Home – Home – Jornals – Journal of Applied Mechanics and Technical Physics 2019 number 4

The previously developed technology of multicriteria optimization of deterministic parabolic distributed parameter systems can be applied in situations with interval uncertainties of parametric characteristics of controlled objects. Minimax tasks of mathematical programming are formed in accordance with a control strategy based on the principle of the best guaranteed result on an expanded set of arguments, which includes all permissible realizations of uncertain factors, in the case of estimation of a given approximation accuracy to a required finite state of the system in uniform metric. These tasks are solved by an alternance method that uses the Chebyshev properties of desired extermals and fundamental laws of the problem domain. Of independent interest is the given example of multicriteria optimization of temperature regimes of induction heating of metallic semifinished products before plastic deformation operations in technological complexes for pressure treatment of metal

The problem of estimating the state vector of a bilinear dynamic system with a vector entrance is under consideration. It is shown that, with fulfillment of multiple restrictions, a Luenberger state observer can be formed, which ensures that the estimation error tends to zero. A step-by-step algorithm for determining the matrices of observer coefficients is proposed, based on matrix canonization and modal control methods

This paper describes the problem of automation of choosing the parameters of an electric hydraulic drive controller for a single-channel strength load stand for airframe elements. A parameter configuration method for a proportional-integral stand controller is proposed, based on the results of relay feedback tests and motion separation method. The results obtained make it possible to automatically configure the controller parameters of the strength test stand and improve the accuracy of implementation of force loading cyclograms of structures, which eventually makes it possible to accelerate strength tests. The results of analyzing the implementation of this technique on an experimental stand are given.

Results of studying the system used to control the flight of a hybrid aerial vehicle prototype in transitional regimes are presented. The hybrid vehicle is equipped with a quadrotor and main propulsion units. The control system developed in the study includes subsystems for attitude stabilization, vertical takeoff, hovering, and landing, as well as a control subsystem operating in transitional regimes from quadrotor to aircraft modes and back.

Operating and engineering characteristics of a hybrid aerial vehicle are presented. A mathematical model in the MATLAB/Simulink environment is described. Results obtained by means of hardware-in-the-loop simulations and confirming the efficiency of the proposed control method are reported

A procedure for designing PID controllers for the class of second-order nonlinear non-stationary objects is proposed. To reduce possible control jumps, its proportional differential components are transferred to the system feedback channel. It is shown that the presence of a special fast response differentiating device in the system generates fast processes against the background of slow operating processes, which are identified using the technique of separation of movements. The controller designed on this basis ensures invariance of the system under external uncontrolled disturbances as well as under a change in the parameters of the object. The results of numerical simulation of the system in MATLAB illustrate its basic properties.

The issues of local navigation of mobile robots are considered. The method of artificial potential fields as a popular method for local navigation of robots is analyzed. The issue of designing attractive potential fields is investigated. The problem of local minima (traps) is discussed. A new method for avoiding obstacles by a robot moving to a target is proposed

A numerical method for designing operating software for digital controllers of hybrid continuous-discrete control systems is considered. The method is based on implementing digital controller control algorithms in the form of rule systems and uses a fuzzy optimization procedure to determine the controller operation rules. The continuous part of hybrid control systems consists of multi-operational process chains, which are nonlinear, multidimensional and multi-loop controlled objects, and the discrete part is digital controllers. The designed digital controllers ensure satisfaction of the most general requirements for controlled processes, including fuzzy ones.

This paper presents a comprehensive simulation model of underground coal mining processes in a fully mechanized long mining face. A number of simulation experiments have been performed. The face performance is estimated as a function of various factors such as the technical parameters of mining machines, length of lava, gas factor, shearer operation process chart, distributed geomechanical characteristics of coal seam.

This paper presents the results of analysis of the influence of interfering factors on changes in the informative parameter of a single-turn eddy current sensors, which are used as initial data in the study of a system for measuring radial clearances with self-compensation of temperature effects on the sensor. Conversion functions of the measuring circuit with a connected single-turn eddy current sensor are obtained in analytical form. The conversion functions are dependences of the extreme values of codes at the measuring circuit output on radial clearances and temperature effects on the sensor taking into account the influence of interfering factors (neighboring blades, blade temperatures, axial displacements of the gas turbine engine compressor rotor). Quantitative estimates are obtained for the influence functions of these interfering factors on the calculated difference of the extreme values of codes in the system, which characterizes the measured parameter.

Time-optimal algorithms of spatial localization of random pulsed-point sources are proposed, and their parameters are calculated. These sources have a two-step probability density in the search interval and are detected due to generation of instantaneous pulses at random time instants (delta functions). The advantage of the developed optimal localization algorithms over the search procedures that ignore specific features of the spatial distribution of the detected pulsed-point objects is demonstrated.

A problem of detection of 3D objects on the basis of imagery information provided by two or three different sensors is considered. The efficiency of object detection with the use of algorithms of integration and data fusion of information from different sensors and also by means of formation of a unified synthetic image from two initial images is estimated. Conditions are determined at which the use of the information integration algorithm and the method of forming a single synthetic image provides a lower efficiency as compared to the use of only one image among those available for detection.

This paper describes a neural network architecture of edge detection. Different filters for first-layer neurons are compared. Neural network learning based on a cosine measure algorithm shows much worse results than an error backpropagation algorithm. Optimal parameters for first-layer neuron operation are given. The proposed architecture fulfills the stated tasks on edge selection.

The Maxwell equations for a composite two-component layered material with a periodic structure in the field of a time-harmonic source acting along the layer are considered. Two-scale homogenization of the equations is performed with allowance for complex conductivity of interphase layers and their thickness. The boundary-value problem for systems of differential equations with boundary conditions is reduced to a problem in a weakly variational formulation. Unique solvability of the problem is established. The case of low frequencies of interphase surface currents of different intensities with allowance for the frequency-dependent wave length and skin layer length is analyzed. Macro-equations are derived, and effective material constants are determined, such as the magnetic and dielectric permeabilities and electrical conductivity. Conditions at which the effective parameters depend on interphase currents are described. It is found that the effective dielectric permeability can be negative at specially chosen parameters of interphase layers, if the effective dielectric permeability is determined on the basis of the effective wave number.

The rotational motion of finned shaped-charge liners is studied. It is shown that the main factors affecting the rotation of a shaped-charge jet are the position of the jet-forming layer and the distribution of the circumferential velocity in the liner cross-section. The proposed method can be used to estimate the average angular velocity of the jet with consideration of the size of the finned shaped-charge liner and the properties of its material. It is shown that the results are consistent with available experimental data.

A thermodynamically equilibrium model is applied for simulating thermodynamic parameters of shock loading of both pure materials and mixtures of homogeneous and porous materials. The model includes a modified equation of state, which has only one fitting parameter determined on the basis of experimental data. The thermodynamic parameters of shock loading of copper and copper-based mixtures with porosities of 1-10 at pressures above 5 GPa are calculated. The results of these calculations are compared to available experimental data (Hugoniot adiabats, double compression by shock waves, and temperature estimates). The possibility of modeling the compression of the mixture as a whole and each component separately is demonstrated.

Results of studying stability of the Blasius boundary layer on a two-layer compliant coating in the linear formulation are reported. The computations are based on experimental parameters of viscoelasticity of a real coating, which reveal the dependences of its elasticity modulus and loss coefficient on frequency. Parametric investigations of the influence of the coating layer thicknesses and free-stream velocity on flow stability, in particular, on the critical Reynolds number, are performed. Regions of a nonmonotonic behavior of the critical Reynolds number are found, which allow one to determine the optimal thicknesses of the upper and lower layers for intense interaction with the flow. An explanation of this effect is proposed.

Starting of an air-breathing engine with fuel injection distributed along the combustion chamber is numerically simulated. Issues of principal importance are the presence of a compressed are jet generating a throttling effect and preliminary deceleration of the flow to transonic velocities. Averaged Navier-Stokes equations closed by the SST, SST κ-ω, or κ-ε turbulence models are solved. Hydrogen and ethylene combustion is simulated by one reaction. The computations are performed for various values of the turbulent kinetic energy in the flow. A pulsed transonic regime of hydrogen and ethylene combustion is discovered.

This paper considers the possibility of using measuring sections with inductive sensors to detect hypersonic particles in time in the simulation of collisions of objects with space debris. A method for determining the average velocity of hypersonic particles simulating the space debris and a method of starting the recording equipment for optical contactless detection of these particles are proposed. Results of experimental studies of the interaction of particles with a simulator of the mesh shield of the spacecraft.

The influence of the shape of the jet head on its impact on a wall covered with a thin layer of liquid has been studied. The conditions characteristic of the impact of the jet arising on the surface of a cavitation bubble upon its collapse near the wall have been considered. It has been established that changing the shape of the jet head can lead to a significant change in the size of the area of maximum loading of the wetted wall and in the magnitude and pattern of loading. In particular, with an increase in the degree of sharpening of the jet head, the pressure on the wall decreases and its spatial distribution becomes more uniform. Dependences of the maximum pressure and integrated wall load on the jet shape were obtained.

The influence of the dimensionless angular and linear parameters of interaction of water droplets shaped as a sphere, an ellipsoid, and a conventionally liquid disk on the characteristics (regimes) of their collisions in air (rebound, coagulation, spreading, or fragmentation) is studied by using a system of high-speed video recording. Conditions of stable realization of this interaction are determined. Charts of the corresponding regimes are constructed and compared with available data. The characteristic sizes, the number of liquid fragments formed in collisions, and total areas of the evaporation surface are calculated. It is demonstrated that the liquid surface area in the case of collisions of conventionally liquid disks is significantly (by several times) greater than that in the case of spherical droplets.

Three-dimensional deformation of two bubbles and bubbles in a cluster in an ideal incompressible fluid exposed to an acoustic field is investigated using the boundary element method for potential flows. The dependence of the dynamics of two interacting bubbles on the frequency and amplitude of the acoustic field and the distance between them is studied. The values of the parameters of the acoustic field and the cluster for which jets are formed and the bubbles are deformed or remain spherical are determined. The behavior of two central bubbles in a structured cluster exposed to an acoustic field with different frequency and amplitude is investigated as a function of the distance between the bubbles of the cluster. A comparative analysis of the deformation of the investigated bubbles in the presence and absence of adjacent bubbles is performed.

Theoretical model describing the movement of particles of saline water in oil flowing over a larger droplet of fresh water has been developed to solve the problem of cleaning oil from salts. The results of calculations of the effect of the radius and the initial velocity of a drop of fresh water on the coagulation of fresh and saline water droplets are presented.

The nonstationary process of extracting material from a porous body simulated by a system of semi-infinite capillaries into a moving liquid is studied; the transfer rate of the material in the flow is a linear function of the cross flow coordinate. The case where the liquid velocity at the interface becomes zero is considered. It is assumed that the diffusion in the flow is quasi-stationary. Analytical dependences at the boundary of the porous material and the flow region are found for mass transfer characteristics of practical interest (concentration, diffusion flow, total diffusion flux and the total yield of the target component through the cross section of the porous body).

Stress relaxation in a nano-sized rod containing structural defects in the course of constant-rate uniaxial straining is studied, and the reasons for the onset of this phenomenon are determined. Under the assumption that structural defects can serve as carriers of irreversible deformation of a higher level than dislocations, the problem is solved by the molecular dynamics method. It is found that stress relaxation is accompanied by the transition of the entire system to a steady state with a deeper potential minimum as compared to the system energy before the stress relaxation process, resulting in a temperature increase and reduction of the strain tensor components.

The differential thermal analysis is applied to study the influence of activated charcoal with multilayer graphenes (three and more layers) on the thermal decomposition of a substance based on hydroxyl ammonium nitrate and carboxyl methyl cellulose. It is demonstrated that addition of activated charcoal with multilayer graphenes lead to an increase in the burning rate of hydroxyl ammonium nitrate up to four times. Addition of activated charcoal at the stage of thermal decomposition leads to a decrease in temperature and time of the chemical reaction until complete decomposition of ammonium nitrate.

Comparative results of experiments aimed at studying the evolution of dust-laden jets induced by the presence of structural elements and grooves on the surface of loaded specimens are reported. The results are obtained with the use of pulsed X-ray radiography and synchrotron radiation. Information on dust density changes in synchrotron diagnostics is obtained by using multiframe filming. In the case of single-frame recording by means of pulsed X-ray radiography, a glancing detonation wave was used for studying the dust behavior instead of the normal wave.

An analytical model of the equation of state is developed based on theoretical ideas about the structure of TATB. The model is validated against experimental data obtained in static and dynamic experiments. The theoretically sound equation of state was used to match different experimental data in order to maximize the use of empirical information. It is expected that the application of the obtained equation of state will increase the accuracy of description thermodynamic parameters of unreacted TATB in numerical simulations of shock-wave and detonation processes.

The detonation pressure of an emulsion explosive sensitized by polymer microballoons was determined for normal and oblique incidence of a detonation wave on the target. The initial density of the explosive ranged from 0.2 to 1.2 g/cm³. The obtained pressure values are in good agreement with the calculated values known from the literature and are compared with the detonation pressure values of an emulsion explosive sensitized by glass microballoons. The reaction time and isentropic exponent of the emulsion explosive used were calculated.

Instability of a conical liner during shaped-charge jet formation has been studied. To establish the metal flow pattern during shaped-charge jet formation, we fabricated three-layer copper-copper-constantan liners consisting of a solid copper conical funnel with an cone angle of 45^oC, a wall thickness 1.5 mm, and a funnel pressed into it and rolled from a copper sheet 1.0 mm thick clad by explosion welding with constantan 0.2 mm thick. Liner implosion was carried out by an RDX charge 20 mm thick. The jet formation process was recorded by flash radiography, and the metal flow pattern was determined by micro sections of recovered slugs. Since the boundary of explosion welded metals is clearly distinguishable on the sections, the residual deformation in different sections of the slug shows the occurrence of instability of the liner during the implosion, which manifests itself in the form of folds oriented along the generatrix of the cone. However, the general flow pattern described in terms of the theory of an ideal incompressible fluid is not disturbed, which follows from radiographs of the shaped-charge jet formation process.

Experiments on the explosive welding of low-plasticity steels through thin plastic layers show that, aside from the geometric features of collision (thickness and angle of collision of plates and contact point velocity), the dimensions of waves arising in the junction region are also highly affected by the mechanical properties of welded materials (hardness, density, and sound velocity). It is determined that waves of different dimensions can be formed under the same conditions, but their length lies in a certain range of values. On the basis of the resulting experimental data and with involvement of the Landau model, which describes the instability of a steady flow of viscous fluid, expressions for estimating the top and bottom boundaries of wavelengths are constructed with allowance for geometric parameters of collision and mechanical properties of colliding metal plates.

This paper describes the structural studies of hollow cylindrical shells made of D16 and AMts aluminum alloys, loaded by sliding detonation. Explosive loading conditions for the complete convergence and closure of shells are established. Light optics scanning electron microscopy, and transmission electron microscopy are applied to study the structural and phase transformations in shells under shock-wave loading. The relation of composition, structure, and mechanical characteristics of alloys with their behavior under the action of shock loading is shown. There are several scenarios of convergence of shells, depending on their composition and loading conditions - from complete and steady convergence to multiple spalling.

The structural mechanisms of buckling and the deformation behavior of copper and steel cylindrical shells (pipes) during convergence under the action of an explosion are studied. The dependence of deformation behavior on the transverse dimensions of the shell and properties of the loaded material is described. It is established that the stability of radial convergence depends on absolute dimensions of the shell rather than relative dimensions, with the convergence of large-diameter shells occurring more stably. It is demonstrated that the convergence stability is violated due to the formation of a characteristic pattern of localized deformation in the sample, consisting of homogeneous, orderly arranged structural elements whose dimension depends little on the material properties and experimental conditions. A criterion for stable radial convergence that relates the characteristic dimensions of the structural element of localized deformation and the shell radius is proposed.

Numerical simulation studies of shaped charges with hemispherical liners of degressive thickness (decreasing from the top to the bottom) have been continued. The possibility of increasing not only the velocity but also the mass of the head sections of the formed shaped-charge jets to the level provided by conical liners of progressive thickness has been analyzed. For this purpose, liners of degressive thickness in the form of a truncated sphere and a semi-ellipsoid slightly elongated along the charge axis have been additionally studied.

The results of numerical simulation of the blast impulse of explosive charges on structural elements are presented. The numerical method was validated against available experimental data describing the blast effect in the near zone of explosion. Additional experiments on explosive acceleration of steel discs were performed. The effect of explosion conditions (the presence or absence of air, additional reflecting surfaces) on the blast impulse was studied.

An X-ray pulse video recording method is used to study the projecting ability of coaxial combined explosive charges containing dispersed aluminum in a thin peripheral layer as compared with charges containing a uniformly distributed aluminum additive and charges with no additives. The significant influence of the burnout of detonation products on the projecting ability of explosive charges containing dispersed aluminum is confirmed. It is shown that aluminum in a composition with explosive charges burns out because of reacting both with detonation products and ambient air, including in a rarefied environment.

Experiments on detonation spraying of ceramic coatings are carried out by feeding a powder as part of a suspension into a barrel for the first time. Spraying of Al₂O₃ and TiO₂ nanopowders and hydroxyapatite shows that the new method for obtaining coatings (suspension detonation spraying) can be implemented on a CCDS2000 detonation device. Unlike conventional detonation spraying technologies using micron-sized powders, suspension spraying makes it possible to work with powders whose particle size is smaller than 1  m, serving as a basis for a suspension fed into the projector barrel during spraying.

Fundamental features of explosive packing of powder mixtures containing refractory metal carbides and metal bonds are under consideration. The effect of acoustic rigidity of metal bonds on the residual porosity of samples after explosive treatment is revealed. It is shown that the degree of packing of mixtures of carbide powders with metals under explosive pressing is determined by the possibility of arrival of shock waves in the metal bond particles at their surfaces free of contacts with other particles and with a mass velocity acquired by the metal bond at these surfaces due to unloading.

A number of modern scientific and practical problems in design of multifunctional safety systems for coal mines and requirements to such systems are discussed. The reasons and the dynamics of accidents in mines are analyzed; examples of approaches to preventing such accidents are given. Available and promising directions of the development of engineering tools and systems for ensuring miners' safety are considered. The efficiency of using the scanning gas monitoring technology is demonstrated. Combining this technology with the automatic system of fire quenching allows the fire to be suppressed at the initial stage of ignition of the methane-air mixture.

One method of pulse pressure loading of material or plasma is axisymmetric compression using a convergent cylindrical detonation wave. Such a wave is often formed by multipoint initiation and has a number of specific features that may affect the properties of the objects under study. To solve specific problems, it is proposed to use an explosive laboratory setup based on a converging cylindrical detonation wave with 12-48 initiation points. The TNT equivalent of the charge is less than 1 kg. The main method of research is process visualization using a domestic high-speed Nanogeit camera with a nanosecond time resolution. The structure and velocity of the converging detonation wave along the radius were determined. It is shown that for a charge of limited thickness, the curvature of the detonation wave front for various explosives depends only on the distance to the initiation point.