Journal of Applied Mechanics and Technical Physics最新文献

This paper presents the results of experimental studies of cooling a zirconium ball in subcooled ethanol under the action of a submerged jet. The degree of subcooling of the cooled liquid and the distance from the nozzle exit to the cooled surface varies during the experiments. The heat patterns of cooling are presented and the effect of the distance between the nozzle and the surface on the duration of cooling and the transition temperature from stable film boiling to intense heat transfer is revealed.

This study describes a method for calculating the Darcy friction coefficient in a flat channel formed by two infinite parallel plates as a function of the Reynolds numbers and the gas rarefaction parameter in the channel. Maxwell’s diffuse reflection model is used as a model for the reflection of gas molecules from the channel walls. The isothermal gas flow is due to the presence of a pressure gradient that is small in absolute magnitude and directed along the channel walls. The method proposed in this paper is based on solving a linearized ellipsoidal-statistical Boltzmann kinetic equation with homogeneous boundary conditions using the Chebyshev polynomial approximation. An unknown function that interpolates the solution to this equation is represented as a partial sum of a series in Chebyshev polynomials of the first kind. The properties of finite sums for an orthonormal system of Chebyshev polynomials are used to reduce the problem to a system of linear algebraic equations with respect to the values of the sought function at interpolation nodes. The results obtained in this study are analyzed.

A system of Navier–Stokes equations is used to calculate rotational modes of thermocapillary fluid flows in a semi-infinite space bounded from above by a non-deformable free boundary, with a local temperature distribution specified on it. It is shown that, near the free boundary in the boundary layer, bifurcation causes rotational modes of fluid flows as this boundary is unevenly cooled. Secondary rotational modes are calculated, which form two families of solutions that depend on several parameters, two of which are not determined by external conditions.

Since, in modern high-performance sports, the technical component is decisive, the ski running surface is an important element of cross-country skiing. This paper presents a review of papers on sliding mechanics, discusses modern methods for improving it, and considers the prospects for the development of this area under current energy and environmental conditions. Various factors affecting the sliding mechanics, in particular, snow cover albedo, and microroughness of the ski running surface are analyzed in detail.

This paper describes the use of a nonlinear viscoelastic model with material properties depending on the strains in the lengthwise fracture analysis of an inhomogeneous cantilever beam structure. The viscoelastic model is obtained by placing a nonlinear spring and a nonlinear dashpot in parallel to a series of a linear spring and a linear dashpot. The modulus of elasticity of the nonlinear spring and the coefficient of viscosity of the nonlinear dashpot depend on strains. The strain energy release rate is determined. The balance of the energy is analyzed to prove the correctness of the strain energy release rate solution.

Implementation of the Candler model of vibrational-vibrational energy transfer between diatomic molecules in an inelastic collision is discussed. An example of oxygen O₂ and nitrogen N₂ interaction is used to analyze the method of simple iterations, the Newton method, the method of bisection, and the approximate formula for calculating the equilibrium vibrational temperature, which is necessary in the Candler model. The method recommended for simulations is the Newton method or bisection. The model of vibrational-vibrational energy transfer is tested by examples of zero-dimensional vibrational relaxation, the flow around a cylinder, and the flow in a wedge-shaped nozzle. It is demonstrated that vibrational-vibrational energy transfer affects the distribution of vibrational temperatures.

An algorithm for controlling submerged jets is developed to calculate the geometry of a jet generator, which provides a velocity profile and (or) the required characteristics of its linear instability in the initial section of the jet. A class of jet generators is considered, whose geometry is similar to the geometry of the device manufactured at the Institute of Mechanics of the Moscow State University. The control algorithm is based on the gradient descent method for the minimization of the functional that relates the parameterization of the forming device geometry and the characteristics of the velocity profile, which is formed by this device. The algorithm operation is tested on the example of a functional describing the deviations of the jet velocity profile from the set one.

Behavior of a transversally flowing fluid in a boundary layer on a plate and a wedge is studied using the Faulkner–Scan equation in the presence and absence of suction and blowing on the body surface. Numerical methods are used to show that, under certain conditions in the boundary layer, one may observe the formation of attraction and repulsion lines (the transverse velocity along these lines is zero) and maximum transverse velocity lines. Different transverse flow regimes in the boundary layer depending on the key parameters of the problem are considered.