Sessions 2017-2018

Based on experiments on the decay of rotational oscillations of an axisymmetric body in the airflow, rotational derivatives of the pitching moment coefficients are determined. It turns out that the more elongated noses are characterized by larger absolute magnitude of rotational derivatives. The presence of a coaxial disk in front of the cylindrical part of the body instead of the streamlined nose also leads to an increase in rotational derivatives in absolute magnitude.

In work on the basis of a hybrid model, numerical experiments were conducted to study the parameters of the dielectric barrier microdischarge at atmospheric pressure in argon in a wide range of input conditions. A comparative analysis of the results obtained with a voltage signal applied to the electrodes in the form of a sinusoidal and rectangular shape is presented. In particular, for both cases, the spatio-temporal dependences of the densities of charged and excited particles, the electric field, the time dependences of the discharge current density and the voltage drop between the electrodes, and the time dependences of the accumulation of charges on the right and left dielectrics are presented. The results of numerical experiments demonstrate the principal dependence of the spatial and temporal characteristics of the barrier microdischarge at atmospheric pressure in argon on the shape of the applied voltage. Thus, in the case of a rectangular-shaped supply voltage applied to the electrodes, two current pulses are always observed for a half-period (regardless of the amplitude of the supply voltage). In the case of a sinusoidal signal, the number of current pulses depends on the amplitude of the applied voltage.

This work is devoted to the study of the transformation plasticity and shape memory effects in the Ti - 50,2 at.% Ni alloy with various grain sizes. The obtained results show that strain variation during cooling occurs in some stages depending on the grain size and stress. In grains with the size of less than 80 nm, strain variation is observed only in the case when the stress acting in cooling and heating overcomes the critical value. An increase in stress leads to the increase in the transformation plasticity and shape memory effects as well as in the temperatures of the martensitic transformations. A decrease in grain size results in the decrease in the transformation plasticity effect and the martensitic transformations temperatures, while the shape memory effect value depends on the grain size in a non-monotonic way. The maximum recoverable strain of 15% is observed in a sample with the grain size of 130 nm.

An influence of thermal treatment and high-pressure torsion (HPT) processing on secondary phase particles formation and mechanical properties of Cu-2Be alloy was studied. An alloy treated with the homogenized solid solution was subjected to three main thermomechanical treatment regimes: a coarse-grained alloy HPT with subsequent aging, coarse-grained alloy aging with subsequent HPT and aging during HPT at the temperature range from 150°C to 250°C.

The results of X-Ray diffraction (XRD) for the obtained materials showed that the thermomechanical treatment regime affects the grain size, internal stress values and the location of secondary phase CuBe particles in the parent matrix material. According to XRD, a secondary phase particle in the HPT-processed alloy can be located at both, the grains boundaries and in grains interiors.

Studies of the mechanical properties by means of uniaxial tensile tests showed that good combination of strength and plasticity was achieved in the alloy subjected to aging at the temperature 325°C for 10 hours with subsequent HPT processing. Fractography analysis via scanning electron microscopy (SEM) revealed a ductile-brittle fracture behavior of nanostructured Cu-2Be alloy.

Results of this work show that the selection of thermomechanical treatment regime can be used as a driving factor for desirable phase formation kinetics with following mechanical properties.

The problem of self-balancing of a statically unbalanced rotor by means of a passive ball auto-balancing device (ABD) is considered. The use of such devices is especially important for rotors with variable unbalance, such as centrifuges for washing or drying machines. A mathematical model was created for a statically unbalanced rotor with a weightless elastic shaft fixed in vertical supports and equipped with a multi-row, multi-ballistic control unit. An algorithm for numerical integration of the system has been developed, taking into account the collision of the balancing balls with each other. The program is written in Mathematica software to calculate the motion of a system containing an ABD with an arbitrary number of concentric circular cavities and an arbitrary number of balls in each cavity. The results of calculations are presented in the form of graphs and computer animation, clearly demonstrating the processes of movement and interaction of balancing balls.

Granulation of powdered materials in a drum-type high-speed granulator was studied. A mathematical model was constructed for describing the granulation in a high-speed granulator in which two processes, coagulation and disintegration, are combined. The constants of the integral transform kernel for coagulation and disintegration were determined from the experimental data. It is shown, that the suggested mathematical model adequately represents the real process of granulation of a hydrophobic additive in the asphalt concrete mix.

In this work we describe the problem of the influence of inhomogeneous field of temperatures on the creep and thermal deformation in the thermocyclic creep simulation. The equilibrium equation and the theory of Zhurkov and Kachanov are used to describe the change of deformation and stress fields. The created algorithm allows us to computerize the given process.

Reverse micelles (basic structural elements of the “water-in-oil” microemulsions) have been considered in the work. Microemulsion is a thermodynamically stable transparent mixture of three or more components: surfactants and two non-miscible liquids. Molecular dynamics simulations of reserve micelles, that contain water and surfactants Span80 and Tween80, have been investigated in a non-polar liquid n-decane. Spherical micelles, which shape can be approximated by an ellipsoid with an axial ratio close to one, have been also obtained. The obtained data on sizes and diffusion coefficients of reverse micelles and water nanodrops are quantitatively close to the corresponding experimental data of dynamic light scattering and NMR.

The report discusses methods for locating additional hinge support in beams. The purpose of the support installation is to fulfill some optimization requirements. The main object of investigation is the cantilever beam which experiences the action of various external loads: concentrated and distributed, longitudinal and transverse. It is shown that it is possible to achieve a significant reduction in the maximum deflection and maximum bending moment or critical force, at which structural stability loss occurs, by optimal installation of an additional support.

Suppression of cargo swings carried by a KKS10 crane for a given time by a specified distance is considered in the report. The control force is sought in two ways - by applying the Pontryagin maximum principle and using the generalized Gauss principle. Solutions obtained by both methods are compared. The problem is solved under the assumption of small swinging motions using the nominal characteristics of a particular gantry crane.

Multilayer corneoscleral shell under various mechanical loads is studied by the finite-element modeling in ANSYS program package. The first part of the dissertation is devoted to a calculation of intraocular pressure (IOP) under a load of the flat base stamp with different weighs depending on a variety of biomechanical characteristics of the corneal multi layered shell. Next part is concerned with studying changes in IOP after intravitreal injection of a standard volume into a multilayer corneoscleral shell of variable thickness and an ellipsoidal shape. In the third part, changes in IOP after refractive correction of hyperopia are considered and also the stress-strain state of the corneal shell with different options for the location of the zone of ablation is analyzed.