552 research outputs found
Predicting wind turbine blade loads using vorticity transport and RANS methodologies
Two computational methods, one based on the solution of the vorticity transport equa-
tion, and a second based on the solution of the Reynolds-Averaged Navier-Stokes equa-
tions, have been used to simulate the aerodynamic performance of a horizontal axis wind
turbine. Comparisons have been made against data obtained during Phase VI of the
NREL Unsteady Aerodynamics Experimental and against existing numerical data for a
range of wind conditions. The Reynolds-Averaged Navier-Stokes method demonstrates
the potential to predict accurately the flow around the blades and the distribution of aero-
dynamic loads developed on them. The Vorticity Transport Model possesses a consid-
erable advantage in those situtations where the accurate, but computationally efficient,
modelling of the structure of the wake and the associated induced velocity is critical,
but where the prediction of blade loads can be achieved with sufficient accuracy using
a lifting-line model augmented by incorporating a semi-empirical stall delay model. The
largest benefits can be extracted when the two methods are used to complement each
other in order to understand better the physical mechanisms governing the aerodynamic
performance of wind turbines
A study on the hot spot cooling using micro thermoelectric cooler
Paper presented at the 6th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 30 June - 2 July, 2008.An experimental apparatus to show the hot spot cooling of
an IC chip using a thermoelectric cooler (TEC) is
developed. The spot heating in very small area is achieved by
applying CO2 laser source and temperatures are measured using
miniature thermocouples. The active effects of thermoelectric
cooler on the hot spot cooling system such as rapid heat
spreading in the chip and lowering the peak temperature around
the hot spot region are investigated. The experimental results
are simulated numerically using the TAS program, which the
performance characteristics, such as Seebeck coefficient,
electrical resistance and thermal conductivity of the
thermoelectric cooler are searched by trial and error. Good
agreements are obtained between numerical and experimental
results if the appropriate performance data of the thermoelectric
cooler are given.vk201
Two-phase refrigerant distribution in a parallel flow minichannel heat exchanger having lower combining/dividing header
Brazed aluminum heat exchangers are recently considered
as evaporators of automotive or residential air conditioners. In
this case, it is very important to distribute the two-phase
refrigerant (especially the liquid) evenly into each tube. In this
study, R-410A distribution in a two pass evaporator with upper
horizontal combining-dividing header was investigated. Tubes
were heated to yield a test section outlet superheat of 5oC with
inlet quality of 0.2. The number of tubes was 10 for the inlet
pass and 12 or 14 for the outlet pass. For each case, mass flux
was varied from 73 kg/m2s to 143 kg/m2s. In the
combining/dividing header, two-phase mixture out of the inlet
pass is first merged and then re-distributed to the outlet pass.
More liquid is forced downstream as mass flux or quality
increases yielding better flow distribution. Effect of insertion
device in the inlet header was also investigated. Efforts were
made to develop correlations to predict the liquid or gas
distribution in a header with limited success. Header pressure
drop data are also provided.Papers presented to the 12th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Costa de Sol, Spain on 11-13 July 2016
Recommended Finite Element Formulations for the Analysis of Off-shore Blast Walls in an Explosion
This study suggests relevant finite element (FE) formulations for the structural analysis of offshore blast walls subjected to blast loadings due to hydrocarbon explosions. The present blast wall model adopted from HSE (2003) consists of a corrugated panel and supporting members, and was modelled with shell, thick-shell, and solid element combinations in LS-DYNA, an explicit finite element analysis (FEA) solver. Stainless and mild steels were employed as materials for the blast wall model, with consideration of strain rate effect throughout ten (10) pulse pressure load regimes. The obtained FEA results were validated by experimental data from HSE (2003) with decent agreement. In the present study, recommended FE formulations with additional hourglass control functions were widely discussed from the perspectives of solution accuracy and computational cost based on a statistical approach. The obtained outcomes could be used for the structural analysis and design of offshore blast walls in the estimations of maximum and permanent deformations under blast loadings.111Ysciescopu
Matrix Compactification On Orientifolds
Generalizing previous results for orbifolds, in this paper we describe the
compactification of Matrix model on an orientifold which is a quotient space as
a Yang-Mills theory living on a quantum space. The information of the
compactification is encoded in the action of the discrete symmetry group G on
Euclidean space and a projective representation U of G. The choice of Hilbert
space on which the algebra of U is realized as an operator algebra corresponds
to the choice of a physical background for the compactification. All these data
are summarized in the spectral triple of the quantum space.Comment: 28 pages, late
Z boson pair production at LHC in a stabilized Randall-Sundrum scenario
We study the Z boson pair production at LHC in the Randall-Sundrum scenario
with the Goldberger-Wise stabilization mechanism. It is shown that
comprehensive account of the Kaluza-Klein graviton and radion effects is
crucial to probe the model: The KK graviton effects enhance the cross section
of on the whole so that the resonance peak of the radion becomes
easy to detect, whereas the RS effects on the process are
rather insignificant. The and invariant-mass distributions are presented
to study the dependence of the RS model parameters. The production of
longitudinally polarized Z bosons, to which the SM contributions are
suppressed, is mainly due to KK gravitons and the radion, providing one of the
most robust methods to signal the RS effects. The sensitivity bounds
on with are also obtained such that
the effective weak scale of order 5 TeV can be experimentally
probed.Comment: 28 pages, LaTex file, 18 eps figure
Observational and Modeling Analysis of Land–Atmopshere Coupling over Adjacent Irrigated and Rainfed Cropland during the GRAINEX Field Campaign
The Great Plains Irrigation Experiment (GRAINEX) was conducted in the spring and summer of 2018 to investigate Land-Atmosphere (L-A) coupling just prior to and through the growing season across adjacent, but distinctly unique, soil moisture regimes (contrasting irrigated and rainfed fields). GRAINEX was uniquely designed for the development and analysis of an extensive observational dataset for comprehensive process studies of L-A coupling, by focusing on irrigated and rainfed croplands in a ~100 x 100 km domain in southeastern Nebraska. Observation platforms included multiple NCAR EOL Integrated Surface Flux Systems and Integrated Sounding Systems, NCAR CSWR Doppler Radar on Wheels, 1200 radiosonde balloon launches from 5 sites, the NASA GREX airborne L-Band radiometer, and 75 University of Alabama-Huntsville Environmental Monitoring Economic Monitoring Sensor Hubs (EMESH mesonet stations). An integrated observational and modeling approach to advance knowledge of L-A coupling processes and precipitation impacts in regions of heterogeneous soil moisture will be presented. Specifically, through observation of land surface states, surface fluxes, near surface meteorology, and properties of the atmospheric column, an examination of the diurnal planetary boundary layer evolving characteristics will be presented. Results from a hierarchy of modeling platforms (e.g. single column, large-eddy, and mesoscale simulations) will also be presented to complement the observational findings. The modeling effort will generate high spatiotemporal resolution datasets to: 1) generate a multi-physics ensemble to test the robustness and potentially advance physical parameterizations in high resolution weather and climate models, 2) comparison of prescribed forcing from observations and those from offline land surface model simulations and high resolution operational analyses, 3) determine the ability of model simulations to reproduce observed boundary layer evolution, with particular attention to the processes that compose the L-A coupling chain and metrics (e.g. mixing ratio diagrams), and 4) in combination with observations, isolate the impacts of soil moisture heterogeneity on planetary boundary layer characteristics, cloud development, precipitation, mesoscale circulation patters and boundary layer development. Initial results from the observational and modeling analysis will be presented
Segmentation in 2D and 3D image using Tissue-Like P System
Membrane Computing is a biologically inspired computational model. Its devices are called P systems and they perform computations by applying a finite set of rules in a synchronous, maximally parallel way. In this paper, we open a new research line: P systems are used in Computational Topology within the context of the Digital Image. We choose for this a variant of P systems, called tissue-like P systems, to obtain in a general maximally parallel manner the segmentation of 2D and 3D images in a constant number of steps. Finally, we use a software called Tissue Simulator to check these systems with some examples
Quasinormal modes from potentials surrounding the charged dilaton black hole
We clarify the purely imaginary quasinormal frequencies of a massless scalar
perturbation on the 3D charged-dilaton black holes. This case is quite
interesting because the potential-step appears outside the event horizon
similar to the case of the electromagnetic perturbations on the large
Schwarzschild-AdS black holes. It turns out that the potential-step type
provides the purely imaginary quasinormal frequencies, while the
potential-barrier type gives the complex quasinormal modes.Comment: 19 pages, 8 figure
Droplet printing reveals the importance of micron-scale structure for bacterial ecology
Bacteria often live in diverse communities where the spatial arrangement of strains and species is considered critical for their ecology. However, a test of this hypothesis requires manipulation at the fine scales at which spatial structure naturally occurs. Here we develop a droplet-based printing method to arrange bacterial genotypes across a sub-millimetre array. We print strains of the gut bacterium Escherichia coli that naturally compete with one another using protein toxins. Our experiments reveal that toxin-producing strains largely eliminate susceptible non-producers when genotypes are well-mixed. However, printing strains side-by-side creates an ecological refuge where susceptible strains can persist in large numbers. Moving to competitions between toxin producers reveals that spatial structure can make the difference between one strain winning and mutual destruction. Finally, we print different potential barriers between competing strains to understand how ecological refuges form, which shows that cells closest to a toxin producer mop up the toxin and protect their clonemates. Our work provides a method to generate customised bacterial communities with defined spatial distributions, and reveals that micron-scale changes in these distributions can drive major shifts in ecology
- …