Introduction. The investigation of the hydrodynamic cavitator operation used under the erosion impact on a solid body surface, and of the device structure optimization for increasing the damage capability of the cavitating jet is presented. The effect of a sporadic defect of the combined nozzle inside on the volume fraction of the vapor content and the cavitation region geometry is considered. The work objective is to identify the influence pattern of the inside defect of cavitators of various sizes on the hydrodynamic and cavitational characteristics of the nozzle through numerical modeling.

Materials and Methods. The features of the ANSYS Workbench finite-element analysis software package and the integrated optimization module of the development and design process in the domain of the computational fluid dynamics ANSYS CFX are used. The simulation is based on the experimental data obtained under the nozzle water discharge at a specially designed laboratory bench under the cavitation condition.

Research Results. Graphic dependences of the volume fraction of the vapor content, total pressure and thelength of the cavitation region on the distance along the axis of the jet for different defect sizes are obtained and presented. Two phases of the cavitating jet flow in a nonideal cavitator are identified, and the transition effect on the velocity distribution in the device section is shown.

Discussion and Conclusions. The occurrence of an internal defect on the surface of the conical pattern of a combined nozzle with the size of less than a quarter-diameter of the central cylindrical portion may not cause visual changes in the cavitation region geometry, but it significantly reduces the erosive capacity of the cavitation jet. A further defect increase results in a total suppression of the cavitation flow, but maintains its dynamic behavior. The obtained results contribute to the improvement of the hydrodynamic cavitators design, to the enhancement of their erosive impact with the use of cavitation for cleaning underwater structures and mechanisms.

Introduction. Heating dynamics under binary mixtures pool boiling is considered. The work objective is to experimentally investigate the hysteresis on heat flux under the liquid binary mixtures boiling.

Materials and Methods. The experiments were conducted on a cylindrical heater which served as a resistance thermometer and a generated power. The heating was carried out by a quasisteady-state method. Binary liquid mixtures were the target of the research.

Research Results. The experiments result in obtaining boiling curves under the saturated and unsaturated boiling. On the generated heating and cooling curves, several specific areas are observed. The first is the area where heat exchange is carried out in a liquid through convection, and the second is the bubble boiling region where the hysteresis is detected by the heat flux. The liquid flashing is followed by the noise generation and a jump in the mean temperature of the heating surface. The hysteresis of heat transfer is found out on the curve α (Тст). The heating curve always passes below the cooling curve. That is, for the given heater temperature, the heat-transfer factor will always be greater under cooling than under heating. This fact is observed both under single and multiple heating and cooling. The boiling curve is two dependences q (Тст) and α (Тст) synchronously obtained in one experiment. The hysteresis of the heat-transfer coefficient is detected on the boiling curve under heating and cooling of the heater.

Discussion and Conclusions. Along with the hysteresis on the heat flux of the boiling mixtures, the hysteresis of the heattransfer coefficient is first detected. The cause of hysteresis on the heat flux is various heat-transfer values on the heating and cooling curves at any specified Тст. The heating dynamics shows that the heating curve, both for heat fluxes and for the heat-transfer factor, always passes at lower values of these quantities (q и α) than the cooling curve.

Introduction. Problems of the adaptive drilling are currently discussed in a number of works. They are largely devoted to the regulation of standard parameters of the borer tools (depending upon the rock physical and mechanical properties at the mine face), and to implementing drill bit adaptation with complete or partial rearrangement of its structure accomplished through introduction of elastic elements. The paper objective is rationale for choosing an elastic element for an adaptive cutting bit, and its parametrization.

Materials and Methods. Experimental research was carried out using a real adaptive cutting bit (dia. 160 mm) with rubber samples having various parameters. For testing, rubber samples with the following varied properties were selected: rubber hardness (Shore scale) 40 to 75 ea; sample height 25 to 60 mm; operating range of pressure load 5 to 30 kN; sample shapes solid parallelepiped, parallelepiped with lateral grooves, perforated parallelepiped, layered parallelepiped with layers ranging from 6 to 15 mm. Based on the experimental results, a comparison was carried out with validation of the most suitable elastic element type and its parameters.

Research Results. Findings of the experimental study on elastic elements for adaptive cutting bits are presented. Following the comparison of the most common shapes of shock dampers, it is established that a multi-layered element serves best as an adapting joint.

Discussion and Conclusions. Using rubber-based elastomers as elastic elements in adaptive cutting bits appears to be feasible for low diameter cutters. Recommendations are provided regarding rubber hardness, layer thickness, and total height of the elastic element for the specified stroke length values of the adaptive drilling bit blade.

Introduction. Biomass is used as foodstuff, for feed making, and for energy production. This is a dispersed material characterized by high porosity and low density, which is poorly adapted for use. Therefore, to improve its processability, biomass is subjected to compaction to shape compacts (feed wafers, granules, etc.).

Materials and Methods. The process of packing biomass in compacts is considered. It is shown that the resistance of dispersed materials to compaction, which includes biomass, is determined by the structural and mechanical properties of the material compacted – structural strength, internal friction, connectivity pressure, strength of the material particles, and bond strength between particles. Theoretical studies have determined the relationships between all the characteristics of dry biomass which form the basis for calculating machines for shaping biomass in compacts.

Research Results. A technique is developed that allows determining the critical parameters of the press with ring dies due to the requirements for the compacts and structural and mechanical properties of the material compacted. The technique is recommended for designing machines providing the formation of biomass in compacts with specified properties. Discussion and

Conclusions. The obtained patterns can be used under designing presses for the production of tailored compacts.

Introduction. The development of the final abrasive processing of parts from polymeric composite materials with the use of the flexible grinding tool is considered. The research objective is to reduce the processing time through displacement of human labour by mechanized work, as well as to improve the treated surface quality.

Materials and Methods. The method of surface preparation of parts made of polymeric composite materials (PCM) is used for gluing through the mechanical abrasive treatment with a flexible grinding tool.

Research Results. Characteristic features of forming the surface microprofile of GRP parts after treatment with a flexible abrasive tool by hand and mechanical methods are analyzed. Need for mechanization of the given operation is determined and validated. The surface parameters affecting the formation of a quality adhesive bond are described. The design features of a flexible grinding tool and their effect on the formation of surface roughness are considered. Data of the surface microprofile treated by a grit cloth and a flap wheel under various cutting conditions are compared.

Discussion and Conclusions. Mechanical processing by flap wheels can replace manual sanding of parts made of polymeric composite materials, drastically reduce the operation time, and improve quality rating of the part surfaces for pasting 

Introduction. The solution to the problem of development of suboptimal evasive strategy of unmanned aerial vehicle (UAV) under the conditions of uncertainty of the current motion characteristics, and the future behavior strategy of the interdictor is considered. The FV (flying vehicle) control is organized with maximum efficiency. Herewith, the maneuvering FV trajectory must satisfy the requirements of optimality for some given functions of the phase variables at the final time and the conditions of its path through a specified terminal area space. The initial conditions and the dynamic facilities of the evading and opposing FV at the initial time are assumed to be known. The evading FV control is developed by its onboard guidance and navigation system in real time on nonlinear position feedback control. The work objective is to build an algorithm for solving the problem of synthesis of terminal optimal control of motion of center of mass of highspeed UAV that allows searching for the optimal control in function of the current coordinates of the object. Consideration of the problem in this formulation distinguishes it from the classical conflict tasks on the prosecution to be solved with the involvement of the theory of differential games, and demands computationally efficient solution methods.

Materials and Methods. For the UAV operating under the conditions of violent disturbances, the most effective hard constraints on the phase variables and control are the so-called methods of optimal terminal control that implement adaptive algorithms with projection. Therefore, the solution to the formulated problem can be obtained precisely with the use of their ideology.

Research Results. A new method of piecewise-software terminal control of the UAV motion is developed. It differs from the known ones in that it is based on the procedure of searching a control strategy upon the best guaranteed result with the terminal restrictions. A methodology for calculating the management strategy for the FV evasive maneuver in a slow loop of the terminal control system is worked out. It is characterized in that instead of the forecast procedure in speed-up time and calculation of residuals, the conversion of a boundary value problem to a one-point task of integration of the ordinary differential equations system with account for the occurrence of non-zero terminal member in the cost functional, is used.

Discussion and Conclusions. Despite the fact that the development of a suboptimal guidance strategy in the terminal area of the evading FV is not in the form of synthesis, the control software adapts to the current conditions. This is achieved through the iterative procedures of regular recalculation of terminal conditions that are equivalent to the periodic circuit feedback. Thus, the evading FV is brought to a specified terminal area through software, while evading an interdictor is developed as synthesis. Limitations to the method are the terms that the movement model of the opposing FV is known, and it forms a natural control of the evader intercept.

Introduction. Many scientists in their research aimed at investigating the cutting process dynamics, the cutting system stability and forming various attracting sets of deformational displacements, consider the machine an autonomous system. In contrast to these works, this paper describes the dynamic properties of the cutting process depending on the dynamic linking parameters under cutting, and on the properties of the subsystems interacting with cutting, taking into account the external disturbances effect. Many of these properties depend on the cutting-tool geometry, and thus the dynamic properties of the treatment process change when the tool geometric characteristics change. In particular, changes in the tool geometric parameters alter the stability of the forming movement trajectories, and their variations can cause bifurcations of the attracting sets of deformation displacements. The forming motion patterns determine both the geometric topology of the workpiece, and the tool wear rate, which depend on the tool geometry.

Materials and Methods. A mathematical model that characterizes the system dynamics disturbed by the spindle group wavering is presented. On its basis, a model that allows for digital experimental research is developed through the use of the software package Matlab.

Research Results. The mathematical simulation results and examples of changes in the system properties depending on the cutting-tool geometry are presented.

Discussion and Conclusions. The problem of matching the control (for example, from the CNC system) and the cutting process dynamics is discussed. One of the directions of this matching is connected with the selection of cutting-tool corners such as forming motion trajectories could remain steady under all variations of the process conditions.

Introduction. The possibility of automated checking the works of participants of the Olympiads in programming is considered. The architecture and operation of the server part of the check system of performing the Olympiad programming tasks is described.

Materials and Methods. The technologies of MySQL, PHP, C ++, JavaScript, HTML, and CSS are considered as the application framework. The test program is implemented in C ++ for operating systems of the Windows NT family.

Research Results. The opportunity of the automated check of the Olympiad participants’ works in a real-time mode is fulfilled. A program-tester of the system is developed to check the programming Olympiad works.

Discussion and Conclusions. As a result of the analysis of the global network and client/server technology operation, capabilities for the organization of interaction of the application with Internet-resources are defined. The developed application has proved expediency and efficiency of the interoperability of the application and Internet-resources.

Introduction. A new type of devices for collecting and accumulating energy – an air-inflatable collector – is considered. As a rule, inflatable collectors are installed permanently which does not imply the orientation of the collector following the solar motion. Due to the low costs of the products in question, it is necessary to offer and investigate the most efficient design.

Materials and Methods. A collector consisting of seriesconnected closed cylindrical segments is considered. Cavities of the cylinders are filled with air which maintains the structure constancy. Mathematical modeling of the definition of the airinflatable collector temperature field is performed using the finite element method.

Research Results. The temperature field distribution as a function of the direction of solar radiation flow is substantiated experimentally. Mathematical models are considered adequate. The increase in temperature of the heat-absorbing layer with respect to the ambient temperature is from 7 ° to 26.2 ° depending on the part of the collector segment.

Discussion and Conclusions. In the course of simulation and experimental studies, it is established that the collector efficiency, apart from solar insolation, is affected by a range of environmental factors: air humidity, wind force, etc. In this case, it is necessary to take into account the device design, as well as the operational and thermophysical characteristics of the materials used. A detailed study of the severity of exposure of external and internal factors on the collector temperature field requires the subsequent development of the software package.

Introduction. A comparative analysis of the modified Whitley model solutions through different methods of forming elite individuals is presented. The algorithms of Kron and Plotnikov-Zverev are used in the study for the formation of elite individuals. The work objectives are the development of the modified Whitley model involving the Kron’s and PlotnikovZverev’s algorithms to form elite individuals, as well as a software tool for solving the scheduling theory problem. It was necessary to obtain the best solution to this problem with various initial data followed by processing the results and identifying a modification of the Whitley model. The distribution problem which implies the search for the optimal distribution of work to the processors with the minimization of the maximum execution time is described.

Materials and Methods. All the algorithms implemented under the development of the software tool for solving the optimization scheduling problem are considered. The following algorithms are presented: the modified Whitley model, the application of the elitism strategy, the Kron’s algorithm, the Plotnikov-Zverev’s algorithm.

Research Results. A software tool is developed. It was applied to conduct a computational experiment with various initial data using one, two, three, and four elite individuals. The experiment was carried out for the most common data sets with a different number of elite individuals. Each Whitley model modification was launched a hundred times with each set of the source data. The comparative analysis of the results shows how the application of the considered elitism strategies in the developed modifications of the genetic algorithm (Whitley model) affects the accuracy of the solution to the homogeneous minimax problem with a different number of elite individuals.

Discussion and Conclusions. The best results of the algorithms are determined; the utilization of elitism in the modified Whitley model when solving a homogeneous minimax problem of scheduling theory is estimated. The algorithm results are compared for one, two, three and four elite individuals.

Introduction. The correction time reduction for the spatial orientation evaluation of a solid under the orientation system initiation is considered. Solid spatial orientation is measured by the integrated values from three orthogonal angular speed sensors. Difference between the actual spatial orientation and the orientation estimated by sensors is adjusted due to the data obtained from other sensors, such as accelerometers and magnetometers. Major existing algorithms deduct data acquired from accelerometers and magnetometers from the evaluation of angular rate through the correction factor thus correcting the spatial orientation assessment error. The higher the solid inclination angle in relation to horizon when the orientation system is switched on, the greater the spatial orientation error is. The algorithm presented herein corrects the spatial orientation evaluation in quaternion components without angular rate sensors which allows minimizing the spatial orientation assessment error within shorter time in comparison with the existing algorithms.

Materials and Methods. To implement the correction algorithm, the MPU6050 sensor is used. It is made with microelectromechanical technology, and its body includes three orthogonally located angular velocity sensors and three orthogonally located accelerometers. The output data from MPU6050 sensor is processed by dsPIC33EP256MU806 microchip. The spatial orientation is calculated by the Rodrigues-Hamilton parameters in the quaternion components. The result is input to the Matlab software package which executes the program of visualizing the dependencies on the time of four quaternion components graphically.

Research Results. In existing algorithms that use the Rodrigues-Hamilton parameters, at the initial initialization of the orientation system, it is suggested to increase the correction factor, or to use the trigonometric formulas to find the Euler angles and translate them into the RodriguesHamilton parameters. In the first case, the initial initialization time remains sufficiently long, in the second case, due to the use of Euler angles, a phenomenon of “gimbal lock” can be observed. The proposed algorithm performs the initial initialization in a time equivalent to the initialization time in the Euler angles parameters, but it applies only the RodriguesHamilton parameters.

Discussion and Conclusions. Using the proposed algorithm will allow a minimum of 5-fold reduction in the initial initialization time of the spatial orientation quaternion. In consequence, the total time required for activating the system will be also reduced due to the fact that the initial initialization is necessary every time the orientation system is switched on. For the correct determination of the spatial orientation according to the proposed algorithm, the necessary condition is the absence of any acceleration on the body other than the gravitational acceleration because the initialization occurs only upon the accelerometer readings. 

Introduction. One of the tasks arising in cryptography is to ensure a safe and fair conduct of e-voting. This paper details the algorithm of electronic elections particularly that part which deals with the cryptographic security.

Materials and Methods. The results are obtained on the basis of the following methodology: finite field theory, projective geometry, and linear algebra. The developed cryptosystem is based on the application of geometric objects from projective geometry over finite fields.

Research Results. The invented algorithm relies on the ElGamal encryption and a new geometric way of secret sharing among election committees. The proposed method uses some features of affine spaces over finite fields to generate special geometric constructions and secret, search of which is a complex algorithmic task for an illegal intruder. The threshold secret sharing is used to prevent voter fraud on the part of the members of election committees. The probability to generate the right share of secret by an illegal intruder in case when he/she knows only a part of secret shares is determined.

Discussion and Conclusions. The described scheme is useful for electronic voting and in other spheres where methods of threshold cryptography are applied.