The paper deals with hard cutters of drill bits for drilling rocks. The research on geometry of hard alloy and steel cutters of bits that work either under conditions of shockless loads was carried ...out in this work. The rationale of tungsten carbide and cobalt composition according to their hardness and robustness is provided. Different alloys were suggested to be used for tools working either under conditions of shockless loads or under shock loads for drilling rocks of high hardness. The rock deformation process was identified to occur by cutting and shearing forces. The highest influence on the cutting process is exerted by the acuity angle and back rake angle. Peculiarities of work of cutters with positive, negative and neutral back rake angles were determined as part of the main research. The dependence of penetration depth on the back rake angle of the cutter was obtained. Indicators of wearing identified in the research are including the type and properties of interacting surfaces characterized by the roughness of cutting bit surface, the hardness of materials in contact zone, friction mode that depends on unit pressure, movement rate, the nature of load application, and the rate of interaction of working parts of bit.
A mathematical model of an induction motor (IM) with a phase rotor is developed on the basis of the usual assumptions that does not use the supposition that there is an annular rotating field in its ...air gap and various transformations of coordinates. The model is valid for both transient and steady-state modes and with various ways of control by changing the parameters of the three-phase feeding voltage system of the IM stator coil. It is shown that the desired stationary operation mode that exists in the developed nonlinear IM model at a constant feeding voltage of the stator and load torque corresponds to the constant electromagnetic torque and spinning frequency of the rotor at sine-wave rotor and stator currents. A digital IM model is developed in the MATLAB system. An analytical solution is derived for the system of linear differential equations that describes the IM with a retarded rotor and allows evaluating the nonlinear digital model for correctness. Examples of applying the IM model in analyzing transient and steady-state operation modes of this motor are provided.
The calculation of a digital regulator intended to ensure the full attenuation of free processes in a linear regulation system for a finite number of quantization periods is considered. It is shown ...that the full attenuation of a free process cannot be achieved for a number of sampling periods smaller than the order of the continuous part of the system. The digital regulator of the system of stabilizing the dc engine rotation frequency, an example of calculating which is discussed in this article, allows trying out a continuous setting action for two time sampling periods at the operation in the linear zone.
The model of an engine has been constructed assuming that the rotor “squirrel cage” is replaced by the closed frames formed by its opposite rods. The method of engine control is proposed ensuring its ...operation in the closed system of rotation speed regulation with constant frequency of rotor currents corresponding to the torque extremum.
The band structure, density of states, and the Fermi surface of a recently discovered superconductor, oxygen-deficient tungsten oxide WO2.9 that is equivalent to W20O58, is studied within the density ...functional theory (DFT) in the generalized gradient approximation (GGA). Here we show that despite the extremely complicated structure containing 78 atoms in the unit cell, the low-energy band structure is quite feasible. Fermi level is crossed by no more than 10 bands per one spin projection (and even 9 bands per pseudospin projection when the spin-orbit coupling is considered) originating from the t2g 5d-orbitals of tungsten atoms forming zigzag chains. These bands become occupied because of the specific zigzag octahedra distortions. To demonstrate the role of distortions, we compare band structures of W20O58 with the real crystal structure and with the idealized one. We also propose a basis for a minimal low-energy tight-binding model for W20O58.
Application of parametric control in a dc voltage stabilizing system is considered. Under parametric control, the resistance of items connected in series with a load resistor changes. The resistance ...control is carried out by changing the relative shunting duration of the resistor with switch contacts occurring with a high frequency. A filter consisting of a choke and capacitor connected between the resistor and the load makes it possible to smooth the voltage ripples at the load up to a permissible level. A limiting continuous model of a voltage stabilizer with an integral controller is constructed. The stationary mode is determined, and the condition of its asymptotic stability is obtained by the linearized equation of perturbed motion. It is revealed that, when secondary power supply sources are used, the parametric control stabilizer has certain advantages relative to a stabilizer with a pulse down-converter. The studies of designed stabilizer by a mathematical model revealed the good coincidence of experimental and designed results.
This article studies the influence of an input ac voltage source on the properties of an ac voltage stabilizer, which not only stabilizes the level of voltage, but also adjusts its shape. A ...continuous boundary model of the power circuit is constructed, which takes consideration of the output resistance of the voltage source. Its equivalent electric circuit with controlled parameters and the static characteristic are determined. A preferred stationary mode is determined for the average value of the source’s harmonic EMF, which corresponds to the specified harmonic voltage at load with an integral controller with two variants: direct stabilization of the output voltage and stabilization of the input voltage of a smoothening
LC
filter. Linearized differential perturbation equations are obtained the asymptotic stability of the trivial solution of which provides asymptotic stability of a nonexcited mode and allows one to expect that stationary modes occurring within the permissible variations of the input voltage with be stable in terms of magnitude and shape. A method of numerical solution for the basic matrix of a linearized system of differential perturbation equations, which has periodic coefficients and eigenvalues defining the stability of the trivial solution to the problem, is suggested. Investigation of the main properties of both options using MATLAB Simulink software showed that appropriate quality of stabilization with adjusting the voltage shape is only possible by excluding the smoothening
LC
filter from the closed circuit of stabilization, which increases the output resistance of the stabilizer.
The band structure, density of states, and the Fermi surface of a tungsten oxide WO
2.9
with idealized crystal structure (ideal octahedra WO
6
creating a “square lattice”) is obtained within the ...density functional theory in the generalized gradient approximation. Because of the oxygen vacancies ordering this system is equivalent to the compound W
20
O
58
(Magnéli phase), which has 78 atoms in unit cell. We show that 5
d
-orbitals of tungsten atoms located immediately around the voids in the zigzag chains of edge-sharing octahedra give the dominant contribution near the Fermi level. These particular tungsten atoms are responsible of low-energy properties of the system.
The article discusses an empirical study that was conducted by the authors, in which they surveyed focus groups of young innovative entrepreneurs who are at different stages of creating their own ...projects. The authors devote particular attention to how training programs for the founders and staff should be implemented as the startup develops from its early phases into a sustainable-growth business.
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