Journal of Applied Mechanics and Technical Physics最新文献

Approximations of the profiles of the longitudinal and transverse velocity components in the boundary layer calculated for the flows around a swept wing and a body of revolution by means of solving the full Navier–Stokes equations and using the boundary layer profiles from the self-similar one-parameter family of the Falkner–Skan–Cooke profiles and two-parameter family of profiles proposed by Gaster are compared. A significant advantage of using the approximation of the numerical profiles near three-dimensional separation by profiles from the two-parameter family is demonstrated.

The flow in a far plane momentumless turbulent wake is described using a mathematical model obtained from the algebraic Rodi model of Reynolds stresses. The model is similar to the two-parameter ((k{-}varepsilon)) turbulence model in the far-wake approximation with a modified empirical constant in the diffusion terms of the equations. A group-theoretical analysis of the mathematical model of the wake is carried out, and a self-similar reduction of the model equations to a system of ordinary differential equations is performed. An approximate solution of the corresponding boundary-value problem is constructed using an asymptotic expansion of the solution in the vicinity of a singular point.

An original numerical framework is developed in the present research work in order to estimate the free field sound radiation from baffled structural panels subjected to nonhomogeneous turbulent boundary layer flow-induced excitation. A sequence of semi-analytical methods is used to estimate the nonhomogeneous turbulent boundary layer wall pressure spectrum, which is decomposed using the Cholesky technique to obtain the random wall pressure in the frequency domain. Structural panels are modeled using the finite element technique, and a coupled finite element-boundary element modeling technique is developed to estimate the sound power level radiated into the free field. Results are obtained for laminated composite structural panels with various fiber orientations.

A nitrogen jet expanding during its exhaustion from a nozzle into a vacuum chamber is numerically simulated by a hybrid approach. The flow parameters in the nozzle and in the near field of the jet are determined by solving the Navier–Stokes equations by using the ANSYS Fluent software. The gas flow at large distances from the nozzle exit is modeled by the Direct Simulation Monte Carlo method by using the SMILE software system. Such an approach makes it possible to perform sufficiently accurate simulations in the near field of the jet; moreover, the temperature nonequilibrium of the expanding gas jet and other effects of rarefaction in the far field of the jet are taken into account. The approach is verified by using various approximate analytical models of gas exhaustion into vacuum. A comparison of the numerical results with available experimental data shows that they are in good agreement.

This paper presents the results of a statistical analysis of turbulent structure in a free bubbly jet at a Reynolds number of 12 500 based on PIV measurements of the carrier-phase velocity. Distributions of higher-order statistical moments for velocity fluctuations (coefficients of skewness and excess) and the turbulence energy spectra for single-phase and gas-saturated jets were obtained after statistical filtering of instantaneous velocity fields. The influence of the dispersed phase (bubbles with an average diameter of 0.8 mm) with a volumetric gas fraction of 0, 1, 2, and 3% on the specified characteristics of the continuous phase was analyzed.

An experimental method is developed that makes it possible to visualize the onset and spreading of damage in each layer of transparent armor. The damage development dynamics in multilayer packages consisting of four (480times 480)-mm layers and eight (300times 300)-mm layers is analyzed. The evolution of damage is obtained under the influence of a 12.7-mm bullet with a two-component core with a total mass of 59.2 g and a 7.62-mm bullet with a two-component core with a total mass of 10.9 g along the normal and at an acute angle in a range of impact velocities of 777–797 m/s. The experimental data are compared with the numerical simulation of interaction between an impactor and a multilayer transparent target.

A passive method for reducing the drag of a cylinder by placing a flat plate behind it at a Reynolds number Re=10⁵ has been studied. The paper presents the results of an ANSYS Fluent simulation of the flow around a cylinder–plate system, including the velocity and pressure fields, streamlines, and the dependences of the drag coefficient and the position of the separation point on the surface of the cylinder on the relative length of the plate. It has been found that the drag coefficient of the cylinder–plate system can be reduced by approximately 40% compared to the case of an isolated cylinder.

The formation of a mixed-type (fracture modes I and II) internal crack in a pipe wall that is made of an ideal elastoplastic material under the action of combined tensile (compression) and bending loads is described. The fracture of such materials is illustrated using a modified Leonov–Panasyuk–Dugdale model, which additionally uses the parameter of fracture process zone diameter. Another case under consideration is complex loading during which the crack path becomes curved, so its bend angle is determined using a force integral criterion based on the stress field asymptotics in the vicinity of the crack tip. Critical fracture parameters are obtained using a two-parameter (dual) strength criterion in the case of a complex stress state. The parameters included in the resulting analytical model are analyzed. The dimensionless geometric parameters of the structure are obtained numerically using the finite element method. Quasibrittle fracture diagrams are constructed.

A linear theory of static cylindrical bending of a thin plate is constructed without using the Kirchhoff hypotheses. Transverse shear, thickness compression, and the resulting longitudinal force are taken into account. In view of changes in the areas of both surfaces during bending, the transverse distributed force is determined. It is assumed that the average pressure on the plate is several orders of magnitude greater than the pressure difference. Bending is considered under the conditions of a plane strain state and a stress state.

This paper describes a numerical simulation within the framework of a two-dimensional shallow water model of interaction of a solitary wave with a steady rectangular semi-submerged structure. The results of this study are compared with the results of calculations based on a model of irrotational three-dimensional flows, and it is shown that the simulation accuracy at small incident wave amplitudes is satisfactory. It is also revealed that, the solitary wave diffraction on the cylinder surface is neglected when using a one-dimensional shallow water model, then the maximum values of wave runup on the edge of the cylinder and the force loads on it become overestimated.