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Due to the important strategic position of Pumped Storage Power Plants (PSPP) in global energy upgrading, conducting in-depth research on the various operating conditions of pump turbine units is important for their safe and stable operation. This study sought to clarify the gas–liquid phase motion and the nonlinear chaotic characteristics of the process of exhaust and pressurization in pump mode; with the simplified objective model proposed here, a visualization of the process is achieved using data-driven methods, and the nonlinear characteristics of gas–liquid phase motion during the process are theoretically demonstrated. A method that combines data-driven and chaotic analysis is proposed to qualitatively and quantitatively analyze the force and torque time- series signals of the runner under different exhaust rates. The results indicate that the chaotic characteristics of the force signals and torque signals of the runner are not in a single linear relationship with the exhaust rates. Therefore, this research also provides guidance on exhaust rates with the aim of informing actual engineering practice, the purpose of which is to reduce the vibration amplitude caused by repetitive torque and improve the stability of the unit operations. [ABSTRACT FROM AUTHOR]

To analyze the effect of blade number on the performance of hydraulic turbines during the transient stage in which the flow rate is not constant, six hydraulic turbines with different blade numbers are considered. The instantaneous hydraulic performance of the turbine and the pressure pulsation acting on the impeller are investigated numerically by using the ANSYS CFX software. The ensuing results are compared with the outcomes of experimental tests. It is shown that the fluctuation range of the pressure coefficient increases with time, but the corresponding range for the transient hydraulic efficiency decreases gradually when the flow velocity transits to larger values. During the transition to small flow velocity, the fluctuation range of the pressure coefficient gradually decreases as time passes, but the corresponding fluctuation range of its transient hydraulic efficiency gradually becomes larger. The fluctuation range in the Z9 case is small during the transition. The main frequency of transient hydraulic efficiency pulsation is equal to the blade frequency. At the main frequency, Z7 has the largest amplitude of the hydraulic efficiency pulsation, Z10 has the smallest amplitude, and the difference between Z7 and Z9 is limited. As the number of blades grows, the pressure pulsation during the transition process gradually decreases, but the pressure pulsation of Z10 at the volute tongue is larger. In the steady state, Z9 has the highest efficiency and in the transient stage, the pressure coefficient fluctuation range is small. Accordingly, for the hydraulic turbine Z9, the performance is optimal. [ABSTRACT FROM AUTHOR]

This paper experimentally studies escape mechanisms in a bi-stable potential well, focusing on critical forcing values depending on system damping, excitation frequency, and initial phase. The experimental setup has a rotational degree of freedom. It comprises a vertical shaft with adjustable air bearings and a copper disk that increases the moment of inertia and serves as an adjustable eddy current brake. The system also includes two coil springs that provide restoring moments. External momentum is provided by an electric motor controlled through a function generator. The paper describes the identification of system parameters and compares numerical and experimental results, validating previous theoretical and numerical findings regarding the saddle and maximum escape mechanisms. [ABSTRACT FROM AUTHOR]

Due to the important strategic position of Pumped Storage Power Plants (PSPP) in global energy upgrading, conducting in-depth research on the various operating conditions of pump turbine units is important for their safe and stable operation. This study sought to clarify the gas–liquid phase motion and the nonlinear chaotic characteristics of the process of exhaust and pressurization in pump mode; with the simplified objective model proposed here, a visualization of the process is achieved using data-driven methods, and the nonlinear characteristics of gas–liquid phase motion during the process are theoretically demonstrated. A method that combines data-driven and chaotic analysis is proposed to qualitatively and quantitatively analyze the force and torque time-series signals of the runner under different exhaust rates. The results indicate that the chaotic characteristics of the force signals and torque signals of the runner are not in a single linear relationship with the exhaust rates. Therefore, this research also provides guidance on exhaust rates with the aim of informing actual engineering practice, the purpose of which is to reduce the vibration amplitude caused by repetitive torque and improve the stability of the unit operations.

A modified onboard neuro-fuzzy adaptive (NFA) helicopter turboshaft engine (HTE) automatic control system (ACS) is proposed, which is based on a circuit consisting of a research object, a regulator, an emulator, a compensator, and an observer unit. In this scheme, it is proposed to use the proposed AFNN six-layer hybrid neuro-fuzzy network (NFN) with Sugeno fuzzy inference and a Gaussian membership function for fuzzy variables, which makes it possible to reduce the HTE fuel consumption parameter transient process regulation time by 15.0 times compared with the use of a traditional system automatic control (clear control), 17.5 times compared with the use of a fuzzy ACS (fuzzy control), and 11.25 times compared with the use of a neuro-fuzzy reconfigured ACS based on an ANFIS five-layer hybrid NFN. By applying the Lyapunov method as a criterion, its system stability is proven at any time, with the exception of the initial time, since at the initial time the system is in an equilibrium state. The use of the six-layer ANFF NFN made it possible to reduce the I and II types of error in the HTE fuel consumption controlling task by 1.36...2.06 times compared with the five-layer ANFIS NFN. This work also proposes an AFNN six-layer hybrid NFN training algorithm, which, due to adaptive elements, allows one to change its parameters and settings in real time based on changing conditions or external influences and, as a result, achieve an accuracy of up to 99.98% in the HTE fuel consumption controlling task and reduce losses to 0.2%. [ABSTRACT FROM AUTHOR]

Electromechanical switching equipment has a finite response time of up to several milliseconds. The switching process is intermittent, caused by the bouncing of mechanical contacts and the formation of an electrical arc. The transient process is accompanied by high-frequency current and voltage oscillations, the phase, amplitude, and spectral composition of which largely have a random character dependent on initial conditions. The article presents the results of a laboratory analysis of signal oscillations during the switching on and off of an asynchronous single-phase motor. It is shown that the structure of high-frequency oscillations is determined by both parasitic parameters of the switching apparatus and electrical circuits in the external circuit. A qualitative analysis of the signal structure based on analytical expressions is provided, demonstrating the possibility of controlling the time intervals between current and voltage surges using neural-network algorithms. An algorithm for training a neural network based on simple equations and the use of a basic perceptron for this purpose is described. The ability to identify time intervals corresponding to contact bouncing in an automated mode with a maximum delay of tens of microseconds is demonstrated. The results can be used in testing electromechanical switching equipment. [ABSTRACT FROM AUTHOR]

Transient processes that occur during any damage to electrical power facilities carry information about the location and nature of the damage. Specific information carriers are not only the readings of observed currents and voltages but also the spectral components of these quantities. Attention is paid to the harmonics of the fundamental frequency. However, their information content cannot be sufficient to identify the damage. Moreover, there are modes in which they are compensated or absent altogether because of the disconnection of sources. The article focuses on spectral components of the free process, which is an integral part of the transient process that accompanies any damage. Being the natural frequencies of the observed network, the complex values of the frequencies of the spectral components are the same for all observation locations of a given object. The equations of the linear model of the object are compiled for these locations on the basis of the complex method, however, based only on the own complex frequency value. The spectral analysis procedures that isolate spectral components with their complex values of frequencies and amplitudes are considered. It is demonstrated that the mode of each individual spectral component can be divided into two parts, normal and local. The ratio of local complexes of the same complex frequency value on various sides of the line is uniquely related to the location of its damage. [ABSTRACT FROM AUTHOR]

Medium-voltage electric networks (ENs) with an inefficiently grounded neutral in many countries of the world have significant total lengths, numbering hundreds of thousands and even millions of kilometers. Due to the large length of ENs, various kinds of damage occur in them, the most common of which are single-phase ground faults (SPGFs). Although this mode is quite acceptable, since it does not interrupt the power supply, the search and repair of insulation damage is inevitable. To select a damaged feeder, zero-sequence currents are usually used, which are measured by means of zero-sequence current transformers (ZS CTs). In cases in which such transformers are not available, it is proposed to use an alternative method in which selection is carried out according to the intensity of transients in the simplest sensors installed in the middle part of the feeders. The essence of the method lies in registering high-frequency transient oscillations that occur in sensors when electromagnetic waves with a steep front are incident on them, formed in the EN during the SPGF. The greatest intensity of the transient process occurs in the sensor of the damaged feeder. Information from transmission line measuring devices (sensors) is collected by telemeasurement channels and processed in the simplest way in the processing unit (center). The proposed method is fundamentally suitable for ENs with any method of ineffective grounding of the neutral. An experiment conducted on a 10-kV air power station demonstrated the operability of the proposed method. [ABSTRACT FROM AUTHOR]

This study models the discharge in a rectangular tank which is full of water as PCM. To accelerate the discharge, nanoparticles have been introduced into the water PCM. The overall efficiency of the unit is significantly prejudiced by the fraction and diameter of nanopowders. To ensure accurate modeling, the extended code of FEM was validated. In this exploration, we delve into the impact of ϕ (concentration of additives) and dp (diameter), providing insights into the completion time for each scenario. However, an increase in particle size from 40 to 50 nm leads to an approximately 41.57% rise in discharging time. When considering dp = 50 nm, the influence of ϕ is marginal, leading to an enrichment in the freezing rate of around 10% with an increase in ϕ. Introducing nanopowders with dp of 40 nm causes decline in freezing time by 16.75%. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Drainage & Irrigation Machinery Engineering / Paiguan Jixie Gongcheng Xuebao is the property of Editorial Department of Drainage & Irrigation Machinery Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In current dual porosity/permeability models, there exists a fundamental assumption that the adsorption-induced swelling is distributed uniformly within the representative elementary volume (REV), irrespective of its internal structures and transient processes. However, both internal structures and transient processes can lead to the non-uniform swelling. In this study, we hypothesize that the non-uniform swelling is responsible for why coal permeability in experimental measurements is not only controlled by the effective stress but also is affected by the adsorption-induced swelling. We propose a concept of the swelling triangle composed of swelling paths to characterize the evolution of the non-uniform swelling and serve as a core link in coupled multiphysics. A swelling path is determined by a dimensionless volumetric ratio and a dimensionless swelling ratio. Different swelling paths have the same start and end point, and each swelling path represents a unique swelling case. The swelling path as the diagonal of the triangle represents the case of the uniform swelling while that as the two perpendicular boundaries represents the case of the localized swelling. The paths of all intermediate cases populate inside the triangle. The corresponding relations between the swelling path and the response of coal multiphysics are established by a non-uniform swelling coefficient. We define this method as the triangle approach and corresponding models as swelling path-based ones. The proposed concept and models are verified against a long-term experimental measurement of permeability and strains under constant effective stress. Our results demonstrate that during gas injection, coal multiphysics responses have a close dependence on the swelling path, and that in both future experiments and field predictions, this dependence must be considered.

Copyright of China Rural Water & Hydropower is the property of China Rural Water & Hydropower Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Vector representations and measurements have been used for many decades in the theory and practice of electrical engineering for testing electrical equipment, and the analysis and synthesis of relay protection, automation, and regulation devices. This article discusses various means of processing and visualization of experimental data obtained in the study of complex oscillatory systems and their models. The aim is to determine the most effective method of presenting transient information. The article demonstrates that representing oscillatory processes on a plane with the two systems of axes allows information on all the parameters of the oscillatory process to be taken into account. All presented means to visualize and analyze the composition of transient processes complement each other and offer their full characterization. This article demonstrates the practical applications of the investigated visualization methods. [ABSTRACT FROM AUTHOR]

Transformers are an indispensable component of various types of electrical circuits. Various restrictions are imposed on the transformer switching operation, which are caused by the functional purpose of the systems, their configuration, parameters and characteristics of existing or available switching components or devices and associated transient processes. When the power transformer is switched on asynchronously, current surges in its primary winding, including in modes close to the minimum load, may exceed its nominal current by several times. Such processes are undesirable from the point of view of energy efficiency, electromagnetic compatibility, transformer reliability and the functioning of protection systems. Proper analysis of electromagnetic processes was performed by numerical calculation methods followed by computer modeling using the MATLAB/Simulink software package. The purpose of the study is to highlight the extreme nature of switching current surges of the primary transformer and their dependence on the relative value of the no-load current of the winding. This current, in turn, depends on the slope of the main functional segment of the magnetization curve of the transformer core corresponding to its stationary mode of operation. The research shows that the increase in the idle speed of the transformer causes a directly proportional decrease in the switching current surges of the primary winding of the transformer. At the same time, the difference between the amplitude values of adjacent semi-periodic current surges decreases. It is noted that an increase in the value of the transformer's no-load current is often aimed at stabilizing the burning of the alternating current arc in electric welding installations. They are characterized by a repeated short-term mode of switching, and therefore the determination of the magnitude of switching current surges is relevant here. [ABSTRACT FROM AUTHOR]

When using lead as a primary circuit coolant, certain difficulties arise not only from the side of the reactor plant (structural materials, fuel, etc.) but also from the side of the steam turbine cycle. A feature of the second circuit of a lead-cooled NPP is noted, such as the need to maintain a high temperature of the feedwater in front of the steam generator, caused by its melting/freezing temperature. For the pilot demonstration power unit with the BREST-OD-300 reactor plant, it was decided to use a mixing feedwater heater, which entailed the appearance of a second rise in the feed pump circuit. Due to the lack of electric drive pumps for such high parameters, it was proposed to use a hydraulic turbine driven pump as a feed pump behind the mixing feedwater heater. These pumps have a significant impact on efficiency due to the multistage energy conversion, and there is no recommendation for selecting resistance on the control valve of these pumps. A computational study was carried out to determine the optimal pressure drop on the control valve of the hydraulic turbine drive of the feed pump of the power unit with the BREST-OD-300 reactor plant. Optimal is understood as the ultimate minimum differential at which the valve is able to carry out regulation with specified quality criteria and ensure the lowest energy consumption for its own needs. Recommendations are given for choosing the optimal pressure drop on the control valve of the hydraulic turbine drive of the feed pump of a turbine unit with the BREST-OD-300 reactor. A methodology has been developed for solving problems of optimizing pressure drop in units of complex hydraulic systems. [ABSTRACT FROM AUTHOR]

Probabilistic damage tolerance is a critical method to understand and communicate risk and safety. This paper reviews recent research on the probabilistic damage tolerance design for life-limited parts. The vision of the probabilistic damage tolerance assessment is provided. Five core parts of the probabilistic damage tolerance method are introduced separately, including the anomaly distribution, stress processing and zone definition, fatigue and fracture calculation method, probability of failure (POF) calculation method, and the combination with residual stress induced by the manufacturing process. The above currently-available risk assessment methods provide practical tools for failure risk predictions and are applied by the airworthiness regulations. However, new problems are exposed with the development of the aero-engines. The time-consuming anomaly distribution derivation process restricts the development of the anomaly distribution, especially for the developing aviation industries with little empirical data. Additionally, the strong transient characteristic is prominent because of the significant temperature differences during the take-off and climbing periods. The complex loads then challenge the fatigue and fracture calculation model. Besides, high computational efficiency is required because various variables are considered to calculate the POF. Therefore, new technologies for the probabilistic damage tolerance assessment are provided, including the efficient anomaly distribution acquisition method based on small samples, the zone definition method considering transient process, and stress intensity factor (SIF) solutions under arbitrary stress distributions combined with the machine learning method. Then, an efficient numerical integration method for calculating failure risk based on the probability density evolution theory is proposed. Meanwhile, the influence of the manufacturing process on residual stress and the failure risk of the rotors is explored. The development of the probabilistic damage tolerance method can meet the requirement of the published airworthiness regulation Federal Aviation Regulation (FAR) 33.70 and guide the modification or amendment of new regulations to ensure the safety of the high-energy rotors.

Discharges of different epilepsies are characterized by different signal shape and duration. The authors adhere to the hypothesis that spike-wave discharges are long transient processes rather than attractors. This helps to explain some experimentally observed properties of discharges, including the absence of a special termination mechanism and quasi-regularity. Analytical approaches mostly cannot be applied to studying transient dynamics in large networks. Therefore, to test the observed phenomena for universality one has to show that the same results can be achieved using different model types for nodes and different connectivity terms. Here, we study a class of simple network models of a thalamocortical system and show that for the same connectivity matrices long, but finite in time quasi-regular processes mimicking epileptic spike-wave discharges can be found using nodes described by three neuron models: FitzHugh – Nagumo, Morris – Lecar and Hodgkin – Huxley. This result takes place both for linear and nonlinear sigmoid coupling. [ABSTRACT FROM AUTHOR]

The problem of increasing the reliability of transport units during maintenance and repair in the locomotive depot is considered. The transient processes in the power circuit of the DC electric locomotive with traction motors was studied and a calculation scheme of a DC electric locomotive with the series connected traction motors was presented. When considering the magnetization curve linearization, small increments in the form of the system magnetization characteristic were applied. On the base of those results, it was determined that the duration of the transient process in the traction motor windings of the DC electric locomotives equals tt = 3τ. [ABSTRACT FROM AUTHOR]

• A coupled hydraulic-mechanical-electrical-structural model for hydroelectric generating system is proposed. • The hydraulic-mechanical-electrical transient process is connected with shafting system. • The dynamic response from shafting system at different stages attached to start-up process are scrutinized. • The kinetic property of structure is illuminated compared with motion trait for system under steady operating condition. The operating parameters of hydroelectric generating system vary constantly in the course of transition, meanwhile, the coupled correlations among hydraulic, mechanical, electrical and structural subsystems are convoluted, which makes the vibration of shafting system prominent, as well as affects the safe and stable operation for hydropower station. In this paper, a coupled hydraulic-mechanical-electrical-structural model for hydroelectric generating system is proposed, while the start-up transient process is incorporated into the investigation system, and the dynamic response from shafting system at different stages attached to start-up process is scrutinized numerically, making allowance for the effect of unbalanced magnetic pull with static and dynamic eccentricity. The kinetic property of structure over the start-up process is illuminated, by means of the comparison with motion trait for system under steady-state operating condition. The results indicate that the dynamic feature of rotor and runner is significantly contrasting in different stages affiliated to the start-up scenario, especially for the voltage building-up subdivision. In addition, the response peculiarity from rotor covering the trajectory, vibration amplitude and frequency components, etc., is markedly altered, due to the participation of static, dynamic eccentricity as well as the matching variation on electromagnetic excitation. The trajectory of rotor evolves from a regular circle to a butterfly-shaped curve, and the associated transient displacement intensifies immensely, besides, the 2x frequency component emerges and corresponding dominant role gradually strengthens, accompanied by a developmental amplitude of 1x frequency in spectrum diagram. Relevant research results can provide profitable reference for the analysis of dynamic characteristic on hydropower station through transient conditions. [ABSTRACT FROM AUTHOR]

Escape and level-crossing are fundamental and closely related problems in transient dynamics. Often, when a particle reaches a critical displacement, its escape becomes inevitable. Therefore, escape models based on truncated potentials are often used, resulting in similar problems to level-crossing formulations. Two different types of dynamics can be identified, leading to different kinds of level-crossing depending on the relationship between the damping and the excitation level. The first one ("fast escape") is mainly governed by the initial energy of the system, which is determined through the initial conditions. The second one ("slow escape") is governed by the beatings determined through the relationship between external excitation and damping. An analytic approach for estimating the size and location of the safe basins (SBs) in the plane of the initial conditions (ICs) of a 1-DOF externally excited oscillator is suggested. It enables the identification of the set of ICs where the particle never reaches a certain threshold under the given excitation. The SBs depend on the damping coefficient and the excitation's amplitude, frequency, and phase. Nonetheless, one can describe the essential properties of an SBs in the case of the almost resonant excitation using only two parameters: the forced response amplitude and the damping coefficient ratio to the difference between the natural and the excitation frequencies. Although the analysis is performed for a linear oscillator, it provides insight into the rush erosion process of the SBs ("Dover cliff" phenomenon), described previously only for nonlinear systems. The analysis reveals that the "Dover cliff" phenomenon is related to the decay rate of the transient motion and that it can occur even in linear systems too. From the engineering point of view, the rush erosion of the SBs is critical in noisy environments where devices operating in regions close to the "Dover cliff" are unsafe. Due to its simplicity, the proposed mechanical model might be generic for further analysis of the escape and level-crossing problems considering various nonlinearities (e.g., Coulomb friction, small polynomial-type nonlinearities of the restoring force, or constant restoring force). Possible applications include but are not limited to avoiding collisions for systems with clearances and durability analysis of brittle materials subjected to noisy loads. [ABSTRACT FROM AUTHOR]

Copyright of China Rural Water & Hydropower is the property of China Rural Water & Hydropower Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Today, high-temperature superconducting (HTS) current limiters and transformers allow to limit the surge short circuit current during failure without negatively affecting on the power grid com-plex at the normal operation mode. However, the transition of a superconductor to a resistive state at the moment of current limitation can cause significant heat generation, which can destroy the transformer windings. The research goal is to provide optimal technical characteristics of the HTS transformer to achieve effective short circuit current limitation and prevent thermal breakdown of its windings. To achieve this goal, a mathematical model of a HTS transformer was developed. The presented method considers the material type and geometry of the superconducting tape, the critical parameters of the superconductor (current and temperature), the parameters of the cryogenic liquid, dependence of the resistance and heat capacity of the HTS tape layers on temperature. The simulation model was created in the Matlab/Simulink software. The most important result is the possibility of obtaining optimal elec-trical and thermal parameters of the HTS transformer windings during the short circuit current limitation, as well as ensuring the thermal stability of the superconducting tape at the quench moment. The obtained results are significant in the design and operation of HTS transformers. For efficient and safe operation in the current-limiting mode, it is necessary to take into account heat generation on the transformer windings. It is important for the superconductor returning to the superconducting state without causing significant overheating of the windings.

Background. Railway transport, due to large volumes of traffic, must be serviced in a timely and high-quality manner. One of the main problems in the transportation process is the occurrence of an uncontrolled electric arc between the current collector and the contact wire. The article describes the importance of the problem of studying transients in the occurrence of an electric arc in DC and AC networks. The purpose of the study is to study the temporary transients of the parameters of the electric arc and to identify the natural features of its occurrence. Materials and methods. A mathematical model of the electric arc of the current "current collector – contact wire" using the Simulink Matlab package is considered. Results and conclusions. The occurrence of an electric arc is accompanied by transient current processes, the value of which can reach several hundred amperes, and these currents, together with the current consumed by the load, can damage the contact wire, burning it out. By analyzing the nature of the transition process, it is possible to predict the wear of the pantograph slide in the early stages, which will avoid negative consequences.

New engineering technologies allow the creation of diagnostic devices for predicting the development of acute tissue ischemia of the extremities and determining the residual time until the removal of the tourniquet, and solving these tasks is particularly relevant during military actions. Acute limb ischemia is a sudden critical decrease in perfusion that threatens the viability of the limb. The incidence of this condition is 1.5 cases per 10 000 people per year. Acute ischemia occurs due to the blockage of blood flow in major arteries (embolism, thrombosis, trauma), leading to the cessation of adequate blood supply to metabolically active tissues of the limb, including the skin, muscles, and nerve endings. To address these issues, the article analyzes the changes in the impedance of biological tissue. The introduction and use of the coefficient of relative electrical conductivity, denoted as k, as a diagnostic criterion parameter, are justified. Experimental studies of changes in the coefficient of relative electrical conductivity k were conducted, confirming that the transition from exponential to linear dependencies of the coefficient establishes the degree of viability of the biological cell (tissue) and the moment of occurrence of reperfusion syndrome. It has been established that a deviation of the value of k by 10–15% from its unit value diagnoses the initial process of blood perfusion impairment and the development of ischemic tissue disease. The rate of change of k serves as a criterion for predicting the progression of the disease and as a corrective factor for therapeutic treatment.

The surge is a typical aerodynamic instability phenomenon in the compression system, which can lead to serious consequences such as engine performance degradation and structural damage. A deep understanding of the surge process can support the development of a compressor with a wider operating range. In this paper, an experimental study was carried out and high-responding pressure sensors were used to obtain the aerodynamic instability process and the post-surge characteristics of an axial–centrifugal compressor at design and off-design speeds. The evolution of the flow field and instability behavior before and after the surge were analyzed. The results showed that the inlet temperature change can reflect the aerodynamic instability to some extent, and as the operating condition moves from the choke to surge boundary, the inlet temperature undergoes a sudden increase at a certain condition and further increases with the decrease in mass flow rate. At the design speed, the instability of the combined compressor featured a deep surge with an obvious rotating stall behavior before its inception, and the amplitude of the stall cell was gradually enhanced, finally leading to the surge. At the off-design speed, affected by the stage mismatching, the axial stage mainly worked near the unstable operating condition. Therefore, the compressor successively experiences two modes of mild surge and deep surge, and the rotating stall can also be observed during the surge cycle. [ABSTRACT FROM AUTHOR]

The paper considers issues associated with identifying equipment onboard spacecraft and formalizing the process of monitoring its technical condition. The ambiguity in assessing the technical condition of onboard equipment on the basis of parameters characterizing transient processes is revealed. In this connection, an approach is proposed to estimate the parameters of transient processes using a neural network. The authors set a mathematical problem to develop a model for monitoring the technical condition equipment onboard spacecraft, minimizing the chances of making incorrect decisions about the technical condition in the process of monitoring. A conceptual model is proposed for monitoring the technical condition of onboard equipment extended by the neural-network transformation of telemetry parameters characterizing transient processes. The use of the model in the distributed system for monitoring the onboard equipment of spacecraft helps to eliminate indirect monitoring on the basis of calculated parameters in order to achieve the maximum monitoring reliability. The effectiveness of the proposed approach is shown using the motion control system of a spacecraft as an example. The features of technical condition are estimated according to the telemetry parameters of angular velocities obtained from the sensors. The obtained results indicate the advantages of using multilayer neural networks for generating the additional features of dynamic systems, as well as the possibility of achieving high accuracy in estimating these features, thus providing the full monitoring of the technical condition of onboard equipment. [ABSTRACT FROM AUTHOR]

The effect of distributed and localized axisymmetric impulsive loads on three-layer cylindrical shell elements of rocket airframes is studied. Localized axisymmetric impulsive external loads applied along the directrix of a cylindrical shell simulate an explosion of a superquick-action elongated shaped charge. Finite-element modeling of transient processes in such elements under such loads allows correct selection of the physical and mechanical parameters of cylindrical rocket airframes. A significant effect of the behavior of dynamic loads on the transient processes in three-layer cylindrical elements is demonstrated. [ABSTRACT FROM AUTHOR]

The results of studying pumping stations of service water systems (SWS) used to cool the condensers of high-power steam turbines are described. The features of transient processes during start-ups of pumping units at stations with different configurations and equipment are considered. Such systems are classified according to the transient conditions. The main characteristics of the software in terms of the factors taken into account and the mathematical apparatus used, the features of the processes in the condenser of a steam turbine, the energy characteristics of angular-flow pumps are given. The start-up processes in various SWS systems (with spillways, with cooling towers, with or without control valves) and the limitations of the parameters of starting processes that ensure their successful and safe operation are described. The transient processes are studied using the method of mathematical simulation and taking into account the elasticity of water. [ABSTRACT FROM AUTHOR]

To meet increasingly stringent emission regulations, this study investigates the transient process of a heavy-duty diesel engine equipped with a two-stage turbocharger. The study focuses on analyzing the impact of the EGR system and fuel injection strategy during a transient process of a load increase (20% to 100% in 1 s) at a constant speed (1300 rpm). The research results showed that delaying the opening time of the high-pressure EGR valve from 0.1 s to 0.5 s reduces peak carbon soot emissions by 51.3%, with only a 3.13% increase in NOx emissions. By extending the high-pressure exhaust gas recirculation mixing length, the issue of an excessively high fuel–oxygen equivalence ratio caused by uneven exhaust gas mixing in individual cylinders can be avoided, resulting in a maximum reduction of 47.0% in peak soot emissions. Building on exhaust gas recirculation optimization, further modifications to the main and post-injection strategies led to a 28.1% reduction in soot emissions, a 4.73% decrease in peak NOx emissions, and a minor increase of 1.87% in the indicated fuel specific consumption compared to the single-injection strategy. The significant reduction in soot emissions will provide benefits for public health and environmental sustainability. [ABSTRACT FROM AUTHOR]

The change in the impedance of biological tissue under the influence of voltage is used in the diagnosis and treatment of various diseases. Mathematical models describing physical and biological processes in biological objects are based on electrical substitution schemes. The subject of research of this work was the study of the change in the impedance of biological tissue in the transient process of ionization under the action of DC voltage. An analysis of the known substitution schemes was carried out, the shortcomings of their application were identified when the transient processes of ionization in the tissue under the action of direct current voltage were studied, and the substitution scheme with the introduction of additional resistance was substantiated, both analytically and experimentally. In the work, the bioimpedance method is applied when direct current voltage is applied to biological tissue, taking into account the law of commutation in transient ionization processes. An invasive measurement of the change in impedance with needle electrodes was carried out, and it was proved that the active component proportionally depends on the distance between the electrodes, while the capacitive component remains unchanged. It is shown that the ionization time constant is a criterion parameter and can be used in the diagnosis of the development of ischemic disease of muscle tissue, the change in the state of biological tissue when blood flow is stopped during the application of a tourniquet. It has been proven that the ionization time constant does not change with an unchanged ionic composition of the tissue and can be used in the analysis of the composition of the intercellular space. A simultaneous invasive measurement was performed in two identical places of different limbs, on one of which a hemostatic tourniquet was applied. The obtained results made it possible to conclude that a change in the constant time from 15% to 50% compared to two constant times allows for rapid diagnosis, within 2 minutes, of the state of biological tissue and can be used in the study of the development of diseases associated with ischemia. The results of the study can be used for rapid diagnosis of the state of a biological object and the creation of an inexpensive device for its use in surgery and research laboratories

Optimizing physical training regimens to increase muscle aerobic capacity requires an understanding of the internal processes that occur during exercise that initiate subsequent adaptation. During exercise, muscle cells undergo a series of metabolic events that trigger downstream signaling pathways and induce the expression of many genes in working muscle fibers. There are a number of studies that show the dependence of changes in the activity of AMP-activated protein kinase (AMPK), one of the mediators of cellular signaling pathways, on the duration and intensity of single exercises. The activity of various AMPK isoforms can change in different directions, increasing for some isoforms and decreasing for others, depending on the intensity and duration of the load. This review summarizes research data on changes in the activity of AMPK, Ca2+/calmodulin-dependent protein kinase II (CaMKII), and other components of the signaling pathways in skeletal muscles during exercise. Based on these data, we hypothesize that the observed changes in AMPK activity may be largely related to metabolic and signaling transients rather than exercise intensity per se. Probably, the main events associated with these transients occur at the beginning of the exercise in a time window of about 1–10 min. We hypothesize that these transients may be partly due to putative trigger-like kinase/protein phosphatase interactions regulated by feedback loops. In addition, numerous dynamically changing factors, such as [Ca2+], metabolite concentration, and reactive oxygen and nitrogen species (RONS), can shift the switching thresholds and change the states of these triggers, thereby affecting the activity of kinases (in particular, AMPK and CaMKII) and phosphatases. The review considers the putative molecular mechanisms underlying trigger-like interactions. The proposed hypothesis allows for a reinterpretation of the experimental data available in the literature as well as the generation of ideas to optimize future training regimens. [ABSTRACT FROM AUTHOR]

The latest results of a series researches of the revealed paradox of energy balance disturb and its manifestations in electrical circuits are presented in order to increase the efficiency of the conversion of energy voltage direct current into pulsed energy of other forms, on the example of improving the use energy of the power source of pulsed solid-state laser range finder. It is show, that the efficiency of simultaneous conversion in a load with active linear or nonlinear resistance of the energy, which accumulated in the inductive and capacitive storage, can reach the efficiency of its accumulation. For this the first time offered the aperiodic mode of the transient process in the oscillating circuit use to combined the dual properties of inductive and capacitive energy storages and method of automatically switching their parallel connection during accumulation by them energy in series connection during conversion accumulated energy, particular, into optical pulses in the range finder. In total, proposed method of converting energy voltage direct current into pulsed energy of other forms, mean of objective control and tool of modeling and analyzing the use of energy primary power sources make up a set of measures for increasing energy efficiency separate nodes mobile devices of telecommunications, automation and robotics, what is especially actual in the existing conditions limited energy resources. [ABSTRACT FROM AUTHOR]

This paper studies the multi-objective control of transient process of hydropower plant with two turbines sharing one penstock under combined operating conditions (COCs). Firstly, the model of transient process of hydropower plant is presented. The illustration of four COCs is provided. Then, the multi-objective control strategy of transient process under COCs is designed. The decision variables and objective functions are selected. The control scheme and decision method are determined. Finally, the most favourable superposition time and the most unfavourable superposition time under COCs are determined. The results indicate that the objective function contains three objectives, i.e. spiral case outlet pressures, draft tube inlet pressures and rotational speeds of turbines. The most favourable superposition time under COC-1 can realize that the objectives reach control requirements simultaneously. The most favourable superposition time under COC-2 and the most unfavourable superposition time under COC-1 and COC-2 cannot realize that the objectives reach control requirements simultaneously, but can balance the objectives to the maximum extent. It is unnecessary to distinguish the most favourable superposition time and the most unfavourable superposition time strictly under COC-3. There is no the concepts of the most favourable superposition time and the most unfavourable superposition time under COC-4. [ABSTRACT FROM AUTHOR]

Variable-speed pumped-storage unit (VSPSU) has advantages in flexibility, efficiency, and reliability. It has become a state-of-the-art technology in pumped-storage industry. However, there is little research about the transient process of VSPSU working at a favorable speed command during power regulation. To study the issue, a refined model considering hydraulic–mechanical and electrical subsystems is built in this work. All submodels are created by the authors as individual modules on Simulink platform, and these modules can be easily combined to model different VSPSUs. For the VSPSU that uses a doubly fed induction machine and adopts the fast power control strategy, there are several speed constraints. To satisfy the speed constraints during transient process, the speed command is adjusted to avoid exceeding the allowable speed variation range and eliminate the oscillation caused by the S-shaped region, while being guided by the optimal speed to achieve higher efficiency. The faster the speed command changes, the more rapid the power regulation could be. But fast-changing speed command also leads to larger pressure fluctuations in penstocks. Hence, different schemes of the speed command are compared, and suitable schemes are proposed by comprehensively considering the balance between rapidity and safety. The dynamic model and analysis of favorable speed command can provide support and advice for engineering practice. • Building a refined model of the hydraulic–mechanical–electrical coupling system. • Obtaining optimal speed for guiding speed command to achieve higher efficiency. • Revealing benefits of adjusting speed command in improving rapidity and safety. • Proposing suitable speed command to achieve a balance between rapidity and safety. [ABSTRACT FROM AUTHOR]

Abstract—A change in the non-stationary electromagnetic (EM) signal over the conducting polarizable Earth covered by sea water on measuring lines located in the axial and equatorial regions of the source—a pulsed horizontal electric line (HEL)—is considered. When the HEL operates under pulsed conditions, it creates a galvanic and eddy current in the medium. If the medium affected by the HEL is heterogeneous, both influences lead to the separation of bound charges. After attenuating the impact of an artificial source, relaxation (depolarizing) processes of various nature appear in such a medium, manifesting themselves, in particular, in the form of an EM signal. As a result, the transient process recorded by the grounded line after the pulsed effect of the HEL is at least a superposition of three components: the transient electromagnetic (TEM) signals, galvanically induced polarization (GIP) and inductively induced polarization (IIP). As the contribution of the TEM field component to the overall signal decreases, the IP signal is manifested in the transient process by a change in the time response of the decay, to the point where the signal reverses polarity. As shown earlier by numerical simulations for the axial region of the HEL, the manifestation of the IIP signal at late transient process times, for most of the geoelectric conditions on land, is invisible against the GIP manifestation (Ageenkov et al., 2020). These calculations also show that in the axial region, the GIP signal manifests itself in the form of a deceleration of the transient process rate, and the IDP signal—an acceleration of the decay rate, to the point where the signal changes its sign. Field measurements performed by the aquatic differential-normalized method of electrical prospecting (ADNME), which uses axial electrical installations, record transient processes with a change in the time response of the decay: it becomes more delayed or, vice versa, runs faster and may be accompanied by a change in the polarity of the signal. In other words, measured signals of different forms are observed, which are presumably associated with the manifestation of the GIP or IIP signals. The relevance of the publication lies in the need to explain the results of field measurements performed offshore, to understand the relationship between the course of the transient process and the geoelectric conditions existing in the water area. And in general, to describe the formation of the transient response of the medium in the axial and equatorial region of the HEL for the conditions of aquatic geoelectrics. The calculated signal for axial and equatorial electrical installations with several spacings under the conditions of the sea shelf water area is studied when the installation is located on the surface of and inside the water layer, and on the seabed of the water area—on geological formations. For axial installations, calculations are made of the quantities used in the ADNME: the transient process ΔU(t), the finite difference of the transient process Δ2U(t) and the transformant P1(t)—the ratio of Δ2U(t) to ΔU(t). For equatorial installations, the signal ΔU(t). is calculated. The signals of a two-layered model of the medium with polarizable and non-polarizable bases are compared. [ABSTRACT FROM AUTHOR]