Vol 45, No 4 (2016)
- Year: 2016
- Articles: 13
- URL: https://journals.rcsi.science/1052-6188/issue/view/12111
Mechanics of Machines
On the description of strongly nonlinear vibroconducting and vibrogenerating media
Abstract
A quite general class of problems is considered, the analysis of which makes it possible to describe the mechanism of for the generation and propagation of broadband vibration in machine structures. Mathematical models based on the theory of strongly nonlinear continuous media with a complex structure are presented. Different types of models of a “linear carrier medium plus attached equipment containing impact pairs” class are presented. It is assumed that the impact is Newtonian. The necessary defining relations are given. An example of vibroconductor analysis with internal breaks is given.
Improving the ecological indices of a hydrogen diesel engine with direct gaseous hydrogen injection
Abstract
A detailed survey of the operating process and formation of nitrogen oxides in the combustion chamber of a hydrogenous diesel has been carried out in three-dimensional space using a mathematical model verified by experimental data. The specific features of the thermophysical processes in the combustion chamber of the hydrogen diesel engine have been specified, providing the applicable ecological and efficient indices of a stationary hydrogen diesel engine.
Realibility, Strength, and Wear Resistance of Machines and Structures
Increasing the lifetime of gas-turbine engine nozzle blades using a new monocrystalline alloy
Abstract
The article presents the results of experiments to study the creep of an intermetallic monocrystalline alloy used to manufacture nozzle blades. The results serve as a basis for calculating the creep-rupture strength and thermal fatigue of gas-turbine engine blades.
Mathematical models for increasing the reliability level of a technical system taking into account control actions in the form of probabilities and imposed constraints
Abstract
Mathematical models for increasing the reliability of a technical system up to the desired level are developed taking into account control actions when the rate and acceleration of design, technological, and operational parameter changes are controlled. Mathematical models are also created to increase reliability while constraints are imposed on the parameters.
Comparative analysis of the results of finite element calculations based on an ellipsoidal shell
Abstract
In the curvilinear coordinate system, we describe an algorithm for generating the stiffness matrix of the quadrilateral element of the middle surface of a thin shell based on Kirchhoff’s hypothesis with nodal unknowns in the form of displacements and their derivatives using a vector approximation of the displacement fields. The developed finite element is verified by calculating the shell with the middle surface in the form of a triaxial ellipsoid in the two-dimensional formulation. The results are compared with the calculation results obtained using ANSYS software. The efficiency of the vector approximation of the displacement fields for the calculation of arbitrary thin shells in the moment stress state is shown.
Numerical simulation of elastohydrodynamic lubrication for an elliptical contact
Abstract
An elastohydrodynamic problem on elliptical contact is formulated and numerically solved. The mathematical model is described by a system of integro-differential equations and inequalities with boundary conditions. The direction of the rolling velocity vector with respect to the axes of the ellipse has a marked influence on the distribution of pressure and the lubricating film thickness in the contact area. The elastohydrodynamic contact parameters are determined depending on the compression force applied thereto. These results are useful for analyzing processes occurring in lubricated concentrated contacts.
Concentration effect of antifrictional additives on local elastic characteristics of randomly reinforced polymer composites
Abstract
The problem of numerical simulation is solved for operators (tensors) of the stress and strain concentrations, which are related material-average stresses and strains with their local values in epoxyphenolic composites reinforced randomly by short polyimide fibers with antifrictional dispersed additives of polytetrafluoroethylene. Simulation is based on the generalized singular approximation of random field theory. The dependences of mentioned operators on the percentage of isotropic components are investigated. It is shown that an increase in the antifrictional additive concentration with a fixed fiber concentration does not result in a substantial decrease in the local elastic characteristics of the composite.
Periodic variational Rayleigh problem of the gas-film lubrication theory
Abstract
A solution to the variational problem for a plain bearing (slider) on gas-film lubricant with periodicity conditions is considered. Using the calculus of variations, the shape of the lubricating layer providing maximum levitation force is determined. Along with the compressibility number, the parameters in the problem are the ceiling value of the profile function, and its limiting value corresponds to the results obtained by Rayleigh. Characteristics are presented for the optimum bearing in the case of different compressibility numbers.
New Technologies in Mechanical Engineering
Impact of waves on porous media and increase in oil recovery of beds
Abstract
The results of studying wave impact on a productive bed for extraction of capillary hydrocarbons are presented. The studies were conducted on experimental equipment that which simulates filtration processes in a system of hydrodynamically related wells. Impact waves are considered that propagated from a processed well inside a bed via a system of fractures and faults with higher permeability. It is shown that impact pressure pulses intensify filtration due to the involvement of capillary hydrocarbons and to the increase in permeability of the porous medium.
Experimental Mechanics, Diagnostics, and Testing
Education and research mechatronic complex for studying vibration devices and processes
Abstract
We describe a new study and research mechatronic complex, which consists of a vibration stand with electric drives of unbalanced rotors, a personal computer for controlling the stand and processing the experiment results, a system of sensors, coupling devices, and an amplifying and transforming unit. We give the results of stand experiments displaying the Sommerfeld effect and suggest ways of applying the complex to create new technologies in the processing industry and in the study process.
Experimental study of residual stresses and interference of locomotive wheels by the acoustoelasticity method
Abstract
ltrasound method to evaluate residual stresses in locomotive wheels using the electromagnetic–acoustic excitation and reception of elastic waves is described. The results of residual stress distribution throughout the wheel thickness before and after fitting of wheel centers are presented. A method for controlling the interference of locomotive wheels by the measured values of residual stresses using the acoustoelasticity method is proposed.
Safety of Machines and Structures
Reliability of an overground oil and gas pipeline with initial bending
Abstract
For a beam sector of an oil and gas pipeline with initial axial bending, a mathematical model is developed that simulates the probability of nondestruction when the pressure, diameter, wall thickness, load, span length, maximum deflection, elastic modulus, and Poisson ratio are normally distributed. The parameters that decrease the number of emergency failures are established.