1,460 research outputs found
development of a bem cfd tool for vertical axis wind turbines based on the actuator disk model
Abstract The present work focuses on the numerical simulation of Vertical Axis Wind Turbines by means of an "in-house" BEM-based User Defined Function to be used 39ith the CFD code ANSYS Fluent. Typical VAWT unsteady and 3D phenomena, such as dynamic stall, flow curvature and tip losses, are taken into account by original and literature-based sub-models. The presence of the blades is mimicked by replacing them with suitable momentum sources. For the present work, the Actuator Cylinder Model has been employed. 3D analysis, of a SANDIA rotor, are carried out in order to assess the accuracy of our model against numerical simulations and experimental data. The current User Defined Function is able to give a satisfactory agreement with the reference cases especially from a qualitative point of view, with a significant computational time reduction to a factor of 10 compared to the case with the moving bodies. A typical wake behavior can be noticed in our simulations even though its recovery is strongly influenced by the lack of turbulence inherent to the chosen actuator model. The torque and the power coefficient of the turbines are also analyzed and compared against the reference cases, finding a remarkable agreement. The model has been successfully applied to predict the transient aerodynamic loads of an offshore 5 MW troposkein turbine subjected to the pitching motion of its platform. The operating conditions have been chosen in order to allow a qualitative comparison with a floating 5 MW horizontal axis turbine which performance under pitching motion is available in literature
The Hilbert space operator formalism within dynamical reduction models
Unlike standard quantum mechanics, dynamical reduction models assign no
particular a priori status to `measurement processes', `apparata', and
`observables', nor self-adjoint operators and positive operator valued measures
enter the postulates defining these models. In this paper, we show why and how
the Hilbert-space operator formalism, which standard quantum mechanics
postulates, can be derived from the fundamental evolution equation of dynamical
reduction models. Far from having any special ontological meaning, we show that
within the dynamical reduction context the operator formalism is just a compact
and convenient way to express the statistical properties of the outcomes of
experiments.Comment: 25 pages, RevTeX. Changes made and two figures adde
T-mixer operating with water at different temperatures: Simulation and stability analysis
In this paper we investigate the transition from the vortex to the engulfment regime in a T-mixer when the two entering flows have different viscosity. In particular we consider as working fluid water entering the two inlet channels of the mixer at two different temperatures. Contrary to the isothermal case, at low Reynolds numbers the vortex regime shows only a single reflectional symmetry, due to the nonhomogeneous distribution of the viscosity. Increasing the Reynolds number, a symmetry-breaking bifurcation drives the system to a new steady flow configuration, usually called the engulfment regime, similar to what it is possible to observe in an isothermal case. This flow regime is associated with an increase of the mixing between the two inlet streams. It is shown by direct numerical simulation (DNS) and by stability analysis that the engulfment regime is promoted by the temperature difference. Starting from the DNSs, the resulting flow fields are analyzed in detail considering different temperature jumps between the two inlet boundaries. Furthermore, dedicated linear stability analyses are carried out to investigate the instability mechanism associated with the occurrence of the engulfment regime. In particular, similarly to the case without temperature differences, the onset of engulfment is driven by the momentum equation, and the temperature field does not lead to any additional instability mechanism. However, the existence of a temperature field leads to quantitative changes of the stability characteristics and of the resulting flow fields via a variation of the viscosity coefficient
Reshaping the Museum of Zoology in Rome by Visual Storytelling and Interactive Iconography
This article summarizes the concept of a new immersive and interactive setting for the Zoology Museum in Rome, Italy. The concept, co-designed with all the museum’s curators, is aimed at enhancing the experiential involvement of the visitors by visual storytelling and interactive iconography. Thanks to immersive and interactive technologies designed by Centro Studi Logos, developed by Logosnet and known as e-REALâ and MirrorMeä, zoological findings and memoirs come to life and interact directly with the visitors in order to deepen their understanding, visualize stories and live experiences, and interact with the founder of the Museum (Mr. Arrigoni degli Oddi) who is now a virtualized avatar, or digital human, able to talk with the visitors. All the interactions are powered through simple hand gestures and, in a few cases, vocal inputs that transform into recognized commands from multimedia systems
Statistical properties of an ideal subgrid-scale correction for Lagrangian particle tracking in turbulent channel flow
One issue associated with the use of Large-Eddy Simulation (LES) to
investigate the dispersion of small inertial particles in turbulent flows is
the accuracy with which particle statistics and concentration can be
reproduced. The motion of particles in LES fields may differ significantly from
that observed in experiments or direct numerical simulation (DNS) because the
force acting on the particles is not accurately estimated, due to the
availability of the only filtered fluid velocity, and because errors accumulate
in time leading to a progressive divergence of the trajectories. This may lead
to different degrees of inaccuracy in the prediction of statistics and
concentration. We identify herein an ideal subgrid correction of the a-priori
LES fluid velocity seen by the particles in turbulent channel flow. This
correction is computed by imposing that the trajectories of individual
particles moving in filtered DNS fields exactly coincide with the particle
trajectories in a DNS. In this way the errors introduced by filtering into the
particle motion equations can be singled out and analyzed separately from those
due to the progressive divergence of the trajectories. The subgrid correction
term, and therefore the filtering error, is characterized in the present paper
in terms of statistical moments. The effects of the particle inertia and of the
filter type and width on the properties of the correction term are
investigated.Comment: 15 pages,24 figures. Submitted to Journal of Physics: Conference
Serie
A time-variable, phase-dependent emission line in the X-ray spectrum of the isolated neutron star RXJ0822–4300
RX J0822−4300 is the central compact object associated with the Puppis A supernova remnant. Previous X-ray observations suggested RX J0822−4300 to be a young neutron star with a weak dipole field and a peculiar surface temperature distribution dominated by two antipodal spots with different temperatures and sizes. An emission line at 0.8 keV was also detected. We performed a very deep (130-ks) observation with XMM–Newton, which allowed us to study in detail the phase-resolved properties of RX J0822−4300. Our new data confirm the existence of a narrow spectral feature, best modelled as an emission line, only seen in the ‘soft’-phase interval – when the cooler region is best aligned to the line of sight. Surprisingly, comparison of our recent observations to the older ones yields evidence for a variation in the emission-line component, which can be modelled as a decrease in the central energy from ∼0.80 keV in 2001 to ∼0.73 keV in 2009–10. The line could be generated via cyclotron scattering of thermal photons in an optically-thin layer of gas, or, alternatively, it could originate in low-rate accretion by a debris disc. In any case, a variation in energy, pointing to a variation of the magnetic field in the line-emitting region, cannot be easily accounted for
Chamber basis of the Orlik-Solomon algebra and Aomoto complex
We introduce a basis of the Orlik-Solomon algebra labeled by chambers, so
called chamber basis. We consider structure constants of the Orlik-Solomon
algebra with respect to the chamber basis and prove that these structure
constants recover D. Cohen's minimal complex from the Aomoto complex.Comment: 16 page
The quantum theory of measurement within dynamical reduction models
We analyze in mathematical detail, within the framework of the QMUPL model of
spontaneous wave function collapse, the von Neumann measurement scheme for the
measurement of a 1/2 spin particle. We prove that, according to the equation of
the model: i) throughout the whole measurement process, the pointer of the
measuring device is always perfectly well localized in space; ii) the
probabilities for the possible outcomes are distributed in agreement with the
Born probability rule; iii) at the end of the measurement the state of the
microscopic system has collapsed to the eigenstate corresponding to the
measured eigenvalue. This analysis shows rigorously how dynamical reduction
models provide a consistent solution to the measurement problem of quantum
mechanics.Comment: 24 pages, RevTeX. Minor changes mad
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