Vol 14, No 2 (2015)

A mathematical model and software implementation of a computational algorithm of forming program motion in a scheduled turn of small spacecraft are described in the article. The algorithm is intended to calculate the key parameters of the path of a scheduled turn of small spacecraft, to specify the time moments when spacecraft motion has to be changed, and motion parameters at these points to determine the intervals characterized by the constancy of object motion laws and the positions of the object rotation axes during these intervals. Information on the equipment used (sensors, mechanisms, flywheels), the basic modes of operation, the principles of organizing the motion control system and flight control software is presented in the article. The AIST-2D Experimental Small Spacecraft has a mass of less than 500 kilograms and can operate on a near-circular orbit of 600 kilometers. The Spacecraft Orientation System comprises sensors and actuator mechanisms as well as its own computer. The Flight Control Software is organized as software incorporated in the technical system and implements full support of spacecraft motion control logic both in normal and abnormal situations. The software is subjected to a multiphase debugging process that ensures the achievement of the required indicators of quality and robustness.

The article presents the results of analyzing the dynamic behavior of a prefabricated single-span pipeline with a tube connection on external cone under the influence of kinematic excitation. Five models of pipelines with different conjugation conditions in tube connection on external cone are described. The results have been obtained by using the finite element method and solving a contact problem of deformable body mechanics. At the first stage amplitude-frequency characteristics for the models of pipeline under consideration are constructed. The result shows the dependence of amplitude-frequency characteristics of the pipeline vibrations on the conjugation conditions in the collecting pipe connection.  It was found in the process of research that the resonant frequency of the pipeline varies with introducing admissible gaps in the tube connection on external cone. This change may lead to a shift of the resonance frequency of the pipeline in the range of operating frequencies of the structure that may lead to the destruction of the pipeline. The article also reflects the influence of the external dynamic load on the distribution of contact pressure in the prefabricated tube connection on external cone while passing the resonance frequency. This distribution determines the tightness of connections.

A procedure of modeling working processes of internal combustion engines (ICE) by using CAD/CAE software is presented. Issues of modeling gas- dynamic and heat process in 4-stroke internal combustion engines by using ANSYS Fluent and ANSYS Steady-State Thermal software which allows obtaining the fields of distribution of the principal thermodynamic parameters are discussed. Special attention is paid to developing a method of strength analysis and the peculiarities of adjusting it to solving of the tasks connected with internal combustion engine designing.

This article deals with methods of non-destructive control of diffusion-saturated layers of polycrystalline alloys, and in particular, in steel hardening. There exist simple and reliable X-ray techniques of studying diffusion processes. Their main advantages are the safety, availability and absence of necessity to destroy the sample. Diffraction scattering of characteristic X-ray character radiation on a crystal lattice of a polycrystalline alloy contains information on the interior structure and concentration distribution of the diffusing material (carbon used as the diffusant impurity) in the solvent lattice (iron alloy) after isothermal annealing. Application of numerical methods makes it possible to simulate the shape of the line profile by varying the parameter of the alloy lattice, caused, for example, by diffusion penetration of carbon in steel. This approach is used for choosing the best conditions of saturating the surface of a metal alloy for the case of steady- source diffusion. With some assumption, the application of the calculation algorithm shows good approximation for the carbonization of polycrystalline alloys, which makes it possible to determine the degree of the diffusion saturation depending on the process parameters and to control them. The curve variations are related to the gradient of concentration of the diffusant and the depth of X-ray penetration. An algorithm of simulation has been developed and tested allowing prediction of diffusion area parameters in carbonization. It is shown that the depth of investigation using X-rays makes it possible, under certain conditions, to obtain information on the dimensions of the diffusion area in layers considerably in excess of half thickness values. The experimental data obtained in carbonization of a sample are compared with the results of simulation of a diffractive profile. 

The results of determining the boundaries of ignition of a turbulent flow of aluminum-air mixture as well as the influence of parameters such as the flow rate, turbulence and particle size on the boundaries of ignition are presented in the paper. It has been found that as the initial turbulence increases the nucleation site for ignition splits under the influence of pulsation and flame tails are carried into the main stream and die out there, thus increasing the time of ignition of the main flow of the mixture; as the initial  turbulence increases the boundaries of aluminum-air mixture ignition expand and the flow rate of the aluminum-air mixture increases; the boundary of ignition of a powdered aluminum-magnesium alloy corresponds to the boundary of ignition for combustion chambers of aircraft gas turbine engines; presence of fine aluminum powder particles in the area of ignition contributes greatly to the expansion of the boundaries of  ignition of the flow of aluminum-air mixture. It has also been established that the maximum velocity of flame propagation and heat generation for aluminum-air mixture is observed when the mixture composition is close to stoichiometric, just as for gas-air mixtures. However, a distinguishing feature of aluminum-air mixture is the presence of the second maximum speed of flame propagation and heat generation for mixture compositions with α<0.3. The resulting boundaries of ignition of aluminum-air mixture lie within the area of flame stabilization.

Calculation of the strained state of structures made of anisotropic viscoelastic materials under the influence of temperatures is reduced to the calculation of the strained state of structures made of elastic materials on the basis of the conformity principle developed earlier.  A method of calculating the strained state of non-uniform anisotropic structures of an arbitrary shape in the case of their static loading under the influence of temperatures has been developed on the basis of this principle. Displacements caused by the influence of external variable pressure and variable temperature field inside a steel square plate with a round cut are calculated. The problem of linear incoherent thermoviscoelasticity selected as a model provides a strict analytical solution, convenient for the analysis of steel parts in different operation modes. 

The influence of different algorithms of generating inlet turbulent fluctuations on the results of calculating the flow parameters downstream the flameholder is discussed in the paper. Large eddy simulation is used on a turbulence model with a subgrid Smagorinsky-Lilli model. Propane-air mixture with a temperature of 300 K in a square-section channel is investigated. A bluff body with a base of an equilateral triangle with the side length equal to 25 mm is placed inside the channel. The mass-averaged inlet velocity is 10 m/s. Several ways of setting inlet boundary conditions are considered. Two cases without turbulence at the inlet (uniform velocity distribution across the inlet section and pipe velocity profile) and two cases with artificially modeled turbulence (vortex method and spectral turbulence synthesizer) are analyzed. The values of flow intensity upstream the stabilizer, the distribution of flow velocity and kinetic energy in longitudinal and cross sections downstream the stabilizer have been obtained. The graphs of the velocity fluctuation power density spectrum are also presented.

The article discusses the development of a new numerical method for determining the parameters of a creep model.  A discrete linear parametric model describing the relationship between successive values of creep strain in the form of a difference equation is proposed. Formulas for describing the relationship between the coefficients of the linear parametric discrete model and the creep model parameters have been obtained. An iterative procedure of mean-square estimation of coefficients of the linear parametric discrete model is described. A technique of estimating the error of calculating the model parameters of creep is shown, numerical and analytical studies of reliability and correctness of the described procedure have been carried out. Experimental verification of the results with good agreement between theoretical and experimental data is presented. The developed numerical method of determining the creep curve parameters can be applied at the stages of stationary and non-stationary creep.

Products of fuel combustion are the working body in the process of expansion cycles of heat engines. The composition of all combustibles is their common property – all of them are hydrocarbons, i.e., their molecules consist of carbon and hydrogen atoms. The article deals only with the properties of the products of fuel stoichiometric combustion in atmospheric air. The combustion products are a mixture of oxides of constituent elements of CO₂, H₂O and the main element of air – nitrogen N₂. It is the products of combustion that determine the expansion processes in the most widespread operation cycle of power plants – the Brayton cycle. This article is an attempt to use the methods of statistical physics to describe the properties of combustion products

The results of numerical modeling of thermodynamics of a swirled flow in an energy separation chamber of vortex devices in stationary and non-stationary settings are presented in the paper. The results of investigation confirmed the presence of precession motion of the paraxial vortex core, velocity, pressure and temperature pulsations in the energy separation chamber. The processing of these made it possible to design a reverse cycle produced by large-scale vortex structures in a p, v-diagram. The cycle is responsible for the major portion of energy transfer from the periphery to the near-axial layers. It was found that the heated masses of gas are added to the cooled flow near the end surface of the diaphragm due to the angle vortex produced. We propose making the nozzle inlet inclined in the form of a slope using the Bernoulli lemniscate, which results in the improvement of energy separation characteristics by 1.5-2.0 per cent. Different areas of the flow such as the recirculation zone, the vortex core, the open jet at the outlet of the slot diffuser are the components of a single vibration system. Numerical simulation of flow in a vortex energy separator and analysis of non-stationary phenomena taking place in a DCVT show that vortex core precession is the source of large-scale periodic vibrations in a vortex tube.

Numerical calculations of the flow downstream the flame tube of the combustion chamber in the conditions of nonstable flow are presented in the paper. The obtained velocity fields were used for the modeling of non-stationary nature of the flow. The comparison of the results of calculations carried out using this model with the results of calculations based on the fluent commercial packages showed their good agreement. It was found that the flow under consideration is essentially nonstationary, with signs of precession. Numerical calculations of liquid fuel droplet distributions in the area stimulating the configuration of the combustor liner were carried out. It was found that a significant portion of the fuel hits the walls of the chamber. The processes of atomization of fuel in a non-stationary precession jet flowing out of the chamber are investigated experimentally. It has been shown that the interaction of fuel jet with precession air flow gives a sufficiently homogeneous air-fuel mixture with an average droplet diameter of about 50 microns or less. Data on the dependence of the concentration distribution and droplet size on flow regimes of air and fuel have been obtained. It is shown that the base of the jet fuel in a swirling air flow under the influence of the vortex precession performs rotational - oscillatory movement. This process is visually observed only in conditions of pulsed illumination of the flow.

Examples of identifying the causes of high vibration of engines during rig tests based on many years of experience in evaluating the vibration behavior of gas turbine engines are presented in the paper. Defects such as slippage of the outer bearing support, failure to comply with the geometric parameters of the hydrodynamic damper with elastic rings and the conditions of oil feeding, unsatisfactory laying of the engine on the engine frame, rubbing of individual elements of the rotors, their wedging and rotational stall are diagnozed. The practice of using  modern methods of processing and analysis of vibration processes that makes it possible to optimize the amount of subsequent work with the engine is shown, with the above-mentioned defects taken as an example. A standard technique for diagnosing the causes of excessive vibration in gas turbine engines using the most efficient methods of signal processing is proposed on the basis of the experience gained. In case of detecting high vibration by bench vibration measuring apparatus we propose to install additional vibration sensors with the registration of vibration in the frequency range of up to 30 kHz parallel to the standard vibration sensors. This is  followed by sequential data processing with obtaining autospectrums in speed and acceleration, calculation of the cospectrum, the spectrum of highs, the envelope spectrum, cascade demodulation on the basis of highs, multiple iterations of the cascade demodulation procedure. The effectiveness of the proposed method has been confirmed by many years of its practical use and can be applied both in the conditions of the test bench and in operation for the evaluation of the  engines’s health. 

The working process of a combustion chamber of the evaporative type used on most types of modern APUs is described in the paper. The combustion chamber discussed is characterized by a highly efficient working process with high combustion, low emissions of CO and NOx and low fuel-injection pressure in steady-state operation. However, the starting characteristics of the evaporative combustion chamber need to be improved. Ways of improving the starting characteristics of the auxiliary GTE with an evaporative type combustion chamber by optimizing the number and location of starting centrifugal injectors, the adjustment of the fuel feed law are discussed. Comparative computational and experimental data on the variations in combustion efficiency, partial operation of the turbine, gas temperature fields at the turbine inlet are given. Modeling of the startup process is performed by the developed nonlinear dynamic model of starting in which the combustion efficiency is represented as the product of two components: a known criterion of forcing Kv and a component approximated according to the thermal condition of the chamber evaporating pipe. Checking the engine starting with the activities for developing the combustion chamber at the high altitude-climatic test bench at the Central Institute of Aviation Motors has shown the necessity of adjusting the characteristics of fuel supply for high-altitude conditions N ≥ 4000m. It is shown that the maximum local gas temperature at the turbine inlet can be reduced by 50-60 ° C andthe range of reliable engine starting by fuel supply  can be increased by the factor of 1.5-2.

The results of the analysis of design and development of data measuring systems of oceanographic parameters in the 60-70s and 80-90s are presented in the paper. Data measuring systems based on the CAMAC standard (created under the leadership of academician Nesterikhin Y.E.) had a great influence on the design of instrumentation. However, their direct use in oceanographic measurements proved impossible. It so happened because of the need for in situ measurement of parameters at a considerable distance from the control devices. A basic structural arangement of a measurement system was developed by the end of the 80s and oceanographic sounding towed autonomous measuring systems were created, certified and put into practice. They were used for experimental studies in the ocean in the range from seconds to tens of days in time and from centimeters to hundreds or thousands of kilometers in distance. Measuring channels are being developed on the basis of  high-speed data receivers (television cameras, acoustic devices). A structural arrangement of a multi-channel hydrological- optical-  and chemical measuring complex that makes it possible to assimilate in its composition measuring channels of oceanographic parameters at different information rates has been developed. A process platform for the development, testing and certification of new measurement channels for the parameters of the marine environment has been designed and built on the basis of this scheme. The results of full-scale tests of the process platform carried out on the Black Sea near Gelendzhik are presented.

Software packages which can be used for the creation of specialized software to investigate the dynamics of micromechanical inertial sensors have been developed. These software packages take full account of the Timoshenko theory and the influence of the gyroscopic effect. The possibility of using the developed software is shown using modeling of a superminiature micromechanical gyro and a micromechanical gyro with a gimbal sensing element as an example. The use of specialized software guarantees the possibility of implementing the required functionality as well as full control of the implementation of the algorithms and visualization of the results at every stage of the investigation. The development and using of specialized software can help to achieve significant reduction of requirements imposed upon the computing resources and calculation time in comparison with universal software of finite-element modeling.

The article presents the results of the analysis of various aspects and status of distance learning to identify the positive aspects and disadvantages, problems, and possible solutions to improve the efficiency of the educational process. Distance learning as an educational problem and at the same time as a new form of getting education calls for teachers of a new breed. This is a teacher who constantly supports the distance learner, has a command of distance learning technologies and a pool of techniques and methods, first of all, computer skills. To solve the problem it is necessary to determine the essence of a number of key concepts of distance learning, to reveal the multidimensionality of the problem of its organization, to analyze the foreign and domestic experience of training teachers for distance learning and plan the ways of preserving and upscaling the human, scientific, educational and material potential accumulated by the domestic system of education, to apply the existing and prospective means of new information technologies.

The article presents indicators characterizing the efficiency of operational and commercial activities of a company in market conditions. The coefficient of economic, social, organizational and technical capacity of the enterprise, economic performance of the company management, the share  of management costs, the ratio of the number of administrative staff to the number of staff personnel of the enterprise, the ratio of line and functional personnel management staff, the cost-effectiveness ratio of administrative activity; the level of organization of production, the impact of production management and sale of products, the level of product profitability; the level of remuneration of staff; the profitability of equity capital, the level of profitability of production and sales, return on assets, the ratio of real equity value, the coefficient of effective use of current assets; the coefficient of effective use of working capital, the coefficient of the utilization of all assets, the cost of one share; earnings per share, dividend per share, the price of one share of income; total assets; profit margin, gross margin ratio, sales gross profit margin; the complex integrated factor of the company’s management efficiency are among the most important of them. Calculation and analysis of the indicators described in the article for a particular company should help to solve the tasks of engineering and reengineering.