Self-oscillating Process Research Articles

Подавление влияния инструментальных возмущений локально инвариантным масштабированием физической модели угловой стабилизации космического аппарата

The study introduces a method of ground conditions physical modeling of the spacecraft motion around a fixed axis. On a natural scale of parameters and variables, the dynamic modes under consideration can be implemented only with an extremely small amount of kinetic energy dissipation. The feasible minimum friction for a test bed of simple design significantly exceeds the required values. In current modes of economical limit cycles, the characteristics of the simulated process are distorted so much that the physical modeling test bed is unsuitable for practical use. The solution to this problem is usually sought by complicating the design of the test bed through the use of air or magnetic suspension. The paper proposes an innovative method of “invariant scaling”, based on the principle of dynamic similarity of self-oscillating processes. Its application makes it possible to drastically reduce the effect of friction on the characteristics of physically modeled modes during ground developmental testing of control algorithms. Computer modeling with the use of this method has confirmed its high efficiency. It has been shown analytically and numerically that the modeling accuracy can be radically improved. An example of reducing the modeling error by 200 times is given.

Excitation of decay-less transverse oscillations of coronal loops by random motions

Context. The relatively large-amplitude decaying regime of transverse oscillations of coronal loops has been known for two decades and has been interpreted in terms of magnetohydrodynamic kink modes of cylindrical plasma waveguides. In this regime oscillations decay in several cycles. Recent observational analysis has revealed so-called decay-less, small-amplitude oscillations, in which a multi-harmonic structure has been detected. Several models have been proposed to explain these oscillations. In particular, decay-less oscillations have been described in terms of standing kink waves driven with continuous mono-periodic motions of loop footpoints, in terms of a simple oscillator model of forced oscillations due to harmonic external force, and as a self-oscillatory process due to the interaction of a loop with quasi-steady flows. However, an alternative mechanism is needed to explain the simultaneous excitation of several longitudinal harmonics of the oscillation. Aims. We study the mechanism of random excitation of decay-less transverse oscillations of coronal loops. Methods. With a spatially one-dimensional and time-dependent analytical model taking into account effects of the wave damping and kink speed variation along the loop, we considered transverse loop oscillations driven by random motions of footpoints. The footpoint motions were modelled by broad-band coloured noise. Results. We found the excitation of loop eigenmodes and analysed their frequency ratios as well as the spatial structure of the oscillations along the loop. The obtained results successfully reproduce the observed properties of decay-less oscillations. In particular, excitation of eigenmodes of a loop as a resonator can explain the observed quasi-monochromatic nature of decay-less oscillations and the generation of multiple harmonics detected recently. Conclusions. We propose a mechanism that can interpret decay-less transverse oscillations of coronal loops in terms of kink waves randomly driven at the loop footpoints.

Структура течения и колебания давления при взаимодействии сверхзвуковой недорасширенной струи газа с трубной полостью

Supersonic jets are widely used in devices based on the phenomenon of a self-oscillating process that occurs when a gas flow interacts with circular cavities (gas-jet sound emitters). The mechanisms of maintaining undamped pressure oscillations and determining the flow field in the tube cavity during the interaction of a supersonic underexpanded jet with cavity are considered. The physical pattern of the flow in the cavity of a gas-jet emitter is discussed, the existence of odd longitudinal modes is shown, and wave diagrams are proposed for describing the flow in odd longitudinal modes. The wave diagrams are based on the analysis of the signals of piezoelectric sensors, recording pressure oscillations in the tube cavity. The calculation of the flow parameters in the tube cavity in longitudinal modes is based on the flow velocity and speed of sound diagram.

INFLUENCE OF SMALL FRACTION OF POLYGRANULAR FILL OF ROTATING DRUM ON SELF-OSCILLATION SWING

The influence of the structure of two-fractional polygranular fill of a rotating drum on the self-oscillation swing is considered. The pulsating mode of flow of such intrachamber fill is used in the self-oscillating grinding process in a tumbling mill. Spherical particles of non-coherent granular material of 2.2 mm size were used as a large fraction modeling the grinding bodies. Cement was used as the small fraction modeling the particles of the crushed material. The factors of experimental studies were accepted: the gaps between particles of large fraction degree of filling at rest dispersed particles of small fraction 0, 25, 50 and 100%, the relative size of particles of large fraction in the drum chamber 0.519, 0.733, 1.04, 1.47, 2.08, 2.93, 4.15 and 5.87% (drum chamber radius 212, 150, 106, 75, 53, 37.5, 26.5 and 18.75 mm), the chamber degree of filling at rest 25, 35 and 45%. The method of visual analysis of fill motion patterns in the cross section of a rotating chamber and measurement of dilatation was applied.Video of the fill pulsating flow was taken. The magnitude of the self-oscillation swing was estimated by the increase in the difference of the maximum and minimum values of the fill dilatation over one period of pulsating. The maximum range of self-oscillation swing reached the value of 1.36. The change of the self-oscillation swing from zero at the beginning of self-excitation of pulsations to the maximum value with the greatest increase of dilatation was revealed. The effect of a decrease in the maximum range of self-oscillation swing with enhanced fill coherent properties has been registered. The attenuation of the spray of particles of large fraction in the chamber due to the coherent effect of the small fraction was established. An increase in the self-oscillation swing of single-grain fill was found with a decrease in the relative particle size and the chamber degree of filling. A decrease in the self-oscillation swing of two-fractional fill was found with an increase in the content of small fraction, a decrease in the relative size of particles of a large fraction, and an increase in the chamber degree of filling.

Establishing the effect of a decrease in power intensity of self-oscillating grinding in a tumbling mill with a reduction in an intrachamber fill

Effect of the degree of chamber filling with the charge on efficiency of the self-oscillating grinding process in a tumbling mill has been assessed.By using the approximate analytical and experimental method, dynamic effect of increasing the self-oscillating impact action of grinding fill on the crushed material was compared with the conventional steady-state motion mode. A significant increase in average sums of vertical components of the self-oscillating collision momenta and the average sums of power of such components with a decrease in the chamber filling degree was found. Manifestation of this effect is due to the increase in the self-oscillations swing with decreasing filling. An increase in the maximum momentum values was found to be approximately 2.4 times at the degree of filling κ=0.45, 3.1 times at κ=0.35 and 5.8 times at κ=0.25. An increase by 5.7 times in maximum values of momentum power was found at κ=0.45, by 9.6 times at κ=0.35 and by 45.5 times at κ=0.25.Technological effect of significant decrease in the specific power intensity and productivity growth of the innovative self-oscillating grinding process as compared to the characteristics of the conventional steady-state process with a reduction in the chamber filling degree have been experimentally established.The process of grinding cement clinker with a complete filling of gaps between spherical grinding bodies with a relative size of 0.026 with particles of the crushed material was considered. It was found that during excitation of self-oscillations, power intensity of grinding decreased and productivity increased. A decrease in relative specific power intensity was observed: 27 % at κ=0.45, 42% at κ=0.35 and 55 % at κ=0.25. A 7 % increase in relative productivity was found at κ=0.45, 30 % at κ=0.35, and 46 % at κ=0.25.The effects established in operation have allowed us to predict rational parameters of the self-oscillating grinding process carried out in a tumbling mill with variation in the chamber filling degree

Seismic and Seismochemical Stimulation Increases Well Injectivity and Productivity

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 190456, “Increasing Well Injectivity and Productivity by Seismic and Seismochemical Stimulation,” by K. Furman, S. Miftakhov, SPE, M. Nazyrov, R. Nefedov, and V. Zamakhaev, Terratec, and A. Andrianov, AIA Consulting, prepared for the 2018 SPE EOR Conference at Oil and Gas West Asia, Muscat, Oman, 26–28 March. The paper has not been peer reviewed. Many oil fields in Russia and the Commonwealth of Independent States are in late-development stages, with waterflooding having being used for decades. A relatively new technology in production optimization is wave stimulation, in which the wellbore and reservoir are treated by acoustic, seismic, or other types of waves generated by tools. Approximately 250 wells have been treated in this manner, with a high success rate and significant oil-production increase. This paper discusses the potential of seismic and seismochemical well simulation in particular within the scope of this recent technology. Introduction Wave-stimulation technologies have short treatment times and can be applied in different types of formations and wells. This paper focuses on seismic-impact well treatment. The well treatment is based on a wellhead pneumatic generator that uses special valves. Energy is generated at the surface with compressed inert gas and released into the well. A shock wave then propagates through the liquid-filled well column and transforms into a seismic wave in situ. Movement of the shock wave creates a damped self-oscillating process with a frequency of 0.2 Hz, the effect of which can stimulate injection and production wells. One method of increasing the efficiency of seismic stimulation is use in conjunction with the injection of chemical reagents. Mechanisms of Seismic and Seismochemical Stimulation No generally accepted theory describes the effects of seismic impact on reservoirs. On the basis of theoretical, experimental, and field research, various authors have proposed mechanisms and concepts, which are described in the complete paper. Porosity and Permeability Change in Dilatancy Area for Sandstones. Studies of dilatancy processes under dynamic effects have shown that, for sufficiently high unevenness of the stressed state, dilatancy processes occur even at stresses that are only 3–5% of the ultimate strength, causing irreversible change in the rock density, porosity, strength, and permeability. Dilatancy is observed in the deformation of soils and rocks. Extensive experimental data on the deformation of a wide class of formations under volumetric stressed-state conditions show that compaction is seen in highly porous rocks, while loosening is seen in dense rocks. Reduction in the volume of highly porous rocks occurs as the result of a reduction in the number of defects. Positive (compaction) and negative (loosening) rock-dilatancy values are related to the value of the initial effective porosity. If the effective porosity value is less than a certain limiting value, then the rock is dense and loosens during deformation. When the effective porosity is greater than its limiting value, the rock is compacted. However, the compaction of the rock can occur up to a certain value, after which it breaks down. The main influence on the amount of dilatancy is the result of an uneven load (i.e., the ratio of the minimum main stress to the maximum). However, at the same level and at the magnitude of the uneven loading in the stronger rocks, the dilatant component of the volume deformation exceeds the rock compaction more than is seen in less-rigid rocks.

Нелинейная динамика автоколебательных процессов, возникающих в системе кофермент Q10 – оксигенированные комплексы кобальта (II)

Нелинейная динамика автоколебательных процессов, возникающих в системе кофермент Q10 – оксигенированные комплексы кобальта (II)

Effects of Synchronization and Switching off Chemical Self-Oscillations upon Periodic Exposure to Light

The effect of synchronization of chemical concentration self-oscillations of the Briggs–Rauscher reaction under the periodic external effect of white light was studied. The change in the frequency of concentration oscillations outside the synchronization band was revealed under external exposure to light with a modulation frequency from 0.029 to 0.039 Hz before synchronization and from 0.1 to 0.14 Hz after it. The dependence of the synchronization band on the power is demonstrated, and the limiting values of the external light power at that self-oscillations are “turned off” are found. The synchronization range of concentration oscillations was revealed under external light exposure with a modulation frequency in the range of 0.04–0.1 Hz. When the light flux from a light source exceeds 5000 lm, the self-oscillation process is turned off.

BACKGROUND TO THE ARRANGEMENT OF AUTOMATING AND VOLVOUS PROCESSES IN THE FORM-FORMING MACHINES WHEN TREATING THE PREPARATIONS AND DETAILS BY THE PLASTIC DEFORMATION METHOD

Purpose. Analysis of surface-hardening technology for cold processing of metals, taking into account the deformation-wave processes occurring in the area in front of the shaping tool. Methodology. To establish the reasons for obtaining finished products with increased roughness, insufficient contact strength, fracturing and peeling of the surface layers, as well as the occurrence of significant dynamic loads in the mechanisms of machines for machining parts using plastic deformation, a two-mass design model is used in which the working tool is connected by friction with the moving processed workpiece. Findings. The results of determining the conditions for the occurrence of self-oscillations in the system “workpiece - tool” are presented. Based on the analysis of the friction characteristics as a function of the mutual slip rate between the workpiece and the shaping tool, the range of slip speeds is set, at which the self-oscillating processes for the friction pair can be excited: "tool - workpiece". Originality consists in the fact that the influence of the variable friction force on the occurrence of sustained self-oscillations between the workpiece being processed and the tool in the machines for “cold” plastic deformation of the metal has been established. The conditions for the occurrence and absence of self-oscillations in the zone of contact between the tool and the workpiece are found. Practical value lies in the fact that the modes of operation of machines for processing products by plastic deformation have been revealed under which unregulated roughness, fracturing and “peeling” of the parts being machined can occur, as well as a high dynamic background during the operation of the shaping tool of driving and power mechanisms. Practical recommendations are given to improve the performance of finished products and reduce vibroactivity in the drive. Keywords: running in, dragging, knurling, plastic deformation, elastic deformation wave, roller, tool, blank.

Nonlinear Dynamics, Quasi-Periodic Summation, Self-Oscillating Processes, and Information Coding in Selective Spiking Neural Networks

Nonlinear dynamics, physical processes, and information processing in selective spiking neurons are investigated. Summation of pulse inputs are considered on the basis of the theory of quasi-periodic functions and nonlinear transformation via relaxation of the self-oscillating system of a neuron. A way of encoding input information is also considered in which the information unit is a pulse sequence, and the intensity of the input signal is encoded by a synchronous change in the frequency of the pulse sequences.

INCREASING THE CENTRIFUGAL PUMP RELIABILITY FOR OIL COLLECTION AND PUMPING SYSTEMS

Background Features of the working conditions of submersible centrifugal oil pumps determine the specific requirements for the shape of the characteristics of the pumps. Fulfillment of these requirements allows preserving the high efficiency of pumps under operating conditions and ensuring the reliability of their operation. Aims and Objectives Substantiation of requirements for the submersible centrifugal pumps characteristics. Results It is revealed that a large steepness of characteristics at low feed rates is economically unprofitable. During prolonged operation of the pump in conditions of ascending the impeller and a large gap between the lower sealing ring of the impeller and the mating surface of the guide vane, a self-oscillating process can occur, leading to rapid wear of pump stage parts.

Эффекты синхронизации и выключения автоколебаний химической реакции при периодическом воздействии света

AbstractThe effect of synchronization of chemical concentration self-oscillations of the Briggs–Rauscher reaction under the periodic external effect of white light was studied. The change in the frequency of concentration oscillations outside the synchronization band was revealed under external exposure to light with a modulation frequency from 0.029 to 0.039 Hz before synchronization and from 0.1 to 0.14 Hz after it. The dependence of the synchronization band on the power is demonstrated, and the limiting values of the external light power at that self-oscillations are “turned off” are found. The synchronization range of concentration oscillations was revealed under external light exposure with a modulation frequency in the range of 0.04–0.1 Hz. When the light flux from a light source exceeds 5000 lm, the self-oscillation process is turned off.

Interdecadal variability in thermal structure of water in the upper active layer in the northwestern Pacific Ocean

The self-oscillation process of heat redistribution in the system ocean–atmosphere–continent should be considered as one of the mechanisms of multidecade climate variability. Based on the data of monitoring for the period 1960–2014, interdecadal variations in heat capacity in the upper active layer are estimated for the northwestern part of the Pacific Ocean, which is one of the most informative regions of the World Ocean.

Strategies for the Analysis of Continuous Bioethanol Fermentation under Periodical Forcing

The process of continuous bioethanol fermentation often exhibits strong nonlinear dynamics and tends to generate self-oscillatory-state trajectories. The aim of this work is to further investigate such oscillators by coupling with outside periodic forcing, so as to improve process performance. To that end, several strategies for analyzing periodically forced self-oscillatory processes are proposed. By periodically and deliberately forcing an operational parameter, the behavior of the forced fermentor is investigated using limit cycle bifurcation analysis. Specifically, periodic doubling and Neimark–Sacker bifurcations are investigated with limit cycle continuation diagrams. The limit cycle bifurcation analysis is compared with the simulation-based methods, such as stroboscopic and maximum bifurcation maps, and it is shown to be an efficient analysis tool for the periodically forced self-oscillatory system. Process performance enhancement by designing the fermentor to be self-oscillatory is also discussed,...

Energy harvesting from aperiodic low-frequency motion using reverse electrowetting.

Mechanical energy harvesting can provide a promising alternative to electrochemical batteries, which are currently widely utilized to power mobile electronics. In this work we present a theoretical analysis of a recently proposed method of mechanical energy harvesting, which combines a reverse electrowetting phenomenon with the fast self-oscillating process of bubble growth and collapse. We investigate the details of the bubble dynamics and analyze the dependence of the energy generation process on the system parameters. The results demonstrate that self-oscillation frequencies of several kHz are possible, which can lead to very high power generation densities in excess of 104 W m-2. The obtained results indicate the possibility of high-power energy harvesting from mechanical energy sources with very low frequencies, well below 1 Hz.

Numerical modeling of the self-oscillation onset near a three-dimensional backward-facing step in a transonic flow

The results of a numerical investigation of the nature of self-oscillation processes occurring in transonic flow past a backward-facing step and a cavity with a flow of the open type are presented. The turbulent flow past the above-mentioned bodies is modeled using the NOISEtte software package intended for solving problems of aerodynamics and aeroacoustics on unstructured grids. The modeling is performed using the eddy-resolving IDDES method that belongs to the class of hybrid RANS-LES approaches. The adequacy of the calculations is confirmed by means of comparing the results obtained with the available experimental data. The structure and the salient features of the self-oscillatory, hydrodynamic-in-nature process, which arises in flow past a cavity and a backward-facing step, are established.

Undamped transverse oscillations of coronal loops as a self-oscillatory process

Context. Standing transverse oscillations of coronal loops are observed to operate in two regimes, the rapidly decaying large amplitude oscillations, and undamped small amplitude oscillations. In the latter regime the damping should be compensated by energy supply, which allows the loop to perform almost monochromatic oscillations with almost constant amplitude. Different loops oscillate with different periods. The oscillation amplitude does not show dependence on the loop length or the oscillation period. Aims. We aim to develop a low-dimensional model explaining the undamped kink oscillations as a self-oscillatory process caused by the effect of negative friction. The source of energy is an external quasi-steady flow, e.g. supergranulation motions near the loop footpoints or external flows in the corona. Methods. We demonstrate that the interaction of a quasi-steady flow with a loop can be described by a Rayleigh oscillator equation that is a nonlinear ordinary differential equation, with the damping and resonant terms determined empirically. Results. Low-amplitude self-oscillatory solutions to the Rayleigh oscillator equation are harmonic signals of constant amplitude, which is consistent with the observed properties of undamped kink oscillations. The period of self-oscillations is determined by the frequency of the kink mode. The damping by dissipation and mode conversion is compensated by the continuous energy deposition at the frequency of the natural oscillation. Conclusions. We propose that undamped kink oscillations of coronal loops may be caused by the interaction of the loops with quasi-steady flows, and hence are self-oscillations, in analogy with producing a tune by a stick moving across a violin string.

Bubbler: A Novel Ultra-High Power Density Energy Harvesting Method Based on Reverse Electrowetting.

We have proposed and successfully demonstrated a novel approach to direct conversion of mechanical energy into electrical energy using microfluidics. The method combines previously demonstrated reverse electrowetting on dielectric (REWOD) phenomenon with the fast self-oscillating process of bubble growth and collapse. Fast bubble dynamics, used in conjunction with REWOD, provides a possibility to increase the generated power density by over an order of magnitude, as compared to the REWOD alone. This energy conversion approach is particularly well suited for energy harvesting applications and can enable effective coupling to a broad array of mechanical systems including such ubiquitous but difficult to utilize low-frequency energy sources as human and machine motion. The method can be scaled from a single micro cell with 10−6 W output to power cell arrays with a total power output in excess of 10 W. This makes the fabrication of small light-weight energy harvesting devices capable of producing a wide range of power outputs feasible.

RADIAL AND AZIMUTHAL OSCILLATIONS OF HALO CORONAL MASS EJECTIONS IN THE SUN

We present the first observational detection of radial and azimuthal oscillations in full halo coronal mass ejections (HCMEs). We analyze nine HCMEs well-observed by the Large Angle and Spectrometric Coronagraph (LASCO) from 2011 February to June. Using the LASCO C3 running difference images, we estimated the instantaneous apparent speeds of the HCMEs in different radial directions from the solar disk center. We find that the development of all these HCMEs is accompanied by quasi-periodic variations of the instantaneous radial velocity with the periods ranging from 24 to 48 minutes. The amplitudes of the instant speed variations reach about a half of the projected speeds. The amplitudes are found to anti-correlate with the periods and correlate with the HCME speed, indicating the nonlinear nature of the process. The oscillations have a clear azimuthal structure in the heliocentric polar coordinate system. The oscillations in seven events are found to be associated with distinct azimuthal wave modes with the azimuthal wave number m = 1 for six events and m = 2 for one event. The polarization of the oscillations in these seven HCMEs is broadly consistent with those of their position angles with the mean difference of 43°. The oscillations may be connected with natural oscillations of the plasmoids around a dynamical equilibrium, or self-oscillatory processes, e.g., the periodic shedding of Alfvenic vortices. Our results indicate the need for an advanced theory of oscillatory processes in coronal mass ejections.

Synthesis of nanostructured carbon fibers from chlorohydrocarbons over Bulk Ni-Cr Alloys

The regularities of the formation and morphology of a nanostructured carbon product obtained by the decomposition of 1,2-dichloroethane on alloyed bulk catalysts Ni1 − x Cr x (x = 1–10 at %) at 600°C are considered. The carbon fibers were found to possess a strongly marked segmented structure consisting of regularly alternating friable and dense graphite-like blocks. The proposed mechanism of growth is based on a self-oscillatory process, which is supposed to take place at the surface of the active particles formed as a result of the carbon erosion of a bulk Ni1 − x Cr x alloy.