Vol 19, No 4 (2020)

We discuss the features of optimal force transfer in a thin-walled structure and use them to develop a method for defining the distribution of material over the structure elements for minimizing its volume. The suggested method works with one or several external loadings and allows one to determine the optimal structure and to recognize the phenomenon of Razani in which a structure with unequal stresses due to several loadings is more light-weight than a fully- stressed one. Using the developed method, we solved the original Razani problem and applied it for the optimization of the wing structure of a novel hypersonic airplane. It is shown that the determined material distribution is 8.78% lighter than that in a conventionally fully-stressed structure.

Recent studies related to fuel economy in air transport conducted in our country and abroad show that the use of recuperative heat exchangers in aviation gas turbine engines can significantly, by up to 20...30%, reduce fuel consumption. Until recently, the use of cycles with heat recovery in aircraft gas turbine engines was restrained by a significant increase in the mass of the power plant due to the installation of a heat exchanger. Currently, there is a technological opportunity to create compact, light, high-efficiency heat exchangers for use on aircraft without compromising their performance. An important target in the design of engines with heat recovery is to select the parameters of the working process that provide maximum efficiency of the aircraft system. The article focused on setting of the optimization problem and the choice of rational parameters of the thermodynamic cycle parameters of a gas turbine engine with a recuperative heat exchanger. On the basis of the developed method of multi-criteria optimization the optimization of thermodynamic cycle parameters of a helicopter gas turbine engine with a ANSAT recuperative heat exchanger was carried out by means of numerical simulations according to such criteria as the total weight of the engine and fuel required for the flight, the specific fuel consumption of the aircraft for a ton- kilometer of the payload. The results of the optimization are presented in the article. The calculation of engine efficiency indicators was carried out on the basis of modeling the flight cycle of the helicopter, taking into account its aerodynamic characteristics. The developed mathematical model for calculating the mass of a compact heat exchanger, designed to solve optimization problems at the stage of conceptual design of the engine and simulation of the transport helicopter flight cycle is presented. The developed methods and models are implemented in the ASTRA program. It is shown that optimal parameters of the working process of a gas turbine engine with a free turbine and a recuperative heat exchanger depend significantly on the heat exchanger effectiveness. The possibility of increasing the efficiency of the engine due to heat regeneration is also shown.

The paper presents an analysis of the component of vibration of the NK-12MP turboprop engine differential gearbox that is generated by the wear of the flanks of the teeth of the “sun gear – planet gear assembly” pair and at certain values of its intensity may cause fatigue breakdown of the engine’s structural elements. A complex of diagnostic indicators is determined on the basis of this component. Its intensity is shown to be maximal in steady-state operation of the engine with the greatest run time. The data obtained by the spectrum of maxima are shown to have higher information content as compared to the autospectrum data. The complex of diagnostic indicators proposed on the basis of the component under consideration makes it possible to successfully control the technical condition of the differential gearbox by the defects of “gear tooth flank wear”.

The paper presents a solution to the problem of determining the basic equation for pressing of porous bodies made of MR material that  relates not only the molding pressure to the MR density, but also other physical parameters, including the technological parameters of blank formation. The paper outlines the basic assumptions of the theory of compression molding of items made of MR fibrous material. It has been proved that the ideal process of pressing porous bodies contains two stages for a range of relative densities [0,15; 0,7]. The basic equation of pressing of MR products was determined. It was proved that the equations of ideal pressing (in the absence of external friction forces) have the form of power-law dependences of the molding pressure on the density of the porous body. The power function of hardening of the wire material in the press was obtained. An experimental test of the hypotheses put forward and the assumptions made was carried out, which showed their validity. The obtained theory of axisymmetric pressing of fiber bodies and the obtained basic equation for pressing the MR material can be extended to various types of pressing modes and product shapes. The results of the performed theoretical and experimental studies, as well as their generalization, can serve as a basis for studying mass molding of porous bodies made of fiber materials, taking into account the uneven distribution of density over the volume.

The paper presents a technique of quantitative assessment of probability of failure-free operation of composite structures containing an ensemble of defects in the form of delamination. This method is based on approaches of general reliability theory. The proposed method was validated relative to the assessment of reliability of a composite conical bay with multiple delaminations generated under loads at the stage of inserting the launch vehicle into orbit. The statistical dynamic problem was solved by using Monte Carlo method which was implemented by means of algorithms developed by the author in ANSYS software. Nonlinear analysis of the conical bay buckling was carried out for each implementation. Quantitative assessment of survival probability was conducted on the basis of the hypothesis of the law of Gaussian distribution of load-bearing capacity and using the graphical method of reliability calculation. Good agreement of the results obtained by both methods was noted.