Technical Physics最新文献

The adhesive strength of coatings prepared by electric arc metallization from a flux-cored wire consisting of a steel shell and a FeCr + Al charge has been studied. From experimental data, a number of process factors have been revealed and a functional dependence that makes it possible to substantiate metallization conditions optimal for the growth of high adhesive strength coatings has been derived.

The purpose of this work is to study the effect of the imbalance of the supply voltage on the service life of an asynchronous motor (AM) with a short-circuited rotor. The main attention is paid to the dynamics of changes in the service life of low-voltage asynchronous electric motors of several series depending on the level of voltage imbalance. Asynchronous electric motors of the classic (4A and AI) and upgraded (5A and AI) series serve as objects under study. Efficient and reliable operation of electric motors is characterized by the service life of the insulation of the windings. A qualitative assessment of the operational reliability of AM is determined by the accuracy of forecasting the real life of their service. Thus, it becomes obvious that the adequate assessment of the operational reliability of low-voltage asynchronous electric motors operating under conditions of low-quality supply voltage directly depends on the complex study of such an external factor as the imbalance of the supply voltage. The problems of the study are solved using the SimPowerSystems software of the Matlab/Simulink interactive programming environment. The research was carried out on asynchronous motors with a short-circuited rotor of classic (4A132S4 and AIR160S8) and upgraded (5A132M6 and AIR132S4) series at P_l = 7.5 kW and a rated rotation rate of n = 1500 rpm. Physical processes of the electric motors are simulated using variations in the negative-sequence voltage imbalance factor (K_2U) from 0 to 5% with a step of 1%. The simulated results are used to construct diagrams of the change in the service life of AM versus external effect. The study based on the SimPowerSystems computer modeling makes it possible to predict changes in the service life of AM, estimate the limits of permissible values of the negative-sequence voltage imbalance factor, and compare electric motors with respect to stability against an external factor. A comprehensive solution of problems related to improvement of the operational reliability of low-voltage asynchronous electric motors is among the priority tasks, mainly aimed at efficient functioning of the electrical complex with an electric-motor load. A detailed assessment and analysis of the effect of imbalance of supply voltage on the operational reliability of low-voltage asynchronous electric motors are performed. The results of the study are discussed, and recommendations for the use of asynchronous electric motors in the presence of imbalance of the supply voltage are formulated.

We describe the techniques and results of measurements of the thermal density of the plasma flux to the test materials in experiments on controlled nuclear fusion. The heat flux has been measured using three different methods: based on the Fourier law (temperature difference in the line of thermocouples in the bulk of the sample), the Stefan–Boltzmann law of radiation (for high temperatures on the surface facing the plasma), and from the temperature difference and the cooling fluid flow rate at the inlet and outlet of the sample cooling system. Experimental values have been obtained for the coefficient of heat-transfer from the helium plasma to the tungsten sample surface.

We describe the algorithm of tangential velocity selection of moving targets with the introduction of the additional synthesis channel displaced relative to the main channel for radars with a synthesized aperture.

An algorithm for implementing a matched filter on a FPGA for a phase-code-shift keyed signal is described. Using complex signals in onboard radar stations allows achieving higher resolution in range and speed, and using a matched filter for such a signal increases the signal-to-noise ratio (SNR).

In this study, we consider the synthesis of a surfactant from an oleochemical raw material. Physicochemical properties of the resulting substance are investigated to determine the optimal targeted application in industry. Using IR spectroscopy, the reaction mixture is tested during the synthesis for different reagent ratios to determine more exactly the structural formula of the obtained chemical compound.

The parameters of a resonator consisting of two dielectric plates with gratings of strip conductors between the layers in the form of squares, and on the outer surfaces in the form of square meshes having the same subwavelength period, have been determined. The quality (Q) factor of the resonator, which has been measured at the normal wave incidence, is determined by the ratio of the widths of the internal and external conductors. Using electrodynamic analysis of a 3D resonator model, the propagation of plane linearly polarized electromagnetic waves when their angle of incidence φ deviates from the normal to the plane of the layered structure has been studied. It is found that for the parallel polarization of the wave, the Q factor of the observed half-wave resonance with increasing φ first drops to a minimum when approaching the Brewster angle, and then increases as φ → 90°. In the case of the perpendicular polarization of the wave, the Q factor of the half-wave resonance gradually increases with increasing φ, approaching the maximum value at φ → 90°.

Diagnostics of electrical components of hydrotechnical equipment used in agricultural production within the planned maintenance intervals with continuous analysis of residual resource is useful for reducing equipment operation costs. The use of inexpensive universal diagnostic equipment in conjunction with primary analysis of the state of units makes it possible to detect 60 to 80% of prefailure states. To ensure efficient application of the complex approach to primary diagnostics of electrical components of hydraulic equipment used in agricultural production, the authors considered the most common electric motors of pumping units, electrohydraulic distributors, and switching equipment. Complex diagnostics included the use of a thermal imager, vibration signal processing systems, and current signal control systems. The vibrograms of equipment control points were analyzed, and the state of bearing units as well as the cavitation characteristics of pumps were assessed by methods of acoustic and vibration diagnostics; hydraulic equipment leaks were searched, and power cables breakdown zones were detected in accordance with methodical instructions for determining the breakdowns of power cables with a voltage of up to 10 kV (RD 34.20.516-90). The article shows the possibilities of applying the diagnostics methodology based on surface thermograms to determine typical defects. Particularly discussed are the parameters of current signals from the electromagnet coils observed in case of distribution equipment malfunction. The authors give comparative estimation of diagnostics methods with calculated efficiency determination. It is established that the method of combined diagnostics using the analysis of external thermal fields can halve the time of preliminary diagnostics of faults with a stable forecast of the failure time 2–3 months before the critical state. This reduces the expenditures for detection of unit failures and simplifies the planning of maintenance procedures.

Reinforced rubber lip seals are used in bearing assemblies. Their reliable operation is ensured by pressing the lip of the seal against the shaft. The produced contact load prevents the outflow of sealed medium and the penetration of an abrasive and of chemically aggressive substances into the assembly, which reduces the service life of the parts. The contact load in the connection is affected by the force generated by the band spring. The method presented here is used to determine the specific contact load of the seal lip on the shaft imposed by the band spring depending on the parameters of the lip seals and springs. To check the adequacy of the methodology, the authors studied a batch of twenty five 1.1-45x65-1 reinforced lip seals (GOST 8752-79). The theoretically calculated contact force exerted by the spring was 2.64 to 3.804 N, specific contact loads were 0.098 to 0.153 N/mm while those according to experimental data were 2.75 to 3.50 N and 0.102 to 0.141 N/mm, respectively. High convergence confirms the correctness of the presented calculated relationships. It was established that the parameters of the lip seals had a large spread, which hampered accurate calculation of the specific load in the shaft–seal connection. To increase the accuracy of readings, it is necessary to reduce the tolerances on the dimensions of rubber products.

Sickle-bar mowers are mainly employed when harvesting forage. To improve their quality and consumption indicators, it is necessary to study the trajectory of movement, speed, and acceleration of the mower leg under changing terrain conditions. For this purpose, a study is performed to analyze the effect of the offset on the quality and energy indicators of the cutting equipment of the mower, as well as control the parameters and operating modes of the mower knife with an axial knife drive mechanism. The experimental results show that the cutting tool in the process of creating a relief contour changes the angle of inclination relative to horizon within ±15°. In this case, the offset ranges from 0.281 to 0.492 m. A change in the offset entails a change in the stroke, speed, and acceleration of the knife. Using the Artobolevsky analytical method of kinematic study of eccentric crank mechanisms and Excel calculations, we obtained graphic data on the dependence of the stroke, speed, and acceleration of the knife on the angular position of the cutting tool with an interval of 0°, 5°, 10°, and 15°. Changes in the position of the cutting tool of up to 15° leads to unequal speeds of the forward and reverse stroke of the knife, and also increases it from 76.2 to 89 mm, which increases the energy consumption for the knife drive to 17%. Another disadvantage of the eccentric crank mechanism of the knife drive is its dynamic imbalance, which is only partially smoothed out using a counterweight. To eliminate the disadvantages, an experimental mower with an axial arrangement of the crank mechanism on the bar of the cutting tool is proposed, allowing the bar handles to be transformed to the transport position in the working mode of the cutting tool when driving around bushes, trees, or rough irregularities.