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# Ongoing research projects

IMMC

### Ongoing research projects in iMMC (February 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:

### List of projects related to: finite elements

Numerical modelling of estuaries and coastal seasResearcher: 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/). |

Finite strain modelling of polymers and continuous fiber reinforced compositesResearcher: 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. |

Automatic hexahedral mesh generation for boundary layersResearcher: 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 tungstenResearcher: 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 bodiesResearcher: 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. |

Simulating flow in Tonle Sap, CambodiaResearcher: 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 adaptationResearcher: 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. |

HextremeResearcher: 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 volumesResearcher: 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. |

BIODEC, STOCCResearcher: Audrey Favache Supervisor(s): Thomas Pardoen obtained a PhD degree in the domain of process control in 2009 at Université catholique de Louvain (Belgium), after having graduated there as chemical engineer in 2005. Since then, she is working as a "senior" researcher on several applied research projects in collaboration with the industry in the domain of mechanics of materials. More particularly, she is interested in the link between the mechanical properties of the individual components of a complex system and the global mechanical response of this system. She applied this approach to the framework of tribology and contact mechanics for understanding the scratch resistance of coatings and multilayered systems. Her work covers both experimental aspects and finite element simulations. |

RESTEARResearcher: Thaneshan Sapanathan Supervisor(s): Aude Simar completed a mechanical engineering degree and a PhD at Monash University (Australia) in 2010 and 2014, respectively. His thesis was entitled “Fabrication of axi-symmetric hybrid materials using combination of shear and pressure”. During his PhD, he worked on architectured hybrid materials fabrication using severe plastic deformation (SPD) processes. Two novel axi-symmetric SPD techniques were investigated to fabricate hybrid materials with concurrent grain refinements. After that, he started a research project at University of Technology of Compiègne (France) in which he investigated the weldability window for similar and dissimilar material combinations using numerical simulations for magnetic pulse welding. He also studied the interfacial phenomena, behavior of material under high strain rate deformation, modeling and simulation of the magnetic pulse welding/forming. Then, I was working as a postdoctoral research fellow at UCL on the topic of characterizations of aluminium to steel welds made by friction stir welds and friction melt bonding. At present, I am working as a FNRS reserch officer (Chargé de recherche) and investigating intermetallic induced residual stresses and mitigation of hot tear in innovative dissimilar joints. |

3D crossfield generation for multibloc decompositionResearcher: 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. |

On a chip fracture mechanics test methodResearcher: Sahar Jaddi Supervisor(s): Thomas Pardoen The aim of this research is to develop a new testing method based on an-on-chip concept to measure the fracture toughness of freestanding submicron films. This device consists of two major components, a notched specimen and two actuators. When the test structure is released by etching the sacrificial layer, the two actuators contract, this in turn loads the specimen in traction. In order to define the stress intensity factor expression, which is given by this new model, analytical analysis and finite element simulations must be performed in addition to the experimental part, which is based on the microfabrication techniques. Silicon nitride, silicon oxide and metallic glass thin films will be studied during this work. The major goal of this model is to extract fracture toughness of 2D materials like graphene. |

Automatic block-structured hexahedral meshingResearcher: 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. |

Improving the properties of glass fiber reinforced acrylic thermoplastic resin based compositesResearcher: Sarah Gayot Supervisor(s): Thomas Pardoen For the manufacturing of continuous fiber reinforced thermoplastic composites (CFRTP), certain monomers can be infused through glass fabric and then polymerized in situ, in order to make a thermoplastic composite part. However, defects - e.g. porosity - can occur in the material, due to the thickness of the laminates and the shrinkage of the resin matrix during polymerization. Such phenomena must be understood, as well as their effects on the mechanical properties of the final composite part. The originality of this work lies in the very nature of the polymeric matrix used for manufacturing the composite parts, which is thermoplastic instead of thermoset. Little is known about the behaviour of such thermoplastic composites, especially at a microscopic scale. During this PhD, we will try to understand how defects occurring in the material can influence the structural properties of the CFRTP, and we will try to mitigate (or at least control) the incidence of such defects. This will imply a better knowledge of how usual characterisation techniques can be applied from thin to thick composite parts. In particular, digital simulation will be used so as to predict the properties of thick composite parts from those of thinner samples. |

Optimization of tensegrity bridges based on morphological indicatorsResearcher: Jonas Feron Supervisor(s): Pierre Latteur Tensegrity structures are composed of struts and tendons in such way that the compression is “floating” inside a net of tension in a stable self-equilibrated state. Although tensegrity forms have inspired artists and architects for many years, there exist very few real construction projects across the world. The main reasons are, among others, the complex construction processes and the lack of design guidelines. This research, performed in collaboration with the company BESIX, aims at proving the feasibility of a first pure tensegrity bridge around the world. When the structure is externally loaded, large displacements occur and require non-linear calculation before reaching an equilibrium. Indeed, in tensegrity structures more than in conventional ones, form and forces are intrinsically correlated. This phenomenon is due to their intern mechanism, unless appropriate pre-stressing is applied. An allowable stiffness can be possible, but at a certain material cost, which in turn justifies the relevance of the optimization of the weight. While designing a tensegrity structure, optimization and form finding are often great challenges. Indeed, the large amount of parameters (span, height, shape, cross sections, materials, loads, pre-stress, etc) makes the search for the structure with the best performances cumbersome. A solution to this problem is to reduce the number of degrees of freedom to consider, by grouping them into dimensionless numbers, the morphological indicators. In 2014, R.E. Skelton et al were pioneers in using a similar approach for optimizing planar tensegrity bridges uniformly loaded. In 2017, P. Latteur et al adapted the morphological indicators methodology, used so far to optimize mainly trusses and arches, to 3D non-linear and pre-stressed lattice structures such as tensegrity structures. In 2019, J. Feron et al used this methodology to investigate the performances of different 3D forms of uniformly loaded tensegrity footbridges. This research focus on the required checks to ensure the practicality, the constructability and the economical and structural efficiency of a pure tensegrity footbridge thanks to non linear finite element analysis, experimental validation, parametric design, prestress optimization and dynamic behavior assessment |

Design of a mechanism to provide the inversion-eversion degree of freedom to the ELSA robotic transtibial prosthesisResearcher: Carlos Salazar Briceño Supervisor(s): Renaud Ronsse Design of a mechanism that will provide the inversion and eversion degree of freedom (DoF) to the biologically inspired Efficient Lockable Spring Ankle (ELSA) robotic transtibial prosthesis which already has an active energized dorsiflexion and plantarflexion DoF. It is desired that the mechanism is active energized and biologically inspired. What are the newest mechanisms utilized in robotic transtibial prosthesis for inversion and eversion DoF and which kind of mechanisms are these ones?. Which are the most important criteria to consider when designing this kind of prosthesis and why are these the most important?. What are the advantages and disadvantages of a biologically inspired design?. The methodology to be used is the mechatronic systems design method of the VDI 2206 german guideline, it comprises the definition of the issue to be solved, the conceptual design which will help to choose the best preliminary design that is the base of the definitive project. Thereupon, leaving the VDI 2206 guideline, the next steps are to do the prototyping, programming, experimentation, validation, analysis, evaluation and relevant improvements on the prototype. There is a proposition of a compliant mechanism's design for the prosthesis which adequacy will be evaluated. |