Розвиток способів діагностики технічного стану обладнання прокатних клітей в перехідних режимах роботи

This paper proposes and substantiates the improvement of the on-board vibration control system of aircraft engines to expand the system’s functional capabilities and provide multi-class diagnostics based on multi-level processing of vibration signals. The possibility of diagnosing initial crack-like damage to the rotor shaft and impeller blade is considered, as well as the possibility of detecting such operational violations of the engine's regular modes, such as minor imbalance, ingress of small and medium-sized foreign objects, and grinding of the impeller blades. Such damages and disturbances do not lead to increased vibration of the rotary harmonics and are not detected by traditional analysis methods. For multi-class diagnostics, multi-level processing of vibration signals based on various combinations and/or sequential application of time-frequency analysis, multi-spectral analysis, and fractal analysis methods were used. This work proposes the structure of a subsystem of multi-class diagnostics as part of the standard on-board engine vibration control system in steady-state and transient operating modes, as well as algorithms for detecting initial crack-like damages of rotating elements and disturbances in standard operating modes. As diagnostic signs, the following are used: the Hurst index of the vibration signal in the region of subharmonic resonance in the transient mode (for the diagnosis of the initial transverse crack of the rotor shaft); dimension of Minkowski time-frequency spectra of vibration signals in stationary and transient modes (for diagnosing the initial crack of the impeller blade); simultaneous use of the Hurst index of samples of vibration signals and dimension of Minkowski estimates of the module of the bispectrum of vibration signals (for diagnosing violations of standard operating modes). The developed software algorithms use received and pre-processed signals from vibration and engine speed sensors, provide the determination of the mode of vibration disturbance, perform time-frequency, bispectral, and fractal analysis in the sequence determined for each diagnostic task, calculate the value of the diagnostic feature and compare it with the reference value, based on the results of the comparison, establish the appropriate diagnosis and submit it to the decision-making system. The proposed algorithms are intended for use in the corresponding blocks of the multi-class engine diagnostic subsystem.

Relative hydraulic resistance, shear rate, and pressure in a vascular network integrate the network's architecture via fluid flow, and determine vein dynamics, with a time delay, in the prototypical organism Physarum polycephalum.

A control strategy, referred to as open-loop predictive ride-through control, is presented and characterized for several transient operation modes. It is shown that it is possible to bring a three-phase rectifier system from a given initial-state to the desired steady-state in the minimum possible time. This provides the system with inherent ride-through capability, and thus eliminates the need for an uninterruptible power supply, if short-term line disturbances are a problem. Experimental data are given to verify the findings.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Introduction. Single-dipper hydraulic excavators are becoming widely used multifunctional machines. Upgrading the machine as a whole and its assemblies is an actual problem to be solved with the aim of reducing material consumption and increasing stability and throughput. The article presents results of computer simulation of the excavating part designed to reduce the weight of the equipment. These data can be used to improve the equipment of excavators when operating with non-standard excavating equipment of increased weight. Materials and methods. The excavating equipment of the Hitachi ZX270 excavator is taken as a prototype. Computer simulating and calculation of the excavating part is conducted using the T-FLEX software. The calculation is carried out for different modes of the excavator operation and for different orientations of the jig boom, dipper stick and dipper relative to each other: excavating with the entire width of the dipper, single-tooth excavating, swiveling the loaded excavator for unloading. The highest stresses arise in structural members in the considered calculation cases. The calculations are performed without accounting the oscillations occurring at transient operating modes and during locking. Results. The study determines a stress-deformed condition of the pseudotruss excavating part structures of the excavator with various lightened makes selected on the basis of computer simulation. Zones of the highest stresses and largest deformations are revealed as well as suggestions on their decrease are made. The research results are used to optimize the jig boom and dipper stick structures by the criterion of generated stress minimization. Conclusions. The obtained data and formulated recommendations are the basis for further detailed simulation of pseudotruss excavating part structures of excavators and other machines of various layouts and purposes.

Delayed feedback and detection of weak periodic signals in a stochastic Hodgkin–Huxley neuron

The object of this research is the process of oscillation of liquid metallurgical slag in a slag bowl under the influence of acceleration. The work considers the oscillation processes in bowls used on railway and road slug cars, which differ in design and operating conditions. One of the key problems associated with the transportation of liquid slag is the dynamic instability of the melt, which leads to oscillations and splashing, which can pose a safety threat and reduce the efficiency of the transportation process. In this regard, the study of the dynamics of liquid slag in bowls of various designs is an urgent task aimed at optimizing transportation parameters and developing measures to reduce the risk of slag splashing. Based on the results of numerical modeling, it was established that the nature of the oscillations of liquid slag in the bowl significantly depends on the magnitude of the acceleration, the type of slag and the design of the bowl. In particular, the acceleration ranges at which different oscillation modes are observed, from minor surface disturbances to intensive slag splashing, have been determined. At the same time, the differences in the nature of oscillations for different types of slag and bowl designs lie within the limits determined by their physicochemical properties and geometric parameters. The results obtained allow to conclude that it is possible to develop measures for the operation of slag bowls, as well as their designs, in the direction of reducing the amplitude of liquid slag oscillations, which, in turn, contributes to increasing transportation safety and reducing dynamic loads on the bowl walls. The obtained data can be used in the design of new bowl designs to optimize their shape and internal elements in order to minimize slag oscillations. In addition, the information provided can be useful for metallurgical enterprises to develop effective methods for controlling and monitoring slag stability during transportation.

Advanced pressurized water reactors are the main part of a new generation of nuclear power plant projects under development that provide cost-effective power production for various needs (Yemelyanov et al. 1982, Klimov 2002, Boyko et al. 2005, Baklushin 2011, Bays et al. 2019, Nuclear Technology Review 2019). The innovative technologies are aimed at improving the safety and reliability as well as at reducing the cost of NPPs. At the same time, improvements in design, technological and layout solutions are focused primarily on the reactor core. Assessments of the efficiency of these improvements are preceded by numerical simulations of the processes in the core, in particular heat generation and sink, with account for the difference between the study object and the standard version tested in operational practice. The authors of the article propose a method for calculating the temperature field in the core of a heterogeneous reactor (using the example of a pressurized water reactor), which makes it possible to quickly assess the level of temperature safety of various changes in the core and has the necessary speed for analyzing transients in real time. This method is based on the energy equation for an equivalent homogeneous core in the form of a heat equation that takes into account the main features of the simulated heterogeneous structure. The procedure for recovering the temperature field of a heterogeneous reactor uses the analytical relation obtained in this work for the heat sink function, taking into account inter-fuel element heat leakage losses. Calculations of temperature fields in the model of the PWR type reactor (The Westinghouse Pressurized Water Reactor Nuclear Plant 1984) were carried out in stationary and transient operating modes. The calculation results were compared with the results of CFD simulation. The area of competing use of the temperature field recovery method was indicated.

In order to ensure reliable operation of the Superconducting Magnet Energy Storage Engineering Test Model (SMES-ETM), the conductor in the power bus must meet similar performance requirements as the entire coil during both steady state and transient operating modes. Lumped parameter thermal analyses are performed to evaluate steady state performance and assess risk involved with failure modes associated with the superconducting bus cryostat. Transient heat fluxes to the superfluid helium vessel are calculated for the loss of bus vacuum and the loss of nitrogen shroud cooling. The elapsed time to reach the critical heat flux in superfluid helium is calculated using the heat conductivity function for these cases. It is concluded that in the event of bus cooling failure, barring catastrophic loss of vacuum, the bus and cryostat can function for limited periods of time without interrupting ETM operations.

In the article, by the example of a walking excavator, the results of a study of a control system of traction electric drive with a rigid and flexible feedback on the load are mentioned. Based on the analysis of known works, the calculation scheme has been chosen; the equations of motion of the electromechanical system have been obtained, taking into account the elasticity of the rope and feedbacks on the load in the elastic element. A simulation model of this system has been developed and mathematical modeling of the transient processes to evaluate the influence of feedback on the dynamic characteristics of the mechanism and its efficiency of work was carried out. It is shown that the use of rigid and flexible feedbacks makes it possible to reduce dynamic loads in the traction mechanism and to limit the elastic oscillation of the executive mechanism in transient operating modes in comparison with the standard control system; however, there is some decrease in productivity. It has been also established that the sign-variable of the loading of the electric drive, connected with the opening of the backlashes in the gearbox due to the action of feedbacks on the load in the elastic element, under certain conditions, can lead to undesirable phenomena in the operation of the drive and a decrease in the reliability of its operation.

Accurate control of the in-cylinder air/fuel ratio level is critical for both fuel saving and harmful emission reduction of an internal combustion engine. The fuel injection quantity is easy to control with today's electronically controlled fuel injection system, the difficulty is how to accurately determine the fresh charge mass trapped in-cylinder at the end of the gas exchange process, especially for transient operation mode of a vehicle when the throttle position, intake air pressure and engine speed are instantaneously changing. No physical airflow meter exists which has satisfactory response time and measurement accuracy. Described in this paper is a renovated air flow measurement technology combining fast response sensors with 1-dimensional pressure wave action simulation. Utilizing two dynamic pressure transducers(2P) to measure pressure fluctuation near the intake and exhaust ports and coupling the measured pressure signals into the numerical solver of a 1-dimensional gas exchange simulation software, together with the instant flow area at valve locations, the instantaneous gas mass flow rate through the engine intake and exhaust ports can be calculated. The fresh mass and un-swept burnt mass fraction trapped in the cylinder could also be traced along the entire gas exchange process. The response time and model accuracy of this synthetic virtual airflow meter technology is validated against GT-Power model and experiment tests, for both steady-state and transient operating modes.

The paper encompasses the study of the evolution of the functional parameters (suction air mass flow rate, plant efficiency, etc.) of naval gas turbines propulsion systems at changes in environmental parameters. The operational parameters of a gas turbine propulsion system and their evolution in relation to the modification of the environmental status parameters have been highlighted by calculation. Another sensitive area in the operation of gas turbine installations is the transient operating modes (stopping, starting, accelerating and decelerating sequences of the installation), which were highlighted by determinating of operating parameters on board the ship.

In this paper, a tumor and immune system interaction model consisted of two differential equations with three time delays is considered in which the delays describe the proliferation of tumor cells, the process of effector cells growth stimulated by tumor cells, and the differentiation of immune effector cells, respectively. Conditions for the asymptotic stability of equilibria and existence of Hopf bifurcations are obtained by analyzing the roots of a second degree exponential polynomial characteristic equation with delay dependent coefficients. It is shown that the positive equilibrium is asymptotically stable if all three delays are less than their corresponding critical values and Hopf bifurcations occur if any one of these delays passes through its critical value. Numerical simulations are carried out to illustrate the rich dynamical behavior of the model with different delay values including the existence of regular and irregular long periodic oscillations.

The transcription factor NF-κB links immune response and inflammatory reaction and its different oscillation patterns determine different cell fates. In this study, a mathematical model with IκBα protein synthesis time delay is developed based on the experimental evidences. The results show that time delay has the ability to drive oscillation of NF-κB via Hopf bifurcation. Meanwhile, the amplitude and period are sensitive to the time delay. Moreover, the time delay threshold is a function of four parameters characterising the negative feedback loop. Likewise, the parameters also have effects on the amplitude and period of NF-κB oscillation induced by time delay. Therefore, the oscillation patterns of NF-κB are collaborative results of time delay coupled with the negative feedback loop. These results not only enhance the understanding of NF-κB biological oscillation but also provide clues for the development of anti-inflammatory or anti-cancer drugs.

The relevance. Associated with the problem of increase in efficiency of algorithms for monitoring and controlling the dynamic operation modes of wells equipped with an electric submersible pump with adjustable supply. The result summarizes and develops the previously published solution on the design of a dynamic well model, through the transition from linearized correlations to quadratic relationships between states at key points of a lift. These points properly reflect the observed forms of behavior in transient and equilibrium operating modes at full start-stop control ranges. The main aim. Updated description of a comprehensive quadratic barometric model of the «reservoir–lift–electric pump–well head» type well, focused on the tasks of automatic control and regulation in real time. Objects. Well with frequency-regulated submersible pump. Methods. Material balance, percolation, hydrostatics, quadratic kinetics of friction losses, numerical modeling of differential equations, finite-dimensional description of the complex hydrodynamics of the well, taking into account the potential and kinetic head losses in the lift. Results: (1) Updated mathematical description of the hydrodynamics of the well with an electric submersible pump creates the basis for: more reliable solution of inverse problems of parametric model support according to the data of field control, refined assessment of the adjustment potential, predicting the dynamics of a possible system output beyond the boundaries of functional stability, technologies of numerical and analytical design of optimal solutions when selecting the parameters of arrangement and laws of operational regulation, synthesis of dynamic observers of an extended state vector synchronously operating with the dynamics of controlling well-head and deep pressure. (2) The results of the computational analysis demonstrate a complex behavior that does not match the graph of the inflow and pump supply, when changing the frequency and wellhead pressure. This explains the observed effect of the multi-tempoity of transient processes during starts and stops and possible instability of the supply with a sharp decrease in frequency. (3) Estimates of discrepancy between the solutions for a quadratic model and a linearized prototype indicate an increase in errors of linearized analysis with strong deviations of operating modes from the equilibrium-calculated states. The refinements in dynamically disturbed operating modes delivered by the updated model are important for improving the reliability of operational control systems and parametric estimation for data control mode states.

In this paper, we investigate the oscillatory expression in Escherichia coli mediated by microRNA with time delays and reaction-diffusion terms. First of all, the integrated effects of delays and diffusions are first introduced into the genetic regulatory networks involving microRNAs, and a general model of genetic regulatory networks is then formulated. Second, two functional issues on gene regulatory networks, i.e. stability and oscillation of such model, are addressed in detail, and an explicit algorithm determining the properties of periodic oscillation is also presented. We demonstrate that the oscillatory expression of Escherichia coli is not only crucially dependent on the transcriptional and translational delays, but also heavily influenced by the diffusion coefficients. The conclusion is practically verified by a lot of biological experiments and observations. We also find that if the diffusion coefficients of miRNA, mRNA, and protein are suitably small, it can predict that inhomogeneous periodic oscillations can occur unless there only exhibits spatially homogeneous periodic oscillations. The obtained results indicate that the effects of transcriptional and translational delays are essential factors for designing or controlling genetic regulatory networks, in the meantime the functions of reaction-diffusion must beconsidered. Finally, numerical examples are presented to illustrate and visualize theoretical results.