Search

Dust generation when handling wood pellets is related to the durability of the product, in other words the wear rate of particles subject to forces. During transport, storage and handling wood pellets undergo different forces when interacting with different pieces of equipment.This paper assesses the representativeness of the tumbling can test in relation to transfer chutes, by comparing forces acting on wood pellets in durability tests and in transfer chutes using DEM. The study also incorporates effects such as shape and size variations. The results showed that the tumbling can test underestimates compressive and tangential forces. Since the tested material is subject to milder conditions than in reality, it can be concluded that this test is not representative for the conditions in the supply chain of wood pellets.

Avalanches, debris flows, and landslides are geophysical hazards, which involve rapid mass movement of granular solids, water and air as a single-phase system. The dynamics of a granular flow involve at least three distinct scales: the micro-scale, meso-scale, and the macro-scale. This study aims to understand the ability of continuum models to capture the micro-mechanics of dry granular collapse. Material Point Method (MPM), a hybrid Lagrangian and Eulerian approach, with Mohr-Coulomb failure criterion is used to describe the continuum behaviour of granular column collapse, while the micromechanics is captured using Discrete Element Method (DEM) with tangential contact force model. The run-out profile predicted by the continuum simulations matches with DEM simulations for columns with small aspect ratios (‘h/r’ < 2), however MPM predicts larger run-out distances for columns with higher aspect ratios (‘h/r’ > 2). Energy evolution studies in DEM simulations reveal higher collisional dissipation in the initial free-fall regime for tall columns. The lack of a collisional energy dissipation mechanism in MPM simulations results in larger run-out distances. Micro-structural effects, such as shear band formations, were observed both in DEM and MPM simulations. A sliding flow regime is observed above the distinct passive zone at the core of the column. Velocity profiles obtained from both the scales are compared to understand the reason for a slow flow run-out mobilization in MPM simulations.

Orientador: Antônio Carlos de Oliveira Ferraz Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Agrícola Resumo: A determinação da força de ruptura de agregados é útil para avaliar as propriedades físicas do solo e para modelar a ruptura de agregados porosos, que é de suma importância para simular fenômenos naturais envolvendo fragmentação de material e melhorar os processos tecnológicos. Por exemplo, projetar ferramentas de cultivo para promover apenas a quantidade necessária de fragmentação do solo com maior eficiência energética tem grande potencial para reduzir os custos de produção concomitantemente com os impactos ambientais. Aqui, propusemos um critério para determinar a resistência à compressão do agregado, considerando que a força de ruptura ocorre simultaneamente com o surgimento de trincas na região equatorial dos agregados (EC). Demonstramos que o EC é um procedimento empírico mais confiável para determinar a resistência à compressão do agregado e, ao usar EC, o modelo em Elementos Discretos (DEM) apresentou maior assertividade. Com base em tais critérios, simulações numéricas em DEM mostraram uma correlação linear entre friabilidade e dimensão fractal de agregados porosos. Em seguida, combinando simulações numéricas com medições em laboratório, estabelecemos um uso exclusivo de friabilidade como uma propriedade macro material para determinar a força de ligação entre as partículas e a densidade de diferentes tamanhos de agregados. Isso permite a parametrização de um modelo DEM para simular como a resistência à tração varia em função do tamanho do agregado. Implementamos este método de parametrização para criar uma caixa de solo contendo diferentes tamanhos de agregados usando o DEM e desenvolvemos uma função para medir o nível de fragmentação de materiais granulares. Usando essa abordagem numérica, simulamos atividades cultivo de solo e criamos um novo conceito de ferramenta de preparo do solo para o plantio de cana-de-açúcar. Esta ferramenta mostrou potencial para diminuir a demanda de energia em 28,5% ao mesmo tempo em que aumenta a a fragmentação fractal em 10% em comparação com a ferramenta convencional. A partir dessas simulações, estimamos que a implementação da nova ferramenta na produção brasileira de cana-de-açúcar possa reduzir o consumo de combustível na ordem de 44% Abstract: Determining the aggregate compressive rupture force is useful to assess soil physical properties and to model rupture of porous aggregates, which is paramount to simulate natural phenomena involving material fragmentation and to improve technological processes. For instance, designing tillage tools to promote only the necessary amount of soil fragmentation with higher energy efficiency have great potential to reduce production costs concomitantly with environmental impacts. Here, we proposed a criteria to determine aggregate tensile strength, considering that the aggregate rupture force occurs simultaneously with aggregate equatorial cracks (EC). We demonstrated that EC is a more reliable empirical procedure to determine aggregate tensile strength and when using EC, the Discrete Element (DEM) model displayed greater assertiveness. Based on such criteria, numerical simulations in DEM showed a linear correlation between friability and fractal dimension of porous aggregates. Then, combining numerical simulations with laboratory measurements, we established a unique use of friability as a material macro property to determine the particle bond strength and density for different aggregate sizes. This allows parameterisation of a discrete element model to simulate how tensile strength varies as a function of aggregate size. We implemented this parameterization method to simulate a soil bin containing a range of aggregate sizes using DEM and developed a function to measure the fragmentation level of granular materials. Using this numerical approach we simulated tillage activities and designed a new concept of tillage tool for sugarcane planting. This tool showed potential to decrease the power demand by 28.5% at the same time it increases the fractal fragmentation by 10% in comparison to the conventional tool. From these simulations we estimated that the implementation of the new tool in the Brazilian sugarcane production may reduce fuel consumption by the order of 44% Doutorado Máquinas Agrícolas Doutor em Engenharia Agrícola CNPQ 140188/2018-5 CAPES 88881.131855/2016-01