Dissertations / Theses on the topic 'Re-suspension'

In this thesis, the theory of three dimensional numerical modeling of transport and re-suspension of fine sediments is studied and a computer program is develped for simulation of the three dimensional suspended sediment transport. The computer program solves the three dimensional advection-diffusion equation simultaneously with a computer program prepared earlier for the simulation of three dimensional current systems. This computer program computes the velocity vectors, eddy viscosities and water surface elavations which are used as inputs by the program of fine sediment transport. The model is applied to Bay of Izmir for different wind conditions.

Anthropogenic inputs of nutrients and sediment are a widespread problem in U.S. streams causing localized impairment and contributing to eutrophication of coastal habitats. Sediments and dissolved nutrients interact through diverse processes including ion exchange, sorption and biotic assimilation by particle-bound bacteria. This study examined the effects of sediment re-suspension on nutrient partitioning in lab microcosms using fine benthic matter collected from two Virginia Coastal Plain streams. Kimages Creek was recently restored following dam removal and was characterized by large deposits of legacy sediments. Courthouse Creek was characterized by sandy substrates typical of Coastal Plain streams. Sediment characteristics differed between the two sites and were influenced by discharge. Net nutrient release rates were similar between streams though reactivity of Courthouse Creek sediments was greater than that of Kimages Creek. Equilibrium Phosphate Concentrations calculated for each site show that fine sediments at Kimages Creek have resulted in higher phosphorus retention potential.

[Truncated abstract] With rapidly increasing population densities along coastlines and rising global sea levels, coastal protection has become a major concern for coastal communities. Predicting sediment transport in nearshore regions, however, is one of the most challenging tasks faced by coastal researchers in designing coastal structures or beach nourishment schemes. Although nearshore sediment transport mainly occurs in the longshore direction, cross-shore sediment transport is crucial in determining the shoreline evolution and beach morphology . . . This study investigated the factors influencing sediment re-suspension and cross-shore suspended sediment flux in the frequency domain through a series of field measurements conducted at several different locations and a numerical model. Only oscillatory flow components were examined and the mean flow components were not considered. Although many different factors such as cross-shore location with respect to breaker line, significant wave height to water depth ratio (Hs/h), normalised horizontal velocity skewness (/‹u²›³/²), median grain size (d50), breaker type, and wave groupiness appeared to influence the magnitude of cross-shore suspended sediment flux, bed ripples was identified as the major contributing factor in changing the direction of suspended sediment flux due to incident swell waves. Moreover, the direction changed significantly with ripple type. High frequency measurements, obtained to examine the influence of turbulent kinetic energy (TKE) on higher sediment suspension events observed under wave groups indicated that higher TKE was generated at the seabed by approaching wave groups, which in turn resulted in higher suspension events.°1

This study is concerned with the modelling of single-phase and two-phase turbulent flows in a square duct over a range of Reynolds numbers with attention focused on the deposition, dispersion and re-suspension of particles. Reynolds averaged Navier Stokes (RANS) modelling is used in conjunction with a Lagrangian particle tracker (LPT). Modelling and simulation of single- and two-phase turbulent flows in circular pipes with the presences of stationary flat beds are also considered using the previously stated methodologies, as well as large eddy simulation (LES). The performance of the RANS modelling technique is evaluated against available experimental, simulation and empirical data. The RANS modelling technique is seen to perform with qualitative accuracy across all of the test cases considered within this thesis, and it can be said that this approach is capable of reproducing many of the key feature' associated with these flows. In almost all cases, qualitative agreement is seen between the RANS modelling results and the available experimental data, simulation results and empirical correlations. A key failing of the RANS modelling technique is the inaccurate representation of the magnitude of the secondary velocities found in square ducts and pipes with variable bed height. The RANS modelling technique with a Reynolds stress model (RSM) for turbulence, coupled with a LPT, can be usefully used in modelling particle-laden duct and pipe flow. across a range of conditions. Important qualitative information can be gained from this technique in terms of particle deposition, dispersion and re-suspension. For more detailed studies on the physics of these flows, the preferred methodologies are the more advanced simulation techniques of LES and direct numerical simulation CDNS), while there is also a clear need for further experimental investigations of such particle- laden flows.

Sediment resuspension and deposition are key processes governing intertidal morphodynamics and are crucially influenced both by physical and biological factors. The present thesis addresses two important aspects of sediment trans- port processes in intertidal areas. The first topic concerns the quantitative analysis of suspended sediment concentration and wind forcing to provide estimates of sediment properties, such as settling velocity and the critical shear stress for erosion, valid at a spatial scale which is relevant for the overall morphodynamics of the system. The first part of the thesis thus develops and describes a method to evaluate sediment properties based on the solution of a sediment mass conser- vation equation in the water column accounting for the effects of wind-induced and current-induced bottom shear stress. The method is applied by using data from a network of in situ sensors in the Venice lagoon and provides estimates which compare favorably with observations in the same shallow tidal areas, and are in line with what is expected for sandy-silt sediments. The proposed estimation method is direct and quantitative, it does not interfere with the local system physical and biological status, and lends itself to the monitoring of sed- iment parameters on a seasonal basis and for long periods of time with limited operational effort. The second, related, topic treated here concerns the labora- tory study of the impact of mats of Ulva intestinalis on sediment stability and flow dynamic in shallow tidal areas. Macroalgae are a controlling factor of flow and sediment stability, as they act to inhibit sediment erosion due to waves or currents and promote sedimentation. Algal mats are increasingly more frequent and extended in many coastal and estuarine intertidal habitats and it is thus important to quantitatively characterize their impact on the flow field and on sediment stability, in order to better understand ongoing degradation of coastal lagoons and to develop suitable mitigation and restoration measures. The second part of the thesis thus describes and analyzes a series of experiments performed in a large open-channel flume (the Total Environment Simulator - TES- facility at University of Hull, UK), set up with a bed of fine sand, partially covered by strands of U. intestinalis. The experiments allowed the accurate measurement, both in space and time, of flow velocity distributions, water levels, bed levels, and suspended sediment concentration. The presence of macroalgae was found to influence both the velocity distribution near the sediment bed, and the Reynolds shear stress acting on it. Direct inspection during the experiments and data analysis suggest that macroalgae exert a significant bio-stabilizing effect.
La risospensione e la deposizione dei sedimenti sono processi chiave nel governo della morfodinamica a marea e sono influenzate in modo cruciale sia da fattori fisici che biologici. La presente tesi affronta due importanti aspetti dei processi di trasporto dei sedimenti negli ambienti a marea. Il primo argomento riguarda l’analisi quantitativa della concentrazione del sedimento in sospensione e della forzante vento per produrre delle stime delle proprietà del sedimento, quali la velocità di sedimentazione e lo sforzo tangenziale critico per l’erosione, a scale spaziali rilevanti per la generale dinamica morfologica del sistema. La prima parte della tesi pertanto sviluppa e descrive un metodo per valutare le proprietà del sedimento sulla base della soluzione di una equazione di conservazione del sedimento nella colonna d’acqua che tiene conto degli effetti dello sforzo tangenziale al fondo dovuto al vento e alle correnti di marea. Il metodo è applicato utilizzando osservazioni da una rete di sensori nella laguna di Venezia e produce stime in buon accordo con osservazioni puntuali negli stessi siti e allineate con i valori attesi per sedimenti sabbiosi- limosi. L’analisi è stata effettuata attraverso serie temporali relative a intensità del vento, fornite da stazioni anemometriche, a misure di torbidità, fornite da sensori torbidimetrici ed a serie temporali relative a livelli di marea acquisite dalla rete telemareografica; tutte le stazioni operano simultaneamente, sono dis- poste in prossimit`a l’un l’altra e ricoprono grossomodo l’intera area lagunare. Per calcolare gli sforzi dovuti all’azione del moto ondoso è stato implementato un modello puntuale forzato dal vento sotto l’ipotesi di fetch illimitato, in cui gli sforzi sono stati calcolati in funzione del coefficiente di attrito, della densità dell’acqua e della velocità orbitale massima al fondo. La velocità orbitale massima al fondo è stata espressa in funzione dell’altezza d’onda ed il periodo d’onda che è stato calcolato in funzione di parametri adimensionalizzati e seguendo la legge di potenza i cui parametri di fitting sono stati adattati alle osservazioni in laguna. L’altezza d’onda è stata calcolata secondo un bilancio energetico in cui si è trascurata la componente advettiva dell’energia dell’onda. Con il modello forzato dalla marea si sono calcolati gli sforzi in funzione del coefficiente di attrito, della densità dell’acqua e della velocità della corrente di marea. Una volta calcolati gli sforzi tangenziali al fondo è stata implementata l’equazione di conservazione della massa di sedimenti assumendo concentrazione dei sedimenti spazialmente uniforme (divergenza del flusso nulla e continuità della massa d’acqua), in cui la variazione nel tempo del prodotto tra il tirante e la concentrazione (la concentrazione viene espressa come differenza tra la concentrazione effettivamente acquisita dai torbidimetri ed una concentrazione residua che rimane sempre in sospensione in laguna) è data dalla somma tra il flusso di erosione ed il flusso di sedimentazione. Nel caso di processo di sedimentazione, il flusso erosivo è stato trascurato, ed i parametri ws (velocità di settling) e Co (concentrazione residua) sono stati calcolati risolvendo un fitting lineare. Una volta calcolati i valori di velocità di deposizione compresi tra 2.7 · 10-4 e 6.3 · 10−4 m/s e la concentrazione residua compresa tra 6.7 e 16.2 mg/l, si sono successivamente calcolati la velocità di erosione, sulla base della quale si è risolto l’algoritmo del simplesso per ottenere la curva di regressione dei valori medi di velocità di erosione. Dalla regressione si sono ottenuti i valori dello sforzo critico di erosione compresi tra 0.1 e 0.5 Pa e del parametro di erosione compresi tra 2 · 10−6 e 3 · 10−4 kg/sm2. E’ stata compiuta inoltre un’analisi stagionale dopo aver suddiviso le serie temporale in stagioni secondo la suddivisione astronomica. I risultati si sono dimostrati in generale in soddisfacente accordo con i valori misurati in situ attraverso le tradizionali strumentazioni, Sea Carousel e Mini Flume. La metodologia implementata ha il vantaggio di stimare i parametri dei sedimenti senza interferire con gli effetti di bio-stabilizzazione operati dai microrganismi e di fornire una stima parzialmente integrata delle soglie di erosione e della velocità di sedimentazione. Si può in definitiva concludere che il metodo di stima proposto è diretto e quantitativo, non interferisce con lo stato fisico e biologico locale del sistema e si presta ad attività di monitoraggio delle proprietà dei sedimenti su base stagionale e per lunghi periodi, con limitato sforzo operativo. Il secondo, correlato, argomento riguarda lo studio di laboratorio dell’impatto della macroalga Ulva intestinalis, sulla stabilità del sedimento e sul campo di velocità in aree a marea. Le macroalghe, infatti, esercitano un controllo importante sulla distribuzione della velocità e sul trasporto di sedimenti, poichè inibiscono l’erosione del sedimento dovuta a onde o correnti e promuovono la sedimentazione. Larghe estensioni di macroalghe sono sempre più frequenti in molti habitat intertidali estuarini e costieri ed è dunque importante caratterizzare quantitativamente il loro impatto sul campo di moto e la stabilità del sedimento, per una migliore comprensione dell’attuale degrado di lagune costiere e per sviluppare adatte misure di mitigazione e ricostruzione ambientale. La seconda parte della tesi, dunque, descrive e analizza una serie di esperimenti condotti in una canaletta di grandi dimensioni (il Total Environment Simulator - TES- presso l’Università di Hull, UK), con sedimento costituito da sabbia fine, parzialmente coperto da individui di U. intestinalis. L’attività sperimentale è stata indirizzata a quantificare l’effetto delle macroalghe sulla dinamica della struttura del campo di moto indotto da correnti e moto ondoso. L’apparato strumentale utilizzato è costituito da una canaletta di 11 metri di lunghezza e 2 di larghezza, su cui è disposto uno strato di sedimenti artificiali non coesivi (sabbia fine: 135μm di diametro). L’apparato è fornito di generatore di flusso ed onde. Attraverso una completa strumentazione costituita da ADV (Acoustic Doppler Profiler), PIV (Particle Image Velocimetry), ABS (Acoustic BackScat- ter) si sono fornite informazioni su: andamento temporale del vettore velocità, evoluzione temporale della superficie del fondo, andamento temporale della concentrazione dei sedimenti sospesi. Si sono infine utilizzate trappole di sedimento posizionate all’uscita del flusso di corrente dalla canaletta per fornire l’integrale della massa solida trasportata. Sono stati compiuti 12 test simulando diverse condizioni idrodinamiche: corrente ed onde per diversi livelli di tirante (0.21 m; 0.31 m; 0.25 m) dapprima in presenza di macroalghe e successivamente su fondo nudo. Le alghe dopo essere state prelevate presso la Riserva Naturale Nazionale di Budle Bay, sulla costa nord-orientale dell’Inghilterra, sono state ripiantate nello strato di sedimenti della canaletta in modo da seguire una disposizione su linee trasversali sfalsate ricoprendo tutta la superficie della canaletta con una densità di circa 12 unità /m2. Con l’obiettivo di quantificare le osservazioni raccolte durante ciascun test ed in particolare al fine di determinare l’intervallo di tempo entro cui calcolare il valor medio delle velocità turbolente, si è inizialmente calcolata la funzione di autocorrelazione della componente longitudinale della velocità di fluttuazione. Dalla funzione di autocorrelazione si sono calcolate la microscala e la macroscala temporale per i diversi esperimenti. Al fine di calcolare la velocità di attrito ed il parametro di scabrezza di Nikuradse, si è implementata la legge universale logaritmica delle velocità media per paretri scabre. Per ottenere questi parametri, si è realizzato il fitting lineare dei dati sperimentali: dalla stima della pendenza ed intercetta si sono ottenuti la velocità di attrito ed il parametro di scabrezza. Al fine di determinare l’esistenza di una relazione statisticamente significativa tra le rette di regressione (fitting lineare per i quattro ADV nelle 4 posizioni in cui sono stati disposti gli strumenti), si è calcolato l’errore standard per la pendenza e l’intercetta da cui si sono de- terminati i relativi intervalli di confidenza al 95 %. Sia la velocità di attrito sia il parametro di scabrezza sono risultati maggiori nei test con macroalghe piuttosto che nei test senza macroalghe, confermando quanto riscontrato in letteratura sul ruolo bio-stabilizzatore delle macroalghe. Sulla base degli sforzi di Reynolds e del gradiente di velocità media si è poi calcolato il profilo verticale degli sforzi tangenziali, i quali hanno dimostrato comportamenti differenti tra i test con e senza macroalghe. Nel primo caso gli sforzi aumentano dal fondo fino ai primi centimetri per poi diminuire quasi linearmente fino alla superficie, mentre nel secondo caso diminuiscono linearmente dal fondo alla superficie. Infine con l’obiettivo di studiare la struttura della turbolenza, si è calcolato lo spettro monodimensionale dell’energia nel tempo, caratterizzato principalmente dalla presenza di vortici di piccole dimensioni corrispondenti alle alte frequenze. Per visualizzare il trend decrescente della densità di energia è stato calcolato il valor medio dell’energia (binning) nell’intervallo inerziale. Si è calcolato il fitting lineare da cui si è ottenuto il valore della pendenza. Dal confronto delle pendenze per i diversi test, si sono ottenuti valori minori per i test con macroalghe che per i test senza macroalghe, poichè si ritiene che queste ultime agiscano interferendo sulla struttura della turbolenza del campo di energia. Attraverso l’ipotesi di Taylor si è calcolata la macroscala spaziale sulla base delle fluttuazioni temporali precedentemente calcolate, in modo da produrre lo spetto monodimensionale dell’energia nello spazio. Anche in questo caso la pendenza nel test con macroalghe è risultata minore rispetto alla pendenza nei test senza macroalghe. Dall’osservazione diretta compiuta durante gli esperimenti e dai risultati ottenuti dall’elaborazione dei dati di velocità acquisiti dagli ADV, si conferma quanto riscontrato in letteratura riguardo al ruolo bio-stabilizzatore delle macroalghe, a cui si associa riduzione del campo di moto in prossimità del fondo, forme di fondo di dimensioni inferiori, minor quantità di materiale solido trasportato sia di fondo sia in sospensione.

A recognized safety issue for future fusion reactors fueled with deuterium and tritium is the generation of sizeable quantities of dust. Several mechanisms [like plasma disruptions, Edge Localized Modes (ELM) and Vertical Displacement Events (VDE)] resulting from material response to plasma bombardment in normal and off-normal conditions are responsible for generating dust of micron and sub-micron length scales inside the VV (Vacuum Vessel) of experimental fusion reactors like the International Thermonuclear Experimental Reactor (ITER). The loss of coolant accidents (LOCA), loss of coolant flow accidents (LOFA) and loss of vacuum accidents (LOVA) are types of accidents expected in experimental fusion reactors like ITER, which may jeopardize the components and the plasma vessel integrity and cause dust mobilization risk for workers and public. A small facility, Small Tank for Aerosol Removal and DUST (STARDUST), was set up to perform experiments concerning the dust mobilization in a volume with the initial condition similar to those existing in ITER VV. The aim of this work was to reproduce a low pressurization rate (300 Pa/s) LOVA event in ITER due to a small air leakage, for two different positions of the leak, at the equatorial port level and at the divertor port level, in order to evaluate a first re-suspension numerical model by the analysis of the: 1. influence of obstacles and temperature on dust resuspension during both maintenance and operative conditions; 2. The velocity field inside STARDUST. For the first experimental purpose the dusts used were tungsten (W), stainless steel (SS) and carbon (C), similar to those produced inside the vacuum chamber in a fusion reactor when the plasma facing materials vaporizes due to the high energy deposition. The experimental campaign has been carried out by introducing inside STARDUST facility an obstacle to simulate the presence of objects, like divertor and the limiter-divertor gap inside ITER VV at different temperatures (25�C maintenance conditions, 110�C during operative conditions). For the second experimental purpose, local measurements of velocity have been acquired by means of a capacitive transducer. A two-dimensional (2D) modelling of STARDUST was made with the commercial CFD code FLUENT, in order to get a preliminary overview of the fluid dynamics behaviour during a LOVA event and to justify the experimental evidence. The results of these simulations were compared against the experimental data for the CFD code validation. For validation purposes, the CFD simulation data were extracted at the same locations as the experimental data were collected. In this work, the computer-simulation data and the comparison with data collected during the laboratory studies will be presented and discussed.

The purpose of this study has two parts directed toward a common goal. First, a state-ofthe-art quarter-car test platform has been designed and constructed to offer increased testing flexibility at a reasonable cost not found commercially. With this new test rig completed, the second objective is a proof-of-concept evaluation of a well known adaptive control algorithm applied to this new quarter-car test rig for the purpose of replicating the dynamic suspension response, such as a response that was recorded during a road test. A successful application of this control algorithm on the quarter-car rig is the necessary first step toward its application on an 8-post test rig for a direct comparison to current practices. Before developing a new test rig, the current state-of-the-art in quarter-car rigs was first evaluated as well as indoor vehicle testing in general. Based on these findings, a list of desired functional requirements was defined for this new design to achieve. The new test rig was built and evaluated to determine how these goals were met and what the next steps would be to improve the rig. The study then focused on evaluating control policies used for reproducing dynamic responses on vehicle road simulators such as 4- post and 7-post shaker rigs. A least-mean squares (LMS) adaptive algorithm is introduced and applied first in software using a linear two-mass quarter-car model, and then to the actual hardware-in-the-loop quarter-car rig. The results of the study show that the resulting quarter-car test rig design is quite flexible in its ability to test a multitude of suspension designs and also its ability to accommodate new hardware in the future such as a body loaders. The study confirms that this particular implementation of the LMS algorithm is a viable option for replicating test vehicle response on an indoor quarter-car test rig. Thus, a future study to compare the use of this algorithm to the current industry standard batch processing method is possible.
Master of Science

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Universidade Federal Fluminense. Instituto de Química. Programa de Pós-Graduação em Geociências-Geoquímica. Niterói, RJ
A ressuspensão de sedimentos por processos naturais ou atividades antrópicas (como as dragagens) pode afetar a biodisponibilidade de metais-traço. Esta hipótese foi testada numa área da Baía de Sepetiba (RJ) afetada por elevada contaminação por Cd e Zn, que recebe aporte fluvial de efluentes industriais e urbanos. Desta forma, o objetivo geral do presente estudo foi avaliar os efeitos da ressuspensão de sedimentos da região afetada pelo Saco do Engenho (Baía de Sepetiba) sobre a biodisponibilidade de metais-traço potencialmente tóxicos (Cd, Cu, Ni, Pb e Zn), por meio de ensaio laboratoriais, como estratégia de abordagem visando subsidiar a avaliação de risco ambiental associado à dragagem. Amostras de 12 pontos de amostragem foram coletadas próximas ao Canal do Saco do Engenho e do Porto de Itaguaí e submetidas a dois intervalos de tempo de ressuspensão (1 hora e 24 horas). Com a exceção do Ni, os metais-traço superaram os valores de background locais. Em particular, concentrações muito elevadas de Cd e Zn foram observadas, acima dos valores de background locais 5-71 vezes e 2-56 vezes, respectivamente, e até 16 e 27 vezes acima dos valores orientadores de qualidade de sedimentos de Nível 1 adotados pela Resolução CONAMA 454/2012, respectivamente. Houve predominância da fração fracamente ligada (extraída em HCl 1 mol/L), exceto para o Ni, ocorrendo tendência de redução da biodisponibilidade potencial com a distância do Canal do Saco do Engenho em relação a Cd, Cu, Pb e Zn. As mudanças nas concentrações fracamente ligadas de Cd e Zn após a ressuspensão foram acima dos valores orientadores de Nível 1 em apenas duas amostras. Foi evidenciado que compostos de Fe e Mn são importantes fatores de influencia sobre a fração fracamente ligada aos sedimentos, enquanto o carbono orgânico total (COT) mostrou correlação com Cd, Zn e Cu na fração fortemente ligada aos sedimentos (extraída em HNO3 concentrado), demonstrando a importância da matéria orgânica para a preservação destes metais nesta fração menos susceptível a incorporação biológica. Embora tenham sido encontradas concentrações de sulfetos voláteis em meio ácido (AVS) suficientes para reter os metais simultaneamente extraídos (SEM) na fase sólida na maior parte das amostras, as concentrações de AVS não apresentaram nenhuma correlação com os metais. Os resultados evidenciam que a ressuspensão afeta a biodisponibilidade de diferentes metais, principalmente no primeiro intervalo de tempo (1 hora), refletindo mudanças abruptas em função da exposição a condições oxidantes
The re-suspension of sediments due to natural processes or anthropogenic activities (such as dredging) can influence the trace metal bioavailability. This hypothesis was tested in an area of Sepetiba Bay (RJ) affected by elevated contamination by Cd and Zn, which receive industrial and urban effluents by fluvial input. Therefore, the main objective of this study was to evaluate the effects of re-suspension of sediments from the region affected by Saco do Engenho (Baía de Sepetiba) on the bioavailability of potentially-toxic trace metals (Cd, Cu, Ni, Pb and Zn), by performing laboratory assays, as a strategy to subside the environmental risks associated to dredging. Samples from 12 sampling points were collected near the Saco do Engenho creek and the Itaguaí Harbor, being submitted to two re-suspension time intervals (1 hour and 24 hours). With the exception of Ni, trace metals exceeded local background values. In particular, very high concentrations were found for Cd (5‒71 times local background) and Zn (2‒56 times local background), corresponding to values above sediment quality guideline of Level 1 adopted by the CONAMA resolution 454/2012 (up to 16-times higher for Cd and 27-times higher for Zn). There was predominance of weakly-bound fraction (extracted in 1 mol/L HCl), except for Ni, occurring a tendency of decrease in the potential bioavailability with the distance from the Saco do Engenho creek in relation to Cd, Cu, Pb and Zn. Changes in the weakly-bound concentrations of Cd and Zn after re-suspension were above the Level 1 for two samples only. It was evidenced that Fe and Mn compounds are important factors affecting the weakly-bound fraction, while total organic carbon (TOC) showed correlations with Cd, Zn and Cu strongly-bound fraction (extracted in concentrated HNO3), demonstrating the importance of organic matter for the preservation of these metals in such fraction less susceptible to biological incorporation. Although there were acid-volatile sulfide (AVS) concentrations sufficient to retain simultaneously-extracted metals (SEM) in the solid phase in most samples, the AVS concentrations were not correlated with metals. Results evidence that re-suspension affects the bioavailability of different metals, principally in the first time interval (1 hour), reflecting abrupt changes due to exposure to oxidizing conditions

La production de pétrole s’accompagne de la formation d’émulsions eau-pétrole dont la séparation est réalisée dans des décanteurs gravitaires horizontaux fonctionnant en continu. La coalescence lente des gouttes d’eau avec l’interface huile-eau forme une zone dense (DPZ) dont les gouttes peuvent être remises en suspension et réentraînée. L’objectif de ce travail consiste à identifier et quantifier les mécanismes de réentraînement par une étude expérimentale. Un canal rectangulaire fermé par un déversoir permet de reproduire l’écoulement stratifié huile-DPZ-eau. Considérant la DPZ comme un système non coalescent, des particules solides remplacent les gouttes d’eau. Trois phénomènes ont été observés. (1) Le charriage des particules à la surface du lit. Contrôlé par la contrainte de cisaillement de l’écoulement du fluide, il apparait si la contrainte adimensionnelle thetadépasse le seuil critique de mise en mouvement estimé à theta c = 0. 23. Une fois les particules en mouvement, le débit adimensionnel de charriage est fonction de theta et s’écrit phi = 0. 417D*3/2. Theta puissance 3. 2) L’arrachage des particules du lit situées juste en amont du déversoir. Ce phénomène transitoire est dû aux recirculations du fluide devant le déversoir et apparait si theta > 0. 7theta c. (3) La déformation du lit de particules en amont du déversoir. Résultat des mécanismes précédents, une dune se crée, suivie d’une zone d’affouillement, et atteint un état stationnaire dont la position et la forme ne dépendent que de la hauteur du déversoir. Les résultats indiquent que la position de la crête de la dune xc est telle que xc /Ho = 0. 75
In crude oil industry, dispersion separation is frequently achieved using continuously running, horizontal gravity settlers designed to produce well defined layers of oil and water. The slow coalescence of the micron-sized water drops at the oil-water interface (OWI), results in an accumulation of drops called dense-packed zone (DPZ), which may be re-entrained into oil. This experimental work aimed at determining and quantifying the mechanisms of re-entrainment of the DPZ. Experiments were conducted in a rectangular open channel ended by a vertical weir in which a mineral oil and tap water were re-circulated. Assuming the DPZ as a non coalescing system, a granular non-cohesive bed was deposited at the OWI to replace the DPZ. Three phenomena were revealed. (1) Bed load transport occurred when the dimensionless shear stress exerted by oil flow on the particles exceeded a critical value theta c = 0. 23. The corresponding dimensionless bed load rate  was found to be a function of theta such that phi = 0. 417D*3/2. Theta puissance 3. (2) Transient particle re-entrainment in the vicinity of the weir. Because of the flow recirculation ahead the weir, particles were lifted and transported above the weir when theta > 0. 7theta c. These two mechanisms drove the formation and the evolution of (3) the bed deformation. Within about 150 mm upstream of the weir, the initial flat bed took the shape of a dune followed by a small scour hole. At steady state, the position and the size of the dune were independent of the operating flow rate Q but were affected by the weir height Ho. Results show that the position of the crest xc is a function of Ho such that xc /Ho = 0. 75

Durant le IVe millénaire, la Mésopotamie et ses voisins ont été reliés via un vaste réseau commercial, établi par des Urukéens lors de leur expansion en Iran et dans le Nord mésopotamien. À la fin du IVe et au début du IIIe, la Mésopotamie et ses voisins ont connu une phase de crise dont les causes nous sont toujours obscures en raison de l’absence des documents écrits remontant à cette phase. A cette phase, le réseau commercial urukéen et la colonisation urukéenne en Iran et en Mésopotamie du Nord, s’étant effondrés, les sites urukéens ont été abandonnés, ainsi qu’un grand nombre de sites indigènes qui ont été abandonnés. Le contact entre le Nord et le Sud mésopotamien fut suspendu. Pourtant, d’autres sites furent fondés que ce soit en Iran ou en Mésopotamie. Bien que la culture céramique mésopotamienne ne se soit modifiée profondément à cette phase cruciale, des traditions peintres réapparaissent soudainement alors que les Mésopotamiens les avaient abandonnées depuis 9 siècles (au Post-Obeid). Trois aires à céramique peinte apparaissent en Mésopotamie : en Irak du centre, de l’Est, du Nord (horizon de Ninive 5) et l’Iran a employé massivement la peinture. Cependant, le Sumer a conservé les traditions urukéennes qui ne connaissent pas de peinture. A noter que la peinture en Iran a été employée avant et durant l’expansion urukéenne. De plus, il semble avoir existé un corridor de contact reliant le West iranien aux trois zones à peinture en Mésopotamie. Mais comment peut-on expliquer ce phénomène de la réapparition de la peinture en Mésopotamie centrale et du Nord : s’agit-il des déplacements des groupes iraniens en Mésopotamie, ou des simples influences ? On ne peut pas traiter de la question de la fin du IVe/début du IIIe millénaire sans confronter, d’une part au problème concernant le destin des Urukéens. Ces derniers ont vécu plus de 4 siècles dans la périphérie durant l’expansion. Et d’autre part on est confronté au problème de la fondation des sites urbain aux touts début du 3e millénaire (Mari, Terqa, Kharab Sayyar et Chuera).Pour répondre à ces questions, nous avons choisi des sites-clés en Iran et en Mésopotamie. Leur céramique (et d’autre matériel) est étudié tout d’abord dans leur position stratigraphique, site par site, puis selon leur répartition dans l’espace. Au même temps, cette étude strato-céramique a été combinée avec une étude portée sur les changements dans l’occupation dans l’espace (abandon et fondation) et sur les transformations culturelles, surtout en Iran du Nord-Ouest et de l’Ouest où le phénomène de l’expansion transcaucasienne s’étend jusqu’au Kermanshah et le Nord du Luristan dans le Zagros central).Basant sur des comparaisons céramiques et sur d’autres aspects archéologiques, nous avons tenté de corréler entre la stratigraphie des sites étudiés. Nous avons évité de faire d’un site ou d’une région le « centre du monde ». Nous avons plutôt regardé chaque site et région à partir de ses voisins. A la fin de chaque partie ou chapitre, nous avons relié entre les régions étudiées, du point de vue culturel, stratigraphique et occupationnel, pour tenter de tirer une conclusion historique concernant le passage entre le IVe et le IIIe millénaires.Vers 2700-2600 av. J.-C., les traditions peintes disparaissent à nouveau de la Mésopotamie, au moment où le contact a été rétabli entre les Sumériens et le Nord mésopotamien (Mari-Brak-Chuera). Concernant cette reprise de contact, nous mettons plus l’accent sur les changements observés dans la stratigraphie (sites abandonnés et/ou incendiés) pour parler d’un phénomène que nous avons appelé la « Sumérianisation ». Nous avons tenté de repérer ce phénomène par le biais de quelques inscriptions datées du Dynastique Archaïque III (vers 2600-2500 av. J.-C.)
During the 4th millennium, Mesopotamia and its neighbours were connected by a vast trade network which was established by Urukians throughout their expansion into Iran and Northern Mesopotamia. At the end of the 4th millennium and at the beginning of the 3rd, all those regions faced a phase crisis whose causes are unknown for us because of the absence of the written documents dated to this phase. At this phase, the Uruk trade network and colonization in Iran and Northern Mesopotamia were collapsed. Uruk sites have been abandoned. In addition, a large number of indigenous sites were abandoned. The contact between Northern and Southern Mesopotamian was suspended. However, other sites were founded in Iran and Mesopotamia. Although, with this crucial phase, the Mesopotamian ceramic culture did not change deeply, the painting traditions reappeared suddenly whereas the Mesopotamian had abandoned them since 9 centuries c. (in Post-Obaid).Three zones with painted ceramics appear in Mesopotamia: centre of Iraq, Eastern Iraq, North Iraq and North-Eastern Syria. Also, Iran employed massively the painting. However, the land of Sumer conserved the Uruk traditions which aren’t painted. Worthily to be noted that the painting traditions existed in Iran before and even during the Uruk expansion. Moreover, a corridor of contact seems to have existed linking Western Iran to those three zones. But, how can one explain this reappearance phenomenon of this painting in the centre and North Mesopotamia: is-it because of the displacements of the Iranian groups into Mesopotamia or is it a simple influence? Likewise, one cannot treat the question of the end of the 4th millennium without being confronted with the problem of the destiny of the Urukians colonists. Those latter lived in the periphery more than 4 centuries during the expansion. On the other hand, one is confronted with the problem of the foundation of urban-cities with the all beginning of the 3rd millennium (Mari, Terqa, Kharab Sayyar and Chuera). To answer these questions, we chose site-keys in Iran and Mesopotamia. First of all, we studied, site by site, their ceramic (and others materials) according to their stratigraphical position (strato-ceramic), and then based on their distribution in the landscape. At the same time, those strato-ceramics analyses have been combined with another study concerning changes in the occupation of landscape (abandonment and foundation), and the cultural transformations, especially for the North-Western and Western Iran where the transcaucasian expansion extends to Kermanshah and Northern Luristan in central Zagros.Based on ceramic comparisons and on other archaeological aspects, we attempted to correlate between the stratigraphy of the studied sites. We avoided making of a site or of a region the “Center of the World”. We rather looked at each site and region starting from its neighbours. At the end of each part or chapter, we linked between the studied regions, from the cultural point of view, stratigraphic and occupational, in order to try to draw a historic conclusion concerning the passage between the 4th and the 3rd millennium.Towards 2700-2600 B.C., the painting traditions disappeared once again from Mesopotamia, at the time when the contact was restored between the Sumerians and Northern Mesopotamian (Mari-Brak-Chuera). For this resumption of contact, we set the accent more on the changes observed in the stratigraphy (abandoned sites or burned) to speak about a phenomenon which we called “the Sumerianisation”. Moreover, we tried to identify this phenomenon by the means of some inscriptions dated to the Dynastic archaic III (towards 2600-2500 B. C.)

碩士
國立臺灣大學
應用力學研究所
89
Due to the effect of rarefied gas in the micro-scale, the Navier-Stokes equation traditionally used in the continuum model is not correct any more. We have to replace it by the Boltzmann equation. This paper is divided into two parts. The first part is an analysis of the plane rarefied Couette flow of binary gas mixture in different flow field condition based on kinetic model equations and discrete ordinate method. The second part is for the first time the application of particle motion equation combined with kinetic theory results to discuss micron size particle re-suspension motion that placed into the shear/Coutte flow obtained from the first part。 The present results of macro flow properties, such as the number density, velocity and temperature etc., are in good agreement with other numerical results. In the particle trajectory analysis, we also can validate the results of nearly continuum flow with the incompressible and compressible Navier-Stokes equation solutions.

Wind induced turbidity within shallow lakes can greatly affect the biological functioning of a system in either a positive or negative manner. This research aims to understand and model the physical processes that cause sediment re-suspension. Lake St Lucia on the east coast of South Africa, a UNESCO World heritage site was used as a case study. Lake St. Lucia is a shallow water system which commonly experiences high levels of turbidity. Coupled with the naturally shallow depth of the lake, it is currently drought stricken, resulting in abnormally low water levels. A simple model has been developed which accounts for sediment re-suspension due to wind-driven waves and their associated bed shear stresses. The wave heights within a shallow lake such as St Lucia are controlled either by the fetch (for a large water depth), or the water depth (for a large fetch). When the wind is strong enough, the wind-driven turbulent mixing causes the water column to become fully mixed. When the wave-driven boundary layer becomes turbulent, sediment, being entrained within the water column increases significantly. The model also accounts for the effects of temporal consolidation on the re-suspension of sediments by setting a time scale for the erosion processes. It was found that the median of the monthly turbidity levels over the past ten years exceeded the average turbidity levels over the past 92 years. In all cases it was shown that mouth linkage with the uMfolozi resulted in lower turbidity levels than without any linkage due to the higher average water levels. The model was then developed to predict the spatial variation in turbidity within the Southern Lake. This was achieved through the use of existing bathymetric data for the Lake. This spatial model was then used to show how the turbidity varied for different wind and water depth conditions. Two conditions were considered, a NE and SW wind blowing at 8m/s for water levels of 0 EMSL and -0.5 EMSL. The spatial model showed that a decrease in water level increases the turbidity within the lake significantly. The wind directions appeared to yield similar results of sediment re-suspension. It was also shown that the high turbidity values were situated in the shallow depths even though the wave heights were small in comparison to those in deeper water.
Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2011.

碩士
中山醫學大學
職業安全衛生學系碩士班
101
The major work of this study was to investigate the characteristics of fugitive dust along the riverside included the bare land, riverbed of rivers which was caused by monsoon in Chunghwa County, Taiwan. This study was conducted for one year which began in June 29th, 2011, until June 28th, 2012. Two rivers, Wu River and Chuoshui River, were recruited in the study. VEREWA-F701 PM10, PM2.5, Micro-Orifice Uniform Deposit Impactor, and TSI 8520 DustTrak Aerosol Monitor were used to sample the concentrations of fugitive dust along the riverside during the monsoon duration. The wind speed, direction, temperature and humidity were measured by Weather Link (Davis Vantage Pro) meteorological monitoring system. The total area of bare land of riverside was estimated each season by means of the image processing techniques of satellites images and photos taken in-site. The surface layer of river sand and soil were collected (Chuoshui River), re-suspended and tested under wind tunnel by using Aerodynamic Particle Sizer. The results of wind tunnel re-suspension indicated the higher wind speed could produce higher particle concentration, and smaller modal size of the size distribution. Moreover, when the water content of the river sand was below 2.5 %, the wind tended to re-suspend the river sand easily even in 1m/s of the wind speed under the wind tunnel. However, if the water content of the river sand was above 2.5 %, even in 14 m/s of the wind speed under the wind tunnel, few particles was re-suspended by wind blow. For instance, when the water content was in 0 % and wind speed in 14 m/s, the 30-second resuspension rate of 200-gram river sand was around 32.3 – 43.9 % in Wu River, but decreased to 11.8 – 12.4 %, when the water content increased to 2.5 %. On the other hand, when the water content was in 0 % and wind speed in 14 m/s, the 30-second resuspension rate of 200-gram river sand was around 43.2 – 51.8 % in Chuoshui River, but decreased to 0 – 1.3 %, when the water content increased to 5 %. Moreover, the statistical results also showed the agreement of the above association. In both rivers, the modal size range of river sand resuspension was around 1.382~1.596 µm under water content of 0 % and wind speed of 14 m/s.