In this work the electrostatics of the pneumatic conveying of granular materials in a non-conducting (PVC) vertical pipe is studied using Electrical Capacitance Tomography (ECT) system. The non-conducting wall in general attains static charges arising from particle-wall collisions in the initial periods of conveying process and then reaches equilibrium with the surroundings. The polarity of particles and conveying pipe inner wall agrees reasonably well with the contact potential difference measurements. The perturbations in the capacitance signal due to charge accumulation are larger with smaller air superficial velocity. The denser flow regimes give larger wall residual charge. Wall charging process shows similar trend by surface potential and ECT measurements. The addition of small amount (0.5% by weight) of anti-static agent (Larostat-519) in the powder form decreases the electrostatic charge generation by altering the patterns for particle-particle and particle-wall collisions. / Singapore-MIT Alliance (SMA)

Terrestrial animals encounter natural surfaces which comprise materials that can yield and flow such as sand, rubble, and debris, yet appear to nimbly walk, run, crawl, or climb across them with great ease. In contrast, man-made devices on wheels and treads suffer large performance loss on these surfaces. Legged locomotion thus provides an excellent source of inspiration for creating devices of increased locomotor capabilities on natural surfaces. While principles of legged locomotion on solid ground have been discovered, the mechanisms by which legged animals move on yielding/flowing surfaces remain poorly understood, largely due to the lack of fundamental understanding of the complex interactions of body/limbs with these substrates on the level of the Navier-Stokes Equations for fluids. Granular media (e.g., sand) provide a promising model substrate for discovering the principles of legged locomotion on yielding/flowing surfaces, because they can display solid- and fluid-like behaviors, are directly relevant for many desert-dwelling animals, can be repeatably and precisely controlled, and the intrusion force laws can be determined empirically. In this dissertation, we created laboratory devices to prepare granular media in well-controlled states, and integrated biological, robotic, and physics studies to discover principles of legged locomotion on granular media. For both animals and bio-inspired robots, legged locomotion on granular surfaces must be achieved by limb intrusion to generate sufficient vertical ground reaction force (lift) to balance body weight and inertial force. When limb intrusion was slow (speed < 0.5 m/s), granular forces were independent of intrusion speed (dominated by grain-grain and grain-intruder friction) and generally increased with intrusion depth (due to granular hydrostatic pressure). Locomotor performance (speed) depended sensitively on limb kinematics, limb morphology, and the strength of the granular media, which together determined vertical force balance (or lack thereof). Based on these findings, we developed a granular resistive force theory in the sagittal plane as a general model for calculating forces during low-speed intrusions relevant to legged locomotion.

No description available.

Thesis (Ph.D.)--University of Delaware, 2009. / Principal faculty advisor: George C. Hadjipanayis, Dept. of Physics & Astronomy. Includes bibliographical references.

Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2002. / Includes bibliographical references (leaves 47-48). Also available in electronic version. Access restricted to campus users.

Thesis (Ph.D.) - University of Queensland, 2005. / Includes bibliography.

Made available in DSpace on 2016-06-02T20:16:45Z (GMT). No. of bitstreams: 1 2809.pdf: 1662385 bytes, checksum: 6fb1703bc2085627924b6689877b0ad9 (MD5) Previous issue date: 2010-02-26 / Universidade Federal de Sao Carlos / The maximum critical current that a granular superconductor is able to transport is, in general, limited by the critical current of the weak-links (WLs), which connect neighbor grains. For samples whose intergranular critical current distributions are sufficiently narrow, the temperature dependence of the AC-susceptibility, ( ) '( ) ''( ) AC&#967; T=&#967;T+i&#967; T, exhibits a characteristic structure, with two plateaus peaks in &#967;´ and two peaks in &#967;´´. The occurrence of an intergranular peak evidences a good control of the WL distribution concerning current transport capability, which, in general, depends on parameters that can be controlled during production of the granular samples. In order to study magnetic flux trapping in superconducting samples, one has to understand the weak-link behavior. The screening and trapping capabilities of a superconducting sample are reflected by the hysteresis loops which, properly treated, reveal the sample maximum capability to transport currents. In this work we have used niobium powder to study the magnetic response of the intergranular regions of compressed pellets; we have managed to understand the role of each of three parameters employed while preparing the pellets: pressure, grain size and its dispersion. We have studied the magnetic response (magnetization and AC susceptibility) dependence on such , controllable parameters. Dissertação de Mestrado Alonso Campoi Trípodi We noticed that samples prepared with higher pressures have larger capability to trap magnetic flux in the intergranular region and stronger WLs. On the other hand, samples with larger particles have WLs with higher critical temperatures, that is, pellets fabricated from larger particles exhibit more robust superconductivity. We have observed the Paramagnetic Meissner Effect, in the form of reentrant curves of Magnetization as a function of Temperature. Comparing pellets with different grain sizes, flux trapping was most efficient for samples with large particles and lower size dispersion. We verified also the metastable character of states prepared in such a way that flux was retained, comparing magnetization measurements before and after application of an AC field, which causes partial release of magnetic flux from intergranular regions, an effect similar to the so-called Vortex Shaking. We also conducted experiments as a function of the applied magnetic field the hysteresis loops aiming at obtaining the magnetic field dependence of the critical current, employing a critical state model for this task. We verified that, for lower temperatures, the critical current density is higher for pellets with larger particles and narrow size dispersion. In summing up, our results clearly indicate that, for a certain granulometry, larger compacting pressures lead to more diamagnetic responses, as well as to WLs with narrower superconducting transitions which turn off at larger temperatures. On the other hand, for a certain compacting pressure in pellets with narrow size dispersions, larger particles lead to stronger WLs. / A máxima corrente crítica que pode ser transportada através de um supercondutor granular é, em geral, limitada pela corrente crítica dos elos fracos (EFRs) que acoplam grãos vizinhos. Para amostras cuja distribuição de correntes críticas intergranulares é suficientemente estreita, a dependência da suscetibilidade-AC com a temperatura, ( ) '( ) ''( ) AC&#967; T=&#967;T+i&#967; T, exibe uma estrutura característica, com dois patamares em &#967; ' e dois picos em &#967; '' . A ocorrência de um pico intergranular estreito evidencia um bom controle da distribuição dos EFRs no que se refere à sua capacidade de transporte, o quê, em geral, depende de parâmetros que podem ser controlados durante a produção de amostras granulares. Para estudar a retenção de fluxo magnético em amostras supercondutoras é preciso entender o comportamento dos elos fracos. A capacidade de blindagem e aprisionamento de uma amostra supercondutora reflete-se diretamente em seu ciclo de histerese que, devidamente tratado, revela a máxima capacidade de transporte de corrente da amostra. Neste trabalho de mestrado, utilizamos pó de nióbio para estudar a resposta magnética das regiões intergranulares de pastilhas formadas a partir da compactação do pó, tratando de compreender o papel de três parâmetros empregados na preparação da pastilha: a pressão de compactação do pó, o tamanho dos grãos e a sua dispersão. Estudamos a dependência da resposta magnética (magnetização e suscetibilidade AC) com tais parâmetros controláveis. Dissertação de Mestrado Alonso Campoi Trípodi Constatamos que amostras preparadas com maiores pressões têm maior capacidade de aprisionamento de fluxo magnético na região intergranular e EFRs mais fortes. Por outro lado, amostras com partículas maiores têm EFRs com temperaturas críticas mais altas, ou seja, pastilhas fabricadas com partículas maiores exibem uma supercondutividade mais robusta. Observamos o Efeito Meissner Paramagnético, na forma de reentrâncias em curvas de Magnetização em função da Temperatura. Comparando pastilhas com diferentes tamanhos de grãos, o ancoramento dos fluxo foi mais eficaz em amostras com partículas grandes e pequena dispersão de tamanho. Verificamos também o caráter metaestável de estados preparados de modo que houvesse fluxo aprisionado, comparando medidas de magnetização antes e depois da aplicação de um campo AC, que causa desprendimento parcial do fluxo magnético aprisionado em regiões intergranulares, efeito similar ao chamado Vortex Shaking. Realizamos também experimentos em função do campo magnético aplicado - os chamados laços de histerese - com vistas à obtenção da dependência da corrente crítica com o campo magnético aplicado, empregando para isso um modelo de estado crítico. Verificamos que para temperaturas mais baixas a densidade de corrente crítica é maior para pastilhas com partículas maiores e pequena dispersão de tamanho. Em resumo, nossos resultados indicam claramente que, para uma mesma granulometria, maiores pressões de compactação propiciam respostas mais diamagnéticas, bem como EFRs com transições mais estreitas e que desligam em temperaturas mais altas. Por outro lado, para uma mesma pressão de compactação em pastilhas com pequena dispersão de tamanho, partículas maiores levam à criação de EFRs mais fortes.

The research reported in this thesis is concerned with the flow of granular systems in response to penetration and compaction. The technique of Digital Speckle Radiography (DSR), which involves analysis of flash X-ray images, has been applied to measure the internal displacement fields within large opaque granular samples. Large samples are desirable as the measured displacements are more representative of the bulk. Current DICC algorithms were found to be unsuitable for analysis of X-ray images of large samples. The large contrast variations present in such X-ray images, due to the X-ray beam profile, sample geometry and the high X-ray absorbance of metal penetrators, are shown to cause significant errors in the calculated displacement fields. A study of image normalisation techniques was carried out, and the effect of each technique on the accuracy of the measured displacements was investigated. A new DICC algorithm for use in DSR was produced which includes image normalisation techniques to correct for uneven contrast in the images. This new DICC algorithm was shown to be far more effective at analysing X-ray images of large samples. This improved DSR technique was applied to measure the internal displacements within a large sample of sand during penetration by projectiles with different nose-shapes (flat, ogive-2 and hemispherical) and at different rates (1.5 mm/min to 200 m/s). The improved technique was found to provide high-resolution displacement data illustrating the response of the material. The dominant material response at low rates (1.5 mm/min) was found to be splitting of the material ahead of the projectile tip, followed by bulk reverse-flow of material towards the penetration face. At the higher rates (200 m/s), the dominant response was compaction of the material ahead of the projectile tip. The transition between the two regimes was found to occur between velocities of 5 and 19 m/s. The streamlined ogive-2 projectile nose-shape was shown to be the most effective for penetration, in that it caused less disruption of the material ahead of the projectile, lost less energy during the early stages of penetration in the dynamic experiments and more effectively split the material ahead of the projectile tip, a process which was shown to be important at all rates of penetration. The compaction properties of a particulate mixture and a granular material, including the effect of factors such as porosity, initial particle arrangement and force chain formation, were investigated. Samples which were conducive to the formation of force chains spanning the whole sample were discovered to have anomalously high strengths. Small amounts of added water were shown to increase the compactability, by lubricating the grain contact points, but larger amounts of water decreased the compactability.

D.Ing. / The quantification of the surface roughness in order to determine the shear behaviour of rock joints has been performed using many approaches, amongst which the most important are the joint roughness coefficient, statistical methods and the fractal approach. None of these approaches explicitly considers the contribution of grain size to the creation of surface roughness. An investigation has been undertaken to determine whether the grain size may be related to the surface roughness characteristics and also to assess its impact on the shear behaviour of rock joints. The influence of grain size on the shear behaviour of rock joints has been experimentally and numerically studied using a profile measurement approach followed by shear tests in the laboratory. Fresh rock joints in model material made of aggregates of no rite in resin and two natural rock types, namely norite and sandstone, were used for the investigation. A numerical analysis of the study has been performed using the Particle Flow Code PFC20 • Investigation of the model material has resulted in the conceptualisation of grain size parameters. Of the proposed grain size parameters, the average particle size index As has been successfully used to define the particle size distribution of a rock joint for both physical and numerical tests. From the profile measurements, four roughness parameters, n~mely the average inclination angle I, the root mean square of the first derivative Z2, the modified root mean square of the first derivative Z2' and the fractal dimension D, have been computed and a regression analysis conducted. Physical and numerical results have demonstrated that grain size distribution, expressed in terms of average particle size index As shows a good correlation respectively with the root mean square ofthe first derivative Z2, and its modified version Z2'. The root mean square of the first derivative Z2, and the modified root mean square of the first derivative Z2' increase with the average particle size index As. However, no correlation has been found between the grain size parameter and the fractal dimension D or the average inclination angle I. It has also been found that the joint roughness coefficient JRC and the peak friction angle ~P correlate very well with the average particle size index As. The greater the average particle grain size the higher the joint roughness coefficient JRC and the peak friction angle ~p· The type of correlation between JRC and ~P with As depends on the rock type. Exponential shear strength model has been derived where the average particle size index As is related to the peak friction angle via the residual friction angle ~r·

Orientador: Ricardo de Lima Isaac / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Civil, Arquitetura e Urbanismo / Made available in DSpace on 2018-08-26T15:48:00Z (GMT). No. of bitstreams: 1 Reis_Gabrielados_M.pdf: 4501335 bytes, checksum: f41add1d19b9cc7987740fb6604a17ed (MD5) Previous issue date: 2014 / Resumo: Dentre as etapas do tratamento de água para abastecimento público a filtração é essencial para remoção de partículas e microorganismos nocivos à saúde humana. Devido ao reduzido tamanho e resistência à cloração, os oocistos de Cryptosporidium tornam-se um problema nas estações de tratamento de água. Neste estudo foi investigada a eficiência da filtração em meio granular constituído de areia recoberta com nanopartículas de prata na remoção de microesferas de poliestireno, que simulam oocistos de Cryptosporidium spp.. A presença das nanopartículas de prata pode ser uma barreira adicional no tratamento de água, proporcionando ao grão de areia uma camada positiva, auxiliando na remoção de oocistos. O sistema de filtração em escala de laboratório foi composto de microcolunas de vidro borossilicato (diâmetro interno 1 cm) preenchidas com areia previamente impregnadas por imersão em solução de nanopartículas de prata (concentração 0,1 g/L). Os filtros foram alimentados por uma suspensão de água deionizada contendo microesferas de poliestireno (diâmetro médio 2 ?m). A influência na qualidade da água na filtração foi avaliada quanto aos parâmetros: concentração de ácido húmico (2,5, 5,0 e 10,0 mg.L-1), pH (6, 7 e 8), força iônica (24, 48 e 105 mM) e concentração inicial de microesferas (1,3 x 105, 2,4 x 106 e 1,4 x 107 partículas/mL). O efeito do parâmetro taxa de filtração foi avaliado sob a condição operacional de 2,4, 4,8 e 48 m3/m2.dia. A remoção de partículas do filtro proposto foi da ordem de 99,0 % contra 92,0 % do filtro controle. Os filtros teste constituídos de camada de areia recoberta com prata tiveram desempenho superior, na remoção da turbidez, aos filtros controle, com eficiência de remoção da ordem de 81,1 %, ao se filtrar até 10 VP (volume de poros). Contudo, a turbidez não se mostrou um bom indicativo da remoção de microesferas. A impregnação por nanopartículas de prata tornou os filtros mais eficientes na remoção de microesferas de poliestireno que simulam oocistos de Cryptosporidium / Abstract: Among the steps in treating water for public supply filtration is essential for removal of particles and microorganisms harmful to human health. Due to the small size and resistance to chlorination, Cryptosporidium oocysts become a problem in water treatment stations. This study investigated the efficiency of the filtration medium consisting of granular sand coated with silver nanoparticles in the removal of polystyrene microspheres that simulate Cryptosporidium spp.. Presence of silver nanoparticles can be an additional barrier for water treatment, providing a positive layer, aiding in the removal of oocysts. The filtration laboratory scale system was composed of borosilicate glass micro columns (inner diameter 1 cm) filled with sand previously impregnated by immersion in a solution of silver nanoparticles (concentration 0.1 g/L). The filters were fed with a suspension of deionized water containing polystyrene microspheres (mean diameter 2 ?m). The influence on water quality in filtration was evaluated for the following parameters: concentration of humic acid (2.5, 5.0 and 10.0 mg.L-1), pH (6, 7 and 8), ionic strength (24, 48 and 105 mM) and initial concentration of microspheres 1.3 x 105, 2.4 x 106 and 1.4 x 107 particles/ml). The effect of the filtration rate parameter was evaluated under operating conditions of 2.4, 4.8 and 48 m3/m2.day. The removal of particles of test filter was approximately 99.0 % compared with 92.0 % of the control filter. The test filters consisting of silver coated sand layer exhibited superior performance in the removal of turbidity, the control filters, with removal efficiency of about 81.1 % when filtering up to 10 filter PV (pore volume). However, turbidity was not a good indicator of removal of microspheres. The impregnation with silver nanoparticles made filters more effective on the removal of polystyrene microspheres that simulate Cryptosporidium oocysts / Mestrado / Saneamento e Ambiente / Mestra em Engenharia Civil