1,630 research outputs found
Widest scales in turbulent channels
The widest spanwise scales in turbulent channel flows are studied through the
use of three periodic channel-flow simulations at friction Reynolds number
. The length and height of the channels are the same in
all cases ( and respectively), while the width is
progressively doubled: . The effects of
increasing the domain can not be determined with statistical significance in
our simulations, since the difference in the statistics between the simulations
is of the same order as the errors of convergence. A channel flow similar to
the smaller one (, vol. 500, 2004, pp. 135--144),
which was averaged over a very long time, was used as a reference. The
one-dimensional spanwise spectrum of the streamwise velocity is computed with
the aim of assessing the domain-size effect on the widest scales. Our results
indicate that of the total streamwise energetic fluctuations is
recovered without a significant influence of the size of the domain. The
remaining of the energy reflects that the widest scales in the outer
layer are the ones most significantly affected by the spanwise length of the
domain. The power-spectral density for remains constant even if the
size of the domain in the spanwise direction is increased up to 4 times the
standard spanwise length, indicating that wide, spanwise coherent structures
are not an artifact of domain truncation
Object oriented data analysis in ALEPH
This article describes the status of the ALPHA^{++} project of the ALEPH collaboration. The ALEPH data have been converted from Fortran data structures (BOS banks) into C^{++} objects and stored in a object oriented database (Objectivity/DB), using tools provided by the RD45 collaboration and the LHC^{++} software project at CERN. A description of the database setup and of a preliminary version of an object oriented analysis program is given.This article describes the status of the ALPHA^{++} project of the ALEPH collaboration. The ALEPH data have been converted from Fortran data structures (BOS banks) into C^{++} objects and stored in a object oriented database (Objectivity/DB), using tools provided by the RD45 collaboration and the LHC^{++} software project at CERN. A description of the database setup and of a preliminary version of an object oriented analysis program is given
Predicting the wall-shear stress and wall pressure through convolutional neural networks
The objective of this study is to assess the capability of convolution-based
neural networks to predict wall quantities in a turbulent open channel flow.
The first tests are performed by training a fully-convolutional network (FCN)
to predict the 2D velocity-fluctuation fields at the inner-scaled wall-normal
location , using the sampled velocity fluctuations in
wall-parallel planes located farther from the wall, at . The
predictions from the FCN are compared against the predictions from a proposed
R-Net architecture. Since the R-Net model is found to perform better than the
FCN model, the former architecture is optimized to predict the 2D streamwise
and spanwise wall-shear-stress components and the wall pressure from the
sampled velocity-fluctuation fields farther from the wall. The dataset is
obtained from DNS of open channel flow at and . The
turbulent velocity-fluctuation fields are sampled at various inner-scaled
wall-normal locations, along with the wall-shear stress and the wall pressure.
At , both FCN and R-Net can take advantage of the
self-similarity in the logarithmic region of the flow and predict the
velocity-fluctuation fields at using the velocity-fluctuation
fields at as input with about 10% error in prediction of
streamwise-fluctuations intensity. Further, the R-Net is also able to predict
the wall-shear-stress and wall-pressure fields using the velocity-fluctuation
fields at with around 10% error in the intensity of the
corresponding fluctuations at both and . These results
are an encouraging starting point to develop neural-network-based approaches
for modelling turbulence near the wall in large-eddy simulations.Comment: 33 pages, 10 figures. arXiv admin note: substantial text overlap with
arXiv:2107.0734
Aerodynamic Effects of Uniform Blowing and Suction on a NACA4412 Airfoil
We carried out high-fidelity large-eddy simulations to investigate the effects of uniform blowing and uniform suction on the aerodynamic efficiency of a NACA4412 airfoil at the moderate Reynolds number based on chord length and incoming velocity of Rec= 200 , 000. We found that uniform blowing applied at the suction side reduces the aerodynamics efficiency, while uniform suction increases it. This result is due to the combined impact of blowing and suction on skin friction, pressure drag and lift. When applied to the pressure side, uniform blowing improves aerodynamic efficiency. The Reynolds-number dependence of the relative contributions of pressure and friction to the total drag for the reference case is analysed via Reynolds-averaged Navier–Stokes simulations up to Rec= 10 , 000 , 000. The results suggest that our conclusions on the control effect can tentatively be extended to a broader range of Reynolds numbers
Magnetic-film atom chip with 10 m period lattices of microtraps for quantum information science with Rydberg atoms
We describe the fabrication and construction of a setup for creating lattices
of magnetic microtraps for ultracold atoms on an atom chip. The lattice is
defined by lithographic patterning of a permanent magnetic film. Patterned
magnetic-film atom chips enable a large variety of trapping geometries over a
wide range of length scales. We demonstrate an atom chip with a lattice
constant of 10 m, suitable for experiments in quantum information science
employing the interaction between atoms in highly-excited Rydberg energy
levels. The active trapping region contains lattice regions with square and
hexagonal symmetry, with the two regions joined at an interface. A structure of
macroscopic wires, cut out of a silver foil, was mounted under the atom chip in
order to load ultracold Rb atoms into the microtraps. We demonstrate
loading of atoms into the square and hexagonal lattice sections simultaneously
and show resolved imaging of individual lattice sites. Magnetic-film lattices
on atom chips provide a versatile platform for experiments with ultracold
atoms, in particular for quantum information science and quantum simulation.Comment: 7 pages, 7 figure
On the decay of turbulence in plane Couette flow
The decay of turbulent and laminar oblique bands in the lower transitional
range of plane Couette flow is studied by means of direct numerical simulations
of the Navier--Stokes equations. We consider systems that are extended enough
for several bands to exist, thanks to mild wall-normal under-resolution
considered as a consistent and well-validated modelling strategy. We point out
a two-stage process involving the rupture of a band followed by a slow
regression of the fragments left. Previous approaches to turbulence decay in
wall-bounded flows making use of the chaotic transient paradigm are
reinterpreted within a spatiotemporal perspective in terms of large deviations
of an underlying stochastic process.Comment: ETC13 Conference Proceedings, 6 pages, 5 figure
Persistent storage of non-event data in the CMS databases
In the CMS experiment, the non event data needed to set up the detector, or being produced by it, and needed to calibrate the physical responses of the detector itself are stored in ORACLE databases. The large amount of data to be stored, the number of clients involved and the performance requirements make the database system an essential service for the experiment to run. This note describes the CMS condition database architecture, the data-flow and PopCon, the tool built in order to populate the offline databases. Finally, the first results obtained during the 2008 and 2009 cosmic data taking are presented.In the CMS experiment, the non event data needed to set up the detector, or being produced by it, and needed to calibrate the physical responses of the detector itself are stored in ORACLE databases. The large amount of data to be stored, the number of clients involved and the performance requirements make the database system an essential service for the experiment to run. This note describes the CMS condition database architecture, the data-flow and PopCon, the tool built in order to populate the offline databases. Finally, the first experience obtained during the 2008 and 2009 cosmic data taking are presented
Individual Rights, Economic Transactions, and Recognition: A Legal Approach to Social Economics
Modernity brought the idea of individual property rights as a com- plex phenomenon. However, economics adopted a simplistic view of property as a fundamental institution, understating the complex interaction of different rights and obligations that frame the legal environment of economic processes with an insufficiently elaborated tool. Here, a more elaborate view of legal elements will be propose
Pursuing interpretations of the HERA large-Q2 data
We explore interpretations of the anomaly observed by H1 and ZEUS at HERA in
deep-inelastic e^+ p scattering at very large Q^2. We discuss the possibilities
of new effective interactions and the production of a narrow state of mass 200
GeV with leptoquark couplings. We compare these models with the measured Q^2
distributions: for the contact terms, constraints from LEP2 and the Tevatron
allow only a few choices of helicity and flavour structure that could roughly
fit the HERA data. The data are instead quite consistent with the Q^2
distribution expected from a leptoquark state. We study the production cross
sections of such a particle at the Tevatron and at HERA. The absence of a
signal at the Tevatron disfavours the likelihood that any such leptoquark
decays only into e^+ q. We then focus on the possibility that the leptoquark is
a squark with R-violating couplings. In view of the present experimental limits
on such couplings, the most likely production channels are e^+d -> scharm_L or
perhaps e^+d->stop, with e^+s->stop a more marginal possibility. Possible tests
of our preferred model include the absence both of analogous events in e^- p
collisions and of charged current events, and the presence of detectable
cascade decays whose kinematical signatures we discuss. We also discuss the
possible implications for K->pi nu nubar, neutrinoless double-beta decay, the
Tevatron and for e^+ e^- ->q qbar and neutralinos at LEP2.Comment: 28 pages, Latex, epsfig, 8 figures. Note added on contact term
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