Home – Home – Jornals – Journal of Applied Mechanics and Technical Physics 2024 number 3

Results of studying interaction of two colliding axisymmetric laminar microjets of hydrogen in the course of their diffusion combustion are reported. Gas exhaustion occurs with identical velocities through pairs of micronozzles, which are thin-walled cylindrical tubes with an inner diameter of 200   m. The transverse positions of the tubes with respect to each other are changed during the experiment. Specific features of flame formation from two interacting microjets are found for different transverse positions of the tubes, and the results are compared with flames of single microjets with the same exhaustion velocity.

This study is aimed at understanding some characteristics of the shock wave generated by a novel composite charge consisting of an inner high explosive, a medium non-detonating layer, and an outer aluminized explosive. The influence of the shell restraints and initiation modes on the peak overpressure and impulse of the charge is investigated. Numerical models are developed based on the mapping function of AUTODYN for determining the spatial distribution of the shock wave overpressure. By means of validation experiments, the accuracy of the developed model is verified. It is found that the peak overpressure and impulse obtained from experiments and simulations are in good agreement, with a deviation of less than 16.9%. The difference in the overpressures at various azimuths decreases with increasing distance, and the shock wave profile eventually evolves into a spherical shape. The radial overpressure of the shelled composite charge is initially greater than that in the axial direction and decays rapidly with increasing distance. The azimuth corresponding to the maximum peak overpressure is shifted from 75oC for the bare charge to 110 °C for the shelled charge. It is found that the energy utilization of the composite charge under inner initiation is apparently smaller than that under simultaneous initiation.

The countercurrent flow of a falling liquid film and a turbulent gas flow in a narrow vertical channel is considered. In the case of small Reynolds numbers and when certain conditions are met for the parameters of such a flow, the problem reduces to the study of one evolutionary integrodifferential equation for the deviation of the film thickness from the unperturbed level. A numerical study of the evolution of periodic disturbances has been carried out. Several solutions to the model equation are presented

A mathematical model is proposed that describes the formation of internal hydraulic jumps and the mixing of co-directed flows of an ideal stratified fluid in the Boussinesq approximation. The model is based on a three-layer representation of the flow taking into account the entrainment of fluid from the outer layers into the intermediate vortex layer and is represented as a system of heterogeneous conservation laws. The speed of entrainment is given by the equilibrium condition within the framework of a more general model of evolution of the mixing layer. The speed of propagation of disturbances and the concepts of subcritical and supercritical flows are formulated. It is shown that the model is suitable for describing the mixing and splitting of flow in deep-sea currents. Solutions corresponding to the flow around an obstacle with the formation of an internal hydraulic jump and a region of intense mixing were constructed. The results of numerical modeling were shown to be in good agreement with experimental data.

Results of studying gas flows in a setup used for cold gas-dynamic spraying are reported. The setup consists of a cylindrical inlet channel with a central rod connected at a right angle with a rectangular slotted channel. Injection of a high-pressure gas through the inlet channel leads to gas acceleration. It is shown that there are velocity and pressure disturbances in a supersonic overexpanded jet exhausting from the channel, which arise due to the presence of compression and expansion waves, as well as streamwise vortices. The contribution of streamwise vortices to pressure and velocity disturbances is approximately 30%. Streamwise vortices are formed at the entrance of the slotted channel owing to curvature of streamlines.

A method for controlling the physical and chemical properties of a formation in order to increase its oil recovery by injecting an acid composition GBK-F into the formation is being considered. An experimental setup has been created for physical modeling of the effect of the composition on an oil reservoir. Experiments were carried out on a flat model with a single injection of the reagent into the central well. The experimental results confirmed the effectiveness of the composition

A two-dimensional exact analytical solution of the thermal field developed during the submerged arc welding process with visualization of the thermal surface contour for analyzing the heat flow in the domain with the hybrid application of Duhamel's theorem and finite integral transform approach is obtained. The thermal field arising in submerged arc welding of thick EH36 steel plates is studied. An ellipsoidal heat source model is assumed. The developed thermal field is investigated with variations of several process parameters, such as the heat source velocity, heat input, and lag time of movement of the heat source involved in the welding process.

In this study, the effect of patient's physical activity in terms of the heart rate on the growth of the thoracic aortic aneurysm (TAA) is studied. Using medical images of the patient, a patient-specific geometry model is constructed. Then the hemodynamic parameters of the blood flow are numerically analyzed for different heart rate conditions. The simulation results show that the maximum wall shear stress, the maximum velocity, and the maximum pressure during a cardiac cycle increase by 19.1, 12.7, and 50%, respectively, as the heart rate increases from 60 to 174 beats per minute. Results also indicate that an increase in the heart rate leads to reduction of the time-averaged wall shear stress and simultaneously to an increase in the wall shear stress oscillations. According to the literature, these hemodynamic conditions are undesirable and can increase the likelihood of aneurysm development and aortic rupture.

The behavior of material under surface laser processing conditions is described taking melting into account. A Maxwellian type is presented that takes into account the change in heat capacity and viscosity with a change in temperature and material composition. This model is used as the bases to develop a model for the change in the properties of a flat layer material using a moving heat source. An algorithm for the numerical solution of the formulated problem is described. Examples are presented to show the effect of heat loss, cohesion, melting, chemical reactions and their acceleration due to the work of stress on the properties of the material

The results of a study of the influence of compaction pressure on the characteristics of radiation-protective composites based on polyethylene and boron carbide B₄C are presented. Using software modeling, the temperature range for heating a mold of a given size was selected. The required holding time of the composite was determined experimentally, and defects that arise from various deviations from the optimal temperature parameters were identified. The results of testing the strength of samples under various pressing pressure conditions are presented, and the optimal pressure value is found. A composite was obtained with the following mechanical characteristics under optimal pressing conditions: density (1.09 ± 0.01) g/cm³, bending strength (5.72 ± 0.18) MPa, sound velocity in the composite (2050.00 ± 0.01) m/s

It is proposed to use the relations of the endochronic theory of thermoplasticity to describe the nonlinear deformation of isotropic materials under non-isothermal loading. A variant of the governing relations in integral and differential form for the general loading case is given. Analytical dependences for a number of material parameters of the model were determined based on the results of uniaxial tension (torsion) tests. A numerical algorithm based on the Euler method with an internal iterative process implemented by the Seidel method is proposed to analyze the governing relations. An example of numerical calculation of the uniaxial tension of a rod under complex thermal force loading. It is shown that the calculation results are in satisfactory agreement with the results obtained using isotropic hardening flow theory

The problem of constrained torsion of thin-walled rods under the action of an end torque is considered. Using the asymptotic splitting method, a system of resolving equations was obtained that describes the combined torsion, tension-compression, and bending of the rod. To test the resulting model using the example of typical sections, a comparison was made of the stress-strain state in the rod, determined in the calculation using the developed model and three-dimensional numerical calculation by the finite element method. The resulting mathematical model was analyzed and its advantages compared to the widely used Vlasov theory were revealed. It is shown that the developed model does not contain the restrictions imposed by the hypotheses in the Vlasov theory, such as the non-deformability of the transverse contour and the absence of shear deformations on the middle surface. In a number of cases, the resulting model makes it possible to more accurately determine the emerging stress-strain state. In particular, it is shown that the developed model takes into account the presence of a boundary layer near the embedment, which arises during torsion of corner sections and makes a significant contribution to longitudinal stresses, while Vlasov’s theory does not allow one to restore the arising longitudinal stresses

A method of determining the dynamic yield strength of heterogeneous materials is proposed, based on comparisons of the processes of cavity formation in the reference and examined materials. A series of computations is performed for penetration of an extended rod into homogeneous and heterogeneous massive targets. A nonmonotonic dependence of the penetration depth on the motion velocity is derived. The yield strength limit of a heterogeneous medium is obtained from the analysis of computation results in the coordinates of the specific kinetic energy of the rod and the work of stresses on plastic strains.

Using the grid-characteristic numerical method on grids of tetrahedrons, wave processes in a composite material are simulated under the action of a pulsed shock load. An approach is proposed to increase the order of approximation of the method on an unstructured mesh in the three-dimensional case. The results of calculations of the propagation of a load impulse in a three-layer composite are presented

A two-layer rod with a box section twisted under the action of tangential stresses at angle θ is considered. It is assumed that the deformations in the rod are elastic and its lateral surface is stress-free. The layers have different elastic properties and different thicknesses. The layer contact line is assumed to be rigid, i.e., the stresses on it coincide. An exact solution describing the stress state of the given structure is constructed using conservation laws. The stress state is determined at each point of the cross section using integrals over external contours

A simplified numerical method for simulating the penetration of projectiles into fabric targets is proposed which takes into account the type of fabric weaving, the friction forces between the fibers and between the projectile and the fabric, and the transverse dimensions of the fabric. The necessary calculated parameters were selected from a comparison of experimental and calculated data. The proposed method was used to estimate the ballistic resistance of a combined protective composition required to reduce the armor impact. The problem of the nfluence of the projectile shape on the ballistic resistance of fabric armor protection

A brief overview of experimental approaches to the study of the tribology of sliding of various bodies on snow or ice is presented, and a model and a digital twin of a tribological device is proposed. The deformation distribution of a tank with snow rotating at a target speed was obtained by modeling, and the work done by the friction force per sliding cycle was determined by testing the movement of a ski sample on a flat snow surface. The proposed device can be used to evaluate the efficiency of sliding on snow at a given temperature, snow structure, humidity, and the roughness of the ski surface sliding on snow

This paper presents an analysis of the effectiveness of using one-dimensional network models for virtual assessment of hemodynamic indices whose values are widely used in clinical practice to choose a treatment strategy for coronary heart disease with stenotic lesions of the coronary arteries. It is shown that existing approaches make it is possible to assess hemodynamic indices based on clinical data collected without intervention in the body with an accuracy comparable to the accuracy of the input data and direct measurements. It is also important to take into account the state of the myocardium microvasculature and its influence on the interpretation of modeling results and direct measurements in the clinic

An approach is proposed for quantitative assessment of the shagginess of the lumen of a pathologically altered aorta, taking into account the three-dimensional morphology of its internal surface. An algorithm for assessing local shagginess has been developed and implemented, and an integral criterion for shaggyness in the anatomical region has been proposed. The algorithm was tested on data from two patients with a shaggy and a smooth lumen. The results obtained are in good agreement with the results of visual assessment by expert surgeons and are confirmed by clinical outcomes during surgery

Salmonella typhimurium and Listeria monocytogenes bacteria, which are two important bacteria used for bacterial therapy purposes in order to limit tumor growth, are studied. Mechanical specifications of the bacteria obtained applying nanoindentation with the use of atomic force microscopy (AFM) are reported. The results show that Salmonella typhimurium bacteria have a greater elastic modulus, but smaller adhesion than Listeria monocytogenes bacteria. The elastic modulus of the AFM extension stroke is larger than that of the retraction stroke. The resonant frequencies and amplitudes of the frequency response function of the AFM beam's vertical movements with two bacteria as samples are investigated using the finite element method. The results show that an increase in the elastic modulus of the sample raises the resonant frequency; therefore, the resonant frequency of Salmonella typhimurium bacteria is greater than that of Listeria monocytogenes bacteria. The results obtained by the finite element method and experimental techniques are found to be in good agreement.