Technical Physics最新文献

The reliability of electromechanical energy converters is a key point for power supply systems with distributed generation, especially for remotely located ones. In this paper, the existing and advanced methods of protecting converters against emergency modes, including voltage unbalance, are analyzed. The physical principles underlying these methods and their application in various fields, including power engineering and control systems, are considered. Special attention is paid to factors causing voltage unbalance and its effect on equipment. The advantages and disadvantages of techniques for reactive power compensation, as well as methods for improving the efficiency of active and hybrid filters, are considered. Recommendations are given for optimizing protection systems used in distributed generation sources with regard to the interdisciplinary context and possible applications in related fields.

Providing consumers with high quality electric power with minimum transmission loss is among the problems of electric power transmission through electrical grids. Increasing reactive power of electric consumers, estimated by the load power factor, results in an increase in electricity loss and quality deterioration. To evaluate the effect of the load power factor on the transmission of active load power and to determine the quality and energy efficiency of electricity transmission through power lines, the authors analyzed the change in the parameters of one phase of a three-phase network without compensation and with reactive power compensation. The problem is solved using methods for calculation of linear ac circuits with the given values of total or active load power, its resistance, and the resistance of power line wires. Then, the processes of power transmission in low-voltage ac networks are simulated using the Electronics Workbench software. The results show that the main changes in the parameters of the electric power system consisting of consumer loads receiving power supply through the power line connected to the low-voltage busbars of the power transformer occur when the system current determined by the load and transmission line resistances is changed. The quality of electric power transmission through the power line is determined by the system current and total load resistance, and the energy efficiency of electric power transmission through the power transmission line is determined by the squared system current and the ratio of the active resistances of the load and power line.

Using electrodynamic analysis of the 3D model of a plane-parallel ideal dielectric plate, the propagation of plane linearly polarized electromagnetic waves is investigated in the case when their angle of incidence φ deviates from the normal to the plane of the plate. It is found that in the case of parallel polarization, when the electric field vector lies in the plane of incidence and magnetic field vector is parallel to the plane of plate, the Q factor of the observed half-wave resonance first decreases to its minimal value with increasing φ as the Brewster angle is approached, and then increases, tending to infinity as φ → 90°. In the case of perpendicular polarization, when the magnetic field vector lies in the plane of incidence and the electric field vector is parallel to the plane of the plate, the Q factor of the half-wave resonance gradually increases with increasing φ, also tending to infinity as φ → 90°. However, the dependences of the observed monotonic increase in the resonance frequencies with the angle of incidence are identical for both polarizations. The results of experiment with a plane-parallel plate made of ultrahigh molecular weight polyethylene with a dielectric constant of 2.5, which has been performed using broadband horn antennas, are in good agreement with the results of the electrodynamic calculation based on the 3D model.

Currently, intensive research is being carried out to improve the operational characteristics of the car: vibration protection, smoothness, stability, and controllability. These properties are largely determined by the characteristics of the vehicle suspension, which provides a connection between the carrier system and the wheels of the vehicle. Significant attention is paid to the development of active suspensions, in which additional actuators are used to form the necessary characteristics, in particular, linear dc motors. The use of active actuators permits to control the position of the car body, including its lateral roll. In the article, relations are obtained that establish the dependence of additional elastic deformations in the suspension and the car roll angle on the centrifugal force in a stationary mode. When developing a linearized mathematical model of the control object for the study of nonstationary modes, a two-mass design scheme is used and operator equations are obtained that take into account the elastic–dissipative properties of the sprung and unsprung parts of the car, as well as an additional control action created by the actuator. It is shown that the dynamic properties of the studied control object can be approximately described by the transfer functions of a second-order aperiodic link or an oscillatory link. For the former case, a single-loop system was developed, which was closed in terms of the roll angle with a proportional-integral-derivative (PID) controller. In the latter situation, it is advisable to use a two-loop system with an internal flexible feedback loop for suspension deformation and an external loop closed for the roll angle using a PID controller. The possibility of forming a feedback signal in the strain rate of the suspension in the internal loop with the help of an EMF sensor of a linear dc motor is demonstrated. On the basis of the block diagram, a computer model of the system is developed, and for typical parameters of the control object, a study is made of transient processes of working off a disturbance in the form of a change in centrifugal force. Based on the simulation results, it was found that the use of the developed automatic control system (ACS) provides high accuracy in stabilizing the vehicle roll angle.

The work is devoted to the study of the influence of the electric energy quality on the service life of electrodes of a plasma thermochemical fuel treatment systems used in thermal power plants running on coal fuel. The issues of moving the near-electrode plasma section using magnetic-wave scanning are discussed in detail. The purpose of the work is to study and evaluate the effect of voltage distortion on the trajectory of the near-electrode plasma section with magnetic-wave scanning and subsequent changes in the service life of the plasmatron under certain operating conditions. The ANSYS Maxwell software was used as the main research tool. The computer simulation was performed with the following main experimental parameters: the coefficient of asymmetry in the zero sequence (K_0U) is 2% and 4%; the coefficient of asymmetry in the negative sequence (K_2U) is 2% and 4%; the voltage deviation δU₍₊₎ is 5% and 10%; the materials used for manufacturing electrodes: copper (Cu), a pseudo-alloy of tungsten, nickel and copper (W + Ni + Cu), and a pseudo-alloy of molybdenum, tungsten, and copper (Mo + W + Cu). Based on the obtained simulation results, graphical representations of changes in the trajectories of the near-electrode plasma section under various distorting factors, dependences of changes in the values of specific erosion of various electrode materials, and graphical dependences of changes in the service life of electrodes of plasma systems are constructed. The studies performed using computer modeling based on the ANSYS Maxwell software product has made it possible to quantify the effect of voltage distortions on the trajectory of the near-electrode plasma section and, consequently, the service life of the plasmatron electrodes. In particular, in the course of the study, a detailed assessment and analysis of the degree of influence of the following indicators of electrical energy quality was performed: the coefficients of asymmetry in the negative and zero sequence and voltage deviations on the operation and technical condition of the electrodes of plasma systems. The results of the study are discussed, and recommendations are formulated for the plasma thermochemical fuel preparation systems used at thermal power plants to ignite the fuel of pulverized coal boilers.

Record-long plasma confinement times in tokamaks could be attained using new methods of erosion protection of plasma-facing materials (including the use of liquid metals). This article reviews the publications on the application of liquid metal droplets in the form of droplet screens to improve the plasma confinement and to protect the vacuum chamber walls from thermal loads. The variants of designs of devices ensuring the injection of droplets into the volume occupied by the plasma and the main results are considered. Analysis of parameters of liquid metals being injected indicates the possibility of controlling the flow parameters such as the droplet size and velocity. The results of investigations show the possibility of using metals in the chamber without violating vacuum conditions and contamination of the plasma. Further experiments are required to substantiate the application of liquid metal droplet screens in plasma devices.

The article considers the use of a new methodological cognitive-variable synergetic (CVS) approach to analysis of the problems in the theory of systems research conducted onboard automatic spacecrafts (AS) [1]. The methodology of the CVS approach is based on cybernetic [2] and synergetic [3] theories of dynamic systems management, as well as the methods of proactive management of the functioning of complex technical objects (CTOs), based on the concept of integrated modeling of CTO [2]. The results of the previously conducted morphological analysis of the problems in the theory of system cybernetic studies of the movement of dynamic systems are known and presented in the form of a morphological tree containing four branches (modeling–analysis–observation–choice) and leaves (particular tasks) [4]. The number of tasks is determined by the interaction of the control system (environment) with four types of effects of the disturbing environment (deterministic, stochastic, purposeful, and with unknown characteristics) in the formation of input effects on the control system. The CVS approach is based on the use of a new type of environment in the management of dynamic systems, viz., synergetically disturbing medium. To display the new environment and tasks on the morphological tree of problem analysis, in addition to the existing tasks of systemic cybernetic research, new leaves (particular tasks of systemic synergetic research) are introduced. The paradigm of problem analysis is formed on the basis of knowledge, management experience, and system research aimed at solving the problem of providing resources for onboard AS systems and the stability of their functioning during flight. The goal-setting of a new methodological approach to analysis of the problems in the theory of systems research is aimed at the rational use of the main structural and functional resources of the onboard systems, obtaining synergetic resources, and preventing failures caused by design and off-design abnormal processes. Further, the term “synergetic” will be applied to a type of resources that is formed by spontaneous self-organization of processes in management systems and transformed into purposeful self-organization in objectively existing polyadic relations describing synergetic mutual assistance and interrelations in the course of processes in a synergetically disturbing environment [5, 6].

The article presents the results of numerical modeling of the effect of the profiled inlet section of a channel on the flow in a confuser with a heated wall. The calculations were performed in the OpenFOAM package using the Navier–Stokes equations of viscous fluid motion, supplemented by the k–ω SST turbulence model. A mesh convergence test and comparison with experimental data were conducted. It was shown that, under quasi-isothermal conditions with a heat flux of 1 kW/m², the presence of an inlet section improves the agreement between the calculated and measured flow parameters at the beginning of the confuser, and then the effect of the inlet section on the flow parameters is absent. It was revealed that, with a heat flux of 6 kW/m², the inlet section has a significant effect on the flow along the entire confuser length, reducing the velocity shoot-through effect and the laminarization of the boundary layer.

In this study, the possibility of using Surfi-Sculpt technology for relief modification of the tungsten surface on a technological electron-beam equipment with an accelerating voltage of 60 kV and an electron gun of the ELA-60 type is investigated. The electron beam power density sufficient for intense evaporation of tungsten and obtaining a relief surface is determined. The dynamics of the surface relief growth rate is analyzed using a six-point star scanning as a function of the electron beam velocity and direction.

Using CST MWS 2023 software, modeling of the S-parameters and the radiation patterns (RPs) of antenna arrays (AAs) based on rectangular graphene microribbons in the THz range has been carried out. It is shown that the unique property of graphene AAs is the possibility of electronic frequency scanning and multiband operation regime, as well as an increase in the gain factor, narrowing of the main RP lobe, a decrease in the level of the side RP lobes with an increase in the value of the chemical potential (from 0.2 to 1.0 eV), and their dependences on the number of AA emitters.