4,808 research outputs found
Hemodynamics of the heart's left atrium based on a Variational Multiscale-LES numerical model
In this paper, we investigate the hemodynamics of a left atrium (LA) by
proposing a computational model suitable to provide physically meaningful fluid
dynamics indications and detailed blood flow characterization. In particular,
we consider the incompressible Navier-Stokes equations in Arbitrary Lagrangian
Eulerian (ALE) formulation to deal with the LA domain under prescribed motion.
A Variational Multiscale (VMS) method is adopted to obtain a stable formulation
of the Navier-Stokes equations discretized by means of the Finite Element
method and to account for turbulence modeling based on Large Eddy Simulation
(LES). The aim of this paper is twofold: on one hand to improve the general
understanding of blood flow in the human LA in normal conditions; on the other,
to analyse the effects of the turbulence VMS-LES method on a situation of blood
flow which is neither laminar, nor fully turbulent, but rather transitional as
in LA. Our results suggest that if relatively coarse meshes are adopted, the
additional stabilization terms introduced by the VMS-LES method allow to better
predict transitional effects and cycle-to-cycle blood flow variations than the
standard SUPG stabilization method
Aerospace Medicine and Biology: A continuing bibliography with indexes, supplement 182, July 1978
This bibliography lists 165 reports, articles, and other documents introduced into the NASA scientific and technical information system in June 1978
Use of Machine Learning for Automated Convergence of Numerical Iterative Schemes
Convergence of a numerical solution scheme occurs when a sequence of increasingly refined iterative solutions approaches a value consistent with the modeled phenomenon. Approximations using iterative schemes need to satisfy convergence criteria, such as reaching a specific error tolerance or number of iterations. The schemes often bypass the criteria or prematurely converge because of oscillations that may be inherent to the solution. Using a Support Vector Machines (SVM) machine learning approach, an algorithm is designed to use the source data to train a model to predict convergence in the solution process and stop unnecessary iterations. The discretization of the Navier Stokes (NS) equations for a transient local hemodynamics case requires determining a pressure correction term from a Poisson-like equation at every time-step. The pressure correction solution must fully converge to avoid introducing a mass imbalance. Considering time, frequency, and time-frequency domain features of its residual’s behavior, the algorithm trains an SVM model to predict the convergence of the Poisson equation iterative solver so that the time-marching process can move forward efficiently and effectively. The fluid flow model integrates peripheral circulation using a lumped-parameter model (LPM) to capture the field pressures and flows across various circulatory compartments. Machine learning opens the doors to an intelligent approach for iterative solutions by replacing prescribed criteria with an algorithm that uses the data set itself to predict convergence
Prognosis of the state of health of a person under spaceflight conditions
Methods of predicting the state of health and human efficiency during space flight are discussed. Diversity of reactions to the same conditions, development of extrapolation methods of prediction, and isolation of informative physiological indexes are among the factors considered
A monolithic and a partitioned Reduced Basis Method for Fluid-Structure Interaction problems
The aim of this work is to present an overview about the combination of the
Reduced Basis Method (RBM) with two different approaches for Fluid-Structure
Interaction (FSI) problems, namely a monolithic and a partitioned approach. We
provide the details of implementation of two reduction procedures, and we then
apply them to the same test case of interest. We first implement a reduction
technique that is based on a monolithic procedure where we solve the fluid and
the solid problems all at once. We then present another reduction technique
that is based on a partitioned (or segregated) procedure: the fluid and the
solid problems are solved separately and then coupled using a fixed point
strategy. The toy problem that we consider is based on the Turek-Hron benchmark
test case, with a fluid Reynolds number Re = 100
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