Home – Home – Jornals – Advanced Search

A linearized model is presented for the scattering problem of flexural gravity waves by the bottom with a finite number of rectangular steps in the ocean. The matched eigenfunction expansion method is used to solve the boundary-value problem, and the results are expressed in terms of a set of integral equations solved by the multiterm Galerkin's approximation technique. Numerical values of the reflection and transmission coefficients are calculated and graphed to display the influence of various parameters of the problem. The accuracy of the present method is verified by using the energy balance relation for the reflection and transmission coefficients. The results are compared with those available in some earlier works.

Theoretical results obtained within the framework of the weakly nonlinear model of a developed boundary layer in a flow past a narrow flat plate are verified with the use of methods of direct numerical simulation of the Navier-Stokes equations. The mechanism of gas ejection (bursting from the surface of a thermally insulated plate in a supersonic gas flow with the Mach number M = 2 is studied within the framework of the model of complete nonlinear interaction. It is demonstrated that the transition from the laminar to turbulent flow past the plate in the case of weak external perturbations occurs due to resonant three-wave interaction. Theoretical results relating the energy redistribution between the oscillations and the process of spatial structure formation are confirmed.

The problem of current spreading across the width of thin foils (in snake-like systems) or planar current sheets is considered. For calculation the evolution of the current distribution across the width of inhomogeneous thin conductive layers or foils is calculated using an integrodifferential equation which reduces the two-dimensional problem for the magnetic field to a one-dimensional problem. An infinite periodic system of plane snake-like foils is considered. It is shown that in this foil system the current distribution corresponding to the ideal foil conductivity is first established and then relaxation of the current distribution to a uniform one occurs. If the foils are used as circuit breakers, current must have time to be distributed uniformly across the foil width during current transfer to the load, so that the corrections for the nonuniformity of the current distribution in the switches should be small.

This study is aimed at designing, optimizing, and validating a posterior lumbar interbody cage (PLIF) model based on the 3D printing method, which provides patients with a suitable customized design capable of providing proper mechanical support. In the content of this study, the CATIA software is used for modeling of three symmetrical cage models with different porosities. Then, two replicates of each cage model are assembled in the disc space of a parametric geometry of the L1-L2 vertebrae. The proposed models are meshed, and a finite element analysis is conducted through compressive and moment loadings. The overall stiffness and von Mises stress and strain of each model are determined.

A new design for continuous separation of multiple blood cells from diluted whole blood in a microfluidic device based on dielectrophoresis phenomenon is presented. Compared to the other studies, the proposed separator is designed for simultaneous separation of more types of blood cells with desirable accuracy. Using finite-element-based simulations, the device efficiency is evaluated for separation of five blood cell types. The proposed separator uses both dielectrophoretic and hydrodynamic drag forces to separate blood cells. The separator performance under different operating conditions is also evaluated.

Aorta is the largest vessel of the human circulatory system, which plays a critical role in the supply of oxygen and nutrients tp all organs of the abdominal cavity and lower limbs. The critical pathology of this vessel is aneurysm. In medical practice, an important problem is aortic aneurysm rupture prediction and surgery planning since aneurysm rupture outside the clinic, as a rule, leads to a lethal outcome. To construct adequate mathematical models that predict such an outcome, it is necessary to determine the strength characteristics of the tissues of the aorta itself, its aneurysm and iliac arteries at various stages of growth of such an aneurysm, and also taking into account patient data. The strength characteristics of tissues of the human aorta, its aneurysm, and iliac arteries have been studied. It has been experimentally proved that in samples of healthy aorta tissues, the differences between the values of the limiting relative deformations in the axial and tangential directions are statistically significant ( p = 0.033), which is not observed in the case of an aortic aneurysm. The results can also be interpreted as the fact of remodeling of the aortic aneurysm wall in comparison with the healthy aorta. These data can be used in personalized hydroelastic simulation during construction of predictive models for the rupture of such aneurysms.

In this paper, SH-wave propagation in an initially stressed triclinic layer welded between two half-spaces is investigated. The upper half-space is considered to be transversely isotropic and elastic, while the lower one is heterogeneous, isotropic, and poroelastic. In the case of the lower half-space, the problem is reduced to the Whittaker differential equation. Frequency equations are derived for the layer as a whole and half-spaces. It is found that the phase velocity is strongly influenced by the initial stress, porosity, and heterogeneity.

Results of a series of experiments aimed at studying laser cladding of individual tracks with the use of the B4C-Ti-6Al-4V cermet powder mixture are reported. The influence of laser cladding parameters (radiation power, beam motion velocity, and focus position) on the characteristics of tracks being formed (geometric sizes, microhardness, and elemental composition) is studied. It is shown that an increase in the concentration of reinforcing particles in the initial powder mixture alters the character of mass transfer inside the melt bath, leading to changes in the shape of the single track. It is found that a complex heterogeneous structure is formed in the melt bath, including secondary phase compounds formed in chemical reactions due to in-situ synthesis. The microhardness values at various points of the single track are observed to differ by more than a factor of 2 (in the interval HV0.3 = 548-1415).

The possibility of obtaining composite coatings from a mixture of aluminum and boron carbide powders for neutron shielding by cold gas-dynamic spraying has been studied. The dependences of the deposition efficiency and the residual content of boron carbide in the coating on its initial content in the sprayed mixture of powders were derived. The obtained regularities have been analyzed, and an approach has been proposed to search for the boron carbide concentration in the powder mixture that is optimal for creating effective neutron-absorbing coatings. It has been shown that the highest productivity of the spraying process is achieved when using the optimal powder composition with (a volume fraction of boron carbide of about 0.5).

This paper describes a numerical-analytical model of the viscoelastic-plastic behavior of flexible shallow shells with account for the dependence of plastic properties of their materials on strain rate. The inelastic behavior of materials is described by the theory of flow with isotropic hardening. Loading functions depend on the hardening parameter and strain rate intensity. Viscoelastic behavior is described by linear constitutive equations from a multiconstant body model. Lateral shears of structures during bending deformation are taken into account within the framework of the Ambartsumyan theory, and geometric nonlinearity within the von Karman approximation. A cross-type explicit scheme is used for the numerical integration of the formulated initial boundary value problem. The dynamic deformation of a cylindrical elongated panel made of a polymer material is studied. The structure is transversely loaded by a pressure generated by an air blast wave. It is shown that neglecting the dependence between the plastic properties of the material and the strain rate may cause one to significantly underestimate the maximum deflection value in absolute value and the largest strain value during oscillations and cause one to overestimate a maximum residual strain. In addition, the diagrams of residual deflections of the structure obtained by such a calculation do not agree with the diagrams obtained by a calculation that takes the mentioned dependence into account.