Ongoing research projects

IMMC

Ongoing research projects in iMMC (January 2020)


This a short description of research projects which are presently under progress in iMMC.
Hereunder, you may select one research direction or choose to apply another filter:

Biomedical engineering

Computational science

Civil and environmental engineering

Dynamical and electromechanical systems

Energy

Fluid mechanics

Processing and characterisation of materials

Chemical engineering

Solid mechanics


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List of ongoing projects in the division: MEMA




Numerical modelling of estuaries and coastal seas
Researcher: Valentin Vallaeys
Supervisor(s): Eric Deleersnijder

The topic of the research is the numerical modelling of the river-to-sea continuum of major rivers (i.e. Congo River and Columbia River). The goal is to study the estuarine and coastal dynamics and their interactions with tides, river discharges and atmospheric/oceanic circulations. This thesis partly answers the following questions: What is the dynamics of the river-to-sea continuum ? How does the small scale influence the larger one (and vice-versa) ? Can Discontinuous Galerkin methods reduce the numerical dissipation in order to simulate sharp fronts of density and velocity fields ? This thesis is performed within the framework of the SLIM project (http://sites.uclouvain.be/slim/).



Contributions to nonlinear micromechanical modeling of composite and porous materials under small and large deformation
Researcher: Marieme Imene El Ghezal
Supervisor(s): Issam Doghri

The goal of my research is to deliver models able to predict the effective mechanical behavior of materials made of at least two different phases and which can be used for complex loading tests like non-proportional loadings. The adopted technique is the Mean Field Homogenization (MFH). The development of such schemes strongly depends on the constitutive laws of the constituents. The range of materials concerned by this research is wide: elastic, viscoelastic, elasto-plastic (in the small strain regime) and hyperelastic-plastic in the finite strain regime. My research interests also include FE analysis of cellular materials, porous materials and composites involved mainly in the validation of the MFH schemes.



Observation and modelling of the link between microstructure evolution and strength in plastically deformed and annealed metals with fine-scale twins
Researcher: Fengxiang Lin
Supervisor(s): Laurent Delannay

This project aims at advancing the current understanding of the evolution of microstructures and strength during plastic deformation of face centered cubic metals in which fine-scale twins influence the dislocation slip activity, the stored energy, and the subsequent annealing. The fine-scale twins can be mechanical twins (e.g. in TWIP steels and high-strain-rate deformed copper) or growth twins in electro-deposited films. These fine-scale twins increase anisotropy, which promotes microscopic shear banding during plastic deformation. This project will specifically address some fundamental questions:
- What is the influence of the interplay of dislocation slip and mechanical twinning on the occurrence of microscopic shear bands (MSBs)?
- What is the influence of MSBs on the deformed microstructure (incl. rotation of twin bundles), the internal stresses, and the stored dislocation density?
- How do hardening and internal stresses (incl. “back-stresses”) develop in small-size samples compared to bulk samples?
- How do structural heterogeneities from MSBs and twin bundles affect the subsequent annealing behavior?



Finite strain modelling of polymers and continuous fiber reinforced composites
Researcher: Muralidhar Reddy Gudimetla
Supervisor(s): Issam Doghri

The main thesis goal is to efficiently integrate the constitutive models of resin, fiber and fiber/matrix interface into a mulit-scale approach to predict the behavior of an uni-directional carbon-epoxy composite ply. This would require an efficient constitutive model for the resin/polymer which would address the experimentally observed features like strain-rate, temperature and pressure-dependency. So, an isotropic thermodynamically based fully coupled viscoelastic-viscoplastic model formulated under finite strain transformations was developed considering isothermal conditions, which is further extended to an anisotropic version suitable for structural composites. This model would be implemented in a multi-scale approach, with corresponding models for fiber and fiber/matrix interface, to predict softening/degradation in an uni-directional composite ply.



Viscoplasticity and strain localization in metallic thin films
Researcher: Guerric Lemoine
Supervisor(s): Laurent Delannay, Thomas Pardoen

Metallic thin films are widely used in the microelectronic industry and for surface functionalization. Owing to their very fine microstructure, thin films generally suffer of a lack of ductility and are prone to creep at room temperature. To avoid such detrimental effects in applications, their mechanical behaviors have to be characterized and modeled. Combining both experiments and simulations, my doctoral research focus on the rate dependent plasticity and the strain localization of metallic thin films. The Lab-on-chip technique is used to characterize the yield stress, the ductility, the hardening behavior and the strain rate sensitivity of Ni thin films. A localized necking model is also developed, dedicated to thin films and nano crystalline metals which aims at accounting for strain gradient plasticity effects, for grain size dependent strength, rate sensitivity and the possible contribution of creep/relaxation mechanisms. A dislocation-based crystal plasticity model has also been developed in order to study the mechanical and creep/relaxation behavior of the polycrystalline Pd thin films with high initial defect concentration, obtained by M-S Colla during her PhD thesis.



Automatic hexahedral mesh generation for boundary layers
Researcher: Christos Georgiadis
Supervisor(s): Jean-François Remacle

The main objective of our work is to provide with a fast and reliable method for generating boundary layer meshes. We follow a strategy that uses direction fields and a frontal point insertion strategy. The input of our algorithm is an initial triangular mesh of our domain and a direction field calculated on it. The goal is to compute the vertices of the final mesh by an advancing front strategy along the direction field. The final mesh will consists of right angle triangles, optimal for merging into quadrilaterals.



Crystal plasticity modelling of thermomechanical fatigue in ITER relevant tungsten
Researcher: Aleksandr Zinovev
Supervisor(s): Laurent Delannay

Tungsten, selected as plasma-facing material for fusion reactors (such as ITER and DEMO), needs to possess high crack resistance and ductility under extreme operation conditions, such as high neutron flux and cyclic thermal load, which lead to material degradation. The objective of this project is to develop a finite element (FE) model capable to simulate mechanical behaviour of polycrystalline tungsten under tensile testing with the focus made on effect of test temperature and irradiation-induced defects. The input for the model is derived from experiments and lower-scale models, such as crystal plasticity (CP), molecular dynamics (MD) and dislocation dynamics (DD). A combination of FE and CP approach allows for investigation of mechanical behaviour of tungsten at the grain level.



The following scientific questions have to be addressed in the frame of this PhD project:

How does the heterogeneity of stress and strain within grains affect the cracking behaviour of tungsten under ITER-like heat loads? How can the impact of neutron irradiation defects be included in the CP model? What is the effect of texture on anisotropy of plastic deformation and fracture properties?



A macroscopic constitutive law, which describes plasticity of tungsten in the ITER-relevant temperature range, has already been constructed. Based on that, two papers have been published in peer-reviewed journals.




Tidal response of Titan liquid bodies
Researcher: David Vincent
Supervisor(s): Eric Deleersnijder

Titan, a moon of Saturn, has various liquid bodies: surface lakes and seas filled with liquid hydrocarbons and a global subsurface ocean of water.



I numerically studied the tidal flow (see Fig. 1, the tidal ellipses of the first tidal component in Kraken and Ligeia Maria) and motion of the surface lakes and seas by means of SLIM (www.climate.be/slim). The harmonics of the tidal motion (for instance, the tidal range and phase in Kraken and Ligeia Maria, see Fig. 2) and eigenmodes were also studied in order to assess the likelihood of resonance (local or global). Values predicted by the model such as the tidal range and flow of the surface lakes and seas are useful for designing some aspects of the future observation missions.



I am currently modeling the tidal response of Titan's global subsurface ocean by taking into account the solid-fluid interactions with Titan icy crust (see Fig. 3, the sea surface elevation of Titan's ocean with a free top boundary). The dissipation and resonance phenomena will then be studied. The originality of this work lies in the fact that the dynamic tides are taken into account.






Multithreaded Mesh Generation
Researcher: Célestin Marot
Supervisor(s): Jean-François Remacle

The main goal of this thesis is to speedup tetrahedral mesh generation by an order of magnitude. To do so, we are parallelizing and enhancing the whole mesh generation process. Promising results are uncovered at




https://www.hextreme.eu/







Simulating flow in Tonle Sap, Cambodia
Researcher: Anh Hoang Le
Supervisor(s): Sandra Soares Frazao

- Simulating flow and sediment transport in the Lower Mekong River;
- Simulating flow in Tonle Sap, Cambodia by SLIM;
- Study on floc characteristics in Luang Prabang, Laos and Mekong Delta



Curvilinear mesh adaptation
Researcher: Amaury Johnen
Supervisor(s): Jean-François Remacle

graduated as a physician engineer at the University of Liège (Belgium) in 2011. Then he accomplished a PhD in the topic of quadrangular mesh generation and cuvilinear mesh validation, under the supervision of professor Christophe Geuzaine. He started a postdoctoral research in January 2016 under the supervision of professor Jean-François Remacle for working on curvilinear mesh generation, hex-dominant mesh generation and mesh validation.



All-hexahedral meshing
Researcher: Kilian Verhetsel
Supervisor(s): Jean-François Remacle

While there exist algorithms to generate hex-dominant meshes, which contain a majority of hexahedra as well as a mixture of tetrahedra, prisms, and pyramids, automatically generating hexahedral meshes with elements of a reasonable quality is not currently possible. Subdividing the elements of a hex-dominant mesh could allow hexahedral meshes to be generated automatically, but the best known subdivision of a pyramid requires too many elements to be practical (see figure).

My work focuses on finding all-hexahedral meshes of small models such as this pyramid by first finding a topological solution using combinatorial search techniques. A geometric mesh will then be produced by finding coordinates for each vertex in the mesh.



Hextreme
Researcher: François Henrotte
Supervisor(s): Jean-François Remacle

completed his Engineering Degree in 1991 and his PhD in 2000, both at the University of Liège in Belgium. He then spent 4 years at the Katholieke Universiteit Leuven and 6 years at the Institut für Elektrische Maschinen in Aachen, Germany, and is now with the UCL and the ULiège. Developer in the open-source packages Gmsh, GetDP and Onelab, he has also developed skills in the multiphysics simulation of electrical machines and drives. His main interests are finite element analysis, numerical modeling, electromechanical coupling, material properties (hysteresis, iron losses, superconductors), applied mathematics (differential geometry, algebraic topology, convex analysis, dual analysis, energy methods), multiscale methods, sensitivity and optimization.



Poly-cube decomposition of 3D volumes
Researcher: Jovana Jezdimirovic
Supervisor(s): Jean-François Remacle

The aim of the research thesis is to push forward the state-of-the-art of mesh generation and propose for the first time a methodology that allows to automatically create structured multi-block meshes for general 3D domains. For that, an innovative approach that enables automatic decomposition of a general 3D domain into “poly-cubes” is proposed. A “poly-cube” map is a mechanism that allows a seamless parameterization of a 3D domain. The “poly-cube” decomposition provides the multi-block structure that is needed for structured meshing. In order to achieve this goal, the first part of the thesis is dedicated to the development of a “poly-quad” decomposition of a general 2D surface. It is relied on solving adequate Ginzburg Landau equations in order to develop a robust procedure that generates cross fields and locates critical points. Existence and location of critical points – represented as elliptic Fekete points are proved in recent results by Jezdimirovic, 2017. Further, critical points will be connected through the integral lines leading to an automatic decomposition of the domain into “quadrilaterals”. In the next step, the presented idea will be extended to 3D in order to create automatic algorithm for the “poly-cube” decomposition of 3D volumes.



Numerical modeling of growth and remodeling in stented arteries
Researcher: Colin Laville
Supervisor(s): Laurent Delannay

The project aims to predict the evolution of the radial contraction of stented arteries using a continuum mechanics model, with application to bio-resorbable stent development. The capture of the stress state evolution in the artery wall requires a material model that includes:

- the modeling of the main constituents such as collagen, elastin and smooth muscles ;

- time dependent evolution such as growth and structural remodeling.

Some developed tools are also used to predict fracture in bended stainless steels.



3D crossfield generation for multibloc decomposition
Researcher: Alexandre Chemin
Supervisor(s): Jean-François Remacle

The aim of the project is to realize multibloc decomposition of 3D volumes in order to generate full hex meshes. Nowadays, this kind of decomposition is done by hand. The purpose of this work is to be able to do it in an automatic way. In order to reach this objective, we are generating 3D crossfields in this volume to locate singular points and automatize the decomposition.



Automatic block-structured hexahedral meshing
Researcher: Maxence Reberol
Supervisor(s): Jean-François Remacle

To automatically build block-structured hexahedral meshes, we generate smooth frame fields which are aligned with the boundary of 3D models and we exploit their geometry and topology to extract block decompositions, which are suited for hexahedral meshing.