Vol 15, No 3 (2016)

Multi-step terminal control of the subhypersonic first stage of an aerospace system in trans-atmospheric climb is considered. Passive motion of spacecraft in conditions of joint influence of atmospheric and aerodynamic disturbance is analyzed. Achieving the prescribed value of the trajectory inclination angle is the terminal motion condition. Terminal height is a controlled value. An algorithm of terminal control for the formation of the command value of aerodynamic lift coefficient is proposed. The Newton method with one or more iterations at a control step is used in determining command control. The serviceability and efficiency of the algorithm compensating the influence of atmospheric and aerodynamic disturbances on the preset terminal altitude condition of spacecraft motion are analyzed. The results of simulating spacecraft motion with terminal control for maximally «rarefied» atmosphere and for different levels of deviation of the drag coefficient are discussed. 

The article presents the results of computational and experimental research of the effect of the number of blades and the diameter on the noise of the propeller operating at Reynolds numbers of more than 106. It is shown that an increase in the number of blades while maintaining the aerodynamic and geometric similarity of the propellers and constant Mach number of the circumferential velocity leads to significant reduction of aerodynamic load noise. At the same time the displacement noise and the broadband noise increase insignificantly. Expressions are proposed that can be used to assess the effect of the diameter and the number of blades on the tonal noise and the noise of the trailing edge of the propeller provided the propeller thrust is constant. Measurements of the acoustic characteristics of light aircraft Yak-18T with two- and three-bladed propellers, MAI-223M and the F30, performed at the local aerodrome in static conditions qualitatively confirmed the estimates of the effect of the diameter and number of blades on the propeller noise. Increasing the number of blades leads to a noticeable decrease in the acoustic efficiency of engine-propeller power plants.

This article is devoted to the investigation of the causes and peculiarities of high-frequency gas-dynamic self-oscillations arising in the outflow line of gas control valves. We have demonstrated that these self-oscillations result in a substantial increase in the level of dynamic loading of the control valve elements due to the occurrence of intense tonal components in the pressure fluctuation spectra in the pipeline, the vibrations of the output flange of the control valve, as well as the external noise of the whole assembly. We have provided the results of investigating the conditions for high-frequency gas-dynamic self-oscillations arising from the gas flow interaction with the control valve elements, as well as with supporting pylons of the central fairing. It is shown that an increase in the flow above a certain value of output speed (40 m/s) results in tonal components of the spectrum of pressure pulsations. We have described the measures to suppress gas-dynamic self-oscillations by means of a perforated sleeve installed in the outflow line of the control valve. Three modifications of the sleeve design have been modeled, numerical simulation of gas-dynamic processes in the control valve exhaust duct with a perforated sleeve installed has been carried out. It is shown that complete elimination of gas-dynamic self-oscillations can be made possible by installing the sleeve in the control valve exhast duct.

The results of development of the technologies ensuring an increase of wear resistance, lowering of noise and vibration level in frictional units are discussed in the paper. The most efficient technologies of formation of fluorinated microsized films on the friction surface improving the wear resistance, contact fatigue and durability of connection of the lubricant layer with friction surfaces; molecular reinforcement of surface defects decelerating the development of fatigue damages; the effect of multilubrication improvng adhesion and load characteristics of the lubricant layer, its absorbing capacity, etc. are determined. The technology of formation of fluorinated films is implemented by the introduction of graphite fluoride additive to lubricant oil. In the case of molecular reinforcement the effect of increasing wear resistance and contact endurance is connected with the passivation of surface defects formed in final treatment. Defect passivation is realized by dipping of the processed details in the oil containing solid particles in the resonant mode. In the case of multilubrication the effect of creating an underlayer of lubricant on the basis of a highly adhesive material, for example, of polimetilsiloksan produced by the JSC «TogliattiAzot» is realized. The creation of a low frequency cavitational method and installations for washing parts of friction units at the «Nadezhnost» Research and Development Center of SSTU is a important collateral development. The first installations are implemented at the JSC «Progress» Space–Rocket Center and the JSC «Aviaagregat» of the «Tekhnodinamika» Holding.

The article presents a new gas-dynamic mixer – a closed-type one. The structure of a two-phase flow generated by the mixer, the disperse phase velocity diagram, the size and concentration of drops are experimentally investigated. Pulsation characteristics of a disperse phase are calculated. The mixer ensures the operation of a system that produces high-concentration two-phase gas-droplet streams for various values of consumption and pressure of working fluids. It is established, that, thanks to the presence of air in a two-phase working fluid the liquid is accelerated in the initial part of the stream and then it is decelerated. It should be noted that the stream under consideration is a polydisperse one: there are sites of very small particles which the optics practically does not resolve, and there are very large drops.  The results of dispersion measurements using different methods are in close agreement. It is also experimentally established that the maximum pulsations take place at the nozzle outlet and there are local minima in the two-phase stream.

This article describes a method of identifying combustion chamber temperature field ripple by the preparation of the set of nozzles in the engine. It shows combustion chamber temperature field ripple with a divergent nozzle and a convergent one used in the burner. The design of the combustion chamber and that of the burners are described. Diagrams are plotted that show variation in circular and radial temperature field ripple depending on the engine behavior. The combustor exit temperature field non-uniformity is assessed using such parameters as the overall temperature distribution factor, the radial temperature distribution factor and the circumferential temperature distribution factor. Comparative analysis of the results of testing two combustion chambers with different modifications of burners is carried out. Conclusions about the effect of the burner design on the temperature field ripple are made.

The feasibility of using ionization sensor for the investigation and diagnosis of the fuel combustion process in piston power plants with spark ignition is substantiated. It is shown that in order to expand the functions and increase the reliability of operation and signal processing accuracy of the ionization sensor it is necessary to know the impact of the flame fluctuating velocity on the latter. Based on the analysis of published data and in-house research a mechanism of the effect of fluctuation velocity on the electrical conductivity of hydrocarbon flame is proposed, estimated by the value of ion current.  A formula for calculating the ion current is proposed, which includes the fluctuation velocity, the flame temperature and the concentration of carbon particles in the fuel. For methane-air flame, it was revealed that for U' < 8 m/s an increase of ion current is observed, which is due to increased flame temperature and concentration of carbonaceous fuel particles in the zone of chemical reactions of the flame. When U' > 8 m/s the ion current decreases due to the growth of heat consumption for heating the incoming fuel in the flame front, directly proportional to the fluctuation velocity. The results can be used to predict and monitor characteristics of turbulence in the combustion chambers of power plants with the aid of the ionization sensor.

The main causes of undesirable changes in signal frequency-amplitude characteristics at the output of modern generators are stated in the paper. A functional scheme of the waveform generator is presented. The generator is constructed with the use of home-produced hardware components. A simplified scheme of the on-board transmitting device for the small spacecraft «Aist-2» is taken as an example. The operation and interaction of units of the scheme, as well as the principle of generation of signals with various types of modulation are described. The device developed is analyzed. The units that make the most undesirable changes in the frequency-amplitude characteristic of the output signal are identified. A method of combatting bandpass flatness of frequency-amplitude characteristics is described. The spectra of the output signal prior to and after frequency correction are presented. The process of origination of parasitic amplitude modulation in a digital computation synthesizer in the case of generating signals with frequencies close to the Nyquist rate is explained. A method of combatting parasitic amplitude modulation caused by the use of a digital attenuator in the digital computation synthesizer is also discussed. It is shown that the application of the methods proposed makes it possible to develop a special waveform generator that can ensure the required spectral characteristics of the signals.

The article presents an analysis of options for designs of the antenna system for a synthetic aperture space radar (SAR), with acceptable performance characteristics in L- and P-bands. At the first stage the analysis of the current state of producing spacecraft with L- and P-band radars that use quite large folding antenna structures is carried out. It is shown that to obtain high performance of SAR in L- and P-band large folding reflectors with the diameter of up to15 meters are used. Further, variants of antenna systems are discussed and compared to determine the best combination in terms of the characteristics obtained and design complexity. An antenna system is proposed in the paper that uses antennae of the Yagi-aerial type as antenna array elements. The possibility of creating a space system consisting of several unified small spacecraft with L- and P-band SAR on board is shown.

The article focuses on the study of the specific application of eddy-current probes (ECP) to monitor the parameters of dispersed media. To do this, a three-dimensional finite element model of the «wear particles – ECP» was constructed in Ansys Maxwell 2015. The analysis of the the radial displacement of particles in the cross section of ECP with the help of the «Sergei Korolyov» supercomputer was carried out. It was found that the non-uniformity of electromagnetic field displacement of a particle from the axis to the periphery of the ECP results in three-fold increase of the insertion parameter. The deviation of the insertion parameters depends mainly on the geometrical position of the particle in the sectional plane of the sensor and it is weakly dependent on the frequency of the exciting field and particle size. On the basis of the established dependency we propose an ECP structure that allows mitigating the influence of the radial displacement of particles on the output signal of the ECP.

The paper deals with the non-contact method of monitoring the integrity of the main rotor blades of a helicopter. The available methods of monitoring the integrity of the main rotor blades of the helicopter are labor-intensive to implement, their reliability is low and they do not allow drawing a general picture of the state of rotor blades in flight. To solve this problem a method based on illumination of the blades by a probing microwave signal is proposed. Particular attention is given to the calculation of the power of the signal reflected from the helicopter main rotor blades. In deriving analytic equations it is assumed that a rotor blade is an undeformed flat metal surface. As a result, a spatial-temporal model of a probing SHF signal reflected from a helicopter’s main rotor blade has been obtained and the parameters of the model make it possible to assess the operational status of the main rotor of the helicopter.

The article deals with the vital task of measuring electromagnetic parameters of thin films and nanomaterials based on the sensing of surface controlled by pulsed electromagnetic signal. A method of non-contact control of such parameters as conductivity, as well as dielectric and magnetic permeability is justified. The proposed method is based on the sensing of the controlled surface by a pulsed electromagnetic signal with its subsequent analysis. Analytical relations that relate the phase and amplitude of the reflected signal to its spectral component, coefficient of reflection, self-surge impedances of the controlled medium and the signal propagation medium, as well as to the design parameters of the measurement system, such as the angle of incidence of the probing pulse and the distance to the object of measurement are presented. A brief mathematical description of the method is given. The dependence of the parameters of the reflected signal on the basic electromagnetic properties of materials is demonstrated.

In the framework of the theory of shallow shells we studied the effect of the initial deviations from the ideal circular cylindrical shape on flexural vibrations of thin isotropic shells. For the first time the possibility of an additional zone of splitting the flexural frequency spectrum due to the presence of initial shell form imperfections is shown in the paper. It is found that the splitting of the frequency spectrum occurs not only in cases when the number of waves of circumferential dynamic strain is equal to the number of waves of shell form imperfections  as generally agreed at present, but also in cases when the number of shape-generating waves is half that of wave imperfections. In the first case, both the split frequencies are lower than the corresponding frequency of the ideal shell. It was established that for some geometrical parameters of the shell the frequencies of radial vibrations may be commensurate with the flexural ones.  Solutions that take into account the interaction of bending and radial mode shapes are complemented with new results and conclusions. It was concluded that under the influence of periodic loads that inevitably arise in the operating conditions of shell structures, non-resonant zones defned according to the traditional approach can, in fact, be resonant. Resonance hazardous vibration conditions of shell structures with irregularities of this kind can occur at frequencies much lower or higher than the traditional theory predicted. This behavior of imperfect shells may lead to high stress-strain state of the structure and complex types of dynamic instability under operating conditions. The results and conclusions obtained in this work call for the revision of problems of the dynamics of shells with form imperfections that were solved earlier.

An algorithm of monitoring the ecological state of coastal waters is presented in the paper. The algorithm makes it possible to detect oil, mineral and organic coarse pollution, thin oil films, to estimate the concentration of mineral organic pollution in the surface layer. A method of identifying shallow water zones including sand-bottomed zones and waterline phytoplankton overgrowth is presented. The pollution level of the coastal zone of the city of Regency (Brazil) is estimated using the analysis of spectral-energy characteristics of polluted and nominally clean surfaces. On the basis of the estimates obtained clustering of the initial data on the component and the total level of pollution is performed. Conclusions are made concerning total pollution of the coastal waters under consideration. An example of data processing on the basis of the algorithm presented is discussed.   A hyperspectral image obtained with the help of the «Resurs-P» No. 2 satellite is considered.