Quaderni MOX
Pubblicazioni
del Laboratorio di Modellistica e Calcolo Scientifico MOX. I lavori riguardano prevalentemente il campo dell'analisi numerica, della statistica e della modellistica matematica applicata a problemi di interesse ingegneristico. Il sito del Laboratorio MOX è raggiungibile
all'indirizzo mox.polimi.it
Trovati 1314 prodotti
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24/2015 - 15/05/2015
Bonaventura, L:
Local Exponential Methods: a domain decomposition approach to exponential time integration of PDE. | Abstract | | A local approach to the time integration of PDEs by exponential methods is
proposed, motivated by theoretical estimates by A.Iserles on the decay of off-diagonal terms in the exponentials of sparse matrices. An overlapping domain decomposition technique is outlined, that allows to replace the computation of a global exponential matrix by a number of independent and easily parallelizable local problems. Advantages and potential
problems of the proposed technique are discussed. Numerical experiments on simple, yet relevant model problems show that the resulting method allows to increase computational efficiency with respect to standard implementations of exponential methods. |
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23/2015 - 08/05/2015
Paolucci, R.; Mazzieri, I.; Smerzini, C.
Anatomy of strong ground motion: near-source records and 3D physics-based numerical simulations of the Mw 6.0 May 29 2012 Po Plain earthquake, Italy | Abstract | | Stimulated by the recent advances in computational tools for the simulation of seismic wave propagation problems in realistic geologic environments, this paper presents a 3D physics-based numerical study on the prediction of earthquake ground motion in the Po Plain, with reference to the Mw 6.0 May 29 2012 earthquake.
To respond to the validation objectives aimed at reproducing with a reasonable accuracy some of the most peculiar features of the near-source strong motion records and of the damage distribution, this study required a sequence of investigations, starting from the analysis of a nearly unprecedented set of near-source records, to the calibration of an improved kinematic seismic source model, up to the development of a 3D numerical model of the portion of the Po Plain interested by the earthquake, including the irregular buried morphology, with sediment thickness varying from few tens of m to some km. The spatial resolution of the numerical model is suitable to propagate up to about 1.5 Hz. Numerical simulations were performed using the open-source high-performance code SPEED, based on the Discontinuous Galerkin Spectral Elements (DGSE) method.
The 3D numerical model coupled with the updated slip distribution along the rupturing fault proved successful to reproduce with reasonable accuracy, measured through quantitative goodness-of-fit criteria, the most relevant features of the observed ground motion both at the near- and far-field scales. These include: (i) the large fault normal velocity peaks at the near-source stations driven by up-dip directivity effects; (ii) the small-scale variability at short distance from the source, resulting in the out-of-phase motion at stations separated by only 3 km distance; (iii) the propagation of prominent trains of surface waves, especially in the Northern direction, induced by the irregular buried morphology in the near-source area; (iv) the map of earthquake-induced ground uplift with maximum values of about 10 cm, in substantial agreement with satellite measurements; and (v) the two-lobed pattern of the peak ground velocity map, well correlated with the distribution of macroseismic intensity. |
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22/2015 - 05/05/2015
Bonaventura, L.; Ferretti, R.
Flux form Semi-Lagrangian methods for parabolic problems | Abstract | | A semi-Lagrangian method for parabolic problems is proposed,
that extends previous work by the authors to achieve a fully conservative, flux-form discretization of linear and nonlinear diffusion equations.
A basic consistency and convergence analysis are proposed. Numerical examples
validate the proposed method and display its potential for consistent semi-Lagrangian discretization of advection--diffusion and nonlinear parabolic problems. |
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21/2015 - 28/04/2015
Arena, M.; Azzone, G.; Secchi, P.; Vantini, S.
Reputational risk and corporate finance: A multi-event model | Abstract | | This paper develops a model for the evaluation of reputational risk and explores if certain characteristics of negative events happening to a company can explain their reputational impacts. To this aim, the paper adopts the share market value as a synthetic measure of a company’s ability to create economic value and explores the reaction of the share market to the announcement of negative events (e.g. protests, accidents, corporate misconducts).
The proposed model contributes to prior research in this field with three innovative dimensions. It applies to events that have a limited impact from an operational perspective (e.g. protests, small environmental events) but could have a considerable reputational effect. It applies to different types of events that can potentially affect the stakeholders’ expectations and perceptions. It addresses the determinants of reputational risk, exploring which characteristics of an event explain the share market reaction.
The empirical analysis is based on data collected over a timeframe of ten years, concerning a leading multinational company, that competes in the Oil & Gas industry and is listed on NY Stock Exchange. 67 events involving this company in this period of time are analysed through the proposed model, leading to the identification of a sub-set of events which significant reputational events are associated with and to the exploration of different factors that can explain the relevance of the reported reputational impacts. |
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20/2015 - 16/04/2015
Antonietti, P.F.; Formaggia, L.; Scotti, A.; Verani, M.; Verzotti, N.
Mimetic finite difference approximation of flows in fractured porous media | Abstract | | We present a possible framework for the numerical simulation of flow in fractured porous media that couples mimetic finite differences for the porous matrix with a finite volume scheme for the flow in the fractures. The resulting method is theoretically analyzed in the case of a single fracture. Moreover, several numerical experiments show the capability of the method to deal also with complicated networks of fractures. Thanks to the implementation of rather general coupling conditions, it encompasses both "conductive fractures", i.e., fractures with high permeability and "sealed fractures", i.e., fractures with low permeability which act as a flow barrier. |
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19/2015 - 11/04/2015
Palamara, S.; Lange, M.; Vergara, C.; Lassila, T.; Frangi, A.F.; Quarteroni, A.
A coupled 3D-1D numerical monodomain solver for cardiac electrical activation in the myocardium with detailed Purkinje network | Abstract | | We present a model for the electrophysiology in the heart to handle the
electrical propagation through the Purkinje system and in the myocardium,
with two-way coupling at the Purkinje-muscle junctions. In both the subproblems
the monodomain model is considered, whereas at the junctions a
resistor element is included that induces an orthodromic propagation delay
from the Purkinje network towards the heart muscle. We prove a sufficient
condition for convergence of a fixed-point iterative algorithm to the
numerical solution of the coupled problem. Numerical comparison of activation
patterns are made with two different combinations of models for
the coupled Purkinje network/myocardium system, the eikonal/eikonal and
the monodomain/monodomain models. Test cases are investigated for both
physiological and pathological activation of a model left ventricle. Finally,
we prove the reliability of the monodomain/monodimain coupling on a real
scenario. Our results underlie the importance of using physiologically realistic
Purkinje-trees with propagation solved using the monodomain model
for simulating cardiac activation |
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18/2015 - 09/04/2015
Masci, C,; Ieva, F.; Agasisti, T.; Paganoni, A.M.
Bivariate multilevel models for the analysis of mathematics and reading pupils' achievements | Abstract | | The purpose of this paper is to identify a relationship between pupils' mathematics and reading test scores and the characteristics of students themselves, stratifying for classes, schools and geographical areas. The dataset of interest contains detailed information about more than 500,000 students at the first year of junior secondary school in the year 2012/2013, provided by the Italian Institute for the Evaluation of Educational System (INVALSI). The innovation of this work is in the use of multivariate models, in which the outcome variable is bivariate: reading and mathematics achievements. Using the bivariate outcome enables researchers to analyze the correlations between achievement levels in the two fields and to estimate statistically significant school and class effects after adjusting for pupil's characteristics. The statistical model employed here explicates account for the potential covariance between the two topics, and at the same time it allows the school effect to vary among them. The results show that while for most cases the direction of school's effect is coherent for reading and mathematics (i.e. positive/negative), there are cases where internal school factors lead to differential performances in the two fields. |
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17/2015 - 09/04/2015
Nestola, M.G.C.; Faggiano, E.; Vergara, C.; Lancellotti, R.M.; Ippolito, S,; Filippi, S.; Quarteroni
Computational comparison of aortic root stresses in presence of stentless and stented aortic valve bio-prostheses | Abstract | | We provide a computational comparison of the performance of stentless and
stented aortic prostheses, in terms of aortic root displacements and internal
stresses. To this aim, we consider three real patients; for each of them
we draw the two prostheses configurations, which are characterized by different
mechanical properties. Moreover, for each patient, we consider also
the healthy configuration. For each scenario, we solve the fluid-structure
interaction problem arising between blood and aortic root, through Finite
Elements. The results show a better agreement between stentless and
healthy displacements and stresses, with respect to the stented case. |
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