Multi-Level Parallelism for Incompressible Flow Computations on GPU Clusters

We investigate multi-level parallelism on GPU clusters with MPI-CUDA and hybrid MPI-OpenMP-CUDA parallel implementations, in which all computations are done on the GPU using CUDA. We explore efficiency and scalability of incompressible flow computations using up to 256 GPUs on a problem with approximately 17.2 billion cells. Our work addresses some of the unique issues faced when merging fine-grain parallelism on the GPU using CUDA with coarse-grain parallelism that use either MPI or MPI-OpenMP for communications. We present three different strategies to overlap computations with communications, and systematically assess their impact on parallel performance on two different GPU clusters. Our results for strong and weak scaling analysis of incompressible flow computations demonstrate that GPU clusters offer significant benefits for large data sets, and a dual-level MPI-CUDA implementation with maximum overlapping of computation and communication provides substantial benefits in performance. We also find that our tri-level MPI-OpenMP-CUDA parallel implementation does not offer a significant advantage in performance over the dual-level implementation on GPU clusters with two GPUs per node, but on clusters with higher GPU counts per node or with different domain decomposition strategies a tri-level implementation may exhibit higher efficiency than a dual-level implementation and needs to be investigated further

Neutrally reinforced holes in symmetrically laminated plates

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76616/1/AIAA-46360-396.pd

Investigation of Reynolds Stresses in a 3D Idealized Urban Area Using Large Eddy Simulation

High resolution, large eddy simulation (LES) of neutral flow through an array of cubes has been conducted with periodic boundary conditions in lateral and longitudinal directions. In this paper, we first describe the model formulation and validate the simulation by comparing the mean flow and turbulence statistics with wind-tunnel experimental data from a cube array of buildings. The LES model is then used to investigate the physical mechanisms that lead to the low turbulent stresses that have been reported in the lower half of the urban canopy layer. To do this, the urban boundary layer is conceptually broken down into three distinct regions: (a) the urban roughness sub-layer, (b) street channels (roads with axis aligned with mean wind direction aloft) and (c) street canyons (roads with axis normal to the mean wind direction aloft). The distribution of the Reynolds stresses differ significantly amongst these regions and we hypothesize that the low stresses in the lower half of the canopy can been attributed to the temporary unstable of the above mentioned regions at different periods of time. In a complex urban area, these regions can be observed intermittently at the same physical location, thus, stresses with opposite signs have the potential to cancel each other and on average yield a low magnitude. In this paper, mean turbulence statistics and spectra from high resolution LES have been analyzed for these scenarios and the results have been interpreted within the context of the proposed idealized flow regions

Generalized conductance sum rule in atomic break junctions

When an atomic-size break junction is mechanically stretched, the total conductance of the contact remains approximately constant over a wide range of elongations, although at the same time the transmissions of the individual channels (valence orbitals of the junction atom) undergo strong variations. We propose a microscopic explanation of this phenomenon, based on Coulomb correlation effects between electrons in valence orbitals of the junction atom. The resulting approximate conductance quantization is closely related to the Friedel sum rule.Comment: 4 pages, 1 figure, appears in Proceedings of the NATO Advanced Research Workshop ``Size dependent magnetic scattering'', Pecs, Hungary, May 28 - June 1, 200

Large-eddy simulation of spectral coherence in a wind turbine wake

This work is mainly dedicated to the study of the characteristics of spectral coherence of turbulence fluctuations in wind turbine wakes. A computational fluid dynamics (CFD) code has been implemented using a large-eddy simulation (LES) approach, which is thought to be conceptually more suitable for studying the turbulence evolution in a wind turbine wake. Comparisons with experimental data from the Nørrekær Enge II Windfarm, in Denmark, and with an analytical model proposed by Panofsky and Dutton have been performed, and the results are found to be in reasonable agreement with both

Thermo-Mixed Hydrodynamics of Piston Compression Ring Conjunction

The final publication is available at http://link.springer.com.A new method, comprising Navier-Stokes equations, Rayleigh-Plesset volume fraction equation, an analytical control-volume thermal mixed approach and asperity interactions is reported. The method is employed for prediction of lubricant flow and assessment of friction in the compression ring-cylinder liner conjunction. The results are compared with Reynolds-based laminar flow with Elrod cavitation algorithm. Good conformance is observed for medium load intensity part of the engine cycle. At lighter loads and higher sliding velocity, the new method shows more complex fluid flow, possessing layered flow characteristics on account of pressure and temperature gradient into the depth of the lubricant film, which leads to a cavitation region with vapour content at varied volume fractions. Predictions also conform well to experimental measurements reported by other authors

RELATIVE RISK OF FACTORS FOR CORONARY HEART-DISEASE IN POPULATION WITH LOW-CHOLESTEROL LEVELS

We studied the odds ratios of seven leading risk variables in a population essentially having a 'low' cholesterol concentration. In a cross-sectional population-based study of 3689 Turkish adults 20 years of age or over, 90 men and 83 women were diagnosed to have definite or suspected coronary heart disease. The criteria were based on history, cardiovascular examination and on Minnesota coding of electrocardiograms. Potential risk factors studied were: plasma total cholesterol (greater than or equal to 240 mg/dl), fasting triglycerides (greater than or equal to 200 mg/dl), diabetes mellitus, hypertension (asystolic greater than or equal to 160 mmHg, diastolic greater than or equal to 95 mmHg, or both, or subjects reporting to take antihypertensive medication), smoking currently or in the past, obesity (body mass index greater than or equal to 30 kg/m(2), and physical inactivity. Hypertension and lack of physical exercise constituted the mast important risk factors in both sexes being valid for all age groups and having high attributable risks; odds ratios in men and women, respectively, were 3.16 and 2.6 for hypertension, and 2.16 and 3.49 for physical inactivity. Hypertriglyceridemia followed these factors in men with an odds ratio of 2.15. In women an additional significant factor was obesity (odds ratio 1.76), while diabetes and hypercholesterolemia revealed to be significant only in those aged 20-59 years, and smoking in women aged 30-59 years. Among men, smoking was a borderline significant risk factor for coronary disease, whereas hypercholesterolemia did not prove to be so. These findings, somewhat at variance with those of industrialized nations, may have significance for policy of cardiovascular disease prevention in third-world populations