The 28 March to 22 April 1999 eruption of Mount Cameroon volcano in southwest Cameroon occurred from multiple vents along fissures at two sites. Vents opened first at the upper site 1 (2650 m) and were more explosive than vents at the lower site 2 (1500 m), which were more effusive. Earthquakes, lava flows, tephra fall, ballistics and gas emissions affected the volcano's west and south flanks, including forests, plantations, stock animals, water supplies, coastal communities and their people. Through an analysis of existing published data and new interview data, we provide an overview of the environmental, social and economic consequences of these hazards on infrastructure, human health, and socio-economic and agricultural activities of the four coastal communities most affected by the eruption: Batoke, Bakingili, Debundscha and Idenau. The collected data provide a more detailed description of the short- and long-term direct and indirect effects of the eruption and response than has been provided to date. Sedimentation of tephra and ballistics from site 1 produced both short-term and long-lasting impacts on people, through the contamination of plants and water supplies, which induced impacts on human health and commercial activities. A ~9.2 km long lava flow erupted from site 2 received significant short-term attention as it severed the only arterial coastal highway, forced the evacuation of some 600 residents of Bakingili, and interrupted commerce between communities. The agricultural sector also suffered due to burning of crops and soils. The only obvious significant benefit of the eruption appears to be that the long lava flow has become a tourist attraction, responsible for bringing in money for food, drink and lodging. However, the long-term cascading effects caused by the hazards have proven to be more severe than the immediate direct and indirect effects during the eruption.

The microcantilever has become a ubiquitous tool for surface science, chemical sensing, biosensing, imaging, and energy harvesting, among many others. It is a device of relatively simple geometry with a static and dynamic response that is well understood. Further, because of it's small size, it is extremely sensitive to small external perturbations. These characteristics make the microcantilever an ideal candidate for a multitude of sensing applications. In this thesis dissertation we use the microcantilever to conduct numerous physical measurements and to study fundamental phenomena in the areas of fluid dynamics, turbulence, and biology. In each area we use the cantilever as a sensitive transducer in order to probe fluctuating forces. In micro and nanometer scale flows the characteristic length scale of the flow approaches and is even exceeded by the fluid mean free path. This limit is beyond the applicability of the Navier-Stokes equations, requiring a rigorous treatment using kinetic theory. In our first study, we conduct a series of experiments in which we use a microcantilever to measure gas dissipation in a nanoscopically confined system. Here, the distance between the gas molecules is of the same order as the separation between the cantilever and the walls of its container. As the cantilever is brought towards the wall, the flow becomes confined in the gap between the cantilever and the wall, affecting the resonant frequency and dissipation of the cantilever. By carefully tuning the separation distance, the gas pressure, and the cantilever oscillation frequency, we study the flow over a broad range of dimensionless parameters. Using these measurements, we provide an in-depth characterization of confinement effects in oscillating nanoflows. In addition, we propose a scaling function which describes the flow in the entire parameter space and which unifies previous theories based on the slip boundary condition and effective viscosity. In our next study, we seek to gain a better understanding of the transition to turbulence in a channel flow. We use a cantilever embedded in the channel wall to perform two sets of experiments: first, we study transition to turbulence triggered by the natural imperfections of the channel walls and second, we study transition under artificially added inlet noise. Our results point to two very different paths to turbulence. In the first case, wall effects lead to an extremely intermittent transitional flow and in the second case, broadband fluctuations originating at the inlet lead to less intermittent flow that is more reminiscent of homogeneous turbulence. The two experiments result in random flows in which high-order moments of near-wall fluctuations differ by orders of magnitude. Surprisingly however, the lowest order statistics in both cases appear qualitatively similar and can be described by a proposed noisy Landau equation. The noise, regardless of its origin, regularizes the Landau singularity of the relaxation time and makes transitions driven by different noise sources appear similar. Our results provide evidence of the existence of a finite turbulent relaxation time in transitional flows due to the persistent nature of noise in the system. In our last study, we turn to biologically-driven fluctuations from bacterial motion. Recent studies suggest that the motion of living bacteria could serve as a good indicator of bacteria species and resistance to antibiotics. To gain a better understanding of these fluctuations, we measure the nanomechanical motion of bacteria adhered to a chemically functionalized silicon microcantilever. A non-specific binding agent is used to attach E. coli to the surface of the device. The motion of the bacteria couples efficiently to the cantilever well below its resonance frequency, causing a measurable increase in its mechanical fluctuations. We vary the bacterial concentration over two orders of magnitude and are able to observe a corresponding change in the amplitude of fluctuations. Additionally, we administer antibiotics (Streptomycin) to kill the bacteria and observe a decrease in the fluctuations. A basic physical model is used to explain the observed spectral distribution of the mechanical fluctuations. These results lay the groundwork for understanding the motion of microorganisms adhered to surfaces and for developing micromechanical sensors for rapid bacterial identification and antibiotic resistance testing.

The specific turbulent kinetic energy, root-mean-square fluctuating vorticity, and mean-vortexwavelength distributions are presented for fully rough pipe flow. The distributions of these turbulence variables are obtained from a proposed turbulence model. Many of the turbulence models commonly used for computational fluid dynamics are based on an analogy between molecular and turbulent transport. However, traditional k-ε and k-ω models fail to exhibit proper dependence on the molecular viscosity. Based on a rigorous application of the Boussinesq’s hypothesis, Phillips proposed a vorticity-based transport equation for the turbulent kinetic energy. The foundation for this vorticity-based transport equation is presented. In future development of this model, a transport equation for the fluctuating vorticity is needed. In order to assess the model and evaluate closure coefficients, the resulting turbulent vorticity distribution must be compared to reference distributions. This dissertation presents reference distributions for the mean fluctuating vorticity and mean turbulent wavelength obtained for fully rough pipe flow. These distributions are obtained from a turbulence model, which involves the proposed transport equation for the turbulent kinetic energy and an empirical relation for the mean vortex wavelength. The empirical relation for the mean vortex wavelength requires numerous closure coefficients. These closure coefficients are determined through gradient-based optimization techniques. The current model gives excellent agreement with well established relations obtained for both the friction factor and velocity distribution.

L’objectif de cette thèse est d’étudier les apports et les limitations de deux méthodes d’origine particulaire, SPH et LBM, dans le cadre de la simulation des écoulements à bouchons dans des conduites. Dans l’industrie pétrolière, ce type d’écoulement, que l’on retrouve par exemple dans les pipelines qui acheminent le pétrole et le gaz jusqu’aux raffineries, est connu pour endommager les installations et pour réduire l’efficacité du transport des fluides. Il est donc important de bien comprendre leur formation. Nous avons donc implémenté ces deux méthodes, ainsi que leurs variantes polyphasiques, et avons mené une campagne de validation et de comparaison afin de sélectionner la méthode la plus adéquate, pour poursuivre ensuite avec des simulations de cas plus appliqués et réalistes. Les contributions présentées se concentrent principalement sur trois axes. Tout d’abord, il a fallu construire les codes de calcul nécéssaires, les valider puis comparer des différentes formulations polyphasiques disponibles pour SPH et LBM. Ensuite, nous avons développé des conditions aux limites d’entrée/sortie adaptées au contexte polyphasique pour être en mesure d’injecter les fluides avec des vitesses imposées et de ler évacuer du domaine avec un pression donnée. Enfin, nous avons simulé différents cas d’écoulements à bouchons académiques avec SPH et LBM, puis sur des cas appliqués avec des géométries réalistes et des ratios de densité et de viscosité de type air/eau avec SPH seulement. / The main objective of this thesis is to study the contributions and limitations of two particle- based methods, SPH and LBM, for the simulation of slug flows in pipes. In the petroleum industry, these flow regimes, found for example during the transportation of oil and gas from reservoirs to refinery facilities through pipelines, are highly undesirable because they are known to damage facilities and to reduce flow efficiency. Therefore, it is important to understand its formation. We have implemented both methods, as well as their multiphase variants, and have led a validation and comparison campaign in order to to select the most suited method and to continue with simulations of more applied and realistic cases. The main contributions of this work can summarized in 3 points. First, we had to write the necessary computation codes, validate them and compare the different multiphase formulations available for SPH and LBM. Then, we have developed inlet/outlet boundary conditions adapted to the multiphase context so that we are able to inject fluids with prescribed velocities and let them exit he domain with a given pressure. Finally, we have simulated different academic test cases of slug flows with SPH and LBM and then on applied cases with realistic geometries and air-water like density and viscosity ratios with SPH only.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第21366号 / 工博第4525号 / 新制||工||1705(附属図書館) / 京都大学大学院工学研究科機械理工学専攻 / (主査)教授 花崎 秀史, 教授 黒瀬 良一, 教授 稲室 隆二 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

In this research, a tribocharging model based on the prominent condenser model was used in combination with an Eulerian-Lagrangian CFD model to simulate particle tribocharging in particle-laden flows. The influence of different parameters on particle-wall interactions during particle transport in a particle-laden pipe flow was elucidated. An artificial neural network was developed for predicting particle-wall collision numbers based on a database obtained through CFD simulations. The particle-wall collision number from the CFD model was validated against experimental data in the literature. The tribocharging and CFD models were coupled with the experimental tribocharging data to estimate the contact potential difference of powders, which is a function of contact surfaces' work functions and depends on the physicochemical properties of materials. While the contact potential difference between the particles and wall is an essential parameter in the tribocharging models, the accurate measurement of the property is a complex process requiring a highly controlled environment and special equipment. The results from this research also confirm that particle tribocharging is very much dependant on the particle-wall collision number influenced by various parameters, such as particle size and density, air velocity, and pipe dimensions. Plotting the experimentally measured charge-to-mass ratios against the calculated contact potential differences for samples with different protein contents uncovered a linear trend, which opens a novel approach for protein quantification of powders for a given particle size. Therefore, an algorithm is proposed for rapid quantification of protein content and particle size determination of samples during transport in particle-laden flows based on the triboelectric charge measurement. The algorithm requires a CFD-based artificial neural network to estimate the particle-wall interactions based on the hydrodynamic characteristics of the particles and flow systems. / Thesis / Master of Applied Science (MASc)

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An accurate and efficient numerical method for Compressible Vorticity Confinement (CVC) was developed. The methodology follows from Steinhoff's vorticity confinement approach that was developed for incompressible flows. In this research, the extension of this approach to compressible flows has been developed by adding a vorticity confinement term as a "body force" into the governing compressible flow equations. This vorticity confinement term tends to cancel the numerical dissipative errors inherently related to the numerical discretization in regions of strong vorticity gradients. The accuracy, reliability, efficiency and robustness of this method were investigated using two methods. One approach is directly applying the CVC method to several real engineering problems involving complex vortex structures and assessing the accuracy by comparison with existing experimental data and with other computational techniques. Examples considered include supersonic conical flows over delta wings, shock-bubble and shock-vortex interactions, the turbulent flow around a square cylinder and the turbulent flow past a surface-mounted 3D cube in a channel floor. A second approach for evaluating the effectiveness of the CVC method is by solving simplified "model problems" and comparing with exact solutions. Problems that we have considered are a two-dimensional supersonic shear layer, flow over a flat plate and a two-dimensional vortex moving in a uniform stream. The effectiveness of the compressible confinement method for flows with shock waves and vortices was evaluated on several complex flow applications. The supersonic flow over a delta wing at high angle of attack produces a leeward vortex separated from the wing and cross flow, as well as bow shock waves. The vorticity confinement solutions compare very favorably with experimental data and with other calculations performed on dense, locally refined grids. Other cases evaluated include isolated shock-bubble and shock-vortex interactions. The resulting complex, unsteady flow structures compare very favorably with experimental data and computations using higher-order methods and highly adaptive meshes. Two cases involving massive flow separation were considered. First the two-dimensional flow over a square cylinder was considered. The CVC method was applied to this problem using the confinement term added to the inviscid formulation, but with the no-slip condition enforced. This produced an unsteady separated flow that agreed well with experimental data and existing LES and RANS calculations. The next case described is the flow over a cubic protuberance on the floor of a channel. This flow field has a very complex flow structure involving a horseshoe vortex, a primary separation vortex and secondary corner vortices. The computational flow structures and velocity profiles were in good agreement with time-averaged values of the experimental data and with LES simulations, even though the confinement approach utilized more than a factor of 50 fewer cells (about 20,000 compared to over 1 million). In order to better understand the applicability and limitations of the vorticity confinement, particularly the compressible formulation, we have considered several simple model problems. Classical accuracy has been evaluated using a supersonic shear layer problem computed on several grids and over a range of values of confinement parameter. The flow over a flat plate was utilized to study how vorticity confinement can serve as a crude turbulent boundary layer model. Then we utilized numerical experiments with a single vortex in order to evaluate a number of consistency issues related to the numerical implementation of compressible confinement. / Ph. D.

No / The aim of this paper is to introduce the Systems State Flow Diagram as a structured approach to high level solution-independent function based decomposition of a complex multi-disciplinary system. The approach is discussed in the context of existing function modelling frameworks and in relation to current practice in industry. A generic case study is used to introduce the approach and to highlight the salient features, followed by an illustration on its application to the analysis of an electric vehicle powertrain. Experience with the practical application of the approach with engineering teams is discussed.