Vol 47, No 3 (2018)

A parallel manipulator with six degrees of freedom is considered. A dynamic model for the spherical part of the manipulator is presented. Dynamic analysis is carried out. The real laws of motion of the output link of the spherical part of the manipulator are determined by the screw theory method based on solution of the inverse dynamic problem and the direct velocity problem. The effect of the initial conditions and feedback coefficients on the error of the real law of motion of the output link is analyzed.

Variations in the mechanical characteristics of a material, intense plastic deformations, and the ablation of the material of working surfaces during high-speed sliding of loads along the rails of a rocket sled track facility are studied.

This article deals with characteristic differences between the power spectral densities of monofractal and multifractal dynamical processes. The differences are analyzed from the point of view of determining the damage to the components of an engineering system by fractal analysis of the diagnostic data. As an example, the rolling bearing of a centrifugal pump is studied.

Two variants of a refined theory for calculating the stress–strain state in the boundary zones of cylindrical shells are presented. The relevant mathematical models are based on equations of the three-dimensional elasticity theory and the increase over the thickness of the shell in the orders of the polynomials that approximate the sought displacements. The Lagrange variational principle is applied to the value of the shell’s total energy functional defined more exactly with respect to the classical Kirchhoff–Love theory. The formulated boundary problems allow determination with different degrees of accuracy of additional stressed states of the “boundary layer” type. The calculated results obtained in this work are compared with the results obtained according to the classical theory. It has been established that the above stresses make a significant contribution to the total stressed state of the shell and should be considered when designing and testing machine structures for strength and longevity.

A mathematical model is constructed describing the thermomechanical action of the elements of a composite structure (platelike inclusion and matrix particles) and isotropic elastic medium with the required thermomechanical characteristics. The model is used at the first stage to obtain the matrix relations by the self-consistent method to find the elastic modulus of the composite. At the second stage, it is used to determine the temperature coefficient of linear expansion. Using the variation approach for the composite considered, the two-way estimates of the volumetric elasticity modulus, shearing modulus, and temperature coefficient of linear expansion are determined. The estimated dependences presented allow forecasting the thermoelastic characteristics of the composite, which is reinforced with the anisotropic platelike inclusions (including in the form of nanostructural elements).

This work presents a method of formation of an accurate self-similar solution of the problem of hydrodynamic calculation of a wedge-shaped support (slide block, guide) operating in the presence of a lubricating material and melt of the guide. Based on the equation of motion of an viscous incompressible liquid for a “thin layer” and the expression for the energy dissipation rate, an analytical dependence is obtained for the profile of the melted surface of the guide. In addition, the main performance characteristics of the friction couple considered are defined. The influence of the parameter specified by the melt of the guide on the bearing capacity and friction force is estimated.

A technology for manufacturing a preform for aerospace composite tubular elements by radial weaving is considered. The procedure for selecting the material, the algorithm for determining the preform parameters, and the process of manufacturing and maintaining the accuracy of the reinforcing angle, which are proposed in this study, allow the required thermomechanical characteristics of the composite structure to be achieved.

A method of semiautomatic control of a full arm prosthesis is proposed. The arm prosthesis is viewed as a robotic manipulation system equipped with a pointing device determining the position of an object among others, a position sensor, and a microcontroller. In this regard, the translational motion of the prosthesis hand is done in the automatic mode, while its orientating motion is accomplished in the tracking mode by moving the foot with a master controller located in the shoe. A functional diagram of the control system is proposed along with an algorithm for controlling the motions.

A model for recognition of the geometric elements of the blade feathers is proposed that allows automated analysis of the measured data and computation of the geometric parameters of the feather using modern coordinate measuring equipment. A description of the mathematical model for recognition of the geometrical elements of the blade feather is provided. The model is based on clustering of the points according to the span, mathematical description of the curves of individual profiles, computation of the curvature values at the curve points, filtering of the curvature values, and clustering of the profile points by the curvature value. The proposed model and the software system for its implementation have been verified by measuring the blade feather of a gas turbine compressor using a coordinate measuring machine.