Steady-state Mode Research Articles

Numerical modeling of an inductively coupled plasma torch using OpenFOAM

A customized code using the free and fully open-source CFD software package OpenFOAM was developed to simulate a two-dimensional axisymmetric model of an inductively coupled plasma torch. To efficiently calculate the high-frequency magnetic fields generated by the inductive coil, a technique based on the vector potential formulation of Maxwell’s equations was implemented using the block coupled matrix solver provided by the foam-extend toolbox. While the fluid equations for the inner torch region are solved under the assumption of a laminar flowing argon plasma under atmospheric pressure and local thermodynamic equilibrium conditions, the electromagnetic equations are solved on an overlapping mesh extended far outside the torch. Moreover, a novel technique for initializing the plasma solver by separately precomputing the velocity and temperature fields is presented. Using this approach our plasma solver can run in both steady-state and transient modes. The implementation has been validated by means of analytical methods, and the simulation results of the Tekna-PL50 plasma torch have been compared against literature data. The results obtained using the OpenFOAM code are in good agreement with those of the commercial CFD codes.

Aircraft Turbine Engine Automatic Control Based on Adaptive Dynamic Models

Abstract One of the most perspective development directions of the aircraft engine is the application of adaptive digital automatic control systems (ACS). The significant element of the adaptation is the correction of mathematical models of both engine and its executive, measuring devices. These models help to solve tasks of control and are a combination of static models and dynamic models, as static models describe relations between parameters at steady-state modes, and dynamic ones characterize deviations of the parameters from static values. The work considers problems of the models’ correction using parametric identification methods. It is shown that the main problem of the precise engine simulation is the correction of the static model. A robust procedure that is based on a wide application of a priori information about performances of the engine and its measuring system is proposed for this purpose. One of many variants of this procedure provides an application of the non-linear thermodynamic model of the working process and estimation of individual corrections to the engine components’ characteristics with further substitution of the thermodynamic model by approximating on-board static model. Physically grounded estimates are obtained based on a priori information setting about the estimated parameters and engine performances, using fuzzy sets. Executive devices (actuators) and the most inertial temperature sensors require correction to their dynamic models. Researches showed, in case that the data for identification are collected during regular operation of ACS, the estimates of dynamic model parameters can be strongly correlated that reasons inadmissible errors. The reason is inside the substantial limitations on transients’ intensity that contain regular algorithms of acceleration/deceleration control. Therefore, test actions on the engine are required. Their character and minimum composition are determined using the derived relations between errors in model coefficients, measurement process, and control action parameters.

Criteria for the existence of established modes of power systems

This article considers the criteria for the existence of established modes of power systems. Nonlinear nodal equations of steady-state modes are presented, which have many solutions or do not have any physically realizable solutions. Criteria for the existence of solutions are given based on derivatives of power losses depending on the parameters of the power system modes. Equivalent circuit of the electrical system was performed using the South-Western MEN (MAIN ELECTRIC NETWORKS). The paper highlights the results of calculations of steady-state modes of the electrical system at weighted values of node 12. The maximum normal modes of electrical systems for the power of nodes was determined by the criteria are set .

Effect of size fractioned alginate-based transparent exopolymer particles on initial bacterial adhesion of forward osmosis membrane support layer

In the forward osmosis (FO) process, biofouling is well pronounced on the active side where wastewater and seawater are used as feed and draw solution, respectively. However, the biofouling tendencies within the support layer are not clear. Therefore, the objective of this study was to investigate the effect of TEP pre-conditioning on hydophobicity and initial bacterial attachment of FO membrane support layer. Two structurally distinct FO membranes from different manufacturers were pre­conditioned by soaking in artificial sea water filtrates containing size fractioned TEP. The conditioning solution pre-treated with a 0.4μm pore size filter, contributed to the highest bacterial adhesion rates during bacterial attachment testing in both steady state and cross-flow mode in a lab-scale FO system for both membrane types. CTA-ES support exhibited higher numbers of adhered bacteria when compared to PA-TFC support in a steady state. Conversely, in cross-flow lab-scale testing, a negative impact of fouling on PA-TFC was more apparent than the CTA-ES membrane. This was attributed to the higher porosity and surface roughness of the PA-TFC membrane. Overall, our findings reinforce the potential impact of hydrodynamics conditions and membrane properties on the fouling behavior of FO membrane support layer.

О возможности получения суперсверхкритических параметров пара на АЭС с реакторами на быстрых нейтронах с использованием неядерного перегрева пара

The objective of this paper is the determination of the most efficient variant of thermal scheme modification of NPP with BN-1200 reactor from the standpoint of thermodynamic. To solve the problems of NPP thermal scheme modeling the authors have used CAD software package United Cycle, which is designed to solve problems, determine the optimal structure and equipment components of the thermo-energetic facility, and calculate steady-state operation modes. The results have shown that implementation in BN-1200 reactor thermal scheme of steam compression up to 30 MPa and its further intermediate non-nuclear (firing) superheating after high-pressure cylinder the unit`s electrical capacity has increased by 50% and net efficiency increased by 5% which leads to the substantial increase of cycle`s thermodynamic effectiveness.

Modeling of Variable Speed Wind Turbines with Doubly Fed Induction Generator for Studying Steady State Operation (Dept.E)

Wind energy conversion has emerged as a viable alternative to meet the increased demand for energy resources in recent years. Wind (arms interconnected to power system bring new challenges to power system op eration. It is imperative to study the impact of variable speed wind turbine coupled to doubly fed induction generator DFIG on utility grid op eration. A mathematical model has been developed to evaluate the steady state performance of the variable speed wind energy conversion system with DFIG. In addition a steady state converter (rectifier-inverter) model as a function of siring angles of the rectifier and inverter is developed and used directly to calculate the influence of DFIG on power system operation through power flow solution. These units are modeled as P-Y bus(es) to manage the reactive power generation inside the wind farmi. The paper presents and validates a model of DFIG suitable for operation in steady state mode and not only able to support voltage by feeding reactive power but also to fulfill grid requirement. The p roposed algorithm is imp lemented and applied to the IEEE 26-bus system and the number of the equivalent wind turbines generating units WTGU at each generating bus is demonstrated and injected as P-V bus(es). The impact of WTGUs on active and reactive power of own generating bus(es) and slack bus at different wind speeds is also investigated.

Analysis of Steady-State Oscillations in an Autonomous Oscillator under Multi-Frequency Excitation

The analysis of the behavior of an oscillator under multi-frequency excitation is considered in the paper. The investigation is based on the phase macromodel. The paper shows that three steady-state modes can exist in oscillator under multi-frequency excitation. The synchronized (locked) mode can be defined as the coincidence of the oscillator fundamentals with the excitation fundamentals in the region of sufficiently large excitation magnitude. The unsynchronized (unlocked) mode exists outside the synchronized region and its spectrum contains additional intrinsic fundamental besides the excitation ones. Singular points mode in some isolated points outside the synchronized region is characterized by the equality of the number of the oscillator fundamentals with the number of the excitation fundamentals. Performed numerical experiments confirmed the appearance of bifurcation points while transition of oscillator into the synchronization mode. The existence of singular points outside the synchronization region and their isolated character was also experimentally demonstrated. The problems of finding a steady-state solution of the phase equation of an excited oscillator by the Harmonic Balance (HB) method are considered. It is shown that main difficulties are connected with the presence of linear term in the steady-state solution. A transformation is proposed to provide the formation of HB equations for the phase micromodel in a standard form. Additional difficulties of HB simulations of synchronized oscillator phase equations are discussed.

Dynamic Simulation Control in a Cryogenic Distillation Column

Chemical industry has a high demand for ethylene quantity, especially with high quality. This paper discusses dynamic simulation models of an ethaneethylene high-pressure cryogenic rectification column with Unisim Design process simulator software. Distillation is one of the most essential technologies in chemical industry, it is important that the operation of the procedure can be modeled not only in steady-state mode but also in a dynamic way. The goal during this study is to make simulations with system-controlling and to investigate the effect the disturbance on the behavior of the columns.

Mathematical modeling start-up and steady state modes of asynchronous motors operation with capacitive compensation of reactive power

Mathematical modeling start-up and steady state modes of asynchronous motors operation with capacitive compensation of reactive power

Polymeric Membrane Sensors for Batch and Flow Injection Potentiometric Determination of Procainamide

Three new potentiometric membrane sensors responsive to procainamide hydrochloride (PR) were constructed and their general performance characteristics were determined. The sensors were constructed from PR ion-association complexes with tetraphenylborate (NaTPB) (1), phosphomolybdic acid (PMA) (2) and phosphotungstic acid (PTA) (3) as exchange sites in a polyvinyl chloride (PVC) matrix. The sensors exhibited stable, rapid and near-Nernstian properties for PR at concentrations of $1\times 10^{{-2 }}$ – $4\times 10^{-6}$ , $1\times 10^{-2}- 5\times 10^{-6}$ , $1\times 10^{-2}$ – $6\times 10^{-6}$ M at 25 °C with cationic slopes of 58 ± 0.5, 57 ± 0.5 and 56 ± 0.5 (mV/decade) for sensor 1, 2 and 3 respectively. The response time of the sensors was 20s in the optimum pH range of 4-8. The sensors were used in steady state and flow injection mode (automated system). Method validation revealed the sensors have high selectivity, low detection limits, long life, wide dynamic ranges as well as high accuracy and precision. Direct determination of 5- $2000~\mu \text{g}$ /ml of PR in solution returned average recoveries of 98.5%, 99.0% and 98.5% and mean relative standard deviations of 1.6%, 1.6% and 1.8% at $200.0~\mu \text{g}$ /ml for sensor 1, 2 and 3 respectively. Further, detection of procainamide in spiked urine exhibited favorable relative standard deviation (1.60-1.76%) and high recovery (98.83-99.26%). The sensors were used as end-point indicators for titration of procainamide with NaTPB.

Особливості аналізу фізичної стійкості усталених режимів електричних систем змінного струму

Особливості аналізу фізичної стійкості усталених режимів електричних систем змінного струму

Accuracy Increase of Discrete Sensors With Time Delay

The discrete sensors of continuous physical quantities are widely used in various technical systems. Real sensors have a considerable inertia and they operate in the conditions of random noises, therefore, they include the analog-to-digital interface. This interface creates discrete values of the input signal and suppresses the influence of random noises almost completely with application of the antialiasing filter. However, the discrete values are formed on the output of the analog-to-digital interface with some time delay. Therefore, the digital sensors have a large error, caused by this delay. In this article to eliminate this error an astatic high-speed discrete corrector is proposed. The error of the corrected discrete sensor is equal to zero at the steady-state mode, if the degree of the input polynomial signal is one unit less than the astatism order of the used corrector. It is supposed that the time delay of the discrete sensor is multiple to the sampling period of the analog-to-digital interface. To determine transfer functions of the discrete sensor and the astatic discrete corrector the formulas are obtained. The operation algorithm of the astatic high-speed discrete corrector is determined on the basis of its transfer function. The efficiency and feasibility with application of digital device of the proposed corrector is illustrated by the example of the sensor design with the astatism of the second order. The obtained results can be used in the development of highly precise discrete sensors of various physical quantities.

An Asymptotic Method for Solving the Problem of Identifying a Curvilinear Crack in an Elastic Layer

We solve an inverse geometric problem of identifying an internal curvilinear defect in an orthotropic elastic layer. Defect parameters (location, depth, size, orientation) are determined based on an acoustic analysis of displacement fields and their characteristics measured on part of layer’s upper boundary. We consider a steady-state oscillation mode and the two cases of antiplane and plane oscillations of the strip. An efficient asymptotic approach is proposed to studying the direct and inverse problems for cracks of a small relative size. The proposed scheme makes it possible to significantly simplify the solution of the direct problem and reduce the solution of the inverse one to characterizing the defect from transcendental equations. Numerical results of computational experiments are presented.

STUDY OF PHYSICAL PROCESSES IN THE DIRECT CURRENT LINK OF THE LOADING-BACK SCHEME OF ASYNCHRONOUS MACHINES

The article notes the tendency of introducing asynchronous engines, entailing the necessity to introduce the equipment which is intended to carry out maintenance, repair and acceptance check-outs. The general part of test circuits for asynchronous motors by the loading-back method with two controlled inverters is emphasized. The mathematical model of similar schemes’ functioning is shown. The article gives the results obtained by mathematic simulation of physical processes in the direct current link in the loading-back scheme for asynchronous machines Significant ripple voltage of constant voltage and DC in these circuits is noted. The issue of measuring power in the DC link passing through one inverter to the test engine and through another inverter from the load generator is considered. The authors carried out calculation of the capacities mentioned in the steady state modes for asynchronous machines with nominal power of 0.37 kW, 5.5 kW and 250 kW at different values of capacitor capacitance included in the DC link. Basing on the results of calculations, the authors found the dependence between the relative value of the procedural error in determining power in the DC link by the product of the current values of pulsed voltages and current. The current value from the product of instantaneous values of voltage and current at some time interval was taken as the true value of power. It is shown that at the capacitor capacity above some critical value this procedural error does not exceed 0.9% at the nominal power of the test engines 0.37 kW; 0.3% – at the power of 5.5 kW; 0.2% – at the power of 250 kW. This error increases dramatically when capacitor capacitance decreases. It is shown that the value of the capacitance corresponding to the inflection of the considered dependence approximately corresponds to the value necessary for limiting ripple voltage in the DC link of up to 600 V.

Online electric network capacity assesment

Reliability of power supply to consumers and the efficient use of energy resources are priority tasks in the process of operational dispatch control of the energy system. Limitations of the throughput capacity of the electric network increases the value of the non-released power reserve, which in case of violation of the normal mode at one electric power facility can lead to a system accident. The aim of the work is to develop an algorithm for assessing the throughput of the electric network. In this study of the steady-state operating modes of the power system, a method is proposed for online modeling of the parameters of the electric power regime and its verification in a real scheme for determining the throughput of the electric grid. To solve the tasks posed in the work, we used: the theory of multivariate experiment, the theory of systems of linear equations, methods of mathematical modeling, software and computer systems Cosmos. The regression function is used to simulate the power flow over a network element. The methods based on the linearized and complete models with the measured values are compared and estimated using the correlation coefficient. The method can be used in the practice of supervisory control and research organizations in solving problems of improving the characteristics of the regimes, planning and operating the power system in real time, as well as the development of electric networks and power systems. The efficiency of the proposed method was verified during the experiment.

A System for Controlling the Thermal Behavior of Voltage Source Inverters

The thermal behavior of semiconductor devices of voltage source inverters for a traction frequency converter and its control systems are investigated. A test bed for studying thermal processes in steady state and transient modes occurring in semiconductor modules with air forced cooling systems is described. The results of an experimental investigation for the Infineon FF300R06KE3 module are analyzed and compared to the results of a mathematical model. Transfer functions of a semiconductor module as an object of temperature control are synthesized with respect to the collector current, cooling air flow, and frequency switching. The control system of thermal behavior of a voltage source inverter with two control actions on the object of temperature control (cooling air flow and frequency switching) is developed. It is proposed to use an electric drive with an induction motor and scalar control system for the purposes of regulating the cooling air flow. The effectiveness of the proposed control system is confirmed by means of simulation in MATLAB/Simulink in transient and steady-state modes.

A Method for Monitoring the Condition of Rotor Windings in Induction Motors during Startup Based on Stator Current

Abstract—At present, one of the most effective methods for detecting dangling bars in squirrel-cage rotor windings of induction motors operating under severe starting conditions is the spectral analysis of stator current in a steady-state operation mode. The existing methods of testing in starting modes are not sensitive enough or their study has not been completed, although it is precisely such methods that allow diagnostics of machines that cannot be inspected in the steady-state operation mode. The purpose of this article is to develop a method for monitoring the state of rotor windings in induction motors operating under severe starting conditions based on the stator current in the starting mode, which is an urgent task. The studies were carried out both on digital models of an induction motor, developed in the Ansys software package, and on an experimental stand with a low voltage supplied to a low-voltage motor to increase the duration of its start. Signal processing is performed in the Matlab software package using the short-time Fourier transform. It is shown that only in the presence of a broken rotor bar, the amplitude of the harmonic component of the order coinciding with the number of motor pole pairs sharply increases at the lower side frequency; this indicates the presence of damage. It is shown that the developed technique for monitoring the condition of rotor windings in induction motors operating under severe starting conditions is more sensitive to broken rotor bars than the existing methods; this makes it possible to timely detect damage to rotor windings and prevent sudden failures of induction motors.

Synchronous target mode decision mechanism of electrically coupled neuron system under asymmetric excitation

Due to the universality of asymmetric coupling-excitation in neuronal system and the important role of firing pattern in neural information coding and transmission, synchronous target mode decision mechanism of electrically coupled neuron system under asymmetric excitation is studied in this paper. In the beginning, based on an asymmetric excitation system with symmetrical coupling, according to the phenomenon that Interval Spike Intervals Sequence (ISI) can coincide with the ISIs of a single neuron stimulated by a certain current, the concept of ‘virtual equivalent symmetrical stimulus current’ is put forward. Furthermore, it is also found that there is no relationship between the steady-state synchronous target mode and the coupling strength of symmetric coupled system under this situation. However, the following experiments of asymmetric coupling-excitation system show that there is a strong internal relationship between the almost complete synchronous stable firing mode and coupling strength as well as exciting currents. According to the experimental conclusion, a qualitative criterion is proposed, and then, on the basis that the system can be fully synchronized, the decision-making quantitative basis of the steady-state synchronization target mode of the given system is derived strictly. This study has important reference value for understanding the working state transition of neuronal system.

Improving Fuel Economy and Engine Performance through Gasoline Fuel Octane Rating

The octane number is a measure of the resistance of gasoline fuels to auto-ignition. Therefore, high octane numbers reduce the engine knocking risk, leading to higher compression threshold and, consequently, higher engine efficiencies. This allows higher compression ratios to be considered during the engine design stage. Current spark-ignited (SI) engines use knock sensors to protect the engine from knocking, usually adapting the operation parameters (boost pressure, spark timing, lambda). Moreover, some engines can move the settings towards optimized parameters if knock is not detected, leading to higher performance and fuel economy. In this work, three gasolines with different octane ratings (95, 98 and 100 RON (research octane number)) were fueled in a high-performance vehicle. Tests were performed in a chassis dyno at controlled ambient conditions, including a driving sequence composed of full-load accelerations and two steady-state modes. Vehicle power significantly increased with the octane rating of the fuel, thus decreasing the time needed for acceleration. Moreover, the specific fuel consumption decreased as the octane rating increased, proving that the fuel can take an active part in reducing greenhouse gas emissions. The boost pressure, which increased with the octane number, was identified as the main factor, whereas the ignition advance was the second relevant factor.

Low-pressure discharge in a trigger unit of pseudospark switch

The paper deals with the investigations of the discharge in the trigger unit of the pseudospark switch. The main attention is payed to study of the low-current auxiliary glow discharge, which is sustained in the steady-state mode before triggering, and to rearrangement of this discharge when the trigger pulse is applied to the trigger unit. The hydrogen pressure is varied through a range from 0.08 to 0.25 Torr and the auxiliary discharge current in the electrode system with hollow cathode and hollow anode is up to 40 mA. The estimates for the plasma density in the cathode cavity are provided. Under the action of the trigger pulse, the breakdown between the trigger electrodes occurs and the pulsed breakdown current is intercepted to the main cathode cavity of the switch. It is demonstrated that the process of the current interception strongly depends on the regime of sustaining the auxiliary discharge and on the fact, whether the potential electrode of the auxiliary discharge plays a role of the hollow cathode or the hollow anode.