Advances in Mechanical Engineering

The paper is devoted to a new heuristic packing compaction algorithm for the rectangular cutting and orthogonal packing problems. This algorithm is based on the idea of iterative local replacement of some objects placed in a container. Six selection rules for deleting placed objects and subsequent redistribution of them with the aim to obtain a packing with a better density are proposed. The effectiveness of the packing compaction algorithm has been investigated on the standard test instances of the rectangular cutting problem.

The wave processes in the infinite and finite periodic shells (cylinder shell, beam, and rod) are explored. Look-alike systems can model different elements of buildings, hydro-technical constructions, bridges, oil rigs, different pipes, etc. The statement of the problem is considered the rigorous statement. In the infinite systems, Floquet solution is founded. The comparison of the wave processes in the rod and beam is fulfilled. The energy fluxes in them are calculated. The main effects are explored with the attraction of the analysis of vibrations, corresponding to different pass- and stopbands. The dependence of character and «heterogeneity degree» of wave process in the finite systems via the position of corresponding wave number in relation to passbands is considered. The modes of free vibrations of a periodic cell in the case of its asymmetry are analyzed with special attention to edge effects via the parameters of the problem.

An example of weld-joint testing of a new pressure vessel made of stainless steel is considered. The main methods of testing were the method of radiography and the method of acoustic emission. Dangerous defects in the refinery column were detected before running began as a result of the joint application of these methods. This example demonstrates the effectiveness of using such the properties of acoustic emission method, as the integral nature of testing, high sensitivity and the ability to record developing (the most hazardous) defects in the application to the diagnosis of the industrial pressure vessels state. Also, the results of metallographic examination of the specimen of column shell with detected defects are presented. The question of the sequence of application of different methods of non-destructive testing for optimization of the procedure for inspection of large-sized equipment is discussed.

The proposed article contains a technique for optimizing the parameters of a gear pair with circular teeth, which can be used both in the design of a new gearbox and in the modernization of an existing gearbox. In both cases, the initial data for the design of the transmission, which is part of the gearbox, are its gear ratio, dimensions and transmitted loads. The only difference is that in the second case, as a rule, it is necessary to place a couple in the same housing, which imposes more stringent restrictions on its size. Two examples of the optimal design search by varying the angle of the spiral and by varying the number of teeth while maintaining the same gear ratio are given.

During experimental research, a deviation of milling system noise level measurement was detected in idle running mode during the period of equipment shift operation. A discrepancy of predicted parameters of predicted vibration activity of the milling system compared to the actual numbers during lowering of the spindle module operating frequencies range in the area of steady cutting. Based on the analysis of the obtained data and additional studies, dependency of system vibration and its noise level from the temperature conditions of the machine working area were identified. This dependency is proposed to be used to adjust the values of the predicted vibration of the milling setup by correlating temperature readings of the system with noise factor by taking into account the operating time of the equipment.

The tribotechnical, metallographic, physical, and chemical properties of nanostructured copper–nickel coatings applied on products made of X12M tool steel were investigated. The results showed that a significant increase (2.3 times) in the wear resistance of the coatings was achieved after high plastic deformation under a stress of 3.5 GPa. A structure was formed with a minimum size of coherent scattering regions (CSR) of 23 nm and a maximum crystal lattice microstrain value (CLM) of 1.25%.

The article provides a solution for the task with regard to synthesis of the laws for motion of the slave cylinders in a parallel-serial structure manipulator to realize the predetermined path of an end effector. The set of points characterizing subsequent positions of the actuators is determined by solving an optimization task on the manipulator’s configuration. The laws for motion of slave cylinders are established by the method of the fifth-order polynomial interpolation of the first and last sections of the determined path. The intermediate path section is described by a typical polynomial. The polynomial coefficients are determined by the point square approximation method.

This study considers the problem of improving test equipment through the use of resonant modes to reproduce harmonic impacts, and examines the influence of various parameters on the reproduction of a wider range of test impacts, including in transient modes.

To identify the gears, tooth shape that ensures optimal gearing quality indicators is a crucial design problem. The authors suggest a new optimization synthesis concept based on the determination of an optimized meshing line to address this issue. The synthesis algorithm including its key and the largest (as concerns calculations) blocks is described in the article. The article introduces derivation of formulae for determination of the tooth profiles with a known meshing line. According to the formulae, profiles for various types of meshing lines (a straight line, a curve, etc.) were obtained. The conclusions were made, and further fields for research were determined.

The aim of this article is modeling of the atomic force microscope as a lumped parameter system in its dynamic contact mode of operation. The Derjaguin–Muller–Toporov (DMT) force is considered as the interaction of the cantilever tip with the sample surface, and it introduces the nonlinearity to the model. The frequency response equation of the model is obtained by the method of multiple scales. As the results, effects of the nonlinearity, amplitude of excitation, and the damping coefficient on the frequency response are investigated.

When structural groups of linkage mechanisms approach singular positions, a self-braking effect may occur due to friction forces. By the example of structural groups with revolute kinematic pairs, conditions that ensure the absence of such undesirable effects are shown. The concept of a structural group with equivalent ideal kinematic pairs is introduced. Getting such a group into a singular position indicates the occurrence of the self-braking effect.

The dependences of the values of angular velocities and angular accelerations of the driven crank on the leading crank are investigated. The methods of synthesis of modifications of Bennett’s mechanism according to the degree of non-uniformity of rotation of the driven crank, according to the positions of the driving and driven units are considered. Formulas are obtained that allow tracing the influence of the geometric parameters of the links of the mechanism on the kinematics of the cranks. The calculation results are displayed in the form of graphs.

Comparative analysis of configurations of test centrifuges designed for mechanical testing of devices and instruments has been performed. Schemes of centrifuges, rotor-balancing devices, have been considered. Recommendations for rotor aerodynamic casings design have been given.

The most effective way to reduce fuel consumption by the vehicle equipped with internal combustion engine is to increase the number of speed ratios in the transmission. It leads to design complication and increasing the number of gear trains used. Here is proposed to make combinations of planetary gear sets and gears with fixed axles for obtaining simple designs of multi-speed transmissions with a small number of shifting elements used. The aim of the paper is to analyze compound transmission structures consisting of three simple gear trains with fixed axles and two planetary differential gear sets which forms three parallel power flows (three-stream transmissions). The possible structures of combined transmissions with planetary gears and gears with fixed axles are considered in the article. Such transmissions have a great perspective because of utilization simple gears and a small number of clutches, while these transmissions allow obtaining a significantly larger number of different speed ratios than the transmissions made up of the identical gears type. The possible three-stream transmissions structures were analyzed and classified, and a general expression is obtained for calculating the number of speeds in such transmission. A technique for synthesizing kinematic diagrams of transmissions with three power flows is described, using which new transmissions designs are obtained for each possible structure.

Friction forces emerge in kinematic pairs of mechanisms; in many cases, these forces significantly affect the movement of the links of the mechanisms and should be taken into account in force calculations. Introduction of friction forces leads to an increase in the number of unknown components of the reactions of the pair while the number of kinetostatic equations does not increase. In order for the problem of force analysis to remain solvable, it is necessary to introduce additional conditions, the number of which is equal to the number of additional unknowns. Usually, additional conditions are selected allowing for the design features of the elements of kinematic pairs, which allow making some a priori assumptions about the nature of the normal forces distribution. The paper considers the formation of such conditions, i.e., essentially, the examples of constructing computational models of kinematic pairs with friction. A force calculation of the mechanism with allowance for friction is shown, which is reduced to the joint solution of the kinetostatic equations and additional equations describing the models of kinematic pairs. It is also shown that for the given kinematic parameters of motion, the system of force calculation equations has one solution, several solutions, or no solution at all.

The results of research mode of the “dangerous” pre-destruction zones at the root of cruciform weld joint are presented. A technique for determining the areas of “dangerous” zones in numerical simulation is proposed. The engineering equation to determine the area of the danger zone as a result of numerical modeling of the elastoplastic problem is received.

The paper deals with new problems related to the excitation of oscillations in the drives of cyclic machines, taking into account the spatial distribution of the characteristics of the working elements and the force closure of systems. Dynamic models based on aggregation and general representations of systems with complex structure are proposed. An original method for studying systems with variable parameters is presented, in which the method of the conditional oscillator is applied to variable spatial and temporal arguments. The paper deals with new problems related to the excitation of oscillations in the drives of cyclic machines, taking into account the spatial distribution of the characteristics of the working elements and the force closure of systems with gaps. Dynamic models based on aggregation and general display of systems with complex structure are proposed. The original method of studying systems with variable parameters is presented, in which the conditional oscillator method is applied to the joint consideration of the variability of spatial and temporal characteristics.

The article presents a mathematical model of the kinematics of angular velocities and accelerations of the connecting rod of a two-movable five-link spatial mechanism with a double crank. Based on the analysis of kinematics studies, the nature of the influence of the input parameters of the basic mechanism of the device on the kinematics of the simulator chair is established. The results of analytical calculations are presented in the form of graphs.

The problem of calculation of the stiffness of a rod equivalent to corrugated thin-walled tube is considered. Tensile stiffness, bending stiffness, and shear stiffness are found from solving static problems for a corrugated shell. A version of the classical theory of thin shells is used. The equivalent stiffness found was used to calculate the statics and stability of corrugated tube as a rod.

The article is devoted to the vibrations of a heavy chain in load-lifting machines in the braking regime, assuming that the braking moment is a linear function of the velocity of the motion mechanism and the chain without a mass on the end. A method of approximate analytical solutions of the system of differential equations of motion is presented. The results obtained are illustrated with an example on the basis of the technical characteristics of the crane trolley that the Visual Fortran program is created for.