Vol 21, No 3 (2022)

The article describes the solution of a complex problem to determine the optimal parameters and engine layout for the power plant of an advanced unmanned aerial vehicle according to the methodology developed by the authors using the author’s complex mathematical model and the well-known method of indirect statistical optimization based on self-organization. At the same time, the main aerodynamic and flight performance characteristics of the unmanned aerial vehicle under study, calculated according to engineering methods, are shown, as well as the parameters and characteristics of its power plant, calculated using the author’s algorithm implemented in a complex mathematical model. The results of parametric studies are also presented using the example of assessing the influence of the bypass ratio on the characteristics of a power plant and the parameters of the unmanned aerial vehicle under study. The process of conducting optimization studies of the “Unmanned aerial vehicle – power plant” system with a bypass turbojet engine with mixing of the circuit flows behind the turbine is described. At the same time, special attention is paid to the formulation of the optimization problem, the choice of criteria and changeable variables, as well as the analysis of the results obtained by comparing the efficiency of the system under study with different engine configurations according to the criteria of the aircraft level: maximum range according to two formed flight programs.

Modern methods of computational fluid dynamics have been used to study flows with mass supply in axisymmetric channels of solid-propellant rocket motor charges. The studies were carried out with the aim of increasing the accuracy of predicting the intraballistic parameters for performing engineering calculations. The analysis of changes in intraballistic characteristics in the flow part of the channel charge in the classical and nozzleless solid propellant rocket motors is carried out for different rates of mass supply from the combustion surface. For an isobaric combustion chamber, a characteristic velocity profile is shown along a tubular charge path and a charge with sudden expansion. It is shown that for a steady cosine profile of axial velocity after sudden expansion of the channel, a length of more than three gauges is required. For a high-speed combustion chamber, a comparison of the axial velocity profile is carried out depending on the flow velocity under different conditions of mass supply. The tendency of the influence of flow velocity on the character of the profile is noted. It is shown that at a Mach number over 0.5, an increase in the mass flow rate from the combustion surface provides a less filled velocity profile tending to cosine. The differences between the pressure losses in the flow passage of the channel charge, calculated in the axisymmetric approximation, and the losses determined using gas-dynamic functions, are shown. An increase of the mass flow rate in the charge channel of a nozzleless solid-propellant rocket motor leads to a decrease in pressure losses at Mach number over 0.8.

The problem of forming a rotating ring-shaped tethered system consisting of three nanosatellites is considered. To analyze the dynamics of the tether system, a mathematical model is developed in the orbital coordinate system using the Lagrange method. Using the sliding mode control method, two control programs for the deployment of tethers are proposed, in which tether tensions and thrust forces created by low-thrust engines are used as controls. In the first control program, the control actions are directly limited by the permissible limits of tether tensions forces and thrust forces, and when designing the second control program, an auxiliary dynamic system is added into the control system, which introduces control corrections that take into account the saturation effect. The stability of motion of the tethered formation system for both control programs is investigated using the Lyapunov theory. The results of numerical simulations confirmed the possibility of using the proposed control programs for the formation of a rotating triangular tethered system in the form of a regular triangle in the presence of disturbances and with account of the given constraints.

As the science of friction developed, tribologists showed that reliable operation of friction units is determined by the wear resistance of the surface layer, its ability to adapt to changing operating conditions. In this regard, there is a need not only to create structures on the surfaces of friction units that have the properties of self-regulation and self-organization, but also to monitor changes in the characteristics of the surface layer. This article presents an innovative methodology for monitoring the life cycle of surface layers coated by vacuum ion-plasma treatment. In this paper, we propose a dynamic model based on the hypothesis that roughness is both a factor that excites mechanical vibrations and a consequence of these vibrations, whereas roughness changes as a result of wear under the influence of local dynamic forces. It is shown that a friction pair is a nonlinear system with complex feedbacks. Its stationary motion can be considered as a strange attractor. The randomness of motion in the vicinity of the limit cycle is due to the presence of a link of constant delay with rigid positive feedback in the model. As a result, there is constant reconfiguration of the amplitude and phase of the oscillations.

When developing models of critical mechanical engineering products, it is necessary to solve dynamic problems, taking into account changes in the dimension chains of links in the process of functioning of mechanisms. A method of calculating dynamic dimension chains as applied to solving direct and inverse problems is proposed. The solution of a direct problem is given under the condition that the stray field of the master link includes the errors of production and those related to the changes in the dimensions of the initial links under the action of operational loads. To obtain the value of the product part wear rate we propose using empirical dependences of the relation between the wear rate and formation of hydrogen in the process of interaction of materials.

The wear of gear tooth flanks of aircraft gas turbine engines is the most common and the most dangerous of their defects. Practice shows that vibroacoustic diagnostics is the most effective method for monitoring the technical condition of rotary machines, including gears. It has been shown that, in this case, it is difficult to use a widely applied diagnostic indicator of gear tooth flank wear as the intensity of an n-dimensional vector from a series of tooth harmonics. This is due to the need to measure vibration parameters in a wide frequency range and low intensity of higher tooth harmonics. The factors affecting the kinematic error, such as: technological factors (manufacturing and assembly defects), operational mode-related factors (speed, temperature, transmitted load), design-related factors (flexibility of gearing parts, tooth flank modification), and tooth flank wear, lead to a significant increase in the width of the tooth spectral component. This allowed us to suggest diagnostic indicators of wear based on the analysis of changes in its width. Using the example of a turboprop differential gearbox, we experimentally confirmed that the use of an auto power spectrum with filter width much smaller than the width of the tooth spectral component is ineffective in studying the defect being considered.  The parameters of the spectral component of the first tooth harmonic such as its width at the selected levels relative to the maximum value and their combinations, and the tooth harmonic intensity defined as a function of the power spectrum density are more sensitive to wear. The resulting dependences of the proposed parameters on the amount of wear have a pronounced non-linear nature. These diagnostic indicators allow several-fold reduction of the frequency range being analyzed.