1,720,969 research outputs found
Transitional regimes and rotation effects in Rayleigh–Bénard convection in a slender cylindrical cell
No full textIn this paper we analyze transitional regimes and mean flow structures for the thermally driven convective flow in a cylindrical cell of aspect-ratio (diameter over cell height) Γ=1/2. The investigation is carried out through the numerical integration of the three-dimensional unsteady Navier–Stokes equations with the Boussinesq approximation. In particular the critical Rayleigh numbers for the onset of convection, for the unsteady, chaotic and turbulent regimes are computed for two values of the Prandtl number and comparisons with cylindrical cells of larger aspect-ratio are performed. The effect of the background rotation on the flow dynamics is also described showing that the heat transfer increase, already evidenced in the literature, is only obtained for a range of rotation rates. The rotation can enhance or inhibit the heat transfer and, at low Rayleigh numbers, it is a very effective way to inhibit vertical motions and to prevent horizontal thermal gradients. This is highly desirable in solidification and crystal growth processes where thermally induced motions cause material defects and crystal inhomogeneities
Investigation of a pressure compensated vane pump
Full text linkVariable displacement hydraulic machines offer a very promising alternative and energy saving solution for many applications in mobile machines, robots and other applications. In the present paper a vane pump will be theoretically analyzed using the software AMESim and/or MATLAB/Simulink, in order to estimate the friction forces and volumetric efficiency loss without hardworking experimental tests. The friction forces taken into account by our model are the friction between vanes and rotor slots and that between vanes and eccentric pump stator. The same design parameters affect the volumetric and mechanical efficiency, whose behavior has been reported and discussed. The behavior of the machine is analyzed and discussed at different angular velocities and pressure regimes
Design of a non-invasive sensing system for diagnosing gastric disorders
No full textGastric disorders are widely spread among the population of any age. At the moment, the diagnosis is made by using invasive systems
that cause several side effects. The present manuscript proposes an innovative non-invasive sensing system for diagnosing gastric
dysfunctions. The Electro-GastroGraphy (EGG) technique is used to record myoelectrical signals of stomach activities. Although EGG
technique is well known for a long time, several issues concerning the signal processing and the definition of suitable diagnostic criteria
are still unresolved. So, EGG is to this day a trial practice. The authors want to overcome the current limitations of the technique and
improve its relevance. To this purpose, a smart EGG sensing system has been designed to non-invasively diagnose gastric disorders. In
detail, the system records the gastric slow waves by means of skin surface electrodes placed in the epigastric area. Cutaneous
myoelectrical signals are so acquired from the body surface in proximity of stomach. Electro-gastrographic record is then processed.
According to the diagnostic model designed from the authors, the system estimates specific diagnostic parameters in time and frequency
domains. It uses Discrete Wavelet Transform to obtain power spectral density diagrams. The frequency and power of the EGG waveform
and the dominant frequency components are so analyzed. The defined diagnostic parameters are put in comparison with the reference
values of a normal EGG in order to estimate the presence of gastric pathologies by the analysis of arrhythmias (tachygastria, bradygastria
and irregular rhythm). The paper aims to describe the design of the system and of the arrhythmias detection algorithm. Prototype
development and experimental data will be presented in future works. Preliminary results show an interesting relevance of the
suggested technique so that it can be considered as a promising non-invasive tool for diagnosing gastrointestinal motility disorders
About 3D Incompressible Flow Reconstruction from 2D Flow Field Measurements
No full textIn this paper, an assessment of the uncertainty affecting a hybrid procedure (experimen-tal/numerical) is carried out to validate it for industrial applications, at the least. The procedure in question serves to depict 3D incompressible flow fields by using 2D measurements of it and computing the third velocity component by means of the continuity equation. A quasi-3D test case of an incompressible flow has been inspected in the wake of a NACA 0012 airfoil immersed in a forced flow of water running in a rectangular open channel. Specifically, starting from a 2D measurement data in planes orthogonal to the stream-wise direction, the computational approach can predict the third flow velocity component. A 3D ADV instrument has been utilized to measure the flow field, but only two velocity components have been considered as measured quantities, while the third one has been considered as reference with which to compare the computed component from the continuity equation to check the accuracy and validity of the hybrid procedure. At this aim, the uncertainties of the quantities have been evaluated, according to the GUM, to assess the agreement between experiments and predictions, in addition to other metrics. This aspect of uncertainty is not a technical sophistication but a substantial way to bring to the use of a 1D and 2D measurement system in lieu of a 3D one, which is costly in terms of maintenance, calibration, and economic issues. Moreover, the magnitude of the most relevant flow indicators by means of experimental data and predictions have been estimated and compared, for further confirmation by means of a supervised learning classification. Further, the sensed data have been processed, by means of a machine learning algorithm, to express them in a 3D way along with accuracy and epoch metrics. Two additional metrics have been included in the effort to show paramount interest, which are a geostatistical estimator and Sobol sensitivity. The statements of this paper can be used to design and test several devices for industrial purposes more easily
Pair and multi-particle dispersion in numerical simulations of convective boundary layer turbulence
No full textTracer dispersion within a highly convective planetary boundary layer is studied by means of a large-eddy simulation (LES) model for the continuous phases describing the temperature and velocity fields, and with the Lagrangian tracking of particle trajectories. Particle velocities are decomposed into their resolved and unresolved (or sub-grid) components. The former are evaluated by interpolation from the LES velocity field, the latter are given by a Lagrangian kinematic model that correctly describes the turbulent dispersion of clouds of particles. It is shown that, thanks to the Lagrangian sub-grid model, a clear inertial range is detectable in the time domain. In this range, particle separation grows according to Richardson's law, and nicely compares with previous experimental and numerical measurements. The collective motion of four particles, initially located at the vertices of regular tetrahedra, is also studied. The evolution of tetrad shape and orientation is contrasted with those obtained in homogeneous and isotropic flows. Results show that an agreement is achieved at small time lags. At larger times, the boundary layer reveals its anisotropic structure and the tetrad shape statistics deviate from results obtained in ideal flows
Fractal dimension of a liquid flows predicted coupling an Eulerian-Lagrangian approach with a Level-Set method
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Discharging shape influence on the performance of a latent heat thermal energy storage
No full textDue to the mismatching between the renewable energy source and the energy demand, the energy storage devices have attracted the attention of the scientific community in order to maximize their performance. Several technologies have been developed and applied in laboratory scale and prototypes in the last decades. The energy storage devices can be mainly defined according to the average working temperature, the storage material, and the geometrical configuration. This work is focused on the 2D axisymmetric finite volume multiphase numerical simulations of the fluid flow and heat transfer within a shell-and-tube type latent heat thermal energy storage (LHTES). The effect of the geometrical parameters on the thermal performance of such systems is investigated. The influence of the LHTES shape is highlighted keeping constant the heat exchange area, the total storable heat and the heated surface temperature. Detailed description of the liquid fraction and temperature distribution during the solidification phase are reported. The solidification phase appears strongly influenced by the geometry. The geometries have been chosen according to fixed volume and heat exchange area condition. The ratio between the external and the internal radius (re/ri) has been changed and its effect on the thermal performance of the thermal storage device is considered. Thus, according to the application requirement, particular care should be taken in the design of the shape of the LHTES device
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