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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57/2022 - 08/15/2022
Ruffino, L.; Santoro, A.; Sparvieri, S.; Regazzoni, F.; Adebo, D.A.; Quarteroni, A.; Vergara, C.; Corno, A.F.
Computational analysis of cardiovascular effects of COVID- 19 infection in children | Abstract | | BACKGROUND. The COVID-19 disease can involve any body part; nevertheless, the most serious consequences affect respiratory and cardiocirculatory systems with variable symptoms. Although the effects of COVID-19 are not fully understood yet, clinical evidence has shown that the virus may cause acute myocardial injury and chronic damages to heart and
blood vessels. There is no or limited experience on pathophysiological effects of COVID-19 infection in children’s cardiovascular system.
OBJECTIVES. The aim of this work is to assess the effects of COVID-19 on the cardiovascular system in children, in terms, e.g., of increased pulmonary resistances, reduced cardiac contraction capacity.
METHODS. We used a computational model based on lumped parameters to describe the whole blood circulation. The model was calibrated to account for data coming from 5 child patients.
RESULTS. Our results highlighted that the effect of COVID-19 on the cardiovascular system in children was characterized by the reduction in cardiac blood pressure and volumes. In particular, we analyzed in detail two patients showing a correlation between myocardial compromise and severity of the infection.
CONCLUSIONS. This study demonstrates that COVID-19 infection causes a complex pathophysiological state to the cardiovascular system, both in asymptomatic and symptomatic pediatric patients. This information is very helpful to prevent long term cardiovascular complications of COVID-19 infection in children. A prospective study with regular cardiology follow-up is recommended. |
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56/2022 - 08/11/2022
Africa, P.C.
lifex: a flexible, high performance library for the numerical solution of complex finite element problems | Abstract | | Numerical simulations are ubiquitous in mathematical and computational modeling, where many industrial and clinical applications are required to deal with multiphysics problems and with complex systems characterized by multiple spatial and temporal scales.
This document introduces the design and the capabilities of lifex, an open source C++ library for high performance finite element simulations of multiphysics, multiscale and multidomain problems. lifex offers a versatile solution to answer the emerging need for efficient computational tools that are also easily approachable by a wide community of users and developers. We showcase illustrative examples of use, benchmarks, advanced application scenarios and demonstrate its parallel performance up to thousands of cores. |
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55/2022 - 08/11/2022
Cavinato, L.; Pegoraro, M.; Ragni, A.; Ieva, F.
Imaging-based representation and stratification of intra-tumor Heterogeneity via tree-edit distance | Abstract | | Personalized medicine is the future of medical practice. In oncology, tumor heterogeneity assessment represents a pivotal step for effective treatment planning and prognosis prediction. Despite new procedures for DNA sequencing and analysis, non-invasive methods for tumor characterization are needed to impact on daily routine. On purpose, imaging texture analysis is rapidly scaling, holding the promise to surrogate histopathological assessment of tumor lesions. In this work, we propose a tree-based representation strategy for describing intra-tumor heterogeneity of patients affected by metastatic cancer. We leverage radiomics information extracted from PET/CT imaging and we provide an exhaustive and easily readable summary of the disease spreading. We exploit this novel patient representation to perform cancer subtyping according to hierarchical clustering technique. To this purpose, a new heterogeneity-based distance between trees is defined and applied to a case study of Prostate Cancer (PCa). Clusters interpretation is explored in terms of concordance with severity status, tumor burden and biological characteristics. Results are promising, as the proposed method outperforms current literature approaches. Ultimately, the pro- posed methods draws a general analysis framework that would allow to extract knowledge from daily acquired imaging data of patients and provide insights for effective treatment planning. |
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54/2022 - 08/11/2022
Bucelli, M.; Zingaro, A.; Africa, P. C.; Fumagalli, I.; Dede', L.; Quarteroni, A.
A mathematical model that integrates cardiac electrophysiology, mechanics and fluid dynamics: application to the human left heart | Abstract | | We propose a mathematical and numerical model for the simulation of the heart function that couples cardiac electrophysiology, active and passive mechanics and hemodynamics, and includes reduced models for cardiac valves and the circulatory system. Our model accounts for the major feedback effects among the different processes that characterize the heart function, including electro-mechanical and mechano-electrical feedback as well as force-strain and force-velocity relationships. Moreover, it provides a three-dimensional representation of both the cardiac muscle and the hemodynamics, coupled in a fluid-structure interaction (FSI) model. By leveraging the multiphysics nature of the problem, we discretize it in time with a segregated electrophysiology-force generation-FSI approach, allowing for efficiency and flexibility in the numerical solution. We employ a monolithic approach for the numerical discretization of the FSI problem. We use finite elements for the spatial discretization of those partial differential equations that contribute to the model. We carry out a numerical simulation on a realistic human left heart model, obtaining results that are qualitatively and quantitatively in agreement with physiological ranges and medical images. |
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53/2022 - 07/28/2022
Antonietti, P.F; Cauzzi, C.; Mazzieri, I.; Melas L.; Stupazzini, M.
Numerical simulation of the Athens 1999 earthquake including simplified models of the Acropolis and the Parthenon: initial results and outlook | Abstract | | In this work we present a preliminary study of the seismic response of the Acropolis and of the Parthenon of Athens to the 1999 Mw 5.9 earthquake. The three-dimensional numerical model includes the surface topography of the Attica region, the seismogenic fault, and the most important geological units in the metropolitan area of Athens: the Acropolis hill and the Parthenon. The multiscale numerical model, designed in order to correctly propagate seismic waves up to $5Hz$, is solved through a discontinuous Galerkin spectral element method implemented in the open source library SPEED (speed.mox.polimi.it).
Numerical results show the effectiveness of this approach and highlight new challenges for dynamic soil-structure interaction problems at the regional scale. |
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52/2022 - 07/28/2022
Fedele, M.; Piersanti, R.; Regazzoni, F.; Salvador, M.; Africa, P. C.; Bucelli, M.; Zingaro, A.; Dede', L.; Quarteroni, A.
A comprehensive and biophysically detailed computational model of the whole human heart electromechanics | Abstract | | While ventricular electromechanics is extensively studied in both physiological and pathological conditions, four-chamber heart models have only been addressed recently; most of these works however neglect atrial contraction. Indeed, as atria are characterized by a complex anatomy and a physiology that is strongly influenced by the ventricular function, developing computational models able to capture the physiological atrial function and atrioventricular interaction is very challenging. In this paper, we propose a biophysically detailed electromechanical model of the whole human heart that considers both atrial and ventricular contraction. Our model includes: i) an anatomically accurate whole-heart geometry; ii) a comprehensive myocardial fiber architecture; iii) a biophysically detailed microscale model for the active force generation; iv) a 0D closed-loop model of the circulatory system, fully-coupled with the mechanical model of the heart; v) the fundamental interactions among the different textit{core models}, such as the mechano-electric feedback or the fibers-stretch and fibers-stretch-rate feedbacks; vi) specific constitutive laws and model parameters for each cardiac region. Concerning the numerical discretization, we propose an efficient segregated-intergrid-staggered scheme and we employ recently developed stabilization techniques - regarding the circulation and the fibers-stretch-rate feedback - that are crucial to obtain a stable formulation in a four-chamber scenario. We are able to reproduce the healthy cardiac function for all the heart chambers, in terms of pressure-volume loops, time evolution of pressures, volumes and fluxes, and three-dimensional cardiac deformation, with unprecedented matching (to the best of our knowledge) with the expected physiology. We also show the importance of considering atrial contraction, fibers-stretch-rate feedback and suitable stabilization techniques, by comparing the results obtained with and without these features in the model. The proposed model represents the state-of-the-art electromechanical model of the iHEART ERC project - an Integrated Heart Model for the Simulation of the Cardiac Function - and is a fundamental step toward the building of physics-based digital twins of the human heart. |
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51/2022 - 07/28/2022
Losapio, D.; Scotti, A.
Local Embedded Discrete Fracture Model (LEDFM) | Abstract | | The study of flow in fractured porous media is a key ingredient for many geoscience applications, such as reservoir management and geothermal energy production. Modelling and simulation of these highly heterogeneous and geometrically complex systems require the adoption of non-standard numerical schemes. The Embedded Discrete Fracture Model (EDFM) is a simple and effective way to account for fractures with coarse and regular grids, but it suffers from some limitations: it assumes a linear pressure distribution around fractures, which holds true only far from the tips and fracture intersections, and it can be employed for highly permeable fractures only. In this paper we propose an improvement of EDFM which aims at overcoming these limitations computing an improved coupling between fractures and the surrounding porous medium by a) relaxing the linear pressure
distribution assumption, b) accounting for impermeable fractures modifying near-fracture transmissibilities. These results are achieved by solving different types of local problems with a fine conforming grid, and computing new transmissibilities (for connections between fractures and the surrounding porous medium and those through the porous medium itself near to the fractures). Such local problems are inspired from numerical upscaling techniques present in the literature. The new method is called Local Embedded Discrete Fracture Model (LEDFM) and the results obtained from several numerical tests confirm the aforementioned improvements. |
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50/2022 - 07/28/2022
Elías, A.; Jiménez, R.; Paganoni, A.M.; Sangalli, L.M.
Integrated Depths for Partially Observed Functional Data | Abstract | | Partially observed functional data are frequently encountered in applications and are the object of an increasing interest by the literature. We here address the problem of measuring the centrality of a datum in a partially observed functional sample. We propose an integrated functional depth for partially observed functional data, dealing with the very challenging case where partial observability can occur systematically on any observation of the functional dataset. In particular, differently f rom m any techniques f or partially observed functional data, we do not request that some functional datum is fully observed, nor we require that a common domain exist, where all of the functional data are recorded. Because of this, our proposal can also be used in those frequent situations where reconstructions methods and other techniques for partially observed functional data are inapplicable. By means of simulation studies, we demonstrate the very good performances the proposed depth on finite samples. Our proposal enables the use of benchmark methods based on depths, originally introduced for fully observed data, in the case of partially observed functional data. This include the functional boxplot, the outliergram and the depth vs depth classifiers. We illustrate our proposal on two case studies, the first concerning a problem of outlier detection in German electricity supply functions, the second regarding a classification problem with data obtained from medical imaging. |
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