Stationary Regime Research Articles

Dynamic behavior of the nonlinear planetary gear model in nonstationary conditions

The nonlinear effects in gearboxes are a key concern to describe accurately their dynamic behavior. This task is difficult for complex gear systems such as planetary gearboxes. The main aim of this work is to provide responses to overcome this difficulty especially in nonstationary operating regimes by investigating a back-to-back planetary gearbox in steady conditions and in the run-up regime. The nonlinear Hertzian contact of teeth pair is modeled in stationary and nonstationary run-up regime. Then it is incorporated in to a torsional model of the planetary gearbox through different mesh stiffness functions. In addition, motor torque and external load variation are taken into account. The nonlinear equations of motion of the back-to-back planetary gearbox are computed through the Newmark- β algorithm combined with the method of Newton–Raphson. An experimental validation of the proposed numerical model is done through a test bench for both stationary and run-up regimes. The vibration characteristics are extracted and correlated to speed and torque. Time–frequency analysis is implemented to characterize the transient regime during the run-up.

Model of water-salt balance in the new irrigation territory of the karshin steppe

The article presents a methodology for the development of a model of salt transfer in the conditions of a stationary water-salt regime of soil-grounds, caused by furrow irrigation of cotton.

Formulation of a phase space exponential operator for the Wigner transport equation accounting for the spatial variation of the effective mass

A novel numerical approximation technique for the Wigner transport equation including the spatial variation of the effective mass based on the formulation of an exponential operator within the phase space is derived. In addition, a different perspective for the discretization of the phase space is provided, which finally allows flexible discretization patterns. The formalism is presented by means of a simply structured resonant tunneling diode in the stationary and transient regime utilizing a conduction band Hamilton operator. In order to account for quantum effects within heterostructure devices adequately, the corresponding spatial variation of the effective mass is considered explicitly, which is mostly disregarded in conventional methods. The results are validated by a comparison with the results obtained from the nonequilibrium Green’s function approach within the stationary regime assuming the flatband case. Additionally, the proposed approach is utilized to perform a transient analysis of the resonant tunneling diode including the self-consistent Hartree–Fock potential.

Income Inequality and Persistence Changes

This paper carries out a time series analysis of the Gini coefficient for disposable income in a sample that includes both advanced and emerging economies. Our results show that, in most countries, inequality has alternated between stationary and nonstationary regimes during the period 1960–2017. These changes coincide with the implementation of structural reforms and with periods of economic and, especially, financial distress. Our findings also suggest that the persistence of income inequality seems to be related to tax progressivity, income for top earners, and working conditions.

Influence of surface radiation on the transition to unsteadiness for a natural convection flow in a differentially heated cavity

The influence of surface radiation on the transition to the unsteady state in natural convection is studied numerically. The configuration of the differentially heated square cavity with adiabatic horizontal walls is chosen to generate an internal natural convection flow. It is known that radiative transfers reduce the temperature difference between the adiabatic walls, which consequently reduces the thermal stratification of the central zone and increases the velocity flow. Many studies have focused on the stationary regime, but few of them have investigated the transition to unsteady flow. For this purpose, the effect of the wall emissivity on the critical Rayleigh number and the associated critical frequency was studied for a given cavity length. The cavity length and mean temperature of isothermal walls are set for the whole study. The results show that all these values are between the values obtained without radiation and those obtained for perfectly conducting horizontal walls. The critical Rayleigh number decreases with emissivity while the associated frequency increases. Moreover, the symmetry of fluctuating properties of the flow is changed when the radiation is taken into account.

Study of VUV Emission From Xe–Ne Microhollow Cathode Discharge in the Self-Pulsing Regime

This article by employing a zero-dimensional model investigates vacuum ultraviolet (VUV) emission from a xenon–neon microdischarge. The effects of the pressure, the input voltage, and the neon fraction are carefully studied. For specific input voltages, the microdischarge operates in an oscillatory regime which is called the self-pulsing regime. The self-pulsing frequency is mainly affected by the input voltage as well as the pressure. Increasing the input voltage enhances the average densities but has no effects on the peak densities. However, the pressure has significant effects on both densities. The main peaks of the VUV emission spectrum are seen at $\lambda =173$ nm and $\lambda =147$ nm which are attributed to xenon triplet-excited dimers and resonance-level excited atoms, respectively. Adding the neon gas enhances the emission at 147 nm through reducing the power loss in elastic collisions, but attenuates the emission at 173 nm. The results also show that steady-state densities of the major VUV emitters in the stationary regime are higher than the time average densities in the self-pulsing regime. Although, the lower power consumption of the self-pulsing regime has a more decisive effect such that the VUV emission efficiency in the self-pulsing regime is greater than that of the stationary regime.

Simulation study of excimer VUV emission from xenon microhollow cathode discharge in the self-pulsing regime

A volume-averaged model is employed to study the dynamics of a microhollow cathode discharge in xenon operating in the self-pulsing regime. The numerical results revealed that the discharge voltage initially increases during the abnormal mode when the discharge current is quite low. Then, the discharge is transferred to a normal mode in which the current shows a steep growth to extremely high values. The results also indicated that the self-pulsing frequency increases with an increase in the input voltage at constant pressure. However, an increase in pressure at a constant input voltage leads to a reduced self-pulsing frequency. The strongest vacuum ultraviolet emission is attributed to xenon triplet excimers at a wavelength of 173 nm. An increase in the input voltage enhances the average densities of the xenon excimers, but has almost no effect on the maximum densities. Compared to the input voltage, an increase of the pressure has a much stronger effect on both the maximum and average densities, such that the maximum density of the triplet excimer is increased from 1.48×1017 m−3 at P = 30 Torr to 2×1021 m−3 at P = 250 Torr. A comparison between the self-pulsing and stationary regimes shows that the maximum densities of the excimers at the self-pulsing regime are an order of magnitude higher than those of the stationary regime. Furthermore, the average densities of the excimers in the self-pulsing regime are higher than those of the stationary regime at higher input voltages. However, the reverse is true for lower voltages.

Stationary regime for a queue of the type M|M|c|c + m with constant retrial rate

Stationary regime for a queue of the type M|M|c|c + m with constant retrial rate

Simulation modelling of cold rolled metal strip by asymmetric technology

In the article provided the results of studies the optimization of energy-saving technologies in mechanical engineering using modern methods of simulation modeling is becoming an urgent area for the informatization of engineering production on the process of cold asymmetric rolling of metal sheets is accompanied by an inhomogeneous stress-strain state.The research considers the noncanonical areas of strain, an approach is proposed for determining the optimal technological parameters and studying the stress state of the cold rolling process using asymmetric rolling technology in the active zone of elastoplastic strains based on simulation using the application software LS-DYNA by LS-PrePost (R) version V4.6.1. To optimize energy-saving for rolling technologies, considered a stationary regime of symmetrical rolling, the kinetic energy does not change over time, and the potential energy in the active zone of elastic-plastic strains tends to increase. For the case of asymmetric rolling, a high level of kinetic energy is observed, and there is a fluctuation over time, explained by different coverage of asymmetric rollers in the zone of active elastic-plastic strains, as a result of which the stationary nature of the metal sheet rolling mode is violated.

Design of spaser-like nanoparticle systems for nonclassical optical states generation

The quantum features of photon generation in multiparticle spaser systems consisting of metal nanoparticles and semiconductor quantum dots are investigated. We found the conditions for stationary regime of single-photon generation in spaser systems. In particular, in order to achieve a balance between gain and loss in the system, we determined the chemical and geometric characteristics of nanoparticles and quantum dots by using the optimization algorithm. The strong dipole-dipole interaction between nanoparticles in the spaser system is studied. We show that these conditions can lead to the violation of Cauchy-Schwartz inequality and appearance of nonclassical correlations in the system. The generation of entangled photons in a three-particle spaser system with nonlinear plasmon-exciton interaction is theoretically demonstrated. The introduction of an additional degree of freedom in the form of an external magnetic field leads to a change in the energy levels of quantum dots and provides the possibility to control the quantum properties of generated photons. We proposed the model of an effective subwavelength source of entangled photons controlled by an external magnetic field.

Slow oscillations in systems with inertial vibration exciters

The problem of the occurrence of semi-slow speed oscillations of an unbalanced rotor during its passage through the resonance zone has been solved using the method of direct separation of motions. It has been proved that when a stationary regime is established, semi-slow damping oscillations of the rotor speed arise in the region of the Sommerfeld effect, they are the result of the superimposement of free accompanying oscillations with a relatively low frequency on forced fast oscillations. In this respect, the initial amplitudes of such oscillations are quite large, and oscillations damping is relatively slow.

Responses of a two degrees-of-freedom system with uncertain parameters in the vicinity of resonance 1:1

We analyze the dynamics of a nonlinear mechanical system under the influence of an external harmonic force. The system consists of a linear oscillator (primary mass) and attached nonlinear dynamic absorber. It is supposed that the frequency of the external force is close to the natural frequency of the main mass. Assuming that the parameters of the system are uncertain, the stability conditions of the stationary regimes of the averaged equations are obtained analytically; these regimes correspond to the quasi-periodic motions of the original input system. An analytical approach to the problem of selecting the parameters of a dynamic absorber is proposed in order to reduce the amplitude of oscillations of the main system. The results obtained are compared with the results of the numerical integration of the equations of the motion with different initial conditions and parameter values.

Multiscale proper orthogonal decomposition (mPOD) of TR-PIV data—a case study on stationary and transient cylinder wake flows

Data-driven decompositions of particle image velocimetry (PIV) measurements are widely used for a variety of purposes, including the detection of coherent features (e.g. vortical structures), filtering operations (e.g. outlier removal or random noise mitigation), data reduction and compression. This work presents the application of a novel decomposition method, referred to as multiscale proper orthogonal decomposition (mPOD, Mendez et al 2019) to time-resolved PIV (TR-PIV) measurement. This method combines multiresolution analysis and standard proper orthogonal decomposition (POD) to achieve a compromise between decomposition convergence and spectral purity of the resulting modes. The selected test case is the flow past a cylinder in both stationary and transient conditions, producing a frequency-varying Karman vortex street. The results of the mPOD are compared to the standard POD, the discrete Fourier transform and the dynamic mode decomposition. The mPOD is evaluated in terms of decomposition convergence and time-frequency localization of its modes. The multiscale modal analysis allows for revealing beat phenomena in the stationary cylinder wake, due to the three-dimensional nature of the flow, and to correctly identify the transition from various stationary regimes in the transient test case.

On the substantial anomalous absorption regime at the extraordinary wave decay into trapped and propagating upper hybrid waves

We analyze the strong nonlinear regime of low power-threshold parametric decay instability (PDI) of a pump extraordinary wave. The PDI leads to the excitation of two upper hybrid (UH) waves only one of which is trapped in the vicinity of the local maximum of a non-monotonic density profile. The pump depletion and the multi-step secondary decays of the localized daughter UH wave are treated as the mechanisms leading to the instability saturation. It is shown that in the case of the even-step secondary cascade decay of trapped primary UH wave the pump wave depletion is responsible for the transition of a nonlinear phenomenon into a stationary regime, and the strong anomalous absorption is possible.

Adaptive estimation of the stationary density of a stochastic differential equation driven by a fractional Brownian motion

We build and study a data-driven procedure for the estimation of the stationary density f of an additive fractional SDE. To this end, we also prove some new concentrations bounds for discrete observations of such dynamics in stationary regime.

Stationary high-performance grassy ELM regime in EAST

A stationary, high-performance grassy edge-localized mode (ELM) regime has been successfully accessed on the EAST tokamak since the 2016 campaign. increase via increase of heating power or q95 are both found to facilitate a higher grassy ELM frequency. Edge measurement of absolute extreme ultraviolet radiation indicates that the affected area by grassy ELMs is localized at the pedestal region and the perturbations there induced by grassy ELMs can be 90% smaller than that by type-I ELMs. Parameter scan demonstrates that the grassy ELM regime has good density control capacity, and the access to the grassy ELM regime is independent of the toroidal field direction and low-hybrid-wave power. Statistical analysis indicates that the grassy ELM regime is highly reproducible in a wide parameter space when edge safety factor and poloidal beta are simultaneously high enough ( and ). High triangularity contributes to the increase of grassy ELM frequency while the requirement on high internal inductance in the JET tokamak for grassy ELMs cannot be found in EAST. The operational space in pedestal top collisionality for the EAST grassy ELMs is in the range of . The exploration towards lower is mainly limited by the available heating power. Evolution of a coherent mode at pedestal top suggests that grassy ELMs most likely generate in the steep-gradient region of the pedestal, rather than on the pedestal top or near the separatrix. The grassy ELM regime offers a highly promising approach for further exploration of long-pulse high-performance H-mode operations in EAST, with potential application to the Chinese Fusion Engineering Test Reactor (CFETR) as the baseline scenario and a primary solution for the control of ELMs.

Study of Shock Initiation of an NTO‐Based Melt‐Cast Insensitive Composition

AbstractThe paper presents research on the shock initiation of a melt‐cast insensitive explosive composition containing 3‐nitro‐1,2,4‐triazole‐5‐one (NTO), 2,4,6‐trinitrotoluene (TNT), wax, and aluminum powder. The composition was elaborated for steel tubes and initiated with the use of boosters of various configurations. Research systems were made to measure the velocity of detonation wave and to determine the type of response of the composition to shock initiation. A relatively long shock to detonation distances after initiation using the boosters with a steel buffer were found. A method of initiating the composition was indicated to guarantees an immediate achievement of the stationary detonation regime. An attempt was also made to explain the observed processes theoretically. The results obtained can be used in the design of munition filled with melt‐cast insensitive explosives.

Direct evaluation of attachment and detachment rate factors of atoms in crystallizing supercooled liquids.

Kinetic rate factors of crystallization have a direct effect on formation and growth of an ordered solid phase in supercooled liquids and glasses. Using the crystallizing Lennard-Jones liquid as an example, in the present work, we perform a direct quantitative estimation of values of the key crystallization kinetic rate factors-the rate g+ of particle attachments to a crystalline nucleus and the rate g- of particle detachments from a nucleus. We propose a numerical approach, according to which a statistical treatment of the results of molecular dynamics simulations was performed without using any model functions and/or fitting parameters. This approach allows one to accurately estimate the critical nucleus size nc. We find that for the growing nuclei, whose sizes are larger than the critical size nc, the dependence of these kinetic rate factors on the nucleus size n follows a power law. In the case of the subnucleation regime, when the nuclei are smaller than nc, the n-dependence of the quantity g+ is strongly determined by the inherent microscopic properties of a system, and this dependence cannot be described in the framework of any universal law (for example, a power law). It has been established that the dependence of the growth rate of a crystalline nucleus on its size goes into the stationary regime at the size n > 3nc particles.

Simulations of stellar winds from X-ray bursts

Context. Photospheric radius expansion during X-ray bursts can be used to measure neutron star radii and help constrain the equation of state of neutron star matter. Understanding the stellar wind dynamics is important for interpreting observations, and therefore stellar wind models, though studied in past decades, have regained interest and need to be revisited with updated data and methods. Aims. Here, we study the radiative wind model in the context of X-ray bursts with modern techniques and physics input. We focus on characterization of the solutions and the study of observable magnitudes as a function of free model parameters. Methods. We implemented a spherically symmetric nonrelativistic wind model in a stationary regime, with updated opacity tables and modern numerical techniques. Total mass and energy outflows (Ṁ, Ė) were treated as free parameters. Results. A high-resolution parameter-space exploration was performed to allow better characterization of observable magnitudes. High correlation was found between different photospheric magnitudes and free parameters. For instance, the photospheric ratio of gravitational energy outflow to radiative luminosity is directly proportional to the photospheric wind velocity. Conclusions. The correlations found here could help determine the physical conditions of the inner layers, where nuclear reactions take place, by means of observable photospheric values. Further studies are needed to determine the range of physical conditions in which the correlations are valid.

Prey refuge and morphological defense mechanisms as nonlinear triggers in an intraguild predation food web

Intraguild predation (IGP) is a type of interaction in which a top predator simultaneously competes and predates an intermediate prey that shares a third prey species with the top predator. While common in nature, most theoretical population dynamics models proposed in the literature predict that this three species interaction usually leads to extinction of the intermediate prey population. Predator-induced defense as well as refuge mechanisms are widely seen in these systems and should be incorporated in IGP models to promote coexistence. With this aim, we introduce a nonlinear response to the predation of IG-predator on IG-prey modelling both prey refuge and morphological defenses. The phase diagram of species coexistence is obtained as function of the attack efficiency and the degree of nonlinearity of the defense mechanisms. Further we show how the nonlinearity affects the equilibrium populations. We unveil that there is an optimal nonlinearity at which the convergence towards the stationary coexistence regime is the fastest.