Variation Of Maximum Velocity Research Articles

Application of Tesla Valve’s Obstruction Characteristics to Reverse Fluid in Fish Migration

More and more activities have caused significant damage to the river environment, among which a typical problem of blocked fish migration is constantly attracting people’s attention. Nowadays, fishways are essential hydraulic facilities to solve such problems. Although a different fishway has a particular blocking effect on the water flow, the flow velocity of the vital positions of fish migration in the fishway could still be relatively high locally, which may pose a certain challenge to the fish migration (the higher flow velocity could lead to the increase in migratory energy consumption of fish). Therefore, further exploration of fish passing facilities may be required. As a check valve without movable parts, the Tesla valve is expected to be used in fish passing facilities because of its substantial obstruction to the reverse flow of internal fluid. This paper conducted numerical simulation experiments on the fish passage pipeline designed based on Tesla valves using the RNG (renormalization group) k-ε model. Grass carp were selected as the primary analysis object, and the simulation results were analyzed from the perspective of turbulence characteristics. The results showed that the fish passage pipeline based on the T45-R Tesla valve was better than that on the GMF (Gamboa, Morris and Forster) Tesla valve in velocity control. The velocity at the vital position of T45-R internal fluid was about 20% lower than that of GMF. The results of the velocity cloud diagram showed apparent high-velocity and low-velocity areas in the fish passage pipeline designed based on the T45-R Tesla valve. The high-velocity area was the vital position for fish upstream, and the maximum velocity variation range in this area was 0.904~1.478 m/s. At the same time, the flow in the low-velocity area is almost static water. The analysis illustrated that the resulting velocity environment could provide conditions for grass carp to move upstream successfully. The results of turbulent kinetic energy inside the fish passage pipeline showed that the maximum value of turbulent kinetic energy was only about 0.043 m2/s2, which could be friendly for fish upstream. In addition, the results show that pressure-related problems could not seem to have an excessive impact on fish migration, such as causing damage. Overall, the results further studied the feasibility of using the Tesla valve as a fish passage pipeline.

Performance Improvement of a Low-Power Wind Turbine Using Conical Sections

This paper examines the performance of conical sections (concentrator and diffuser) to improve the energy-recovery prospects of small-scale wind turbines. Detailed simulation studies of the conical sections with convergence angle viz., concentrator, and divergence angle viz., diffuser were conducted using ANSYS Fluent® software. Using simulation data, a trend analysis was conducted, and the empirical equations were derived for calculating the velocity variation and power variation in terms of the convergence/divergence angles. Working prototype models with optimum angles were fabricated for both the diffuser and concentrator. These models were then augmented with a wind turbine coupled with a 100 W, 24 V DC generator and tested to validate the simulation results. Upon analyzing the simulation data, it was found that a maximum velocity variation of 23.3% was achieved at an angle of 4.5° for the diffuser, whereas a maximum power variation of 65.1% was achieved at an angle of 3.6° for the same diffuser. The aforementioned improvement was achieved by optimizing divergence angle alone. The proposed designs of the diffuser- and concentrator-augmented wind turbine, as well as the empirical equations for calculating the velocity variation and power variation in terms of the divergence and convergence angle, are the major contributions of this article.

The Magnitude of Diurnal/Semidiurnal Atmospheric Tides (S1/S2) and Their Impacts on the Continuous GPS Coordinate Time Series

The site displacement due to diurnal and semidiurnal atmospheric tides (S1/S2) is often neglected in the routine precise GPS data processing. We recall the S1/S2 modeling method and show the magnitude of the S1/S2 tides under the Center of Mass (CM) frame. The results show that the annual amplitudes caused by both S1 and S2 tides exceed 1 mm for stations near the equator. The impact of S1/S2 on the 24-h Global Positioning System (GPS) solution is typically at the sub-mm level, and the scatter of the S1/S2 caused displacement difference increases with the decreasing latitude for northern hemisphere stations, among which the maximum Standard Deviation (STD) reaches up to 1.5 mm, 1 mm and 0.7 mm for the Up, East and North components, respectively, at low-latitude stations. We also find that 65% of the stations’ vertical velocity change caused by S1/S2 is larger than 1%, among which the maximum velocity variation rate reaches more than 40% for some coastal/island stations, while stations with the weighted root mean square reduced account for 65%, 39%, and 38% for the up, east, and north components respectively, in particular for most coastal/island stations. Furthermore, the S1/S2 correction could partly reduce the annual and the semi-annual signals of the global stacked vertical component together with the semi-annual amplitude of the east component. The power of some anomalous harmonics of 1.04 cycle per year also decreased a lot. These results further prove the benefits of S1/S2 correction in the precise GPS data processing.

Chemical composition characterization of Ca3Ta(Ga0.5Al0.5)3Si2O14 single crystal by the line-focus-beam ultrasonic material characterization system

A new method for evaluation of homogeneity of Ca3Ta(Ga0.5Al0.5)3Si2O14 (CTGAS) single crystals was established based on leaky surface acoustic wave (LSAW) velocity measurements performed by the line-focus-beam ultrasonic material characterization (LFB-UMC) system. Three plate specimens cut perpendicular to X-, Y-, and Z-axes were prepared from the CTGAS crystal ingot and LSAW velocity distributions were examined for these specimens. LSAW velocity changes due to Al-substitution effect were successfully extracted by using a relationship between two LSAW velocities propagating along different directions for Ca3TaGa3Si2O14 (CTGS) and Al-substituted CTGS. Comparison of measured LSAW velocities and the results of chemical composition analysis performed by electron probe microanalysis (EPMA) demonstrated that LSAW velocity is mainly affected by Al-content change in CTGAS. Maximum velocity variation was observed in radial direction of the crystal ingot through the Z-axis propagating LSAW velocity measurements for Y-cut CTGAS specimen corresponding to Al-content change of 0.226mol%. Accuracy of evaluation of Al content by velocity measurement for Y-cut Z-propagating LSAW is estimated to be ±0.0047mol% and is superior to that by EPMA.

Parametric study on the three-dimensional distribution of velocity of a FENE-CR fluid flow through a curved channel

In order to better understand the three-dimensional non-Newtonian flow in an 180° curved duct of square cross-section, simulations were carried out considering an incompressible viscoelastic fluid, which follows the non-linear FENE-CR model, having constant shear viscosity. A fully implicit finite-volume method was used for the solution of the governing equations. Numerical simulations were performed for different Reynolds and Weissenberg numbers, and by varying the model parameters, namely the retardation ratio (β) and the extensibility (L2). The aim was to analyse the development and distribution of velocity field in the cross-sections along the curved channel and as a consequence to understand the variation of maximum velocity with these parameters. The results reveal complex changes with increasing extensibility and decreasing retardation parameter, which are associated to transition from one to two pairs of vortices in the secondary flow. Comparison with the literature confirms and reveals that the absence of shear-thinning delays this transition.

Adaptive interrogation for 3D-PIV

A method to adapt the shape and orientation of interrogation volumes for 3D-PIV motion analysis is introduced, aimed to increase the local spatial resolution. The main application of this approach is the detailed analysis of complex 3D and vortex-dominated flows that exhibit high vorticity in confined regions like shear layers and vortex filaments. The adaptive criterion is based on the analysis of the components of the local velocity gradient tensor, which returns the level of anisotropy of velocity spatial fluctuations. The principle to increase the local spatial resolution is based on the deformation of spherical isotropic interrogation regions, obtained by means of Gaussian weighting, into ellipsoids, with free choice of the principal axes and their directions. The interrogation region is contracted in the direction of the maximum velocity variation and elongated in the minimum one in order to maintain a constant interrogation volume. The adaptivity technique for three-dimensional PIV data takes advantage of the 3D topology of the flow, allowing increasing the spatial resolution not only in the case of shear layers, but also for vortex filaments, which is not possible for two-dimensional measurement in the plane normal to the vortex axis. The definition of the ellipsoidal interrogation region semi-axes is based on the singular values and singular directions of the local velocity gradient tensor as obtained by the singular values decomposition technique (SVD). The working principle is verified making use of numerical simulations of a shear layer and of a vortex filament. The application of the technique to data from a Tomo-PIV experiment conducted on a round jet, shows that the resolution of the shear layer at the jet exit can be considerably improved and an increase of about 25% in the vorticity peak is attained when the adaptive approach is applied. On the other hand, the peak vorticity description in the core of vortex rings is only slightly improved with approximately a 5% increase in the peak value. Results are in good agreement with the values obtained by means of the numerical simulations. From experiments conducted on a turbulent boundary layer it is observed that the strong curvature of the mean profile is better captured with adapted ellipsoidal interrogation and the amplitude of the spurious oscillation in the vorticity profile observed in the proximity of the wall (ringing) is reduced by nearly a factor 2 after the adaptive interrogation is applied.

Turbulence characteristics in the bottom layer of a shallow tidal channel

Observation of a shallow tidal channel was executed to examine turbulent evolution in ideal condition of weak, stratified flow for a complete cycle of semi-diurnal tide. Duration of this study allows a maximum velocity variation and therefore gives comprehensive interpretation of the relevant processes such as momentum and heat transfer, turbulent kinetic energy (TKE) production and dissipation rates. Under weak stratification condition dominant through the observation period testing the parameterization of dissipation rate in the Mellor–Yamada type models revealed that close to the bed perhaps due to boundary effects experimental dissipation closure constant values were remarkably larger than commonly used value of 16.6. Also, the effect of extending critical Richardson number Ricr to infinity on parameterization of stability functions, eddy viscosity, and turbulent Prandtl number in Kantha–Carniel model was also examined. It was found that despite Kantha–Carniel model reconstructed bottom boundary layer (BBL) turbulence characteristics well during the flooding tide, it underestimates those parameters during the ebbing tide partially due to underestimation of turbulence macroscale.

Wind tunnel velocity profiles generated by differentially-spaced flat plates

Abstract Production of linear shear with low turbulence level in a wind tunnel provides a convenient environment for testing the results of computational fluid dynamics simulations and equipment calibration. Boundary layer flow over a flat plate at zero incidence provides controlled deceleration of the approach flow according to plate length, with interacting boundary layers between adjoining flat plates merging to provide fully developed duct flow. In this way, an array of differentially-spaced flat plates can be used to modify a uniform wind tunnel velocity field to a specified velocity profile. A one-step iterative scheme is offered to determine plate spacings for simulation of weakly sheared flows, constrained by zero vertical pressure gradient in the downstream flow (representative of boundary layer conditions). The scheme is tested for realisation of uniform shear flow (maximum velocity variation ±10% of centreline velocity) by wind tunnel simulation, and produces reasonable results, at least comparable with previous studies.

An ultra-high-stability Mössbauer spectrometer drive using a type-2 feedback system

A new electromechanical drive for 57Fe Mössbauer spectroscopy has been designed and implemented. The drive, a highly modified version of a commercially available drive, comprises a “type-2” servo mechanism — meaning that its open-loop transfer function has a second-order pole at zero frequency. This constant-acceleration drive is therefore highly linear and immune to drifts in velocity and position regardless of the duration of data acquisition. The maximum velocity variation at any point is less than ±1 μm/s at low velocity scans and ±3 μm/s at high scans. The performance of the spectrometer is documented by a measurement of velocity using a Moiré fringe interferometer over a 10 h run. This measurement shows a correlation that could only result if the drive repeated the position of its motion during each sweep of the acquisition to an accuracy much better than 12 microns, the fringe repeat distance. This performance is unprecedented in the history of the spectroscopy, especially for a vertical geometry spectrometer, and allows the acquisition of Mössbauer spectra of arbitrary precision over extended time periods. The need for this precision is two-fold: (1) to permit high-resolution spectrometry of enriched multi- 57Fe compounds over short time periods, and (2) to make natural abundance spectrometry possible. Circuit descriptions are included. The circuits are simple combinations of operational amplifiers that are readily available and inexpensive.

A biochemical-morphological study on microvillus plasma membrane development

The microvillus plasma membrane of the human placental syncytiotrophoblast at term has been extensively studied, while little is known about the characteristics of its development. The aim of the present work was to compare functional and structural properties of this membrane at early and term gestational age. Ten normal term placentas (40 weeks) and ten placentas at 10 weeks of gestational age were studied. The Na + K + -ATPase activity is significantly decreased in the syncytiotrophoblast plasma membrane obtained from term placentas as compared to the early ones, with significant variation of maximum velocity ( V max). The microviscosity, evaluated by the P parameter of DPH and S n parameters of 5- and 16-NS, is increased in the term placentas compared to the early placentas. This alteration is accompanied by an increased cholesterol to phospholipids ratio in term placentas, while there is a decreased unsaturated to saturated fatty acid ratio. As follows from morphological studies, an increased mean diameter in the E face was observed in the term placenta with respect to the early placenta. The distribution factor DF, wich indicates the particle aggregation state, decreased in the E face in the term placenta as compared to the early one. The present biochemical morphological study shows that a deep modification of the membrane is at the basis of the syncytiotrophoblast plasma membrane development.

Shortening velocity and myosin heavy chains of developing rabbit muscle fibers.

The regulation of vertebrate muscle contraction with respect to the role of the different subunits of myosin remains somewhat uncertain. One approach to gaining a better understanding of the molecular basis of contraction is to study developing muscle which undergoes changes in myosin isozyme composition and contractile properties during the normal course of maturation. The present study utilizes single fibers from psoas muscles of rabbits at several ages as a model system for fast-twitch muscle development. This approach eliminates the inherent problems of interpreting results from studies on whole muscles which usually contain heterogeneous fiber types with respect to contractile properties and isoenzyme composition. Maximum velocity of shortening and tension-generating ability of individual fibers were measured and the myosin heavy chain composition of the same fibers was examined using an ultrasensitive sodium dodecyl sulfate-polyacrylamide gel system. The results indicate that 1) with regard to contractile properties, there is a transitional period from slow to fast shortening velocities within the first postnatal month; 2) a strong, positive correlation exists between the speed of shortening and tension-generating ability of individual postnatal day 7 fibers, suggesting that as more myosin is incorporated in these developing fibers it is of the fast type; and 3) there is a wide variation in maximum velocity of shortening among postnatal day 7 psoas fibers which is also a time when a mixture of heavy chain isoforms characterizes the myosin composition of single muscle fibers.