Thesis (Ph. D.)--University of Canterbury, 2009. / Typescript (photocopy). "Fire engineering research thesis August 2009." Includes bibliographical references (p. 411-421). Also available via the World Wide Web.

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Αντικείμενο της παρούσας διδακτορικής διατριβής αποτέλεσε η ανάπτυξη μιας ακριβούς υπολογιστικής μεθοδολογίας για τη μελέτη της μαγνητοϋδροδυναμικής και θερμικής ροής ενός ηλεκτρικώς αγώγιμου ρευστού υπό την επίδραση ενός εξωτερικού μαγνητικού πεδίου, για μεγάλο φάσμα τιμών των παραμέτρων της ροής. Η μελέτη της διαμόρφωσης της μαγνητορευστοδυναμικής και θερμικής ροής των ηλεκτρικώς αγώγιμων ρευστών, όπως είναι τα υγρά μέταλλα, υπό την επίδραση της εφαρμογής ενός εξωτερικού μαγνητικού πεδίου, είναι ιδιαίτερα σημαντική για την εκτίμηση της μείωσης της αξονικής βαθμίδας της πίεσης, του συντελεστή μεταφοράς θερμότητας και άλλων φυσικών ποσοτήτων, σε μια σειρά προβλημάτων όπως είναι η σταθεροποίηση και ο περιορισμός του πλάσματος, η ψύξη των αντιδραστήρων σύντηξης με υγρά μέταλλα, η χύτευση μετάλλων με ηλεκτρομαγνητικά μέσα, η χρήση ηλεκτρομαγνητικών αντλιών για υγρά μέταλλα, στη γεωλογία, για τη μελέτη του εσωτερικού της Γης, και στην αστροφυσική όπου μελετώνται μεταξύ άλλων αστέρες, νεφελώματα και σχετικιστικά τζετ. Η ροή θεωρείται ασυμπίεστη και στρωτή, ενώ μελετάται για τις περιπτώσεις της πλήρως ανεπτυγμένης και της αναπτυσσόμενης ροή στην περιοχή μεταξύ δύο ομοαξονικών ευθύγραμμων ή καμπύλων αγωγών κυκλικής διατομής, υπό την επίδραση ισχυρού εξωτερικού μαγνητικού πεδίου. Τα τοιχώματα των αγωγών είναι ηλεκτρικώς μονωμένα και ανάλογα με το πρόβλημα βρίσκονται σε διαφορετικές σταθερές θερμοκρασίες ή σε διαφορετικές ροές θερμότητας. Από τα αποτελέσματα προέκυψε πως το μαγνητικό πεδίο έχει πολύ σημαντική επίδραση στην κατανομή της ταχύτητας και στην πτώση πίεσης, ενώ η επίδραση του στη μετάδοση θερμότητας στην περίπτωση των υγρών μετάλλων είναι μηδαμινή. / The aim of the present doctorate thesis was the development of an accurate και robust computational methodology for the study of the magnetohydrodynamic flow of an electrically conducting fluid under the effect of an external magnetic field, for large regions of values of the parameters of the flow. The study of the magnetohydrodynamic και thermal flow of an electrically conducting fluid, such as liquid metals, is very important for the estimation of the pressure drop, the heat transfer coefficient και other physical quantities in several engineering applications such as stabilization και control of plasma, fusion reactor blankets, metallurgy, electromagnetic pumps, geology for the study of the inner core of the earth και astrophysics where stars, nebula και relativity jets are studied. The flow is considered as incompressible και laminar και it is studied for the cases of the fully developed και the developing flow in the region between two homoaxial straight or curved ducts of circular cross-sections, under the effect of an external magnetic field. The duct walls are considered as electrically insulated και maintained at uniform temperatures or uniform heat fluxes. The results show that the magnetic field has a significant effect on the velocity distribution και the pressure drop και a minor effect on the heat transfer.

In silico models of intracranial aneurysm (IA) evolution aim to reliably represent the mechanical blood flow environment, the biology of the arterial wall and, crucially, the complex link between the two, namely the mechanobiology of healthy and diseased arteries. The ultimate goal is to create diagnostic tools for personalized management and treatment of aneurysm disease. Towards that target, the work presented in this thesis aims to establish a directly interactive link between experimental (in vivo and in vitro) and computational work for biologically and clinically relevant research on aneurysm disease. Mechanobiological hypotheses were firstly investigated in a novel 1D mathematical conceptual model of aneurysm evolution: for the first time these included representations of endothelial heterogeneity and smooth muscle cell (SMC) active stress response and apoptosis. The 1D investigations analysed and assessed the role of wall shear stress (WSS) homeostasis in elastin degradation, and the evolving role of the adventitia as a protective sheath in health and primary load-bearer in disease. The 1D framework was applied to a specific patient's aneurysm using both imaging and histological data to parameterise the model, calculating a material parameter for the adventitital collagen. The predicted evolution captured aspects of tissue changes measured with time focusing on the remodelled tissue wall thickness consistent with the experimental measurements, and physiological cyclic deformation in order to propose an approach to modelling adventitia's adaptive role to load bearing. Furthermore, an existing Fluid-Solid-Growth (FSG) computational framework was adapted and calibrated for the same patient-specific case with the help from the experimental data and the analysis from the 1D framework. This FSG model quantifies the arterial mechanical environment and captures the mechanical response of the fibrous arterial constituents. Comparing 1D and 3D investigations to establish consistency for our models, the 3Dmodel tested the hypothesis of WSS homeostasis, additionally introducing the element of spatial heterogeneity in the definition, and a new hypothesis linking cyclic deformation with collagen growth that ensures a physiological mechanical environment in stabilised aneurysms. Moreover, the FSG framework was applied in a specific rabbit aneurysm case and extended to link growth and remodeling to the detailed representation of the pulsatile blood flow mechanical environment. This research illustrates the power of computational modelling when coupled with rich data sets on the physiology, histology and geometry of healthy and diseased vascular tissue. In particular, the integrative modelling framework provides the foundation for establishing mechanobiological links crucial to aneurysm progression, and a basis for further research towards creating reliable aneurysm clinical tools.

abstract: Energy efficient design and management of data centers has seen considerable interest in the recent years owing to its potential to reduce the overall energy consumption and thereby the costs associated with it. Therefore, it is of utmost importance that new methods for improved physical design of data centers, resource management schemes for efficient workload distribution and sustainable operation for improving the energy efficiency, be developed and tested before implementation on an actual data center. The BlueTool project, provides such a state-of-the-art platform, both software and hardware, to design and analyze energy efficiency of data centers. The software platform, namely GDCSim uses cyber-physical approach to study the physical behavior of the data center in response to the management decisions by taking into account the heat recirculation patterns in the data center room. Such an approach yields best possible energy savings owing to the characterization of cyber-physical interactions and the ability of the resource management to take decisions based on physical behavior of data centers. The GDCSim mainly uses two Computational Fluid Dynamics (CFD) based cyber-physical models namely, Heat Recirculation Matrix (HRM) and Transient Heat Distribution Model (THDM) for thermal predictions based on different management schemes. They are generated using a model generator namely BlueSim. To ensure the accuracy of the thermal predictions using the GDCSim, the models, HRM and THDM and the model generator, BlueSim need to be validated experimentally. For this purpose, the hardware platform of the BlueTool project, namely the BlueCenter, a mini data center, can be used. As a part of this thesis, the HRM and THDM were generated using the BlueSim and experimentally validated using the BlueCenter. An average error of 4.08% was observed for BlueSim, 5.84% for HRM and 4.24% for THDM. Further, a high initial error was observed for transient thermal prediction, which is due to the inability of BlueSim to account for the heat retained by server components. / Dissertation/Thesis / M.S. Mechanical Engineering 2012

Made available in DSpace on 2015-09-17T15:26:45Z (GMT). No. of bitstreams: 0 Previous issue date: 2015-06-25. Added 1 bitstream(s) on 2015-09-17T15:45:16Z : No. of bitstreams: 1 000846822.pdf: 4839529 bytes, checksum: c4b8326579b8c8a11a6d43fb64caa62f (MD5) / O motor de combustão interna é a principal fonte de energia de automóveis, sendo de grande importância para o setor de energia no mundo. Com o aparecimento de problemas relacionados com a emissão exagerada de poluentes e gases de efeito estufa, o desenvolvimento de modelos que corretamente descrevem os fenômenos físicos que ocorrem no interior da câmara de combustão de motores tornou-se relevante. Assim, na primeira parte deste trabalho a biblioteca de modelos de fonte aberta de dinâmica de fluidos computacional (CFD) OpenFOAM com módulos desenvolvidos na Universidade de Duisburg-Essen foi utilizada para investigar o efeito do volume das fendas no desenvolvimento da combustão em motores convencionais com ignição por centelha. As simulações de grandes escalas (LES, large eddy simulation) realizadas foram validadas com visualizações de câmeras de alta velocidade obtidas do motor óptico de Duisburg, que mostraram a presença de uma frente luminosa no interior da fenda anular que poderia ser associada a uma chama se propagando. Os resultados apresentados mostraram boa concordância qualitativa com os dados experimentais, o que permitiu concluir que no caso do motor de Duisburg, a chama é realmente capaz de penetrar no volume da fenda. Em seguida, um estudo sobre sprays combustíveis foi realizado, por se tratar de uma tendência muito promissora em motores modernos. Atenção especial foi dada aos fenômenos de conservação de momento, ruptura, evaporação e mistura do caso de teste Spray G da rede de combustão em motores (ECN, engine combustion network). Os processos de ruptura e evaporação foram investigados e simulados, sendo os resultados interpretados de acordo com os modelos utilizados. O comprimento de penetração foi validado com experimentos e uma boa concordância foi atingida. Finalmente, um estudo de sensibilidade da malha foi realizado e seus resultados apresentados e discutidos / The internal combustion engine is the major energy source of automobiles and is of large importance for the energy sector worldwide. As problems related to exaggerated pollutant and greenhouse gases emissions emerged, the development of models to correctly describe the physical phenomena taking place inside the combustion chamber of engines became relevant. Thus, in the first part of this work the open source CFD library OpenFOAM with modules developed at the University of Duisburg-Essen was used to investigate the effect of the crevice volume on the performance of the combustion in port fuel injection spark ignition engines. The LES (large eddy simulation) simulations were validated against high speed flame visualization obtained from the Duisburg optical engine, which showed the presence of a luminous front inside the top land crevice that could be a wrinkled flame. The presented results showed good qualitative agreement with the experimental data, which allowed the conclusion that in the case of the Duisburg engine, the flame indeed penetrates into the crevice volume. Furthermore, a study on fuel sprays was performed, since this is a very promising trend related to modern engines. Special attention was given to the phenomena of momentum exchange, droplet breakup, evaporation and mixture from the test case Spray G provided by the Engine Combustion Network (ECN). The processes of droplet breakup and evaporation were investigated and simulated, being the results interpreted according to the models used. The penetration length was validated against experiments and good agreement was obtained. Finally, a mesh sensitivity study was performed and the results presented and discussed

Turbulent buoyant jets are a major feature in fire hazards. The solution of the Reynolds Averaged Navier-Stokes (RANS) equations through computational fluid dynamic (CFD) techniques allow such flows to be simulated. The use of Reynolds averaging requires an empirical model to close the set of equations, this is known as the turbulence model. This thesis undertakes to investigate linear and nonlinear approaches to turbulence modelling and to apply the knowledge gained to the simulation of compartment fires. The principle contribution of this work is the reanalysis of the standard k- ε turbulence model and the implementation and application of more sophisticated models as applied to thermal plumes. Validation in this work, of the standard k- ε model against the most recent experimental data, counters the established view that the model is inadequate for the simulation of buoyant flows. Examination of previous experimental data suggests that the measurements were not taken in the self-similar region resulting in misleading comparisons with published numerical solutions. This is a significant conclusion that impacts of the general approach taken to modelling turbulence in this field. A number of methods for modelling the Reynolds stresses and the turbulent scalar fluxes have been considered and, in some cases for the first time, are applied to nonisothermal flows. The relative influence of each model has been assessed enabling its performance to be gauged. The results from this have made a valuable contribution to the knowledge in the field and have enabled the acquired experience to be applied to the simulation of compartment fires. The overall conclusion drawn from this thesis is that for the simulation of compartment fires, the most appropriate approach with current computational resources, is still the buoyancy corrected standard k- ε model. However, the turbulence scalar flux should be modelled by the generalised gradient diffusion hypothesis (GGDH) rather than the eddy-diffusivity assumption.

This thesis promotes the responsible use of CFD technology through the development of the simulation based design strategy applicable to the design of the tire engineered smoke control ventilation systems. The correct representations of the problem of interest and measures that may be adopted to ensure the accuracy of the simulated solution are two key aspects of this promotion. The development process presents the application of the proposed procedure through three industrial challenges that have subsequently been approved by the relevant fire authorities. The challenges consist of the design of fire engineered systems for residential high rise buildings and covered car parks which in turn demonstrate the robustness of the proposed procedure. The proposed procedure consists of four key stages namely: Qualitative Design Review (QDR); Quantitative Analysis (QA); Assessment; and Fire Services' comments. QDR identifies the ventilation strategy, the potential tire scenario and the appropriate assessment approach applicable to the problem of interest. QA uses the chosen tire analytical approach to evaluate parameters identified in the QDR. The assessment stage is where outputs from the analysis are assessed based on the assessment criteria defined in the QDR. Fire Services' comments are there to account for any additional requirements the fire officer responsible might had have as he/she has the final say on whether the fire engineered system is approved for installation. A review of the current legislative literature i.e. building code, prescriptive and performance based codes is presented. Furthermore, the criteria applicable for the assessment of simulation based design solution are also discussed. The concept of smoke control is discussed in detail which includes an overview of the mechanism of smoke movement and the provisions available to limit smoke spread. A survey of the current Computational Fluid Dynamics (CFD) software packages suitable for the assessment of smoke movement is also included.

Coating flows can be defined as a laminar free surface flows, whereby a liquid layer is applied onto a solid substrate. A typical industrial application consists of co-rotating cylindrical rollers, which are used to apply a liquid coating (paint) onto a moving substrate, and depending on the direction of the rollers, can be configured in either forward or reverse mode. These types of coating solution flows are industrially important applications, and convey viscoelastic aspects due to their polymeric content and unsteady polymeric behaviour. The process often possesses localized regions of high shear and extension rates (narrow nip and wetting-line zones), which may cause instabilities on the coated substrate (ribbing, leveling, striping). These non-Newtonian and viscoelastic studies for industrial reverse roll coating focus on the use of computational techniques to model these types of coating flows, alongside the analysis of the fluid flow behaviour and under varied rheological properties. Two flow problem configurations have been considered, a model benchmark problem of mixed combined-separating flow, and the industrial application of reverse roll coating flow. Predictions and corresponding solutions are reported for viscous, inelastic and complex viscoelastic fluid properties. The numerical formulation adopts a Taylor-Galerkin pressure-correction (TGPC) scheme, using a finite element method for viscous, inelastic flows and a hybrid finite element/finite volume method for their viscoelastic counterparts. The research plan is centered around computational fluid dynamics and rheological studies, with the main target focused on industrial roll-coating operations. From simple theory, Newtonian and non-Newtonian coating flows possess specific, yet disparate characteristics. This may lead to distinct and significant differences in their detailed flow behaviour, and in the stressing levels generated, dependent upon the nature of the flow configuration. The study is segmented into several stages: initially, solution was sought for a benchmark flow problem, where a semi- implicit time stepping finite element procedure was employed to simulate a mixed combined- separating flow. Here, both viscous and viscoplastic material approximations have been introduced. Secondly, the industrial application of reverse roll coating flow was addressed for viscous inelastic coating fluids. This incorporated scenarios of inclusion and not of a dynamic wetting line and consideration of the effects of a rubber elastomer-cover upon the applicator roll. Thirdly, viscoelastic paint coatings were addressed for the industrial reverse roll coating flow. Here, a hybrid finite element/finite volume sub-cell method was utilized, and with inclusion of a dynamic wetting line. Of the various viscoelastic material models available, use has been made of the Phan-Thien Taimer (PTT) network class of models, in both linear and exponential variety, and of the FENE class of models, with FENE-CR and FENE-P versions. This has offered a richness in capacity over variation of rheological properties. The choice of computational methods has been justified and the TGPC algorithm was deemed suitable for problem solution. The methodology tested on combined-separating flow provided high-quality numerical results, which compare favorably against experiments, literature and theory. When applied to the reverse roll coating problem, the TGPC algorithm has been coupled to a time-dependent free-surface update procedure, to determine the dynamic movement of the meniscus and the wetting line. Around the nip-region, the flow problem manifests strong flow features, which have been investigated for a range of rheological properties of varying shear and extensional response. The direct impact these have on localized peak nip-pressures and distributional lift levels has been observed, where several relief mechanisms have been successfully identified (important to optimize process control). The influence of solvent fraction, extensional viscosity and increasing elasticity, up to critical stress states have been analysed in considerable detail. In summary, the success of this work indicates optimal flow process settings and preferential Theological coating properties to employ, with respect to this industrial coating process. As such, it lays the foundation and guide towards achieving a stable and consistent coating application - specifically, as high-speed high-gain production is of current demanded.

Devido à crescente preocupação com as questões ambientais envolvendo as emissões de gases que potencializam o efeito estufa e outros problemas associados aos combustíveis fósseis, o hidrogênio aparece como uma fonte de energia alternativa capaz de promover o desenvolvimento de forma sustentável. A produção de hidrogênio via fermentação anaeróbia é uma das rotas mais atraentes atualmente, envolvendo processos físicos, químicos e biológicos com inúmeras interações entre gases, líquidos e sólidos. No entanto, as pesquisas atuais têm dedicado especial atenção às características químicas e biológicas. Muitos reatores em escala real e de laboratório ainda são dimensionados por correlações empíricas, mas a compreensão dos fenômenos hidrodinâmicos envolvidos na produção de hidrogênio é um precursor necessário para a aplicação em projetos de escala industrial. Para otimizar o desempenho do reator, é essencial compreender a dinâmica das fases em seu interior. Neste contexto, o objetivo deste trabalho é empregar técnicas de fluidodinâmica computacional (CFD) para estudar e otimizar o comportamento fluidodinâmico de um reator anaeróbio sequencial em batelada (ASBR). Para tanto, foi adotada uma modelagem bifásica, tridimensional e turbulenta conduzida com o programa computacional OpenFOAM. Diferentes condições operacionais, configurações geométricas, bem como diferentes modelos, foram avaliados. Os resultados obtidos no estudo das forças interfaciais reforçam a importância e a necessidade de validar as simulações com dados experimentais, devido à grande variação nos resultados obtidos em cada caso simulado. Do ponto de vista das configurações geométricas e operacionais, observa-se que modificações na vazão e no sentido da recirculação, bem como alterações na geometria dos distribuidores afetam significativamente a velocidade de mistura e a energia cinética turbulenta no interior do reator. Estas modificações afetam a transferência de massa, a qual influencia diretamente na cinética das reações e possibilita uma maior produção e hidrogênio. Determinar o comportamento do reator de forma precisa é um precursor para propor alterações que melhorem a sua eficiência. / Submitted by Ana Guimarães Pereira (agpereir@ucs.br) on 2015-02-23T13:55:23Z No. of bitstreams: 1 Dissertacao Guilherme Zanella Maurina.pdf: 2001909 bytes, checksum: f1de7c235fc3a85355a86042b3c96826 (MD5) / Made available in DSpace on 2015-02-23T13:55:23Z (GMT). No. of bitstreams: 1 Dissertacao Guilherme Zanella Maurina.pdf: 2001909 bytes, checksum: f1de7c235fc3a85355a86042b3c96826 (MD5) / PETROBRAS, Brasil / Due to the growing concern with environmental issues involving the emission of gases that enhance the greenhouse effect and other problems associated with fossil fuels, hydrogen arises as an alternative source of energy capable of promoting development on a sustainable manner. Hydrogen production via anaerobic fermentation is currently one of the most attractive routes, involving physical, chemical and biological processes with numerous interactions between gas, liquid and solid. However, current research has devoted special attention to chemical and biological characteristics. Many full-scale and laboratory-scale reactors are still dimensioned using empirical correlations, but the understanding of hydrodynamic phenomena involved in the production of hydrogen is a necessary precursor for the application in industrial scale projects. To optimize the performance of the reactor, it is critical to understand the dynamics of the phases inside. In this context, the aim of this work is to employ computational fluid dynamics (CFD) techniques to study and optimize the fluid dynamic behavior of an anaerobic sequential batch reactor (ASBR). Thus, a two-phase, threedimensional and turbulent modeling was adopted, and simulations were conducted with the computer program OpenFOAM. Different operating conditions, geometric configurations and different models were evaluated. The results obtained in the study of interfacial forces reinforce the importance and the need to validate the simulations with experimental data, due to the large variation in the results obtained in each simulated case. Concerning geometric and operational settings, it was observed that changes in flow direction and recirculation, as well as changes in the geometry of distributors, affect significantly the velocity and the turbulent kinetic energy inside the reactor. These changes affect the mass transfer, which directly influences the reaction kinetics and enables greater production of hydrogen. The accurate establishment of the reactor behavior is a precur or to propose changes in order to improve its efficiency.