Publications

Compact list of publications and talks

An optimisation-based domain-decomposition reduced order model for the incompressible Navier-Stokes equations

Published in arXiv preprint, 2022

The aim of this work is to present a model reduction technique in the framework of optimal control problems for partial differential equations. We combine two approaches used for reducing the computational cost of the mathematical numerical models: domain-decomposition (DD) methods and reduced-order modelling (ROM). In particular, we consider an optimisation-based domain-decomposition algorithm for the parameter-dependent stationary incompressible Navier-Stokes equations. Firstly, the problem is described on the subdomains coupled at the interface and solved through an optimal control problem, which leads to the complete separation of the subdomain problems in the DD method. On top of that, a reduced model for the obtained optimal-control problem is built; the procedure is based on the Proper Orthogonal Decomposition technique and a further Galerkin projection. The presented methodology is tested on two fluid dynamics benchmarks: the stationary backward-facing step and lid-driven cavity flow. The numerical tests show a significant reduction of the computational costs in terms of both the problem dimensions and the number of optimisation iterations in the domain-decomposition algorithm. Download paper

Recommended citation: I. Prusak, M. Nonino, D. Torlo, F. Ballarin and G. Rozza. "An optimisation-based domain-decomposition reduced order model for the incompressible Navier-Stokes equations." (2022) arXiv preprint, arXiv:2211.14528. https://arxiv.org/abs/2211.14528

A necessary condition for non oscillatory and positivity preserving time-integration schemes

Published in arXiv preprint, 2022

Modified Patankar (MP) schemes are conservative, linear implicit and unconditionally positivity preserving time-integration schemes constructed for production-destruction systems. For such schemes, a classical stability analysis does not yield any information about the performance. Recently, two different techniques have been proposed to investigate the properties of MP schemes. In Izgin et al. ESAIM: M2AN, 56 (2022), inspired from dynamical systems, the Lyapunov stability properties of such schemes have been investigated, while in Torlo et al. Appl. Numer. Math., 182 (2022) their oscillatory behaviour has been studied. In this work, we investigate the connection between the oscillatory behaviour and the Lyapunov stability and we prove that a condition on the Lyapunov stability function is necessary to avoid oscillations. We verify our theoretical result on several numerical tests. Download paper

Recommended citation: T. Izgin, P. Öffner and D. Torlo. "A necessary condition for non oscillatory and positivity preserving time-integration schemes." (2022) arXiv preprint, arXiv:2211.08905. https://arxiv.org/abs/2211.08905

A new efficient explicit Deferred Correction framework: analysis and applications to hyperbolic PDEs and adaptivity

Published in arXiv preprint, 2022

Deferred Correction methods are arbitrarily high order methods that consists of an iterative procedure. At each iterations the high order reconstruction is updated leading to costs that scale as the square of the order of accuracy. We propose a way to cut up to half of the computational costs for this methods by increasing the order of the reconstruction at each iteration. An adaptive version allows also to set a priori a tolerance to reach a certain error. Applications to PDEs within the RD-DeC frameworks allows as well a great computational advantage. Download paper

Recommended citation: L. Micalizzi and D. Torlo. (2022). "A new efficient explicit Deferred Correction framework: analysis and applications to hyperbolic PDEs and adaptivity. " arXiv preprint, 2022. https://arxiv.org/abs/2210.02976. https://arxiv.org/abs/2206.03889

Spectral analysis of continuous FEM for hyperbolic PDEs: influence of approximation, stabilization, and time-stepping

Published in arXiv, 2022

In this paper, we study different high order FEM methods for hyperbolic problems, providing parameters that lead to stable and reliable schemes for triangular meshes. Download paper

Recommended citation: Michel, S., Torlo, D., Ricchiuto, M. and Abgrall, R.. Spectral analysis of high order continuous FEM for hyperbolic PDEs on triangular meshes: influence of approximation, stabilization, and time-stepping. arXiv:2206.06150 (2022). https://arxiv.org/abs/2206.06150

High order entropy preserving ADER scheme

Published in arXiv preprint, 2022

In this paper, we develop a fully discrete entropy preserving ADER-Discontinuous Galerkin (ADER-DG) method. To obtain this desired result, we equip the space part of the method with entropy correction terms that balance the entropy production in space, inspired by the work of Abgrall. Whereas for the time-discretization we apply the relaxation approach introduced by Ketcheson that allows to modify the timestep to preserve the entropy to machine precision. Up to our knowledge, it is the first time that a provable fully discrete entropy preserving ADER-DG scheme is constructed. We verify our theoretical results with various numerical simulations. Download paper

Recommended citation: E. Gaburro, P. Öffner, M. Ricchiuto and D. Torlo. "High order entropy preserving ADER-DG scheme." Applied Mathematics and Computation, 440:127644, 2023. doi:10.1016/j.amc.2022.127644. https://doi.org/10.1016/j.amc.2022.127644

Arbitrary High Order WENO Finite Volume Scheme with Flux Globalization for Moving Equilibria Preservation

Published in arXiv preprint, 2022

We introduce arbitrary high order WENO finite volume schemes with global fluxes. The global flux includes the integral of the source term, so that it is natural to balance the moving equilibria for this kind of schemes. We show for shallow water equations with bathymetry that we can exactly preserve the discharge for moving steady states. Morover, we can apply a correction to be also well-balanced with respect to the lake at rest steady state. Download paper

Recommended citation: M. Ciallella, D. Torlo and M. Ricchiuto. (2022). "Arbitrary High Order WENO Finite Volume Scheme with Flux Globalization for Moving Equilibria Preservation. " arXiv preprint, 2022. https://arxiv.org/abs/2205.13315. https://arxiv.org/abs/2205.13315

Some preliminary results on a high order asymptotic preserving computationally explicit kinetic scheme

Published in Communications in Mathematical Sciences, 2022

In this short paper, we intend to describe one way to construct arbitrarily high order kinetic schemes on regular meshes. The method can be arbitrarily high order in space and time, run at least CFL one, is asymptotic preserving and computationally explicit, i.e., the computational costs are of the same order of a fully explicit scheme. We also introduce a nonlinear stability method that enables to simulate problems with discontinuities, and it does not kill the accuracy for smooth regular solutions. Download paper

Recommended citation: R. Abgrall and D. Torlo. (2022). "Some preliminary results on a high order asymptotic preserving computationally explicit kinetic scheme. " Communications in Mathematical Sciences, 20, 2, 297-326. https://dx.doi.org/10.4310/CMS.2022.v20.n2.a1. https://dx.doi.org/10.4310/CMS.2022.v20.n2.a1

Model order reduction strategies for weakly dispersive waves

Published in arXiv, 2021

Water waves can be approximated with different models. Dispersive-hyperbolic models serve this scope under smallness conditions of nonlinearity and shallowness parameters. The discretization of these models consists often of a hyperbolic system coupled with an elliptic system. In this work we reduce with standard model order reduction techniques the elliptic operator. Finally, we apply some hyperreduction to reduce the whole system. Download paper

Recommended citation: D. Torlo and M. Ricchiuto. "Model order reduction strategies for weakly dispersive waves. " Mathematics and Computers in Simulation, (205), pages 997-1028, 2023. https://doi.org/10.1016/j.matcom.2022.10.034

An Arbitrary High Order and Positivity Preserving Method for the Shallow Water Equations

Published in Computer and Fluids, 2021

In shallow water equations simulations the positivity of water height is a fundamental property to preserve. We use a linearly implicit modified Patankar Deferred Correction method to guarantee its positivity without any restriction on the time step. The rest of the discretization is obtained with a classical WENO5 finite volume method. Download paper

Recommended citation: M. Ciallella, L. Micalizzi, P. Öffner and D. Torlo. (2022). "An Arbitrary High Order and Positivity Preserving Method for the Shallow Water Equations. " Computers & Fluids, 247, page 105630. https://doi.org/10.1016/j.compfluid.2022.105630

Analytical traveling vortex solutions of hyperbolic equations for validating very high order schemes

Published in arXiv, 2021

Testing the order of accuracy of (very) high order methods for shallow water (and Euler) equations is a delicate operation and the test cases are the crucial starting point of this operation. We provide a short derivation of vortex-like analytical solutions in 2 dimensions for the shallow water equations (and, hence, Euler equations) that can be used to test the order of accuracy of numerical methods. These solutions have different smoothness in their derivatives (up to arbitrary derivatives) and can be used accordingly to the order of accuracy of the scheme to test. Download paper

Recommended citation: M. Ricchiuto and D. Torlo. (2021). "Analytical traveling vortex solutions of hyperbolic equations for validating very high order schemes. " arXiv preprint, https://arxiv.org/abs/2109.10183. https://arxiv.org/abs/2109.10183

Issues with Positivity-Preserving Patankar-type Schemes

Published in Applied Numerical Mathematics, 2021

We study various properties for a class of positivity-preserving nonlinear schemes (Patankar-type schemes) and we discover two types of issues: oscillations around stady states when the timestep is too large and spurious steady states where some methods get stuck. Download paper

Recommended citation: D. Torlo, P. Öffner and H. Ranocha. (2022). "Issues with Positivity-Preserving Patankar-type Schemes. " Applied Numerical Mathematics, 182, 117-147. https://doi.org/10.1016/j.apnum.2022.07.014

Relaxation Deferred Correction Methods and their Applications to Residual Distribution Schemes

Published in The SMAI Journal of computational mathematics, 2021

In this paper, we study different high order FEM methods for hyperbolic problems, providing parameters that lead to stable and reliable schemes. Download paper

Recommended citation: R. Abgrall, E. Le Mélédo, P. Öffner and D. Torlo. (2022). "Relaxation Deferred Correction Methods and their Applications to Residual Distribution Schemes. " The SMAI Journal of computational mathematics, Volume 8 (2022), pp. 125-160. doi:10.5802/smai-jcm.82 https://doi.org/10.5802/smai-jcm.82

Spectral analysis of continuous FEM for hyperbolic PDEs: influence of approximation, stabilization, and time-stepping

Published in arXiv, 2021

In this paper, we study different high order FEM methods for hyperbolic problems, providing parameters that lead to stable and reliable schemes. Download paper

Recommended citation: Michel, S., Torlo, D., Ricchiuto, M. and Abgrall, R.. Spectral Analysis of Continuous FEM for Hyperbolic PDEs: Influence of Approximation, Stabilization, and Time-Stepping. J Sci Comput 89, 31 (2021). https://doi.org/10.1007/s10915-021-01632-7 https://doi.org/10.1007/s10915-021-01632-7

DeC and ADER: Similarities, Differences and a Unified Framework

Published in Journal of Scientific Computing, 2021

In this paper, we demonstrate that the explicit ADER approach can be seen as a special interpretation of the deferred correction (DeC) method. Download paper

Recommended citation: M. H. Veiga, P. Öffner, and D. Torlo. (2021). "DeC and ADER: Similarities, Differences and a Unified Framework." Journal of Scientific Computing, 87, 2 (2021). https://doi.org/10.1007/s10915-020-01397-5. https://doi.org/10.1007/s10915-020-01397-5

Arbitrary high-order, conservative and positivity preserving Patankar-type deferred correction schemes

Published in Applied Numerical Mathematics, 2020

Applying the modified Patankar approach to the DeC scheme results in provable conservative and positivity preserving methods. Furthermore, we demonstrate that these modified Patankar DeC schemes can be constructed up to arbitrarily high order. Download paper

Recommended citation: P. Öffner and D. Torlo. (2020). "Arbitrary high-order, conservative and positivity preserving Patankar--type deferred correction schemes." Applied Numerical Mathematics, 153:15 – 34. https://doi.org/10.1016/j.apnum.2020.01.025

High Order Asymptotic Preserving Deferred Correction Implicit-Explicit Schemes for Kinetic Models

Published in SIAM Journal on Scientific Computing, 2020

This work introduces an extension of the residual distribution (RD) framework to stiff relaxation problems. The RD is a class of schemes which is used to solve a hyperbolic system of partial differential equations. Download paper

Recommended citation: R. Abgrall, and D. Torlo. (2020). "High Order Asymptotic Preserving Deferred Correction Implicit-Explicit Schemes for Kinetic Models." SIAM Journal on Scientific Computing, 42(3): B816--B845. https://doi.org/10.1137/19M128973X

Model Reduction for Advection Dominated Hyperbolic Problems in an ALE Framework: Offline and Online Phases

Published in arXiv, 2020

In this work, we study MOR algorithms for unsteady parametric advection dominated hyperbolic problems, giving a complete offline and online description and showing the time saving in the online phase. Download paper

Recommended citation: D. Torlo. (2020). "Model Reduction for Advection Dominated Hyperbolic Problems in an ALE Framework: Offline and Online Phases." arXiv preprint, arXiv:2003.13735. https://arxiv.org/abs/2003.13735

Model order reduction for parametrized nonlinear hyperbolic problems as an application to uncertainty quantification

Published in Journal of Computational and Applied Mathematics, 2019

In this work, we present a model order reduction (MOR) technique for hyperbolic conservation laws with applications in uncertainty quantification (UQ). Download paper here

Recommended citation: R. Crisovan, D. Torlo, R. Abgrall, and S. Tokareva. (2019). "Model order reduction for parametrized nonlinear hyperbolic problems as an application to uncertainty quantification." Journal of Computational and Applied Mathematics, 348:466 – 489. https://doi.org/10.1016/j.cam.2018.09.018

Published in , 1900

Stabilized weighted reduced basis methods for parametrized advection dominated problems with random inputs

Published in SIAM/ASA Journal on Uncertainty Quantification, 2018

In this work, we propose viable and efficient strategies for stabilized parametrized advection dominated problems, with random inputs. Download paper

Recommended citation: D. Torlo, F. Ballarin, and G. Rozza. (2018). "Stabilized weighted reduced basis methods for parametrized advection dominated problems with random inputs." SIAM/ASA Journal on Uncertainty Quantification, 6(4): 1475--1502. https://doi.org/10.1137/17M1163517