IMPROVING THE MASS EFFICIENCY OF A COMPOSITE LAUNCH VEHICLE HEAD FAIRING WITH A SANDWICH STRUCTURE (p. 6–18)

Analysis of practical experience in the construction and operation of the main fairings of launch vehicles has revealed the currently widely used sandwich structures with composite load-bearing sheathing combined with a cellular filler

The paper has examined the potential of using nonlinear models of strength in determining the initial critical load on soil, as well as the standardized and estimated base resistance, which makes it possible to reduce labor intensity in the process of determining the strength properties of soils.
Based on the analysis and generalization of results from theoretical studies into geomechanical processes using analytical mathematical methods, the formula modifications have been derived that are intended for determining the initial critical load on soil, as well as the standardized and estimated base resistances.
We have established interrelation between strength, in particular specific cohesion, and the angle of internal friction, which are included in the strength conditions by Mohr-Coulomb and A. Shashenko, thereby making it possible to improve the procedure for calculating external loads on soil.
The dependences of critical loads on base on the mean pressure under the sole of the foundation haven been analyzed in the range of pressure Р = 100...500 kPa using the strength conditions by Mohr-Coulomb and A. Shashenko. It has been established that when using generally accepted estimation formulae to determine the critical loads on base, it is required that the pressure range should be taken into consideration at which the properties of soil strength were determined. In this case, using the Shashenko failure criterion to determine critical loads on base makes it possible to properly consider the impact exerted by the mean pressure on them under the sole of the foundation.
In contrast to dependences used currently in the Ukrainian, Belarusian, Russian regulatory documents, as well as in other countries' standards, the resulting formulae make it possible to take into consideration the dependences of soil strength properties on the mean pressure on soil under the sole of the foundation. The results obtained make it possible to improve the reliability of determining the initial critical load on soil, as well as the standardized and estimated base resistances. This is achieved by taking into consideration the nonlinearity of the Mohr limiting circles' envelope using the strength condition by A. Shashenko.
Keywords: failure criteria by Mohr-Coulomb and A. Shashenko; load on soil, cohesion, angle of internal friction.

Pavlo Humeniuk
National Aviation University, Kyiv, Ukraine ORCID: http://orcid.org/0000-0003-3532-2555 The purpose of this work is to estimate the aerodynamic characteristics of the stepped nacelle of a gas turbine engine with a turbofan unit. The research was based on the method of model physical experiment. The wind tunnel applied for the study was provided with the necessary equipment, which includes various nozzles of static and dynamic pressure with coordinate devices, etc. For the experimental study, we built the models of nacelles for an aviation power plant with front location of the fan module and with the rear arrangement of a turbofan unit. We have experimentally investigated the aerodynamic characteristics of the stepped nacelle for a gas turbine engine with a turbofan unit.
The results of this study demonstrated a possibility to decrease the aerodynamic drag of the stepped nacelle for an engine with a turbofan unit compared to the nacelle of a turbojet double-pass engine with the front arrangement of the fan. In the range of angles of attack α = 0...20° the value of aerodynamic drag of the stepped nacelle for a gas turbine engine with a turbofan unit decreases by 49...55 %.
The obtained results showed that the coefficient of lifting power of the stepped nacelle for a gas turbine engine with a turbofan unit increases by 24...64 %. The coefficient of aerodynamic drag is lower by 18...28 % compared with the aerodynamic drag coefficient of a cylindrical nacelle for a double-pass turbojet engine in the range of angles of attack α = 2...20°. Our findings indicate the prospects of using engines with a turbofan unit. The structural feature of the stepped nacelle would reduce the loss of efficient engine thrust by decreasing aerodynamic drag almost by two times and could increase fuel efficiency of the engine.
We have analytically examined the steady motion modes of the system, composed of a balanced rotor on the isotropic elastic-viscous supports, and a load (a ball, a roller, a pendulum), mounted inside the rotor, thus enabling its relative motion. In this case, the pendulum is freely mounted onto the rotor shaft, while the ball or roller rolling without slipping along a ring track centered on the longitudinal axis of the rotor.
The physical-mathematical model of the system has been described. We have recorded differential equations of the system's motion with respect to a coordinate system rotating at a constant speed of rotation in the dimensionless form.
All steady motion modes of the system have been defined under which a load rotates at a constant angular velocity. In the coordinate system that rotates synchronously to a load, these motions are stationary.
Our theoretical study has shown that under motion steady modes: -in the absence of resistance forces in the system, a load rotates synchronously with the rotor; -in the presence of resistance forces in the system, a load is lagging behind the rotor.
The load jamming regimes are the one-parameter families of steady motions. Each jamming mode is characterized by the corresponding jam frequency. Depending on the system parameters, one, two, or three possible load jam velocities may exist. If, at any rotor speed, there is only a single angular velocity of a load jam, then the corresponding motion mode (a one-parameter family) is globally asymptomatically steady. If the number of jam velocities varies depending on the angular rotor speed, the asymptomatically steady are: -the only existent mode of jamming (globally asymptomatically steady when there are no others); -jamming modes with the smallest and greatest velocities.
A load jam mode with the lowest angular velocity (close to resonance) can be used in order to excite resonance oscillations in vibration machines. The highest frequency of a load jam is close to the rotor speed. This mode can be used to excite the non-resonance oscillations in vibration machines.

Yuriy Naumenko National University of Water and Environmental
Engineering, Rivne, Ukraine ORCID: http://orcid.org/0000-0003-3658-3087 Effect of the degree of chamber filling with the charge on efficiency of the self-oscillating grinding process in a tumbling mill has been assessed.
By using the approximate analytical and experimental method, dynamic effect of increasing the self-oscillating impact action of grinding fill on the crushed material was compared with the conventional steady-state motion mode. A significant increase in average sums of vertical components of the self-oscillating collision momenta and the average sums of power of such components with a decrease in the chamber filling degree was found. Manifestation of this effect is due to the increase in the self-oscillations swing with decreasing filling. An increase in the maximum momentum values was found to be approximately 2.4 times at the degree of filling κ = 0.45, 3.1 times at κ = 0.35 and 5.8 times at κ = 0.25. An increase by 5.7 times in maximum values of momentum power was found at κ = 0.45, by 9.6 times at κ = 0.35 and by 45.5 times at κ = 0.25.
Technological effect of significant decrease in the specific power intensity and productivity growth of the innovative self-oscillating grinding process as compared to the characteristics of the conventional steady-state process with a reduction in the chamber filling degree have been experimentally established.
The process of grinding cement clinker with a complete filling of gaps between spherical grinding bodies with a relative size of 0.026 with particles of the crushed material was considered. It was found that during excitation of self-oscillations, power intensity of grinding decreased and productivity increased. A decrease in relative specific power intensity was observed: 27 % at κ = 0.45, 42% at κ = 0.35 and 55 % at κ = 0.25. A 7 % increase in relative productivity was found at κ = 0.45, 30 % at κ = 0.35, and 46 % at κ = 0.25.
The effects established in operation have allowed us to predict rational parameters of the self-oscillating grinding process carried out in a tumbling mill with variation in the chamber filling degree.
Keywords: tumbling mill, chamber filling degree, fill selfoscillation, specific power intensity in grinding. This study addresses the construction of a mathematical model, the statement of boundary-value problems on the statics of a grainy material related to the technological processes of agricultural production. A working apparatus employed to construct the model of a grainy material is the methods of equilibrium thermodynamics. We have stated the main thermodynamic equality, which makes it possible to derive a rheological ratio that establishes the connection between stresses and deformations of the granular material. The chosen grainy material is a granular medium that manifests a Reynolds effect. This effect occurs in the case of small deformations and indicates the presence of a dependence of dilation on the stress tensor deviator. In contrast to the classical methods that consider a model of continuous medium with the non-deformed and smooth grain's particles, the present work takes into consideration both a Reynolds effect and the presence of elastic deformations. The resulting rheological ratio produces the dependence for a stress tensor on the deformation tensor corresponding to ratios from the linear theory of elasticity.
For the case of an isothermal process of deformation, a boundary-value problem on the grain material's statics in the field of gravity has been stated. This paper shows the statement and solution to two particular tasks on the balance of a granular layer along the horizontal plane: in the absence of surface forces and under the action of tangent surface forces on a free surface.
The boundary problems on the equilibrium of a granular material are nonlinear in character, and the resulting solution represents a complex mathematical apparatus involving numerical methods.
The obtained models for the statics of a continuous environment precede the consideration of dynamic problems, in particular, the study of equilibrium stability.
Keywords: granular materials, equilibrium thermodynamics, Reynolds effect, horizontal grain layer, boundaryvalue problem, boundary conditions. Experimental research into determining the mechanical properties (elastic and dissipative) of the pressure fire hose of type «T» with an inner diameter of 66 mm under conditions of static load were presented. The experiment was conducted on the experimental setup, which makes it possible to measure force and deformation. In the course of research, a series of field experiments in stretching with the sample under conditions of static loading-unloading cycles was carried out. The tests consisted of 5 cycles (modes) of loading-unloading, which were performed with a twominute interval. Taking into consideration the experimental data, the elasticity module at stretching the material of the hose in the longitudinal (along the base) direction was determined. It was established that numerical results of mechanical properties depend on the hose loading «history», that is, in the first two load modes, elasticity modules increased and were stabilized only in the subsequent modes. The above, along with a significant reduction in residual deformations, increases the elastic properties of the fire hose material.

Gennadiy Chernobay
The results of the conducted studies showed that in the first two cycles, the material demonstrates short-term creep, which gets stabilized in modes 4-5. To generalize the experimental research, the results were approximated by corresponding trend lines. The curves of the sample deformation, which under conditions of cyclic loading-unloading formed the hysteresis loops, were determined. The hysteresis loops obtained during the study showed that in the first two modes, the loop are subjected to quantitative and qualitative changes, specifically, the slope of the hysteresis loop and its area decreases.
It was determined that a change of the properties of the material of the fire hose at consecutive loading-unloading deformation cycles are reversed, the gaps between the deformation cycles result in partial restoration of the mechanical characteristics, approximating them to the initial values. Relaxation time is from several hours to several days and even weeks, which depends heavily on the magnitude of the previous relative deformation. The scheme of a feeder has been constructed, in which, along with conventional lobed rollers, the pinned or pinnedplanked loosening rollers are used. The feeder of such a design achieves both a smooth and uniform feed of cotton to the machine and a change in the technological characteristics of raw cotton. Additional rollers lead to a change in the technological characteristics of raw cotton, thereby forming a process of intensive removal of weed impurities. The mechanics of interaction between the working elements of feeding devices and the layer of a transported material has been investigated; in addition, the feed systems with a directed change in the technological properties of raw cotton have been selected.
It has been proven that a high cleaning effect could be achieved not only by intensifying the cleaning process, but also by a directed change in the technological properties of raw cotton while maintaining or improving the quality of the resulting product. It is obvious that the deformation that a particle undergoes in the examined scheme would be maximally possible, limiting, because the structure excludes the slippage of a product in the zones between the lobed and loosening rollers, which is not excluded in an actual design.
The technological properties of raw cotton as a cleaning material have been studied, the structural characteristics of cotton have been investigated, as well as the relation between their kinetics and cleaning processes. Relations between a structure coefficient and the magnitude of open surfaces of the raw cotton structural units have been established. The spatial characteristics of raw cotton clogging and the conditions of interaction between fiber and weeds in the volume of clogged cotton mass have been studied. Variants of combinations of feed rollers with various structures of pinned rollers have been given, which make it possible to formulate the main ways to intensify the existing, and create new, technological processes of raw cotton cleaning.
Based on the established functional links, it becomes possible to construct new, or improve existing, structures of pinned sections in the cleaning machines ChKh-3M1. Experience shows that the application of the developed scheme of the feeder in the cleaners from large impurities produces a significant increase in the cleaning effect of the machine.