Hydraulic modeling of the flow in the delta of the River Neva and in the eastern part of the Gulf of Finland

In connection with the construction of Leningrad's flood defenses the flow in the mouth of River Neva has been investigated on hydraulic models of different scales both unpressurized (see, for example, [1, 2]) and pressurized (see, for example, [3]). Since the results of these investigations are being intensively debated in connection with the discussion of the effect of defensive structures on the ecology of the Leningrad region, it is important to analyze the scientific basis for the hydraulic modeling of such flows.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 5, pp. 57–65, September–October, 1990.     

Changes in the experimentalist's role in the future of mechanics

At present there exist considerable opportunities for experimental studies. In large part this prognosis derives from the observation that analytical capability has, to some extent, outstripped our detailed understanding of many aspects of engineering concerns, so that there exists a need for providing input into the modeling of mechanics (of materials) problems. This favorable situation is supported by increasingly sophisticated experimental methods which, in turn, depend heavily on the computer, as well as on optical and other field methods. Examples are given that illustrate the gradual transition of macroscopic material related studies to those that require submicron resolution as demanded by ever increasing relevance in advanced materials related research. Paper was invited lecture at the 1995 SEM Spring Conference on Experimental Mechanics held in Grand Rapids, MI on June 12–14.     

Influence of the macrotransport processes in gases on the change in the hydrodynamic parameters in the presence of a resonance radiation pulse

The effect of a resonance radiation pulse on the gas parameters is investigated. It is assumed that the pulse duration is large enough for the diffusion and heat conduction to be taken into account. It is shown that the diffusion and heat conduction may be significantly influenced by the processes of excitation of the internal degrees of freedom of the molecules.Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No.4, pp. 120–128, July–August, 1992.     

Symmetrization of the tensor operator of the compatibility equations in stresses in the anisotropic theory of elasticity

The general form of the term whose addition to the left-hand side of the compatibility equation in stresses in anisotropic elasticity symmetrizes the rank four differential tensor operator of these equations is obtained. In the case of an arbitrary type of anisotropy, this term contains two arbitrary parameters of dimension of elastic compliances. The symmetrized compatibility equations themselves contain only one of these parameters, and the combination of the terms with this parameter can be separated from the terms containing the tensor of elastic compliances.     

Criterion of Hyperbolicity in Hyperelasticity in the Case of the Stored Energy in Separable Form

We consider the equations of hyperelasticity for isotropic solids in the Eulerian coordinates in a special case where the specific stored energy is a sum of two functions. The first one, the hydrodynamic part of the energy, depends only on the solid density and the entropy, and the second one, the shear energy, depends on the invariants of the Finger tensor in such a way that it is unaffected by the volume change. A new sufficient criterion of hyperbolicity for such a system is formulated: if the sound velocity is real and a symmetric 3×3 matrix determined in terms of the shear energy is positive definite on a one-parameter family of surfaces of the unit-determinant deformation gradient, the equations are hyperbolic.     

The evaluation of the surface impedance in the theory of the anomalous skin effect in metals

Summary A simple method is described for obtaining series expansions for the integrals which represent the surface impedance in the theory of the anomalous skin effect in metals. The results agree with those recently obtained by Dingle¹) by means of an intuitive procedure.     

Modeling the disturbances in the lake Chebarkul caused by the fall of the meteorite in 2013

The results of numerical simulation of the possible hydrodynamic disturbances in lake Chebarkul caused by the fall of the meteorite in 2013 are presented. In the calculations the system of Navier–Stokes equations is used. The entry of the meteorite into the water at an angle of 20° is modeled. The numerical experiments are performed both with and without account for the ice cover of the lake. The dimensions of the ice cover disruption are evaluated. The dimensions of the ice-hole observable in the place of the meteorite fall are shown to be in good agreement with the theoretical predictions and the preliminary estimations.     

Oil recovery in the presence of microbubbles in the filtration flow

This paper presents mathematical models for oil-gas flow taking into account the various processes due to the formation of gas micronuclei (microbubbles) in oil: slip of oil relative to the walls of the pore channels (gas lubrication), changes in oil viscosity, and motion of microbubles with respect to oil. We consider examples of oil flow in the near-wellbore zone for the case where a reduction in pressure to the saturation pressure leads to the formation of gas microbubbles and micronuclei and examples of the action of a water-gas mixture in the case where oil foams in the contact area with the injected gas, i.e., a finely dispersed mixture of oil and microbubbles is formed. The behavior of indicator curves for an oil well with the formation of microbubbles is simulated, and the effect of microbubbles on the oil recovery factor in a water-alternating-gas injection process is studied.     

Generalized logistic growth modeling of the COVID-19 outbreak: comparing the dynamics in the 29 provinces in China and in the rest of the world

Nonlinear Dynamics - Started in Wuhan, China, the COVID-19 has been spreading all over the world. We calibrate the logistic growth model, the generalized logistic growth model, the generalized...     

Changes in the type of the shock-wave structure in high-velocity flows

Physical aspects of nonuniqueness of shock-wave structures in supersonic and hypersonic flows are considered. Thermodynamic conditions determining the dual solution domains are analyzed, and the boundaries of the transition from Mach to regular reflection are examined.Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 46, No. 2, pp. 23–32, March–April, 2005.     

Measurements of the dissipation coefficient at the wavemaker in the process of generation of the resonant standing waves in a tank

The complex dissipation at the wavemaker used for direct excitation of nonlinear standing waves in the vicinity of the cut-off frequency, is measured experimentally. The results indicate that the absolute value of this dissipation coefficient exceeds significantly the estimate based on purely viscous dissipation. This is attributed to the turbulent effects resulting from the vortex shedding at the discontinuities of the wavemaker surface. It is shown that incorporation of this dissipation in the boundary condition at the wavemaker as a nonlinear term in a form generally used to describe dissipation in a turbulent boundary layer, is more appropriate allowing to remove hysteresis in the value of the wavemaker dissipation coefficient. Such hysteresis is observed when a linear dissipation model is applied.     

试论静力学在流体力学课程中的地位

从材料的本构方程和基本运动方程出发, 比较了静力学在弹性力学和流体力学中的 地位. 与弹性静力学在弹性力学中占有重要地位不同, 流体静力学在流体力学中仅处 于次要地位, 它不是流体动力学的基础, 而只是一个特例. 确立这种观点有助于提高对流体 力学学科特点的认识, 提高流体力学教学质量.     

The plane contact problem in the electrodynamics of continuous media in the presence of the Hall effect

Solutions are given for the distributions of current density, field strength and electric field potential in the neighborhood of the point of contact of two conducting media with different scalar electrical conductivities a and Hall constants R_H. Problems of this type are encountered in magnetohydrodynamic theory, and in semiconductor physics, for example, in investigating the fields in piecewise-inhomogeneous media or on the electrodes in magnetohydrodynamic channels and electrical engineering apparatus. If one of the two media has ideal properties =, R_H=0, then within the framework of the approximate theory (the induced magnetic field is neglected) the problem reduces to finding an analytic function in the region occupied by the second medium, and this can often be solved by carrying out a conformal mapping of the region onto a polygon [1, 2]. In other cases the electric field in each medium depends jointly on the physical properties and geometries of regions of the two media, and a solution must be found which is joined at the contact. The theory of singular integral equations [3,4] is a convenient mathematical tool for solving such problems.     

On the size of the hysteresis in pseudoelasticity

Pseudoelasticity is a phenomenon that occurs in alloys with shape memory: In a loading-unloading cycle a body will return to its original configuration, but its path in a load-deformation diagram will run through a hysteresis loop.Pseudoelastic behaviour can be modelled by statistical mechanics which produces a non-monotone load-deformation isotherm. Once such a nonmonotone curve has been calculated there is the possibility of a phase transition that is connected with a hysteresis loop.The paper describes a method for the calculation of the width of the hysteresis. It comes to the conclusion that this width is determined by the interfacial energy associated with domain boundaries between the phases. The bigger that energy is the bigger is the hysteresis loop.