Search

Some basic characteristics of a classic hydraulic jump flow over a pebbled rough bed, as well as on a smooth bed as a reference, are presented in this experimental study. For the experiments, an inflow Froude number Fr1 from 1.54 to 4.94 and inflow Reynolds number Re1 from 42 000 to 230 000 were considered. Visual observations and measurements suggested some differences between the formation of a hydraulic jump on rough and smooth bed configurations, including different air entrainment processes, larger vortical structures in the roller length and stronger backward flow in the upper layer. Furthermore, the jump roller and aerated flow lengths were shorter on a pebbled rough bed than on a smooth bed, while the dimensionless advection velocity of large vortices was the same for both bed types. The instantaneous jump toe perimeter showed the largest variation at the largest Fr1 and was generally larger on rough bed than on smooth bed. Larger oscillations of the free-surface profile were observed on smooth bed, highlighting that roughness resulted in smaller free-surface oscillations, suggesting the higher rate of energy dissipation.

The dynamics of round and elliptical liquid jets in subsonic crossflow was studied using high-speed imaging technique. The experiments were performed at constant gaseous Weber number and liquid–gas momentum flux ratios of 6.45 and 17.87, respectively, with orifices of different aspect ratios (AR) having an equivalent diameter of 0.43 mm. All of the cases were carried out inside an open-loop subsonic wind tunnel with a test section of 100 mm × 100 mm × 750 mm. For each case, dynamic modes were generated directly from the snapshots using a variant of the Arnoldi method known as the dynamic mode decomposition (DMD). The DMD results indicate that elliptical liquid jets have more small-scaled patterns with higher frequencies compared with the round liquid jets. As the first attempt to investigate the dynamics of elliptical liquid jets in crossflow, this study captures the dominant spatiotemporal structures. We also found that the orifice AR can significantly alter the jet wavelengths. The data from this study contribute to understanding the behavior of elliptical liquid jets exposed to gas crossflow in an enhanced capillary breakup regime.

Although much is known about the environmental conditions necessary for supercell tornadogenesis, the near-ground vorticity dynamics during the tornadogenesis process itself are still somewhat poorly understood. For instance, seemingly contradicting mechanisms responsible for large near-ground vertical vorticity can be found in the literature. Broadly, these mechanisms can be sorted into two classes, one being based on upward tilting of mainly baroclinically produced horizontal vorticity in descending air (here called the downdraft mechanism), while in the other the horizontal vorticity vector is abruptly tilted upward practically at the surface by a strong updraft gradient (referred to as the in-and-up mechanism). In this study, full-physics supercell simulations and highly idealized simulations show that both mechanisms play important roles during tornadogenesis. Pretornadic vertical vorticity maxima are generated via the downdraft mechanism, while the dynamics of a fully developed vortex are dominated by the in-and-up mechanism. Consequently, a transition between the two mechanisms occurs during tornadogenesis. This transition is a result of axisymmetrization of the pretornadic vortex patch and intensification via vertical stretching. These processes facilitate the development of the corner flow, which enables production of vertical vorticity by upward tilting of horizontal vorticity practically at the surface, i.e., the in-and-up mechanism. The transition of mechanisms found here suggests that early stages of tornado formation rely on the downdraft mechanism, which is often limited to a small vertical component of baroclinically generated vorticity. Subsequently, a larger supply of horizontal vorticity (produced baroclinically or via surface drag, or even imported from the environment) may be utilized, which marks a considerable change in the vortex dynamics.

Dynamic variables of drop impact such as force, drag, pressure, and stress distributions are key to understanding a wide range of natural and industrial processes. While the study of drop impact kinematics has been in constant progress for decades thanks to high-speed photography and computational fluid dynamics, research on drop impact dynamics has only peaked in the last 10 years. Here, we review how recent coordinated efforts of experiments, simulations, and theories have led to new insights on drop impact dynamics. Particularly, we consider the temporal evolution of the impact force in the early- and late-impact regimes, as well as spatiotemporal features of the pressure and shear-stress distributions on solid surfaces. We also discuss other factors, including the presence of water layers, air cushioning, and nonspherical drop geometry, and briefly review granular impact cratering by liquid drops as an example demonstrating the distinct consequences of the stress distributions of drop impact.

Modern turbomachinery relies on accurate prediction of the flow and especially the state of turbulence to achieve the required level of performance. Transition, relaminarization, wake interactions,...

The dynamical characteristics of a gyrostat system with intermittent forcing are investigated, the main work and contributions are given as follows: (1) The gyrostat system with an intermittent forcing is studied, and its dynamical characteristics are investigated by the corresponding Lyapunov exponent spectrums and bifurcation diagrams with respect to the amplitude of intermittent forcing. The modified gyrostat system exists chaotic motion when the amplitude of intermittent forcing belongs to a certain interval, and it can be at a state of stable point or periodic motion by the design of amplitude. (2) The gyrostat system with multiple intermittent forcings is also investigated through the combination of Lyapunov exponent spectrums and bifurcation diagrams, and it behaves periodic motion or chaotic motion when the amplitude or forcing width is different. (3) By the selection of parameters in intermittent forcings, the modified gyrostat system is at a state of stable point, periodic motion or chaotic motion. Numerical simulations verify the feasibility and effectiveness of the modified gyrostat system.

The paper deals with the attitude dynamics of CubeSats with flexible stabilizing panels in free molecular flow taking into account the aerodynamic damping. In addition to the operating position, characterized by zero angle of attack, aerodynamically stabilized satellites may have intermediate equilibrium positions. The presence of unstable equilibrium positions and small perturbations such as the oscillations of the flexible panels is the cause chaos in the attitude motion. An analysis of the chaotic motion is carried out using Poincare sections and Lyapunov exponents. Numerical simulations show that the chaos intensity is sensitive to the geometric and environmental parameters of the system.

In this study, the dynamic response of the tension leg platform (TLP) under sea waves excitation is investigated. One establishes the analytical framework consisting of mathematical modeling of TLP taking into account the tendons and the delay. We analyse the stability and determine the physical characteristics of tendon system that allow the system to be always stable. Conditions on the space parameters of the system for which harmonic, subharmonic, superharmonic, combination resonants states are obtained using the multiple time scales method. The results show that the stability area of the system decreases when the delay increases and increases when the damping coefficient increases. Furthermore, increasing the time- delay only increases the value of the maximum amplitude response of the system. However, reasonable selection of the system parameters can effectively reduce the level of vibration of the system.

A rotary dust collector has been developed that works on the principle of a centrifugal separator. A feature of its design is the presence of a bypass recirculation channel of cleaned air with a flow regulator, two outlet pipes with flow uncoilers in the form of spiral channels. The calculation of the motion of dust particles with a density of 3000 kg/m3 and a diameter of 1 to 100 microns has been performed. Research has been carried out to improve the efficiency of the apparatus using a central compositional plan and to establish rational design and operating parameters of the mixer for recirculating and purified air.

A filament bundle is a type of yarn, which is composed of nearly parallel and highly oriented polymer monofilaments. Due to its nonlinearity both in material constitutive properties and structure, the filament bundle possesses nonlinear viscoelastic properties. It is important to study the dynamic behavior of the filament bundle accurately during its high-speed movement. Therefore, an accurate expression of the constitutive relation of the filament bundle is an essential prerequisite for its dynamic simulation and analysis. Continued the previous study in Part I: modeling filament bundle method, in this paper, an approach was proposed to identify the equivalent dynamic constitutive parameters of the filament bundle considering frequency-dependent characteristics. Firstly, the identification formulas of the dynamic elastic modulus and viscoelastic coefficients were derived based on the Kelvin model. Then, a testing method of the cross-sectional parameters of the filament bundle under a certain tension was proposed, and the testing device was developed to obtain the area of the filament bundle; The dynamic loading test of the bundle filament was conducted in a DMA Q800 dynamic mechanical tester. Thirdly, the equivalent dynamic elastic modulus and viscoelastic coefficients were obtained through the experimental test. Finally, an analytical method was proposed to verify the correctness of experimental results through simulation. The results show that the excitation frequency has a significant influence on the dynamic elastic modulus and viscoelastic coefficient, and the curves of the equivalent dynamic elastic modulus and viscoelastic coefficient present nonlinear variation characteristics.

The direct formation of drops at the edge of a spinning disc is of fundamental interest. We use high-speed imaging to report here on the process of release of drops from a perfectly wetted disc at ...

The effect of nozzle geometry on the dynamics and mixing of turbulent jets is experimentally investigated. The jets with a Reynolds number of 13,000 were issued from four different pipes with circular, elliptical, square and triangular cross sections. The velocity field was measured in the self-similar region of the jets using an acoustic Doppler velocimeter. Statistical parameters, such as the mean velocities, velocity variances, spreading rates, mass flow rates, and entrainment rates are presented. The results show that despite having approximately similar decay rates for the mean centerline velocities, the radial profiles of the axial mean velocity varied in jets with different nozzle cross sections and were widest for elliptical jets and narrowest for the triangular ones. On the other hand, velocity variances were greatest for the triangular jet when compared to the jets released from cross sections of other geometries. Furthermore, the spreading rate, mass flow rate, and entrainment rate were highest for the elliptical jet, and lowest for the triangular jet. From this it can be inferred that the elliptical jet has the highest mixing and dilution. The results of this study could help to improve the initial mixing of pollutants by optimizing the initial conditions. HIGHLIGHTS Radial velocity profiles were widest for the elliptical jets and narrowest for the triangular jets.; In the self-similar region, velocity variances were greatest for the triangular jets.; Elliptical jets have the highest entrainment and mixing.

Contact resonance atomic force microscopy, piezoresponse force microscopy, and electrochemical strain microscopy are atomic force microscopy modes in which the cantilever is held in contact with the sample at a constant average force while monitoring the cantilever motion under the influence of a small, superimposed vibrational signal. Though these modes depend on permanent contact, there is a lack of detailed analysis on how the cantilever motion evolves when this essential condition is violated. This is not an uncommon occurrence since higher operating amplitudes tend to yield better signal-to-noise ratio, so users may inadvertently reduce their experimental accuracy by inducing tip–sample detachment in an effort to improve their measurements. We shed light on this issue by deliberately pushing both our experimental equipment and numerical simulations to the point of tip–sample detachment to explore cantilever dynamics during a useful and observable threshold feature in the measured response. Numerical simulations of the analytical model allow for extended insight into cantilever dynamics such as full-length deflection and slope behavior, which can be challenging or unobtainable in a standard equipment configuration. With such tools, we are able to determine the cantilever motion during detachment and connect the qualitative and quantitative behavior to experimental features.

This work uses a recently developed MRI method to measure the solid fraction and velocity in three-dimensional (3D) hoppers quantitatively. We demonstrate that the measurements are quantitative by calculating the mass flow rate within the hopper using MRI and show good agreement with the mass flow rate measured gravimetrically. We study the velocity and solid fraction in hoppers with various angles and outlet sizes. We show that the solid fraction decreases smoothly from the bulk value above the outlet, indicating that the assumption of a “free-fall arch” used in some mass flow correlations is invalid. Furthermore, we show that the solid fraction, velocity and vertical evolution of the acceleration are all self-similar when normalised by the value at the centre of the outlet in a 3D hopper, in agreement with recent studies of 2D hoppers. Thus, these quantitative measurements enable evaluation of phenomenological models describing the flow rate from hoppers.

This paper presents the dynamics and adaptive control of an airfoil with structural stiffness and damping uncertainties, which is subjected to atmospheric gusts. The motion of the airfoil is modele...

A Free Energy Lattice Boltzmann Method has been developed to characterize dominant forces and regimes involved in the capillary rise imbibition process. The comparison of the capillary rise behavior at the initial stages, reveals significant differences between numerical and theoretical models. This is attributed to the simplifying assumptions, ignoring the entrance region, dynamic contact angle, and inertial term in the theoretical model. By relaxing these assumptions in numerical formulations, the proposed model prevails the theoretical model limitations and shows closer results to the experimental records. However, as the capillary tube size decreases, the capillary force overcomes the inertia and the theoretical and numerical curves converge. Comparing the numerical curves and the experimental results indicates that the dynamics of the capillary ascent predicted by the present model is similar to the dry tube data. It should be mentioned that the inertial regime, the viscous regime, and the gravity-viscous regime can be considered as the successive regimes involved. Further investigations reveal a transition regime at the beginning of the process, which appears due to singular pressure loss. Therefore, the capillary rise phenomenon develops during these regimes as h ~ t2, h ~ t, h ~ t1/2 and relaxing to a constant value, respectively. Finally, for better understanding of the phenomenon, sensitivity analysis on the dominant forces has been performed.

Purpose The purpose of this paper is to find the droplets impact on the airplane wing structure. Two kinds of characteristics of the droplet at different velocity and viscosity are assumed. The droplet is assumed to be spherical cubic form and it is injected from the convergent divergent nozzle with a passive control. Design/methodology/approach This paper presents the results of a numerical simulation of droplet impact on the horizontal surface. The effects of impact parameters are studied. The splash effect of the droplet also visualized. The results are presented in form of stress, strain, displacement magnitude of the droplet. Findings Crosswire is used as passive control. The behavior of the droplet impact is observed based on the kinetic energy and the gravitational forces. Originality/value The results predict that smooth particle hydrodynamic designed droplet not only depend on the equation of state of the droplet but also the injection velocity from the nozzle. It also determined that droplet velocity is depending on the viscosity of the fluid.

We present a subcritical fracture growth model, coupled with the elastic redistribution of the acting mechanical stress along rugous rupture fronts. We show the ability of this model to quantitatively reproduce the intermittent dynamics of cracks propagating along weak disordered interfaces. To this end, we assume that the fracture energy of such interfaces (in the sense of a critical energy release rate) follows a spatially correlated normal distribution. We compare various statistical features from the hence obtained fracture dynamics to that from cracks propagating in sintered polymethylmethacrylate (PMMA) interfaces. In previous works, it has been demonstrated that such approach could reproduce the mean advance of fractures and their local front velocity distribution. Here, we go further by showing that the proposed model also quantitatively accounts for the complex self-affine scaling morphology of crack fronts and their temporal evolution, for the spatial and temporal correlations of the local velocity fields and for the avalanches size distribution of the intermittent growth dynamics. We thus provide new evidence that Arrhenius-like subcritical growth laws are particularly suitable for the description of creeping cracks., Comment: 22 pages, 14 figures, 5 appendices

The dynamics of water droplets on fiber layers are investigated by fiber-scale simulation using volume of fluid (VOF) method. The effects of fiber spaces, contact angles at fibers and numbers of layers on droplet dynamics are investigated. Force analysis for the pinned and moving droplets on fiber layers shows that the resistant forces from the wetted fibers at the edge positions rather than middle positions are the dominant force to control the droplet mobility. Force analysis for droplets on the dual-layers fiber layer are also conducted. The results show that the second layer contributes little to hinder the droplet directly due to the insignificant resistant force they provided. However, the second fiber layer enhances the total resistant force from the first layer. Furthermore a simplified model is used to compare with the fiber model. The results indicate that the simplified model can also be used to predict the droplet mobility once the contact angle is given.

Accumulation of associated petroleum gas in the annulus is one of the negative factors that impede the intensification of mechanized oil production. An increase in annular gas pressure causes growth of bottomhole pressure, a decrease in back pressure to the formation and the inflow of formation fluid. In addition, accumulation of gas in the annulus leads to displacement and a decrease in the liquid level above the submersible pump. Insufficient level of the pump submersion (rod or electric submersible) causes a number of complications in the operation of mechanized production units associated with overheating of the elements in pumping units. Therefore, the development of technologies for optimizing the gas pressure in the annulus is relevant. Method for calculating the intensity of gas pressure increase in the annulus of production wells operated by submersible pumps has been developed. Analytical dependence for calculating the time interval of gas accumulation in the annulus, during which the dynamic level decreases to the pump intake, is obtained. This value can be used to estimate the frequency of gas withdrawal from the annulus using compressors. It has been found that the rate of increase in annular gas pressure in time increases non-linearly with a rise in the gas-oil ratio and a decrease in water cut, and also linearly increases with a rise in liquid flow rate. Influence of the operating (gas-oil ratio) and technological (value of the gas pressure maintained in the annulus) factors on the flow rate of the suspended reciprocating compressor driven by the beam engine, designed for forced withdrawal and redirection of the annular gas into the flow line of the well is analyzed.

The computational study of transient immiscible and incompressible two-phase flows is one of the most common and desirable way for investigation of engineering phenomena and physics science. In the previous studies, generally bubbles current have been used as an active method for increasing heat transfer, however, due to existence of hydraulic boundary layers, the bubbles were not able to cross over this layer to thinning the thermal boundary layer and consequently the efficiency of this method was not very considerable. In this study, by considering potential of magnetic field, the effect of co-applying of external non uniform magnetic field and magnetic bubbles in enhancing the heat transfer efficiency in a 3-D tube has been investigated. The computational model consisted of the Navier–Stokes equation for liquid phase and VOF model for interface tracking are carried out by OpenFOAM. The external magnetic field has been considered non-uniform and time dependent. The results predicted that magnetic bubbles and external magnetic field due to their effect on thermal boundary layer increased significantly heat transfer and Nusselt number. Furthermore, results indicated magnetic bubbles can act as an active torbulators in the flow field and can be applied for increasing recirculation and secondary flow in the flow field. The average temperature and magnetic field over times for different cases have been discussed in the results.

The peridynamic model of a solid is suitable for studying the dynamics of defects in materials. We use the bond-based peridynamic theory to propose a one-dimensional nonlocal continuum model to study a defect in equilibrium and in steady propagation. As the defect propagates, the material particles undergo a transition between two states. By using the Wiener–Hopf method, an explicit analytical solution of the problem is obtained. The relation between the applied force and the propagation speed of the defect is determined; our results show that the defect does not propagate if the applied force is less than a critical value, whereas propagation occurs when the force exceeds that value. The energy properties of the system are investigated.

Direct numerical simulations of a turbulent channel with liquid infused surfaces made of longitudinal micro-ridges have been performed to study the effect of texture geometry and interface deformat...

In the present work, a method for the analysis of short time intervals in ball bearings is proposed. We study the effect of the internal clearance on the dynamics of ball bearings using recurrence plots and the recurrence quantification approach. In the proposed method, we focused on the analysis of dynamic states generated from the 2-DOF mathematical model, to which a function changing the damping coefficient in the clearance domain was added. Chosen recurrence methods showed the specific dynamic responses by different values of the radial clearance. The effect of self-consistency concerning the damping effect and vibration development is confirmed. The proposed method can be useful for the prediction of variable radial clearance in time by analysis of the acceleration response of ball bearing during its operation.

The dynamics of a constrained three-vortex system, a pair of point vortices of arbitrary non-zero circulations in the velocity field of a fixed point vortex, is investigated. The underlying dynamical system is simplified using a coordinate transformation and categorized into two cases based on the zero and non-zero values of the constant of angular impulse. For each case, dynamical features of the vortex motion are studied analytically in the transformed plane to completely classify the vortex motions and understand the boundedness and periodicity of the inter-vortex distances. The theoretical predictions are also verified numerically and illustrated for various sets of initial conditions and circulations.

The author has earlier considered the dynamics of an isolated thermic arising from an instant heat release. The rigorous analytical, as well as simplified, solutions describing the dynamics of the uplifting of a spherical thermic have been obtained. Such a thermic appears during a short-term release of heat, e.g., during an explosion. The uplifting of a meteoroid thermic has also been studied. The theory of the thermic has found applications in the magnetic precursors of earthquakes. At the same time, the heat can be supplied during many hours or even days when big forest fires occur, peat fires burn, volcano eruptions occur for a long time, and during the release of heat before earthquakes. The dynamics of the uplifting of a thermal under these circumstances is considerably different from an instantaneous energy release. Employing the cylindrical model of a thermic, the dynamics of the thermic has been studied in the case of the continuous supply of heat. Within the model, the analytical solutions to the set of equations governing the temporal dependences of the velocity of a parcel of the heated air and the position of the upper bound of the thermic, as well as the excess temperature in the heated parcel have been obtained. The upper thermal boundary speed and location has been shown to increase with uplifting, while the excess temperature to gradually decrease. The numerical estimation has been performed for characteristic situations. The ecological consequences of large-scale fires, as well as the mechanisms for generating gravity waves by the thermals, are discussed. The physics-based mechanisms for generating acoustic wide-band emissions by the thermals have been analyzed; the wave periods have been estimated to be 1–103 s. The energy of acoustic emissions from a big fire has been estimated to be approximately 1014 J. At the same time, the energy of acoustic emissions from all fires that occurred in the Russian Federation in 2020 amounts to 7∙1016 J, while in Ukraine it is three orders of magnitude lower.

This paper is concerned with an oscillator attached to a crank-slider mechanism, where the driving torque is not assumed as constant, but as dependent on its angular velocity. Moreover, it is affected by the motion of the oscillator, i.e. it represents the so-called non-ideal excitation. The displacement of the oscillator is limited by a barrier, and the impact can occur. Consequently, the system response can be both impact and non-impact, which makes the influence on the driving torque unknown, and important to predict for practical applications in hand-held percussion machines, pile driving machines, cutting and grinding machines, etc. This work provides the analytical analyses of the regular behaviour of such vibro-impact system with non-ideal excitation system for the first time. New insight into its dynamics is gained, in terms of the appearance of impact and non-impact solutions, values of the impact velocity and their dependence on other system parameters. Amplitude–frequency diagrams are also obtained, showing the regions of non-impact, impact behaviour, non-existence of period-one steady-state response, stable and unstable solutions and oblique jumps in the amplitude and frequency. The stability issue is also investigated, and novel results are obtained with respect to the impact velocity and the associated steady-state response. The analytical solutions are verified numerically, confirming their validity and accuracy.

This paper studies the flame dynamics near lean blowout (LBO) conditions in a stratified swirl burner. The novel BASIS burner is used and fueled with premixed methane/air mixture at atmospheric conditions. In the experiments, only the pilot flame works with four different equivalent ratios. It is found that as the flame changes from stable combustion to near LBO, the flame macrostructure changes from V-shape to M-shape. Meanwhile, a characteristic frequency of 405 Hz is found in the spectrum of heat release signal. The closer to LBO, the higher amplitude is found at the frequency peak. Post-processing of flame images illustrates that the 405 Hz comes from the circumferential movement of the flame. Large-eddy simulations (LESs) via OpenFOAM reproduce the flame dynamics near LBO, which agrees with the experimental results. LESs provide more insights into the flow fields, showing that the characteristic frequency of 405 Hz comes from the flame-vortex interaction. This study reveals the mechanism of flame and vortex interactions in a stratified swirl burner near LBO. The heat release signal is also found can be used as a candidate precursor for LBO.

In this paper, the dynamics of the flexible riser are investigated based on the absolute nodal coordinate formulation (ANCF). The stiffness, generalized elastic force, external load, and mass matrixes of the element are deduced based on the principle of energy conversion and assembled with the finite element method. The motion equation of the flexible riser is established. The influence of the environmental load conditions on the flexible riser model is studied in the MATLAB environment. Moreover, the accuracy and reliability of the programs are verified for a beam model with theoretical solutions. Finally, the static and dynamic characteristics of the flexible riser are analyzed, systematically adopting the ANCF method, which in turn proves the effectiveness and feasibility of the ANCF. Therefore, the proposed method is a powerful scheme for investigating the dynamics of flexible structures with large deformation in ocean engineering.

Parameterization of theeffective properties as input in hydrogeological models for simulating water flow is a time consuming and costly process, and it is characterized by high uncertainty because of the spatial variability of soil properties. Integrating visible-near-infrared spectroscopy (vis-NIRS) models and a developed pedotransfer function, a hydrogeological tool was suggested by Varvaris et al. in 2019 for estimating the hydraulic properties used in an equilibrium approach. In the current study, the proposed concept was further expanded for assisting on a rapid and inexpensive parameterization of effective parameters in nonequilibrium models. In our approach, the soil-water retention curves for the wet and hyper-dry ends were predicted using existing vis-NIRS calibration models for obtaining the parameters for the Campbell retention model and the Campbell and Shiozawa model, respectively. The HYDRUS-2D software package was used to simulate tile drainage discharge in a loamy structured field using as initial input hydraulic parameters the output from the suggested concept. The estimated parameters were validated based on measured hydraulic properties in the laboratory. Two-dimensional models incorporating nonequilibrium flow were used to evaluate the ability of each approach to predict the tile drainage discharge: a single-porosity with modified van Genuchten function, a dual-porosity model, and a dual-permeability model. All approaches gave a fairly good fit to the hydrograph features for both calibration and validation datasets with dual-porosity to present the highest predictive ability. Finally, the suggested initial parameterization concept proved its potential to be used as an alternative for covering the absence of measured data of soil hydraulic properties.

Increasingly agile manoeuvre is an advantage in the flight of aircraft, missiles and aerial vehicles, but the principles of accelerating aerodynamics in the transonic regime are only now being fully investigated. This study contributes to the understanding of shock and separation effects on drag during axial acceleration, using a simple geometric configuration. Unsteady shock wave behavior was numerically investigated for an axisymmetric cone-cylinder using a commercial solver and the Moving Reference Frame acceleration technique. This acceleration technique was validated using unsteady numerical and experimental methods. The cone-cylinder was accelerated from Mach number 0.6 to Mach number 1.2 at 100g constant and deceleration was from Mach number 1.2 until Mach number 0.6 at –100g constant. Three cone angles were tested for the cone-cylinder with uniform cylinder diameter. Acceleration through the transonic Mach regime was characterised by a delayed and gradual shock wave development when compared to steady state, demonstrating a clear flow history effect. Deceleration through the transonic Mach regime was characterised by shock wave propagation from the base to the nose. New flow structures appeared during deceleration that do not have counterparts in the steady state, including shock interactions and propagating expansion-compression features. Gross changes in the unsteady drag coefficient curves for each cone-angle are explained with reference to unsteady shock wave behaviour for accelerating and decelerating motion.

Field observations suggest that the Lane-Changing (LC) processes are often interrupted by the surrounding vehicles. Understanding these intermediate interruptions and evasive behavior during an LC ...

Pulsations are generated by the generator at the values of the initial pressure applied to the well. Depending on these pulsations, the well pressure and the resulting oil production also change. In this issue, changes in well pressure and oil production are studied.

Aims/ Objectives: This paper examines the dynamics of multiple slip together with thermal radiation effects on the transport of a magnetohydrodynamic Casson nanofluid passing a nonlinear porous stretchable sheet in the existence of viscous dissipation and chemical reaction.Study Design: Cross-sectional study. Methodology: The outlining equations modeling the transport phenomenon are simplified into nonlinear ordinary differential equations via the approach of similarity transformations and subsequently analyzed numerically by shooting techniques alongside Runge-Kutta Fehlberg scheme.Results: The outcomes of decisive parameters affecting the flow, heat, and nanoparticle concentration are graphically deliberated. From the investigation, it is revealed that Brownian motion, viscous dissipation, and thermophoresis parameters augment the thermal boundary layer and propel an upward growth in the temperature profile. Furthermore, the slip factor decelerates the flow and heat dissipation while the fluid movement drags in the existence of the magnetic field. Conclusion: The results obtained in this study compared favourably well with existing related studies in literature under limiting scenarios.

The electromagnetic fields and processes of current flow in the plasma channel of the plasma opening switch were considered in the electron hydrodynamics approximation. Taking into account the nature and features of the current flow through the plasma filled region of plasma opening switch allowed to obtain the structure of the current channel and its dynamics along the plasma. The current flow is a wave process. When this wave reaches the boundary of plasma it seems to be the break of current at this moment. The criterion of this break is obtained.

The forces that enter the mounted tire spindle of laboratory-type tire dynamics test machines include the following items: (1) direct tire-generated forces, tire nonuniformities, and tread pattern vibrations; (2) direct tire-transmitted rough road surface or cleat impact forces; (3) direct machine resonance-amplified versions of items 1 and 2; (4) machine frame backpath-transmitted versions of items 1–3; (5) dynamic loadcell crosstalk; (6) external noise from foundation vibrations; and (7) adjacent load station vibrations traveling through the machine frame. Although items 1 and 2 are sought in spindle vibration measurements, items 3–7 are also included in the mix and confound the measurement, confusing the analyst into thinking that machine properties are tire properties. Not only do items 3–6 not exist in vehicle operation but also comparison of results from one test machine to another can be an exercise in comparing machine to machine, not tire to tire. Tire dynamics measurements should simulate tires in roadway operation, not create a whole new set of problems that do not exist in vehicles. Elimination of item 7 paved the way to developing a tire failure warning system that operates on tire endurance test machines and can be adapted for operation on passenger vehicles to warn the driver of tire trouble. This article develops the theory of stray force measurement, describes a method for eliminating stray forces from experimental tire dynamics data, and provides experimental verification of the effectiveness of these methods.

The interaction of a sandwich plate with a damped cylindrical wave in the ground has been investigated. A sandwich plate is considered as a model of a barrier in the ground, described by a system of equations by V. N. Paimushin, placed in the ground dividing it into two parts. The plane problem formulation is considered. The boundary conditions correspond to the hinge attachment of the barrier, and the initial conditions are zero. A cylindrical damped wave is considered as an external influence. To describe the ground movement, the equations of the elasticity theory, the Cauchy relations and the physical principle, or equivalent displacements in potentials and the Lame equations are used. The problem is solved in a related formulation, where the movement of the plate and its surrounding media is considered together. All components of the equations of motion of the plate and media are decomposed into trigonometric series and the Laplace transform is applied to them. As the conditions for the contact of the plate and the ground, the equality of normal displacements at the boundary of the medium and the plate is assumed. It is also assumed that the pressure amplitudes and normal stresses coincide. After determining the constants from the contact conditions, the displacement values and the values of normal and tangential stresses are found, after which their originals are found.

Rapid rupture fronts—akin to earthquakes—mediate the transition to frictional motion. Once formed, their singular form, dynamics and arrest are well described by fracture mechanics. Ruptures, however, first need to be created within initially rough frictional interfaces. Hence, static friction coefficients are not well defined, with frictional ruptures nucleating over a wide range of applied forces. A critical open question is, therefore, how the nucleation of rupture fronts actually takes place. Here we experimentally show that rupture fronts are preceded by slow nucleation fronts—self-similar entities not described by fracture mechanics. They emerge from initially rough frictional interfaces at a well-defined stress threshold, evolve at the characteristic velocity and timescales governed by stress levels, and propagate within a frictional interface to form the initial rupture from which fracture mechanics take over. These results are of fundamental importance to questions ranging from earthquake nucleation and prediction to processes governing material failure. Frictional motion between two surfaces in contact starts with the formation of nucleating rupture fronts. It is now shown that these emerge from nucleation fronts, which develop from a certain stress level onwards and with a characteristic velocity.