Efficient Multiscale Coarse Approximations for Diffusion Problems in Perforated Domains

Concetti Chiave

The authors propose a low-dimensional coarse approximation space based on a coarse polygonal partitioning of the domain to efficiently solve diffusion problems in perforated domains. The coarse space is spanned by locally discrete harmonic basis functions with piecewise polynomial traces along the subdomain boundaries. The method provides superconvergence for a specific edge refinement procedure, even if the true solution has low regularity.

Sintesi

The content presents a numerical strategy for solving diffusion problems in perforated domains, which arise in applications such as urban flood modeling. The key aspects are:

1. Coarse Mesh and Space Decomposition:

   • The domain is partitioned into a coarse polygonal mesh Ω𝑗.
   • The solution is decomposed into a locally harmonic component 𝑢Δ and a local "bubble" component 𝑢𝑏.

2. Continuous Trefftz Approximation:

   • A finite-dimensional coarse space 𝑉𝐻,𝑝is introduced, spanned by functions that are piecewise polynomial on the coarse skeleton Γ.
   • An error estimate is provided, showing that the error in approximating 𝑢Δ by the Trefftz space depends only on the regularity of the solution along the coarse edges.
   • For a specific edge refinement procedure, the error analysis establishes superconvergence of the method.

3. Discrete Trefftz Space and Two-level Schwarz Method:

   • The continuous Trefftz space is discretized using a finite element approach.
   • The discrete Trefftz space is combined with a two-level domain decomposition method, leading to an efficient iterative linear solver.
   • The coarse Trefftz space can also be used as a preconditioner for Krylov methods, providing robustness and scalability with respect to the number of subdomains.

The proposed method aims to achieve computational efficiency compared to classical fine-scale solution methods, while handling the multiscale features of the urban geometries.

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Approfondimenti chiave tratti da

Robust Methods for Multiscale Coarse Approximations of Diffusion Models in Perforated Domains

by Miranda Bout... alle arxiv.org 04-11-2024

https://arxiv.org/pdf/2310.15669.pdf

Domande più approfondite

How can the proposed coarse approximation space be extended to handle more complex physical models beyond the linear diffusion problem, such as nonlinear or time-dependent problems

The proposed coarse approximation space can be extended to handle more complex physical models beyond the linear diffusion problem by incorporating higher-order basis functions and adapting the methodology to accommodate the specific characteristics of the new model. For nonlinear problems, the basis functions can be modified to capture the nonlinearity of the equations, potentially by introducing additional terms or functions that account for the nonlinear behavior. This may involve solving nonlinear subproblems within each coarse element or incorporating nonlinear constraints into the approximation space.
For time-dependent problems, the coarse approximation space can be extended to include temporal basis functions that capture the evolution of the solution over time. This could involve using a time-discretization scheme to approximate the time-dependent terms in the model and updating the coarse space at each time step. Additionally, techniques such as reduced basis methods or proper orthogonal decomposition can be integrated into the coarse approximation to handle the time-dependent nature of the problem efficiently.

What are the potential challenges in applying the two-level domain decomposition method to large-scale, realistic urban geometries with thousands of perforations

Applying the two-level domain decomposition method to large-scale, realistic urban geometries with thousands of perforations may face several challenges. One significant challenge is the computational complexity and memory requirements associated with solving the linear systems arising from the fine-scale finite element discretization. As the number of perforations and the complexity of the geometry increase, the size of the linear systems grows, leading to increased computational costs and memory usage.
Another challenge is the scalability of the method with respect to the number of subdomains and perforations. Ensuring load balancing and efficient communication between subdomains becomes more challenging as the problem size increases, potentially leading to bottlenecks and reduced parallel efficiency. Additionally, handling the heterogeneity and irregularity of the urban geometries, especially with complex boundary conditions and material properties, can pose difficulties in accurately capturing the behavior of the system within each subdomain.

Can the Trefftz coarse space be combined with other types of domain decomposition methods or multigrid techniques to further improve the efficiency and scalability of the solver

The Trefftz coarse space can be combined with other types of domain decomposition methods or multigrid techniques to further improve the efficiency and scalability of the solver. By integrating the Trefftz coarse space into a multigrid framework, it is possible to leverage the coarse approximation at different levels of the multigrid hierarchy, allowing for faster convergence and reduced computational costs. The combination of domain decomposition methods with the Trefftz coarse space can enhance the parallel scalability of the solver by distributing the computational workload across multiple subdomains and processors efficiently.
Additionally, the Trefftz coarse space can be used as a preconditioner for iterative solvers within domain decomposition methods, improving the convergence rate of the iterative solver and reducing the number of iterations required to reach a solution. By incorporating the Trefftz coarse space into a hybrid solver that combines domain decomposition with multigrid techniques, it is possible to achieve a robust and scalable solver for large-scale problems with complex geometries and heterogeneous properties.