Intitulé de l'offre : Ph.D. in phase field sea ice modelling (M/F) (H/F)
Référence : UMR5275-VERDAN-005
Nombre de Postes : 1
Lieu de travail : ST MARTIN D HERES
Date de publication : jeudi 18 janvier 2024
Type de contrat : CDD Doctorant/Contrat doctoral
Durée du contrat : 36 mois
Date de début de la thèse : 1 octobre 2024
Quotité de travail : Temps complet
Rémunération : 2 135,00 € gross monthly
Section(s) CN : Material and structural engineering, solid mechanics, biomechanics, acoustics
Description du sujet de thèse
Sea ice, like several other geophysical objects (e.g., rocks of the Earth's crust, soils, snow), is a very complex material that exhibits various mechanical behaviors, depending on its local state and on the time and space scales at which it is observed. Indeed, when and where it is dense (in winter and in the central Arctic), it behaves as a continuous and damageable solid. Where it is locally broken and loosened, it behaves like a frictional granular media. Between these two different regimes, solid and granular, the intensity of energy, gas, and momentum exchanges between the ice, the atmosphere and the ocean are widely different, hence the importance of capturing their essence in continuum models such as the ones used for climate predictions. Equally important is the capability to simulate the transition between these regimes, or granularization, as it strongly controls both the local, seasonal and the large-scale, long-term evolution of polar sea ice.
This Ph.D. project aims at developing a continuum model that is able to capture this granularization transition, by representing the propagation of a fragmented (i.e., damaged) phase into a continuous solid using the phase field approach.
Regarding this approach, the project will tackle several fundamental challenges that stem from the context of sea ice and similarly behaving geophysical objects, for instance: coupling the phase field to a visco-elastic constitutive equation of the Maxwell type, which allows irreversible deformations in the damaged phase as well as formulating and treating numerically a critical energy criterion for shear-compressive failure.
This model development work opens up to several geophysical applications. For instance, the future model could be compared to existing visco-elastic-brittle sea ice models that are based on a classical continuum damage mechanics approach, to contrast and give insights on both their simulated mechanical behavior and numerical efficiency. Importantly, it could also be used to investigate the evolution of the macroscopic mechanical resistance of sea ice or other geophysical objects across the granularization transition and thereby inform large-scale constitutive equations and parameterizations of this transition.
The aim of this thesis work is to propose a new, phase-field model of the granularization transition in sea ice, which will constitute a relevant alternative to existing visco-elasto-brittle sea ice models, as it will incorporate a more physical formulation of damage propagation in sea ice. The student will have to:
• Develop a phase-field model for the granulation transition as a fracturing process: (1) extend the phase-field formulation of fracture propagation to visco-elastic rheologies (of the Maxwell type in particular), (2) implement the appropriate fracture criterion for sea ice within the phase-field formulation and evaluate its robustness (is it a critical stress — which component?, is it a critical strain or critical energy?); (3) couple the visco-elastic rheology with the dynamics of the phase-field (derive the evolution equation for the fracture propagation coupled with the viscoelastic response across the granulation transition); 4) understand how the granulation transition, i.e. the resulting fracturing pattern, is sensitive to spatio-temporal heterogeneities in the visco-elastic material properties.
• Compare the numerical outputs with (eg., satellite and radar) observations of sea ice fragmentation.
• Compare the numerical results with that of existing models of sea ice deformation, on both a physical and computational basis.
Required skills include:
• computational physics skills, and theoretical background in statistical physics and continuum mechanics of solids and fluids,
• a theoretical background in mathematical methods in physics, i.e. variational calculus, PDEs,
• an experience with coding (C++, Python or similar language).
Contexte de travail
The work will be supported and carried within the Scale-Aware Sea Ice Project (SASIP, https://sasip-climate.github. io/), an international collaboration funded (2021-2027) by the Virtual Earth System Research Institute (https://schmidtfutures.com/ourwork/scientific-knowledge/vesri/) of Schmidt Futures – a philanthropic initiative that seeks to improve societal outcomes through the development of emerging science and technologies. It will also be carried as part of a collaboration between SASIP, ISTerre in particular, and the Njord Center at the University of Oslo.
SASIP aims to develop an innovative, physically rigorous and data-constrained model of the sea ice that can improve predictions of the polar and global climate. The project is divided into five main scientific work packages. Work package 2, in which the proposed work is included, concerns (i) the improved understanding of the brittle solid to granular transition in sea ice and its impact on the spatio-temporal evolution of the sea ice cover and (ii) the representation of this granularization transition in continuum, large-scale sea ice models.
The candidate will interact with a team of researchers, PhD students, post-docs and engineers, in particular SASIP project participants, who are distributed between the Njord Center at the University of Oslo (Norway), the Institut des Sciences de la Terre (ISTerre), the Institut de Géosciences de l'Environnement (IGE) in Grenoble and the Nansen Environmental and Remote Sensing Center (NSERC) in Bergen (Norway).
The thesis must start on October 1st at the latest. An earlier start is possible.
Contraintes et risques
This work is numerical in nature and therefore involves no physical risk.