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| Author(s): |
Willian Righi Assis
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | Campinas, SP. |
| Institution: | Universidade Estadual de Campinas (UNICAMP). Faculdade de Engenharia Mecânica |
| Defense date: | 2023-11-06 |
| Examining board members: |
Erick de Moraes Franklin;
Ascânio Dias Araújo;
Douglas J Jerolmack;
Orencio Duran Vinent;
Yuri Dumaresq Sobral
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| Advisor: | Erick de Moraes Franklin |
| Abstract | |
Crescent-shaped dunes, known as barchans, are found in environments with limited amounts of granular material and mainly unidirectional fluid flow. In nature, they belong to a dune field, where one dune can influence and be influenced by others. This thesis seeks to understand the behavior of a dune field, as well as the dynamics of 2D (two-dimensional) dune in comparison with 3D (three-dimensional) ones, and the interactions between dunes and static objects. On the one hand, experimental approaches are employed to obtain information from a binary field of subaqueous dunes both at the bedform and particle scales. The results show that there are five different patterns of interactions and that these patterns are well organized based on the total amount of granular material in each dune and the Shields number. In addition, typical lengths and velocities of particles are computed and a diffusion-like component is observed after a collision takes place. Furthermore, different interactions are observed in the presence of more than one type of particle within the dunes, and a timescale is proposed for the interaction of both monodisperse and bidisperse barchans. On the other hand, a numerical investigation is carried out using CFD-DEM (computational fluid dynamics - discrete element method) to select the parameters and numerical models necessary to reproduce the behavior of underwater dunes. Comparisons between morphology, timescales, and particle trajectories are computed, generating a robust and effective tool, which will enable future investigations in a dune field. Investigations, in order to compare experiments of 2D dunes and numerical simulations of the midline of barchans, are performed under bi-modal changes in the flow direction. We could show that the timescale for the development of 2D dunes scales with that for 3D barchans and that a considerable part of grains remains static during the process. At last, the behavior of subaqueous barchans when reach a dune-size obstacle is investigated. It is observed that the dune can pass over, bypass, or be blocked, with some intermediate situations. A classification map is proposed based on the obstacle-dune size ratio and the modified Stokes number. The items presented in this work can help to better understand the behavior of dune interactions, revealing insights into questions that were still unanswered (AU) | |
| FAPESP's process: | 19/10239-7 - Bed-load instabilities: granular dynamics and interaction with the fluid flow |
| Grantee: | Willian Righi Assis |
| Support Opportunities: | Scholarships in Brazil - Doctorate (Direct) |