1,721,250 research outputs found
Interpreting proper orthogonal decomposition modes extracted from partial cavity oscillation
No full textThis study employs the two-dimensional proper orthogonal decomposition approach to analyze the pressure, vapor fraction, and streamwise velocity flowfields of partial cavity oscillation. The interrelations among mode, energy ratio, temporal coefficient, and flowfield reconstruction are thoroughly examined, thereby augmenting comprehension of the cavitating flow mechanism and bubble dynamics. It is found that the first modes of the pressure, vapor fraction, and streamwise velocity flowfields contain 56.31%, 36.37%, and 31.81% energy, respectively; the decrease in energy ratio results in the variation of its temporal coefficient close to sinusoidal configurations. Moreover, the temporal coefficient of the first mode varies closely related to the flowfield-relevant variable. The first modes of the pressure, vapor fraction, and streamwise velocity flowfields are significantly different, but all have two highlighted structures closely related to the self-variable system. The strong nonlinearity and high dimensionality of the cavitation flowfield render precise reconstruction using a limited number of modes exceedingly challenging. The data approximate the original snapshot more closely when the flow field is reconstructed with a greater number of modes. Although the location with a relatively high root mean square reconstruction error is significantly different when the first nine modes are used for flowfield reconstruction, its order of magnitude is less than the self-variable system, and the order discrepancy is fixed, equal to 1
Compressibility characteristics of transient sheet/cloud cavitation – a numerical survey
No full textIn this study, the transient compressible sheet/cloud cavitation around the stationary blade is investigated using a Computational Fluid Dynamics (CFD) method. The instantaneous characteristics of the cavity, such as the destabilization of the sheet cavity, the transformation of the sheet topology into the cloud topology, and the process of shrinking and collapsing of the cloud cavity, are reasonably replicated. The examination of the sheet cavity reveals that the disturbance moving upwards within the cavity is a condensation shock. This shock adheres to the classical Rankine–Hugoniot jump conditions and travels at a hypersonic speed. Once the condensation shock reaches the point where the cavity separates, the sheet cavity unlocks from the surface and transitions into a cloud cavity. The cloud cavity undergoes a reduction in size as it is carried downstream and collapses in the zone of high pressure. Investigations of a small cloud cavity reveal that its collapse results in the release of immense pressure, reaching several million Pascals. Furthermore, the relationship among potential energy, kinetic energy, and pressure wave energy during the collapse of the cavity is exposed, contributing to a more comprehensive comprehension of this intricate phenomenon
Using Weeder for the discovery of conserved transcription factor binding sites
No full textOne of the greatest challenges facing modern molecular biology is the understanding of the complex mechanisms regulating gene expression. A fundamental step in this process requires the characterization of motifs involved in the regulation of gene expression at transcriptional and post-transcriptional levels. In particular, transcription is modulated by the interaction of transcription factors with their corresponding binding sites. Weeder is a software package freely available for non commercial users as a stand-alone or Web-based application for the automatic discovery of conserved motifs in a set of related DNA sequences from coregulated genes. The motifs found are likely to represent instances of binding sites for some common transcription factor regulating the genes of the set. The program has been designed to make its usage as simple as possible and to require very little prior knowledge about the length and conservation of the motifs to be found
In-Pipe Micro-Cycloidal Water Turbine for Energy Harvesting
No full textThis paper analyses a cycloidal turbine to improve power generation in water distribution systems. The turbine is a straight blade type and adopts a cycloidal system that actively controls the rotor blades to improve the efficiency of the turbine, depending on the operating conditions. By utilizing CFD analysis, a parametric study is carried out to investigate the impact of several characteristics. These characteristics encompassed factors, such as variations in chord length, different tip speed ratios, different case size and various phase angles. The study aimed to explore the relationship between these variables and their effects on the overall system. The optimal parameters are determined, and the performance of the turbine improved by about 25 % compared with that of a fixed pitch turbine
Several compressible computational fluid dynamics methods applied to transient sheet/cloud cavitation
No full textThis paper introduces several compressible computational fluid dynamics (CFD) methods and assesses their ability to simulate typical sheetto-cloud cavitating flow around a hydrofoil. More precisely, the Tait equation of state is used to describe the density of water, while the ideal gas equation of state is used to model the density of vapor. The first method assumes that the cavitation is a multiphase flow with isothermal
conditions, meaning that it exhibits isothermal compressibility. Based on the first method, the second and third methods take into account the thermal energy and total energy equations, respectively, i.e., the thermal energy compressibility and the total energy compressibility. An incompressible simulation is also performed for the comparison. The results show that all of the strategies successfully replicate the periodic breakup of the sheet cavity and the formation of the cloud cavity. The predicted frequency of cavity shedding using compressible methods is higher than that using the incompressible method. In addition, all the CFD simulations confirm that the disturbance moving upward in the sheet cavity is actually a condensation shock. The overpressure resulting from the collapse of the cavity can be captured using three compressible approaches. The boundary layer and time-averaged hydrofoil pressure coefficient are compared and analyzed, revealing a negligible difference among the three compressible simulation results
Clipping of unruptured middle cerebral artery aneurysms in an average caseload center: a sustainable procedure?
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Hydraulics/turbo machinery research. Effects of mechanical losses on the affinity characteristics of turbopumps
No full textExperiments on three different designs of pumps, one fitted with a hydraulic thrust control bearing, employed various speeds and geometric similarity extending also to the wall surface roughness and the play between the rotor and the stator. The experiments show that the efficiency values can differ in homologous operating conditions, without any clearly defined law of affinity between the power and the shaft. Applying the similarity law to the overall power, disregarding the mechanical losses, however, permits accurate forecasting of the operating parameters thoughout. A recalculation formula considering separately the hydraulic and mechanical efficiencies, with correction base on a statistical analysis, is probably a more realistic solution to the problem
On the choice of the vane curvature of centrifugal impellers
No full textA computer programme has been develop to investigate the influence that curvature of the blade exercises on the fluid in radial and mixed flow impellers. Point by point method is used for shaping the blade surface. The results of numerical analysis show that a linear variation of the blade angle with the ordinate in the conformal plane is a satisfactory compromise between flow behaviour and geometrical requirements. Blades having NACA profile sections are compared with other configurations. It was observed that the former produce a remarkable fluctuation of the angle of the absolute velocity at the discharge section
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