Stable Mode Operation Research Articles

Comprehensive index of compound blast furnace smelting

An actual direction in the development of blast-furnace smelting technology is the implementation of stable operating modes of blast furnaces in terms of the parameters of the used charge materials and hot combined blast. For this purpose, complex indicators characterizing the thermal and reduction modes of blast furnace smelting, and integral indicators of iron ore raw materials (IORM) quality are being studied. The object of the study is the blast furnace process under the conditions of PJSC NLMK. The database of the main indicators of the operation of blast furnaces No. 4, 6 and 7 for the period 2013–2018 was analyzed. The furnaces operate under raw material conditions, with similar combined blast parameters and coke consumption. When the consumption of natural gas, pulverized coal and process oxygen changes, the values of the degree of compensation (the ratio of the consumption of reducing additives to the consumption of process oxygen) are in the range of 0.9–1.1. This provides a constant level of hearth heating, stability of the gas-dynamic mode of melting and coke consumption. At the same time, the different level of development of the processes of indirect (Ri) and direct (rd) reduction in blast furnaces No. 4, 6 and 7 makes it possible to perform correct studies of the features of blast furnace smelting in a wide range of Ri and rd values. It has been established that under the conditions of stable operation of blast furnaces on raw materials from sinter and pellets using combined blast, the type of dependence of the sulfur and silicon content in pig iron on the values of the integrated iron ore raw materials quality index is determined by degree development level of direct reduction processes rd. It has been established that the mode of blast furnace smelting with natural gas, pulverized coal and process oxygen, characterized by the level of rd values less than 20–25 %, is distinguished by the presence of a pronounced extreme dependence of coke consumption and productivity on the parameters of the combined blast.

DETERMINATION OF THE ZONE OF THERMAL INFLUENCE OF FIRE BY RESULTS INSPECTION OF FLOOR STRUCTURES

The results of the study of the technical condition of 14 round-hollow slabs according to the series II-03-02 within the basement of two entrances of a residential building after a fire, lasting about 8 hours. More than 40 years passed from the commissioning of the building to the fire, and all this time the basement slabs were in a non-aggressive environment, but with high relative humidity, which had a positive effect on increasing the concrete strength of typical slabs. Inspection of slabs in adjacent rooms for a long time of operation did not reveal significant defects from their humidification and insufficient thermal insulation properties of the floor above the basement.
 In the inspection area, some floor slabs above the basement were found to be defective due to high temperatures, which reduced their rigidity.
 The information obtained from the survey is necessary to perform verification calculations to determine the load-bearing capacity and stiffness of the floor slabs and compare them with the data from the survey results. The data of test calculations are also needed to substantiate the need for reinforcement work on the slabs, to ensure their further normal operation on the operating loads on the ground floor.
 To analyze the impact on the deflections of slabs of constant and payloads, some of their actions are considered and verified calculations of the deflections of the floor slabs for the four adopted separate stable modes of normal operation.
 A histogram of the change in the actual deflections of the floor slabs above the basement is constructed, according to the analysis of which the area with the largest deflections is clearly traced, which indicates the location of the highest temperatures in this place. That is, the level of vertical deformations of floor slabs can determine the relative temperature distribution within them. Deflections of slabs due to high temperatures should be considered as damage that interferes with normal operation and significantly reduces the durability of slabs.
 Considered after the fire condition of the slabs showed that in the absence of impact on them payloads, the obtained additional temperature deflections are greater than the calculated, which are obtained by verification calculations for the action of full operating loads.
 Also offered different options for strengthening both the slabs themselves and the seams between them, for their joint work on different combinations of loads.

Studies on of phase error oscillations in a class of third-order optical phase locked loop and its effect on a slave optical phase locked loop

Dynamics of a third-order optical phase locked loop (OPLL) with a resonant type loop filter (LF) has been studied analytically and numerically. The range of stable synchronous operating zone of such OPLL has been estimated analytically in system and signal parameters and obtained predictions are in good agreement with numerical results. Beyond the stable region, it is found that chaotic oscillation of phase error occurs through a sequence of period doubling bifurcation. In addition to this, tracking of such periodic as well as chaotic dynamics of third-order OPLL by another OPLL in master-slave configuration has also been explored here. The tracking is possible by slave OPLL within a very short range of effective frequency offset by keeping other design parameters within the stable mode of operation. The synchronization of the master and slave OPLLs has been studied in generalized sense by considering auxiliary system. The study is very important and helpful for optical signal processing and also in chaos-based secure communication.

Spike type of stall inception in the tandem rotor

There are two known mechanisms of inception of rotating stall in the compressor, modal wave inception and spike inception. However, the stall inception mechanisms for a tandem-rotor have not been explored so far in detail. The paper explores the unsteady behaviour of the tandem rotor. Unsteady casing pressure measurements are carried out with the help of seven equispaced unsteady pressure sensors. The casing pressure traces are analysed using wavelet transforms, fast Fourier transform, discrete spatial Fourier series, travelling wave energy method and correlation techniques to identify the nature of the stall cells. The changes observed in the stall cells during the transition from the stable mode of operation to the fully stalled mode and back from the stall regime to the stable operating condition are investigated in detail. It is observed that the stall incepts in the form of a low-intensity spike, which later evolves as a long-length scale disturbance in the fully developed stall region. The initial stall disturbance is found to be rotating with 75% of the rotor speed. The speed of the stall cells is reduced to 61% of the rotor speed in a fully developed region. The number and size of stall cells increase as the mass flow is throttled. The number and size of the stall cells are strongly coupled with the leading-edge incidence pattern. During the transition from the stall regime to the stable operating condition, the mass flow of the compressor increases, which reduces the flow incidence angle of the tandem rotor. Thus, the separation region shrinks during this transition leading to a reduction in the size of the stall cells. The stall in the tandem-rotor is primarily associated with the tip leakage flow. The rotating disturbances in the tandem-rotor originate due to the leading-edge flow separation of the forward rotor blade. Leading-edge separation of the aft rotor, which arises due to interaction of the forward rotor tip leakage vortex, is effectively suppressed with the help of the gap-nozzle flow. For a comprehensive unsteady analysis, the different techniques need to be used in combination.

New results from the CUORE experiment

The Cryogenic Underground Observatory for Rare Events (CUORE) is the first bolometric experiment searching for neutrino-less double-beta (0[Formula: see text]) decay that has been able to reach the one-ton scale. The detector, located at the Laboratori Nazionali del Gran Sasso in Italy, consists of an array of 988 TeO2 crystals arranged in a compact cylindrical structure of 19 towers. Following the completion of the detector construction in August 2016, CUORE began its first physics data run in 2017 at a base temperature of about 10 mK. Following multiple optimization campaigns in 2018, CUORE is currently in stable operating mode. In 2019, CUORE released its second result of the search for 0[Formula: see text] corresponding to a TeO2 exposure of 372.5 kg[Formula: see text]⋅[Formula: see text]yr and a median exclusion sensitivity to a 130Te 0[Formula: see text] decay half-life of [Formula: see text] yr. We find no evidence for 0[Formula: see text] decay and set a 90% C.I. Bayesian lower limit of [Formula: see text] yr on the 130Te 0[Formula: see text] decay half-life. We present the current status of CUORE’s search for 0[Formula: see text]. We give an update of the CUORE background model and the measurement of the 130Te two neutrino double-beta (2[Formula: see text]) decay half-life. Eventually, we show the preliminary results on half-life limits from the analysis of 130Te 0[Formula: see text] and 2[Formula: see text] decay to the first 0[Formula: see text] excited state of [Formula: see text]Xe.

Scheduling networked control systems under known data loss patterns

This paper deals with the design of scheduling logics for Networked Control Systems (NCSs) whose shared networks have limited communication capacity and are prone to data losses. We assume that an upper bound on the number of consecutive data losses is known a priori, and present an algorithm to allocate the network among the plants of the NCS such that stability of each plant is preserved under all admissible data loss signals. The main apparatus for our analysis is a switched systems representation of the individual plants in an NCS. We rely on matrix commutators (Lie brackets) between the stable and unstable modes of operation of the plants to guarantee stability under our scheduling logics.

ОРГАНІЗАЦІЯ АСИНХРОННОЇ КОМУТАЦІЇ ТРАНСФОРМАТОРА З УРАХУВАННЯМ ІНЕРЦІЙНОСТІ ЕЛЕКТРОМАГНІТНИХ ПРОЦЕСІВ

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. The purpose of the study is to organize the switching of the transformer in such a way that it achieves its output to a stable mode of operation with a minimum amplitude of the input current and the duration of the transition process, without extreme manifestations in the switching process.Algebraic, graphic, and simulation-visual aspects of the analysis of the processes occurring during power transformer commutation are considered in the work. It is shown that the repeated switching on of the transformer can lead to a significantly larger current surge in the primary winding compared to the first switching on, and the reason for this phenomenon is the magnitude of the magnetic flux at the time of repeated commutation. It is shown that the value of the flux and its change depends on the amount of load on the secondary winding, and lower values of the load correspond to higher values of the rate of decline of the magnetic flux of the transformer core and vice versa. The following switching algorithm of the transformer is recommended, in which each subsequent switching on of the transformer will start with a close to zero value of the magnetic field flux

Research and Analysis of Stable Operation Mode of Generating Unit for Autonomous Consumer in Microgrid System

Research and Analysis of Stable Operation Mode of Generating Unit for Autonomous Consumer in Microgrid System

Experimental study of an internal combustion engine fueled by a low-calorific value producer gas

This paper describes an experimental study of the operation of an internal combustion engine of fueled by a low-calorific value gas. The main operating parameters of low-power ICE were determined. Efficiency was also evaluated when the ICE was converted to operate on producer gas. In the experiment, it was shown that the engine reached a stable operating mode under load and data on the temperature and exhaust gases composition were obtained. According to our estimates, in the steady-state operation of the internal combustion engine with a load, the efficiency factor was about 22 %. When using the model gas, the from generator output power, was about 30-40 % of the nominal value, under variable load conditions. However, it was found that in steady-state operation, the power of the internal combustion engine was 40-55% of the nominal value.

The relative intensity noise of a vertical-cavity surface-emitting laser with a fiber Bragg grating external cavity

The research deals with the topical problem of stabilizing the optical parameters of a single-mode vertical-cavity surface-emitting laser. A solution to the problem is proposed by forming an external cavity based on a Bragg grating induced into an optical polarization-maintaining fiber. In this experimental research, the authors estimated the contribution of an external cavity to the relative intensity noise of a vertical-cavity surface-emitting laser. The stability of the laser generation with a varying phase of back reflections at various pump currents is investigated. The relative intensity noise of laser radiation in the pump current range of 1.1–6.3 mA is estimated using a photodetector with a bandwidth of 8.5 MHz. The phase change of the back reflections was carried out by shifting the optical fiber end with a 100 nm step. As a result of the research, it was obtained that the vertical-cavity surface-emitting laser with such an external cavity shows a stable emission in the current range of 1.8–3.2 mA. However, one can observe instability with constant switching between adjacent longitudinal modes outside this range. The most stable laser operation mode with an external cavity against a change in the phase of back reflections is registered at a pump current of 2.78 mA. Utilizing an external cavity with the fiber Bragg grating made it possible to reduce the relative intensity noise from 7.2∙10–10 1/Hz to 1.5∙10–11 1/Hz in the currents range 1.86–3.2 mA. The study can be useful in applications that require an optical radiation coherent source with a low relative intensity noise level (such as coherent optical communication or fiber-optic sensors).

Dynamics features of a resonant vibromachine with self-synchronizing inertial vibroexciters in the presence of vibration limiter

The work is devoted to the problem of ensuring the near-resonance vibration modes stability of the technological vibromachines at fluctuating mass of processed material. Vibrations of the machine are excited by two self-synchronizing inertial vibroexciters driven by asynchronous electric motors rotating in opposite directions. A planar model of a vibromachine on a linear elastic suspension is considered. The interaction of the machine working element with the processed material is described using the added mass and viscous friction forces proportional to the material mass. To expand the frequency range of vibration exciter self-synchronization the possibility of using an additional elastic limiter is considered. The limiter is mounted between the working element and the machine foundation with a predetermined initial clearance. The modes of the working element vibrations and vibroexciter self-synchronization are analyzed depending on the change in the material mass and the initial clearance. It is found that the introduction of the elastic limiter allows to significantly reduce the sensitivity of the vibration amplitudes to material mass changes in the resonant frequency range, and also leads to stabilization of the mutual phase of vibration exciters rotation. A decrease in the initial clearance leads to an expansion of the stable operating modes frequency range, at the same time the vibration amplitudes decrease.

Electron gun and collector for RAON EBIS charge breeder

A heavy-ion accelerator facility, called RAON, is being constructed in Korea. RAON is a large scale experimental facility for basic science research through nuclear physics experiments using various rare-isotope (RI) beams. An Electron Beam Ion Source (EBIS) will be utilized as a charge breeder in the isotope separation on-line (ISOL) system of RAON. The electron gun (e-gun) and electron collector are essential components of the EBIS to charge-breed the RI beams. The e-gun, a magnetically immersed type, has been designed to generate electron beams with currents up to 3 A. The material of the cathode is IrCe, which provide a higher current density and longer lifetime than the LaB6 cathodes. In addition, the collector which can dissipate electron beam power up to 20 kW has been designed and built. A test bench has been designed and constructed to commission the e-gun and collector sub-systems. The test bench is equipped with a negative high-voltage platform, called a cathode platform, to provide an independent electron beam current loop. The control system was also designed and implemented to be able to control two different platforms, such as the cathode and ground platforms, using the NI LabVIEW hardware and software. The experimental goals of the tests described in this paper are to generate and transport to collector 2 A electron beam, and to demonstrate a stable operation mode with electron beam width of 50 ms and a repetition rate of 10 Hz. These goals have been determined for the first charge breeding experiment, which is to obtain the charge-bred beam of Cs33+, in the future. This paper presents the electron gun and collector sub-system of RAON EBIS, including the cathode tests, the simulation results, and the electron beam experiment.

DYNAMIC CONTROL OF HEAT EXCHANGE PROCESSES FOR TRIGENERATION POWER SYSTEMS WITH FUEL CELLS

The article considers the issues related to the development of energy technologies based on trigeneration with the use of fuel cells, which is expedient to use for additional generation of electrical energy. The possibilities of fuel cells to integrate them into traditional energy systems are shown; technological schemes using PEMFC, PAFC, and MCFC fuel cells are given. Maintaining a stable operating mode depends on temperature stability, so models of heat exchange processes are given and calculations of dynamic parameters for process stabilization under various external influences and dynamic control correction schemes are presented. The tools MatlabSimulink are used as a research tool.

Investigation structure and properties of wire from the alloy of AL-REM system obtained with the application of casting in the electromagnetic mold, combined rolling-extruding, and drawing

The paper presents the results of studies of the structure and properties of a wire with a diameter of 0.5 mm from an alloy of the Al-REM system with a rare-earth metal content of 7–9%. Wire obtained as a result of the implementation of the technology of its manufacture using the methods of casting into an electromagnetic mold (EMM), continuous extruding, and drawing. The rheological properties of the metal of continuously cast round billets from the experimental alloy obtained using an electromagnetic mold are determined. The modeling and analytical assessment of the possibility of carrying out the process of combined rolling-extruding (CRE) of such billets in a closed box-type roll groove of a continuous extruding unit are carried out. The features of metal shaping have been studied. The temperature-speed and technological parameters were found at which the CRE process can be carried out in a stable mode of operation. Data have been obtained for the forces acting on the die and rolls during rolling-extruding. The results of experimental studies of the process of obtaining longish deformed semi-finished products from an experimental alloy on the laboratory unit CRE-200 and the pilot plant unit CRE-400 are presented. The structure of the metal has been studied; data on the ultimate tensile strength, yield strength, relative elongation, and electrical resistance of hot-extruded rods and wires in cold-worked and annealed states have been obtained. It was found that the proposed processing modes make it possible to obtain by the method of combined rolling-extruding rods with a diameter of 9 mm in industrial conditions from longish billets with a diameter of 18 mm, cast by means of EMM. Wire in a cold-deformed and annealed state with a diameter of 0.5 obtained by drawing from the rods with a diameter of 9 mm from an experimental alloy of the Al-REM system containing 7–9% rare-earth metals with the required physical and mechanical properties.

Stability of Heat and Energy Characteristics of Refrigerating Units as a Condition of Quality Increase of Agricultural Production Storage

This article provides information about the importance of stable thermal operating modes of refrigeration machines in the condition of changes in the thermal load on the compressor. We also consider the problem of the minimum energy consumption of refrigeration machines. These two parameters characterize the storage quality of agricultural products in refrigeration machines. It is shown that the temperature stability of the cooling chambers and the minimum energy consumption of the cooling process determine the refrigerator efficiency and, ultimately, the production cost. The article proposes continuous monitoring of the heat and energy indicators of refrigerators. These indicators are recorded and after the set period of operation, control and verification measurements of the control refrigeration machine’s heat and energy indicators are performed. The convergence or divergence of these indicators is used to evaluate the stability of the cooling chambers’ temperature regimes and the specific energy consumption. We also consider the influence of time on the performance of the compression refrigeration machine changes and methods of current technical condition diagnostics. If the deviations are insignificant, the program goes through the cycle to the beginning of monitoring and after a set period of time again automatically performs control measurements and evaluation of deviations. In the case of significant deviations, the decision-making subroutine is activated: either to operate the refrigerator further; perform its maintenance; suspend its operation; or replace it.
 Keywords: refrigeration units, cooling, heat and power characteristics, management controller, storage quality of agricultural production

Optimization of reservoir operating curves and hedging rules using genetic algorithm with a new objective function and smoothing constraint: application to a multipurpose dam in Morocco.

Long-term operation optimization of multipurpose reservoirs is highly important in arid and semi-arid countries challenged by climate change. This paper suggests an objective function combining two competitive shortage indicators for multi-objective reservoir operation optimization. An improved genetic algorithm including a smoothing constraint, reducing infeasible fluctuations of the operation policy, is developed to solve this problem. Operating curves were optimized jointly to hedging factors aiming at avoiding severe droughts and high damages for users. The proposed function was compared with the conventional objective function of minimizing the sum of squared deviations (SSD) between releases and demands. Different combinations of weights of the objectives linked to the Moroccan reservoir were studied. The proposed objective function yields to improved results in terms of computation requirements since it converges quicker and it leads to better supply performance. For drinking water use, the frequency of shortage was reduced by 66% and the maximum deficit by 14% whereas for irrigation the frequency of shortage was curtailed by 6%. The operating curves obtained by the developed optimization model were then compared with static operating rule curves simulated in RIBASIM. The superiority of variable optimized rule curves was proven compared with stable operating mode over time.

Determination of dynamic properties of the caterpillar drive of hydraulic reclamation machines and the method of articulated attachment of the working body of the trenchless pipelayer

Objective. The objective of the study is to determine the requirements for various devices of hydraulic reclamation machines, which are widely used in the construction of canals and drains, to maintain a given slope, as well as the calculation of the executive mechanism that serves to eliminate the oscillating movement of the working body relative to the line of the specified slope.Methods. A mathematical description of the vibrations of the working body for caterpillar hydraulic reclamation machines with mounted working bodies is given.Results. The article presents the results of research to identify the main factors affecting the oscillations of the working body of caterpillar reclamation machines. As a result of theoretical and experimental studies, it was found that when a caterpillar machine with a rigid undercarriage crosses single and multiple irregularities, the movement of the cutting edge of the rigidly mounted working body is graphically depicted by sinusoidal curves. The obtained dependencies allow conducting calculations of the automatic system of maintaining the specified slope and establish the area of stable modes of system operation. A geometric method for optimizing the hinge linkage of the working body of trenchless pipelayer is presented.Conclusion. The proposed methods of improving the performance of caterpillar hydraulic reclamation machines with mounted working bodies when moving on uneven ground surfaces can be used to create a wide class of mounted earthmoving machines, both with passive and active working bodies.

ШВИДКОДІЮЧИЙ АДАПТИВНИЙ ЗАХИСТ ВІД КОРОТКИХ ЗАМИКАНЬ В ЕЛЕКТРИЧНИХ МЕРЕЖАХ MICROGRID З РОЗПОДІЛЕНОЮ ГЕНЕРАЦІЄЮ

Protection against short circuits in microgrid networks with distributed generation is proposed, in which the power of the power sources and loads are constantly changing, which leads to a change in the sensitivity of relay protection. The response current of the proposed protection automatically adapts to the current value of the line operating current. The protection includes measures to block its action in the event of short-term interference in current circuits. Protection is installed on both sides of the line and protects the entire line, provides a stable mode of operation of the network due to the quick shutdown of short circuits. The algorithm of operation and the scheme for implementing protection are given. The protection operation was tested using the parameters of the real short circuit mode. References 7, figures 3.

Модернизация насадочных ректификационных колонн с применением математической модели разделения многокомпонентной смеси

The scientific and technical problem of mathematical modeling and calculation of separation of hydrocarbon mixtures in industrial columns with chaotic and regular nozzles is solved. Multicomponent transfer is calculated using a matrix of volumetric mass transfer coefficients, and the reverse (longitudinal) mixing of steam and liquid flows by Pekle numbers with back-mixing coefficients. The task of developing options for upgrading the stabilization column of the oil and gas condensate mixture at an oil refinery is considered. Calculated profiles of concentrations of key components in the mixture are presented. The required height of the nozzle layer has been determined. After upgrading the column with a new nozzle, a stable mode of operation of the unit is provided in the specified range of loads and the composition of the mixture. We also solved the problem of designing two industrial columns in the technological scheme for the separation of benzene from stable condensate (gasoline fraction). As a result of calculations based on a mathematical model, the operating and structural characteristics of columns with the use of chaotic metal nozzles "Injekhim-2012"were established.

Visual experimental investigation on stable operating process of the plane-radial rotating detonation engine

Using visual observation methods, assisted by synchronous measurement of dynamic pressure and ion tracks, the flow field structures of stable operating modes in plane-radial rotating detonation engine (RDE) are revealed, and the influences of injection conditions on the RDE stable operating range are analyzed. The flow field structures of single-wave mode, symmetric dual-wave mode and triple-wave mode are observed. Typical structures such as rotating detonation wave (RDW), oblique shock wave, combustion products, deflagration surface and contact discontinuity are obtained in the flow fields. Obvious reactants pre-combustion ahead of detonation wave is found in the combustor, and low-frequency oscillation phenomenon is gained under specific conditions. With the increase of wave-head number in combustor, the detonation-wave height and parameters decrease. The RDW propagating velocity and pressure peak are higher in single-wave operating mode, but the flow fields in multi-wave mode are more stable. Both the RDW velocity and pressure peak increase generally with equivalence ratio. Keeping the equivalent ratio (ER) fixed, as the mass flow rate increases, the number of detonation wave in combustor increases, and the operating mode transforms from single-wave mode to multi-wave mode. Keeping the mass flow rate fixed, when the equivalent ratio deviates from stoichiometric ratio, the operating mode varies from multi-wave mode to single-wave mode. Additionally, with the mass flow rate increasing, the ER upper and lower limits of multi-wave mode decrease linearly, and the operating range of dual-wave mode remains unchanged. Mass flow rate has little influence on the ER lower limit of the RDE stable operation, which is approximately ER=0.55 in this structure.