Home – Home – Jornals – Journal of Applied Mechanics and Technical Physics 2017 number 5

This paper describes the results of intraoperational monitoring of hemodynamic parameters (velocity and pressure) in brain vessels, carried out within the framework of 50 neurosurgical operations using a Volcano ComboMap instrumental measuring system. It is established that the introduced parameter of specific load used during the neurosurgical operations is a significant parameter for the success of the operation.

This paper presents a variational approach to the solution of direct and inverse problems based on the joint use of mathematical models and monitoring data for processes of geophysical hydrothermodynamics. This approach is used to solve problems related to environmental protection. A variational principle with weak restrictions is formulated to account for uncertainties and errors in models and data. Inclusion of uncertainties makes it possible to construct direct non-iterative algorithms for sequential assimilation of data obtained by various observational systems. Criteria and functions for controlling the quality of the natural environment are introduced into the modeling system to solve inverse problems of environmental safety. The problem with data assimilation for the Novosibirsk agglomeration is considered.

A review of publications on the Rayleigh-Taylor instability arising due to high-velocity implosion of liners is presented. Papers that describe experimental testing and numerical simulation of the development and suppression of this instability are also considered.

Characteristics of a system of equations that describe three-dimensional motion of an incompressible viscoelastic Maxwell medium with the upper and lower convective derivatives and the rotational Jaumann derivative being used in the rheological relation are calculated. An initial-boundary-value problem is formulated for the system linearized in the vicinity of the quiescent state, and its unique solvability is established.

For the numerical simulation of aerodynamics problems, the Euler and Navier-Stokes equations written in integral form are used to construct an implicit finite-dimensional predictor-corrector scheme. At the predictor stage, the splitting of equations into physical processes and spatial directions is introduced, which makes it possible to reduce the solution of the original system to the solution of individual equations on fractional steps by the scalar sweep method and ensure the stability of the algorithm as a whole. The paper also describes the supersonic gas flows in a narrowing channel with regular and non-regular reflection of the compression shock from the symmetry plane and the numerical substantiation of the existence of pulsating flow with a supersonic flow past a cylinder with a needle.

This paper presents the observation results for the internal wave boron in the coastal region of the Sea of Japan with the use of vertical thermistor chains. The data obtained is interpreted by the mathematical models of shallow water in which the effect of nonlinearity and variance on the propagation of internal wave packages is taken into account. Within the framework of the theory of multilayer shallow water, the problem of transformation of a solitary wave into an internal boron is solved, and the possibility of recovery of a space-time picture of the flow during the passage of an internal boron in the section between adjacent experimental bottom stations is demonstrated.

Magnetohydrodynamic (MHD) flow of a viscous electroconductive incompressible fluid between two stationary impermeable disks is considered. A homogeneous electric current density vector along the normal to the surface is specified on the upper disk, and the lower disk is non-conductive. The exact von Karman solution of the complete system of MHD equations is studied in which the axial velocity and the magnetic field depend only on the axial coordinate. The problem contains two dimensionless parameter: the electric current density on the upper plate Y and the Batchelor number (the magnetic Prandtl number). It is assumed that the external source producing the axial magnetic field is absent. The problem is solved for the Batchelor number in the range of 0-2. Fluid flow is produced by electric current. It is shown that for small values of Y , the fluid velocity vector of the has only axial and radial components. The rate of motion increases with increasing Y , and at a critical value of Y , there is a bifurcation of a new stable flow regime with fluid rotation, while the flow without rotation becomes unstable. A feature of the obtained new exact solution is the absence of an axial magnetic field necessary for the occurrence of an azimuthal component of the ponderomotive force, as is the case in the MHD dynamo. A new mechanism of the bifurcation of rotation in the MHD flow is found.

Direct numerical simulations of instability development and transition to turbulence in a supersonic boundary layer on a flat plate are performed. The computations are carried out for moderate supersonic (free-stream Mach number M = 2) and hypersonic (M = 6) velocities. The boundary layer development is simulated, which includes the stages of linear growth of disturbances, their nonlinear interaction, stochastization, and turbulent flow formation. A laminar-turbulent transition initiated by distributed roughness of the plate surface at the Mach number M=2 is considered.

The problem of experimental modeling of discontinuity formation in a cavitating liquid layer under shock wave loading is considered. It is shown that the discontinuity takes the shape of a sphere segment and retains it up to the closure instant. The discontinuity surface becomes covered with a dynamically growing thin boundary layer consisting of bubbles, which transforms to a ring-shaped vortex bubble cluster at the instant of closure of the discontinuity emitting a secondary shock wave. Specific features of the structure of the cavitating flow discontinuity arising at loading intensities lower than 0.1 and 5 kJ are discussed.

The influence of a cylinder-shaped single roughness element on the laminar-turbulent transition in the presence of an entropy layer is experimentally studied. The experiments are performed on a blunted cone mode at the Mach number M=5. The roughness element is located on the blunted tip of the model. Information about the mean and fluctuating parameters of the boundary layer in the wake behind the roughness element is obtained by using hot-wire anemometry. It is shown that flow turbulization behind the roughness elements occurs at the local Reynolds number calculated on the basis of the roughness element height and equal to 400-500. It is found that the presence of the roughness element exerts a significant effect on the unsteady characteristics of the boundary layer if the roughness element height is smaller than the effective value.

The existing algorithm for determining mass flow in gas production and transportation systems from output pressure measurements is extended to the case where the internal section of the tube changes with time and is also to be determined in the course of solving the general problem. It is proposed to use this algorithm to determine the presence of hydrates in such systems. An example of determining the presence of hydrates in a main gas pipeline section in permafrost is considered.

Pressure filtration waves in cracks in porous permeable medium are studied. The effect of the porosity and permeability of the formation and crack, the crack width, and the rheological properties of the saturating fluid on the dynamics of perturbations in the crack are studied. It is shown that in a porous permeable formation, a crack is a wave channel through which low-frequency pressure fluctuations in wells propagate. Accurate solutions are obtained which describe the evolution of pressure fields in a crack with an instantaneous pressure change in the well by a constant value. Based on these solutions, the corresponding dependences of the fluid flow on time and the pressure at the boundaries are determined.

The operation of rapid-fire multi-rail electromagnetic launchers of solids in a burst mode is analyzed by numerical modeling in two-dimensional and three-dimensional nonstationary formulations. In the calculations, the launchers are powered from a Sakhalin pulsed magnetohydrodynamic generator. Launchers with three and five pairs of parallel rails connected in a series electrical circuit are considered. Bursts of different numbers of solids having different weight are modeled. It is established that the heating of rails is one of the main factors limiting the performance of launchers under such conditions is. It is shown, that the rate of heating of the rails is determined by the inhomogeneity of the current density distribution over the rail cross-section due to the nonstationary diffusion of the magnetic field into the rails. Calculations taking into account the nonstationary nature of the current density distribution in the rails of a multi-rail launcher have shown that a proper choice of the weight of the accelerated solids (up to 800 g), their number in the burst, and the material of the rails makes it possible to attain launching velocities of 1.8-2.5 km/s at moderate heating of the rails.

The flow of a hydrogen-methane mixture through heated coaxial cylindrical tungsten channels with a built-in tungsten wire is studied by the Direct Simulation Monte Carlo method. The purpose of the study is further development of the gas-phase method of deposition of diamond structures. The axial distributions of the concentrations of the components of the hydrogen-carbon mixture are calculated by means of solving a system of chemical kinetics equations. A series of experiments on deposition of diamond structures from various flows of the hydrogen-methane mixture is performed. The calculated results are compared with the experimental data. Based on these comparisons, it is concluded that numerical optimization of operation modes of gas-dynamic reactors can be used for deposition of diamond structures.

Evaporation rates of water droplets in high-temperature gases were experimentally determined using high-speed video recording cameras and low-inertia thermocouples (for heated air flow as an example). The experiments were carried out for droplets of initial size (radius) of 1-3 mm at an air temperature 500-1000 K. Dependences of the evaporation rate of water droplets on time and gas temperature for various initial droplet sizes were obtained.

Titanium dissolution in the aluminum melt and synthesis of an intermetallic compound at constant temperature and pressure are numerically simulated by the molecular dynamics method. Owing to titanium dissolution, the TiAl₃ intermetallic compound is formed near the interface between the titanium crystal and aluminum melt. Based on the theory of weak solutions, a mathematical model of titanium dissolution in the aluminum melt is constructed. Dependences of the diffusion coefficient, equilibrium concentration of titanium, and dissolution rate on temperature are obtained.

This paper describes the modified bending equations of layered orthotropic plates in the first approximation. The approximation of the solution of the equation of the three-dimensional theory of elasticity by the Legendre polynomial segments is used to obtain differential equations of the elastic layer. For the approximation of equilibrium equations and boundary conditions of three-dimensional theory of elasticity, several approximations of each desired function (stresses and displacements). The stresses at the internal points of the plate are determined from the defining equations for the orthotropic material, averaged with respect to the plate thickness. The construction of the bending equations of laminated plates for each layer is carried out with the help of the elastic layer equations and the conjugation conditions on the boundaries between layers, which are conditions for the continuity of normal stresses and displacements. The numerical solution of the problem of bending of the rectangular laminated plate obtained with the help of modified equations is compared with an analytical solution. It is determined that the maximum error in determining the stresses does not exceed 3%.

The constitutive equations of motion of an elastic medium with given initial stresses are formulated in the form of a hyperbolic system of differential equations of the first order. Equations describing the propagation of small perturbations in a prestressed isotropic medium with an arbitrary energy dependence of the elastic deformation in the strain tensor are derived, and equations for the quadratic dependence of elastic strain energy on the strain tensor are given.

This paper presents of an geometrically nonlinear analytical model of a flexible cylindrical frame (rim) of the transformable precision large-size reflector of space antennas made using polymer composite materials with form memory. A nonlinear boundary-value problem for the frame in a deformed (collapsed) state is formulated and exact analytic solutions in elliptic functions and integrals which describe the deformation modes of the rim. A geometrically nonlinear model us used to obtain exact analytical solutions which allow preliminary determination of the geometric dimensions and the optimal shape of the flexible frame and estimate the stored energy.

Numerical schemes for determining the shape and dimensions of radial cracks formed during confined explosions of linear charges located in a monolithic rock massif at a great depth and near its surface. The influence of the charge length on the dimensions of radial cracks in a confined explosion is studied. The amount of undercharging of a borehole or blast charge for which the area radial cracks is maximal is determined.

Results of experimental investigations of welded joints of high-strength aluminum-lithium alloys of the Al-Cu-Li and Al-Mg-Li systems are reported. The welded joints are obtained by means of laser welding and are subjected to various types of processing for obtaining high-strength welded joints. A microstructural analysis is performed. The phase composition and mechanical properties of the welded joints before and after thermal treatment are studied. It is found that combined thermal treatment of the welded joint (annealing, quenching, and artificial aging) increases the joint strength, but appreciably decreases the alloy strength outside the region thermally affected by the welding process.

A method is proposed for creating principally new functionally graded heterogeneous materials on the basis of B₄C ceramic powders with different mass fractions in the initial mixture and plastic metallic additive of Ni by a combined method of cold gas-dynamic spraying with a subsequent layer-by-layer laser action. Mechanical properties of the resultant tracks are examined. It is shown that the track microhardness increases with increasing B₄C concentration in the initial mixture. The track structure is found to depend on the size of ceramic particles in the interval from 3 to 75 μm. Reduction of the B₄C particle size (approximately by a factor of 2-3) inside the track owing to fragmentation under the action of the laser beam is observed for the first time.