Awards

Dr. Lucas Frérot is one of two winners of the SWICCOMAS prize 2021

His thesis was selected as the Swiss-based candidate for the 2020 ECCOMAS PhD thesis award on Computational Methods in Applied Sciences and Engineering.

For the thesis dissertation:

« Bridging scales in wear modeling with volume integral methods for elastic-plastic contact »
Supervised by Professor Jean-François Molinari and Dr Guillaume Anciaux, EPFL

Abstract:
Friction and wear are fundamental tribological phenomena that affect many aspects of our society: from the gears of a Swiss watch to car brakes and earthquakes. Despite being integral parts of everyday life, friction and wear remain elusive to quantitative predictions. Their systematic study, since the seminal experiments of Da Vinci, Amontons and Coulomb, has been quasi-exclusively experimental. This limits our capacity to understand tribological systems to those that can be reproduced experimentally. Perhaps the most challenging factors are the profoundly multi-scale and multi-physics aspect of both friction and wear, as well as the difficulty of observing what occurs at frictional interfaces. Due to natural or artificial roughness, things that appear in contact at the macro-scale actually only interact on an area that is much smaller than their apparent contact area. The processes that give rise to macroscopic friction and wear occur that the micro-contacts that make up this “true” contact area. During my thesis, I have developed simulation methods to accurately compute contact interfaces with multi-scale roughness. Because the true contact area is small, contact pressures can be very large, causing plastic (irreversible) deformation of the bodies in contact. To account for this effect, I developed a new approach to volume integral methods. My contributions allowed large scale simulations of plastic rough contact, which contributed to the understanding of the role of plasticity on the formation of cracks that can lead to wear debris detachment.

 

Dr. Tommaso Vanzan is one of two winners of the SWICCOMAS prize 2021

For the thesis dissertation:

« Domain decomposition methods for multiphysics problems »
Supervised by: Professor Martin J. Gander, UNIGE

Abstract:
This thesis contributes to the development of Domain Decomposition (DD) methods which are numerical algorithms to solve efficiently large linear and nonlinear systems arising from the discretization of Partial Differential Equations (PDE).
The main focus is on Optimized Schwarz Methods (OSMs) as they are the natural DD framework for multiphysics problems due to their property of convergence in the absence of overlap and the possiblity to tune the transmission conditions according to the physical parameters.
We study one-level and multilevel OSMs and derive optimized transmission conditions for several couplings of second order PDEs.
We then introduce a new substructured framework for a two-level and multilevel parallel Schwarz method, and provide a convergence analysis both for geometric and spectral coarse spaces. This framework is further extended to nonliner systems.
Finally, we present some results on the scalability of DD methods for specific geometries and for discrete fracture networks.
As an application, the methods developed have been applied to the Stokes-Darcy coupling, which is an instance of a multiphysics problem describing the filtration of fluids in porous media.

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Dr. Predrag Andric is one of two winners of the SWICCOMAS prize 2020

His thesis was selected as the Swiss-based candidate for the 2019 ECCOMAS PhD thesis award on Computational Methods in Applied Sciences and Engineering.

For the thesis dissertation:

« The mechanics of crack-tip dislocation emission and twinning »
Supervised by Professor Bill Curtin, EPFL

Abstract:
This thesis proposes two new theories for describing the mechanics of crack tip dislocation emission and twinning. Dislocation emission from a crack tip is a necessary mechanism for crack tip blunting and toughening, and at the same time one of the classical problems in mechanics of materials. A material is intrinsically ductile under Mode I loading when the critical stress intensity factor for dislocation emission KIe is lower than the critical stress intensity factor KIC for cleavage. KIe is usually evaluated using the approximate Rice theory. Atomistic simulations have shown that this theory is reasonable but not highly accurate. The discrepancy arises because Mode I emission is accompanied by the formation of a surface step that is not considered in the Rice theory. In this work we propose a new theory for Mode I emission based on the idea that (i) the stress resisting step formation at the crack tip creates “lattice trapping” against dislocation emission such that (ii) emission is due to a mechanical instability at the crack tip. Furthermore, a theory for crack-tip twinning has been proposed accounting for (i) the absence of the step formation, and (ii) the fact that nucleation does not occur directly at the tip. Both theories are quantitatively validated against atomistic simulations across a wide set of fcc materials.

 

Dr. Maria Han Veiga is one of two winners of the SWICCOMAS prize 2020

For the thesis dissertation:

« High order structure preserving numerical schemes for astrophysical flows »
Supervised by: Professor Rémi Abgrall and Romain Teyssier, UZH

Abstract:
In the thesis, we develop high order numerical methods which are structure preserving, as well as structure preserving data-driven method that aim to provide better numerical tools for simulations in astrophysics.

Motivated by the early stages of planet formation, we present a method that solves the unsteady compressible Euler system with gravity type source terms which can capture steady states beyond hydrostatic equilibrium on Cartesian coordinates. Then, motivated by the growing interest in high-order magneto-hydrodynamics (MHD) solvers in astrophysics and the difficulty in addressing the divergence free condition of magnetic fields, we present two methods that solve the linear induction equation (a simplification of MHD) while fulfilling the divergence constraint. We also present work towards structure preserving learning algorithms: a data-driven limiter which is symmetry and scale invariant as well as a methodology to transfer the data-driven limiter across different numerical schemes. Finally, we present some work towards high fidelity multi-scale modeling, combining two distinct simulation regimes (that model different space and time scales) with data-driven methods.

2019

Dr. Max Hodapp is one of two winners of the SWICCOMAS prize 2019
and has been selected as the Swiss-based candidate for the 2018 ECCOMAS PhD thesis award on Computational Methods in Applied Sciences and Engineering.

For the thesis dissertation:

« On flexible Green function methods for atomistic/continuum coupling”
Thesis director – William Curtin, EPFL

Abstract:
Atomistic/continuum (A/C) coupling schemes have been developed during the past twenty years to overcome the vast computational cost of fully atomistic models, but have not yet reached full maturity to address many open problems in metal plasticity. This thesis has therefore been devoted to the development of an extension of the coupled atomistic/discrete dislocations method to three dimensions (CADD-3d). To simulate the motion of hybrid dislocations along A/C interfaces a simplified solution procedure, which updates the boundary conditions on the atomistic problem based on the Green function of the entire dislocation network, has been introduced and validated. In order to solve the complementary elasticity problem a discrete boundary element method (DBEM) has been developed and implemented using an efficient hierarchical representation of the dense system matrices. The coupled atomistic/DBEM problem is solved using a fast stabilized monolithic Newton-Krylov method and an improvement of the overall accuracy by several orders of magnitude has been found in comparison with naive clamped boundary conditions. In addition, a semi-monolithic solution procedure has been conceptually proposed for CADD-3d which iterates between the entire physical and the discrete dislocation problem. Using the atomistic/DBEM coupling the computational complexity of this method becomes highly favorable in comparison with existing schemes in terms of the required degrees of freedom if many dislocations have passed the A/C interface.

 

Dr. Paola Bacigaluppi is one of two winners of the SWICCOMAS prize 2019

For the thesis dissertation:

“High Order Fully Explicit Residual Distribution Approximation for Conservative and Non-Conservative Systems in Fluid Dynamics”
Thesis director – Rémi Abgrall, UZH

Abstract:
In this work we collect several studies that embroil diverse techniques to tackle some of the many unsolved challenges linked to the study of strong interacting discontinuities for multidimensional, time-dependent hyperbolic systems of equations in Fluid Dynamics written both in conservative and non-conservative form.

To this end, we propose methodologies based on Residual Distribution schemes, which can be reinterpreted as non-standard Finite Volume and Finite Element approaches (Abgrall, Computational Methods in Applied Mathematics 2018).  In particular, we develop fully explicit high-order oscillation-free numerical methods without exceeding dissipation across shocking waves and allow to work directly with non-conservative variables, like pressures and internal energies, without any loss of conservation, and thus of information.

The robustness and accuracy of the novel strategies are assessed on several challenging benchmark problems in the context of the Euler equations for single phase flows and reduced Baer and Nunziato type systems for two-phase flows.


Dr. Joseph B. Nagel won The SWICCOMAS prize 2018

For the thesis dissertation:

« Bayesian techniques for inverse uncertainty quantification »

ETH Zürich – Thesis director Prof. Dr. Bruno Sudret

Abstract:

The thesis deals with Bayesian techniques for inverse problems under uncertainty. A probabilistic framework for treating both epistemic (lack of knowledge) and aleatoric uncertainties (natural variability) is established. Hamiltonian Monte Carlo is then proposed in order to tackle the computational challenge of exploring possibly high-dimensional posterior distributions. Beyond that, novel approaches to computational Bayesian inference are developed on the basis of variational methods and polynomial chaos expansions. They try to overcome the shortcomings of traditional sampling-based Markov chain Monte Carlo algorithms. A variety of problems, either simple or realistically complex, from the domain of civil, mechanical and hydrological engineering serve for demonstration purposes.