Home – Home – Jornals – Journal of Applied Mechanics and Technical Physics 2024 number 6

This paper presents the results of numerical simulation of magnetic field cumulation and the Joule heating of shaped-charge jets produced by explosive compression of a metal cone in which a magnetic field was preliminary generated. The problem is considered in an axisymmetric two-dimensional non-stationary formulation. The final electrical conductivity of the cone material is taken into account, and various methods of generating the initial magnetic field (using one or two solenoids) are considered. It is found that that during cone compression, the magnetic field induction can increase several hundred-fold. For a relatively low initial magnetic field induction on the cone axis (0.09-0.17 T), the temperature increase near the axis of the shaped-charge jet due to heating by eddy currents is 200-300 °C. This heating can be accompanied by thermal softening of the shaped-charge jet material and an increase in its ultimate elongation and hence penetration capability.

This paper presents preliminary results of refinement of the mathematical model of plasma transport in a helical open magnetic trap (HOMT). Plasma is contained in the device by transferring a magnetic field pulse with helical symmetry to the rotating plasma. The mathematical model is based on the stationary equation of plasma transport. The paper presents a method for taking into account the effect of the model coefficients using additional information. The calculated dependence of temperature on coordinates is obtained, which qualitatively agrees with the experimental data. Ordinary differential equations are obtained, which follow from the original model and can be used to refine the coefficients. The mathematical model is developed to predict the plasma confinement parameters in devices with a spiral magnetic field.

The crystallization of a gallium alloy in a rectangular flat cuvette located vertically under external electromagnetic influence has been studied experimentally. It has been shown that the speed of movement and shape of the crystallization front can be effectively controlled by changing the power parameters of the electromagnetic stirrer. A mode characterized by intense mixing flow and significant inhomogeneity of the crystallization front has been selected by varying the amplitude of electromagnetic forces. In this mode, changing the phase angles of the supply currents of the linear induction machine allows one to fundamentally change the topology of hydrodynamic melt flows at a constant power supply of the stirrer. This, in turn, leads to a change in heat and mass transfer characteristics and hence the conditions in the interfacial region, making it possible to indirectly control the homogeneity of the crystallization front and, to a lesser extent, the phase transition rate. The contribution of convection to flow formation and its influence on the crystallization process have been studied. In particular, it has been shown that thermal convection can lead to the formation of additional vortex structures near heat exchangers, which prevents metal crystallization.

Coupled aerodynamics and rigid body dynamics are used to develop a numerical method for the rigid motion of the object on the ground under shock waves based on the collision theory and dynamic mesh method. The effects of the mass and centroid height of the object on the rigid motion are analyzed. Furthermore, the effect of object motion on shock wave propagation is examined. The results suggest that the rigid motion behavior of the object remains similar under different positive pressure times; the motion laws of the object are similar under different masses, while a small mass can alter the rotational direction; increasing the centroid height can reverse the rotational direction, and diffraction may induce a further reversal when the centroid height increases to a certain value; the rigid motion reduces the pressure decay rate near the leeward side during shock wave propagation over the object.

The states of liquid albumin droplets sitting on a non-wetting horizontal elastic substrate which was first cyclically stretched and then relaxed have been studied experimentally. Multi-branch hysteresis of the states of the droplet gave been found. The number of hysteresis branches can be regulated by changing the law of motion of the substrate.

This paper describes the propagation of vertically polarized surface acoustic waves at an interface between porous media saturated with methane hydrate and ice (water), as well as horizontally polarized waves at an interface between a hydrate-saturated porous medium and a water-saturated porous medium. A mathematical model is developed for plane harmonic waves. The porous medium saturated with gas hydrate or ice (water) is assumed to be an elastic isotropic body. The mathematical model includes wave equations for scalar and vector potentials of wave velocities with account for displacement and stress vector components of the medium particles. Conditions for the continuity of displacements and stresses in porous media at the interface are given. The obtained dispersion equations are analyzed, and the results are compared with experimental data. It is revealed that the penetration depth of a transverse wave into hydrate-saturated sand is greater than the penetration depth of a longitudinal wave. It is proposed to determine the presence of hydrate-saturated sand at positive temperatures of bottom sediments by the penetration depth and the variation of the zero mode velocity of the horizontal polarization wave.

A setup for experimental studies of the structure, shape, and size of the gas-liquid interface under ultrasonic exposure and forced aeration has been developed. It has been found that ultrasonic exposure leads to a factor of about 1.5 increase in the interfacial area during aeration. The existence of an optimal intensity of ultrasonic exposure that provides maximum increase in interfacial area per unit supplied ultrasonic energy has been found.

The paper presents solutions to problems of nonstationary filtration to an imperfect well with an arbitrary angle of inclination from the vertical, allowing for the interpretation of data based on pressure transient test and production forecasting. Solutions are obtained for various conditions on the top and bottom of the reservoir, while two algorithms are implemented to describe the bottom-hole pressure: a multi-segment and a single-segment algorithm with the determination of an equal pressure point. A computational experiment shows that the calculation results obtained using single- and multi-segment algorithms are in good agreement.

Results of studying an oblique impact of heavy solid spheres 6 mm in diameter onto an undisturbed surface of water by the method of high-speed visualization are reported. The dynamics of interaction of the body with the liquid in the cases of sphere ricochet and immersion is compared. It is found that air bubbles are intensely captured in the wake behind the body in situations with body immersion owing to a collision of the edges of the “crown” generated at the cavity boundaries and to formation of a jet penetrating through the cavity bottom and entraining air bubbles. The effects of the sphere material density and of the impact velocity and angle on the scenario of sphere-liquid interaction are studied. Comparisons with previous experiments show that a decrease in the sphere size leads to reduction of the critical angle, while the opposite effect (increase in the critical angle) is observed if the impact velocity is increased. Such effects cannot be explained by theoretical approaches developed earlier for impacts of large spheres because these approaches ignore the dynamics of the liquid jet generated ahead of the body and the changes in the flow pattern as a whole.

The influence of various individual and phantom boundary conditions on the results pre-operative numerical simulations of hemodynamics of a fusiform aneurysm of cerebral vessels is numerically simulated. It is found that allowance for individual mechanical properties of the aneurysm tissue affects the results of predicting the aneurysm status, but does not affect predicting the rupture zone, which can be detected by using the CFD approach under the assumption of rigid walls with phantom boundary conditions and with the condition of the maximum shear stresses on the wall as a criterion of rupture zone determination.

Results of a methodical study aimed at modeling a spatially inhomogeneous transition line are reported. The results are obtained by an in-house software module for the CFD package and an in-house program for predicting the laminar-turbulent transition based on the  e<i>^N</i>-method. Numerical simulations are performed for a hybrid laminar-turbulent transition, where the regular and bypass transition scenarios take place in different regions of the flow in the boundary layer on a swept wing.

A method is developed for determining residual stresses in a thin metal plate via shot peening of its surface. The reference configuration of the plate is assumed to be flat with a layer of hardened material of known thickness with a uniform longitudinal initial stress; its value is determined by solving the inverse problem of establishing the equilibrium state of a bent plate. The problem of bending a plate with initial stresses is solved numerically by the finite element method using the model of an isotropic hypoelastic material. As a result of solving the problem, a residual stress field is determined, allowing one to estimate the degree of danger of positive principal stresses that can lead to destruction of the plate material.

One of the most important factors determining dental implants' longevity and effectiveness is the connection between the abutment and the implant. This investigation focuses on studying how bone shielding is affected by the interface between dental implants and abutments. In a computer-aided design (CAD) environment, three dental implant connectors and carbon-reinforced PEEK are modeled. A comparison is made between the modern dental implant locking mechanism and the more traditional internal hexagonal and conical abutment interfaces to evaluate the former's effectiveness. ANN is employed in the process of developing the precise modulus of the dental implant material for the human jaw. Studying the von Mises stress and deformation of dental interface materials makes it possible to discover a unique locking system that exhibits the highest von Mises stress and deformation, virtually on par with the bone. However, the carbon-reinforced PEEK composite material demonstrates high bone shielding.

A method for selecting an appropriate ice model and its parameters using numerical simulation is developed. The process of low-velocity impact of a spherical indenter with an ice plate is studied, and numerical calculation data are compared with experimental data. This paper describes well-known rheological models of elastoplasticity with the von Mises and von Mises-Schleicher yield criteria, as well as an elasticity model with a constant-size elastoplastic inclusion. A system of isotropic linear elasticity equations, solved by the grid-characteristic method, is used as the determining system of equations. The effect of the model parameters on the calculated instantaneous velocities and coordinates of the ball is investigated. Criteria for selecting the model characteristics are formulated, and approximations of dependences of these criteria on various parameters are constructed.

A single integral form of the postulates of continuum mechanics in the form of laws of change (conservation) of certain quantities is represented as a table of postulates. It is assumed that in a continuous medium, both purely mechanical and various non-mechanical interactions occur, which are described by scalar, vector, and second-rank tensor energetically conjugate pairs of quantities, one of which characterizes a process and the other defines the response of the environment to this process. The first three rows of the table of postulates are used to construct the fourth and fifth rows corresponding to the laws of change in internal energy and the quantity that, in the case of the thermodynamic pair “temperature-entropy” coincides with entropy. It is shown that the assignment of sources, flows through the boundary, and productions in the fourth and fifth rows of the table of postulates actually makes these rows definitions. The principles used in nonisothermal mechanics to construct constitutive relations linking dependent and independent state variables for each type of interaction are generalized.