Increase In Rotational Velocity Research Articles

A Comparison of Throwing Arm Kinetics and Ball Velocity in High School Pitchers With Overall Fast and Overall Slow Cumulative Joint and Segment Velocities

Background: Individual maximum joint and segment angular velocities have shown positive associations with throwing arm kinetics and ball velocity in baseball pitchers. Purpose: To observe how cumulative maximum joint and segment angular velocities, irrespective of sequence, affect ball velocity and throwing arm kinetics in high school pitchers. Study Design: Descriptive laboratory study. Methods: High school (n = 55) pitchers threw 8 to 12 fastball pitches while being evaluated with 3-dimensional motion capture (480 Hz). Maximum joint and segment angular velocities (lead knee extension, pelvis rotation, trunk rotation, shoulder internal rotation, and forearm pronation) were calculated for each pitcher. Pitchers were classified as overall fast, overall slow, or high velocity for each joint or segment velocity subcategory, or as population, with any pitcher eligible to be included in multiple subcategories. Kinematic and kinetic parameters were compared among the various subgroups using t tests with post hoc regressions and multivariable regression models created to predict throwing arm kinetics and ball velocity, respectively. Results: The lead knee extension and pelvis rotation velocity subgroups achieved significantly higher normalized elbow varus torque (P = .016) and elbow flexion torque (P = .018) compared with population, with equivalent ball velocity (P = .118). For every 1-SD increase in maximum pelvis rotation velocity (87 deg/s), the normalized elbow distractive force increased by 4.7% body weight (BW) (B = 0.054; β = 0.290; P = .013). The overall fast group was older (mean ± standard deviation, 16.9 ± 1.4 vs 15.4 ± 0.9 years; P = .007), had 8.9-mph faster ball velocity (32.7 ± 3.1 vs 28.7 ± 2.3 m/s; P = .002), and had significantly higher shoulder internal rotation torque (63.1 ± 17.4 vs 43.6 ± 12.0 Nm; P = .005), elbow varus torque (61.8 ± 16.4 vs 41.6 ± 11.4 Nm; P = .002), and elbow flexion torque (46.4 ± 12.0 vs 29.5 ± 6.8 Nm; P < .001) compared with the overall slow group. A multiregression model for ball velocity based on maximum joint and segment angular velocities and anthropometrics predicted 53.0% of variance. Conclusion: High school pitchers with higher maximum joint and segment velocities, irrespective of sequence, demonstrated older age and faster ball velocity at the cost of increased throwing shoulder and elbow kinetics. Clinical Relevance: Pitchers and coaching staff should consider this trade-off between faster ball velocity and increasing throwing arm kinetics, an established risk factor for elbow injury.

Hydrodynamic features specific to the dynamic movements of an underwater glider

The purpose of this study was to show the influence of the underwater glider's motion on its hydrodynamic coefficients. The proposed drone was based on a scaled-down geometry of the DARPA suboff bare hull model that was equipped with wings and fins. A series of Computer Fluid Dynamics simulations were performed using the ANSYS Fluent software. It was shown that with the increase of the drone's rotational velocity, the detachment of flow on the wings was delayed, and thus, the overall lift was increased. The hysteresis present in the characteristics of hydrodynamic properties during pitching movement had higher amplitude with increased pitching frequency. It was concluded that the parameters of the underwater glider's motion can have a significant influence on its hydrodynamic properties.

Ion temperature and rotation velocity measurements of carbon and boron ions using VUV spectroscopy on EAST.

A space-resolved vacuum ultraviolet spectroscopy is employed to measure impurity emission profiles (500-3200Å) on EAST. This study successfully captures C IV (1548.20 and 1550.77Å) lines emitted from carbon ions and derives ion temperatures using Doppler broadening and a collision model based on their intensity ratios. Both the emission intensity and ion temperature profiles are determined. However, the calculated results reveal a lower temperature of around 10-20eV with the collision model, suggesting a potential need for further correction in subsequent calculations. Furthermore, this study explores relative rotation velocities from the Doppler shift, indicating an increase in toroidal rotation velocity with applied neutral beam injection. The measured results exhibit concordance with the charge exchange recombination spectrometer data. Furthermore, during boron powder dropping discharges on EAST, B II (1623.60, 1623.79, 1623.95, 1624.02, 1624.17, and 1624.38Å) emission lines exhibiting a similar time behavior trend with boron powder injection are identified. Ion temperatures are measured using B II (1362.46Å) through the Doppler broadening method. These techniques hold significant promise for future impurity analysis at the edge of EAST, providing valuable insights into the behavior of carbon and boron ions.

A numerical investigation on the effect of rotation on the cone penetration test

The cone penetration test (CPT) is one of the most popular in situ soil characterization tools. However, the test is often difficult to conduct in soils with high penetration resistance. To resolve the problem, a rotary CPT device has recently been adopted in practice by rotating the rod to increase the penetrability, particularly in deep dense sand. This study investigates the underlying mechanism of the rotation effects from a micromechanical perspective using models based on the discrete element method. With rotation, the cone penetration resistance ( qc) decreases by up to 50%, while the cone torque resistance ( tc) increases gradually. These results are also used to successfully assess existing theoretical solutions. The mechanical work required during penetration is observed to keep rising as the rotational velocity increases. Microscopic variables including particle displacement and velocity field show that rotation reduces the volume of disturbed soil during penetration and drives particles to rotate horizontally, while contact force chain and contact fabric indicate that rotation increases the number of radial and tangential contacts and the corresponding contact forces, forming a lateral stable structure around the shaft, which can reduce the force transmitted to the particles below the cone, thus decreasing the vertical penetration resistance.

Experimental investigations on mechanisms of RMP-induced intrinsic rotations at EAST

Plasma spontaneous rotation significantly influences confinement performance and stability in tokamaks. Effectively inducing this rotation is essential for stabilizing resistive wall modes (RWMs) and ensuring the stable operation of the International Thermonuclear Experimental Reactor (ITER). Recent experiments on the Korea Superconducting Tokamak Advanced Research (KSTAR) device demonstrated that resonant magnetic perturbations (RMPs) can induce neoclassical toroidal viscosity (NTV) torque under certain conditions, successfully driving plasma rotation. Similarly, an increase in plasma rotation in the direction of the plasma current following RMP application has been observed on the Experimental Advanced Superconducting Tokamak (EAST). However, unlike the KSTAR findings, NTV torque simulations for EAST are two orders of magnitude lower than experimental measurements, suggesting additional mechanisms beyond NTV may be driving the observed plasma rotations. To investigate these mechanisms, momentum balance, causality, and statistical analyses have been performed at EAST. An increase in rotation velocity has been found to correlate with significant changes in the &lt;i&gt; &lt;b&gt;E&lt;/b&gt; × &lt;b&gt;B&lt;/b&gt; &lt;/i&gt; flow, matching the RMP-induced torque distribution. This alignment suggests that residual stress, arising from variations in &lt;i&gt; &lt;b&gt;E&lt;/b&gt; × &lt;b&gt;B&lt;/b&gt; &lt;/i&gt; shear, may drive the observed rotation increases. The effects of stochastic fields on multi-scale turbulence are proposed as a possible explanation for correlations between &lt;i&gt; &lt;b&gt;E&lt;/b&gt; × &lt;b&gt;B&lt;/b&gt; &lt;/i&gt; velocity and toroidal rotation. Stochastic fields appear to enhance the inertia of large-scale turbulence while driving small-scale turbulence to maintain quasi-neutrality. The resulting turbulent Reynolds stress, generated by small-scale turbulence, may account for the observed &lt;i&gt; &lt;b&gt;E&lt;/b&gt; × &lt;b&gt;B&lt;/b&gt; &lt;/i&gt; velocity increases during RMP application. Statistical analysis further highlights the importance of island width in understanding the threshold RMP current in ramping-up RMP experiments, supporting the conclusion that turbulence-driven &lt;i&gt; &lt;b&gt;E&lt;/b&gt; × &lt;b&gt;B&lt;/b&gt; &lt;/i&gt; shear-related residual stress is the key mechanism driving plasma rotation following RMP application.

Философское осмысление связи движения и взаимного положения материи как условия обратимости их изменений

The fact of existence of the limit of divisibility of matter, established earlier by the author, has an inevitable con-sequence of permanent loss by interacting matter of its motion. Since “heat death” due to this loss of motion has not occurred, therefore, there is a law providing restoration of motion. This law is the law of motion-position of matter. As an analog of the law of motion-position of matter, the article considers the law of conservation of mechanical energy, according to which kinetic energy (reflecting the motion of matter) can be reversibly trans-formed into potential energy (reflecting the mutual position of matter). The fundamental incompatibility of, on the one hand, the law of conservation of energy, corresponding to the relative description of being, and, on the other hand, the fact that motion is not irretrievably lost, corresponding to the absolute description of being close to absolute, is stated. The law of motion-position of matter in the assumption of birth of motion in the state of the greatest convergence of matter agrees with the existing cosmological ideas about the Big Bang and expan-sion of the Universe. The Universe in this case can be represented as an “energy independent” system. As the main problem, the study examines the determination of the mechanism of the growth of the velocity of material structures. The probable sought mechanism is the increase of (circumferential) rotational velocity at decreasing radius of rotation of material bodies, which can be rather complex material structures.

CATHODIC PROTECTION OF CARBON STEEL IN 0.1N NaCl SOLUTION UNDER FLOW CONDITIONS USING ROTATING CYLINDER ELECTRODE

The effect of applied current on protection of carbon steel in 0.1N NaCl solution (pH=7) was investigated under flow conditions (0-0.262 m/s) for a range of temperatures (35-55°C) using rotating cylinder electrode. Various values of currents were applied to protect steel from corrosion, these were Iapp.=Icorr., Iapp.=2Icorr. and Iapp.=2.4Icorr. under stationary and flow conditions. Corrosion current was measured by weight loss method. The variation of protection potential with time and rotation velocity at various applied currents was assessed. It is found that the corrosion rate of carbon steel increases with rotation velocity andhas unstable trend with temperature. The protection current required varies with temperature and it increases considerably when the rotation velocity was increased. The protection potential decreases appreciably (shifts to more negative) with time and with increasing rotation velocity. Also it shifts to more positive with increasing temperature.

Hydrogen-free Wolf-Rayet stars: Helium stars with envelope-inflation structure and rotation

Context. Observations have shown that the effective temperature of hydrogen-free Wolf-Rayet (WR) stars is considerably lower than that of the standard model, which means that the radius of the observed H-free WR stars is several times larger than that estimated by the standard model. The envelope inflation structure (EIS) caused by the radiation luminosity being close to the Eddington luminosity in the iron opacity peak region of H-free WR stars may be the key to resolving the radius problem of H-free WR stars. Aims. We study the structure and evolution of helium (He) stars with the EIS and discuss the influence of rotation on these He stars. We aim to explain the radius problem of H-free WR stars observed in the Milky Way (MW) and the Large Magellanic Cloud (LMC) through the He stars. Methods. Using the Modules for Experiments in Stellar Astrophysics code, we compute the evolution of He stars with and without MLT++ prescriptions, and discuss their effects on the EIS. We calculated the evolution of He stars using a new mass-loss rate formula and three different relative rotational velocities and compared our results with observations on Hertzsprung–Russell diagrams. Results. The EIS has different effects on the structure and evolution of He stars with different masses. Due to the luminosity well below the Eddington limit, low-mass He stars with an initial mass of less than 12 M⊙ do not produce EIS with or without the MLT++ prescription. High-mass He stars with an initial mass exceeding 12 M⊙ and without the MLT++ prescription produce the EIS. Since the EIS is Eddington factor Γ-dependent, its radius increases with the increase in metallicity and decreases with rotational velocity increase. For rotating low-mass He stars, since the rotational mixing timescale is smaller than the evolutionary timescale, rotational mixing can increase the lifetime and allow He stars to evolve into WC stars during the helium giant phase. For rotating high-mass He stars, since rotation increases the mass-loss rate, the radius of the EIS decreases as rotational velocity increases. The rotation-decay timescale of rapidly rotating He stars is very short, and the rapidly rotating He stars only appear within the first one-tenth of their lifetime, which is consistent with the observations of WR stars. Conclusions. The low-luminosity (log(L/L⊙)≤5.2) H-free WR stars in the MW and the LMC can be explained by the helium giant phase in low-mass He stars, the high XC and XO in WC stars can only evolve through low-mass He stars with a rapid rotation. High-mass He stars with the EIS can explain H-free WR stars with a luminosity exceeding 105.7 L⊙ and an effective temperature above 104.7 K in the MW. They can also explain H-free WR stars on the right-hand side of the He zero-age main sequence in the LMC. High-mass stars with the EIS evolve into WO stars at the final evolution stage, and the shorter lifetime fraction is consistent with the small number of observed WO stars.

DEM analysis of the cyclic behavior of ballast mixed with crumb rubber

This study presents a numerical investigation of the cyclic behavior of ballast mixed with crumb rubber (CR) using the discrete element method (DEM). To this aim, a series of box tests on ballast mixed with different percentages (0%, 5%, 10% and 20% by volume) of CR were simulated by a three-dimensional DEM code, PFC3D. First, the macroscopic mechanical behavior, i.e., the sleeper displacement, the dissipated energy, and the vertical stiffness of the samples, were compared with previous experimental results to validate the proposed DEM model. Further, the microscopic response, including the coordination number, sliding contact ratio, particle displacement and rotation, contact force ratio, contact force and its distribution, and energy evolution were analyzed to mainly reveal the mechanism underlying the sample deformation and ballast degradation. The results show that the simulation results can well capture the effect of CR on the macro-mechanical behavior of ballast with different CR percentages. On the micro-scale, the sliding contact ratio and particle rotation velocity increase with increasing CR percentage, leading to an increase in sleeper settlement. In addition, as the CR percentage increases, the coordination number for the ballast-ballast contacts decreases while the occurrence of larger contact forces increases. The effect of CR on reducing the coordination number for the ballast-ballast contacts outweighs increasing the occurrence of larger contact forces. At the same time, the contact force distribution for the ballast with a higher CR percentage tends to be more homogeneous. These will reduce the risk of ballast breakage; however, as the CR percentage increases, the frictional energy dissipated by the ballast-ballast contacts increases, indicating an increase in ballast abrasion.

Prediction of residual stresses within dissimilar Al/steel friction stir lap welds using an Eulerian-based modeling approach

Friction stir welding (FSW) was applied to fabricate dissimilar welds between 5052 aluminum alloy and DP590 dual-phase steel with a lap configuration. The interfacial formation and microstructure were investigated experimentally, and in-process thermomechanical conditions with emphasis on resultant residual stress distribution were numerically studied through a fully coupled three-dimensional (3D) Eulerian-based finite element modeling. The Al/steel thermal-mechanical interaction driven by the rotational pin penetrating the steel produced the serrated bonding interface. The brittle intermetallic layer was formed in the interface, showing distribution discontinuity along the welding direction. The simulation results showed that increasing rotation velocity resulted in higher welding temperature and cooling rate, leading to the increment in the residual stress level of the weld zone. Near interfacial residual stresses exhibited an M-shape in the Al alloy while it showed W-shape in the steel, which originated from the thermomechanical processing condition and the effect of mismatch of thermal expansion coefficient. Increasing rotation velocity decreased the near interfacial compressive stress in the steel side. Numerically predicted residual stresses were in acceptable agreement with those measured using the X-ray diffusion measurement with the cosα method, validating prediction reasonability. Hopefully, the current simulation work will provide a new alternative modeling strategy for predicting residual stress fields within the same or dissimilar FSW.

Nanoparticles transportation with turbulent regime through a solar collector with helical tapes

Utilizing hybrid nanomaterial, fin and helical turbulator were suggested in present investigation to intensify the efficiency of absorber unit. Mixture of water with Al2O3 and CuO creates the working fluid and due to low fraction of nano-powders, formulations were incorporated according to homogeneous modeling approach. Longitudinal plate with circular gaps was considered as fin and helical tape was utilized as turbulator. Verification based on experimental previous work reveals nice concordance. Fraction of hybrid nano-powders, Re and two geometrical factors (pitch factor (Pi) and diameter of circular gaps (D1)) have been reported in outputs. It should be mentioned that number of circular gaps is depend on Pi. Finite volume approach was selected with involve of k-ε RNG technique for simulating turbulent forced convection. As diameter of gap augments, fluid movement becomes easier and pressure loss decreases while better mixing of upper hot fluid and cold one can be reached. As pitch factor declines, the revolution of tapes augments and number of circular gaps increases, too. Although, increase of rotational velocity makes the stronger interaction with wall, the pressure drop can be reduced because of positive effect of higher number of gaps when the diameter of gaps has maximum value. Temperature of absorber plate reduces 0.15% with intensify of Re while it grows about 0.007% and 0.012% with augment of D1 and Pi. Nu augments about 73.59% with augment of pumping power while friction factor declines about 18.32%. In greatest level of Re, rise of D1 and Pi leads to augment of Nu about 6.47% and 6.43%. Also, friction factor reduce about 11.22% and 17.47% with growth of D1 and Pi. Adding hybrid nanomaterial makes Nu and f to rise about 5.26% and 1.52%.

Numerical Investigation of Flow and Heat Transfer From a Rotating Sphere With Constant Angular Velocity Around Vertical Axis Floating in Stationary Fluid

Abstract Convective heat transfer for a rotating sphere around a vertical axis floating in stationary fluid is studied numerically using the model of volume of fluid (VOF). The effects of the immersion angle and rotating velocity on the streamlines, isotherm and volume fraction contours, mean and local Nusselt numbers, volumetric flow rate, and water film thickness are investigated for the angular rotational velocity, 1500≤Ω≤3500 and the immersion angle, 30 deg≤θi≤60 deg. The results show that the sphere's rotation causes the liquid to be sucked from the lower pole of the sphere, which is thrown out after stopping in the equator. Due to the strong jet flow in the equatorial zone, heat is transferred by forced convection, but diffusion is dominant for heat transfer in other zones. At low rotational velocities, the liquid film is thrown out of the equator in the form of large droplets, but as the rotational velocity increases, its shape changes to a jet. Also, it is found that there is a direct relation between the Reynolds number and mean Nusselt number at different immersion angles so that an average of 27.5% increase for the mean Nusselt number is achieved by increasing the immersion angle from θi=30 deg to θi=60 deg. In addition, at a constant rotational velocity, the volumetric flow rate increases with increasing immersion angle.

Lithium abundance in a sample of active stars: High-resolution spectrograph observation with the 1.8 m telescope

Context. Observations of young, low-mass, main-sequence, and zero-age main-sequence stars show evidence of a correlation between lithium abundance and chromospheric activity, albeit with a very large scatter. Fast rotation stars (including T Tauri stars, RS CVn, and BY Dra systems) show the Li I doublet at 6707.8 Å in their spectra. The lithium depletion is probably related to the rotation (turbulent diffusion induced by rotation). Because the flare activity of stars increases with decreasing rotation period, a correlation can be expected between lithium abundance and chromospheric activity for active stars. Aims. The aim of this paper is to investigate the relation between lithium abundance and the Ca II H and K emission index (R′HK = LHK/Lbol) for a sample of active stars. Methods. Based on the high-resolution spectroscopic observations, we calculated lithium abundance for 14 chromospherically active late-type stars using the comparison of the measured Li I λ670.8 nm equivalent width with curve of growth calculations in non-local-thermodynamic-equilibrium conditions. We also searched the correlation between lithium abundance and the Ca II H &amp; K emission index (log R′HK) for the 14 chromospherically active late-type stars. Results. The study of the relationship between lithium abundance and the Ca II H &amp; K emission index (log R′HK) found that the activity of sample stars increases with increasing lithium abundance. Next, the lithium abundance analogs progressively decrease as the rotation periods increase (rotation becomes slow) and the large values of the log R′HK along with small values of Rossby numbers for the sample of chromospherically active stars. Conclusions. The lithium abundance (log N(Li)) versus the chromospheric activity and log N(Li) against the rotation period both indicate that the lithium abundance analogs progressively increase as the chromospheric activity index increases and/or the rotation velocity increase (rotation period becomes small) for our sample of active stars. On the other hand, the log R′HK against the Rossby number RO shows that there is a clear trend of increasing activity with increasing rotation velocity for these active stars. Considering that the lithium abundance decreases with increasing stellar age in late-type stars, we can deduce that the chromospheric activity and the rotation velocity both decrease with the increase of stellar age for our sample active stars.

Theoretical study on the leakage characteristics of Disc-Seal Single Screw Pump used in oily sludge waste heat source absorption refrigeration system

The disc-seal single screw pump (DSSP) used in the field of oily sludge transport has a huge advantage. However, there is no research on the leakage characteristics of the DSSP at present, which makes its application limited. Therefore, the mathematical calculation model of leakage amount of each leakage channel was established in this paper according to the geometric model of the leakage channel. By using this mathematical model, the influence rule of working parameters on the leakage characteristics was analyzed. The results show that the total leakage amount per unit time of the DSSP varies periodically with the rotation of the screw, and the total leakage per unit time of the DSSP will increase with the increase of outlet pressure and screw rotation velocity. When the dynamic viscosity coefficient of the medium increases, the corresponding leakage will be reduced, in which the transmission medium dynamic viscosity is the main factor affecting the total leakage of the DSSP. The study of the leakage characteristics of the DSSP can provide a theoretical basis for the optimal design of its structure in the future.

The Tully-Fisher relation in dense groups at z ∼ 0.7 in the MAGIC survey

Context. Galaxies in dense environments are subject to interactions and mechanisms that directly affect their evolution by lowering their gas fractions and consequently reducing their star-forming capacity earlier than their isolated counterparts. Aims. The aim of our project is to get new insights into the role of environment in the stellar and baryonic content of galaxies using a kinematic approach, through the study of the Tully-Fisher relation (TFR). Methods. We study a sample of galaxies in eight groups, over-dense by a factor larger than 25 with respect to the average projected density, spanning a redshift range of 0.5 &lt; z &lt; 0.8 and located in ten pointings of the MAGIC MUSE Guaranteed Time Observations program. We perform a morpho-kinematics analysis of this sample and set up a selection based on galaxy size, [O II]λλ3727,3729 emission line doublet signal-to-noise ratio, bulge-to-disk ratio, and nuclear activity to construct a robust kinematic sample of 67 star-forming galaxies. Results. We show that this selection considerably reduces the number of outliers in the TFR, which are predominantly dispersion-dominated galaxies. Similar to other studies, we find that including the velocity dispersion in the velocity budget mainly affects galaxies with low rotation velocities, reduces the scatter in the relation, increases its slope, and decreases its zero-point. Including gas masses is more significant for low-mass galaxies due to a larger gas fraction, and thus decreases the slope and increases the zero-point of the relation. Our results suggest a significant offset of the TFR zero-point between galaxies in low- and high-density environments, regardless of the kinematics estimator used. This can be interpreted as a decrease in either stellar mass by ∼0.05 − 0.3 dex or an increase in rotation velocity by ∼0.02 − 0.06 dex for galaxies in groups, depending on the samples used for comparison. We also studied the stellar and baryon mass fractions within stellar disks and found they both increase with stellar mass, the trend being more pronounced for the stellar component alone. These fractions do not exceed 50%. We show that this evolution of the TFR is consistent either with a decrease in star formation or with a contraction of the mass distribution due to the environment. These two effects probably act together, with their relative contribution depending on the mass regime.

Non-Newtonian flow past a rotating circular cylinder with forced convection heat transfer

Time-dependent and incompressible flow of non-Newtonian fluids past an unconfined isothermal rotating circular cylinder is investigated numerically. The numerical results of drag-coefficient (Cd) and Nusselt number (Nu) are validated for Reynolds number (Re) = 100, Prandtl number (Pr) = 1 and for Power-law indices of n = 0.4, 1, 1.8. This study is focused on determining the dependence of the individual drag components and heat transfer characteristics on the power-law index (0.4≤n≤1.7) and magnitude of the rotational velocity of the cylinder (α = 0, 1). The Re and Pr are 100 and 10 respectively in the present study. The results reported herein provide fundamental knowledge of the flow and heat transfer behavior for the flow of non-Newtonian fluids over the circular cylinder with and without rotation. It is noted that the drag coefficient (Cd) of the flow enhances with the power-law index ‘n’ and degrades with the increase in rotational velocity ‘ α.’ Correspondingly, Nu reduces with ‘n.’ It is also observed that the variation of Nu in shear-thickening and shear-thinning fluids are different. The related explanation has been given in the domain of the result in our present work.

Experimental Studies on Friction Processes in Sliding Thrust Bearings

A technique for conducting experiments on determining wear features for thrust slide bearings is presented. The friction coefficient depending on the load and on the rotation velocity of the samples, on the changes in the wear weight fraction, and on the surface roughness parameters are determined. The effect of thickness, propagation, and interaction on the oil film formed in a hydrodynamic friction mode on the wear of friction pairs is considered. An instrumental support of the experiment is described, the results and conclusions are presented. It is noted that the local maximum of the friction coefficient is reached at approximately 900 rpm for all the samples and, for each load level, a corresponding minimum of friction coefficient is observed, which increases with increasing rotation velocity. In the course of testing, the minimum values of friction coefficient have been observed in the ranges of 550–650 rpm and 1050–1150 rpm. For the used testing mode, the smallest change in the surface roughness of the samples amounted to Ra = 0.46–045 μm for steel samples and Ra = 0.75–0.89 μm for bronze samples, respectively. These roughness values have been subjected to changes to a lesser extent, being close to the equilibrium roughness in the course of the testing. It should be noted that the greatest weight wear level of the samples occurs under running-in, and, when equilibrium roughness and the minimum friction coefficient have been reached, the sample wear level exhibits a decrease. In addition, upon the experiments, the distribution of the hydrodynamic oil film pressure over the surfaces of the samples was revealed based on the wear scars in the outer circuit, and its high-pressure belt was expanded in the circumferential direction.

The influence of planetary engulfment on stellar rotation in metal-poor main-sequence stars

Context. The method of gyrochronology relates the age of its star to its rotation period. However, recent evidence of deviations from gyrochronology relations has been reported in the literature. Aims. We study the influence of tidal interaction between a star and its companion on the rotation velocity of the star to explain peculiar stellar rotation velocities. Methods. We followed the interaction of a star and its planet using a comprehensive numerical framework that combines tidal friction, magnetic braking, planet migration, and detailed stellar evolution models from the GARSTEC grid. We focus on close-in companions from 1 to 20 MJup orbiting low-mass (0.8 − 1 M⊙) main-sequence stars with a broad metallicity of [Fe/H] = − 1 up to solar. Results. Our simulations suggest that the dynamical interaction between a star and its companion can have different outcomes that depend on the initial semi-major axis and the mass of the planet, as well as on the mass and metallicity of its host star. In most cases, especially in the case of planet engulfment, we find a catastrophic increase in stellar rotation velocity from 1 kms−1 to over 40 kms−1 while the star is still on the main-sequence. The main prediction of our model is that low-mass main-sequence stars with abnormal rotation velocities should be more common at low-metallicity, as lower [Fe/H] favours faster planet engulfment, based on the assumption that the occurrence rate of close-in massive planets is similar at all metallicities. Conclusions. Our scenario explains peculiar rotation velocities of low-mass main-sequence stars by the tidal interaction between the star and its companion. Current observational samples are too narrow and incomplete, and, thus, they are not sufficient for our model to be tested.

Numerical analysis of the flow mechanism and axial force characteristics of the cavity in a centrifugal pump with a front inducer

At three flow conditions (0.8Qd, 1.0Qd, and 1.2Qd), the centrifugal pump cavity with front inducer was expanded at 0°, 90°, 180°, and 270°, and a flow path analysis of the axial cross section at the four angles was performed. This revealed that the circumferential and radial velocities of the liquid in the pump cavity along the same angle at different radii follow an axial and radial variation law to different degrees. The pump cavity center axial liquid velocity component along the radial distribution at different angles was analyzed, and liquid pressure in the pump cavity along the radial distribution was numerically analyzed from different points of view. The mean pump cavity pressure was plotted along the radial distribution curve, and a detailed numerical calculation of the axial force of the centrifugal pump and pump cavity was developed. The influence of flow conditions on the liquid flow mechanism and axial force characteristics in the pump cavity was thoroughly discussed. The results showed that liquid flow in the centrifugal pump cavity with the front inducer is mainly restricted by the main flow of the volute. The liquid eddy current in the pump cavity is mainly concentrated near the volute and the hub at 90° and 180° angles, and the higher the flow rate, the larger is the area of the side vortex of the impeller-cover plate, and the smaller is the area of the side vortex of the pump-cover plate. When the flow rate increases, the flow direction of the eddy current at the same angle in the pump cavity remains unchanged, but when the flow rate becomes too high, the flow direction of the eddy current at the same angle in the pump cavity changes. When the range of circumferential and radial partial velocities decreases, the rotational angular velocity increases, and the pressure decreases. At low flow rate, the larger the area of the volute corresponding to the pump cavity, the higher the speed becomes. The axial force in the pump cavity is the most important factor determining the axial force of the centrifugal pump.

Dynamic analysis of rotating double‐tapered cantilever Timoshenko nano‐beam using the nonlocal strain gradient theory

Based on the nonlocal strain gradient theory, the coupling nonlinear dynamic equations of a rotating double‐tapered cantilever Timoshenko nano‐beam are derived using the Hamilton principle. The equation of motion is discretized via the differential quadrature method. The effects of the angular velocity, nonlocal parameter, slenderness ratio, cross‐section parameter, and taper ratios are examined and discussed. It is shown that taper ratios and cross‐section parameter play a significant role in the vibration response of a rotating cantilever nano‐beam. Further as rotational angular velocity increases, the taper ratios and cross‐section parameter effect on the frequency response are increased for first modes of vibration.