Vol 64, No 2 (2019)

Amorphous alloys of Fe_{85 –x}Cr_xB₁₅ (x = 0–20) obtained by ultrafast melt quenching are investigated by the pulsed ¹¹В nuclear magnetic resonance (NMR) method at a temperature of 4.2 K. The amorphous alloys consist of microdomains (nanoclusters) with short-range orders of the tetragonal (Fe,Cr)₃B and α-(Fe,Cr)(B) phases, containing chromium atoms in the nearest neighbor environment of the iron atoms. The mean magnetic moments of the magnetic atoms in the nearest sphere of the boron atoms and their dependence on the composition in the nanoclusters are estimated.

This paper presents the experimental results of studying the effect of nonlinear wave and cavitation processes occurring in the working elements of a flow in hydrodynamic vortex- and plane-type generators with differently shaped flow bodies on the physicomechanical properties of a clay suspension. The models of a vortex-type generator with tangential and radial channels for the supply of a working fluid to the generator representing a plane channel with three cylindrical flow bodies have been studied. As a result of the studies performed, it has been revealed that the wave treatment of a clay suspension improves the quality of its colloid fraction and thereby decreases the consumption of clay powder and the time required for the preparation of a drilling mud in comparison with the traditional technology. The highest efficiency of wave treatment is attained by hydrodynamic generators in which the flowing section provides the most intensive wave and cavitation processes. The laboratory studies have been confirmed by industrial experiments, which provide the possibility to increase appreciably (by several tens of percentage points) the efficiency of drilling. The laboratory and industrial experiments performed open principally new directions for control over the rheological properties of solutions, in particular, drilling muds.

The problem of modeling the angular momentum control modes of small spacecraft using electromagnetic systems interacting with the Earth’s magnetic field is considered. The electromagnetic system control law has been constructed for various compositions of measurable parameters. A set of scale factors has been formed to investigate the angular momentum control mode of dynamically similar models. Based on a dynamical test stand, we have carried out experimental studies to model the angular motion dynamics of small spacecraft with a magnetic attitude control system.

The basic conservation laws in the Green–Naghdi model of shallow-water theory are derived from the two-dimensional integral conservation laws of mass and the total momentum describing the plane-parallel flow in an ideal incompressible fluid above a horizontal bottom. This conclusion is based on the concept of a local hydrostatic approximation, which generalizes the concept of the long-wavelength approximation and is used for analyzing the applicability of the Green–Naghdi equations in modeling the wave flows of a fluid with undular bores.

General theoretical relations for calculating the redistribution of the preliminary irreversible strain field during unloading or elastic loading of a medium are obtained for the nonlinear multiplicative gradient model of large elastic–plastic deformations. It is shown that the dynamics of elastic shock waves does not depend directly on the previously accumulated plastic strains. A formula for the plastic-strain rotation tensor is obtained. It is shown that rigid rotation of plastic strains under elastic shock waves can be jump-like. All results are obtained for the general case of model relations of isotropic media and are valid for both compressible and incompressible materials.

The limitations imposed on the orbit and the distribution of the density of the early Moon by present-day measurements of its fossil tidal bulge are studied. A semi-analytical method has been developed for calculating gravitational potentials, which makes it possible to investigate the equipotential surfaces of a self-gravitating inhomogeneous mass in an external field. Universal expressions are obtained for the two-layer mantle–crust model of the early Moon, which makes it possible to make general estimates of the density of the upper crust and semiaxes of its orbit in the case of tidal capture by the Earth.