An iterative Bayesian filtering framework for fast and automated calibration of DEM models

The nonlinear, history-dependent macroscopic behavior of a granular material is rooted in the micromechanics between constituent particles and irreversible, plastic deformations reflected by changes in the microstructure. The discrete element method (DEM) can predict the evolution of the microstructure resulting from interparticle interactions. However, micromechanical parameters at contact and particle levels are generally unknown because of the diversity of granular materials with respect to their surfaces, shapes, disorder and anisotropy. The proposed iterative Bayesian filter consists in recursively updating the posterior distribution of model parameters and iterating the process with new samples drawn from a proposal density in highly probable parameter spaces. Over iterations the proposal density is progressively localized near the posterior modes, which allows automated zooming towards optimal solutions. The Dirichlet process Gaussian mixture is trained with sparse and high dimensional data from the previous iteration to update the proposal density. As an example, the probability distribution of the micromechanical parameters is estimated, conditioning on the experimentally measured stress–strain behavior of a granular assembly. Four micromechanical parameters, i.e., contact-level Young’s modulus, interparticle friction, rolling stiffness and rolling friction, are chosen as strongly relevant for the macroscopic behavior. The a priori particle configuration is obtained from 3D X-ray computed tomography images. The a posteriori expectation of each micromechanical parameter converges within four iterations, leading to an excellent agreement between the experimental data and the numerical predictions. As new result, the proposed framework provides a deeper understanding of the correlations among micromechanical parameters and between the micro- and macro-parameters/quantities of interest, including their uncertainties. Therefore, the iterative Bayesian filtering framework has a great potential for quantifying parameter uncertainties and their propagation across various scales in granular materials

Effects of reservoir compaction on seismic and gravity monitoring

The compacting reservoir embedded in a homogeneous, isotropic and elastic medium, known as Geertsma’s model, is a model commonly used in feasibility studies for forecasting time-lapse changes due to hydrocarbon production. The scope of the thesis is to include a rigid basement to Geertsma’s formulation, and to study how breaking the model symmetry affects the estimated changes in reservoir monitoring. The objective of introducing the rigid basement is to capture a general increase in rock stiffness with depth. In this way, the model narrows the gap between the analytical modelling and the effective deformation of the rocks surrounding the reservoir . The ultimate goal is to get a better estimation of the time-lapse changes expected from reservoir compaction. An analytical solution for the displacement field caused by the compacting reservoir above a rigid basement is derived. The analytical model is introduced in a forward model for forecasting time-lapse changes in seismic monitoring and gravity monitoring. The results obtained in this way are compared with those obtained using Geertsma’s model for the same forward model. The most visible effects of the presence of the rigid basement are the increase of subsidence and the lowering of the top reservoir. Relevance should be also given to the increase of vertical stretching in the overburden and a corresponding stretching decrease in the underburden. In the time-lapse seismic modelling, these effects result in higher time-shifts in the overburden and lower in the underburden. In the time-lapse gravity modelling, the redistribution of the rocks around the compacting reservoir above the rigid basement causes a visible change in gravity, otherwise negligible in the homogeneous half-space. By extending Geertsma’s solution with a rigid basement below the compacting reservoir, the thesis provides a model that can reproduce the geomechanical behaviour of a subsurface where rock stiffness increases with depth. The model needs few parameters, and it can be implemented in a code that uses Geertsma’s solution. A feasibility study that includes the rigid basement model could bring interesting information to be taken into consideration in production management.

Construindo coletivamente os saberes docentes

This study aims to present the extension project " Formation Group: Dialogue and Otherness" which is part of a range of projects from the University Estadual Paulista (UNESP), Campus of Rio Claro. Consider paramount the importance of this training space, since it provides direct contact of the academic community with the school environment. Assuming that both the university as a school are institutions that produce knowledge on education, provides the ability to leverage one another, we emphasize that to relate cause several benefits in both contexts. We emphasize that within the university our project provides the host Full in Education Degree Course students often encounter difficulties in coping with issues involving the complex school environment and the teaching profession, however, linking theories and practices socialized the group has collectively finding ways to overcome these challenges.O presente trabalho visa apresentar o projeto de extensão “Grupo de Formação: Diálogo e Alteridade” que faz parte de uma gama de projetos de extensão da Universidade Estadual Paulista (UNESP), Câmpus de Rio Claro. Consideramos primordial pontuarmos a importância desse espaço formativo, uma vez que o mesmo proporciona o contato direto da comunidade acadêmica com o espaço escolar. Partindo do princípio de que tanto a universidade quanto a escola são instituições produtoras de conhecimentos relativos à educação, possibilita a capacidade de uma potencializar a outra, destacamos que ao se relacionarem ocasionam diversos benefícios em ambos os contextos. Ressaltamos que dentro da universidade o nosso projeto proporciona o acolhimento de estudantes do curso de Licenciatura Plena em Pedagogia que muitas vezes encontram dificuldades no enfrentamento de questões que envolvem o complexo universo escolar e a profissão docente, porém, vinculando as teorias e as práticas socializadas o grupo coletivamente vem encontrando meios para a superação desses desafios