MOX Reports
The preprint collection of the Laboratory for Modeling and Scientific Computation MOX. It mainly contains works on numerical
analysis and mathematical modeling applied to engineering problems. MOX web site is mox.polimi.it
Found 1239 products
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61/2017 - 11/22/2017
Vadacca, L.; Colciago, C. M.; Micheletti, S.; Scotti, A.
Three-dimensional fault representation by interface and solid elements: effects of the anisotropy of the fault zone permeability on the timing of triggered earthquakes | Abstract | | In the last years numerous seismological evidences have shown a strict correlation between fluid injection and seismicity. An important topic that is currently under discussion in the scientific community concerns the prediction of the earthquake magnitude that may be triggered by fluid injection activities. Coupled fluid flow and geomechanical deformation models can aim at understand the evolution of pore pressure and rock deformation due to fluid injection in the subsurface. To perform an accurate numerical study of the correlation among fluid injection, seismicity rates and maximum earthquake magnitude, it is necessary to characterize the model with two fundamental features: first, the presence of a system of faults possibly intersecting among each other; second, the variability of the hydro-mechanical properties across the region surrounding each fault plane (fault zone). The novelty of this work is to account for these two aspects combining together two different numerical techniques that have been proposed in literature for the fault's modelling: for the first feature, interface elements are used to describe the frictional contacts occurring on the faults surfaces; for the second feature, solid elements are adopted to describe the heterogeneous hydro-mechanical behavior across the fault zone. Moreover, we account for a spatial variation of the permeability in the fault zone both along the dip and the normal direction with respect to the fault plane. We compute the numerical solution for six models among which we vary the permeability contrasts between protolith rocks and damage zone and between damage zone and fault core. We demonstrate that the anisotropy of permeability of the fault zone has a strong impact both on the timing and on the magnitude of triggered earthquakes. We suggest that a similar approach, which includes the entire architecture of the fault zone, shall be included in fluid-flow-geomechanical simulations to improve fault stability analysis during fluid injection. |
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60/2017 - 11/07/2017
Bonaldi, F.; Di Pietro, D. A.; Geymonat, G.; Krasucki, F.
A Hybrid High-Order method for Kirchhoff-Love plate bending problems | Abstract | | We present a novel Hybrid High-Order (HHO) discretization of fourth-order elliptic problems arising from the mechanical modeling of the bending behavior of Kirchhoff--Love plates, including the biharmonic equation as a particular case. The proposed HHO method supports arbitrary approximation orders on general polygonal meshes, and reproduces the key mechanical equilibrium relations locally inside each element. When polynomials of degree $kge 1$ are used as unknowns, we prove convergence in $h^{k+1}$ (with $h$ denoting, as usual, the meshsize) in an energy-like norm. A key ingredient in the proof are novel approximation results for the oblique biharmonic projector on local polynomial spaces. Under biharmonic regularity assumptions, a sharp estimate in $h^{k+3}$ is also derived for the $L^2$-norm of the error on the deflection. The theoretical results are supported by numerical experiments, which additionally show the robustness of the method with respect to the choice of the stabilization. |
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59/2017 - 11/03/2017
Grujic, O.; Menafoglio, A.; Guang, Y.; Caers, J.
Cokriging for multivariate Hilbert space valued random fields. Application to multifidelity computer code emulation | Abstract | | In this paper we propose Universal trace co-kriging (UTrCoK), a novel methodology for interpolation of multivariate Hilbert space valued functional data. Such data commonly arises in multi-fidelity numerical modeling of the subsurface and it is a part of many modern uncertainty quantification studies. Besides theoretical developments we also present methodological evaluation and comparisons with the recently published projection based approach by Bohorquez et al (2016). Our evaluations and analyses were performed on synthetic (oil reservoir) and real field (Uranium contamination) subsurface uncertainty quantification case studies. Monte Carlo analyses were conducted to draw important conclusions and to provide practical guidelines for all future practitioners. |
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58/2017 - 11/02/2017
Landajuela, M.; Vergara, C.; Gerbi, A.; Dede', L.; Formaggia, L.; Quarteroni, A.
Numerical approximation of the electromechanical coupling in the left ventricle with inclusion of the Purkinje network | Abstract | | In this work, we consider the numerical approximation of the electromechanical
coupling in the left ventricle with inclusion of the Purkinje network.
The mathematical model couples the 3D elastodynamics and bidomain
equations for the electrophysiology in the myocardium with the 1D
monodomain equation in the Purkinje network. For the numerical solution
of the coupled problem, we consider a fixed-point iterative algorithm that
enables a partitioned solution of the myocardium and Purkinje network
problems. Different levels of myocardium-network splitting are considered
and analyzed. The results are compared with those obtained using standard
strategies proposed in the literature to trigger the electrical activation. Finally,
we present a physiological cardiac simulation, including the initiation
of the signal in the Purkinje network, the systolic phase and the beginning
of the filling phase. |
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57/2017 - 10/31/2017
Ballarin, F.; D'Amario, A.; Perotto, S.; Rozza, G.
A POD-Selective Inverse Distance Weighting method for fast parametrized shape morphing | Abstract | | Efficient shape morphing techniques play a crucial role in the approximation of partial differential equations defined in parametrized domains, such as for fluid-structure interaction or shape optimization problems. In this paper, we focus on Inverse Distance Weighting (IDW) interpolation techniques, where a reference domain is morphed into a deformed one via the displacement of a set of control points. We aim at reducing the computational burden characterizing a standard IDW approach without compromising the accuracy. To this aim, first we propose an improvement of IDW based on a geometric criterion which automatically selects a subset of the original set of control points. Then, we combine this new approach with a model reduction technique based on a Proper Orthogonal Decomposition of the set of admissible displacements. This choice further reduces computational costs. We verify the performances of the new IDW techniques on several tests by investigating the trade-off reached in terms of accuracy and efficiency. |
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56/2017 - 10/31/2017
Alberti, G. S.; Santacesaria, M.
Infinite dimensional compressed sensing from anisotropic measurements | Abstract | | In this paper, we consider a compressed sensing problem in which both the measurement and the sparsifying systems are assumed to be frames (not necessarily tight) of the underlying Hilbert space of signals, which may be finite or infinite dimensional. The main result gives explicit bounds on the number of measurements in order to achieve stable recovery, which depends on the mutual coherence of the two systems. As a simple corollary, we prove the efficiency of non-uniform sampling strategies in cases when the two systems are not incoherent, but only asymptotically incoherent, as with the recovery of wavelet coefficients from Fourier samples. This general framework finds applications to several inverse problems in partial differential equations, in which the standard assumptions of compressed sensing are not satisfied: several examples are discussed. |
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53/2017 - 10/23/2017
Bertagna, L.; Deparis, S.;Formaggia, L.; Forti, D.; Veneziani A.
The LifeV library: engineering mathematics beyond the proof of concept | Abstract | | LifeV is a library for the finite element (FE) solution of partial differential equations in one, two, and three dimensions. It is written in C++ and designed to run on diverse parallel architectures, including cloud and high performance computing facilities. In spite of its academic research nature, meaning a library for the development and testing of new methods, one distinguishing feature of LifeV is its use on real world problems and it is intended to provide a tool for many engineering applications. It has been actually used in computational hemodynamics, including cardiac mechanics and fluid-structure interaction problems, in porous media, ice sheets dynamics for both forward and inverse problems. In this paper we give a short overview of the features of LifeV and its coding paradigms on simple problems. The main focus is on the parallel environment which is mainly driven by domain decomposition methods and based on external libraries such as MPI, the Trilinos project, HDF5 and ParMetis.
(Dedicated to the memory of Fausto Saleri) |
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54/2017 - 10/23/2017
Dede', L; Quarteroni, A.
Isogeometric Analysis of a Phase Field Model for Darcy Flows with Discontinuous Data | Abstract | | We consider a phase field model for Darcy flows with discontinuous data in porous media; specifically, we adopt the Hele-Shaw-Cahn-Hillard equations of [Lee, Lowengrub, Goodman, Physics of Fluids, 2002] to model flows in the Hele-Shaw cell through a phase field formulation which incorporates discontinuities of physical data, namely density and viscosity, across interfaces. For the spatial approximation of the problem, we use NURBS-based Isogeometric Analysis in the framework of the Galerkin method, a computational framework which is particularly advantageous for the solution of high order Partial Differential Equations and phase field problems which exhibit sharp but smooth interfaces. In this paper, we verify through numerical tests the sharp interface limit of the phase field model which in fact leads to an internal discontinuity interface problem; finally, we show the efficiency of Isogeometric Analysis for the numerical approximation of the model by solving a benchmark problem, the so-called "rising bubble" problem. |
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