Search results for "Numerical"
showing 10 items of 2002 documents
Steady, periodic, quasi-periodic and chaotic flow regimes in toroidal pipes
2012
Incompressible flow in a toroidal pipe was investigated by direct numerical simulation. The curvature a/c (radius of the cross section / radius of the torus) was 0.3 or 0.1 and the bulk Reynolds number ranged between 3500 and 14 700. The study revealed a rich scenario of transition to turbulence. For the higher curvature a/c = 0.3, a supercritical transition from stationary to periodic flow (Hopf bifurcation) was observed at Re=4600. The periodic flow was characterized by a travelling wave which, in the whole periodic Re range, took the form of a varicose modulation of the twin Dean vortex rings, included 8 wavelengths along the axis of the torus, and exhibited instantaneous anti-symmetry a…
Corrigendum to “Smooth and non-smooth traveling wave solutions of some generalized Camassa–Holm equations” [19 (6) (2014) 1746–1769]
2015
Corrigendum Corrigendum to ‘‘Smooth and non-smooth traveling wave solutions of some generalized Camassa–Holm equations’’ [19 (6) (2014) 1746–1769] M. Russo , S. Roy Choudhury , T. Rehman , G. Gambino b University of Central Florida, Department of Mathematics, 4000 Central Florida Blvd., Orlando, USA University of Palermo, Department of Mathematics and Computer Science, Via Archirafi 34, 90123 Palermo, Italy
Corrigendum to “Regular and singular pulse and front solutions and possible isochronous behavior in the short-pulse equation: Phase-plane, multi-infi…
2022
Section 7 of the original paper contained several errors which are corrected here. Equations (54) and (55) are incorrect. In the following, the corrected versions of these equations are given and the subsequent results of Section 7 are also revised.
Boundary-layer Flows Past an Hemispherical Roughness Element: DNS, Global Stability and Sensitivity Analysis
2015
Abstract We investigate the full three-dimensional instability mechanism arising in the wake of an hemispherical roughness element immersed in a laminar Blasius boundary layer. The inherent three-dimensional flow pattern beyond the critical Reynolds number is characterized by coherent vortical structures called hairpin vortices. Direct numerical simulation is used to analyze the formation and the shedding of hairpin packets inside the shear layer. The first bifurcation characteristics are investigated by global stability tools. We show the spatial structure of the linear direct and adjoint global eigenmodes of the linearized Navier-Stokes operator and use structural sensitivity analysis to …
On solving separable block tridiagonal linear systems using a GPU implementation of radix-4 PSCR method
2018
Partial solution variant of the cyclic reduction (PSCR) method is a direct solver that can be applied to certain types of separable block tridiagonal linear systems. Such linear systems arise, e.g., from the Poisson and the Helmholtz equations discretized with bilinear finite-elements. Furthermore, the separability of the linear system entails that the discretization domain has to be rectangular and the discretization mesh orthogonal. A generalized graphics processing unit (GPU) implementation of the PSCR method is presented. The numerical results indicate up to 24-fold speedups when compared to an equivalent CPU implementation that utilizes a single CPU core. Attained floating point perfor…
Twenty-year trends in the prevalence of Down syndrome and other trisomies in Europe : impact of maternal age and prenatal screening
2013
This study examines trends and geographical differences in total and live birth prevalence of trisomies 21, 18 and 13 with regard to increasing maternal age and prenatal diagnosis in Europe. Twenty-one population-based EUROCAT registries covering 6.1 million births between 1990 and 2009 participated. Trisomy cases included live births, fetal deaths from 20 weeks gestational age and terminations of pregnancy for fetal anomaly. We present correction to 20 weeks gestational age (ie, correcting early terminations for the probability of fetal survival to 20 weeks) to allow for artefactual screening-related differences in total prevalence. Poisson regression was used. The proportion of births in …
Identifying Rossby wave trains and quantifying their properties
2013
A novel method is introduced to automatically identify upper-level Rossby wave trains and to objectively diagnose their properties. Based on the envelope of the upper tropospheric meridional wind represented in a Hovmoller diagram, the algorithm identifies individual Rossby wave trains as objects. These depend to some extent on user defined parameters. The utility of the method is demonstrated in two areas of application. First, the skill of a particular numerical weather prediction model is analysed for a specific case of a long-lived Rossby wave train. For this purpose, a novel diagnostic is designed based on a Hovmoller diagram of the Rossby wave train objects that contains forecast data…
High-accuracy approximation of piecewise smooth functions using the Truncation and Encode approach
2017
Abstract In the present work, we analyze a technique designed by Geraci et al. in [1,11] named the Truncate and Encode (TE) strategy. It was presented as a non-intrusive method for steady and non-steady Partial Differential Equations (PDEs) in Uncertainty Quantification (UQ), and as a weakly intrusive method in the unsteady case. We analyze the TE algorithm applied to the approximation of functions, and in particular its performance for piecewise smooth functions. We carry out some numerical experiments, comparing the performance of the algorithm when using different linear and non-linear interpolation techniques and provide some recommendations that we find useful in order to achieve a hig…
Design and experimental test of a low costweather buoy
2013
The importance of prevention plans based on realistic inundation scenarios was dramatically highlighted by the Indian Ocean Tsunami of 26 December 2004. But also in the Mediterranean, sea storms basin are a quite common event especially during winter months. These scenarios are generally based on numerical models of tsunami wave propagation that can become more realistic and effective when calibrated with the distribution of true data acquired by special weather buoy. In this paper we present the result of an experimental weather buoy built by DEIM of University of Palermo, that is characterized by small cost and big versatility.
Modeling multiple taxis: Tumor invasion with phenotypic heterogeneity, haptotaxis, and unilateral interspecies repellence
2021
We provide a short review of existing models with multiple taxis performed by (at least) one species and consider a new mathematical model for tumor invasion featuring two mutually exclusive cell phenotypes (migrating and proliferating). The migrating cells perform nonlinear diffusion and two types of taxis in response to non-diffusing cues: away from proliferating cells and up the gradient of surrounding tissue. Transitions between the two cell subpopulations are influenced by subcellular (receptor binding) dynamics, thus conferring the setting a multiscale character. We prove global existence of weak solutions to a simplified model version and perform numerical simulations for the full se…