnent mieux que la méthode traditionnelle avec un flux fondamental. Deuxièmement, une estimation a priori pour une discrétisation optimale est obtenue pour la méthode avec le flux intégré en temps. Il est montré que d’autres divisions du domaine en temps réduisent l’erreur sur plusieurs métriques jusqu’au moment où les erreurs numériques deviennent dominantes.Pour montrer que ces méthodes fonctionnent bien pour des calculs de grande taille, un calcul sur un cœur REB réduit est effectué. Cette simulation est basée sur un accident de chute de grappe dans un REB au démarrage. / Multiphysics coupling is becoming of large interest in the nuclear engineering and computational science fields. The ability to obtain accurate solutions to realistic models is important to the design and licensing of novel reactor designs, especially in design basis accident situations. The physical models involved in calculating accident behavior in nuclear reactors includes: neutron transport, thermal conduction/convection, thermo-mechanics in fuel and support structure, fuel stoichiometry, among others. However, this thesis focuses on the coupling between two models, neutron transport and thermal conduction/convection.The goal of this thesis is to develop a multiphysics solver for simulating accidents in nuclear reactors. The focus is both on the simulation environment and the data treatment used in such simulations.This work discusses the development of a multiphysics framework based around the Jacobian-Free Newton-Krylov (JFNK) method. The framework includes linear and nonlinear solvers, along with interfaces to existing numerical codes that solve neutron transport and thermal hydraulics models (APOLLO3 and MCTH respectively) through the computation of residuals. A new formulation for the neutron transport residual is explored, which reduces the solution size and search space by a large factor; instead of the residual being based on the angular flux, it is based on the fission source.The question of whether using a fundamental mode distribution of the neutron flux for cross section homogenization is sufficiently accurate during fast transients is also explored. It is shown that in an infinite homogeneous medium, using homogenized cross sections produced with a fundamental mode flux differ significantly from a reference solution. The error is remedied by using an alternative weighting flux taken from a time dependent calculation; either a time-integrated flux or an asymptotic solution. The time-integrated flux comes from the multiphysics solution of the accident on a subdomain and an integration in time. The integration can be broken into several “chunks” that capture similar time-dependent behavior. The asymptotic solution comes from an alpha-eigenvalue calculation and uses one or several alpha modes as the weighting flux. Between the two methods, the time-integrated flux is more accurate, but takes longer to obtain a solution.The usability of these new homogenization methods is further developed by studying the effects of spatial heterogeneities and of the discretization of the time-chunks. First, a case with spatial heterogeneities and a localized perturbation is used to show that these methods can be applied to assembly level homogenization. The new methods are shown to perform well with spatial heterogeneities when compared to using a traditional, fundamental mode, homogenization method. Second, an a priori estimate for an optimal time discretization is obtained for the time-integrated flux method. It is shown that further divisions of the time domain reduce the error for several metrics until numerical errors become dominant.To show that these methods work well for industrial sized calculations, a reduced size BWR core calculation is performed. This simulation is based on a rod-drop accident in a BWR core during startup.

In aviation industry, one of the most important aspects is weight savings. This since with a lowered weight, the performance of the aircraft can be increased together with increased fuel savings and thus lowered running costs. One way of saving weight is to reduce energy consumption, since with lowered energy consumption, lowered mass of fuel is required etc. Most aircraft are today maneuvered with hydraulic systems due to its robustness and power density. It is the primary source of power for primary and secondary flight controls. The control of a conventional system which is using proportional valves is done by altering flow by restricting it to the extent where the desired output is achieved, which implies heat losses since the full performance of its supply is wasted through the valve. In previous research, more energy efficient hydraulic systems called digital hydraulics has been investigated. In difference with conventional hydraulics, digital hydraulics uses low cost, high frequency on/off valves, which either are fully opened, or fully closed, instead of proportional valves to achieve the desired output. With this comes the benefit of no energy losses due to leakage and restriction control. The downsides with digital hydraulics is the controlabillity. One way of controlling it is by using several pressure sources which outputs different pressure levels. By using the on/off valves in different combinations, different outputs can be achieved in a discrete manner. In this thesis, the aim was to remove the impact of the discrete force steps which are present in digital hydraulics by creating concepts with hybrid solutions containing both digital hydraulics and restrictive control. Three concepts were developed and investigated using simulation. The energy consumption and performance was analysed and compared with a reference model, the concepts redundancy compared to conventional systems was discussed and finally the concepts were tested with an aircraft simulation model. The concepts were found to reduce the energy consumption with different magnitude depending on the load cycle. The performance was found to be almost as good as the reference model. The redundancy compared with conventional systems should be possible to maintain with slight modifications, but further investigation is needed. It was found that one of the most important aspects regarding energy consumption is which combination of supply pressures is used to supply the system since it influences leakage and flow due to compression.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第22055号 / 工博第4636号 / 新制||工||1723(附属図書館) / 京都大学大学院工学研究科都市社会工学専攻 / (主査)教授 細田 尚, 教授 戸田 圭一, 准教授 音田 慎一郎 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

<div>Gerotor pumps are positive displacement pumps that are frequently used in low-pressure applications such as lubrication and charge pumps. They are characterized by their unique gearset that is an internal gearset with one tooth difference that has continuous contact throughout the entire rotation. Recent trends especially in the automotive industry suggest an increased demand for greater performance from these pumps, e.g. operating with higher pressure, higher speed, lower viscosity fluid, less noise emission, and greater energy efficiency. The shape of the gears is one of the most important aspects of a gerotor pump, as it determines the pump's size and flow, affects its internal leakages, and influences its amount of wear. Although gerotors have been in operation for nearly 100 years, no design methodology has emerged in scientific literature that fully considers all the main performance aspects simultaneously and identifies the best designs. This problem is made more difficult, as gerotors can have an infinite number of different types of profiles. The main goals of this work are therefore to define a method to design gerotor gear geometry for several performance goals, identify the best designs for a given gear profile type, compare the best designs among the various profile types, and invent a new profile type that can offer improved performance over conventional designs.</div><div><br></div><div>Gerotor profile generation is described in the beginning, first for the conventional epitrochoidal, hypotrochoidal, and standard cycloidal profile types. Then a description of how to generate gerotors from an arbitrary curve is given and applied to elliptical, generalized cycloidal, cosine, and asymmetric elliptical gerotors. The generalized cycloidal profile type is new to this work.</div><div><br></div><div>Multi-objective optimization is used as the method to identify the best gear profiles for a given application considering seven performance metrics and ensuring a feasible gear profile. The seven performance goals to minimize are the radius of a pump for a given geometric displacement and face width, the kinematic flow ripple, the adhesive wear, the contact stress, the tooth tip leakage, the lateral gap leakage, and the mean displacement chamber inlet velocity. The conditions to generate feasible gerotor profiles without cusps or self-intersections are also given as constraints for the optimizations.</div><div> </div><div> Seven gerotor profiles were then optimized using a genetic algorithm to consider all the performance aspects. The design space for each profile type was thoroughly explored, and clear Pareto fronts were identified. The Pareto fronts from each profile type were then combined, and a new Pareto front was identified from the best designs of each profile type. No single profile type proves to be objectively better than the others, but the epitrochoidal, hypotrochoidal, elliptical, and generalized cycloidal profile types tend to produce the best designs. Two methods to select a design from the Pareto front that consider the relative importance of each performance goal were presented.</div><div> </div><div> The optimization strategy was then further validated by demonstrating significant possible performance improvement over state-of-the-art designs in industry and suggesting alternative designs to a specific gearset used in industry that were tested in simulation and experiment. Two generalized cycloidal profiles were selected as alternative designs: the first design matched the fluid dynamic performance of the reference design with significantly reduced contact stress, and the second is a profile that could reduce the outlet flow ripple while fitting within the same pump housing. The contact stress of the reference and alternative designs when including clearance between the gears was compared in finite element analysis. Prototypes of the alternative designs were then manufactured and tested in experiment. The experimental pressure ripples of the alternative designs were compared, and the second design showed a reduction in outlet pressure ripple that validates the proposed design methodology.</div><div> </div><div> This work has thoroughly explored the performance possibilities of the gerotor mechanism and presented a method to select an optimal profile geometry depending on the desired performance characteristics. It has therefore accomplished its goals in making a contribution toward improving the performance gerotor gear geometry.</div>

The subject of this thesis is realization of short research of current compact hydraulic power unit, realization of FEM analysis with aim to find inappropriately dimensioned parts of structures. Based on this data design optimized solution of structures and create drawings of weldments. This thesis is carried out in cooperation with company Bosch Rexroth, spol.s.r.o.

The assignment of my diploma thesis is to design the family house heating system. The source of energy is heat pump for heating which takes heat from areal collector.

The first part of this masters thesis deals with research of modulat type hydraulics power units from other significant world producers. Design part of thesis contains complete design of three product ranges of hydraulics power units. It also includes simulation by FEM method. Last part descibe safety of machine and brief economic evaluation of product.