We present our joint work with many collaborators on multi-physics and multiple scales, with focus on processes in the Arctic, a vast and complex environment of great current interest, with physical models sharing some (but not all) features with high alpine environments and other cold regions. Our interest is in robust, accurate and conservative computational schemes for the multi-physics: thermal, flow and mechanical deformation (TpHM) in the snow, ice and soils responding to the forcings from the environment for which the data is sparse. The models account for multiple phases and components and present challenges due to the presence of free boundary e.g. of freezing/thawing/sublimation, strong dependence of constitutive parameters on the micro-physics of TpHM, disparate time scales, and micro- and macro heterogeneity. We show how to build constitutive relationships for Darcy scale models from the first principles at the interface- and pore-scale by a combination of mathematically rigorous theory, practical computational upscaling, and surrogate data science tools. We illustrate with simulations of practical scenarios.
This initiative is part of the “Ph.D. Lectures” activity of the project "Departments of Excellence 2023-2027" of the Department of Mathematics of Politecnico di Milano. This activity consists of seminars open to Ph.D. students, followed by meetings with the speaker to discuss and go into detail on the topics presented at the talk.
Contatto:
alessio.fumagalli@polimi.it
The finite element method (FEM) is one of the great triumphs of applied mathematics, numerical analysis and software development. Recent developments in sensor and signalling technologies enable the phenomenological study of complex natural and physical systems. The connection between sensor data and FEM has been restricted to solving inverse problems placing unwarranted faith in the fidelity of the mathematical description of the system under study. If one concedes mis-specification between generative reality and the FEM then a framework to systematically characterise this uncertainty is required. This talk will present a statistical construction of the FEM which systematically blends mathematical description with data observations by endowing the Hilbert space of FEM solutions with the additional structure of a Probability Measure.
I will discuss the application of compatible finite element methods to large scale atmosphere and ocean simulation. Compatible finite element methods extend Arakawa's “C-grid” finite difference scheme to the finite element world. They are constructed from a discrete de Rham complex, which is a sequence of finite element spaces which are linked by the operators of differential calculus. The use of discrete de Rham complexes to solve partial differential equations is well established, but in this talk I focus on the specifics of dynamical cores for simulating weather, oceans and climate. The most important consequence of the discrete de Rham complex is the Hodge-Helmholtz decomposition, which has been used to exclude the possibility of several types of spurious oscillations from linear equations of geophysical flow. This means that compatible finite element spaces provide a useful framework for building dynamical cores. In this talk I will introduce the main concepts of compatible finite element spaces, and discuss their wave propagation properties. I will then cover a selection of the following topics (depending on recent advances, and interests of the audience): practical application to numerical weather prediction and ocean models, structure preserving methods, and scalable iterative solver techniques.
