Moscow University Mechanics Bulletin最新文献

A plane problem of the formation of a crater as a result of the explosion of a line charge on the surface of the ground is investigated within the solid–liquid formulation. The explosion crater is supposed to be a polygonal line with two angular points. The exact solution to the problem is constructed. A parametric analysis is performed. The calculated profiles of the explosion crater are presented for some governing parameters of the problem. Restrictions on the governing parameters are given, and limiting cases are considered.

A classification option is proposed for the manifestations of Ratcheting—one-sided accumulation of deformation in a material during its cyclic loading—depending on the degree of complexity of the entire deformation process. The absence of experimentally important experiments with extremely small cycle amplitudes is noted and some programs of such experiments are formulated. The names of the two types of ratcheting are offered.

A method for well placement optimization to maximize oil production during a given time interval is proposed. The method is based on an empirical approach related to the enumeration of possible well positions, rather than calculating the gradient of the objective function. This provides, on the one hand, effective paralleling of the well placement optimization algorithm and, consequently, acceleration of the method, and, on the other hand, the global extremum of the objective function. The application of the method to well placement using a digital 3D model of an oil field is considered.

The mutual influence of round and elliptical cracks in three-dimensional space is investigated. The stress intensity factors for various problems are calculated. The dependence of the stress intensity factors on the ratio of the semiaxes of the ellipse is investigated. The computational error does not exceed 1(%).

It is shown on the example of elastic (SH) wave diffraction by an obstacle like a half-plane that barriers can be used to attenuate vibrations and waves in elastic media. It is found that not only a solid barrier, but also a cut or a natural fracture in soil can protect foundations and buildings against shear bulk waves.

Applicability indicators of the linear viscoelasticity constitutive relation for isotropic time-dependent materials with arbitrary shear and bulk creep compliances are considered. General properties of the creep curve families for volumetric, longitudinal, and lateral strains generated by this linear relation under constant uniaxial tension and constant hydrostatic pressure are studied analytically. It is proved that the linear theory of viscoelasticity is able to describe the effect of (monotonic) expansion of a linear behavior range of material qualitatively as the hydrostatic pressure grows; more precisely, the effect of expansion of a range of axial stress values under which the axial compliance is independent of the stress level. The analysis reveals a number of specific features of the theoretical creep and compliance curves that can be conveniently employed as the applicability or non-applicability indicators of the linear viscoelasticity theory by the data of material creep tests under action of tensile load and hydrostatic pressure.

The second-order oscillatory system with constant coefficients in the presence of a time-varying bounded external perturbation is considered. Extreme points of the limit cycle, the boundary of the attainability set, are determined. The limit cycle is used to obtain the quality estimates of the system robust stability against the time-varying perturbation.

The motion of a biaxial four-wheeled vehicle is simulated on the (mu)-split surface, which is a section of the reference plane containing regions with different friction coefficients, in the case when the friction coefficient for one of the wheels of the driving axis turns out to be significantly less than the friction coefficient for the remaining wheels. The effects of the longitudinal and transverse deformations of the wheels and of the aligning moments on the dynamics of its body are studied under the assumption that the wheels of the vehicle do not lose grip with the reference plane.

A special subclass of solutions of the three-dimensional system of ideal polytropic gas equations corresponding to an atmospheric model is considered. The properties of these solutions are completely characterized by a high-order nonlinear system of ordinary differential equations. Unlike the corresponding two-dimensional model, all singular points of this system have been found to be unstable. Some first integrals of this system have been found. In the case of axial symmetry, the system can be reduced to a single equation. If the adiabatic exponent is equal to 2, the system is integrable.