Relative Velocity Research Articles

Effect of Induced Wheel and Impeller Inlet Diameter on the Hydrodynamic Performance of High-speed Centrifugal Pumps

The high-speed centrifugal pump plays a crucial role in fields such as aerospace and petrochemical industries, owing to its characteristics of elevated rotational speed and high head. During high-speed operation, the centrifugal pump is prone to cavitation, which alters the fluid flow state within the pump, leading to vibrations, noise, and a sudden decrease in pump head and efficiency. Simultaneously, the collapse of cavitation bubbles generates impact pressure that can damage the pump's internal flow components, significantly reducing its operational lifespan and causing severe consequences. Moreover, under constant-flow conditions, the absolute and relative velocities of the fluid at the impeller inlet are functions of the suction pipe diameter. Therefore, there exists an optimal value for the impeller inlet diameter to enhance the centrifugal pump's resistance to cavitation. Similarly, the different geometric and structural parameters of the inducer also influence the hydraulic performance of the centrifugal pump. The focus of this study is on the external characteristics and internal flow patterns of an optimized high-speed centrifugal pump. In this paper, the entire flow field of the model pump is numerically simulated using ANSYS CFX software. The performance and overall flow field state of the high-speed centrifugal pump under different impeller configurations and inlet diameters are explored. The influence of blade wrap angle and inlet diameter on the high-speed centrifugal pump is revealed, providing a theoretical basis for subsequent optimal design.

Study on Relative Velocity of Moving Disk for Novel HTS Movable Tooth Motor

Study on Relative Velocity of Moving Disk for Novel HTS Movable Tooth Motor

Experimental investigation of particle impact dampers: Vibration reduction and noise levels with varied particle numbers

Structural vibrations present significant challenges in engineering systems, and particle impact dampers (PIDs) have emerged as a promising solution for vibration control. This paper presents a comprehensive experimental investigation on the damping performance of PIDs with varying numbers of particles. The experimental setup involves subjecting a single-degree-of-freedom (SDOF) structure to base motion excitations. Frequency response analysis is conducted to assess the dynamic behavior of the primary system using different PID designs. PIDs with one mass, two masses, three masses and multiple particles are designed and analyzed using the same mass ratio. Additionally, time domain displacement responses of the top of the structure and the base are measured to capture the system's response characteristics. The frequency response analysis reveals the influence of different particle configurations on the system's response amplitude at various frequencies. Interestingly, the results show that a PID with multiple particles exhibits reduced damping performance due to excessive particle-particle collisions. These collisions decrease the energy of the particles, leading to lower velocity before impact. This highlights that the impact itself is the primary source of damping in PIDs, and any other phenomena, such as particle-particle collisions, directly affect the relative velocity before impact. The outcomes demonstrate that an optimal design of PID can reduce vibration amplitude by approximately 85 % with single mass, two masses, and three masses configurations. Conversely, the best-case scenario of PID with multiple particles provides a vibration amplitude reduction of 75 % compared to the absence of a damper. Furthermore, noise data is recorded for all cases, as noise generation is a significant concern associated with PIDs. The results indicate noise magnitudes of 62.5 dB, 70.60 dB, 73.24 dB and 78.64 dB for PIDs with single mass, two masses, three masses, and multiple particles, respectively. Overall, the relationship between the number of particles and damping performance provides valuable insights for optimizing PID designs and ensuring comfortable operation. The findings have broad implications for diverse engineering systems, leading to improved structural performance, reduced noise, and enhanced safety. This study could serve as the basis for several potential applications of PID in structural vibration control with enhanced performance and reduced noise.

Methodology for determining the heat distribution in disc brakes of mine hoisting machines

Purpose. To study the course of heat phenomena in disc brakes using modern computing systems in order to determine and substantiate the operating parameters for the hoisting machine components. Methodology. The research uses software packages, with the help of which a computational-theoretical apparatus is developed for heat mode modeling processes. In particular, the mentioned function is used in the SolidWorks Simulation software with the ability to evaluate the errors of the calculation results. Findings. In the course of the research, the dependence of the hoisting machine disc brake performance on the operating parameters of its components was determined. The research has led to a better understanding of the heat transfer processes in disc braking devices, as well as the ability to study the friction response of various materials and determine optimal parameters that help improve the performance of braking systems. The effectiveness has been proven of the proposed method for analyzing the heat distribution processes of the mine hoisting machine drum components under the influence of operating and emergency braking modes. Originality. For the first time, a methodology for calculating the heating temperature distribution along the brake rim plane during a safety stop has been developed and substantiated. A method has also been developed for determining the temperature field arising under steady-state heating conditions, which occur after repeated operating braking and cooling of the device. In this case, when using the formula for determining the temperature on the brake rim surface, the sample length, the relative velocity between the friction components and the heat flow distribution coefficient are taken into account. The brake disc geometric model developed in the SolidWorks software package makes it possible to study the temperature change on the device rim in real time. Practical value. The proposed design improvement based on the research results of heating processes should improve vehicle safety. The cost of braking systems is expected to be reduced through the use of optimal materials and production technologies. The software methods for modeling and analyzing the temperature influence on brake discs of the Mine Hoisting Machine (MHM) have been improved. Based on the research results, recommendations have been developed for the optimum braking process of machines in various operating conditions.

Friction in soft biological systems and surface self-organization: the role of viscoelasticity

AbstractFriction is a critical factor in the proper functioning of human organs as well as in the potential development of disease. It is also important for the design of diagnostic and interventional medical devices. Nanoscale surface roughness, viscoelastic or plastic deformations, wear, and lubrication all influence the functions of individual cells. The effects of friction in soft matter systems are quantified using different types of frictional coefficients, including the dynamic friction coefficient, friction-skin drag, and pressure drag. These coefficients are determined by the viscoelastic properties of the two systems in contact and their relative velocity. In this review, several biological systems are considered, including (i) epithelial tissues in contact with soft hydrogel-like implants, (ii) the collective migration of epithelial monolayers on substrate matrices, (iii) blood flow through blood vessels, and (iv) the movement of cancer cells past epithelial clusters along with the migration of epithelial cells within the cluster.

Stable-to-unstable transition in quantum friction

We investigate the frictional force arising from quantum fluctuations when two dissipative metallic plates are set in a shear motion. While early studies showed that the electromagnetic fields in the quantum friction setup reach nonequilibrium steady states, yielding a time-independent force, other works have demonstrated the failure to attain steady states, leading to instability and time-varying friction under sufficiently low-loss conditions. Here, we develop a fully quantum-mechanical theory without perturbative approximations, and we unveil the transition from stable to unstable regimes of the quantum friction setup. Due to the relative motion of the plates, their electromagnetic response may be active in some conditions, resulting in optical gain. We prove that the standard fluctuation-dissipation leads to inconsistent results when applied to our system, and, in particular, it predicts a vanishing frictional force. Using a modified fluctuation-dissipation relation tailored for gain media, we calculate the frictional force in terms of the system Green's function, thereby recovering early works on quantum friction. Remarkably, we also find that the frictional force diverges to infinity as the relative velocity of the plates approaches a threshold. This threshold is determined by the damping strength and the distance between the metal surfaces. Beyond this critical velocity, the system exhibits instability, akin to the behavior of a laser cavity, where no steady state exists. In such a scenario, the frictional force escalates exponentially. Our findings pave the way for experimental exploration of the frictional force in proximity to this critical regime. Published by the American Physical Society 2024

Risk-stratified CA125 screening integrating CA125 trajectories, trajectory-specific progression and transvaginal ultrasound for ovarian cancer

BackgroundsCancer antigen 125 (CA125) is widely used for screening ovarian cancer (OC), yet its effectiveness remains debated. Potential factors may include ineffective cut-off value for CA125 in screening, as well as a lack of consideration for CA125 trajectories and trajectory-specific progression.MethodsBased on data from multiple rounds of CA125 tests and transvaginal ultrasound (TVU) examinations conducted on 28,456 women in the PLCO Trial, time-dependent receiver-operating-characteristic curves (ROCs) and area-under-the-curves (tdAUCs) analyses were employed to identify the optimal CA125 cut-off values for OC screening. Participants were categorized into four CA125 trajectories: stable negative CA125 (CA125SN), loss of positive CA125 (CA125LP), stable positive CA125 (CA125SP), and gain of positive CA125 (CA125GP). The associations between different CA125 trajectories, trajectory-specific progression indicators, and OC risk were explored. The effectiveness of risk-stratified CA125 screening, incorporating CA125 trajectories, trajectory-specific progression, and TVU, was evaluated using hazard ratio and 95% confidence intervals [HR (95%CIs)], with adjustments for potential confounders.ResultsAfter a median follow-up of 14.8 years for OC incidence and 23.8 years for OC mortality, 250 OC cases and 218 OC deaths were identified. The tdAUC for 10-year OC incidence with CA125 was 0.663, with an optimal cut-off value of 13.00 U/ml. Trajectory analyses showed that both CA125SP and CA125GP were significantly associated with increased risks of OC incidence [HRs (95%CIs): 2.00(1.47–2.73) and 3.06(2.25–4.16)] and mortality [HRs (95%CIs):1.58(1.13–2.21) and 2.60(1.87–3.62)] compared to CA125SN. Trajectory-specific progression analyses identified relative velocity as the optimal progression indicators for both CA125SP and CA125GP (tdAUCs: 0.712 and 0.767), with optimal cut-off values of 9% and 32% per year, respectively. Positive progression was associated with significantly increased risks of OC incidence [HRs (95%CI): 7.26(4.00-13.17) and 3.83(1.96–7.51) CA125GP and CA125SP] and mortality [HRs (95%CI): 8.03(4.15–15.56) and 6.04(2.78–13.14)] compared to negative progression. Optimized risk-stratified CA125 screening, which integrated CA125 trajectories, trajectory-specific progression, and TVU, reduced missed OC by 3.6% and improved accuracy compared to traditional screening methods.ConclusionsIncorporating CA125 trajectories and trajectory-specific progression into screening protocols enhances the identification of the population at high-risk of OC. An optimized screening strategy, which includes these factors along with TVU, is recommended to improve the effectiveness of OC screening.

A novel ultrasonic-velocity-based concrete carbonation monitoring method based on step-wise stretching technique

Carbonation is a common and slow process that occurs in cement-based material, resulting in durability degradation of reinforced concrete structures. In this research, the relative velocity change (d v/ v) of both ultrasonic direct waves and coda waves are extracted based on the step-wise stretching method for concrete carbonation monitoring. To this end, two-dimensional mesoscale models are established to investigate the ultrasonic propagation behaviors and assess the effectiveness of direct waves and coda waves on concrete carbonation monitoring. The numerical results indicate that direct waves could evaluate the initial carbonation, but exhibit limited sensitivity for severe carbonation. Conversely, the d v/ v values of coda waves show a linear correlation with carbonation depth in all conditions. Accelerated concrete carbonation experiments are conducted to validate the numerical findings. The experimental results and numerical findings mutually corroborate, validating the effectiveness of velocity changes of coda waves on all-stage concrete carbonation monitoring. This research contributes a novel method for monitoring concrete carbonation and enhances the understanding of ultrasonic wave propagation in concrete.

An optimization DEM modelling method for soil-fibre undrained cyclic loading tests model based on the influence range of fibre

The computational cost of discrete element modelling is high owing to the limitations of particle size and contact in fibre modelling. This paper proposes an optimised discrete element method (DEM) for a hybrid model of soil and fibres based on the fibre influence range. First, a relative velocity state function is established based on the relative motion state between the fibres and soil particles under undrained cyclic loading. Subsequently, the influence range of the fibres is determined using the relative velocity function based on the first few cycles of the undrained cyclic loading numerical tests. Cluster and clump models of the fibre are then generated based on the influence range of the fibre. Finally, a symmetrical shape of the optimised model is developed by extracting the distribution length of the edge curve of the influence range along the vertical direction of the axis. In this study, the proposed optimised DEM was validated through a series of undrained cyclic loading numerical tests on fibre-reinforced soil. The results of the optimised model were highly consistent with those of the traditional model, and the computational time was significantly reduced. The cyclic loading timing for determining the range of influence of the fibre was analysed. The optimised model based on the influence range of the 15th cycles not only restored almost the same results but also saved the calculation cost by nearly eight times. The optimised model established based on the influence range after the 15th cycles had a slight influence on the results. In addition, the applicability of the optimised model is discussed. This paper provides new insights into the establishment of a hybrid model of soil and fibres.

Comprehensive validation of a compact laser speckle contrast imaging system for vascular function assessment: from the laboratory to the clinic.

Proper organ functioning relies on adequate blood circulation; thus, monitoring blood flow is crucial for early disease diagnosis. Laser speckle contrast imaging (LSCI) is a noninvasive technique that is widely used for measuring superficial blood flow. In this study, we developed a portable LSCI system using an 805-nm near-infrared laser and a monochrome CMOS camera with a 10 × macro zoom lens. The system achieved a high-resolution imaging (1280 × 1024 pixels) with a working distance of 10 to 35 cm. The relative flow velocities were visualized via a spatial speckle contrast analysis algorithm with a 5 × 5 sliding window. In vitro experiments demonstrated the system's ability to image flow velocities in a fluid model, and a linear relationship was observed between the actual flow rate and the relative flow rate obtained by the system. The correlation coefficient (R2) exceeded 0.83 for volumetric flow rates of 0 to 0.2 ml/min when channel widths were greater than 1.2 mm, and R2 > 0.94 was obtained for channel widths exceeding 1.6 mm. Comparisons with laser Doppler flowmetry (LDF) revealed a strong positive correlation between the LSCI and LDF results. In vivo experiments captured postocclusive reactive hyperemic responses in rat hind limbs and human palms and feet. The main research contribution is the development of this compact and portable LSCI device, as well as the validation of its reliability and convenience in various scenarios and environments. Future applications of this technology include evaluating blood flow changes during skin injuries, such as abrasions, burns, and diabetic foot ulcers, to aid medical institutions in treatment optimization and to reduce treatment duration.

Gravity-driven flow of liquid bridges between vertical fibres

Liquid bridges are formed when a flowing liquid interacts with multiple parallel fibres, as relevant to heat and mass transfer applications that utilize flow down fibre arrays. We perform a comprehensive experimental study of flowing liquid bridges between two vertical fibres whose spacing is controlled dynamically in our experimental apparatus. The bridge patterns exhibit a regular periodic spacing typical of absolute instability for low flow rates, but become spatially inhomogeneous above a critical flow rate where the base flow is convectively unstable. The shapes of individual bridges and their associated dynamics are measured, as they depend upon the liquid properties, and fibre geometry/spacing. The bridge length scales similarly to static bridges between parallel fibres. The bridge dynamics exhibits a dependence on viscosity and scale with the impedance. A simple energy balance is used to derive a scaling relationship for the bridge velocity that captures the general trend of our experimental data. Finally, we demonstrate that these scalings similarly apply when the fibres are dynamically separated or brought together.

Constrained cosmological simulations of the Local Group using Bayesian hierarchical field-level inference

We present a novel approach based on Bayesian field-level inference that provides representative initial conditions for simulation of the Local Group (LG) of galaxies and its neighbourhood, constrained by present-day observations. We extended the Bayesian Origin Reconstruction from Galaxies ( algorithm with a multi-resolution approach, allowing us to reach the smaller scales needed to apply the constraints. Our data model simultaneously accounts for observations of mass tracers within the dark haloes of the Milky Way (MW) and M31, for their observed separation and relative velocity, and for the quiet surrounding Hubble flow, represented by the positions and velocities of 31 galaxies at distances between one and four megaparsec. Our approach delivers representative posterior samples of realisations that are statistically and simultaneously consistent with all of these observations, leading to significantly tighter mass constraints than found if the individual datasets are considered separately. In particular, we estimate the virial masses of the MW and M31 to be $ (M_ 200c /M_ and $12.33 respectively, their sum to be $ 200c /M_ and the enclosed mass within spheres of radius $R$ to be $ (M(R)/M_ and $12.96 for $R=1$ Mpc and $3$ Mpc, respectively. The M31-MW orbit is nearly radial for most of our realisations, and most of them feature a dark matter sheet aligning approximately with the supergalactic plane, despite the surrounding density field not being used explicitly as a constraint. High-resolution, high-fidelity resimulations from initial conditions identified using the approximate simulations of our inference scheme continue to satisfy the observational constraints, demonstrating a route to future high-resolution, full-physics simulations of ensembles of LG look-alikes, all of which closely mirror the observed properties of the real system and its immediate environment.

Investigation of friction and wear characteristics between modular charge and aluminum alloy for feeding process in artillery systems

In modern artillery systems, frictional properties of modular charge significantly impact the operation of artillery feeding system. In this study, Tribology performance between modular charge and aluminum alloy were investigated under simulated environment of artillery. The result indicates that the COF initially increased and then decreases with the temperature dropped from 50 °C to −40 °C. Additionally, COF increased from 0.19 to 0.41 when relative velocity increased from 100 mm/s to 2000mm/s. SEM detection and chemical composition analysis demonstrated that the main wear forms are adhesive wear and abrasive wear. The tribofilm including aluminum titanium oxide and aluminum nitrides generated through tribochemical reaction, which are beneficial for boundary lubrication. This work provides theoretical reference for artillery tribology research.

High‐speed escape jumps in haptophytes: Mechanism and triggering fluid signal

AbstractSome planktonic organisms can remotely sense and evade predators by powerful escape jumps. Remote perception typically happens through the fluid disturbance generated by the approaching predator or its feeding current. In copepods and ciliates with mechanosensors, the perception and jump mechanisms are well understood. But how some flagellates perceive the fluid disturbance and achieve similar relative speeds with only two flagella is less explored. Here, we examined the ability of three haptophytes, Chrysochromulina simplex, Prymnesium polylepis, and Prymnesium parvum, to sense and evade the fluid disturbance generated by the feeding current of a copepod nauplius. Chrysochromulina simplex has a long haptonema (14 cell diameters), while the haptonema of the two other species are shorter (1 and 0.5 cell diameters). Only C. simplex responded to the fluid disturbance by fleeing at high speeds. The jump mechanism consists of two phases: the rapid coiling of the haptonema that pulls the cell about two cell diameters in the direction of the haptonema, followed by flagellar reversal and high‐speed swimming (70 cell lengths per second) in the opposite direction. We rationalize cell displacements and escape speeds from haptonema and flagellar kinematics and fluid dynamics. Using a microfluidic channel, we demonstrate that the component of the fluid signal that triggers the jumps is the maximum deformation rate rather than the magnitude of deformation. High‐speed escape jumps may be an avoidance mechanism evolved by haptophytes with long and coiling haptonema, while species with shorter haptonema may use other defense mechanisms, such as stealth and toxicity.

Development of an evaluation method for precipitation particle types by using disdrometer data

Abstract A method for evaluating precipitation particle types from the size-fall velocity data observed by disdrometers by combining an expectation-maximization (EM) algorithm and a self-organizing map (SOM) was developed. An EM algorithm was used to estimate the particle size-fall velocity relationships according to previous work, and the SOM map was used to classify the relationships into graupel or snow categories. The method was applied for snowfall data observed by the volume scanning video disdrometer at a site in Sapporo, Japan, and the daily graupel-to-solid precipitation ratio (G/S ratio) from 1 December, 2017 to 28 February, 2018 was obtained. The sensitivity of the results to different SOM configurations, SOM node groupings, and training datasets was also tested. The G/S ratio obtained from the simulation data of a meteorological model was compared as an example of the application of the product created by the new method.

The study of the calculation method of the triboelectric rate of particles and surface materials at different collision velocities

In this paper, a triboelectric rate calculation model based on the relative collision velocity between the material and the particle is put forward. The model demonstrates distinct trends of the triboelectrification rate's increase with velocity, ranging from a 9/5 power to a linear function increase. Meanwhile, a test system is devised to simulate the high-speed collision process between ions and materials, and the derived model is validated through experiments.

Investigation of dynamic response characteristics of light fixed-wing aircraft

In order to ensure the stability of light fixed-wing aircraft during flight missions, considering the effects of relative airflow velocity and angle of attack, the distribution characteristics of velocity and pressure fields under different conditions, as well as the law of change of dynamic parameters, were derived by using aerodynamic methods. In the free modal condition, the modal truncation method was used to simulate and analyze the low-order modal shapes. Based on the modal analysis results, the sweep frequency range was set to 3-50 Hz, with a step size of 1.6 Hz, for a total of 30 substeps. A harmonic load of 1500 N was applied to the fuselage, and the displacement-frequency response curves and stress-frequency response curves of the fuselage structure and wing structure were extracted after the calculation. The results shows that the maximum lift-drag ratio occurs when the angle of attack is 6°, and the peak displacement deformation of the aircraft occurred around 24 Hz.

Analysis of aerodynamic characteristics of drone wing based on CFD

In order to improve the aerodynamic characteristics of the drone wings, CFD method was used to simulate and calculate the lift coefficient, drag coefficient, and lift-drag ratio under different relative inflow velocities, as well as the velocity and pressure fields under different attack angles. Modal calculations were conducted on the wing to obtain the first four modal shapes, providing a basis for analyzing flutter characteristics. An iterative calculation method of incompressible potential flow-boundary layer based on surface element method was combined with the software XFOIL to optimize the airfoil at low wind speeds. The results indicate that the airfoil is susceptible to stall at high angles of attack, with the pressure of the separation flow being nearly equivalent to that at the separation point. Subsequent to separation, there is an increase in differential pressure resistance, resulting in a marked rise in the drag coefficient. At the optimized angle of attack, the lift-drag ratio of the optimized wing increases by 12.58 %, while there is a decrease of 0.084 % in lift coefficient and an increase of 11.21 % in drag coefficient.

Application of meta-heuristic hybrid models in estimating the average air temperature of Caspian sea coast of Iran

The rise of industrial societies leads to higher greenhouse gas emissions, profoundly affecting the climate in coastal regions. Consequently, air temperature readings from standard meteorological stations are key indicators of the Earth's environmental condition. Therefore, accurate estimation of daily temperature in each region is one of the important prerequisites for agricultural planning as well as water resources management and drought prevention, which can be done in different ways such as experimental, semi-experimental and intelligent models. In this research, WSVR, AIG-SVR, GWO-SVR and BAT-SVR hybrid models were investigated and evaluated in order to estimate the average daily air temperature on the shores of the Caspian Sea located in the north of Iran. For modeling, weather station data from Babolsar meteorological station located in Mazandaran province were used. During the water year from 2012 to 2022, daily parameters including relative humidity, maximum temperature, minimum temperature, wind speed, and evaporation were selected as network inputs, with the average daily air temperature as the network output. To assess and compare model performances, several criteria were employed including correlation coefficient, root mean square error (RMSE), mean absolute error (MAE), Nash-Sutcliffe efficiency (NSE), and percentage bias. Comparative analysis revealed that the WSVR model surpassed other models, demonstrating the highest correlation coefficient (0.992), lowest RMSE (0.096), and lowest MAE (0.042). The highest Nash Sutcliffe criterion (0.996) and bias percentage (0.001) were prioritized in the validation stage.

Inelastic deformation accrued over multiple seismic cycles: Insights from an elastic-plastic slider-and-springboard model

We study a toy model designed to build physical insight into the problem of slow accumulation of non-recoverable strain in fault blocks over multiple earthquake cycles. The model consists of a thin, horizontal elastic-plastic plate (springboard) in frictional contact with a vertical, rigid wall moving downward at a steady speed. Our model produces stick-slip cycles consisting of interseismic plate downwarping and coseismic plate upwarping as long as the moment of the frictional force at the contact does not exceed the maximum (purely plastic) bending moment the plate can sustain. We show that the duration of individual earthquake cycles and the spatial pattern of interseismic deflection are controlled by two stress ratios involving the peak yield stress of the plate, the frictional strength of the fault and the coseismic stress drop. We show that non-recoverable plate deflection accumulates over successive earthquake cycles if the plate’s yield strength decreases through time, causing a progressive decrease of the aforementioned stress ratios. We derive scaling relations between the rate of accumulation of inelastic deformation, the relative tectonic plate velocity, and the rate of lithospheric weakening. Our results are consistent with observations of long-term permanent deformation of natural fault regions.