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Publié le 11 mars 2023

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1

Roman, Federico. « Large eddy simulation tool for environmental and industrial processes ». Doctoral thesis, Università degli studi di Trieste, 2009. http://hdl.handle.net/10077/3210.

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2007/2008
Computational Fluid Dynamics (CFD) is an established tool for consulting and for basic research in fluid mechanics. CFD is required to provide information where analytical approaches or experiments would be impossible or too expensive. Most of the flows of engineering interest are turbulent. Turbulence is an unresolved problem of classical physics, because of the non linearity of the fluid motion equations. At the moment the only way to face them is numerically. Turbulence is composed of eddies in a broad range of size. To solve numerically the Navier-Stokes equations, the equations set that governs the fluid motion, a very fine grid is necessary in order to catch also the smallest eddies. The computational cost increases as Re3 (Re = ul/ is the Reynolds number with u and l an inertial velocity and length scales and the kinematic viscosity). Real life problems are characterized by very large Reynolds numbers and the consequent computational cost is enormous. So the direct solutions of Navier-Stokes equations (DNS) is not feasible. In many applications it is not necessary to solve all the eddies, it can be sufficient to supply the effects of unresolved scale to the flow. In Large Eddy Simulation (LES) most of the scales of motion are directly solved, in particular all the large energy carrying scales. These scales are influenced by the boundaries and they are strongly anisotropic. The smaller and dissipative scales must be modeled, but these scales loosing memory of the boundary conditions are more isotropic and hence formulating a general model that accounts for their effect is relatively easier. Large Eddy Simulation is a prospective tool for investigation in real life problems, in particular when high detailed analysis is required. This is the case for many industrial and environmental processes. For example, acoustic problems due to hydrodynamic noise are governed over a range of large scales which are easily reproduced by LES solution. However in these types of flows many difficulties arise also for LES. In general these flows are characterized by high Reynolds number. Wall-bounded flow at high Re requires high computational cost because LES is constrained to be DNS-like. Besides complex geometries are often involved. Structured or Unstructured body-fitted grid can be very hard to made, moreover unstructured grid can be expensive and not suited for LES. Scope of this thesis is to develop tools to apply LES to such configurations in order to make numerical simulation more adaptable to real life problems. In particular to deal with complex geometry an Immersed Boundary Methodology has been developed for curvilinear coordinates. The method has been applied to several test cases with good results. Then this methodology has been extended to high Reynolds number flows through the use of a wall model. In order to work on anisotropic grid, typical in sea coastal domain, a modified Smagorisky model has been proposed. Finally particle dispersion has been considered in stratified environmental flow. These tools has been applied to an industrial and to an environmental problem with good results.
La fluidodinamica computazionale (CFD) ´e uno strumento affermato per le consulenze e per la ricerca di base nella meccanica dei fluidi. Alla CFD ´e richiesto di fornire informazioni quando approcci analitici o sperimentali sarebbero impossibili o troppo costosi. La maggior parte dei flussi di interesse ingegneristico ´e di tipo turbolento. La turbolenza ´e uno dei problemi irrisolti della fisica classica, ci´o ´e dovuto alla non linearit´a delle equazioni che governano il moto dei fluidi. Al momento l’unico modo per affrontarle ´e numericamente. La turbolenza si compone di vortici di diverse dimensioni. Per risolvere numericamente le equazioni di Navier-Stokes, le equazioni che governano il moto dei fluidi, una griglia molto fine ´e necessaria al fine di simulare propriamente anche i vortici di scala pi´u piccola. Il costo computazionale cresce come Re3 (Re = ul/ ´e il numero di Reynolds, con u e l una velocit´a ed una lunghezza scala caratteristici e la viscosit´a cinematica). I problemi reali sono caratterizzati da numeri di Reynolds altissimi e conseguentemente il costo computazionale di queste simulazioni ´e enorme. Per questo motivo la soluzione diretta delle equazioni di Navier-Stokes (DNS) non ´e possibile. In molte applicazioni non ´e necessario risolvere tutte le scale dei vortici, pu´o essere sufficiente fornire l’effetto delle scale non risolte al flusso. Nella Large Eddy Simulation gran parte delle scale di vortici ´e direttamente risolta, in particolare le larghe scale energetiche. Queste scale sono influenzate dalle condizioni al contorno e sono fortemente anisotrope. Le scale piccole e dissipative devono essere modellate, ma queste scale perdendo memoria delle condizioni al contorno sono generalmente isotrope ed un modello per riprodurre il loro effetto risulta semplice. La LES ´e uno strumento d’avanguardia per lo studio di flussi realistici, in particolare risulta molto potente quando vengono richieste analisi dettagliate del moto. Questo ´e il caso di molti problemi in campo industriale ed ambientale. Per esempio problemi acustici dovuti a rumore idrodinamico sono governati dalle grandi scale che nella LES sono facilmente riprodotte. Comunque anche per la LES sorgono molte difficolt´a nel affrontare questi problemi. Generalmente questi flussi sono caratterizzati da alti numeri di Reynolds. Flussi di parete ad alti Re richiedono un costo computazionale elevatissimo e alla fine la LES deve soddisfare a requisiti tipici della DNS. Inoltre spesso questi flussi sono caratterizzati da geometrie complesse. Griglie strutturate o non strutturate che si adattano alle geometrie possono essere molto difficili da sviluppare, inoltre le griglie non strutturate possono essere molto costose e non particolarmente adatte alla LES. Lo scopo di questa tesi ´e di sviluppare degli strumenti atti a rendere efficiente l’applicazione della LES a flussi realistici. In particolare per affrontare le geometrie complesse ´e stata sviluppata una metodologia Immersed Boundary per coordinate curvilinee. Il metodo ´e stato provato su diversi casi con buoni risultati. La metodologia ´e stata quindi estesa al caso di flussi ad alto numero di Reynolds tramite lo sviluppo di un modello parete. ´E stato quindi sviluppato un modello modificato di Smagorinsky per lavorare con griglie fortemente anisotrope, tipiche per flussi in ambito marino costiero. Infine ´e stata studiata la dispersione di particelle in flussi ambientali stratificati. Gli strumenti sviluppati sono stati quindi applicati ad un problema industriale ed ad uno ambientale con ottimi risultati.
XXI Ciclo
1976
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2

PASINATO, HUGO DARIO. « TURBULENCE IN WALL REGION MODELING ». PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1998. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=19290@1.

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CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
Neste trabalho são apresentados de uma pesquisa orientada à modelagem da turbulência de baixos números de Reynolds. Com esse objetivo foi caracterizado o escoamento turbulento de baixos números de Reynolds na região viscosa vizinha a uma parede, na base de dados experimentais e correlação empírica. Sobre essa caracterização foi feita uma análise dos valores médios de interesse para modelos de turbulência de duas equações, a qual permitiu obter conclusões sobre o comportamento da turbulência de baixos Reynolds e propor modelos para a mesma. Essa modelagem implica em fornecer um fechamento para a equação de dissipação de energia cinética turbulenta e uma expressão para a viscosidade efetiva da turbulência, na região viscosa. O fechamento da equação de dissipação foi feito analisando os termos fontes de vorticidade, usando resultados prévios da ordem de grandeza relativa dos mesmos. A equação de dissipação obtida desse modo não contém funções de amortecimento. Com relação à expressão proposta para calcular a viscosidade efetiva de turbulência, considera-se que a transferência de quantidade de movimento devido à turbulência pode ser obtida em função da energia cinética do escoamento médio. Considera-se que a modelagem proposta é uma complementação para modelos de turbulência de duas equações, para simular zonas de baixos Reynolds incluídos os casos em sub-camada logarítmica aparente. Problemas de escoamentos turbulentos com cisalhamento médio com diferentes características, usualmente utilizadas para avaliar modelos de turbulência, foram usados como testes. Como resultados relevantes desta pesquisa, considera-se o fato de se usar em forma sistemática informação experimental para o desenvolvimento de modelos de turbulência, a obtenção de um fechamento para a equação de dissipação sem funções de amortecimento e uma expressão para a viscosidade da turbulência na região viscosa. No caso da viscosidade da turbulência, a expressão proposta permite obter a distribuição da velocidade média na região amortecedora, apresentando boa concordância com dados experimentais.
This thesis presents the results of research work aiming at low Reynolds turbulence modeling. For an stablished boundary layer turbulent low Reynolds flow in the viscous layer near a wall was characterized based on experimental data and empirical polynomials. On this basis an analysis of the distribuition of the mean values in the near-wall region was performed allowing for the proposal of a low Reynolds turbulence model within a two-equation model methodolgy. The low Reynolds proposal involves a closure to the dissipation equation and the proposal of an effective turbulence viscosity expression. The dissipation equation closure like as the effective viscosity proposal were made based on previous results of scale time rate analysis through the viscous region. On the other hand, the effective turbulence viscosity expression allows for the representation of the Reynolds stress as a function of mean flow kinetic energy. The low Reynolds turbulence modeling proposal can be seen as a complementation of two eqaution models for low Reynolds turbulence. The model was tested in several case tests of turbulent flow with different kind of mean shear, frequently used for turbulence model assessment. As main results of this work can be mentioned the systematic use of experimental data to build, analyze and test turbulence models; the closure of the dissipation equation without damping functions and the turbulence effective viscosity expression for the viscous region. This last proposed relation allows for the attainment of a mean velocity distribuition profile in the buffer region, which adequately fits experimental data.
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3

Lubchenko, Nazar. « Near-wall modeling of bubbly flows ». Thesis, Massachusetts Institute of Technology, 2018. https://hdl.handle.net/1721.1/121709.

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This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2018
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 119-127).
Multiphase computational fluid dynamics (M-CFD) codes are gaining acceptance in the nuclear industry for the prediction of thermal-hydraulic behavior, offering the potential to improve the operation, economics, and safety of current systems, and enhance the design of next generation reactors. The common approach when applying M-CFD methods to the bubbly flow regime is to use an Eulerian-Eulerian two-fluid model, which solves for averaged mass and momentum equations for liquid and gas phases, as well as the k-epsilon turbulence model with modifications to account for the presence of bubbles. The resulting partial differential equations require well-posed boundary conditions, with special treatment at the walls, where there exist strong gradients of all variables. The present work systematically addresses the boundary conditions at solid walls for turbulent bubbly flows.
The complete coupled problem involving six variables is decoupled into three separate tasks, which consider void fraction profile, turbulent quantities, and gas velocity near the wall. Based on available experimental data it is shown that the reduction in void fraction near the wall is a consequence of the bubble shape, and not the wall lubrication effect repelling bubbles from the wall. Aiming at restoring the correct profile, a new wall force is derived from consideration of the interfacial forces balance near the wall. Its performance is evaluated through simulations of bubbly pipe flow experiments, confirming its improvements when compared to previous models. Three phenomena, namely, bubble-induced turbulence, buoyancy of gas, and displacement of liquid by gas, are speculated to have effect on the near-wall turbulent boundary layer.
These effects are incorporated in the Analytical Wall Functions (AWF), which provide quantitative treatment of these bubble effects in the boundary layer. The boundary layer model is validated on the existing experimental data, and the AWF are assessed based on simulations of bubbly pipe flow experiments, as well as at the prototypical reactor conditions. It is demonstrated that most of the effects that arise due to bubbles in the boundary layer can be neglected, and consequently, single phase wall functions can be used in numerical simulations. Finally, through analysis of experimental data, it is suggested that the relative velocity between bubbles and the surrounding liquid does not remain constant throughout the domain in the Eulerian-Eulerian representation of the flow, but instead increases near the wall. A corresponding correction to the drag coefficient is proposed and validated against the experimental data.
by Nazar Lubchenko.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Nuclear Science and Engineering
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4

Calafell, Sandiumenge Joan. « Efficient wall modeling for large eddy simulations of general non-equilibrium wall-bounded flows ». Doctoral thesis, Universitat Politècnica de Catalunya, 2019. http://hdl.handle.net/10803/667230.

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The main purpose of this thesis has been to contribute to the development of methodologies for wall modeling Large Eddy Simulations (LES) of wall-bounded flows, especially those at high Reynolds numbers. This flow configuration is widely found in a vast range of industrial applications. Unfortunately, given the physical nature of boundary layers, their accurate numerical resolution can be computationally unaffordable. Wall modeling aims at reproducing the inner layer effects on the flow without resolving it explicitly. This allows performing accurate numerical simulations of high Reynolds number wall-bounded flows at a fraction of the cost that would be incurred if the inner layer was temporally and spatially resolved. This work comprises six chapters. The first one is an introduction to the existing Computational Fluid Dynamics (CFD) approaches, from the most accurate and general methodologies to the most simplified and specific techniques. The second chapter introduces relevant physical magnitudes to be analyzed to ensure the reliability of a given high fidelity CFD simulation. Spatial and temporal aspects, both crucial for a correct and accurate resolution of a turbulent flow, are considered. In the third chapter, a Two-Layer wall shear stress model (TLM) for LES and suitable for non-equilibrium flows and complex geometries is presented. Wall shear stress models in general, and RANS-based wall models (WM) in particular, are affected by the "log-layer mismatch" (LLM) and the resolved Reynolds stresses (RRS) inflow problems which undermine the quality of the WM numerical predictions. The model presented in this work features a temporal filter in the WM/LES interface which allows solving both problems at once with a single and low-computational-cost step. Until now, these two problems have been dealt with separately with different techniques, which in some cases were complex and computationally expensive. On the other hand, a methodology intended to determine the optimal temporal filter length is proposed and validated in equilibrium and non-equilibrium conditions. This new technique is based on the velocity power spectrum which reveals the flow characteristic time-scales in the near-wall region. According to the results obtained in the validation tests, it is concluded that for RANS-based TLM methods, time-resolved frequencies higher than the energy-containing/inertial range limit must be filtered. In chapter four, the mathematical model of the TLM, based on the URANS equations, is presented. Moreover, its numerical resolution through the finite volume method is developed and finally summarized in a flow-chart. Then, in chapter five, the algorithmic implementation of the numerical model described in chapter four is presented. The TLM is a fully operational and independent CFD solver based on the URANS equations, which has been developed from scratch. Given that the primary objective of wall modeling is reducing the computational costs, an efficient algorithmic and parallel implementation is a key aspect of the global modeling strategy. Thus, the parallel efficiency is evaluated through a strong scalability test. Good results are obtained although some aspects to be improved are identified. Finally, in the last chapter, general conclusions concerning the whole work are given together with future research proposals aimed at going further in the methodologies studied in this thesis.
El principal objectiu d’aquesta tesi ha estat contribuir al desenvolupament de metodologies relacionades amb wall modeling aplicat a Large Eddy Simulations (LES) de fluxos de paret, especialment per a números de Reynolds alts. Aquesta configuració de flux es troba en un ampli número d’aplicacions industrials. Tot i això, donada la naturalesa de les capes límit, la resolució numèrica acurada d’aquest tipus de flux de manera rutinària és inviable. La tècnica de wall modeling pretén reproduir els efectes de la capa límit interna sense necessitat de resoldre-la explícitament. Això permet la resolució de fluxos de paret a alts números de Reynolds amb una fracció del cost que tindria si la capa límit interna fos resolta tant des d’un punt de vista espacial com temporal. Aquest treball està format per sis capítols. El primer és una introducció a la dinàmica de fluids computacional (CFD en les seves sigles en anglès), des de les metodologies més acurades i generals, fins a les tècniques més específiques i simplificades. Al segon capítol s’introdueixen les magnituds físiques rellevants que s’han d’analitzar per a avaluar i confirmar la fiabilitat d’una determinada simulació numèrica CFD d’alta fidelitat. Es consideren tant els aspectes espacials com temporals, els quals són fonamentals per a la correcta resolució d’un flux turbulent. Al tercer capítol es presenta un model de paret Two-Layer per a fluxos de no-equilibri i geometries complexes. Els models wall shear stress en general i els models basats en RANS en particular, estan afectats per els problemes de “log-layer mismatch” i “resolved Reynolds stresses inflow”, que deterioren la qualitat de les prediccions numèriques. El model proposat incorpora un filtre temporal a la interfície entre el model de paret i el domini LES, el qual suprimeix els dos errors comentats prèviament amb un sol pas de baix cost computacional. Fins ara, la eliminació d’aquests dos errors es duia a terme amb tècniques separades que en alguns casos eren complexes i costoses des d’un punt de vista computacional. A més a més, es proposa una metodologia per a la determinació de la longitud de filtre temporal òptima, la qual és validada tant en condicions d’equilibri com de no-equilibri. La nova tècnica està basada en l’obtenció de l’espectre de freqüències de la velocitat, el qual revela les característiques de les escales temporals del flux en la regió propera a la paret. Segons els resultats obtinguts en els tests, es conclou que per als models Two-Layer basats en RANS, les freqüències més altes que el límit entre el rangs energy-containing i inercial, s’han de filtrar. En el capítol quatre es presenta el model matemàtic del Two-Layer model basat en les equacions URANS. A més a més, es detalla la metodologia numèrica utilitzada per a la seva resolució a través del mètode dels volums finits. Al capítol cinc es presenta la implementació del model numèric presentat al capítol quatre. El model desenvolupat en aquesta tesi és un solver de CFD complert basat en les equacions URANS. Donat que el principal objectiu del wall modeling és la reducció de costos computacionals, és necessària una implementació eficient del model. És per això que la eficiència paral·lela del codi implementat s’analitza a través d’un strong scalability test. En aquestes proves es determina el bon comportament del codi, encara que s’identifiquen punts en els que es pot optimitzar la implementació actual. Finalment, a l’últim capítol es presenten les conclusions generals del treball. A més a més, s’hi inclouen un seguit de propostes sobre futures línies de recerca dirigides aprofundir en les conclusions obtingudes durant la realització del present estudi.
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5

Krank, Benjamin [Verfasser], Wolfgang A. [Akademischer Betreuer] Wall, Wolfgang A. [Gutachter] Wall et Claus-Dieter [Gutachter] Munz. « Wall Modeling via Function Enrichment for Computational Fluid Dynamics / Benjamin Krank ; Gutachter : Wolfgang A. Wall, Claus-Dieter Munz ; Betreuer : Wolfgang A. Wall ». München : Universitätsbibliothek der TU München, 2019. http://d-nb.info/1180602099/34.

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6

Pajayakrit, Palanunt. « Turbulence modeling for curved wall jets under adverse pressure gradient ». Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ26861.pdf.

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7

Kamel, Sherif I. (Sherif Ibrahim). « Mathematical modeling of wet flashover mechanism of HVDC wall bushings ». Thesis, McGill University, 1994. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=28792.

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HVDC wall bushings constitute a basic component of converter stations and their adequate performance is vital to insure a highly reliable level of operation. Service records show that the number of flashovers in converter stations has increased substantially during recent years and that the majority of flashovers occurred on HVDC wall bushings. This work presents the first mathematical model to provide the necessary and sufficient conditions for flashover of HVDC wall bushings under nonuniform wetting. The model suggests that the onset of streamers bridging the dry zone and initiated by the nonuniform voltage distribution along the bushing triggers the process of flashover. Fast voltage collapse across the dry zone due to the energy stored in the bushing internal and external leakage and stray capacitance leads to impulsive stressing of the wet part of the bushing. The nonuniform distribution of that impulse and the process of streamer bridging, fast voltage collapse as well as subsequent recharging of the bushing capacitance may lead to consequent discharges and arc propagation along the bushing and eventually to a complete flashover.
The random processes associated with the wetting dynamics and pattern as well as the air gaps breakdowns are accounted for in a novel statistical approach to model the flashover process of the HVDC wall bushings under the proposed mechanism.
The work is supported by an experimental investigation into surface resistance and minimum flashover stress of full scale HVDC wall bushings under nonuniform rain.
The findings of the model have been satisfactorily compared with experiments and field observations and can for the first time account for the following aspects of flashover mechanism: critical dry zone length, polarity effect, specific leakage length, wet layer conductance, dry zone position as well as DC system voltage. The model was also used to assess the performance of RTV coated bushings and to compare the strength or an SF$ sb6$ bushing to that of a conventional oil-paper design under nonuniform rain.
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Pajayakrit, Palanunt Carleton University Dissertation Engineering Mechanical and Aerospace. « Turbulence modeling for curved wall jets under adverse pressure gradient ». Ottawa, 1997.

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9

Mensah-Gourmel, Johanne. « Modeling biodegradable stents and their effect on the arterial wall ». Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLX034/document.

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Les stents sont aujourd’hui le traitement le plus courant des stades avancés de l’athérosclérose. Le concept de stents bioresorbables (BRS) est basé sur l’idée qu’un stent n’est nécessaire que jusqu’à la guérison de l’artère – suite à quoi il serait préférable que le stent disparaisse, afin de retrouver un état plus physiologique. Le déploiement d’un stent altère significativement les contraintes mécaniques exercées sur la paroi artérielle, or celles-ci jouent un rôle important dans l’incidence de complications telle que la resténose et l’hyperplasie néointimale. Dans le cas d’un BRS, les contraintes mécaniques dans le stent comme dans la paroi artérielle évoluent au fur et à mesure que le stent se dégrade. De plus, la dégradation du stent par hydrolyse peut être accélérée par ces contraintes : un couplage supplémentaire qui doit être pris en compte. Nous nous intéressons à la détermination de l’évolution des contraintes dans le stent et dans l’artère pendant le déploiement puis la dégradation du stent, ainsi qu’à l’influence de ces contraintes sur la dégradation du stent et sur le remodelage de la paroi, qui est également influencé par la dénudation de l’endothélium et par l’inflammation induite par l’implantation d’un BRS. Pour atteindre ces objectifs, nous avons développé un modèle 3D par éléments finis du déploiement et de la dégradation d’un BRS en acide polylactique tenant compte du couplage entre l’artère et le stent. Il permet notamment de prédire les zones de démantèlement dustent et l’évolution de l’épaisseur de la paroi artérielle en réponse à l’implantation d’un BRS. Etant donné que le modèle repose fortement sur des paramètres qui doivent être déterminés expérimentalement, nous nous sommes intéressés au développement d’une méthode expérimentale pour suivre la dégradation d’un BRS. Nous avons utilisé la tomographie par cohérence optique (OCT) pour suivre régulièrement la dégradation de stents déployés dans des tubes et immergés dans du sérum physiologique à 37°C pendant deux ans. Nous avons ensuite développé une méthode qui détecte automatiquement les struts des stents sur les images OCT et quantifie leur intensité de niveau de gris. Les résultats suggèrent que cette méthode automatisée d’analyse d’images OCT est un outil prometteur pour évaluer quantitativement l’état de dégradation d’un BRS. Enfin, nous nous sommes intéressés à la capacité d’une artère stentée à s’adapter à une modification du cisaillement ressenti. Nous avons étudié l’évolution de la lumière artérielle de porc stentés suivis in vivo par OCT ainsi que le cisaillement associé. Alors qu’un stent métallique bloque le remodelage artériel, nous avons observé qu’un BRS – probablement grâce au démantèlement du stade final de la dégradation – libère le vaisseau et permet ainsi l’adaptation de son diamètre de manière à diminuer le cisaillement et l’inadéquation avec l’artère non stentée. L’adaptation de la lumière artérielle permise par le démantèlement du stent pourrait être prise en compte dans de futurs modèles numériques
Today, sent deployment is the most common treatment for symptomatic atherosclerosis. Bioresorbable stents (BRS) are based on the premise that a stent is needed only until arterial wound healing occurs after which it would be desirable for the stent to degrade so that the arterial wall recovers its natural compliance. Deployment of a stent profoundly alters the mechanical environment in the arterial wall, and these alterations play an important role in regulating the incidence of complications such as restenosis and neointimal hyperplasia. In the case of a BRS, the mechanical stresses in both the stent and the arterial wall evolve as the stent degrades. Furthermore, the hydrolysis-driven degradation of the stent can be accelerated by mechanical stresses in the stent, an additional coupling that needs to be taken into account. We are interested in determining the evolution of stresses in both the stent and the arterial wall during the stent deployment and degradation process and in elucidating the effect of these stresses on the stent degradation and on the remodeling process in the wall, which would also be influenced by the loss of endothelial cells and the amount of inflammation induced by the stent deployment and degradation. To this end, we have developed a 3D finite element model of the deployment and degradation of a polylactic acid (PLA) BRS that integrates the coupling between the stent and the artery.This allows one to predict the zones of dismantling of the stent and the evolution of the arterial thickness in response to a BRS stenting procedure. Since the model relies strongly on parameters that need to be determined experimentally, we became interested in developing methods to follow stent degradation. With this aim, we used optical coherence tomography (OCT) to image several BRS that were deployed into tubes and allowed to degrade in a saline solution at 37°C over a period of two years. We subsequently developed a versatile method for automatically detecting stent struts on the OCT images and quantifying the strut gray scale intensity. The results suggest that this automated method of OCT image analysis represents a promising tool to quantitatively assessing BRS degradation states. Lastly, we were interested in establishing the ability of a stented artery to adapt to a modification in its wall shear stress. Studying the in vivo evolution of the lumen of stented mini-swine arteries followed by OCT imaging allowed us to demonstrate that whereas a bare metal stent cages the artery, a BRS, presumably due to its degradation-induced dismantling, frees the vessel and enables it to adapt its lumen diameter in order to decrease its absolute level of shear stress and the compliance mismatch with the unstented portion of the artery. This lumen adaptation allowed by the stent dismantling could be taken into account in future computational models
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Sjölinder, Emil. « Spray and Wall Film Modeling with Conjugate Heat Transfer in OpenFOAM ». Thesis, Linköpings universitet, Mekanisk värmeteori och strömningslära, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-84487.

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This master thesis was provided by Scania AB. The objective of this thesis was to modify an application in the free Computational Fluid Dynamics software OpenFOAM to be able to handle spray and wall film modeling of a Urea Water Solution together with Conjugate Heat Transfer. The basic purpose is to widen the knowledge of the vaporization process of a Urea Water Solution in the exhaust gas after treatment system for a diesel engine by using OpenFOAM. First, urea has been modeled as a very viscous liquid at low temperature to mimic the solidication process of urea. Second, the development of the new application has been done. At last, test simulations of a simple test case are performed with the new application. The results are then compared with simplied hand calculations to verify a correct behavior of certain exposed source terms. The new application is working properly for the test case but to ensure the reliability, the results need to be compared with another Computational Fluid Dynamics software or more preferable, real experiments. For more advanced geometries, the continued development presented last in this thesis is highly recommended to follow.
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Thiele, Roman. « Mechanistic Modeling of Wall-Fluid Thermal Interactions for Innovative Nuclear Systems ». Doctoral thesis, KTH, Reaktorteknologi, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-177370.

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Next generation nuclear power plants (GEN-IV) will be capable of not only producing energy in a reliable, safe and sustainable way, but they will also be capable of reducing the amount of nuclear waste, which has been accumulated over the lifetime of current-generation nuclear power plants, through transmutation. Due to the use of new and different coolants, existing computational tools need to be tested, further developed and improved in order to thermal-hydraulically design these power plants.This work covers two different non-unity Prandtl number fluids which are considered as coolants in GEN-IV reactors, liquid lead/lead-bismuth-eutectic and supercritical water. The study investigates different turbulence modeling strategies, such as Large Eddy Simulation (LES) and Reynolds-Averaged Navier-Stokes (RANS) modeling, and their applicability to these proposed coolants. It is shown that RANS turbulence models are partly capable of predicting wall heat transfer in annular flow configurations. However, improvements in these prediction should be possible through the use of advanced turbulence modeling strategies, such as the use of separate thermal turbulence models. A large blind benchmark study of heat transfer in supercritical water showed that the available turbulence modeling strategies are not capable of predicting deteriorated heat transfer in a 7-rod bundle at supercritical pressures. New models which take into account the strong buoyancy forces and the rapid change of the molecular Prandtl number near the wall occurring during the transition of the fluid through the pseudocritical point need to be developed. One of these strategies to take into account near-wall buoyancy forces is the use of advanced wall functions, which cannot only help in modeling these kind of flows, but also decrease computational time by 1 to 2 orders of magnitude. Different advanced wall function models were implemented in the open-source CFD toolbox OpenFOAM and their performance for different flows in sub- and supercritical conditions were evaluated. Based on those results, the wall function model UMIST-A by Gerasimov is recommended for further investigation and specific modeling tactics are proposed.Near-wall temperature and velocity behavior is important to and influenced by the wall itself. The thermal inertia of the wall influences the temperature in the fluid. However, a more important issue is how temperature fluctuations at the wall can induce thermal fatigue. With the help of LES thermal mixing in a simplified model of a control rod guide tube was investigated, including the temperature field inside the control rod and guide tube walls. The WALE sub-grid turbulence model made it possible to perform LES computations in this complex geometry, because it automatically adapts to near-wall behavior close to the wall, without the use of ad-hoc functions. The results for critical values, such as the amplitude and frequency of the temperature fluctuations at the wall, obtained from the LES computations are in good agreement with experimental results.The knowledge gained from the aforementioned investigations is used to optimize the flow path in a small, passively liquid-metal-cooled pool-type GEN IV reactor, which was designed for training and education purposes, with the help of 3D CFD. The computations were carried out on 1/4 of the full geometry, where the small-detail regions of the heat exchangers and the core were modeled using a porous media approach. It was shown that in order to achieve optimal cooling of the core without changing the global geometry a ratio of close to unity of the pressure drop over the core and the heat exchanger needs to be achieved. This is done by designing a bottom plate which channels enough flow through the core without choking the flow in the core. Improved cooling is also achieved by reducing heat losses from the hot leg through the flow shroud to the cold leg by applying thermal barrier coating similar to methods used in gas turbine design.
Nästa generations kärnkraftverk (GEN-IV) kan inte bara producera el på ett pålitligt, säkert och hållbart sätt, utan det kan också reducera mängden kärnavfall, som har producerats under tiden som man använt nuvarande generationen kärnkraftverk, genom att transmutera avfallen. Framtidens kärnkraftverk använder andra kylmedel än nuvarande kraftverk som t.ex. flytande bly, gas eller superkritiskt vatten. Det betyder att många beräkningsverktyg måste testas, utvecklas och förbättras så att man kan genomföra termohydrauliska designberäkningar. Den här avhandlingen omfattar två olika kylmedel, flytande bly och superkritiskt vatten, som har ett Prandtl-tal som skiljer sig från 1 och kommer att användas i GEN-IV reaktorer. Studien undersöker olika strategier för att modellera turbulens som Large Eddy Simulation (LES) och Reynolds-Averaged Navier-Stokes (RANS) och hur man kan använda dessa strategierna i beräkningar av strömning och värmetransfer i den nya kylvätskan. Undersökningen visar att RANS turbulensmodeller delvis kan förutsäga värmeöverföringen vid en vägg i en ringformad strömningsgeometri. Förbättringar av förutsägelsen ska vara möjlig genom användning av avancerade strategier för turbulensmodellering, t.ex. termiska turbulensmodeller. En stor prestandajämförelse för värmeöverföring i superkritiskt vatten visade att ingen av nuvarande strategier för turbulensmodellering kan förutsäga försämrad värmeöverföring i en 7-stavknippet under superkritiskt tryck. Nya modeller, som omfattar de starka flytkrafterna och den snabba förändringen av den molekulära Prandtl-tal vid väggen som uppstår när vätskan går genom pseudokritiska punkten, måste utvecklas. Avancerade väggfunktioner är en av strategierna som kan ta hänsyn till dessa fenomen. Väggfunktioner kan inte bara hjälpa till att modellera de typer av flöden som behövs utan kan också hjälpa till att sänka beräkningstiden med en eller två tiopotenser. Olika avancerade väggfunktioner i open-source beräkningsverktyget OpenFOAM implementerades och deras prestation i sub- och superkritiska vattenflödar värderades. Baserat på detta rekommenderas Gerasimovs modell för ytterligare utredning. Dessutom läggs olika strategier fram för att utöka modellens validitet till flöde med superkritiskt vatten i sammanband med försämrad och förbättrad värmeöverföring. Kunskap om beteendet av temperatur och hastighet i väggens närhet är viktigt för väggens integritet, detta då väggen även påverkar beteendet. Väggens termiska tröghet påverkar flödets temperatur och hastighet. Dock är ett ännu viktigare problem, som kan uppträda, är att temperaturfluktuationer kan framkalla termisk utmattning i en vägg. Med användning av LES utreds termisk blandning av varmt och kallt vatten i en simplifierad modell av ett styrstavsledrör, inklusive temperaturfältet i styrstaven och ledrörsväggen. Användningen av WALE LES-turbulensmodellen gör det möjligt att utföra beräkningar i den komplexa geometrin, detta eftersom modellen anpassar sig automatiskt till fenomenen nära väggen utan användning av ad-hoc funktioner. LES resultaten för alla värden som är viktiga för att bestämma utmattningsbeteende, som amplitud och frekvens av temperaturfluktuationer i väggens närhet och i väggen själv, är i god överensstämmelse med resultaten från experiment från KTH i samma geometri.Kunskapen som vunnits genom ovannämnda utredningar användes för att optimera den termohydrauliska designen av en liten, pool-typ GEN-IV reaktor som är passivt kyld med flytande bly. Reaktorn är designad som en utbildnings- och träningsreaktor och optimeringen genomfördes med hjälp av 3D CFD. Beräkningarna genomfördes på en fjärdedel av reaktorns hela geometrin. Regioner med små detaljer, som de åtta värmeväxlarna och reaktorns kärna, modellerades genom porösa material. Det visar sig att för att ha en optimal kylning av kärnan, utan att förändra reaktorns globala geometri, måste förhållandet mellan tryckförlust i reaktorkärnan och värmeväxlarna vara nära 1. Detta uppnås genom att designa plattan vid ingången till kärnan så att tillräckligt med bly flödar genom kärnan utan att kväva flödet i denna. Ytterligare en förbättring i reaktorkylningen uppnås genom att reducera värmeförlusten genom väggen som skiljer varm och kall vätska. Detta görs med en strategi som förekommer i gasturbinteknologin, genom att man lägger till ett tunt skikt av termiskt isolerande material på väggen, som reducerar värmeöverföring med ungefär 50%.

QC 20151123


THEMFA
GENIUS
THINS
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Rausch, Sophie [Verfasser], Wolfgang A. [Akademischer Betreuer] Wall et Markus [Akademischer Betreuer] Böl. « Computational and Experimental Modeling of Lung Parenchyma / Sophie Rausch. Gutachter : Wolfgang A. Wall ; Markus Böl. Betreuer : Wolfgang A. Wall ». München : Universitätsbibliothek der TU München, 2012. http://d-nb.info/1025150422/34.

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Pfaller, Martin [Verfasser], Wolfgang A. [Akademischer Betreuer] Wall, Wolfgang A. [Gutachter] Wall et Dominique [Gutachter] Chapelle. « Predictive Computational Modeling of Patient-Specific Cardiac Mechanics / Martin Pfaller ; Gutachter : Wolfgang A. Wall, Dominique Chapelle ; Betreuer : Wolfgang A. Wall ». München : Universitätsbibliothek der TU München, 2019. http://d-nb.info/1190818744/34.

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Ismail, Mahmoud [Verfasser], Wolfgang A. [Akademischer Betreuer] Wall et Perumal [Akademischer Betreuer] Nithiarasu. « Reduced Dimensional Modeling of the Entire Human Lung / Mahmoud Ismail. Gutachter : Wolfgang A. Wall ; Perumal Nithiarasu. Betreuer : Wolfgang A. Wall ». München : Universitätsbibliothek der TU München, 2014. http://d-nb.info/1068315776/34.

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Li, Jinxia. « Lubricating grease Experiments and modeling of wall-bounded- and free-surface flows ». Doctoral thesis, Luleå tekniska universitet, Maskinelement, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-26489.

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Lubricating grease is commonly applied to lubricate e.g. rolling bearings, sealsand gears. Grease has some clear advantages over lubricating oil: it is a semisolidmaterial, which prevents it from flowing/ leaking out from the bearingsystem and gives it sealing properties, and it also protects the system fromcontaminants and corrosion. Due to its consistency, lubricating grease has manyadditional advantages over lubricating oil: it does not require pumps, filters andsumps. However, the rheology of grease makes it more difficult to measure andstudy its flow dynamics. This study focuses on the influence of rheology ongrease flow in different geometries involving a straight channel with restrictions,concentric cylinder geometry, and free-surface flow on a rotating disc.To better understand grease flow in bearings and seals, two types of flowrestrictions were applied into the straight channel in order to simulate the flowof grease near a seal pocket. In the case of a single restriction, the horizontaldistance required for the velocity profile to fully develop is approximately thesame as the height of the channel. In the corner before and after the restriction,the velocities are very low and part of the grease is stationary. For the channelwith two flow restrictions, this effect is even more pronounced in the narrowspace between the restrictions. Clearly, a large part of the grease is not moving.This condition particularly applies in the case of a low-pressure gradient andwhere high-consistency grease is used. In practice this means that grease may belocally trapped and consequently old/contaminated grease will remain in theseal pockets.A configuration comprising a rotating shaft and two narrow gap sealing-likerestrictions (also called Double Restriction Seal, DRS) was designed to simulatea sealing contact. Two different gap heights in the DRS have been used tocompare the grease flow. It is shown that partially yielded grease flow isdetected in the large gap geometry and fully yielded grease flow in the small gapgeometry. For the small gap geometry, it is shown that three distinct grease flowregions are present: a slip layer close to the stationary wall, a bulk flow layer,and a slip layer near the rotating shaft. The shear thinning behaviour of thegrease and its wall slip effects have been determined and discussed.Free-surface flow of grease occurs in a variety of situations such as during relubrication and inside a rolling element bearing which is filled to about 30%with grease in order to prevent heavy churning. Here the reflow of lubricant tothe bearing races is a key point in the lubricant film build-up, and centrifugalforces have a direct impact on the amount of available grease. Understanding ofthe free-surface flow behaviour of grease is hence important for theunderstanding of the lubrication mechanism. Adhesion and mass loss aremeasured for greases with different rheology on different surfaces andtemperatures. It is shown that the critical speed at which the grease starts tomove is mostly determined by grease type, yield stress and temperature ratherthan surface material. A developed analytical model covers a stationary analysisof the flow resulting in solutions for the velocity profile of the grease as well as asolution for the thickness of the viscous layer remaining on the disc.
Godkänd; 2014; 20141017 (jinlit); Nedanstående person kommer att disputera för avläggande av teknologie doktorsexamen. Namn: Jinxia Li Ämne: Maskinelement/Machine Elements Avhandling: Lubricating Grease Experiments and Modellingo f Wall-Bounded and Free-Surface Flours Opponent: Professor Arto Lehtovaara, University of Technology, Tampere, Finland Ordförande: Professor Erik Höglund, Institutionen för teknikvetenskap och matematik, Luleå tekniska universitet Tid: Fredag den 19 december 2014, kl 09.00 Plats: E632, Luleå tekniska universitet
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Gil, Edward Matthew. « Computational Modeling of Glass Curtain Wall Systems to Support Fragility Curve Development ». Thesis, Virginia Tech, 2019. http://hdl.handle.net/10919/94051.

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With the increased push towards performance-based engineering (PBE) design, there is a need to understand and design more resilient building envelopes when subjected to natural hazards. Since architectural glass curtain walls (CW) have become a popular façade type, it is important to understand how these CW systems behave under extreme loading, including the relationship between damage states and loading conditions. This study subjects 3D computational models of glass CW systems to in- and out-of-plane loading simulations, which can represent the effects of earthquake or hurricane events. The analytical results obtained were used to support fragility curve development which could aid in multi-hazard PBE design of CWs. A 3D finite element (FE) model of a single panel CW unit was generated including explicit modeling of the CW components and component interactions such as aluminum-to-rubber constraints, rubber-to-glass and glass-to-frame contact interactions, and semi-rigid transom-mullion connections. In lieu of modeling the screws, an equivalent clamping load was applied with magnitude based on small-scale experimental test results corresponding to the required screw torque. This FE modeling approach was validated against both an in-plane racking displacement test and out-of-plane wind pressure test from the literature to show the model could capture in-plane and out-of-plane behavior effectively. Different configurations of a one story, multi-panel CW model were generated and subjected to in- and out-of-plane simulations to understand CW behavior at a scale that is hard to test experimentally. The structural damage states the FE model could analyze included: 1) initial glass-to-frame contact; 2) glass/frame breach; 3) initial glass cracking; 4) steel anchor yielding; and 5) aluminum mullion yielding. These were linked to other non-structural damage states related to the CW's moisture, air, and thermal performance. Analytical results were converted into demand parameters corresponding to damage states using an established derivation method within the FEMA P-58 seismic fragility guidelines. Fragility curves were then generated and compared to the single panel fragility curves derived experimentally within the FEMA P-58 study. The fragility curves within the seismic guidelines were determined to be more conservative since they are based on single panel CWs. These fragility curves do not consider: the effects of multiple glass panels with varying aspect ratios; the possible component interactions/responses that may affect the extent of damages; and the continuity of the CW framing members across multiple panels. Finally, a fragility dispersion study was completed to observe the effects of implementing the Derivation method or the Actual Demand Data method prescribed by FEMA P-58, which differ on how they account for different levels of uncertainty and dispersion in the fragility curves based on analytical results. It was concluded that an alternative fragility parameter derivation method should be implemented for fragility curves based on analytical models, since this may affect how conservative the analytically based fragility curves become at a certain probability of failure level.
Master of Science
Performance-based engineering (PBE) can allow engineers and building owners to design a building envelope for specific performance objectives and strength/serviceability levels, in addition to the minimum design loads expected. These envelope systems benefit from PBE as it improves their resiliency and performance during natural multi-hazard events (i.e. earthquakes and hurricanes). A useful PBE tool engineers may utilize to estimate the damages an envelope system may sustain during an event is the fragility curve. Fragility curves allow engineers to estimate the probability of reaching a damage state (i.e. glass cracking, or glass fallout) given a specified magnitude of an engineering demand parameter (i.e. an interstory drift ratio during an earthquake). These fragility curves are typically derived from the results of extensive experimental testing of the envelope system. However, computational simulations can also be utilized as they are a viable option in current fragility curve development frameworks. As it’s popularity amongst owners and architects was evident, the architectural glass curtain wall (CW) was the specific building envelope system studied herein. Glass CWs would benefit from implementing PBE as they are very susceptible to damages during earthquakes and hurricanes. Therefore, the goal of this computational research study was to develop fragility curves based on the analytical results obtained from the computational simulation of glass CW systems, which could aid in multi-hazard PBE design of CWs. As v opposed to utilizing limited, small experimental data sets, these simulations can help to improve the accuracy and decrease the uncertainties in the data required for fragility curve development. To complete the numerical simulations, 3D finite element (FE) models of a glass CW system were generated and validated against experimental tests. 11 multi-panel CW system configurations were then modeled to analyze their effect on the glass CW’s performance during in-plane and out-of-plane loading simulations. These parametric configurations included changes to the: equivalent clamping load, glass thickness, and glass-to-frame clearance. Fragility curves were then generated and compared to the single panel CW fragility curves derived experimentally within the FEMA P-58 Seismic Fragility Curve Development study. The fragility curves within FEMA P-58 were determined to be more conservative since they are based on single panel CWs. These fragility curves do not consider: the effects of multiple glass panels with varying aspect ratios; the possible component interactions/responses that may affect the extent of damages; and the continuity of the CW framing members across multiple panels. Finally, a fragility dispersion study was completed to observe the effects of implementing different levels of uncertainty and dispersion in the fragility curves based on analytical results.
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Bair, Shawn D. « Computational Modeling of the Electrical Sensing Properties of Single Wall Carbon Nanotubes ». Youngstown State University / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ysu1441813278.

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Habteyes, Firdaweke. « Modeling Acute Changes in Bladder Wall Tension, Shape and Compliance During Filling ». VCU Scholars Compass, 2014. http://scholarscompass.vcu.edu/etd/3537.

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The bladder wall consists primarily of detrusor smooth muscle. Tension-sensitive nerves in the bladder wall are responsible for providing bladder fullness information that is interpreted as urgency. Bladder wall tension, and therefore nerve output, is a function of bladder volume, shape and material properties. Studies have shown that the bladder wall exhibits acutely regulated detrusor compliance. In addition, bladder shape throughout filling depends on intra-abdominal forces and material properties of the bladder wall, such as regulated detrusor compliance. This thesis focused on modeling the potential influence of acute changes in bladder compliance, shape and bladder wall tension during filling. Laplace’s Law was used to demonstrate how wall tension can vary significantly with geometry in a vessel with uniform internal pressure and constant volume. A finite deformation model of the bladder was previously used to show that wall tension can increase significantly during filling with relatively little pressure change. In this thesis, published experimental data were used to determine ranges for regulated detrusor compliance, and the finite deformation model was expanded to illustrate the potential effects of regulated ix detrusor compliance on filling pressure and wall tension. Also, a geometric model was used to demonstrate that constraining a perfectly spherical bladder to fill as an oblate sphere increases wall tension, and therefore should increase nerve output, for a given volume. In addition, a spheroidal model consisting of three orthogonal circular rings was developed to predict the increase in pressure and wall tension associated with deforming a spherical bladder into an oblate spheroid. Together, these models demonstrate that defects in regulated detrusor compliance and/or acute or chronic changes in bladder shape due to changes in compliance or intra-abdominal forces could contribute to changes in wall tension for a given volume that could lead to urgency.
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Hörmann, Julia Maria [Verfasser], Wolfgang A. [Akademischer Betreuer] Wall, Wolfgang A. [Gutachter] Wall et Björn H. [Gutachter] Menze. « Multiphysics Coupled Computational Modeling in Cardiac Electromechanics / Julia Maria Hörmann ; Gutachter : Wolfgang A. Wall, Björn H. Menze ; Betreuer : Wolfgang A. Wall ». München : Universitätsbibliothek der TU München, 2019. http://d-nb.info/1186889403/34.

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Roth, Christian J. [Verfasser], Wolfgang A. [Akademischer Betreuer] [Gutachter] Wall et Marcel [Gutachter] Filoche. « Multi-dimensional Coupled Computational Modeling in Respiratory Biomechanics / Christian J. Roth ; Gutachter : Wolfgang A. Wall, Marcel Filoche ; Betreuer : Wolfgang A. Wall ». München : Universitätsbibliothek der TU München, 2017. http://d-nb.info/1140165925/34.

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LEE, KWANGDEOK. « QUANTIFYING BARRIERS TO MACROMOLECULAR TRANSPORT IN THE ARTERIAL WALL ». Case Western Reserve University School of Graduate Studies / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=case1152557910.

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Valsecchi, Pietro. « Temporal Numerical Simulations of Turbulent Coanda Wall Jets ». Diss., The University of Arizona, 2006. http://hdl.handle.net/10150/195025.

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In a novel application of the temporal numerical simulation, an investigation ofturbulence modeling techniques is carried for the turbulent wall jet over aconvex surface (Coanda wall jet.) The simultaneous presence of multipleinstability mechanisms and the interaction with the turbulence dynamics at thesolid boundary produces a unique combination of different large turbulentcoherent structures that constitutes both a consistent challenge for numericalsimulations and an ideal test bed for turbulence models.The Temporal Direct Numerical Simulation (TDNS) of the Coanda wall jetrestricts the focus from the global turbulent Coanda wall jet to a smaller, localportion of the flow and offers a wide array of advantages to the present work. Inparticular, the size of the computational domain can be arbitrarily chosen inboth the spanwise and the streamwise directions. This allows to either suppressor enhance individual physical mechanisms and, consequently, to selectivelyreproduce different large coherent structures within the local flow. In the firstpart, temporal numerical simulations are employed to reproduce four differentflow scenarios of the local Coanda wall jet with a level of numerical resolutionthat, because of the reduced size of the computational domain, cannot be matchedby standard DNS of the entire physical flow (spatial DNS, or SDNS.)The TDNS of these four flow scenarios are then used in the second part for ana--posteriori analysis of different turbulence models in order to addresscommon shortcomings shown by Hybrid Turbulence Models (HTM). For each flowscenario, the turbulent flow field is deliberately decomposed in resolved andunresolved flows by the application of different filters in space correspondingto different grid resolution. The behavior of turbulence models can be reproducedfrom the resolved flow and compared to the turbulent stress tensor directlycalculated from the unresolved part of the flow field. Starting from the RANSlimit, turbulence models with different levels of complexity are studied.Successively, the performance of these models is analyzed at intermediatenumerical resolutions between RANS, LES, and DNS. Finally, an improvedformulation of the Flow Simulation Methodology (FSM) is proposed.
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Chung, Daniel Pullin Dale Ian Pullin Dale Ian. « Numerical simulation and subgrid-scale modeling of mixing and wall-bounded turbulent flows ». Diss., Pasadena, Calif. : California Institute of Technology, 2009. http://resolver.caltech.edu/CaltechETD:etd-05292009-123828.

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Thesis (Ph.D.) -- California Institute of Technology,2009.
Advisor name found in the Acknowledgments pages of the thesis. Title from home page (viewed 05/04/2010). Includes bibliographical references.
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Barp, Stefan. « Numerical prediction of horizontal, thermally unstably stratified, turbulent wall flows by RANS modeling / ». Zürich, 2005. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=16016.

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Papadimitriou, Andreas. « Modeling, Identification and Control of a Wall Climbing Robot Based on Vortex Actuation ». Thesis, Luleå tekniska universitet, Drift, underhåll och akustik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-70626.

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Gupta, Ankit. « Multi-Scale Modeling of Mechanical Properties of Single Wall Carbon Nanotube (SWCNT) Networks ». Research Showcase @ CMU, 2017. http://repository.cmu.edu/dissertations/1022.

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Single wall carbon nanotubes (SWCNTs) show a variety of unparalleled properties such as high electrical and thermal conductivity, high specific surface area (SSA) and a large stiffness under axial loads. One of the major challenges in tapping the vast potential of SWCNTs is to fabricate nanotube based macrostructures that retain the unique properties of nanotubes. Pristine SWCNT aerogels are highly porous, isotropic structures of nanotubes mediated via van der Waals (VDW) interactions at junctions. The mechanical behavior of such aerogels is examined in several experimental studies. However, it is necessary to supplement these studies with insights from simulations in order to develop a fundamental understanding of deformation behavior of SWCNT aerogels. In this study, the mechanical behavior of SWCNT networks is studied using a multi-scale modeling approach. The mechanics of an individual nanotube and interactions between few nanotubes are modeled using molecular dynamics (MD) simulations. The results from atomistic simulations are used to inform meso-scale and continuum scale finite element (FE) models. The deformation mechanism of pristine SWCNT networks under large compressive strain is deduced from insights offered by meso-scale simulations. It is found that the elasticity of such networks is governed by the bending deformation of nanotubes while the plastic deformation is governed by the VDW interactions between nanotubes. The stress response of the material in the elastic regime is dictated by the VDW stresses on nanotubes while in the plastic regime, both the VDW and axial deformation stresses on nanotubes drive the overall stress response. In this study, the elastic behavior of a random SWCNT network with any set of junction stiffness and network density is also investigated using FE simulations. It is found that the elastic deformation of such networks can be governed either by the deformation of the nanotubes (bending, axial compression) or deformation of the junctions. The junction stiffness and the network density determine the network deformation mode. The results of the FE study are also applicable to any stiff fiber network.
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Barrows, Richard James. « Two Dimensional Finite Element Modeling of Swift Delta Soil Nail Wall by "ABAQUS" ». PDXScholar, 1994. https://pdxscholar.library.pdx.edu/open_access_etds/4741.

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Soil nail walls are a form of mechanical earth stabilization for cut situations. They consist of the introduction of passive inclusions (nails) into soil cut lifts. These nailed lifts are then tied together with a structural facing (usually shotcrete) . The wall lifts are constructed incrementally from the top of cut down. Soil nail walls are being recognized as having potential for large cost savings over other alternatives. The increasing need to provide high capacity roadways in restricted rights of way under structures such as bridges will require increasing use of techniques such as combined soil nail and piling walls. The Swift Delta Soil Nail wall required installing nails between some of the existing pipe piling on the Oregon Slough Bridge. This raised questions of whether the piling would undergo internal stress changes due to the nail wall construction. Thus, it was considered necessary to understand the soil nail wall structure interaction in relation to the existing pile supported abutment. The purpose of this study was to investigate the Swift Delta Wall using finite element (FE) modeling techniques. Valuable data were available from the instrumentation of the swift Delta Wall. These data were compared with the results of the FE modeling. This study attempts to answer the following two questions: 1. Is there potential for the introduction of new bending stresses to the existing piling? 2. Is the soil nail wall system influenced by the presence of the piling? A general purpose FE code called ABAQUS was used to perform both linear and non-linear analyses. The analyses showed that the piling definitely underwent some stress changes. In addition they also indicated that piling influence resulted in lower nail stresses. Comparison of measured data to predicted behavior showed good agreement in wall face deflection but inconsistent agreement in nail stresses. This demonstrated the difficulty of modeling a soil nail due to the many variables resulting from nail installation.
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Kormendy, Imre, et Mustafa Muwaili. « Timber Shear Wall Analysis : Parameterized Finite Element Modelling ». Thesis, Linnéuniversitetet, Institutionen för byggteknik (BY), 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-77199.

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This paper investigates the linear elastic behavior of timber shear walls under monotonic prescribed displacement. ABAQUS© 16.4-5, is a numerical finite element software used as the primary analysis methodology.  Parameterized models are created for two shear wall specimens of different geometry concerning door and window configurations. The shear walls are simulated as solid timber framing which is mechanically connected to gypsum sheathing board through fasteners. The primary findings are the linear elastic shear force distribution of the mechanical joints. Additionally, deformations and reaction forces of the shear walls are determined. The overall horizontal shear wall behavior of each specific wall was also studied in the presence of door and window openings. The simulations indicate there is a clear deformation difference in the behaviors of the two shear walls. Furthermore, the highest shear force values of the fasteners are located around the corners of the openings. The findings are supported by other researcher’s experiments and analytical tests, timber shear wall theory and Eurocode design requirements.
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Mahmud, Khan Raqib. « Sensitivity Analysis of Near-Wall Turbulence Modeling for Large Eddy Simulation of Incompressible Flows ». Thesis, KTH, Numerisk analys, NA, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-146098.

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Wall layer models are very important for the simulation of turbulent flows in complex geometries to characterize the significant flow features. For the simulation of turbulent flows, the performance of Large Eddy Simulation techniques with different wall layer models which we refer to as near-wall turbulence modeling for turbulent flows are analyzed. The wall shear stress model and Delayed Detached Eddy Simulation wall model are two options, that can be used to model the turbulent boundary layer. In this project, a wall shear stress model is used as a near-wall turbulence model in the G2 simulation technique. A sensitivity analysis of this near-wall turbulence modeling with respect to model parameters in the simulation techniques of incompressible turbulent flows is presented.
Väggmodellering är viktigt i simuleringar av turbulenta flöden ikomplexa geometrier då de mest inverkande flödesegenskaperna skakarakteriseras. Prestandan hos Large Eddy Simulation-tekniker med olikaväggmodeller analyseras för simuleringar av turbulenta flöden med höga Reynoldstal.Två alternativ som kan användas för turbulenta gränsskikt är “Wall Shear StressModel” och “Delayed Detached Eddy Simulation Wall Model”. I detta projektanvänds en wall shear stress modell för det turbulenta flödet vid väggentillsammans med G2 simuleringsmetodiken. En känslighetsanalys av denna modellmed hänsyn till modellparameterar presenteras för simuleringar avinkompressibla turbulenta flöden
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Luo, Haoxiang. « The interaction of near-wall turbulence with compliant tensegrity fabrics : modeling, simulation, and optimization / ». Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2004. http://wwwlib.umi.com/cr/ucsd/fullcit?p3144307.

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31

Jayamon, Jeena Rachel. « Seismic Performance Assessment of Wood-Frame Shear Wall Structures ». Diss., Virginia Tech, 2017. http://hdl.handle.net/10919/84902.

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Wood-frame shear wall structures are widely used for residential and commercial buildings. These buildings are lightweight, have very ductile connections and includes multiple load paths. The main objective of this dissertation is to evaluate the seismic performance of a wide range of wood-frame shear wall building designs under the influence of modeling and analysis parameter variations. The first step towards the broad objective of seismic performance evaluation is to identify the different modeling and analysis parameters that can have a potential influence in the seismic response variations. The major variations considered in this study include level of critical damping, analytical modeling of damping, hysteresis model shape variations, ground motion characteristics, level of gravity loads, and floor acceleration variations. A subset of building model designs that were originally designed for the development of FEMA P-695 methodology is adapted for the numerical evaluations and a baseline for the variations is established. To study the sensitivity of inherent damping in wood-frame shear wall structures, an extensive literature survey is completed to find the experimentally observed damping levels in these buildings. Later, nonlinear dynamic analysis is performed for the range of damping levels using different Rayleigh damping models. Ground motion scaling methods, source-to-site distance, and peak intensity levels are the selected variations in ground characteristic group. To assist with the ground motion scaling procedures, a computational toolkit is created to produce amplitude and spectrum matched ground motions for response history analysis. The particular hysteresis model CASHEW that is used for the wood-frame shear wall system has a specific load-displacement shape which is a function of the shear wall design. Three key parameters of this model are varied in a range of values that were observed during experimental tests and seismic performance responses are computed for this variations. From the performance evaluations it is observed that the seismic response is quite sensitive to several of the modeling parameter variations and analysis variations mentioned above and has a unique response based on the design of the building. The range of performance variations for the different models are outlined in the chapters included in this dissertation.
Ph. D.
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32

Alaoui, Miloud. « Coherent structures and wall-pressure fluctuations modeling in turbulent boundary layers subjected to pressure gradients ». Thesis, Paris, ENSAM, 2016. http://www.theses.fr/2016ENAM0077/document.

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L'écoulement autour des véhicules produit une couche limite turbulente très proche de la paroi. Le caractère turbulent induit des fluctuations de pression pariétale qui font vibrer les panneaux du véhicule. Ces vibrations sont alors transmises à travers la structure et rayonnent du bruit dans l’habitacle. Les niveaux sonores dus à l'écoulement augmentent avec la vitesse du véhicule. Pour cette raison, cette problématique connaît un intérêt croissant dans le secteur aéronautique.Le but de cette thèse est double : comprendre les mécanismes à l’origine de ces fluctuations de pression à la paroi et prédire l’excitation de la structure avion due à l’écoulement turbulent.Pour ce faire, des calculs Large Eddy Simulation (LES) sont disponibles. Il s’agit de bases de données numériques d’écoulements de couches limites turbulentes en présence de gradients de pression favorable, adverse et nul. Ceci permet de caractériser l’écoulement sur des géométries courbes telles que la pointe avant d’un avion. L’effet du gradient de pression sur des structures cohérentes de type « hairpins » et paquets de « hairpins » a pu être identifié et quantifié à travers des méthodes de visualisation et d’analyse statistique. Une méthode d’estimation stochastique du champ de vitesse a révélé la présence de tourbillons contra-rotatifs au-dessus des paquets de hairpins. Ces tourbillons ont une vorticité opposée à celle des hairpins et un modèle de « hairpins inversé » a été proposé.En s’inspirant du travail de Ahn et al. (2010), un modèle stochastique de spectre de la pression pariétale a été développé. Il s’agit de reconstruire un champ stochastique de vitesse instantanée et d’en déduire le champ de pression à la paroi en résolvant une équation de Poisson sur la pression. Le champ de vitesse est obtenu en soumettant des structures de type paquets de hairpins à un écoulement moyen. Les caractéristiques des paquets de hairpins en fonction du gradient de pression sont basées sur l’analyse des bases LES. Les résultats de ce modèle sont comparés à ceux issues de bases de données numériques et expérimentales. Enfin, ce modèle est utilisé pour caractériser l’écoulement de couche limite turbulente dans une simulation de Statistical Energy Analysis (SEA) afin de prédire les niveaux de vibration des panneaux d’une portion de fuselage d’avion
The flow around vehicles creates a turbulent boundary layer in the vicinity of the wall. The turbulent behavior induces pressure fluctuations that make the panels vibrate. These vibrations are then transmitted though the structure of the vehicle and radiate noise inside the cabin. The flow-induced noise levels increase with the speed of the vehicle. For this reason, aircraft manufacturers show a great interest in this topic.There are two objectives for this thesis: understand the mechanisms responsible for the wall-pressure fluctuations and predict this source of aircraft panel excitation.A study of available Large Eddy Simulation (LES) computations was performed. The database consists in simulations of turbulent boundary layer flows submitted to favorable, adverse and zero pressure gradients. This is necessary to understand the nature of the flow over curved geometries such as the aircraft flight deck. The effect of pressure gradients on coherent hairpin structures and hairpin packets could be identified and quantified based on visualization and statistical analysis methods. Linear stochastic estimation of the velocity fields revealed a pair of counter-rotating streamwise vortices above hairpin packets. These vortices have a vorticity opposite to that of the hairpins and an “inverse hairpin” model was proposed.Following the work of Ahn et al. (2010), a stochastic model for wall-pressure spectrum was developed. The idea is to build a stochastic turbulent velocity field using hairpin packets which are subjected to a mean flow. The characteristics of the packets depending on the pressure gradient are based on the analyses of the LES database. The pressure field at the wall is obtained by solving a Poisson equation. The results of the hairpin packet model are compared to numerical and experimental data. Finally, the model is used as input for a Statistical Energy Analysis (SEA) simulation in order to predict the levels of vibrations of panels submitted to a turbulent boundary layer flow over a portion of an aircraft cabin
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Golshan, Roozbeh. « Residual-based Variational Multiscale LES with Wall-modeling for Oceanic Boundary Layers in Shallow Water ». Scholar Commons, 2014. https://scholarcommons.usf.edu/etd/5489.

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Large-eddy simulation (LES) of wind and wave forced oceanic turbulent boundary layers is performed using the residual-based variational multiscale method (RBVMS) and near-wall modeling. Wind and surface gravity wave forcing generates Langmuir turbulence characterized by Langmuir circulation (LC) with largest scales consisting of streamwise vortices aligned in the direction of the wind, acting as a secondary flow structure to the primary wind-driven component of the flow. The LES here is representative of a shallow water continental shelf flow (10 to 30 meters in depth) far from lateral boundaries in which LC engulfs the full depth of the water column and disrupts the bottom log layer. Field measurements indicate that occurrence of full-depth LC is typical during the passage of storms. The RBVMS method with quadratic NURBS (Non-Uniform Rational B-splines) with near-wall resolution is shown to possess good convergence characteristics for this flow. The use of near-wall modeling facilitates simulations with expanded domains over horizontal directions. Thus, these simulations are able to resolve multiple Langmuir cells permitting analysis of the interaction between the cells. Results in terms of velocity statistics are presented from simulations performed with various domain sizes and distinct near-wall treatments: (1) the classical treatment based on prescription of the wall shear stress assuming a law of the wall and (2) a recent treatment based on weak imposition of the no-slip bottom boundary condition.
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Wiechert, Lena [Verfasser], Gerhard A. [Akademischer Betreuer] Holzapfel et Wolfgang A. [Akademischer Betreuer] Wall. « Computational Modeling of Multi-Field and Multi-Scale Phenomena in Respiratory Mechanics / Lena Wiechert. Gutachter : Gerhard A. Holzapfel ; Wolfgang A. Wall. Betreuer : Wolfgang A. Wall ». München : Universitätsbibliothek der TU München, 2011. http://d-nb.info/1013436458/34.

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35

Metzke, Robert [Verfasser], Wolfgang A. [Akademischer Betreuer] Wall et Mohammad R. K. [Akademischer Betreuer] Mofrad. « Modeling and experimental investigation of the mechanobiological environment associated with alveolar pneumocytes / Robert Metzke. Gutachter : Wolfgang A. Wall ; Mohammad R. K. Mofrad. Betreuer : Wolfgang A. Wall ». München : Universitätsbibliothek der TU München, 2014. http://d-nb.info/1064695000/34.

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36

Laing, Jeffrey M. « Finite Element Modeling and Validation of a Novel Process for Extruding Thin Wall Hollow Copper Profiles ». Ohio University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1327333357.

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Hazer, Dilana [Verfasser]. « Automated Patient-Specific Modeling of Blood Flow and Vessel Wall Mechanics in Aortic Pathology / Dilana Hazer ». München : Verlag Dr. Hut, 2010. http://d-nb.info/100948530X/34.

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Wu, Ai. « Etudes comparatives des architectures des reseaux locaux et implementation du protocole x. 25 sur ibm pc ». Paris, ENST, 1987. http://www.theses.fr/1987ENST0017.

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Ce travail est compose de deux parties: 1) etude comparative des architectures des reseaux locaux. Les problemes lies a la modelisation de protocoles et a l'evaluation de performances d'un systeme de communication sont analyses. 2) l'implementation du protocole x. 25 sur ibm-pc a pour objectif de connecter cette importante famille des ordinateurs personnels sur les reseaux x. 25. La conception du systeme et la realisation du logiciel sont presentees. Une serie de mesures de performance a ete realisee en utilisant une application de transfert de fichier. Les resultats sont analyses
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Vaal, Michael Hamman de [Verfasser], Wolfgang A. [Akademischer Betreuer] Wall, Ulrich A. [Akademischer Betreuer] Stock et Michael W. [Akademischer Betreuer] Gee. « Computational modeling, clinical comprehension and improvement of aortic manipulation / Michael Hamman de Vaal. Betreuer : Wolfgang A. Wall. Gutachter : Wolfgang A. Wall ; Ulrich A. Stock ; Michael W. Gee ». München : Universitätsbibliothek der TU München, 2015. http://d-nb.info/1079323937/34.

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Maier, Andreas [Verfasser], Wolfgang A. [Akademischer Betreuer] Wall, C. Alberto [Akademischer Betreuer] Figueroa et Hans-Henning Georg Ulrich [Akademischer Betreuer] Eckstein. « Computational Modeling of Rupture Risk in Abdominal Aortic Aneurysms / Andreas Maier. Gutachter : C. Alberto Figueroa ; Wolfgang A. Wall ; Hans-Henning Georg Ulrich Eckstein. Betreuer : Wolfgang A. Wall ». München : Universitätsbibliothek der TU München, 2012. http://d-nb.info/103626243X/34.

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41

Andrae, Johan. « Wall Related Lean Premixed Combustion Modeled with Complex Chemistry ». Doctoral thesis, KTH, Kemiteknik, 2002. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3455.

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Increased knowledge into the physics and chemistrycontrolling emissions from flame-surface interactions shouldhelp in the design of combustion engines featuring improvedfuel economy and reduced emissions. The overall aim of this work has been to obtain afundamental understanding of wall-related, premixed combustionusing numerical modeling with detailed chemical kinetics. Thiswork has utilized CHEMKIN®, one of the leading softwarepackages for modeling combustion kinetics. The simple fuels hydrogen and methane as well as the morecomplex fuels propane and gasified biomass have been used inthe model. The main emphasis has been on lean combustion, andthe principal flow field studied is a laminar boundary layerflow in two-dimensional channels. The assumption has been madethat the wall effects may at least in principle be the same forlaminar and turbulent flames. Different flame geometries have been investigated, includingfor example autoignition flames (Papers I and II) and premixedflame fronts propagating toward a wall (Papers III and IV).Analysis of the results has shown that the wall effects arisingdue to the surface chemistry are strongly affected by changesin flame geometry. When a wall material promoting catalyticcombustion (Pt) is used, the homogeneous reactions in theboundary layer are inhibited (Papers I, II and IV). This isexplained by a process whereby water produced by catalyticcombustion increases the rate of the third-body recombinationreaction: H+O2+M ⇔ HO2+M. In addition, the water produced at higherpressures increases the rate of the 2CH3(+M) ⇔ C2H6(+M) reaction, giving rise to increased unburnedhydrocarbon emissions (Paper IV). The thermal coupling between the flame and the wall (theheat transfer and development of the boundary layers) issignificant in lean combustion. This leads to a sloweroxidation rate of the fuel than of the intermediatehydrocarbons (Paper III). Finally in Paper V, a well-known problem in the combustionof gasified biomass has been addressed, being the formation offuel-NOx due to the presence of NH3 in the biogas. A hybridcatalytic gas-turbine combustor has been designed, which cansignificantly reduce fuel-NOx formation. Keywords:wall effects, premixed flames, flamequenching, numerical modeling, CHEMKIN, boundarylayerapproximation, gasified biomass, fuel-NOx, hybrid catalytic combustor.
QC 20100504
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42

Wang, Jin. « Modeling of concrete dehydration and multhiphase transfer in nuclear containment concrete wall during loss of cooling accident ». Thesis, Toulouse 3, 2016. http://www.theses.fr/2016TOU30098/document.

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Les centrales nucléaires jouent un rôle important au niveau mondial dans la production d'électricité aujourd'hui. Dans l'histoire humaine, deux accidents tragiques ont déjà eu lieu, à Tchernobyl et Fukushima, provoquant des fuites des matières radioactives. Pour éviter ce genre d'accident dans la future, la construction en béton prend un rôle important en tant que matériau de construction de confinement qui est la dernière barrière pour isoler la matière radioactive de l'environnement. La compréhension des transferts dans le béton dans des circonstances graves, en particulier à étudier le comportement du béton sous haute température jusqu'à 200°C. Dans la première partie, un modèle de déshydratation a été appliqué dans le modèle thermo-hygro. Le modèle thermo-hygro a ensuite été mis en oeuvre pour simuler une maquette dont les résultats expérimentaux sont disponibles dans la littérature, sans tenir compte des comportements mécaniques. Enfin, des études paramétrique ont été réalisées pour étudier l'influence de certains paramètres. Le modèle à ensuite été appliqué à des structures sous vitesse de chauffage différente, et le modèle à ensuite été appliqué à des structure sous rythme de chauffage différents et celles avec des épaisseurs différentes pour comparer les profiles de température et de pression de gaz à travers de la mur
Nuclear power plant now takes an important part in the world's electricity generation. In human history, there have already been two tragic accidents in Chernobyl and Fukushima causing severe radioactive matter leakage. To pre- vent this kind of accident from happening again, concrete structure plays an important role as material of containment building, which is the last barrier to isolate the radioactive matter from the environment. Hence, the transfer properties of concrete under severe circumstances, especially high tempera- ture, are important for this usage. This PhD thesis aims to investigate the behavior of the concrete under high temperature up to 200°C. In the first part, a dehydration model was proposed. The model consists of different dehydration sub-models for main hydrates in the cement paste. In the second part, the dehydration model was implemented in a thermo-hygral model. The thermo- hygral model was then used to simulate a mock-up for which experimental results are available in the literature, without considering the mechanical behaviors. At last, parametric studies were performed to investigate the influ- ence of some parameters, and the model was then applied to structures under different heating rates, and structures with different thicknesses to compare the temperature and gas pressure profiles across a wall
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Wells, Jesse Buchanan. « Effects of Turbulence Modeling on RANS Simulations of Tip Vortices ». Thesis, Virginia Tech, 2009. http://hdl.handle.net/10919/34343.

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The primary purpose of this thesis is to quantify the effects of RANS turbulence modeling on the resolution of free shear vortical flows. The simulation of aerodynamic wing-tip vortices is used as a test bed. The primary configuration is flow over an isolated finite wing with aspect ratio, , and Reynolds number, . Tip-vortex velocity profiles, vortex core and wake turbulence levels, and Reynolds stresses are compared with wind tunnel measurements. Three turbulence models for RANS closure are tested: the Lumley, Reece, and Rodi full Reynolds stress transport model and the Sparlart-Allmaras model with and without a proposed modification. The main finding is that simulations with the full Reynolds stress transport model show remarkable mean flow agreement in the vortex and wake due to the proper prediction of a laminar vortex core. Simulations with the Spalart-Allmaras model did not indicate a laminar core and predicted over-diffusion of the tip-vortex. Secondary investigations in this work include the study of wall boundary layer treatment and simulating the wake-age of an isolated rotorcraft in hover using a steady-state RANS solver. By comparing skin friction plots over the NACA 0012 airfoil, it is shown that wall functions are most effective in the trailing edge half of the airfoil, while high velocity gradient and curvature of the leading edge make them more vulnerable to discrepancies. The rotorcraft simulation uses the modified Spalart-Allmaras turbulence model and shows proper, qualitative, resolution of the interaction between the vortex sheet and the tip vortex.
Master of Science
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44

Andersson, Johan, et Oscar Wyckman. « Modeling of Fuel Dynamics in a Small Two-Stroke Engine Crankcase ». Thesis, Linköpings universitet, Fordonssystem, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-119061.

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For any crankcase scavenged two-stroke engine, the fuel dynamics is not easily predicted. This is due to the fact that the fuel has to pass the crankcase volume before it enters the combustion chamber. This thesis is about the development of a model for fuel dynamics in the crankcase of a small crankcase scavenged two-stroke engine that gives realistic dynamic behavior. The crankcase model developed in this thesis has two parts. One part is a model for wall wetting and the other part is a model for concentration of evaporated fuel in the crankcase. Wall wetting is a phenomenon where fuel is accumulated in fuel films on the crankcase walls. The wall wetting model has two parameters that have to be tuned. One is for the fraction of fuel from the carburetor that is not directly evaporated and one parameter is for the evaporation time of the fuel film. The thesis treats tuning of these parameters by running the model with input data from measurements. Since not all input data are possible to measure, models for these inputs are also needed. Hence, development of simple models for air flows, fuel flow, gas mixing in the exhaust and the behavior of the λ-probe used for measurements are also treated in this thesis. The parameter estimation for the crankcase model made in this thesis results in parameters that corresponds to constant fraction of fuel from the carburetor that evaporates directly and a wall wetting evaporation rate that increases with increasing engine speed. The parameter estimation is made with measurements at normal operation and three specific engine speeds. The validity of the model is limited to these speeds and does not apply during engine heat-up. The model is run and compared to validation data at some different operation conditions. The model predicts dynamic behavior well, but has a bias in terms of mean level of the output λ. Since this mean value depends on the relation between input air and fuel flow, this bias is probably an effect of inaccuracy in the simple models developed for these flows.
För alla tvåtaktsmotorer med bränslematning genom vevhuset är bränsledynamiken svårpredikterad. Detta beror på att bränslet måste passera vevhusvolymen innan det når förbränningskammaren. Denna uppsats handlar om utveckling av en modell som ger realistisk dynamik för bränslet i tvåtaktsmotorers vevhus. Vevhusmodellen i denna uppsats har två delar. Den ena delen är en modell för bränslefilm på motorväggar och den andra delen är en modell för koncentration av förångat bränsle i vevhusvolymen. Bränslefilmsmodellen har två parametrar som måste trimmas. Den ena är andelen bränsle från förgasaren som inte förångas direkt och den andra är tidsåtgången för förångning av bränslefilmen. Uppsatsen behandlar trimning av dessa parametrar genom körning av modellen med indata från mätningar. Eftersom inte all indata kan mätas behövs även modeller för dessa. Därför behandlar uppsatsen även utveckling av enkla modeller för luftflöde, bränsleflöde, gasblandning i avgasvolymen och beteende hos den för mätningar använda λ-sonden. Parameterestimeringen för vevhusmodellen som är gjord i denna uppsats resulterar i parametrar som svarar mot konstant andel av bränslet från förgasaren som förångas direkt och en förångningshastighet för bränslefilmen som ökar med ökande motorhastighet. Parameterestimeringen är gjord med mätdata från normal körning vid tre olika motorhastigheter. Giltigheten för modellen är begränsad till dessa hastigheter och kan inte appliceras på körning av motorn vid kallstart. Modellen är körd och jämförd med valideringsdata från olika körfall. Modellen förutser dynamiska beteenden väl, men har ett systematiskt fel gällande medelvärdet på λ. Eftersom detta medelvärde beror på förhållandet mellan luftflöde och bränsleflöde in i vevhuset är sannolikt detta systematiska fel en effekt av osäkerhet i de enkla modeller som utvecklats för dessa flöden.
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Maurya, Abhilasha. « Computational simulation and analytical development of Buckling Resistant Steel Plate Shear Wall (BR-SPSW) ». Thesis, Virginia Tech, 2012. http://hdl.handle.net/10919/34466.

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Steel plate shear walls (SPSWs) are an attractive option for lateral load resisting systems for both new and retrofit construction. They, however, present various challenges that can result in very thin web plates and excessively large boundary elements with moment connections, neither of which is economically desirable. Moreover, SPSW also suffers from buckling at small loads which results in highly pinched hysteretic behavior, low stiffness, and limited energy dissipation. To mitigate these shortcomings, a new type of SPSW has been developed and investigated. The buckling resistant steel plate shear wall (BR-SPSW) utilizes a unique pattern of cut-outs to reduce buckling. Also, it allows the use of simple shear beam-column connections and lends tunability to the shear wall system. A brief discussion of the concept behind the BR-SPSW is presented. A detailed parametric study is presented that investigates the sensitivity of the local and global system behavior to the geometric design variables using finite element models as the main tool. The key output parameters which define the system response are discussed in detail. Analytical solutions for some output parameters like strength and stiffness have been derived and resulting equations are proposed. Finally, preliminary suggestions have been made about how this system can be implemented in practice to improve the seismic resistance of the buildings. The proposed BR-SPSW system was found to exhibit relatively fuller hysteretic behavior with high resistance during the load reversals, without the use of moment connections.
Master of Science
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Faisal, Md Tanvir. « A multiscale approach to mechancial modeling of a leaf petiole : integrating cell wall, cellular tissues, and structural morphology ». Thesis, McGill University, 2014. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=121448.

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A plant is a natural hierarchical structure, which exhibits remarkable mechanical properties. The macro (scale) mechanical properties of a plant are the cumulative outcome of the structural properties of its preceding level of structural hierarchy. To develop engineering structures inspired by a plant and its organs, a comprehensive characterization of its mechanical properties exhibited at multiple hierarchical orders is essential to mimic such structures for engineering application. This thesis presents a set of theoretical and computational models at various orders of the structural hierarchy to capture the overall structural properties of a plant petiole. The modeling method is framed within a multiscale mechanics framework, which is essential for any structure displaying hierarchical orders of organization. The macro structural properties, i.e. flexural and torsional stiffness, of a plant petiole are obtained by correlating cell wall construction, tissue microstructure, and structural shape morphology. The stiffness of the cell wall is modeled using the theory of a fiber reinforced composite material. The microarchitecture of the constituent tissues that govern the properties of the petiole are modeled with a novel algorithm – finite edge centroidal Voronoi tessellation (FECVT) - that is capable to provide a realistic visualization of the tissue. The effective stiffness properties of the constituent tissues are obtained via finite element analysis of the FECVT models coupled with cell wall properties. With the properties of the tissues, the cross-sectional shape of the petiole at the structural level is considered to determine its flexural and torsional stiffness, which are also validated experimentally for rhubarb petiole. This multiscale mechanical model will elucidate the role of each order of structural hierarchy to determine the structural compliance of the petiole. A hierarchical modeling approach that captures the overall structural properties of a petiole has been introduced in this thesis. In particular, the model develops a relationship between the micro and macrostructural properties using a tailored multiscale mechanics approach. Therefore, this research can bridge the gap between plant biology and engineering to develop novel bio-inspired material and structures. This research can also help to develop fundamental knowledge of plant cellular bio-mechanics and its impact on the macroscopic mechanics of stems and petioles with the end goal of transferring this knowledge to the processing and design of compliant engineering structures and materials.
Une plante est une structure hiérarchique naturelle, qui présente des propriétés mécaniques remarquables. Les propriétés mécaniques à grande échelle d'une plante sont le résultat cumulatif des propriétés structurelles du niveau précédent de la hiérarchie structurelle. Pour développer des structures de génie inspirées par une plante et ses organes, une caractérisation détaillée de ses propriétés mécaniques manifestées aux multiples niveaux hiérarchiques est essentielle pour imiter ces structures pour les applications d'ingénierie. Cette thèse présente un ensemble de modèles théoriques et numériques à divers niveaux hiérarchiques structuraux afin de capturer les propriétés structurelles aux niveaux globaux d'un pétiole d'une plante. La méthode de modélisation est cadrée au sein d'un système mécanique à niveaux multiples, qui est essentiel pour toute structure composée de plusieurs ordres hiérarchiques d'organisation. Les propriétés structurelles à grande échelle, c.à.d. la raideur en flexion et en torsion, d'un pétiole d'une plante sont obtenues par la corrélation entre la construction de la paroi cellulaire, la microstructure des tissus, et la morphologie de la forme structurelle. La raideur de la paroi cellulaire est modélisée en utilisant la théorie des matériaux composites à renfort fibreux. La microarchitecture des constituants des tissus qui gouverne les propriétés du pétiole est modélisée avec un nouveau algorithme – La tessellation de Voronoi de centre à bord fini (FECVT) - qui est capable de fournir une visualisation réaliste du tissu. La raideur effective des constituants des tissus est obtenue par la méthode des éléments finis des modèles FECVT accouplée avec les propriétés de la paroi cellulaire. La forme du pétiole en coupe transversale au niveau structural ensemble avec les propriétés des tissus sont considérées afin de déterminer sa raideur en flexion et en torsion, qui sont également validés expérimentalement pour le pétiole de la rhubarbe. Ce modèle mécanique à échelles multiples éclaircira le rôle de chaque niveau de la hiérarchie structurelle pour déterminer la souplesse structurelle du pétiole. Une méthode de modélisation hiérarchique qui capture les propriétés structurelles globales d'un pétiole a été introduite dans cette thèse. Notamment, le modèle établit une relation entre les propriétés du micro et macro niveaux structuraux en utilisant un procédé mécanique adapté, à échelles multiples. Par conséquent, cette recherche peut combler le vide entre la biologie végétale et le génie afin de développer de nouveaux matériaux et des structures bio-inspirées. Cette recherche peut également aider à développer les connaissances fondamentales de la biomécanique cellulaire des plantes et son impact sur la mécanique macroscopique des tiges et des pétioles avec l'objectif final de transférer ces connaissances pour le traitement et la conception des structures et matériaux souples de génie.
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Almohammed, Naser [Verfasser]. « Modeling and Simulation of Particle Agglomeration, Droplet Coalescence and Particle-Wall Adhesion in Turbulent Multiphase Flows / Naser Almohammed ». Hamburg : Helmut-Schmidt-Universität, Bibliothek, 2018. http://d-nb.info/1153126729/34.

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Schrottenbaum, Ines. « Influence of Wall Biofilm on Pathogen Transport in Water Distribution Systems. Modeling Estimates Derived from Synthetic Biofilm Experiments ». University of Cincinnati / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1427812859.

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Sharma, Abhinav. « ESTIMATING THE EFFECTS OF BLASTING VIBRATIONS ON THE HIGH-WALL STABILITY ». UKnowledge, 2017. https://uknowledge.uky.edu/mng_etds/38.

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The stability of the high-walls is one of the major concerns for open pit mines. Among the various factors affecting the stability of high-walls, blast vibrations can be an important one. In general, worldwide the established respective government regulations and industry standards are used as guidance to determine the maximum recommended levels of the peak particle velocity and frequency from the blast to avoid any effects on the structures around the mining project. However, most of the regulations are meant for buildings or houses and do not concern high-walls. This thesis investigates the response of high-walls under the effects of vibrations from mine blasting. In this research, the relationship between the high-wall response, the geometry of the slope, the frequency and the amplitude, of the ground vibration produced by blasting, is explored using numerical models in 3DEC. The numerical models were calibrated initially with data collected using seismographs installed in a surface mine operation and recording vibrations produced by an underground mine drill and blast operation. Once the calibration was accomplished, a parametric study was developed to explore the relationships between various parameters under study and its impact on the stability of high-walls.
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Ben, Nasr Ouissem. « Numerical simulations of supersonic turbulent wall-bounded flows ». Phd thesis, INSA de Rouen, 2012. http://tel.archives-ouvertes.fr/tel-01059805.

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This work deals with spatially-evolving supersonic turbulent boundary layers over adiabatic and cold walls at M∞ = 2 and up to Re0 ≈ 2600 using 3 different SGS models. The numerical methodology is based on high-order split-centered scheme to discretize the convective fluxes of the Navier-Stokes equations . For the adiabatic case, it is demonstrated that all SGS models require a comparable minimum grid-refinement in order to capture accurately the near-wall-turbulence. Overall, the models exhibit correct behavior when predictiong the dynamic properties, but show different performances for the temperature distribution in the near-wall region. For the isothermal case, it is found that the compressibility effects are not enhanced due to the wall cooling. As expected, the total temperature fluctuations are not negligible in the near-wall region. The study shows that the anti-correlation linking both velocity and temperature fields, derived from the Morkovin's hypothesis, is not satisfied.
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