Academic literature on the topic 'Re-suspension'

Abstract. The long-term effect of 137Cs re-suspension from contaminated soil and forests due to the Fukushima nuclear accident has been quantitatively assessed by numerical simulation, a field experiment on dust emission flux in a contaminated area (town of Namie, Fukushima prefecture), and air concentration measurements inside (Namie) and outside (city of Tsukuba, Ibaraki prefecture) the contaminated area. In order to assess the long-term effect, the full year of 2013 was selected to study just after the start of the field experiments. The 137Cs concentrations at Namie and Tsukuba were approximately 10−1–1 and 10−2–10−1 mBq m−3, respectively. The observed monthly median concentration at Namie was 1 to 2 orders of magnitude larger than that at Tsukuba. This observed difference between the two sites was consistent with the simulated difference, indicating successful modeling of 137Cs re-suspension and atmospheric transport. The estimated re-suspension rate was approximately 10−6 day−1, which was significantly lower than the decreasing rate of the ambient gamma dose rate in Fukushima prefecture (10−4–10−3 day−1) as a result of radioactive decay, migration in the soil and biota, and decontamination. Consequently, re-suspension contributed negligibly in reducing ground radioactivity. The dust emission model could reproduce the air concentration of 137Cs in winter, whereas the summer air concentration was underestimated by 1 to 2 orders of magnitude. Re-suspension from forests at a constant rate of 10−7 h−1, multiplied by the green area fraction, could explain the air concentration of 137Cs at Namie and its seasonal variation. The simulated contribution of dust re-suspension to the air concentration was 0.7–0.9 in the cold season and 0.2–0.4 in the warm season at both sites; the remainder of the contribution was re-suspension from forest. The re-suspension mechanisms, especially through the forest ecosystems, remain unknown. This is the first study that provides a crude estimation of the long-term assessment of radiocesium re-suspension. Additional research activities should investigate the processes/mechanisms governing the re-suspension over the long term. This could be achieved through conducting additional field experiments and numerical simulations.

A micro-thermistor probe was inserted into the buccal cavity of freely swimming paddlefish to measure flow velocity during ram ventilation, ram suspension feeding and prey processing. Swimming speed was measured from videotapes recorded simultaneously with the buccal flow velocity measurements. Both swimming velocity and buccal flow velocity were significantly higher during suspension feeding than during ram ventilation. As the paddlefish shifted from ventilation to feeding, buccal flow velocity increased to approximately 60 % of the swimming velocity. During prey processing, buccal flow velocity was significantly higher than the swimming velocity, indicating that prey processing involves the generation of suction. The Reynolds number (Re) for flow at the level of the paddlefish gill rakers during feeding is about 30, an order of magnitude lower than the Re calculated previously for pump suspension-feeding blackfish. These data, combined with data available from the literature, indicate that the gill rakers of ram suspension-feeding teleost fishes may operate at a substantially lower Re than the rakers of pump suspension feeders.

The flow of a suspension through a bifurcating channel is studied experimentally and by computational methods. The geometry considered is an ‘asymmetric T’, as flow in the entering branch divides to either continue straight or to make a right angle turn. All branches are of the same square cross-section of side length $D$, with inlet and outlet section lengths $L$ yielding $L/D=58$ in the experiments. The suspensions are composed of neutrally buoyant spherical particles in a Newtonian liquid, with mean particle diameters of $d=250~\unicode[STIX]{x03BC}\text{m}$ and $480~\unicode[STIX]{x03BC}\text{m}$ resulting in $d/D\approx 0.1$ to $d/D\approx 0.2$ for $D=2.4~\text{mm}$. The flow rate ratio $\unicode[STIX]{x1D6FD}=Q_{\Vert }/Q_{0}$, defined for the bulk, fluid and particles, is used to characterize the flow behaviour; here $Q_{\Vert }$ and $Q_{0}$ are volumetric flow rates in the straight outlet branch and inlet branch, respectively. The channel Reynolds number $Re=(\unicode[STIX]{x1D70C}DU)/\unicode[STIX]{x1D702}$ was varied over $0<Re<900$, with $\unicode[STIX]{x1D70C}$ and $\unicode[STIX]{x1D702}$ the fluid density and viscosity, respectively, and $U$ the mean velocity in the inlet channel; the inlet particle volume fraction was $0.05\leqslant \unicode[STIX]{x1D719}_{0}\leqslant 0.30$. Experimental and numerical results for single-phase Newtonian fluid both show $\unicode[STIX]{x1D6FD}$ increasing with $Re$, implying more material tending toward the straight branch as the inertia of the flow increases. In suspension flow at small $\unicode[STIX]{x1D719}_{0}$, inertial migration of particles in the inlet branch affects the flow rate ratio for particles ($\unicode[STIX]{x1D6FD}_{\mathit{particle}}$) and suspension ($\unicode[STIX]{x1D6FD}_{\mathit{suspension}}$). The flow split for the bulk suspension satisfies $\unicode[STIX]{x1D6FD}>0.5$ for $\unicode[STIX]{x1D719}_{0}<0.16$ while $\unicode[STIX]{x1D719}_{0}=0.16$ crosses from $\unicode[STIX]{x1D6FD}\approx 0.5$ to $\unicode[STIX]{x1D6FD}>0.5$ at $Re\approx 100$. For $\unicode[STIX]{x1D719}_{0}\geqslant 0.2$, $\unicode[STIX]{x1D6FD}<0.5$ at all $Re$ studied. A complex dependence of the mean solid fraction in the downstream branches upon inlet fraction $\unicode[STIX]{x1D719}_{0}$ and $Re$ is observed: for $\unicode[STIX]{x1D719}_{0}<0.1$, the solid fraction in the straight downstream branch initially decreases with $Re$, before increasing to surpass the inlet fraction at large $Re$ ($Re\approx 500$ for $\unicode[STIX]{x1D719}_{0}=0.05$). At $\unicode[STIX]{x1D719}_{0}>0.1$, the solid fraction in the straight branch satisfies $\unicode[STIX]{x1D719}_{\Vert }/\unicode[STIX]{x1D719}_{0}>1$, and this ratio grows with $Re$. Discrete-particle simulations employing immersed boundary and lattice-Boltzmann techniques are used to analyse these phenomena, allowing rationalization of aspects of this complex behaviour as being due to particle migration in the inlet branch.

The centrifugo-pneumatic particle sedimentation, re-suspension and transport do not require any auxiliary means besides rotation and can be used for magnetic or non-magnetic particles with different particle sizes and densities.

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

In June 1975 Prime Minister Indira Gandhi imposed a state of emergency, resulting in a twenty-one-month suspension of democracy. Jaffrelot and Anil revisit the Emergency to re-evaluate characterisations of India as the ‘world’s largest democracy.’ They explore India’s first experiment with authoritarianism, which resulted in a constitutional dictatorship with an unequal impact across states. The impact was felt more strongly in the capital, its neighbouring states and in the Hindi belt than in states ruled by the opposition—the North East and South India. This was largely due to the resilience of federalism and local socio-political factors in these regions. India’s First Dictatorship focuses on Mrs Gandhi and her son, Sanjay, who was largely responsible for the mass sterilization programs and deportation of urban slum-dwellers. However, it equally exposes the facilitation of authoritarian rule by Congressmen, Communists, trade unions, businessmen and the urban middle class, as well as the complacency of the judiciary and media. While opposition leaders eventually ended up in jail, many of them—especially in the RSS—tried to collaborate with the new regime. Those who resisted the Emergency, in the media or on the streets, were far and few between. The Emergency accentuated India’s political culture, which is reflected in the current zeitgeist, as the illiberal aspects of Indian democracy yet again resurface with the rise of Hindu nationalist authoritarian populism. This episode was neither a parenthesis nor a turning point, but a style of rule that is very much alive today.

The historical development of Istanbul’s gecekondu areas (informally-originated neighborhoods) can be broadly interpreted as a progression toward the center and subsequent re-peripheralization, both in sociopolitical terms and in actual urban geography. While Istanbul emerged in recent decades as a magnet for transnational migrants and for capitals pouring into the debt-fueled real estate sector, many such neighborhoods have been targeted by speculative socio-spatial restructuring projects, while also absorbing much of the migratory influx. The recent economic crisis plunged these urban redevelopment sites into a deadlock, generating a fragmented urbanscape in which multiple layers of uncertainty, suspension, and informalization overlap and interact. This chapter explores the unfolding transformation in Fikirtepe, the largest ongoing redevelopment project in the city, which has seen its social and urban fabric torn apart by the redevelopment and is currently stuck in an unstable but protracted limbo. As Fikirtepe becomes “unlivable” for many of its long-time dwellers, a number of migrants are moving in, etching out a living: a collateral effect of redevelopment failure, creating a space of opportunity for new disenfranchised populations with varied backgrounds, legal statuses, and life trajectories. Within this setting, this chapter analyzes the periphery as a condition that is articulated, reproduced, and transformed through embodied practices. With their practices, narratives, and trajectories, those who inhabit such botched urban transformation embody different layers of the periphery, contributing to shape an understanding of it as a perspectival condition with a polyvalent spatiality and temporality.

During normal operation of the ITER tokamak, few hundred kilograms of dust containing beryllium (Be) and tungsten (W) will be produced due to the erosion of the walls of the vacuum chamber by the plasma. During a loss of coolant accident (LOCA) or a loss of vacuum accident by air ingress (LOVA), hydrogen could be produced by dust oxidation with steam. Evaluation of the risk of dust and hydrogen explosion, that may lead to a loss of containment, requires studying the physical processes involved in the dust re-suspension and its distribution in the tokamak chamber. This experimental study is conducted by the Institut de Radioprotection et de Sûreté Nucléaire (IRSN) to simulate dust re-suspension phenomena induced by high velocity jet under low pressure conditions. Tests are conducted in a large scale facility (TOSQAN, 7 m3) able to reproduce primary vacuum conditions (1 mbar). Optical diagnostics such as PIV technique (Particles Image Velocimetry) are implemented on the facility to provide time resolved measurements of the dust re-suspension in terms of phenomenology and velocity. We present in this paper the TOSQAN facility with its configuration for studying dust re-suspension under low pressure conditions and underway experiments showing the mechanism of dust re-suspension by sonic and supersonic flows.

Cold heat storage utilizing night-time electricity is one of the relevant technologies for the electric load leveling. Latent heat storage system with a large number of small paraffin particles is one of the promising technologies for the cold heat storage system. Small paraffin particles are generated by nozzle injection of liquid paraffin into cold water. Direct heat transfer between the ascending particles and surrounding cold water enhances the storage of latent heat in a short time. Transportation of solid paraffin particles suspended in water should be the best way to transport cold heat, because the density of cold heat stored in water/paraffin-particle mixture is very high. The present paper aims at investigating flow patterns and pressure loss of water/nonadecane-particle mixture flowing in horizontal and vertical pipes. The inner diameter and the average diameter of the nonadecane particle were 20mm and 3.7mm, respectively. Reynolds number, Froude number and volumetric concentration of nonadecane particles were varied in the ranges of 5000 ≤ Re ≤ 80000, 1 ≤ Fr ≤ 260 and 0.02 ≤ Cv ≤ 0.25. We found the following main results: (1) Four flow patterns were observed in the horizontal flow, (a) flow with a stationary particle bed, (b) flow with a sliding particle layer (c) heterogeneous suspension flow and (d) homogeneous suspension flow. The flow pattern shifted from (a) to (d) with increasing Reynolds number. (2) Homogeneous suspension flow was observed in the vertical up-flow. (3) Homogeneous and heterogeneous suspension flow was observed in the vertical down-flow. (4) The pressure loss coefficients λ of the horizontal flow were correlated by a function of λ and Re (λ = 0.479 Re−0.311) for the heterogeneous and homogeneous suspension flows (Re ≥ about 25000) and by a function of the excess pressure loss coefficient Φ, Fr and Cv (φ/Cv0.58 = 72.4Fr−1.25) for the flow with a sliding particle layer (Re ≤ about 20000). (5) The pressure loss coefficients of the vertical up-flow were correlated by a function of λ and Re (λ = 4.45 Re−0.501) in a large Reynolds number range of Re ≥ about 40000 and by a function of Φ, Fr and Cv (φ/Cv0.47 = 282Fr−1.47) in a small Reynolds number range of Re ≤ about 40000. (6) The pressure loss coefficients of the vertical down-flow were correlated by a function of Φ and Fr (φ = 73.0Fr−0.765).

A project to design and implement suspension improvements to Amtrak’s F-40 Non-Powered Control Unit (NPCU) cars is described. The cars, built from former F-40 locomotives, had a history of poor ride quality. Rail Sciences Inc. (RSI) inspected one of the cab cars and measured its ride quality. Peter Klauser modeled the vehicle in NUCARS™ and validated the model against the test data. The vehicle response was primarily in pitch and bounce modes. To optimize the suspension, Klauser simulated vehicle response for a range of four suspension parameters: primary stiffness and damping, and secondary stiffness and damping. Nearly 2600 suspension combinations were considered. Simulation file setup and data analysis were performed automatically using parameter analysis software interacting with NUCARS™. The result was a five-dimensional response contour for each output variable, such as the engineer’s seat vertical and lateral accelerations, and car body acceleration. The most cost effective stiffness and damping parameters were selected from the response contour and translated into component specifications. RSI then provided Amtrak with new axle box springs and dampers, and re-tested the vehicle. The test result closely followed the predicted results from the simulation. Engineer’s seat vertical and cab lateral accelerations improved by 42% and 32% respectively for the worst-case conditions in the test territory.

Since the outbreak of COVID-19 at the end of 2019, the pandemic has brought both social and economic impacts to global communities, although to varying degrees. Since the onset of the pandemic, different regions have responded in various ways by taking different measures to fight the pandemic and its effects. In Tanzania, the first case was recorded on 16 March 2020 and, to contain the spread of the virus, on 17 March 2020, the Prime Minister announced measures including the closure of all education institutions, the suspension of public gatherings and international passenger flights, and mandatory quarantine for individuals entering Tanzania. However, in June 2020, the government announced the easing of the restrictions after observing a significant decrease in the COVID-19 infection rate and, despite a subsequent ‘second wave’ of the virus, the government declined to re-institute movement restrictions. This decision led to the implementation of non-tariff trade barriers which were imposed on cargo carrying grain and other exports to neighbouring countries, especially Kenya. The situation became so bad that diplomatic intervention had to be sought. In order to understand the resulting socio-economic impacts of the COVID-19 crisis in Tanzania, data were collected in three waves during mid-July2020, October 2020 and February 2021. This paper presents a synthesis of the results of these three survey rounds.