Vol 23, No 3 (2022)

The study solves the problem of filtering nonlinear systems based on the minimax adaptive algorithm of nonlinear systems by Volterra series of the second order, provided that the autocorrelation functions of the useful signal and interference are known with some errors according to the criterion of the maximum standard error of filtering. The author analyses the stationary performance of a minimax adaptive Volterra filter of the second order with the least mean square (LMS) with a constant step size of µ with a time-varying setting. A quantitative assessment of the steadystate excess root-mean-square error (RMSE) has been established, in which the contribution of incorrect gradient adjustment and tracking error is well characterized. Then the optimal step size is set for a time-varying secondorder minimax Volterra filter. Thus, we can study the correlation between the excess MSE and the optimal step size, on the one hand, and the parameters of a time-varying nonlinear system, on the other hand. A simple solution with minimal root-mean-square error for the minimax Volterra filter is obtained, based on the assumption that the input signal of the filter is Gaussian. In addition, we propose an iterative factorization method for developing a subclass of minimax Volterra filters, which can greatly simplify filtering operations. In addition, an adaptive algorithm for the Volterra filter is investigated, as well as its average convergence and asymptotic excess root-mean-square error. Finally, the usefulness of the Volterra filter is demonstrated by its use in studies of nonlinear drift oscillations of moored vessels exposed to random sea waves.

The study is devoted to the determination of the coefficients of the degree of contact of rolling surfaces, considering the tolerance field of rolling bodies, as well as the influence of the coefficients of the degree of contact on the maximum contact stresses in ball radial bearings. A method has been developed for determining the maximum value of the coefficient of the degree of contact of rolling surfaces of ball radial bearings, taking into account the tolerance field of rolling bodies. It is established that the coefficient of the degree of contact of the rolling surfaces for each bearing size with a certain radius of the raceways is located in a range that depends on the limiting dimensions of the rolling elements. It is shown that the coefficient of the degree of contact of the rolling elements with the tracks of the outer ring, with the same auxiliary value, considering the sum and difference of the curvatures of the rolling surfaces, is greater than the inner one. Therefore, in order to reduce contact stresses on the outer ring of the bearing, the radius of its raceway can be made smaller than the inner one. A method has been developed for calculating the maximum contact stresses on the raceways of radial ball bearings, taking into account the coefficient of the degree of contact of rolling surfaces and the tolerance field of rolling bodies, which allows calculating contact stresses for radial ball bearings of any size at any coefficients of the degree of contact of rolling surfaces.

In the 20th century, great attention in the world was paid to the study, exploration, development of natural gas deposits, which are ordinary (traditional) gas-containing accumulations of hydrocarbons. The limited and irreplaceable resources of free natural gas, the growing demand for this energy carrier inevitably forced in the 21st century to pay attention to the significant potential resources of natural gas contained in unconventional sources. These include coal-bearing methane, shale gas, water-dissolved gases of the underground and aboveground hydrosphere, natural gas hydrates. The authors discuss modern technologies for the development of natural gas hydrates, in particular the pilot development of the Nankai field on the shelf of Japan and a number of large deposits on the shelf of China. The results of scientific research are presented, as well as practical experience in the application of various methods of influencing deposits of unconventional hydrocarbons. The study introduces a number of key technical solutions for the development of gas hydrate deposits, such as sand control during extraction, artificial lifting, geological monitoring and environmental monitoring. The information and regulatory framework of the study reflects the current level of development of science and technology in the development of mineral deposits. The world and domestic experience in the development of technologies for the impact on unconventional hydrocarbon deposits in order to optimize and intensify the production process is reflected.

Sedimentary basins of Late Phanerozoic rift origin are located in Africa and on its underwater margins. The reasons for the oil and gas specialization of basins of this class remain largely unclear. Patterns have been identified that could be of decisive importance in this regard. The intracontinental basins are characterized almost exclusively by oil deposits. In the pericontinental basins, the value of gas deposits decreased, and oil increased in accordance with the decrease in the time of their reef laying and deflection (from C3, P-J1, K1 to J5-K12). The differentiation of basins into tectonotypes of “incomplete” and “completed” development, as well as the asynchronous deflection of the latter reflected in their oil and gas specialization, correlate accordingly with the size and age of the Pan-African granulite belts in which the basins were laid. Since these belts were the most active core structures, this pattern can be considered as evidence of the influence of their inherited or reborn deep “energy systems” on the processes of rifting and generation of hydrocarbons. The use of seismography data showed that mainly oil and gas-bearing rift basins are located in areas of less and more heated mantle respectively. An example of the probable influence of Cenozoic island volcanism centers on oil and gas basin systems is given. A comparative analysis of geological and geophysical data, including heat flows, leads to the conclusion that the temperature conditions of hydrocarbon formation in the rift basins of Africa were determined by a combination of deep thermal systems of different scales: regional (continent - ocean), subregional (cow-structural) and local (volcanic centers).