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 1251 products
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28/2010 - 11/03/2010
Crosetto, Paolo; Reymond, Philippe; Deparis, Simone; Kontaxakis, Dimitrios; Stergiopulos, Nikolaos; Quarteroni, Alfio
Fluid Structure Interaction Simulations of Physiological Blood Flow in the Aorta | Abstract | | The numerical tools to simulate blood flow in the cardiovascular system are constantly developing due to the great clinical interest and to scientifi c advances in mathematical models and computational power. The present work aims to address and validate new algorithms to efficiently predict the hemodynamics in large arteries. The latter rely on fi nite elements simulation of the fluid-structure interaction between blood flow and arterial wall deformation of a healthy aorta. Di fferent sets of boundary conditions are devised and tested. The mean velocity and pressure time evolution is plotted
on di erent sections of the aorta and the wall shear stress distribution is computed. The results are compared with those obtained with a rigid wall simulation. Pulse wave velocity is computed and compared with the values available from the literature. The flow boundary conditions used for the outlets are obtained using the solution of as one dimensional model. The results of the simulations are in agreement with the physiological data in terms of wall shear stress, wall displacement, pressure waveforms and velocities. |
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27/2010 - 11/02/2010
Bruggi, Matteo; Verani, Marco
An adaptive algorithm for topology optimization with goal-oriented error control | Abstract | | We present an adaptive scheme, named ATOPT algorithm, to address volume–constrained compliance minimization, a benchmark problem in topology optimization.
The algorithm performs a set of optimization loops on an underlying grid that is iteratively adapted to improve the description quality of the topology of the structure and the accuracy of the finite element compliance approximation of the
evolving solution. Two suitable error estimators are defined in order to address both the issues. Numerical simulations show that ATOPT algorithm achieves optimal layouts that are in full agreement with standard results obtained by employing large scale uniformly refined grids. However, the ATOPT algorithm turns out to be more
accurate in terms of the approximation of both the elastic behavior and the topology, while the computational cost spent in the minimization algorithm is remarkably reduced.
Keywords: topology optimization, minimum compliance, adaptive mesh refinement.
2000 Mathematics Subject Classification. 65N30, 93B40 |
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26/2010 - 07/16/2010
Ieva, Francesca; Paganoni, Anna Maria
Designing and mining a multicenter observational clinical registry concerning patients with Acute Coronary Syndromes | Abstract | | In this work we describe design, aims and contents of the ST-segment Elevation Myocardial Infarction (STEMI) Archive, which is a multicenter
observational clinical registry planned within the Strategic Program Exploitation, integration and study of current and future health databases
in Lombardia for Acute Myocardial Infarction . This is an observational disease registry that collects clinical indicators, process indicators and outcomes concerning STEMI patients admitted to any hospital in Lombardia Region.
This registry is arranged to be automatically linked to the Public Health Database, the on going administrative databank of Lombardia
Region. In this work we also provide an example of statistical tools implemented on a pilot integrated database in order to explore and model such an informative database. |
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25/2010 - 07/15/2010
Pena, G.; Prud'homme, C.; Quarteroni, A.
High Order Methods for the Approximation of the Incompressible Navier-Stokes Equations in a Moving Domain | Abstract | | In this paper we address the numerical approximation of the incompressible Navier-Stokes
equations in a moving domain by the spectral element method and high order time integrators. We present the Arbitrary Lagrangian Eulerian (ALE) formulation of the incompressible
Navier-Stokes equations and propose a numerical method based on the following kernels: a Lagrange basis associated with Fekete points in the spectral element method context, BDF time integrators, an ALE map of high degree, and a robust algebraic linear solver.
In particular, the high degree ALE map is appropriate to deal with a computational domain whose boundary is described with curved elements. Finally, we apply the proposed strategy to a
test case. |
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24/2010 - 07/14/2010
Tamellini, Lorenzo; Formaggia, Luca; Miglio, Edie; Scotti, Anna
An Uzawa iterative scheme for the simulation of floating boats | Abstract | | The numerical simulation of a floating boat requires to solve a complex interaction between free surface flow and the dynamics of the boat. In this work we focus on solution schemes with an explicit representation of the fluid surface and on the speci c problem of the imposition of the presence of a floating object. The floating object represents an unilateral constraint on
the fluid surface, which cannot rise above a the level de ned by the floating object itself.
We propose an Uzawa type iterative scheme for this type of situations and we describe an efficient implementation in the context of a
particular finite element discretization and algebraic splitting procedure. |
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23/2010 - 07/13/2010
Baeck, Joakim; Nobile, Fabio; Tamellini, Lorenzo; Tempone, Raul
Stochastic Spectral Galerkin and collocation methods for PDEs with random coefficients: a numerical comparison | Abstract | | Much attention has recently been devoted to the development of Stochastic Galerkin (SG) and Stochastic Collocation (SC) methods for uncertainty quanti fication. An open and relevant research topic is the comparison of these two methods. By introducing a suitable generalization of the classical sparse grid SC method, we are able to compare SG and SC on the same underlying multivariate polynomial space in terms of accuracy versus computational work.
The approximation spaces considered here include
isotropic and anisotropic versions of Tensor Product (TP), Total Degree(TD), Hyperbolic Cross (HC) and Smolyak (SM) polynomials.
Numerical results for linear elliptic SPDEs indicate a slight computational work advantage
of isotropic SC over SG, with SC-SM and SG-TD being the best choices of approximation spaces for each method. Finally, numerical results
corroborate the optimality of the theoretical estimate of anisotropy ratios introduced by the authors in a previous work for the construction of
anisotropic approximation spaces. |
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22/2010 - 07/12/2010
D'Angelo, Carlo; Zunino, Paolo
Numerical approximation with Nitsche s coupling of transient Stokes /Darcy s flow problems applied to hemodynamics | Abstract | | In this work, we consider a time dependent coupled Stokes-Darcy flow problem and study an approximation method based on a unifi ed finite element scheme complemented with implicit time stepping. Our fi nite element formulation relies on a weighing strategy in which the physical and discretization parameters are taken into account to robustly enforce interface and boundary conditions by means of the Nitsche s method. We prove unconditional absolute stability and optimal convergence of the scheme, and discuss the
algebraic properties of the associated discrete problem. Finally, we present numerical experiments con firming the predicted convergence behavior and algebraic properties, and report an application to the computational analysis of
blood flow and plasma filtration in arteries after the implantation of a vascular
graft. |
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21/2010 - 06/30/2010
Grieco, Niccolò; Ieva, Francesca; Paganoni, Anna Maria
Provider Profiling Using Mixed Effects Models on a Case Study concerning STEMI Patients | Abstract | | Provider profi ling is the evaluation process of the performance of hospitals, doctors, and other medical practitioners to enhance the quality of
medical care. In this work we describe statistical analyses conducted on MOMI2 (MOnth MOnitoring Myocardial Infarction in MIlan) survey, a collection of data concerning patients admitted with STEMI (ST-Elevation Myocardial Infarction) diagnosis in one of the hospitals belonging to the Milan urban area Network, with the aim of pointing out process indicators
to be used in health-care evaluation. An ff ective statistical support to decisional process for clinical and organizational governance is then obtained analyzing and modelling data coming from clinical registers and administrative data banks. Typically this kind of data are grouped at first level by structure where patients are admitted to, so multilevel models have been considered and tted to catch and explain overdispersion phenomena.
Moreover, we compare three di fferent techniques of hospitals classi cation based respectively on traditional survival rates comparison, on analysis of variance components in fitted generalized linear mixed e ects models and
non parametric random e ects estimation.
Key words:
Generalized Linear Mixed Models
In-hospital survival
ST-Elevation Myocardial Infarction
Provider Pro filing |
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