다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

Statistics For Spatial Data

Fluid dynamic turbulence is one of the most challenging computational physics problems because of the extremely wide range of time and space scales involved, the strong nonlinearity of the governing equations, and the many practical and important applications. While most linear fluid instabilities are well understood, the nonlinear interactions among them makes even the relatively simple limit of homogeneous isotropic turbulence difficult to treat physically, mathematically, and computationally. Turbulence is modeled computationally by a two-stage bootstrap process. The first stage, direct numerical simulation, attempts to resolve the relevant physical time and space scales but its application is limited to diffusive flows with a relatively small Reynolds number (Re). Using direct numerical simulation to provide a database, in turn, allows calibration of phenomenological turbulence models for engineering applications. Large eddy simulation incorporates a form of turbulence modeling applicable when the large-scale flows of interest are intrinsically time dependent, thus throwing common statistical models into question. A promising approach to large eddy simulation involves the use of high-resolution monotone computational fluid dynamics algorithms such as flux-corrected transport or the piecewise parabolic method which have intrinsic subgrid turbulence models coupled naturally to the resolved scales in the computed flow. The physical considerations underlying and evidence supporting this monotone integrated large eddy simulation approach are discussed.

New insights into large eddy simulation

Boundary Value Problems in Physics and Engineering By Frank Chorlton. Pp. 250. (Van Nostrand: London, July 1969.) 70s

Boundary value problems

a 'sleeper', receiving only modest attention for 50 years before emerging as a cornerstone of communications engineering in more recent times. Roughly one in six of Walsh's 281 publications are included, photographically reproduced. Reproduction is excellent except for one paper from 1918. The book also reproduces three brief papers about Walsh and his work, by W. E. Sewell, D. V. Widder and Morris Marden. The first two were written for a special issue of the SIAM Journal celebrating Walsh's 70th birthday; the third is an obituary.

Matrix iterative analysis (2nd edn), by Richard S. Varga. Springer Series in Computational Mathematics 27. Pp. 358. £55. 2000. ISBN 3 540 66321 5 (Springer Verlag).

This article can be considered as an extension of the paper of Fukagata et al (Phys Fluids 14:L73, 2002) who derived an analytical expression for the componential contributions into skin friction in a turbulent channel, pipe and plane boundary layer flows In this paper, we extend theoretical analysis of Fukagata et al limited to canonical cases with two-dimensional mean flow to a fully three-dimensional situation allowing complex wall shapes We start our analysis by considering arbitrarily-shaped surfaces and then formulate a restriction on a surface shape for which the current analysis is valid Theoretical formula for skin friction coefficient is thus given for streamwise and spanwise homogeneous surfaces of any shape, as well as some more complex configurations, including spanwise-periodic wavy patterns Current theoretical analysis is validated using the results of Large Eddy Simulations of a turbulent flow over straight and wavy riblets with triangular and knife-blade cross-sections Decomposition of skin friction into different componential contributions allows to analyze the influence of different dynamical effects on a drag modification by riblet-covered surfaces

Theoretical prediction of turbulent skin friction on geometrically complex surfaces

It is known that longitudinal ribs manufactured in a flat surface act to reduce turbulent skin-friction drag, providing a moderate drag reduction of 4 to 8%. It is shown in this paper that this value can be increased by at least 50% if sinusoidal-like rods are used instead of conventional straight riblets. Large Eddy Simulation of a turbulent flow over a riblet-covered surface is performed for three cases: straight riblets and sinusoidal riblets with two different values of wavelength. All riblets have triangular cross-section. It is found that drag reduction with sinusoidal riblets depend strongly on the wavelength, showing a benefit over straight riblets for a larger value of the wavelength, and an opposite trend for a smaller value. Different nature of the flow over straight and sinusoidal riblet surfaces is revealed by looking at crossflow motion in transverse planes, mean and instantaneous streamwise vorticity, and organized coherent structures. Turbulent statistics is compared between all three cases, crossflow turbulence intensity is reduced for sinusoidal riblets as opposed to straight riblets.

Yulia Peet

Papers

Theoretical prediction of turbulent skin friction on geometrically complex surfaces

Turbulent Drag Reduction using Sinusoidal Riblets with Triangular Cross-Section

Pressure loss reduction in hydrogen pipelines by surface restructuring

Large-scale thermal motions of turbulent Rayleigh–Bénard convection in a wide aspect-ratio cylindrical domain

A spectrally accurate method for overlapping grid solution of incompressible Navier-Stokes equations