Kharkiv Polytechnic Institute

Carbon monoxide oxidation over Co3O4 catalysts supported on cordierite with oxide loadings ranging from 10 to 100 wt

The main goal of this study is an application of the R-functions theory to investigate the free linear and geometrically nonlinear vibrations of the sandwich auxetic composite plates. The sandwich plate consists of three layers. The central layer is auxetic honeycomb structure with negative Poisson’s ratio. The face sheets are made of functionally graded materials (FGM). Mathematical statement of the problem is fulfilled by the first-order shear deformation theory (FSDT) with the geometrical nonlinear in von Karman. Nonlinear vibrations are studied using the Ritz method, Galerkin’s procedure and Runge–Kutta method based on the original approach proposed. Rectangular plates with special type of the boundary conditions (partially clamped and partially simply supported along each side) are studied. The corresponding system of the admissible functions is constructed by the R-functions theory. The influence of the geometrical parameters of the cell, types of FGM, thickness of the core on the natural frequencies and nonlinear behavior of sandwich auxetic honeycomb plates are analyzed.

Magnetoresistance hysteresis is often used to estimate the coercive field of a magnetic material. We reanalyse our published magnetotransport and magnetometry data on compacted powders of the half-metallic ferromagnet CrO2 and show that this identification can fail in a granular conductor. The field Hp at the resistance maximum may be close to, above, or below the bulk coercive field Hc, depending on temperature and measuring current. For three samples with different particle shapes and insulating-shell thicknesses, the digitized ratio Hp/Hc follows the same qualitative sequence and suggests a common crossover near 15 K. We interpret this behaviour as a change in which interparticle junctions control the electrical response. Bulk magnetometry averages over the entire magnetic volume, whereas tunnelling resistance gives the largest weight to the small set of links that carries the current. Cohn's exact network-sensitivity theorem provides a rigorous linear-response definition of these transport weights. In simple terms, Cohn showed that the influence of a given contact on the total resistance is proportional to the square of the current flowing through that contact. Combined with known magnetic pair-correlation effects, this leads to the concept of transport-weighted coercivity. In granular sensors and spin-dependent composites, the resistance peak cannot automatically be treated as the bulk coercive field. Conversely, the difference Hp - Hc may serve as a diagnostic of current-path localization, barrier evolution, and device-to-device variability.

This work deals with the theoretical modeling of the vertical dynamics of a specialized vehicle featuring a dual suspension system. Vehicle ride quality is essential for ensuring the safety and comfort of passengers and the protection of sensitive or hazardous cargo. The study focuses on a two-axle vehicle model with a dual suspension system. The first-level comprises a traditional suspension with linear stiffness, while the second-level features nonlinear quasi-zero-stiffness (QZS) characteristics. The research employs a discrete nonlinear dynamic model that considers the vertical displacements and angular rotations of the vehicle masses. The nonlinear QZS response is modeled to optimize vibration isolation performance under varying load conditions, while damping effects are included via a Rayleigh dissipation function. The integral characteristics of the QZS element are also studied in detail using finite element (FE) computer simulations in a 3D setting. These simulations provide a comprehensive understanding of the mechanical response and stress-strain distribution within the QZS element, validating its performance under real-world conditions. The results demonstrate the influence of the nonlinear suspension characteristics on vibration isolation performance and load stability. The QZS-based suspension effectively reduces dynamic stresses, particularly under low-frequency excitations, while maintaining structural integrity and operational efficiency.

This study investigates the film cooling process on a flat plate. The task addressed relates to the identification of the most universal CFD model for different film cooling hole shapes. The task has been solved by selecting an optimal computational mesh and determining the most suitable turbulence models for predicting film cooling effectiveness over a wide range of parameters. To investigate mesh‑independence effects, four levels of polyhedral computational grids were generated. It was shown that the mesh with 5.8 million elements, selected based on the mesh‑convergence analysis, performs nearly as well as a block‑structured mesh with identical settings. A validated CFD model based on a polyhedral mesh was built. A distinctive feature of the results is that the CFD model covers 4 hole geometries spaced 5D apart and inclined at 30° to the mainstream flow (classical cylindrical, fan‑shaped, oval, and a diffused slot). The results include a comparison of seven RANS turbulence models with experimental data. It was found that for the considered flow and geometric conditions, the most robust and generally applicable model is the k‑ε Realizable turbulence model. Its advantages may be explained by its improved stability and better sensitivity to regions of complex flow kinematics, which enables more accurate prediction of expanding (fan‑shaped and diffuser‑type) holes. Additionally, the model feasibility was verified for the 7-7-7 hole configuration. For this type of hole, a preliminary analysis of the influence of thermal barrier coating configurations on film cooling effectiveness is presented. The proposed computational model could be used for optimizing hole geometry and blowing conditions in gas turbine blade cooling applications