Heat Transfer in Turbulent Rayleigh-Benard Convection below the Ultimate Regime

A Rayleigh-B\'enard cell has been designed to explore the Prandtl (Pr) dependence of turbulent convection in the cross-over range $0.7<Pr<21$ and for the full range of soft and hard turbulences, up to Rayleigh number $Ra\simeq 10^{11}$. The set-up benefits from the favourable characteristics of cryogenic helium-4 in fluid mechanics, in-situ fluid property measurements, and special care on thermometry and calorimetric instrumentation. The cell is cylindrical with $diameter/height=0.5$. The effective heat transfer $Nu(Ra,Pr)$ has been measured with unprecedented accuracy for cryogenic turbulent convection experiments in this range of Rayleigh numbers. Spin-off of this study include improved fits of helium thermodynamics and viscosity properties. Three main results were found. First the $Nu(Ra)$ dependence exhibits a bimodality of the flow with $4-7$ difference in $Nu$ for given $Ra$ and $Pr$. Second, a systematic study of the side-wall influence reveals a measurable effect on the heat transfer. Third, the $Nu(Pr)$ dependence is very small or null : the absolute value of the average logarithmic slope $(dlnNu/dlnPr)_{Ra}$ is smaller than 0.03 in our range of $Pr$, which allows to disciminate between contradictory experiments [Ashkenazi \textit{et al.}, Phys. Rev.Lett. 83:3641 (1999)][Ahlers \textit{et al.}, Phys.Rev.Lett. 86:3320 (2001)].Comment: submitted for publication to JLTP (august 2003

A bodner-partom visco-plastic dynamic sphere benchmark problem

Developing benchmark analytic solutions for problems in solid and fluid mechanics is very important for the purpose of testing and verifying computational physics codes. Our primary objective in this research is to obtain a benchmark analytic solution to the equation of motion in radially symmetric spherical coordinates. An analytic solution for the dynamic response of a sphere composed of an isotropic visco-plastic material and subjected to spherically symmetric boundary conditions is developed and implemented. The radial displacement u is computed by solving the equation of motion, a linear second-order hyperbolic PDE. The plastic strains εp and εp are computed by solving two non-linear first-order ODEs in time. We obtain a solution for u in terms of the plastic strain components and boundary conditions in the form of an infinite series. Computationally, at each time step, we set up an iteration scheme to solve the PDE-ODE system. The linear momentum equation is solved using the plastic strains from the previous iteration, then the plastic strain equations are solved numerically using the new displacement. We demonstrate the accuracy and convergence of our benchmark solution under spatial mesh, time step, and eigenmode refinement

Energy cascade and the four-fifths law in superfluid turbulence

The 4/5-law of turbulence, which characterizes the energy cascade from large to small-sized eddies at high Reynolds numbers in classical fluids, is verified experimentally in a superfluid 4He wind tunnel, operated down to 1.56 K and up to R_lambda ~ 1640. The result is corroborated by high-resolution simulations of Landau-Tisza's two-fluid model down to 1.15 K, corresponding to a residual normal fluid concentration below 3 % but with a lower Reynolds number of order R_lambda ~ 100. Although the K\'arm\'an-Howarth equation (including a viscous term) is not valid \emph{a priori} in a superfluid, it is found that it provides an empirical description of the deviation from the ideal 4/5-law at small scales and allows us to identify an effective viscosity for the superfluid, whose value matches the kinematic viscosity of the normal fluid regardless of its concentration.Comment: 6 pages, 7 figure

Experimental Design for Determining the Cyclic Behavior of Skewed Reduced Beam Section Moment Connections having Composite Slabs

This paper details the experimental design for determining the cyclic behavior of skewed Reduced Beam Section (RBS) moment connections having composite slabs. The effects of composite concrete slabs on skewed RBS connections subjected to cyclic seismic prequalification loading are addressed in this test setup. Full-scale double-sided RBS SMF specimens representing both interior and exterior column connections are designed and fabricated in this work. Experimental test fixturing and a lateral load application setup within the existing Grady E. Harvell Civil Engineering Research and Education Center (CEREC) are designed. All cyclic loading protocols required for the prequalification testing are described herein. Prequalification of the skewed SMF specimens requires the application of a total story drift of 0.04 radian before a 20% reduction in plastic moment capacity (Mp)

Experimental Design for Determining the Cyclic Behavior of Skewed Reduced Beam Section Moment Connections having Composite Slabs

This paper details the experimental design for determining the cyclic behavior of skewed Reduced Beam Section (RBS) moment connections having composite slabs. The effects of composite concrete slabs on skewed RBS connections subjected to cyclic seismic prequalification loading are addressed in this test setup. Full-scale double-sided RBS SMF specimens representing both interior and exterior column connections are designed and fabricated in this work. Experimental test fixturing and a lateral load application setup within the existing Grady E. Harvell Civil Engineering Research and Education Center (CEREC) are designed. All cyclic loading protocols required for the prequalification testing are described herein. Prequalification of the skewed SMF specimens requires the application of a total story drift of 0.04 radian before a 20% reduction in plastic moment capacity (Mp)

The DELPHI Silicon Tracker in the global pattern recognition

ALEPH and DELPHI were the first experiments operating a silicon vertex detector at LEP. During the past 10 years of data taking the DELPHI Silicon Tracker was upgraded three times to follow the different tracking requirements for LEP 1 and LEP 2 as well as to improve the tracking performance. Several steps in the development of the pattern recognition software were done in order to understand and fully exploit the silicon tracker information. This article gives an overview of the final algorithms and concepts of the track reconstruction using the Silicon Tracker in DELPHI.Comment: Talk given at the 8th International Workshop on Vertex Detectors, Vertex'99, Texel, Nederland