131 research outputs found
Volume penalization for inhomogeneous Neumann boundary conditions modeling scalar flux in complicated geometry
We develop a volume penalization method for inhomogeneous Neumann boundary
conditions, generalizing the flux-based volume penalization method for
homogeneous Neumann boundary condition proposed by Kadoch et al. [J. Comput.
Phys. 231 (2012) 4365]. The generalized method allows us to model scalar flux
through walls in geometries of complex shape using simple, e.g. Cartesian,
domains for solving the governing equations. We examine the properties of the
method, by considering a one-dimensional Poisson equation with different
Neumann boundary conditions. The penalized Laplace operator is discretized by
second order central finite-differences and interpolation. The discretization
and penalization errors are thus assessed for several test problems.
Convergence properties of the discretized operator and the solution of the
penalized equation are analyzed. The generalized method is then applied to an
advection-diffusion equation coupled with the Navier-Stokes equations in an
annular domain which is immersed in a square domain. The application is
verified by numerical simulation of steady free convection in a concentric
annulus heated through the inner cylinder surface using an extended square
domain.Comment: 32 pages, 19 figure
Scale-dependent statistics of inertial particle distribution in high Reynolds number turbulence
Multiscale statistical analyses of inertial particle distributions are
presented to investigate the statistical signature of clustering and void
regions in particle-laden incompressible isotropic turbulence.
Three-dimensional direct numerical simulations of homogeneous isotropic
turbulence at high Reynolds number () with up to
inertial particles are performed for Stokes numbers ranging from to
. Orthogonal wavelet analysis is then applied to the computed particle
number density fields. Scale-dependent skewness and flatness values of the
particle number density distributions are calculated and the influence of
Reynolds number and Stokes number is assessed. For , both the scale-dependent skewness and flatness values become larger as
the scale decreases, suggesting intermittent clustering at small scales. For
, the flatness at intermediate scales, i.e. for scales larger than
the Kolmogorov scale and smaller than the integral scale of the flow, increases
as increases, and the skewness exhibits negative values at the
intermediate scales. The negative values of the skewness are attributed to void
regions. These results indicate that void regions at the intermediate sales are
pronounced and intermittently distributed for such small Stokes numbers. As
increases, the flatness increases slightly. For , the skewness shows negative values at large scales, suggesting that void
regions are pronounced at large scales, while clusters are pronounced at small
scales.Comment: 26 pages, 9 figure
A wavelet-based three-dimensional Convolutional Neural Network for superresolution of turbulent vorticity
We develop a wavelet-based three-dimensional convolutional neural network (WCNN3d) for superresolution of coarse-grained data of homogeneous isotropic turbulence. The turbulent flow data are computed by high resolution direct numerical simulation (DNS), while the coarse-grained data are obtained by applying a Gaussian filter to the DNS data. The CNNs are trained with the DNS data and the coarse-grained data. We compare vorticity- and velocity-based approaches and assess the proposed WCNN3d method in terms of flow visualization, enstrophy spectra and probability density functions. We show that orthogonal wavelets enhance the efficiency of the learning of CNN
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Participation in Sports Organizations and the Prevention of Functional Disability in Older Japanese: The AGES Cohort Study
Background: We sought to examine prospectively the difference in the association between incident functional disability and exercise with or without sports organization participation. Methods: The study was based on the Aichi Gerontological Evaluation Study (AGES) Cohort Study data. In October 2003, self-reported questionnaires were mailed to 29,374 non-disabled Japanese individuals aged 65 years or older. Of these, 13,310 individuals were introduced to the Study, and they were followed for 4 years. Analysis was carried out on 11,581 subjects who provided all necessary information for the analysis. Results: Analysis was carried out on incident functional disability by 4 groups of different combinations of performance of exercise and participation in a sports organization Active Participant (AP), Exercise Alone (EA), Passive Participant (PP) and Sedentary (S). Compared to the AP group, the EA group had a hazard ratio (HR) of 1.29 (1.02–1.64) for incident functional disability. No significant difference was seen with the PP group, with an HR of 1.16 (0.76–1.77). When a measure of social networks was added to the covariates, the HR of the EA group dropped to 1.27 (1.00–1.61), and significant differences disappeared. In contrast, it showed hardly any change when social support was added. Conclusion: The results suggested that, even with a regular exercise habit, incident functional disability may be better prevented when a person participates in a sports organization than when he/she does not. In addition, participation in a sports organization correlates positively with social networks, which may lead to a small decrease in incident functional disability
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