Vol 48, No 3 (2019)
- Year: 2019
- Articles: 12
- URL: https://journals.rcsi.science/1052-6188/issue/view/12191
Mechanics of Machines
Profiling of the Surface of the Working Elements of Mixing Devices
Abstract
The results of computer modeling of mixing in a system of mobile coaxial cylinders are presented. Detailed spatial-temporal descriptions of the processes are obtained, and the principal structures in the flow field are determined. On the basis of the analysis of the singular points of the fluid vector field, a way of rotor profiling is proposed. The similarity numbers are introduced, which allow us to proceed from laboratory stand installations to real industrial devices.
Induced Oscillations in Worm-Gear Drives of Rotary-Type Manufacturing Machines
Abstract
Induced oscillations in the electromechanical worm-gear drives of rotary-type manufacturing machines are investigated. Using two design models, viz., a model with rigid linkages and a model that accounts for elastic linkages, natural frequencies have been determined and amplitude-frequency characteristics have been constructed. An asynchronous drive motor is described by the dynamic characteristic. A comparison of the results calculated using two models has established the range of the initial parameters within which the dependences can be used that were obtained from the simplest design model with rigid linkages. This will allow considerable simplification and reduction in the time of synthesizing the drive under consideration.
Calculation of Delta-Type Mechanisms with Linear Actuators and Different Numbers of Degrees of Freedom
Abstract
This work is dedicated to consideration of generalized mathematical models of parallel structure of the Delta type. The main design dependences for kinematic chains with four or six degrees of freedom are presented. An example of calculation of the working space, as well as the solutions of inverse problem on speeds (using theory of screws) for the mechanism with four degrees of freedom, are presented.
Reliability, Strength, and Wear Resistance of Machines and Structures
Nonlinear Bending of a Shallow Panel under the Effect of Gas Pressure
Abstract
In this paper, we considered the bending of a round shallow panel under the effect of excessive pressures on the lower and upper surfaces. A refined expression of the distributed transverse force that depends on both the pressure drop on the surface and the interaction of the average overpressure and curvature of the middle surface is used. This refinement is performed in a linear approximation. The panel edge is assumed to be isolated from excessive pressure. The classical theory of nonlinear bending of a round shallow panel under the effect of pressures on its surface is supplemented.
Two-Dimensional Plastic Flow of a Flange when Deep Drawing a Thin-Walled Polygonal Prism
Abstract
Two-dimensional plastic flow of a flange when deep drawing a thin-walled polygonal prism with a flat bottom of round blank provided with Mises yield criterion based on the theory of plane stress condition according to Sokolovskii is simulated. The slip lines, the stress condition, the hodograph of displacement velocities, and the dissipative function of plastic flow are calculated. The limit parameters of deep drawing are defined by the maximum tensile stress at the mold contour and by zones with negative dissipative function, which depends on the radius of rounding of mold angles and the prism height.
Nonparametric Methods of Calculation of the Required Quantity of Test Objects and the Duration of Lifetime Tests
Abstract
Formulas for calculating the required number of test objects and the duration of lifetime tests are proved depending on the estimate of the reduced mean lifetime lower confidence limit for a given confidence probability. The calculation formulas are valid for any time-to-failure law for a technical object. Examples of application of the lifetime test results are given.
Thermohydrodynamic Model of the Tilting-Pad Journal Bearing
Abstract
A thermohydrodynamic model of a bearing is developed based on separate submodels selected by sufficient modeling accuracy for an algorithm of moderate complexity. Thermal processes in the bearing are taken into account along with mechanical ones. Modeling of the temperature regime between the pads is considered in detail. Numerical calculations are carried out. The results are compared with experimental data.
Influence of Structural Changes on the Brittle Fracture Strength in Metal Springs of Kamaz Trucks Used in a Northern Environment
Abstract
To make structural components and vehicle parts reliable, it is necessary to study accumulated structural damage and its influence on the properties of materials, taking into account the operational environment. To discover the relation between structural changes in and brittle fracture strength of materials, we studied the degree and kind of structural damages, impact toughness, and microscale processes of destruction observed in the metal of springs mounted on Kamaz trucks driven in a northern environment. The techniques used in this article include optic and electron microscopy and structural statistical analysis of the microhardness and porosity according to which the structural damage was evaluated. New data are derived about accumulated fatigue damages and their influence on the brittle fracture resistance of the metal in springs used in a cold climate environment. The results can be used to extend the service life of elastic parts of automotive vehicles.
New Technologies in Mechanical Engineering
A Mathematical Model of the Locomotion Mechanism of a Mobile Track Robot with the Magnetic-Tape Principle of Wall Climbing
Abstract
A magnetic-tape locomotion mechanism of a wall-climbing robot is developed. A mathematical model of the motion of a mobile robot on vertical surfaces is proposed. The basic hierarchical elements of the mathematical model are considered. A method for automated formation of a set of differential equations for complex mechanical systems is developed. The motion stability of the mobile robot and the dependence of the capacity of drive motors on the locomotion speed are investigated.
Temperature Distribution in the “Material-Coating” Interface from a Fast-Moving Heat Emission Source for Electromagnetic Surfacing
Abstract
During simulation of the surfacing process, it is proposed to present the heat emission source in the form of the system of instantaneous point sources flickering for some time; and the period between flashes tends to zero. The final results of the temperature distribution are determined by summing the solitary impacts according to the proposed computational pattern. The obtained characteristics and analytical curves allow presenting, at a first approximation, the value and intensity of the temperature fields in the working zone during the electromagnetic surfacing of the large size blanks with sufficient heat removal from the restored surface. The proposed method may be applied for repair and modernization of the railway vehicles elements.
Automation and Control in Mechanical Engineering
Reducing Motor Fuel Consumption Using Mechanochemical Methods
Abstract
Results and hypotheses are presented concerning the reasons for decreasing fuel consumption by automotive-and-traction internal combustion engines in the case of fuel activation using a combined static mixing activator (RF patent no. 2411074) designed for the economically efficient operation of motor transport, and for the production of various grades of motor fuel.
Renewal Function under Prefailure Lives Distributed as a Mixture of n Exponential Distributions: Obtaining the Parameters of Mixtures Using the Method of Moments
Abstract
This paper deals with the problems of the theory of reliability of technical systems for the case when the prefailure lives of the restored (replaced) elements are distributed as a mixture of distributions. For a simple renewal process, when the prefailure lives are distributed as a mixture of exponential distributions, a method for obtaining the renewal function (average number of failures in the range from 0 to t) is presented. For the case n = 3, its explicit formula is written out. The case of n = 2 was considered in [1]. For mixtures of two and three distributions, such as exponential, Erlang, Rayleigh, and Maxwell distributions, an algorithm to obtain point estimates of the unknown parameters of the mixture in an explicit form is presented. In this work, the studies begun in [1, 2] are continued.