Constant Velocity Research Articles

Gravity train of variable mass

The gravity train is a virtual vehicle that travels in a tunnel across Earth, and its motion due to only gravity is a simple harmonic oscillator. It can run at a constant velocity by appropriately exhausting fuel. In this case, the train obeys the equation of motion for a variable mass system. We discuss the mass and energy reduction of the gravity train during travel and find the optimal conditions for economical travel. This study is suitable for university students in physics classes.

New exact solutions of the (3+1) dimensional Charney - Obukhov equation for the ocean in the case of “separation” of variables

Exact solutions describing Rossby waves and vortices in ocean propagating along the zonal direction at a constant velocity are considered for the (3 + 1) -dimensional nonlinear Charney – Obukhov equation. We give examples of solutions of the Charney-Obukhov equation that satisfy the nonlinear boundary conditions for the ocean, for a special case that corresponds to the “separation” of variables. The following example is considered: a lattice of vortices with 3D flow in lattice cells, the inclination of vortex cells in the meridional plane, and the dependence of the inclination angle on depth.

Optimum frequency tracking of the ultrasonic motor based on a three-level constant voltage drive

Abstract Ultrasonic motors are widely used in aerospace, smart cameras, and other applications. For ultrasonic motors to have the highest operating efficiency, the operating frequency of the motor needs to be adjusted in real time so that the motor’s operating frequency tracks the optimum frequency. Since the current research is limited to the optimum frequency tracking under constant velocity, the three-level drive parameters need to be adjusted to stabilize the velocity, which lacks precision and does not consider the frequency tracking under variable velocity. This paper explores an optimum frequency tracking scheme for ultrasonic motors under the three-level constant voltage input drive and proposes a variable step-size optimum frequency tracking scheme. The experimental results show that the optimum frequency of ultrasonic motors in variable velocity motion exists, and the proposed tracking scheme with three-level drive parameters can effectively improve the efficiency of the motor and significantly broaden the application scenario of the optimum frequency of ultrasonic motors.

Nonlinear electrodynamics for the vacuum of Dirac materials: Photon magnetic properties and radiation pressures

We investigate the magnetic properties of photons propagating through Dirac materials in a magnetic field, considering both vacuum and medium contributions. Photon propagation properties are obtained through a second-order expansion of nonlinear Euler-Heisenberg electrodynamics at finite density and temperature considering Dirac material parameters (Dirac fine structure constant, band gap, and Fermi velocity). Total magnetization (including electron and photon contributions) and photon-effective magnetic moment are computed. Observables such as photon energy density, radiation pressure, and Poynting vector are obtained by an average of components of the energy-momentum tensor. All quantities are expressed in terms of Lagrangian derivatives. Those related to the vacuum are valid for any value of the external magnetic field, and both the weak- and strong-field limits are recovered. We discuss some ideas of experiments that may contribute to testing in Dirac materials the phenomenology of the strong magnetic field in the quantum electrodynamic (QED) vacuum and how nonlinear corrections on the magnetization, radiation pressure, and birefringence are amplified up to 103 times QED corrections. Published by the American Physical Society 2024

Analysis of drying characteristics and quality attributes in peach slices dried via electrohydrodynamic, hot air and electrohydrodynamic-hot air methods

This study aimed to investigate drying times mathematical models and assess the color, rehydration capacity, and microstructure of dried peach using electrohydrodynamic (EHD), hot air, and electrohydrodynamic-hot air (EHD-hot air) drying methods. Peach samples were subjected to drying with two different air temperatures (50 and 55 °C) and electric field (EF, 6.67 and 10 kV cm−1) under constant air velocity (1.5 m s−1). The longest drying durations were obtained in the EHD method (720 and 600 min), followed by hot air (290 and 260 min) and EHD-hot air method (120, 140, 170, and 200 min), respectively. The drying curves were best described by the Midilli et al. and Logarithmic models. The L* values of the samples subjected to hot air drying were found to be lower than those obtained through other methods. No significant effect of the electric field on rehydration capacity was observed. The study revealed that increased temperature and electric field led to surface cracks on the peach. The study highlights the compatibility of the EHD method with the hot air method, suggesting its potential application within the drying industry. From these findings, it was seen that the EHD-hot air combination method could be an alternative to the hot air method in the food industry by reducing the drying time of peaches and considering that the color parameters are generally better than the hot air method.

Atomistic simulations of oblique collisions between crystalline and amorphous SiC nanoparticles: Mechanisms of deformation and scaling coefficients of restitutions

Systematic atomistic simulations of oblique collisions between spherical crystalline, 6H and 3C, and amorphous SiC nanoparticles (NPs) are performed in the bouncing and fragmentation regimes for the particles with diameters from 8 nm to 30 nm, impact velocities from 100 ms−1 to 5000 ms−1, and in the whole range of the geometric impact parameter. The critical sticking velocity of 6H-SiC NPs reduces from ∼490 ms−1 to ∼150 ms−1 when the NP diameter increases from 10 nm to 30 nm. Below the melting threshold, the collision of crystalline NPs induces the formation of localized zones of densified material, while the remaining parts of NPs are not affected by plastic deformations. The impact of amorphous NPs results in the plastic deformation of significant parts of the NP material and much larger irreversible losses of mechanical energy. The post-collision translational and rotational velocities of crystalline NPs as well as coefficients of restitution (CORs) demonstrate weak dependence on the NP size if the NP diameter is greater than 20 nm. At constant impact velocity, the normal COR only marginally varies for head-on and oblique collisions, when the collision angle is smaller than ∼53°. The tangential center-of-mass and point-of-contact CORs, as functions of the impact parameter, demonstrate extremal behavior with the minima at collision angles from ∼27° to ∼37°. The normal COR exhibits a linear decay as a function of the impact velocity where the slope coefficient is different below and above the melting threshold. The tangential CORs attain the minimum values at the impact velocity of ∼300 ms−1. The obtained results are summarized in the form of fitting equations for CORs as functions of the impact parameter and velocity, which can be readily used to predict the post-collision translational and angular velocities of NPs in large-scale simulations of granular gas flows.

Effects of the filter media pack configurations on the air filtration performance

Abstract High efficiency particulate air (HEPA) filters are widely used in various industries to contain airborne contamination. The pressure drop of the filters is a crucial performance parameter when designing a HEPA filter as it is the resistance that the filter offers to the flow of air. Thus, it is critical to find the effect of each configuration and integrate an optimal setup for the filter to avoid high-pressure drops. Set against these backgrounds, this study aims to study the effect of different configurations on the total pressure drop of the filter, and to review how each configuration can affect each other using a commercial software ANSYS Fluent. The different filter media pack configurations and boundary conditions investigated here are including pleat shape (V-shaped and U-shaped), pleat density (1-7 pleat/cm), pleat height (1cm, 1.3cm), and inlet velocity (0.02-0.2 m/s) on the pressure drop of the filter. A two-dimensional geometrical model is developed, and then validated with respect to the data obtained from Lydall M3004-06 property sheet. Upon successful validation exercise, a series of parametric studies is conducted to numerically examine the impact of changing each configuration on the total pressure drop of the filter. Results show that an optimal pleat density is attained where the total pressure drop is minimized, i.e., 3 pleat/cm for V-shaped and 4 pleat/cm for U-shaped for inlet velocity of 0.02 m/s. At a constant inlet velocity, the U-shaped pleat has a lower pressure drop than the V-shaped pleat at low pleat densities, but a higher pressure drop at higher densities. This behaviour can be attributed to the balance between inertial and viscous resistance. Increasing the inlet velocity increases the total pressure drop for all pleat heights and decreases the optimal pleat density. This effect is less pronounced on the V-shaped pleat. Increasing the pleat height for the U-shaped pleat decreases the pressure drop and optimal pleat density but increases pressure drop in the viscous dominated region. Conversely, increasing the pleat height for the V-shaped pleat decreases the pressure drop for all pleat counts and only decreases the optimal pleat density at high velocity.

Rarefied cylindrical Couette problem: Effect of a very sharp transition from weakly rarefied flow near the inner cylinder to free molecular flow at very low average Knudsen numbers

We consider the rarefied cylindrical Couette flow. The outer cylinder rotates at a constant angular velocity, and the inner one is at rest. The Knudsen number, calculated from the average gas density, is much less than one. To find the fluid dynamic variables and fluxes, the direct simulation Monte Carlo method (DSMC) is used. We find the effect of a very sharp decrease in shear stress and energy fluxes transferred to the cylinders if the Knudsen number is sufficiently low and the rotation speed of the outer cylinder is sufficiently high. We show that when the average Knudsen number is sufficiently low, if the velocity is initially high and increases slightly further, the weakly rarefied flow regime near the inner cylinder transitions abruptly to a free molecular flow regime. Thus, the flow abruptly separates from the inner cylinder. We compare the fluxes obtained by solving the Navier–Stokes equations and by the DSMC method. It turns out that the solutions of the Navier–Stokes equations with slip boundary conditions also change abruptly at certain critical values, and these critical values are close to the appropriate DSMC values.

Revisiting the Matter of Time Dilation in Special Relativity

There are different interpretations of the Lorentz transformations of the Special Theory of Relativity (SR) concerning the relative rates of two clocks that are moving at constant relative rectilinear velocity (Einstein’s definition of conditions necessary for SR). [It is common to talk in terms of how one observer “views” another clock that is moving at constant velocity relative to them. This carries an implication of visual observation. That is a limitation avoided in this contribution by the use of “as determined”, without specifying the means employed, but wherever “as viewed” does occur, it is to be considered as “as determined”]. One opinion, which is the settled opinion among physicists, holds that the clocks are “actually” going at different rates. Another opinion holds that it is merely a matter of how observers determine the clocks’ rates to be related, with the clocks in fact going at the same rate. The differences in these interpretations are resolved analytically. Five arguments are presented [excluding an inference from the first postulate]. The clocks are determined to have the same rates, i.e. there is no “time dilation” under SR conditions. The related opinion – that the clocks are going at the same rate, but are determined by observers to be going at different rates - is seen to be consistent. Experimental reports, which directly conclude that the clocks are going at different rates, are shown to be seriously flawed, or to not even comply with Einstein’s definition of SR

Vibration and stability of axially moving beam on multiple intermediate elastic supports with transfer matrix method

This study delves into the vibration characteristics and stability of an axially moving beam with multiple intermediate elastic supports. Initially, the motion equation of the beam is developed, setting the stage for an in-depth investigation of its free vibration characteristics through the transfer matrix method. This analysis covers the beam’s natural frequencies and critical velocity when moving at a constant velocity. Additionally, the dynamic behavior of the beam is investigated when it is subjected to constant axial movement and a concurrent traveling load. The multi-scale method is used to analyze the instability regions of the axially moving beam on multiple intermediate elastic supports as disturbance of the axial movement approaches subharmonic and sum-type combined resonances. The investigation further considers how alterations in the stiffness and configuration of the elastic supports influence the dynamic behavior and stability of the beam. Unique dynamic characteristics arise when the axially moving beam is supported by multiple elastic elements, contrasting with those observed in beams without such supports. An increase in support stiffness enhances the critical velocity at which the beam axially moves, potentially causing modal transformations of the structure prior to reaching this critical velocity, and diminishing the instability regions associated with sum-type combined resonances under disturbance velocities.

Structures of Laminar Lean Premixed H2/CH4/Air Polyhedral Flames: Effects of Flow Velocity, H2 Content and Equivalence Ratio

Polyhedral Bunsen flames, induced by hydrodynamic and thermo-diffusive instabilities, are characterized by periodic trough and cusp cellular structures along the conical flame front. In this study, the effects of flow velocity, hydrogen content, and equivalence ratio on the internal cellular structure of premixed fuel-lean hydrogen/methane/air polyhedral flames are experimentally investigated. A high-spatial-resolution one-dimensional Raman/Rayleigh scattering system is employed to measure the internal scalar structures of polyhedral flames in troughs and cusps. Planar laser-induced fluorescence of hydroxyl radicals and chemiluminescence imaging measurements are used to quantify the flame front morphology. In the experiments, stationary polyhedral flames with varying flow velocities from 1.65 to 2.50 m/s, hydrogen contents from 50 to 83%, and equivalence ratios from 0.53 to 0.64 are selected and measured. The results indicate that the positively curved troughs exhibit significantly higher hydrogen mole fractions and local equivalence ratios compared to the negatively curved cusps, due to the respective focusing/defocusing effect of trough/cusp structure on highly diffusive hydrogen. The hydrogen mole fraction and local equivalence ratio differences between troughs and cusps are first increased and then decreased with increasing measurement height from 5 to 13 mm, due to the three-dimensional effect of the flame front. With increasing flow velocity from 1.65 to 2.50 m/s, the hydrogen mole fraction and local equivalence ratio differences between troughs and cusps decrease, which is attributed to the overall decreasing curvatures in troughs and cusps due to the decreased residence time and increased velocity-induced strain. With increasing hydrogen content from 50 to 83%, the hydrogen mole fraction and local equivalence ratio differences between troughs and cusps are amplified, due to the enhanced effects of the flame front curvature and the differential diffusion of hydrogen. With increasing equivalence ratio from 0.53 to 0.64, a clear increasing trend in hydrogen mole fraction and equivalence ratio differences between troughs and cusps is observed at constant flow velocity condition, which is a trade-off result between increasing effective Lewis number and increasing curvatures in troughs and cusps.

Failure pattern of dispersive soil slopes under the action of rainfall conditions

Dispersive soil slopes are widely distributed in Northeast China. To analyze the failure caused by such slopes under various rainfall conditions, section K27 of the road-cutting slope of the Sui-Da Expressway in Heilongjiang Province, China, is considered an example. A 3D slope model was created using the similarity theory and visualized through close-range photogrammetry in a self-made model box. Six model tests were conducted under varying rainfall conditions to investigate the failure modes of dispersive soil slopes. Test results revealed that dispersive soil slopes are subject to two types of failure depending on the rainfall intensity. Slope erosion was divided into three stages by surface random roughness (SRR): initial erosion, constant velocity erosion, and accelerated erosion. Similarity theory suggests that the slope enters the accelerated erosion stage in the actual project when the SRR reaches around 31.95–46.5 cm. Furthermore, the reciprocal of the SRR change rate during the accelerated erosion stage exhibits a linear correlation with time. The time of the slope’s complete failure can be estimated when the reciprocal of the SRR change rate is 0 min/cm. The research findings are significant for comprehending the failure process of dispersive soil slopes.

Classical acceleration temperature from evaporated black hole remnants and accelerated electron-mirror radiation

We investigate the radiation from accelerating electrons with asymptotic constant velocity and their analog signatures as evaporating black holes with left-over remnants. We find high-speed electrons, while having a high temperature, correspond to low-temperature analog remnants.

Enhancement of swimmer diffusion through regular kicks: analytic mapping of a scale-independent parameter space

Depending on their mechanism of self-propulsion, active particles can exhibit time-dependent, often periodic, propulsion velocity. The precise propulsion velocity profile determines their mean square displacement and their effective diffusion coefficient at long times. Here, we demonstrate that any periodic propulsion profile results in a larger diffusion coefficient than the corresponding case with constant propulsion velocity. We investigate, in detail, periodic exponentially decaying velocity pulses, expected in propulsion mechanisms based on sudden absorption of finite amounts of energy. We show, both analytically and with numerical simulations, that in these cases the effective diffusion coefficient can be arbitrarily enhanced with respect to the case with constant velocity equal to the average speed. Our results may help interpret, in a new light observations on the diffusion enhancement of active particles.

Application of Gray Wolf Particle Filter Algorithm Based on Golden Section in Wireless Sensor Network Mobile Target Tracking

In order to address the issue of low tracking accuracy caused by particle depletion in the particle filter, a mobile target tracking algorithm tailored for wireless sensor networks (WSNs) is presented. This algorithm, based on the golden-section gray wolf particle filter (PF), represents a novel approach to target tracking. The algorithm’s originality lies in its ability to guide the particle swarm toward regions of higher weights, thereby striking a balance between global and local exploration capabilities. This not only alleviates issues related to sample depletion and local extrema but also enhances the diversity of the particle swarm, significantly improving tracking performance. To assess the effectiveness of the proposed algorithm, a series of simulation experiments were conducted, comparing it with the extended Kalman filter (EKF) and the standard PF algorithm. The experiments employed a constant velocity circular motion model (CM) for filtering and tracking. The root mean square error metric demonstrated a significant reduction in error of 57% and 37% in comparison to the extended Kalman filter (EKF) and the particle filter (PF), respectively. This serves to illustrate the superiority of our method in enhancing tracking accuracy.

Critical velocities of a three-layer composite tube incorporating the rotary inertia and material anisotropy

Critical velocities of a three-layer composite tube subjected to a uniform internal pressure moving at a constant velocity are obtained in closed-form expressions. A Love–Kirchhoff thin shell model including the rotary inertia and material anisotropy effects is used in the formulation. The composite tube is made of three perfectly bonded cylindrical layers of dissimilar materials, each of which can be orthotropic, transversely isotropic, cubic or isotropic. Closed-form formulas for the critical velocities are first derived for the general case by incorporating the effects of material anisotropy, rotary inertia and radial stress. Specific formulas are then obtained for composite tubes without the rotary inertia effect and/or the radial stress effect and with various types of material symmetry for each layer as special cases. It is also shown that the current model for three-layer tubes can be reduced to those for single- and two-layer tubes. To illustrate the newly derived formulas, an example is provided for a composite tube consisting of an isotropic inner layer, an orthotropic core, and an isotropic outer layer. All four critical velocities of the composite tube are computed using the new closed-form formulas. Three values of the lowest critical velocity of the three-layer composite tube are analytically obtained from three sets of the new formulas, which agree well with the value computationally determined by others.

Data-Driven Machine Fault Diagnosis of Multisensor Vibration Data Using Synchrosqueezed Transform and Time-Frequency Image Recognition with Convolutional Neural Network

Accurate vibration classification using inertial measurement unit (IMU) data is critical for various applications such as condition monitoring and fault diagnosis. This study proposes a novel convolutional neural network (CNN) based approach, the IMU6DoF-SST-CNN in six variants, for robust vibration classification. The method utilizes Fourier synchrosqueezed transform (FSST) and wavelet synchrosqueezed transform (WSST) for time-frequency analysis, effectively capturing the temporal and spectral characteristics of the vibration data. Additionally, was used the IMU6DoF-SST-CNN to explore three different fusion strategies for sensor data to combine information from the IMU’s multiple axes, allowing the CNN to learn from complementary information across various axes. The efficacy of the proposed method was validated using three datasets. The first dataset consisted of constant fan velocity data (three classes: idle, normal operation, and fault) at 200 Hz. The second dataset contained variable fan velocity data (also with three classes: normal operation, fault 1, and fault 2) at 2000 Hz. Finally, a third dataset of Case Western Reserve University (CWRU) comprised bearing fault data with thirteen classes, sampled at 12 kHz. The proposed method achieved a perfect validation accuracy for the investigated vibration classification task. While all variants of the method achieved high accuracy, a trade-off between training speed and image generation efficiency was observed. Furthermore, FSST demonstrated superior localization capabilities compared to traditional methods like continuous wavelet transform (CWT) and short-time Fourier transform (STFT), as confirmed by image representations and interpretability analysis. This improved localization allows the CNN to effectively capture transient features associated with faults, leading to more accurate vibration classification. Overall, this study presents a promising and efficient approach for vibration classification using IMU data with the proposed IMU6DoF-SST-CNN method. The best result was obtained for IMU6DoF-SST-CNN with FSST and sensor-type fusion.

Semi-Analytical Solution for a Single-Phase Thermal Conduction Problem of a Hollow Cylinder with a Growing or Receding Inner Radius

Abstract A semi-analytical solution for the thermal conduction of a single phase, homogeneous, circular, hollow-cylinder with a growing or receding inner radius at a constant rate under unit-loading was derived using conformal mapping, Laplace transformation, and a Zakian series representation of the inverse Laplace transform. All solutions allow for convection on the fixed outer radius. Predictions were compared to finite-element simulations with excellent agreement observed. Given the changing thickness, thermal transients could not reach true steady-state equilibrium, especially for faster growth or recession rates. Indeed, the temperature states become somewhat linear with respect to time, reflecting the constant velocity of growth or recession. In practice, the resulting solutions can be used to determine temperatures during machining, wear, erosion, corrosion, and/or additive manufacturing, especially for lower temperature solid-state methods such as cold-spray.

Stability patterns in plane porous Poiseuille flow with uniform vertical cross-flow: A dual approach

In this study, we examine the effects of a porous parameter and a uniform vertical cross-flow on the onset of instability in a plane Poiseuille flow (PPF) subjected to infinitesimal disturbances. The linearized Navier-Stokes (N–S) equations, which govern the stability of the fluid flow system, are addressed using the Chebyshev collocation method (CCM). Our approach includes both modal and non-modal analyses, each providing distinct insights into the system's behavior. The modal analysis involves a linear stability assessment using both non-normalized and normalized basic velocity approaches. Assuming a constant pressure gradient, the first approach aligns with the traditional Poiseuille flow framework, where a uniform pressure difference drives the flow. This simplifies calculations and aids in predicting flow characteristics. The second approach, which varies the pressure gradient to maintain a constant maximum streamwise velocity, offers a different perspective by focusing on a specific flow velocity profile through the porous medium. This variation in the pressure gradient allows us to explore changes in flow behavior and the system's responses under these conditions. This analysis includes examining the eigenspectrum, neutral stability curves, and determining critical triplets. On the non-modal front, we explore the intricacies of the non-normal Orr-Sommerfeld (O–S) operator. This involves studying the pseudospectrum and transient energy growth rate (G(t)) plots for optimal perturbations. Identification of regions of stability, potential instability, and instability is achieved using contour plots of maximum transient energy growth (Gmax). Interestingly, our results reveal that the porous parameter acts as a stabilizing agent, mitigating instability. In contrast, the uniform vertical cross-flow plays a dual role, contributing to both stabilization and destabilization of the system. Additionally, our study highlights the impact of examining basic velocity through both normalized and non-normalized approaches, leading to different stability predictions.

Optimal hybrid strategy in adaptive cruise control system for enhanced autonomous vehicle stability and safety

The adaptive cruise control system relies heavily on the vehicle's longitudinal control algorithm. Traditional longitudinal control algorithms typically depend on precise vehicle dynamic modeling or complex controller parameter calibrations. In the research, an optimal hybrid strategy for the control of basic adaptive cruise control system is proposed. The proposed hybrid strategy is the combination of both the Model Predictive Control (MPC) and Coati Optimization Algorithm (COA) and hence it is named as MPCCOA strategy. The fundamental goal of the proposed work is that a vehicle should maintain its current velocity when it approaches another vehicle that is driving at a steady velocity. The inputs for the proposed strategy are vehicle speed and acceleration. The inter-vehicle distance error, velocity error and acceleration are regulated based on the upper and lower limit of acceleration command with the help of proposed strategy. For accomplishing the required steadiness with the limitations in the given input and actual velocity with constant previous vehicle velocity, the proposed controller is utilized. The proposed controller is used to control the traction force of the host vehicle such that the vehicle speed follows the optimal speed trajectory as good as possible while ensuring constraints like distance to a preceding vehicle or speed limits. The performance of the proposed is implemented in the MATLAB platform and compared with existing approaches. The proposed technique demonstrates superior performance metrics, achieving the collision rate, rate of reaching maximum deceleration and ratio of exceeding comfortable deceleration or jerk are 1.27 %, 3.131 % and 9.052 %, respectively.