1,721,131 research outputs found
ENERGY RECOVERY VALVE SYSTEM WITH SPHERICAL SEGMENT VALVE FOR CONTROLLING THE FLUID FLOW IN A DUCT
No full textENERGY RECOVERY VALVE SYSTEM WITH LATERAL FLOW VALVE FOR CONTROLLING THE FLUID FLOW IN A DUCT
No full textPrediction of flow-control devices' noise with modified acoustic perturbation equations
Full text linkFluid-dynamic noise emissions produced by flow-control devices inside ducts are a concerning issue for valve manufacturers and pipeline management. This work proposes a modified formulation of Acoustic Perturbation Equations (APE) that is applicable to industrial frameworks where the interest is addressed to noise prediction according to international standards. This formulation is derived from a literature APE system removing two terms allowing for a computational time reduction of about 20%. The physical contribution of the removed terms is discussed according to the literature. The modified APE are applied to the prediction of the noise emitted by an orifice. The reliability of the new APE system is evaluated by comparing the Sound Pressure Level (SPL) and the acoustic pressure with the ones returned by LES and literature APE. The new formulation agrees with the other methods far from the orifice: moving over nine diameters downstream of the trailing edge, the SPL is in accordance with the other models. Since international standards characterize control devices with the noise measured 1 m downstream of them, the modified APE formulation provides reliable and faster noise prediction for those devices with outlet diameter, d, such that 9d < 1 m
Performances of Pressure Reducing Valves in Variable Demand Conditions: Experimental Analysis and New Performance Parameters
Full text linkPressure Reducing Valves (PRV) play a critical role in Water Distribution Networks (WDN): they regulate pressure ensuring an efficient service to users and preventing damage to pipelines. In recent years, the attention of water utilities towards pressure management and leakage control led to the necessity of more flexible and responsive technologies that can guarantee a higher level of pressure control accuracy. Because of this the common performance parameters based on steady state conditions are no longer satisfactory to evaluate the effective behaviour of the devices when used in situations where demand can change. In the present paper the pressure control effectiveness of different types of PRV (electric actuated, pilot operated and direct acting) in variable demand conditions is discussed. The data used are from experimental tests, literature and field application. To assess valves’ pressure control performance, the use of new parameters, which consider the peak of pressure reached during control operations and the accuracy of target pressure regulation, has been proposed. The use of these parameters allows the comparison between different type of valves giving to WDN managers a direct overview on the valves ability to regulate pressure under variable demand condition
Laboratory testing of a combined heaving-surging wave energy converter for the nearshore zone
No full textThe EDS (Energy Double System) is a combined heave-surge oscillating-body WEC (wave energy converter) designed for the nearshore zone, composed by a heaving float and a surging paddle supported by a unique structure. This paper investigates, through laboratory modelling, the behavior of EDS at various water depths along a sloping beach. The float alone, obtained by removing the paddle from the EDS, was also tested for comparison. Tests were performed with regular waves. Results shows that, as water depth decreases, the upward motion of the float and the forward motion of the paddle are more energetic and faster than their opposite motions (downward and backward, respectively). The CWRs (capture width ratios) of the float alone and the float inside the EDS are similar and they increase as water depth increases. Thanks to the presence of the paddle, the CWR of the EDS is larger than that of the float alone at all the tested water depths; it presents a maximum off the breaking point, and then decreases as water depth increases. The interpretation of the laboratory results allowed to draft a method for detecting the optimal water depth to install the EDS in a real sea site
Voice and data services in multicode and variable spreading factor DS-CDMA systems
No full textThis paper analyzes the uplink capacity of multicode and variable spreading factor DS-CDMA cellular systems which accommodate users with different transmission rate requirements. It takes into account imperfect power control on slow signal fluctuations due to shadowing, the presence of Rayleigh fading and a random location of the users. The circumstance where the portable transmits to the nearest base station is examined; when shadowing only is present, the possibility that the user chooses the least interfered among Nc nearest base stations is also considered. System capacity is determined analytically, employing two distinct approximations featuring low computational costs, as well as by simulation. The latter approach allows to compare the accuracy of the analytical approximations for a wide range of system parameters
Estimation of aerodynamic noise of diaphragms through IEC 60534-8-3 and CFD
Full text linkThe aerodynamic noise emitted by a subsonic flow of dry air through an orifice plate is estimated in terms of internal sound power level and external sound pressure level (SPL) by application of the methodology described in the international standard IEC 60534-8-3. A shortcoming of the standard in defining the efficiency of the transformation of the mechanical energy of the flow into acoustic energy is discussed. Experimental evidence of the matter is also described. An alternative model employing the resolution of Reynolds Averaged Navier-Stokes equations (RANS) by means of Computational Fluid Dynamics (CFD) techniques for the calculation of the acoustic power generated by the turbulent flow through the orifice plate is applied so as to overcome the issue
An analysis method of the vortex-induced vibrations of a tethered sphere
Full text linkVortex-induced vibrations (VIV) in systems with more than one degree of freedom often present complex synchronization among the motion components, also hidden by the randomness that characterizes the motion itself. A phase average method has been here developed and applied to the displacements of a tethered sphere, at low mass and damping, to analyze its xy trajectories over a wide range of reduced velocities, 5 ≤ U* ≤ 25 (Reynolds numbers, 5.1 × 103 ≤ Re ≤ 2.67 × 104). This method has allowed the identification of both the periodic and chaotic contribution of each motion component, accurately reconstructing the underlying trajectory periodic pattern. The two classical vibration modes, I and II, have been also observed. The method developed here was able to better rebuild the experimental data compared to other methods found in the relevant literature, providing useful insights into the study of the dynamic response of a freely-oscillating tethered sphere immersed in a steady flow
Analisi dell’influenza della superficie libera sulle vibrazioni di una sfera investita da una corrente stazionaria ed uniforme
No full textNel presente lavoro si studiano gli effetti della superficie libera sui movimenti di una sfera investita da una corrente
fluida stazionaria e uniforme. La sfera è caratterizzata da un basso valore del parametro combinato massa-smorzamento
(m*ζ=0.005) ed è libera di muoversi sia nella direzione principale della corrente sia in quella trasversale. In
tutti gli esperimenti il coefficiente di bloccaggio γb (rapporto tra la superficie frontale del corpo e la sezione trasversale
della corrente) viene mantenuto costante, mentre la sfera viene posizionata a diverse distanze dalla superficie libera.
Gli spostamenti nella direzione della corrente e in quella trasversale sono stati misurati contemporaneamente attraverso
una telecamera ad alta risoluzione che ha permesso la ricostruzione bidimensionale delle traiettorie e l’analisi in
frequenza del segnale. I risultati sottolineano un cambiamento della risposta dinamica della sfera all’aumentare della
velocità media della corrente e all’avvicinarsi del corpo alla superficie libera
Interaction between a tethered sphere and a free surface flow
No full textThe paper analyses the vibrations and the flow field around a tethered sphere in a free surface flow in order to study the influence of the vortex shedding process on the dynamic response of the obstacle and on its oscillation frequency. The system is characterized by a low value of the mass ratio (ratio between the mass of the system and the added mass), a low value of damping and a low value of relative submergence (ratio between the depth of the current and the diameter of the sphere). The experiments are set up to measure the movements of the sphere in the main and transversal directions of the fluid flow with laser sensors and image analysis, whereas the description of the main wake structures of the flow downstream of the sphere are provided using the PIV technique
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