Technical Physics最新文献

A drum-type installation for humidifying finely dispersed material is proposed. When implementing the installation concept at the stage of design and technological calculations, an important role is played by determining the rotation angle of the nozzle that sprays the humidifying liquid and the spraying time required to apply the liquid to the surface of the finely dispersed material layer. In order to implement the installation, mathematical calculations were performed, according to which, for a prototype humidifying installation with a drum with a diameter of 480 mm and a depth of 250 mm, a drum angular velocity of 1.256 rad/s, and a height of the humidified material layer corresponding to an angle of 0.42 rad, the calculated nozzle rotation angle was 0.39 rad. The liquid spraying time with the probability of droplet–particle interaction P = 0.95 was 126.9 s. To automate and simplify calculations when designing technological humidification lines, a program in Visual C# has been developed which allows calculating the nozzle rotation angle and liquid spraying time based on the characteristics of finely dispersed material and the geometric parameters of the drum. The calculation results obtained from the models are to be further verified by experiments.

The purpose of the work is the development, software implementation, and testing of algorithms designed to find resonant frequencies in an inhomogeneous dielectric ball coated with graphene. The relevance of the task is due to the widespread use of graphene in engineering due to its unique properties. The Galerkin method is applied to discretize a vector integrodifferential equation; piecewise-constant basis vector functions are determined on a three-dimensional body and on its surface, and a parallel algorithm for solving the problem is developed using the MSMPI library. The effectiveness of the parallel algorithm, which makes it possible to detect the sought resonances under specified conditions, has been confirmed. An effective parallel algorithm has been created for discretizing the integrodifferential equation, finding the determinant of the matrix, and searching for resonant frequencies.

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.

The reliability and efficiency of equipment depend, among other things, on the operation of the cylinder–piston group (CPG)—the most frequently repaired unit in automotive and tractor engines. The quality of the CPG assembly is ensured by group interchangeability methods (selective assembly). In mechanical engineering, the human-readable marking of parts based on color schemes is insufficiently informative, so it is advisable to move from human-readable to machine-readable marking. In order to implement digital marking for spare parts and digital transformation of repair enterprises, the main quality indicators of CPG spare parts of engines and selective assembly of piston–liner joints of ZMZ-402 engines in 10 groups are considered. To improve the accuracy of the basic assembly conditions when implementing the method of intergroup interchangeability of CPG engines and automate the assembly process, it is proposed to use machine-readable marking based on a QR code or radio frequency tags. The advantages of a QR code are low cost of creation, fast readability of information, the ability to create a redundant QR code, high capacity, and the ability to read several tags simultaneously. Marking using radio frequency tags (RFID, NFC) allows encoding and reading information without direct contact. It is more resistant to mechanical impacts compared to a QR code. Significant disadvantages of radio frequency tags are the difficulty of reading when shielding the signal and the high cost of implementing this marking system. Digital marking of spare parts will help to forecast demand, improve automation, ease of use of warehouse databases and transparency of operations, and more accurately predict the timing and cost of repairs. Using a QR code together with the information environment (Internet catalog) of an enterprise will improve collection during selective assembly and reduce the likelihood of personnel errors.

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.