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We consider a cylinder immersed in viscous fluid moving near a flat substrate covered by an incompressible viscoelastic fluid layer, and study the effect of the fluid viscoelasticity on the lift force exerted on the cylinder. The lift force is zero when the viscoelastic layer is not deformed, but becomes non-zero when it is deformed. We calculate the lift force by considering both the tangential stress and the normal stress applied at the surface of the viscoelastic layer. Our analysis indicates that as the layer changes from the elastic limit to the viscous limit, the lift force decreases with the decrease of the Deborah number (De). For small De, the effect of the layer elasticity is taken over by the surface tension and the lift force can become negative. We also show that the tangential stress and the interface slip velocity (the surface velocity relative to the substrate), which have been ignored in the previous analysis, give important contributions to the lift force. Especially for thin elastic layers, they give dominant contributions to the lift force. [ABSTRACT FROM AUTHOR]

The Cattaneo–Vernotte model has been widely studied to take momentum relaxation into account in transport equations. Yet, the effect of reactions on the Cattaneo–Vernotte model has not been fully elucidated. At present, it is unclear how the current density associated with reactions can be expressed in the Cattaneo–Vernotte model. Herein, we derive a modified Cattaneo–Vernotte model by applying the projection operator method to the Fokker–Planck–Kramers equation with a reaction sink. The same modified Cattaneo–Vernotte model can be derived by a Grad procedure. We show that the inertial effect influences the reaction rate coefficient differently depending on whether the intrinsic reaction rate constant in the reaction sink term depends on the solute relative velocity or not. The momentum relaxation effect can be expressed by a modified Smoluchowski equation including a memory kernel using the Cattaneo–Vernotte model. When the intrinsic reaction rate constant is independent of the reactant velocity and is localized, the modified Smoluchowski equation should be generalized to include a reaction term without a memory kernel. When the intrinsic reaction rate constant depends on the relative velocity of reactants, an additional reaction term with a memory kernel is required because of competition between the current density associated with the reaction and the diffusive flux during momentum relaxation. The competition effect influences even the long-time reaction rate coefficient. [ABSTRACT FROM AUTHOR]

SiCp/Al composites are widely used in the aerospace field due to their excellent properties. However, the huge difference in the properties of silicon carbide and aluminum matrix materials can easily lead to machining defects. Ultrasonic vibration-assisted machining is an effective method to deal with difficult-to-machine materials. In this study, ultrasonic elliptical vibration is applied to the helical milling of SiCp/Al composites. Firstly, the ultrasonic elliptical vibration-assisted helical milling (UEVHM) cutting-edge trajectory is modeled, and the equation of the UEVHM tool-chip separation condition is established, which lays a foundation for the analysis of the cutting mechanism. Then, the influence of ultrasonic elliptical vibration on the removal mechanism of SiCp/Al composites was investigated by finite element simulation. It was found that UEVHM can reduce the tearing of aluminum matrix and reduce the hole damage by changing the direction of the cutting velocity and the relative position of the cutting edge and particles. Finally, the single-factor experiment was carried out, and the surface morphology and roughness of HM and UEVHM were compared. The influence of process parameters on the surface roughness of UEVHM was analyzed. The experimental results show that compared with HM, UEVHM can reduce surface defects and exit damage, to obtain better surface roughness and exit edge quality. The increase in cutting speed can reduce the roughness, and the increase in pitch and revolution speed will increase the surface roughness. [ABSTRACT FROM AUTHOR]

This study analyzes the steady-state dynamics and stability of a structure with a particle damper considering the friction effect between the particle and container, with a focus on whether the system can maintain stable-state motion for an extended period. The determination of friction's contribution and the maximum allowable gap clearance for steady-state motion is demonstrated through the solution of motion of the primary structure with a particle damper subjected to low-frequency vibration conditions. Additionally, stability analysis is conducted to assess if initial disturbances cause deviations from the original stable state and identify necessary parameters for stability when the system parameters are uncertain. Analytical descriptions for the stability of the system are derived. The effects of friction on the dynamics and stability regions of the particle dampers are systematically revealed, where the theoretical and numerical models are mutually verified and supported by the cases of previous studies. Results show that the inclusion of the rolling friction effect will disrupt the steady-state motion as gap clearance approaches the optimal value. As the coefficient of rolling friction increases, the stability region's area gradually decreases with a notable leftward shift of its right boundary. This shift ultimately leads to a leftward shift in the optimal vibration reduction curve. In the range of gap clearance variation allowing for steady-state motion with two symmetrical impacts per cycle, the relative velocity of the particle is more effective and intuitive to reveal the vibration reduction mechanism of particle dampers than other perspectives such as momentum, energy, and phase. [ABSTRACT FROM AUTHOR]

The article "Minkowski Diagrams Aid Understanding of Special Relativity" discusses the use of Minkowski space-time to visually represent special relativity, providing students with an alternative perspective to equations and thought experiments. It explains how Minkowski's work connects space and time, allowing for the visualization of events in both dimensions. The article also delves into the twin paradox and length contraction, showcasing how Minkowski spacetime can help resolve complex physics problems. Overall, the paper aims to encourage educators to incorporate visual approaches like Minkowski diagrams when teaching special relativity. [Extracted from the article]

• A new viscous damping factor is proposed. • A new viscous impact model is proposed. • The proposed viscous contact model is the most accurate impact model. • The new viscous contact model is proved by the experimental data. The accurate calculation of energy dissipation during impact plays a decisive role in the prediction of the motion status after impact and the maximum contact force. However, how to precisely depict the energy loss and simplify the contact evaluation process meanwhile is an intractable issue. This investigation aims at analyzing the capacity of accurately evaluating the dissipated energy during impact based on the viscous damping factor contingent on frequency dependency and developing a new viscous damping factor by integrating the relative impact velocity from the linearized underdamped vibration system associated with the energy conservation during impact. Two pivotal dissipative coefficients are introduced into the damping force terms in the elastoplastic and plastic contact phases for the sake of compensating the derivation error of the new viscous damping factor. A new contact model with a viscous damper is proposed based on the Hertz contact theory and dimension analysis approach in conjunction with the linearized elastoplastic stiffness from the ML model. A comparative analysis between the novel contact model and the available contact models with viscous damping factors is conducted using an external impact scenario involving two spheres, which proves that the proposed contact model is the most precise viscous contact model in calculating the loss energy during impact. Finally, the slider-crank mechanism with clearance and horizontal granular chain are considered as the numerical example to illustrate the correctness of the new viscous contact model. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Backgrounds: Cancer 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. Methods: Based 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. Results: After 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. Conclusions: Incorporating 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. [ABSTRACT FROM AUTHOR]

Sliding electrical contact involves multiple conductors sliding in contact at different speeds, with current flowing through the contact surfaces. The Lagrangian method is commonly used to describe the electromagnetic field in order to overcome the trouble of convective dominance, especially in high‐speed sliding electrical contact problems. However, to maintain correct field continuity, magnetic vector potential A′$$ {\mathbf{A}}^{\prime } $$ and scalar potential ϕ′$$ {\phi}^{\prime } $$ taken as variables cannot be continuous simultaneously at the ideal sliding electrical contact interface. This involves a strongly discontinuous condition for variables. Further, commonly used spatial–temporal discretization algorithms are invalid, for example, the classic finite element (CFEM) framework does not allow discontinuous variables, and the backward Euler method in time domain introduces a significant interface error source associated with the velocity of relative motion. To accurately handle strongly discontinuous conditions in numerical calculations, a mixed nodal finite element scheme and a higher‐order accurate temporal discretization scheme are introduced. In this scheme, classical finite element method is performed in each subdomain, and the derivative terms at the boundary are added as new variables. The effectiveness and accuracy of the above methods are verified by comparing them with a standard solution in a two‐dimensional railgun model and analyzing the current density distribution in a three‐dimensional railgun model. [ABSTRACT FROM AUTHOR]

This paper mainly discusses the dynamics of poroelastic media using the finite element analysis based on the u‐v‐p full formulation, where u${{\bm u}}$, v${{\bm v}}$, and p denote the solid displacement, relative fluid velocity with respect to solid velocity, and pore fluid pressure. It incorporates the effect of relative fluid acceleration with respect to solid acceleration on soil dynamic response. The u${ {\bm u}}$‐v${ {\bm v}}$‐p formulation is first verified through the comparison with the analytical solution. After that, the response of one‐dimensional saturated soil column and two‐dimensional partially saturated soil layer subjected to vertical loading with different combinations of soil permeability and loading frequency are investigated using the analyses with the u${ {\bm u}}$‐v${ {\bm v}}$‐p and u${ {\bm u}}$‐p formulations, based on which the effect of relative pore fluid motion is discussed and the differences in the soil response between two kinds of analysis approaches are examined. Results reveal that the rapid fluid flow has a pronounced effect on soil dynamics and the soil with a greater degree of saturation is more sensitive to the increase of loading frequency and soil permeability. The soil dynamic response can basically be divided into two main categories that represent insignificant and significant flow motion depending on loading frequency and soil permeability. Furthermore, despite vertical loading, horizontal soil response can also be affected by the large relative pore fluid flow when loading frequency and soil permeability are large. In addition, the simplified formulation can still be applicable to predict dynamics of poroelastic media in cases with high loading frequency and low soil permeability. [ABSTRACT FROM AUTHOR]

AbstractThe determination of the pullout capacity of anchors has been a key point of offshore and onshore applications, considering factors such as the shape, size, penetration velocities, and pull-out velocities of the anchors. Multi-plate expandable anchors can be considered as an alternative that exhibits higher capacity compared to single plate anchors. While previous studies have demonstrated the influence of penetration velocity, there is a lack of research investigating the pullout capacity of multi-plate expandable anchors. In the present study, experimental tests were conducted to investigate the effect of various pull-out velocities. Different soil relative densities and the distance between anchors were examined in the laboratory tests. The study also employed two analytical methods—constant control volume and movement control volume—to investigate the results of pull-out velocity. In addition, the Discrete Element Method (DEM) was used to analyze the effect of particle shape on the results. In the experimental tests, the findings suggest that increasing the pull-out velocity from 10 to 30 mm/min improved the pullout capacity of anchors and the optimal distance between plate anchors was determined to be 1B. The DEM findings showed that the sharp-cornered shape had good agreement with experimental results. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the problem of distributed optimization for second-order multi-agent systems with fixed-time flocking. The objective is to concurrently steer the agents towards a common velocity while optimizing the global objective function. To solve the problem, we first design a fixed-time estimator to predict the global gradient of the objective functions, then based on which, each agent is endowed with fixed-time tracking controller to track the optimal solution. Motivated by the fact that the relative velocity information is difficult to obtain accurately, the proposed algorithm is designed without using neighbors’ velocity. The upper bounds of the settling time are provided without relying on the initial states of the agents, only requiring the adjustment of parameters. The effectiveness of the proposed control protocol is also demonstrated through numerical simulations. [ABSTRACT FROM AUTHOR]

The tower wake usually induces large-amplitude vibrations in adjacent suspenders of a long-span suspension bridge. In order to interpret the underlying mechanism of the significant wake-induced vibrations of ultra-long suspenders, the wake-induced vibration characteristics of tandem suspenders beside the bridge tower are investigated using computational fluid dynamics based simulation. First, the computational model of the bridge tower and suspenders is established. Subsequently, the effect of tower wake on suspender vibration is analyzed considering the inflow velocity and relative position between the tower and suspenders. Based on the proper orthogonal decomposition (POD), the flow characteristics behind the tower and around the suspenders are investigated, and the governing mechanism of wake-induced vibrations of the suspenders is revealed ultimately. The results indicate that the wake-induced vibration of the suspender exhibits a lock-in phenomenon with large cross-wind amplitudes at specific incoming wind velocities. The wind loads on the suspender in both along-wind and cross-wind directions exhibit components with frequencies that are multiples of the vortex shedding frequency. The flow field can be accurately constructed using the first four POD modes with the largest energy. The symmetric POD modes are the primary components that contribute to the significant wake-induced vibrations of the suspenders. [ABSTRACT FROM AUTHOR]

The interaction dynamics between particles and bubbles in turbulent flow fields are crucial for optimizing multiphase flow systems. In this work, direct numerical simulation is combined with advanced K-means++ clustering algorithms to quantify the spatial distribution and enrichment effects of particle–bubble clusters under different turbulence conditions. The results indicate that the Stokes number increases with particle and bubble size, demonstrating stronger inertial effects, but decreases with higher turbulence intensity. Radial relative velocity and collision frequency also exhibit a positive correlation with size and turbulence intensity. Clustering analysis reveals that larger particles and bubbles form more pronounced clusters, particularly in high turbulence conditions, leading to higher local densities and interaction frequencies. Overlap ratios suggest increased interactions with growing size and turbulence intensity. These findings highlight the importance of optimizing particle and bubble sizes to match specific turbulence conditions, enhancing interaction dynamics in multiphase flow systems. This research provides valuable insights for improving various industrial processes involving particle–bubble interactions. [ABSTRACT FROM AUTHOR]

The continuum level hydrodynamic equations of a simple fluid were derived by Irving and Kirkwood directly from discrete particle dynamics using statistical mechanics almost 75 years ago. Their elegant derivation demonstrated the fundamental molecular basis of macroscopic fluid flow and culminated in molecular expressions for the stress tensor and heat current density that have since been employed in countless molecular simulations to date. In this article, an alternative derivation is presented, which leads to more general expressions for the fundamental transport relationships and which arrives at them in a more straightforward chain of consistency that ensues directly from the Principle of Least Action. The main point of departure from the Irving–Kirkwood derivation is the application of a transformation mapping of the total momentum of each individual particle onto the sum of its peculiar momentum and its momentum relative to the local velocity field. This mapping provides a phase-space distribution function applicable in the space of particle positions and peculiar momentum, from which a noncanonical Poisson bracket can be derived in terms of the same set of microscopic variables. For a given dynamic variable, expressed in terms of particle positions and peculiar momenta, the expectation value of the noncanonical Poisson bracket of the dynamic variable is shown to correspond to the evolution equation of the expectation value of the dynamic variable. This allows for a direct derivation of all macroscopic density evolution equations (mass, momentum, and energy density fields) using a systematic procedure free of assumptions concerning the macroscopic state of the system. Furthermore, an explicit expression of the time evolution of the entropy density at the hydrodynamic level is derived following the same procedure. Finally, in the limit of short-range interparticle interactions, a molecular-based expression for the local stress tensor as properly defined from continuum mechanics is developed at the hydrodynamic level that elucidates the continuum mechanics connection of the general stress expression of Irving and Kirkwood. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Background: The Food and Drug Administration (FDA) blood pump is an open‐source benchmark cardiovascular device introduced for validating computational and experimental performance analysis tools. The time‐resolved velocity field for the whole impeller has not been established, as is undertaken in this particle image velocimetry (PIV) study. The level of instantaneous velocity fluctuations is important, to assess the flow‐induced rotor vibrations which may contribute to the total blood damage. Methods: To document these factors, time‐resolved two‐dimensional PIV experiments were performed that were precisely phase‐locked with the impeller rotation angle. The velocity fields in the impeller and in the volute conformed with the previous single blade passage experiments of literature. Results: Depending on the impeller orientation, present experiments showed that volute outlet nozzle flow can fluctuate up to 34% during impeller rotation, with a maximum standard experimental uncertainty of 2.2%. Likewise, the flow fields in each impeller passage also altered in average 33.5%. Considerably different vortex patterns were observed for different blade passages, with the largest vortical structures reaching an average core radii of 7 mm. The constant volute area employed in the FDA pump design contributes to the observed velocity imbalance, as illustrated in our velocity measurements. Conclusions: By introducing the impeller orientation parameter for the nozzle flow, this study considers the possible uncertainties influencing pump flow. Expanding the available literature data, analysis of inter‐blade relative velocity fields is provided here for the first‐time to the best of our knowledge. Consequently, our research fills a critical knowledge gap in the understanding of the flow dynamics of an important benchmark cardiovascular device. This study prompts the need for improved hydrodynamic designs and optimized devices to be used as benchmark test devices, to build more confidence and safety in future ventricular assist device performance assessment studies. [ABSTRACT FROM AUTHOR]

In a review paper in this same volume, we present the state of the art on modeling of compressible viscous flows ranging from single‐phase to two‐phase systems. It focuses on mathematical properties related to weak stability because they are important for numerical resolution and on the homogenization process that leads from a microscopic description of two separate phases to an averaged two‐phase model. This review serves as the foundation for Parts I and II, which present averaged two‐phase models with phase exchange applicable to magma flow during volcanic eruptions. Here, in Part I, after introducing the physical processes occurring in a volcanic conduit, we detail the steps needed at both microscopic and macroscopic scales to obtain a two‐phase transient conduit flow model ensuring: (1) mass and volatile species conservation, (2) disequilibrium degassing considering both viscous relaxation and volatile diffusion, and (3) dissipation of total energy. The resulting compressible/incompressible system has eight transport equations on eight unknowns (gas volume fraction and density, dissolved water content, liquid pressure, and the velocity and temperature of both phases) as well as algebraic closures for gas pressure and bubble radius. We establish valid sets of boundary conditions such as imposing pressures and stress‐free conditions at the conduit outlet and either velocity or pressure at the inlet. This model is then used to obtain a drift‐flux system that isolates the effects of relative velocities, pressures, and temperatures. The dimensional analysis of this drift‐flux system suggests that relative velocities can be captured with a Darcy equation and that gas–liquid pressure differences partly control magma acceleration. Unlike the vanishing small gas–liquid temperature differences, bulk magma temperature is expected to vary because of gas expansion. Mass exchange being a major control of flow dynamics, we propose a limit case of mass exchange by establishing a relaxed system at chemical equilibrium. This single‐velocity, single‐temperature system is a generalization of an existing volcanic conduit flow model. Finally, we compare our full compressible/incompressible system to another existing volcanic conduit flow model where both phases are compressible. This comparison illustrates that different two‐phase systems may be obtained depending on the governing unknowns chosen. Part II presents a 1.5D version of the model established herein that is solved numerically. The numerical outputs are compared to those of another steady‐state, equilibrium degassing, isothermal model under conditions typical of an effusive eruption at an andesitic volcano. [ABSTRACT FROM AUTHOR]

We discuss a model describing the spin orbit resonance cascade. We assume that the body has a two-layer (core–shell) structure; it is composed of a thin external shell and an inner and heavier solid core that are interacting due to the presence of a viscous friction. We assume two sources of dissipation: a viscous one, depending on the relative angular velocity between core and shell and a tidal one, smaller than the first, due to the viscoelastic structure of the core. We show how these two sources of dissipation are needed for the capture in spin–orbit resonance. The shell and the core fall in resonance with different time scales if the viscous coupling between them is big enough. Finally, the tidal dissipation of the viscoelastic core, decreasing the eccentricity, brings the system out of the resonance in a third very long time scale. This mechanism of entry and exit from resonance ends in the 1 : 1 stable state. [ABSTRACT FROM AUTHOR]

Explosions or collisions of satellites around the Earth generate space debris, whose uncontrolled dynamics might raise serious threats for operational satellites. Mitigation actions can be realized on the basis of our knowledge of the characteristics of the fragments produced during the breakup event and their subsequent propagation. In this context, important information can be obtained by implementing a breakup simulator, which provides, for example, the number of fragments, their area-to-mass ratio or the relative velocity distribution as a function of the characteristic length of the fragments. Motivated by the need to analyze the dynamics of the fragments, we reconstruct a simulator based on the NASA/JSC breakup model EVOLVE 4.0 that we review for self-consistency. This model, created at the beginning of the XXI century, is based on laboratory and on-orbit tests. Given that materials and methods for building satellites are constantly progressing, we leave some key parameters variable and produce results for different choices of the parameters. We will also present an application to the Iridium–Cosmos collision and we discuss the distribution function after a breakup event. The breakup model is strongly related to the propagation of the fragments; in this work, we discuss how to choose the models and the numerical integrators, we propose examples of how fragments can disperse in time, and we study the behavior of multiple simultaneous fragmentations. Finally, we compute some indicators for detecting streams of fragments. Breakup and propagation are performed using our own simulator SIMPRO, built from EVOLVE 4.0; the executable program will be freely available on GitHub. [ABSTRACT FROM AUTHOR]

Recently, auxetic honeycombs have attracted widespread attention with characteristics of lightweight, excellent energy absorption capacity and high shear stiffness. The present paper proposes the hybrid star-shaped tetra-chiral honeycomb (STCH) by embedding the tetra-chiral honeycomb (TCH) into the star-shaped honeycomb (SSH). The deformation mode and compression behavior of the STCH were studied numerically and compared with that of the SSH and TCH. Particularly, under the impact velocity of 2 m/s, the specific energy absorption (SEA) of the STCH increases by 80 and 179% than that of the SSH and TCH, respectively. Through investigating the effect of impact velocity and relative density on the crushing behavior of the STCH, the deformation modes map was summarized, and the empirical formula of the plateau stress was presented. Subsequently, the detailed parameter analysis of the STCH revealed that in a certain range, the SEA and stability of the STCH increase with the increase of N x , θ , and R , and with the decrease of L 2 and L 1. Finally, the improved STCH (ISTCH) with stable deformation and better crashworthiness was further proposed, and the crashworthiness of it was comprehensively compared with other structures. The result shows the excellent crashworthiness of the ISTCH. Particularly, the SEA of ISTCH can be nearly 8 times higher than that of the TCH. The novel star-shaped tetra-chiral honeycomb (STCH) can absorb more energy due to the increase of plastic hinges and the complex coupling deformation. The deformation modes map of the STCH was summarized and the plateau stress was fitted. The change of radius and cell wall angle can greatly change the Poisson's ratio from positive to negative. The STCH and improved STCH have excellent crashworthiness. [ABSTRACT FROM AUTHOR]

Stratospheric balloons are platforms with great relevance in space missions to reach scientific observations. The payload thermal analyses of such missions are usually focused on the float phase. However, during the ascent phase, the coolest temperatures of the entire mission may be reached, mainly due to the convective cooling in the tropopause. This can be explained by the combination of relative wind speed and the harsh thermal environment. The aim of this work is to evaluate the impact of the thermal environment on the relative wind speed to determine the worst-case thermal analysis. Therefore, in order to perform a robust payload thermal during the ascent phase, the uncertainty in the thermal environment and the relative velocity must be evaluated. The former are reduced by defining the thermal environment based on real-data. The latter are reduced by evaluating the parameters involved in the ascent rate. For this purpose, a dynamic model has been developed to characterise the ascent rate and the horizontal relative velocity of the balloon-borne system. This tool has been validated with flight data from the REXUS/BEXUS programme, with the BEXUS missions launched from Esrange, Kiruna, Sweden from 2014 to 2018. The thermal analysis performed shows a temperature difference greater than 10 °C depending on the thermal worst-case selection. The work here presented reduces the uncertainties of the stratospheric payloads ascent phase thermal analysis. [ABSTRACT FROM AUTHOR]

Most metal turning processes utilize cutting fluids. Despite extensive experimental and analytical studies, the mechanisms of chip formation under consideration of a cutting fluid are still not entirely understood. Due to fluid-structure interaction, simulating wet cutting processes for an extended duration has not been feasible. The primary objective of this study is to utilize a simulation approach to provide additional information about the wet chip formation process in contrast to measurement methods, with a view to drawing conclusions. As methodology the Finite-Pointset-Method (FPM) is employed to simulate the chip formation process for dry, flood and specifically high-pressure cooling conditions during machining of carbon steel C45 as well as nickel-based alloy Inconel 718. Due to the increased relative velocity between workpiece and cutting fluid with the use of high-pressure cooling compared to flood cooling, numerical stability issues are present. Initially, the modeling approach to handle high-pressure cooling conditions is described and validated by an impact test. Subsequently the cutting simulation model is presented in detail and verified by measurements. The simulation results of stress, temperature and plastic strain rate fields are used to elucidate the observed discrepancies between various cutting fluid strategies in detail. These findings suggest explanations for the high efficiency of high-pressure cooling such as a decline of hydrostatic stresses or activation of ductile damaging. [ABSTRACT FROM AUTHOR]

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Purpose: Chemical immobilization using hydroxyapatite (HAP) is a cost effective and environmentally sound strategy for remediating lead-contaminated soils, such as shooting range soils. Understanding the combined impact of soil chemical and physical properties on enhancing the formation of pyromorphite, a lead-insoluble phase, is crucial for mitigating environmental risks associate with contaminated soil. This study aimed to elucidate the relationship between percolation velocity and lead leaching as well as pyromorphite transformation to optimize pyromorphite formation in water-unsaturated soils. Methods: Two up-flow suction percolation tests were performed: one varying percolation velocity with soil porosity achieved by incorporating clay minerals, and the other varying percolation velocity while keeping soil porosity constant. Results: Application of HAP substantially suppressed lead leaching in both percolation tests. Enhanced pyromorphite formation was observed with higher percolation velocities relative to soil porosity. Pyromorphite formation was more pronounced at lower percolation velocities compared to higher velocities at equivalent soil porosity level. The percentages of lead formed as pyromorphite in HAP-treated soil were higher than those of lead leached in non-HAP-treated soil among the lower percolation velocities. Conclusions: This study provides experimental evidence indicating pyromorphite formation is favored in soils with lower percolation velocities and higher soil porosities. Therefore, considering both soil chemical and physical properties is essential for understanding immobilization mechanisms in contaminated soils. [ABSTRACT FROM AUTHOR]

Due to the numerous practices of non-Newtonian fluids in technological and industrial fields, the attention towards such fluids increases incredibly. The highly nonlinear equations emerge in the modeling of the non-Newtonian fluids. The differential transform method is one of the analytical methods which is used to acquire the solution to these complicated nonlinear equations in the series form. The current analysis comprises the squeeze flow of non-Newtonian fluid in two dimensions. Two infinite parallel plates are considered in which the time-dependent fluid is squeezed. The heat transfer mechanism is deliberated with the significance of heat absorption/generation. The nonlinear setup of ordinary differential equations is acquired by practicing the appropriate similarity variables on the governing equations of the concerned flow mechanism. The nonlinear setup is analytically resolved with the help of an analytical differential transform method. For the authenticity of the differential transform method, the analytical outcomes are compared with the numerical results. Graphical illustrations of fluid temperature and velocity profiles relative to the pertinent parameters are briefly explicated numerically and analytically. The fluid velocity demonstrates the descending behavior and the temperature field exhibits the expanding nature relative to the squeezing parameter. [ABSTRACT FROM AUTHOR]

The velocity and acceleration of a soccer player varies depending on the specific demands of the field position as well as individual characteristics, establishing the need to determine relative profiles by position. A cross-sectional study was conducted in 18 semi-professional soccer players to determine (i) the specific demands of external load according to playing position, (ii) distances covered at different intensities and the number of sprints, and (iii) the number of accelerations at moderate and high intensity. GPS tracking systems were used to collect data, and the relative acceleration profiles were analyzed based on initial velocity (0–7 km/h; 7.1–14.3 km/h; >14.3 km/h), intensity (moderate 50–75% and high > 75% of maximal acceleration), number of sprints/accelerations, and distance covered. Additionally, relative speed profiles were evaluated through the distance covered at moderate intensity (40–60% Vmax), high intensity (60–75.5% Vmax), very high intensity (>75.5% Vmax), total distance, and number of sprints. Statistically significant differences were observed in the distance covered at moderate and high intensity (midfielders), distance covered sprinting (center backs), and acceleration at moderate and high intensity in all positions (p < 0.05). These findings will enhance the monitoring of external loading strategies and prescription of specific training exercises for soccer players based on their respective playing position, ultimately contributing to optimized performance. [ABSTRACT FROM AUTHOR]

The impact of wettability on the co-moving velocity of two-fluid flow in porous media is analyzed herein. The co-moving velocity, developed by Roy et al. (Front Phys 8:4, 2022), is a novel representation of the flow behavior of two fluids through porous media. Our study aims to better understand the behavior of the co-moving velocity by analyzing simulation data under various wetting conditions. We analyzed 46 relative permeability curves based on the Lattice–Boltzmann color fluid model and two experimentally determined relative permeability curves. The analysis of the relative permeability data followed the methodology proposed by Roy et al. (Front Phys 8:4, 2022) to reconstruct a constitutive equation for the co-moving velocity. Surprisingly, the coefficients of the constitutive equation were found to be nearly the same for all wetting conditions. On the basis of these results, a simple approach was proposed to reconstruct the relative permeability of the oil phase using only the co-moving velocity relationship and the relative permeability of the water phase. This proposed method provides new information on the interdependence of the relative permeability curves, which has implications for the history matching of production data and the solution of the associated inverse problem. The research findings contribute to a better understanding of the impact of wettability on fluid flow in porous media and provide a practical approach for estimating relative permeability based on the co-moving velocity relationship, which has never been shown before. [ABSTRACT FROM AUTHOR]

We report on an experimental study in which Lagrangian tracking is applied to millions of microscopic particles floating on the free surface of turbulent water. We leverage a large jet-stirred zero-mean-flow apparatus, where the Reynolds number is sufficiently high for an inertial range to emerge while the surface deformation remains minimal. Two-point statistics reveal specific features of the flow, deviating from the classic description derived for incompressible turbulence. The magnitude of the relative velocity is strongly intermittent, especially at small separations, leading to anomalous scaling of the second-order structure functions in the dissipative range. This is driven by the divergent component of the flow, leading to fast approaching/separation rates of nearby particles. The Lagrangian relative velocity shows strong persistence of the initial state, such that the ballistic pair separation extends to the inertial range of time delays. Based on these observations, we propose a classification of particle pairs based on their initial separation rate. When this is much smaller than the relative velocity prescribed by inertial scaling (which is the case for the majority of the observed particle pairs), the relative velocity transitions to a diffusive growth and the Richardson–Obukhov super-diffusive dispersion is recovered. [ABSTRACT FROM AUTHOR]

Summary Contradictory evidence exists regarding the relevance of Péclet‐like gradients in leaf water isotopes, making it difficult to accurately predict variation in isotope composition. Here, we use H218O vapour labelling to directly test whether leaf water isotopes diffuse back into the xylem to be carried forward to more distal leaf portions. Backward diffusion has been assumed, due to observations of increasing enrichment towards the tip and outer edges of some leaves. Further complicating the selection of leaf water isotope models is the observation that some, but not all, leaves demonstrate a radial Péclet effect in bulk leaf water and that the hydraulic design of leaves may influence the development of isotope gradients in leaves. Carry‐forward of H218O vapour label was detected in the two monocot species assessed (oat and corn), but not in the two dicot species (foxglove and sunflower). Further, bulk leaf water measurements at differing transpiration rates indicated that a bulk leaf water Péclet effect was relevant for foxglove only. We conclude that both leaf hydraulic design and relative velocities of water within transport pathways influence leaf water isotope composition, reconciling seemingly contradictory previous results regarding the relevance of Péclet effects to leaf water isotopes. [ABSTRACT FROM AUTHOR]

The usual gravitational wave memory effect can be understood as a change in the separation of two initially comoving observers due to a burst of gravitational waves. Over the past few decades, a wide variety of other, 'persistent' observables which measure permanent effects on idealized detectors have been introduced, each probing distinct physical effects. These observables can be defined in (regions of) any spacetime where there exists a notion of radiation, such as perturbation theory off of a fixed background, nonlinear plane wave spacetimes, or asymptotically flat spacetimes. Many of the persistent observables defined in the literature have only been considered in asymptotically flat spacetimes, and the perturbative nature of such calculations has occasionally obscured deeper relationships between these observables that hold more generally. The goal of this paper is to show how these more general results arise, and to do so we focus on two observables related to the separation between two, potentially accelerated observers. The first is the curve deviation, which is a natural generalization of the displacement memory, and also contains what this paper proposes to call drift memory (previously called 'subleading displacement memory') and ballistic memory. The second is a relative proper time shift that arises between the two observers, either at second order in their initial separation and relative velocity, or in the presence of relative acceleration. The results of this paper are, where appropriate, entirely non-perturbative in the curvature of spacetime, and so could be used beyond leading order in asymptotically flat spacetimes. [ABSTRACT FROM AUTHOR]

AbstractVoid fraction and relative velocity between phases are parameters of key importance when analyzing two-phase flow systems. The drift flux model is a simple, yet robust, method of predicting these parameters. Detailed drift flux analyses have focused on vertical flows, with recent work investigating horizontal flows. There is comparatively little work performed involving inclined two-phase flows—and fewer specifically for inclined bubbly flows. Depending on the orientation, the buoyancy force may not act parallel to the flow direction and can induce asymmetry and bubble clustering, which may affect relative velocity and void fraction. The current work seeks to characterize the effects of inclination on void fraction and relative velocity in bubbly two-phase flows. This is done by performing one-dimensional drift flux analyses and by comparing closure relations proposed in the literature. Experiments are performed focusing on bubbly flows in an inclinable test facility with an inner diameter of 25.4 mm. Time-averaged two-phase flow parameters are measured using four-sensor conductivity probes, and these measurements are benchmarked to ensure reliability. It is found that as the inclination angle is reduced from vertical, the relative velocity changes rapidly, yielding a slip ratio of less than unity for angles investigated below 80°. This corresponds to changes in the distribution parameter and drift velocity. The effects of angle are also apparent in changes in the area-averaged void fraction. These findings challenge previously developed correlations, which are generally unable to predict the experimental void fraction and have suggested slip greater than unity for inclined-upward bubbly flows. [ABSTRACT FROM AUTHOR]

The design of water structures is crucial for efficient hydraulic performance. Open irrigation canals are designed with specific inside slopes to ensure maximum stability, while the wing walls of water structures constructed across the canal are designed to maximize hydraulic performance. Therefore, ensuring compatibility between the canal inside slopes and the wing wall types used on both the upstream and downstream sides is of great importance for achieving optimum hydraulic performance. However, our literature review indicates that this necessary compatibility between the canal inside slope and the wing wall type has not been adequately researched and studied. This present study aims to numerically investigate the relationship between open canals inside slopes and wing wall types, as well as examine the impact of using different wing wall types with varying canals inside slopes on hydraulic performance efficiency. Four canal inside slope ratios (Z) (H: V = 2:1, 1.5:1, 1:1, and 0.75:1) are simulated using the HEC-RAS program, along with two types of water structure wing walls (box and broken). The HEC-RAS numerical model provides accurate and reliable estimations of the hydraulic characteristics of flowing water through the structure, and the results are verified using previous experimental measurements available in the literature. The variation (ε%) between the measured and computed results is consistent for estimating specific energy, velocity, heading (afflux), and water depths. The simulation results demonstrate that changing the canal inside slope (Z) from 0.75:1 to 2:1 results in a relative increase of approximately 27.84% in heading up and 15.06% in velocity. Additionally, the broken wing wall proves to be more effective than the box type. The study confirms that the optimal configuration for the most efficient performance of water structures involves utilizing broken-type wing walls on the upstream side, along with a 1H:1V canal inside slope. This configuration reduces the relative velocity and relative heading by approximately 12% and 20%, respectively, which is considered highly favorable. [ABSTRACT FROM AUTHOR]

Lorentz invariance underlies special relativity, and the energy formula and relative velocity formula are well known to be invariant under a Lorentz transformation. Here, we determine the functional forms in terms of four arbitrary functions for those three dimensional velocity fields that are automatically invariant under the most general fully three-dimensional Lorentz transformation. For general three-dimensional motion, using rectangular Cartesian coordinates (x , y , z) , we determine the first-order partial differential equations for the three velocity components u (x , y , z , t) , v (x , y , z , t) and w (x , y , z , t) in the x − , y − and z − directions respectively. These partial differential equations and the associated partial differential relations connecting energy and momentum are fully compatible with the Lorentz-invariant energy–momentum relations and appear not to have been given previously in the literature. We determine the spatial and temporal dependence of the functional forms for those three-dimensional velocity fields that are automatically invariant under three-dimensional Lorentz transformations. An interesting special case gives rise to families of particle paths for which the magnitude of the velocity is the speed of light. This is indicative of the abundant possibilities existing in the "fast lane". [ABSTRACT FROM AUTHOR]

This article presents an overall examination of how small temperature fluctuations affect P-wave velocity (Vp) measurements and their uncertainties in concrete using embedded piezoelectric transducers. This study highlights the fabrication of custom transducers tailored for long-term concrete monitoring. Accurate and reliable estimation of ultrasonic wave velocities is challenging, since they can be impacted by multiple experimental and environmental factors. In this work, a reliable methodology incorporating correction models is introduced for the quantification of uncertainties in ultrasonic absolute and relative velocity measurements. The study identifies significant influence quantities and suggests uncertainty estimation laws, enhancing measurement accuracy. Determining the onset time of the signal is very time-consuming if the onset is picked manually. After testing various methods to pinpoint the onset time, we selected the Akaike Information Criterion (AIC) due to its ability to produce sufficiently reliable results. Then, signal correlation was used to determine the influence of temperature (20 °C to 40 °C) on Vp in different concrete samples. This technique proved effective in evaluating velocity changes, revealing a persistent velocity decrease with temperature increases for various concrete compositions. The study demonstrated the capability of ultrasonic measurements to detect small variations in the state of concrete under the influence of environmental variables like temperature, underlining the importance of incorporating all influencing factors. [ABSTRACT FROM AUTHOR]

Sediment management is a significant part of the decision-making process that hydraulic engineers need to undertake as it has a direct bearing on the environment. Sediment dredging from around intake structures and reservoirs impose a high operating cost. Jets can efficiently remove large quantities of sediment at low operational costs. This study assesses the scouring pattern development by changing nozzle parameters to achieve maximum scouring conditions. Toward this end, scour holes induced by jets generated using the nozzles with four inner angles (30°, 45°, 60°, and 90°) are tested on a cohesionless sediment bed. The experimental results show that the inner nozzle angle, α, and the densimetric Froude number, F0, affect the scour pattern. This work illustrates that the scour hole dimensions grow with increasing α and F0. Based on the velocity measurements, for the range of jet discharges considered herein, the relative velocity Um/U0 is increased by 20%–25% for the nozzle with α = 90° compared to the nozzle with α = 30°. [ABSTRACT FROM AUTHOR]

Over the last couple of years, the appearance of the third data release from the Gaia satellite has triggered various wide binary low acceleration gravity tests. Wide binaries with typical total masses |$\approx 1.0 - 1.6\,\mathrm{ M}_{\odot }$| and separations above a few thousand au probe the low acceleration |$a \lesssim a_{0}$| regime, where at galactic and larger scales gravitational anomalies typically attributed to the presence of an as yet undetected dark matter component appear, where |$a_{0} \approx 1.2\times 10^{-10}$| m s |$^{-2}$| is the acceleration scale of Modified Newtonian Dynamics (MOND). Thus, studies of the relative velocities and separations on the plane of the sky, |$v_{2\mathrm{ D}}$| and |$s_{2\mathrm{ D}}$|⁠ , respectively, of wide binary stars extending to separations above a few kau, provide an independent approach on the empirical study of gravity in the interesting |$a \lesssim a_{0}$| acceleration range. Two independent groups, through complementary approaches, have obtained evidence for a departure from Newtonian predictions in the low acceleration regime, in consistency with MOND expectations for wide binary orbits in the Solar Neighbourhood. Two other groups however, have instead reported results showing a clear preference for Newtonian gravity over various MOND alternatives tested, over the same low acceleration regime. We here take a critical look at the various studies in question, from sample selection to statistical treatment of the wide binary relative velocities obtained. We discover a couple of critical problems in the formal design and statistical implementation shared by the two latter groups, and show explicitly how these yield biased conclusions. [ABSTRACT FROM AUTHOR]

This article describes a two-year project conducted by a high school astronomy club, in which they built a radio telescope to measure Doppler-shifted radio signals from within the Milky Way galaxy. The club analyzed the data and found that the orbital velocity of matter around the galactic center remains relatively constant as one travels outward, supporting the existence of dark matter. The article provides detailed information on the telescope design and data collection process. It also discusses the velocity profiles of the Milky Way galaxy based on intensity vs. relative velocity plots, which indicate that the velocities do not conform to the expected trend if all the mass is concentrated at the galactic center. This suggests the presence of dark matter distributed differently from visible matter, consistent with previous studies. The article also mentions the challenges and strengths of the project, which involved constructing a radio telescope to collect data on the hydrogen distribution in the galaxy. [Extracted from the article]

Bernoulli's equation is a famous, elegant fluid mechanics relation that, in its most popular version, relates pressure, velocity, and elevation changes along each streamline in a steady barotropic inviscid flow. Despite its simplicity and restrictive assumptions, this equation is a powerful and effective analysis tool in a variety of real-flow situations. However, the Bernoulli equation is unfortunately not Galilean-invariant, i.e., it does not satisfy the desirable property of remaining unchanged under a Galilean transformation between two inertial reference frames reciprocally moving with constant velocity. In a previous paper, the author presented a Galilean-invariant formulation of the Bernoulli equation, in which a new term is introduced in the definition of the Bernoulli constant. In the present technical note, this Galilean-invariant form of the Bernoulli relation is extended to (1) unsteady flow, (2) compressible flow, and (3) a noninertial frame of reference accelerating with constant rectilinear acceleration. Similar extensions are consolidated for the classic Bernoulli equation and treated in fundamental fluid mechanics textbooks. The use of the updated Galilean-invariant Bernoulli equation in these less-restrictive contexts is illustrated with typical engineering application examples. The results demonstrate that the extended version of the Bernoulli principle can also be applied along the same flow lines in a reference frame moving with constant velocity relative to another reference frame in which the conventional Bernoulli equation is valid, provided that the Bernoulli constant includes a suitable additional term. [ABSTRACT FROM AUTHOR]

The purpose of the study was the impact of different types of ventilation systems in boar`s pen on the microclimate and their physiological parameters. The control group of boars was kept in a house with a transverse ventilation system, and the animals of the experimental group were kept in a geothermal air supply. It was found that, regardless of the season, transverse ventilation provides a significantly higher air velocity and relative humidity: in Winter - 0.15 m s–1 and 5.4%; in Spring - 0.35 m s–1 and 5.3%; in Summer - 0.41 m s–1 and 0.7%; in Autumn - 0.28 m s–1 and 8.1%. Maintaining a stable temperature by the normative values in the boar housing was due to geothermal ventilation, regardless of the season, especially the "basement effect" was observed in the summer months, where the air temperature was cooled to 4.5°C (P < 0.001), compared to the transverse ventilation system. Compared with the boars in the experimental group, under the influence of the temperature increase in Summer, the boars in the control group increased significantly the respiratory rate to 50.9 ppm (P < 0.001) and heartbeat rate of 45.7 ppm (P < 0.001). An increase in rectal temperature in boars at elevated ambient temperature under both air ventilation systems was not found. The obtained results make it possible to introduce the use of cost-effective geothermal air supply technology in pig farms to harmonize the physiological parameters of boars to meet their biological needs, even in closed housing to improve their welfare. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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We address the collision of two superfluid 4He droplets at non-zero initial relative velocities and impact parameters within the framework of liquid 4He time-dependent density functional theory at zero temperature. Despite the small size of these droplets (1000 He atoms in the merged droplet) imposed by computational limitations, we have found that quantized vortices may be readily nucleated for reasonable collision parameters. At variance with head-on collisions, where only vortex rings are produced, collisions with a non-zero impact parameter produce linear vortices that are nucleated at indentations appearing on the surface of the deformed merged droplet. Whereas for equal-size droplets, vortices are produced in pairs, an odd number of vortices can appear when the colliding droplet sizes are different. In all cases, vortices coexist with surface capillary waves. The possibility for collisions to be at the origin of vortex nucleation in experiments involving very large droplets is discussed. An additional surprising result is the observation of the drops coalescence even for grazing and distal collisions at relative velocities as high as 80 and 40 m/s, respectively, induced by the long-range van der Waals attraction between the droplets. [ABSTRACT FROM AUTHOR]

This study experimentally and numerically investigated the characteristics of heat transfer between particle flow and a cylindrical wall. The theoretical model of the heat transfer coefficient calculation was verified and modified according to experimental data. In the experimental scheme, the temperature at the axis of the cylinder under different conditions was measured to determine the effects of temperature, relative motion velocity, and cylinder diameter on the heat transfer coefficient between the particle flow and the cylindrical wall. Results revealed the benefits of using high temperature for increasing the heat transfer coefficient. The relative motion velocity between the wall and particles had no significant effect on the heat transfer coefficient. Furthermore, the change in the heat transfer coefficient was less than 10% in the range of relative velocity v = 0.03 to 0.12 m·s−1 between the wall and particles. The heat transfer coefficient almost independents on cylinder diameter under constant particle diameter conditions. [ABSTRACT FROM AUTHOR]

Based on observations from the Magnetospheric Multiscale mission, this study presents an analysis of a short large‐amplitude magnetic structures (SLAMS) event with simultaneous occurrence of low‐ and high‐frequency magnetosonic whistler waves. It was found that low‐frequency magnetosonic whistler waves around the lower‐hybrid frequency emerge in the presence of solar wind ions and local low‐energy ions in the trailing region of SLAMS. Additionally, counter‐propagating whistler waves (the high‐frequency branch of the magnetosonic whistler wave) are observed within SLAMS, coinciding with a perpendicular temperature anisotropy in the electron population. Instability analyses demonstrate that these low‐frequency waves are induced by the two‐stream instability associated with the cross‐field relative velocity between low‐energy ions and electrons, while whistler waves are locally generated by the whistler anisotropy instability. Our results shed light on the impact of SLAMS on particle and wave dynamics in the terrestrial foreshock. Plain Language Summary: Short large‐amplitude magnetic structures (SLAMS) are frequently observed within the terrestrial foreshock. They play a significant role in particle dynamics, often leading to the formation of unstable ion and electron velocity distributions. Consequently, plasma waves are excited across both ion and electron scales. Despite their importance, direct observational evidence linking SLAMS to the local excitation of plasma waves has been lacking. In this study, we utilized observations from the Magnetospheric Multiscale mission to investigate the local excitation of magnetosonic whistler waves associated with SLAMS. We revealed the presence of counter‐propagating whistler waves within SLAMS. We attributed the generation of these waves to the local whistler anisotropy instability. Furthermore, we found the occurrence of low‐frequency magnetosonic whistler waves in the trailing region of SLAMS. We identified their excitation mechanism as the two‐stream instability relating to local low‐energy ions. These results offer valuable insights into the intricate interplay between SLAMS and particle‐wave dynamics within the terrestrial foreshock. Key Points: MMS observes both low‐ and high‐frequency magnetosonic whistler waves associated with SLAMS in Earth's foreshockCounter‐propagating high‐frequency magnetosonic whistler waves are proposed to be excited by the whistler anisotropy instability in SLAMSLow‐frequency magnetosonic whistler waves are excited by the cross‐field relative velocity between low‐energy reflected ions and electrons [ABSTRACT FROM AUTHOR]

This paper is concerned with the nonlinear stability of planar Couette flow for the three‐dimensional NS‐NS equations, which are used to model the motion of two‐phase flow. Our result shows that the planar Couette flow is asymptotically stable for the initial perturbations sufficiently small in some Sobolev space if the background velocity and the Reynolds number are sufficiently small. Moreover, it is proved that the solution converges to the stationary state (ρ∗,us,n∗,ws)$$ \left({\rho}_{\ast },{u}_s,{n}_{\ast },{w}_s\right) $$ at an algebraic time decay rate, and we also give the decay rate of the relative velocity. [ABSTRACT FROM AUTHOR]

The flow rate is a significant factor in the operation of centrifugal pumps. The characteristic curve of the pump head is frequently employed in the calculation of the flow rate. Nevertheless, this may be subject to alteration because of prewhirl on the suction side of the pump. Calculating the changes in the head's characteristic curve reveals a change in hydraulic losses. The impact of prewhirl on hydraulic losses is investigated by experimental and numerical analysis of two radial centrifugal pumps. It is demonstrated that the primary changes occur in the pump impeller losses. Relative velocity is a significant factor in this context. Alterations in the pumps' configurations result in a range of secondary flows and shock losses at the leading edge of the blades. A physical model, derived on the basis of the relative velocity, is used to predict the characteristic curves of radial centrifugal pumps with prewhirl with a high degree of accuracy. The results demonstrate a notable enhancement in comparison to modelling techniques that do not incorporate the fluctuating hydraulic losses. [ABSTRACT FROM AUTHOR]

To determine the relative distances and peculiar velocities of 140 groups and clusters of galaxies at low redshifts (z < 0.12), we used the fundamental plane (FP) of early-type galaxies (from the Sloan Digital Sky Survey (SDSS) data). We constructed the Hubble diagram for the relative distances of galaxy groups/clusters versus their radial velocities in the cosmic microwave background (CMB) reference frame in the flat Λ cold dark matter (ΛLCDM) model (Ωm = 0.3 and H0 = 70 km s–1 Mpc–1). We have found that the standard logarithmic deviation for groups and clusters of galaxies on the Hubble diagram (minus peculiar velocities) is ±0.0173 (N = 140), which corresponds to a deviation of 70 ± 2.8 km s–1 Mpc–1 in the Hubble constant. For a sample of galaxy systems (N = 63), the X-ray luminosity of which is in an interval of (0.151‒4) × 1044 erg/s, this quantity turned out to be 70 ± 2.1 km s–1 Mpc–1. The root-mean-square deviations of peculiar velocities with quadratic accounting for errors are = 714 ± 7 and 600 ± 7 km/s, respectively. For five large superclusters of galaxies from the SDSS region, the average peculiar velocity relative to the CMB reference frame is +240 ± 250 km/s. We detected no outflow of galaxy systems from the void (Giant Void; α ≈ 13h, δ ≈ 40°, and z ≈ 0.107) formed by groups and clusters of galaxies. [ABSTRACT FROM AUTHOR]