Combustion instabilities (thermo-acoustic pressure oscillations) have been recognised for some time as a problem limiting the development of low emissions (e.g., lean burn) gas turbine combustion systems, particularly for aviation propulsion applications. Recently, significant research efforts have been focused on acoustic damping for suppression of combustion instability. Most of this work has either been experimental or based on linear acoustic theory. The last 3-5 years has seen application of density based CFD methods to this problem, but no attempts to use pressure-based CFD methods which are much more commonly used in combustion predictions. The goal of the present work is therefore to develop a pressure-based CFD algorithm in order to predict accurately acoustic propagation and acoustic damping processes, as relevant to gas turbine combustors. The developed computational algorithm described in this thesis is based on the classical pressure-correction approach, which was modified to allow fluid density variation as a function of pressure in order to simulate acoustic phenomena, which are fundamentally compressible in nature. The fact that the overall flow Mach number of relevance was likely to be low ( mildly compressible flow) also influenced the chosen methodology. For accurate capture of acoustic wave propagation at minimum grid resolution and avoiding excessive numerical smearing/dispersion, a fifth order accurate Weighted Essentially Non-Oscillatory scheme (WENO) was introduced. Characteristic-based boundary conditions were incorporated to enable accurate representation of acoustic excitation (e.g. via a loudspeaker or siren) as well as enable precise evaluation of acoustic reflection and transmission coefficients. The new methodology was first validated against simple (1D and 2D) but well proven test cases for wave propagation and demonstrated low numerical diffusion/dispersion. The proper incorporation of Characteristic-based boundary conditions was validated by comparison against classical linear acoustic analysis of acoustic and entropy waves in quasi-1D variable area duct flows. The developed method was then applied to the prediction of experimental measurements of the acoustic absorption coefficient for a single round orifice flow. Excellent agreement with experimental data was obtained in both linear and non-linear regimes. Analysis of predicted flow fields both with and without bias flow showed that non-linear acoustic behavior occurred when flow reversal begins inside the orifice. Finally, the method was applied to study acoustic excitation of combustor external aerodynamics using a pre-diffuser/dump diffuser geometry previously studied experimentally at Loughborough University and showed the significance of boundary conditions and shear layer instability to produce a sustained pressure fluctuation in the external aerodynamics.

In the subject of Computational Fluid Dynamics (CFD), there seems to be small number of important progress in the pressure-based methods for several decades. Recent studies on the implicit coupled algorithms for pressure-based methods have brought a new insight. This method seems to provide a huge reduction in the solution times over segregated methods. Fully implicit coupled algorithm for pressure-based methods is very new subject with only few papers in literature. One of the most important work in this area is referenced as [1] in this thesis. Another source of information about the method comes from a commercially available code FLUENT which includes the algorithm as an option for pressure-based solver. However the algorithm in FLUENT does not seem to be a fully implicit with a little information in its manual. In this thesis, a fully implicit coupled pressure-based solver is developed mainly based on the available literature. The developed code is succesfully tested against some test cases.

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A non-iterative pressure based algorithm which consists of splitting the solution of momentum energy and species equations into a sequence of predictor-corrector stages was developed for the simulation of transient reacting radiating flows. A semi-discrete approach called the Method of Lines (MOL) which enables implicit time-integration at all splitting stages was used for the solution of conservation equations. The solution of elliptic pressure equation for the determination of pressure field was performed by a multi-grid solver (MUDPACK package). Radiation calculations were carried out by coupling previously developed gray and non-gray radiation models with the algorithm. A first order (global) reaction mechanism was employed to account for the chemistry. The predictions of the algorithm for the following test cases: i) non-isothermal turbulent pipe flow and ii) laminar methane-air diffusion flame / were benchmarked against experimental data and numerical solutions available in the literature and the capability of the code to predict transient solutions was demonstrated on these test cases. Favorable agreements were obtained for both test cases. The effect of radiation and non-gray treatment of the radiative properties were investigated on the second test case. It was found that incorporation of radiation has significant effect on Temeprature and velocity fields but its effect is limited in species predictions. Executions with both radiation models revealed that the non-gray radiation model considered in the present study produces similar results with the gray model at a considerably higher computational cost. The algorithm developed was found to be an efficient and versatile tool for the timedependent simulation of different flow scenarios constitutes the initial steps towards the computation of transient turbulent combustion.

The main purpose of this research is to develop a Computational Fluid Dynamics (CFD) software to be used as an educational tool in teaching introductory level fluid mechanics and CFD courses. The software developed for this purpose is called Virtual Flow Lab. It has a graphical user interface (GUI) that enables basic pre-processing, solver parameter and boundary condition setting and post-processing steps of a typical CFD simulation. The pressure-based solver is capable of solving incompressible, laminar, steady or time-dependent problems on two-dimensional Cartesian grids using the SIMPLE algorithm and its variants. Blocked-cell technique is implemented to extend the types of the problems that can be studied on a Cartesian grid. A parametric study is conducted using a number of benchmark problems in order to test the accuracy and efficiency of the solver and successful results are achieved.

The aim of this study is to develop a two-dimensional pressure-based Navier-Stokes solver for incompressible/compressible flows. Main variables are Cartesian velocity components, pressure and temperature while density is linked to pressure via equation of state. Modified SIMPLE algorithm is used to achieve pressure-velocity coupling. Finite Volume discretisation is performed on non-orthogonal and boundary-fitted grids. Collocated variable arrangement is preferred because of its advantage on staggered arrangement in non-orthogonal meshes. Face velocities are calculated using Rhie-Chow momentum interpolation scheme to avoid pressure checkerboarding effect. The solver is validated by solving a number of benchmark problems.

Many of the present problems that we are facing arise as unanticipated side-effects of our own actions. Moreover, the solutions implemented to solve important problems often create new problems. To avoid unintended consequences, understanding complex systems is essential in devising policy instruments and in improving environmental management. Thus, this thesis investigated systems modeling approaches to under- stand complex systems and monitor the environmental performance of management actions. The overall aim of the work was to investigate the usefulness of different systems modeling approaches in supporting environmental management. A driver- based, pressure-oriented approach was adopted to investigate systems modeling tools. Material/substance flow analysis, environmental footprinting, input-output analysis, process-based dynamic modeling, and systems dynamics modeling approaches were applied in different cases to investigate strengths and weaknesses of the tools in generating an understanding of complex systems. Three modeling and accounting approaches were also tested at different systems scales to support environmental mon- itoring. Static modeling approaches were identified as fundamental to map, account, and monitor physical resource metabolism in production and consumption systems, whereas dynamic modeling showed strengths in understanding complex systems. The results suggested that dynamic modeling approaches should be conducted on top of static analysis to understand the complexity of systems when devising and testing policy instruments. To achieve proactive monitoring, a pressure-based assessment was proposed instead of the mainstream impact/state-based approach. It was also concluded that the LCA community should shift the focus of its assessments to pressures instead of impacts. / Många nuvarande miljö- och utvecklingsproblem har uppstått som oförutsedda biverkningar av människans egna handlingar. De lösningar som prövats har i sin tur ofta skapat  nya problem. Det därför viktigt att förstå hur komplexa system fungerar och att utforma styrmedel och ledningssystem som minimerar risken för oönskade bieffekter. Den här avhandling har använt olika modelleringsmetoder för att öka förståelsen för komplexa system och bidra med kunskaper om hur miljöprestanda och förvaltningsåtgärder kan följas upp på ett mer effektivt sätt. Det övergripande syftet med arbetet var att undersöka användbarheten av olika modelleringsmetoder för att effektivisera den fysiska resurshanteringen i samhället. I arbetet har ett flödesbaserat och aktörsinriktat arbetssätt (pressure based and driver oriented approach) använts i modelleringen.  Material- och substansflödesanalys, miljöfotavtryck, input-output analys, processbaserad dynamisk modellering och systemdynamiska modelleringsmetoder studerades för att undersöka styrkor och svagheter hos de olika metoderna/verktygen.  Tre olika modellerings- och redovisningsmetoder för att stödja miljöövervakning testades också i olika systemskalor. Statiska modelleringsmetoder (räkenskaper) identifierades som grundläggande för att kartlägga, kontoföra och övervaka den fysiska resursmetabolismen i produktions- och konsumtionssystem, medan dynamisk modellering visade sin styrka i att skapa förståelse för komplexa system. Resultaten pekar på att dynamiska modelleringsmetoder bör användas som ett komplement till statiska analyser för att förstå komplexiteten i systemen när man utformar och testar styrmedel. För att uppnå proaktiv övervakning bör flödesbaserade räkenskaper utnyttjas i större utsträckning i stället för den vanliga tillstånds- och påverkansövervakningen (state/impact monitoring). En viktig slutsats är därför att LCA-samfundet bör flytta fokus i sina bedömningar från påverkan till flöden. / <p>QC 20160830</p>

A growing population is driving automatization in agricultural industry to strive for more productive arable land. Being part of this process, this work is aimed to investigate the possibility to implement sensor-based automation in a particular system called Front End Loader, which is a lifting arms that is commonly mounted on the front of a tractor. Two main tasks are considered here, namely Electronic Self Leveling (ESL) and payload estimation. To propose commercially implementable solutions for these tasks, specific objectives are set, which are: 1) to propose a controller to perform ESL under typical disturbances 2) to propose a methodology for payload estimation considering realistic estimation conditions. Lastly, aligned with these goals, 3) to propose models for the Front End Loader under consideration for derivation of solutions of the specified tasks. The self-leveling task assists farmers in maintaining the angular position of the mounted implements, e.g. a bale handler or a bucket, with respect to the ground when the loader is manually lifted or lowered. Experimental results show that different controllers are required in lifting and lowering motions to maintain the implement's angular position with a required accuracy due to principle differences in gravity impact. The gravity helps the necessary correction in lifting motion, but works against the correction in lowering motions. This led us to propose a controller with a proportional term, a discontinuous term and an on-line disturbance estimation and compensation as well as the tuning procedure to achieve a 2 degrees tracking error for lowering motions in steady state. The proposed controller shows less sensitive performance to lowering velocity, as the main disturbance, in comparison to a linear controller. The second task, payload estimation, assists farmers to work within safety range as well as to work with a weight measurement tool. A mechanical model derived based on equations of motion is improved by a pressure based friction to sufficiently accurately represent the motion of the front end loader under consideration. The proposed model satisfies the desired estimation accuracy of 2\% full scale error in a certain estimation condition domain in constant velocity regions, with off-line calibration step and off-line payload estimation step. An on-line version of the estimation based on Recursive Least Squares also fulfills the desired accuracy, while keeping the calibration step off-line.

A linear model of consumption − produce-use-dispose − has constantly increased the pressure on the environment in recent decades. There has been a great belief that technology will solve the problem, but in many cases it is only partly contributing to the solution. For a full solution, the root causes of problems need to be identified. The drivers-pressures-state-impact-response (DPSIR) framework allows the drivers of a specific problem to be identified by structuring the causal relations between humans and the environment. A state/ impact-based approach can help identify pressures and drivers, and make what can be considered an end-of-pipe response. Rather than that mainstream approach, this thesis adopts a pressure-based driver-oriented approach, which could be considered a proactive approach to environmental resource management. In physical resource management, material flow analysis (MFA) is one of the tools used for communication and decision support for policy response on resource productivity and pollution abatement. Here, element flow analysis (EFA), a disaggre- gation of MFA for better mass balance, was applied in pollution control and resource management. The pressure-based driver-oriented approach was used to model element flows and thus identify the drivers of problems in order to improve pollution control and resource management in complex systems. In one case study, a source-storage-transport model was developed and applied in five lakes in the Stockholm region to identify the drivers of copper pollution by monitoring the state of the environment through element flow modeling linking diffuse sources and fate in the lakes. In a second case study, a system dynamics modeling approach was applied in dynamic element flow modeling of the global mobile phone product system to investigate the drivers for closing the material flow loop through a sensitivity analysis. In a third case study, causal loop diagram modeling was used for proactive resource management to identify root causes of a problem in a complex system (product systems of physical consumer goods) by qualitatively analyzing unintended environmental consequences of an improvement action. In the case study on lakes in the Stockholm region, the source-transport-storage model proved capable of predicting copper sources through monitoring the sediment copper content in the heavily copper-polluted lakes. The results also indicated how the model could help guide policy makers in controlling copper pollution. The system dynamics study proposed an eco-cycle model of the global mobile phone product system by tuning the drivers, which could lessen the pressures on resources by decreasing the resource demands for production and increasing resource recovery at product end-of- life. The causal loop diagram study showed that a broader systems approach is required to understand and identify the drivers for proactive resource management in a complex system, where improvement actions can lead to unintended consequences. / <p>QC 20150420</p>

Les surfaces tactiles ayant connu un grand essor ces dernières années, le grand public les utilise quotidiennement pour de multiples tâches, telles que la consultation d'e-mail, la manipulation de photos, etc. En revanche, très peu d'applications 3D existent sur ces dispositifs, alors que de telles applications pourraient avoir un grand potentiel dans des domaines variés, telles que la culture, l'architecture, ou encore l'archéologie. La difficulté majeure pour ce type d'applications est d'interagir avec un espace défini en trois dimensions à partir d'une modalité d'interaction définie en deux dimensions. Les travaux effectués dans cette thèse explorent l'association entre surfaces tactiles et manipulation de contenu 3D pour le grand public. Les premières études ont été réalisées afin de comprendre comment l'utilisateur réagit pour manipuler un objet virtuel 3D avec une surface tactile sans lui imposer de techniques d'interaction particulières. De par les connaissances acquises sur les utilisateurs, les travaux suivants présentent l'élaboration de nouvelles techniques d'interaction ainsi que leur évaluation. / Since the emergence of tactile surfaces in recent years, the general public uses them every day for multiple tasks, such as checking email, photo manipulation, and so on. However, very few 3D applications on these devices exist, although such applications may have great potential in various fields, such as culture, architecture, or archeology. The major difficulty for such applications is to interact with a defined space in three dimensions from an interaction modality defined in two dimensions. Work in this thesis explores the association between tactile surfaces and manipulation of 3D content for the general public. The first studies were conducted to understand how the user tends to manipulate a 3D virtual object with a touch surface without imposing specific interaction techniques. Throughout knowledge gained by users, the following works are developing new interaction techniques and their evaluation.