Technical Physics最新文献

The need to apply nonlocal heat conduction theory in the physical sciences and engineering dates to the mid-20th century and is associated with attempts to describe experimental data based on the Biot–Fourier hypothesis. In this paper, we investigate the steady-state temperature state of a homogeneous plate, considering spatial nonlocality described by a convolution-type integral term. Analytical solutions are obtained for a one-dimensional problem by considering a simple influence function. The influence of the nonlocality coefficient on the degree of deviation of the temperature distribution across the plate thickness from the classical solution is investigated. The temperature state of the plate, obtained using a macroscale approach, is compared with the results of mathematical modeling of the temperature distribution at the nanoscale using nonequilibrium molecular dynamics.

Large-scale structures should be delivered to orbit in a transport tightly packed form, allowing their transformation from a folded state to an expanded one. The very procedure of deploying the structure occurs under the influence of force actuators. In order to avoid dynamic loads affecting the elements of the transformed system, it is necessary to use actuators that operate without impact and have a relatively small mass. It is advisable to use an actuator with an active element made of titanium nickelide material with a shape memory effect. For these active elements, the control effect is the temperature field. The phase transformations of the titanium nickelide material are highly sensitive to temperature changes, which necessitate its precise control.

During operation of the fuel element, cracking of the uranium dioxide fuel pellet is observed. This phenomenon has a significant effect on the stress-strain state of the structure. Thermomechanical loading of the fuel element area was simulated in an axisymmetric approximation, considering non-ideal thermal and mechanical contact of the pellet with the cladding. To simulate the cracking of the pellet material, a smeared crack model is used, which uses effective Young’s moduli calculated from the fracture curve of the material. A series of calculations was carried out simulating the output of the fuel element section to the mode with the nominal heat generation power. The results showed that large areas corresponding to the cracked material were formed in the pellet during calculations. Due to the selected model of smeared cracks, the maximum values of radial, axial and circumferential tensile stresses in the pellet do not exceed the selected ultimate strength of the material.

This work proposes a mathematical model for describing the nonlinear deformation of isotropic materials under non-isothermal loading. The model is formulated within a thermodynamic framework employing internal state variables, whose number, physical nature, and kinetic equations are explicitly defined. The proposed formulation yields a constitutive relation and the heat conduction equation, which together form the system of governing equations for the coupled thermoplastic boundary-value problem. As a special case, the model reduces to the constitutive framework of endochronic thermoplasticity. Analysis of the constitutive relations yields functional dependencies for the model’s material parameters. The model’s practical applicability is validated by comparing its numerical predictions with experimental data for aluminum alloy 7075-T6. The favorable agreement confirms the model’s effectiveness and its utility for analyzing the thermomechanical behavior of isotropic materials.

The paper presents a mathematical model and the results of numerical simulation of the high-pressure fast-filling process of type 3 composite pressure vessels with hydrogen. The model is based on a system of ordinary differential equations describing mass and energy balances, accounting for the real gas properties (compressibility factor), as well as the non-steady-state heat conduction equation for the multilayer vessel shell. The influence of various gas supply modes—with constant and decreasing mass flow rates – on the dynamics of pressure and temperature changes inside the vessel is investigated. A quantitative analysis was conducted for type 3 cylinders with various material combinations: a standard aluminum liner (AMg6) with reinforcing microplastic and an alternative version made of corrosion-resistant steel (12Kh18N10T) in combination with high-strength carbon fiber reinforced plastic (CFRP). It was established that the cylindrical geometry and thermophysical properties of the selected materials significantly affect the heat transfer intensity and the final thermal state of the shell. The results obtained allow for the optimization of fueling parameters to prevent hydrogen overheating above the permissible safety limit (358 K) and to reduce the filling time of cylinders under the conditions of modern hydrogen refueling stations.

This article considers the calculation of the stress-strain state of the cylindrical part of a metal-composite pressure vessel using the deformation theory of plasticity for isotropic materials. Since the stress state of the metal liner is not plane, the calculation was performed using the method of variable elastic parameters, accounting for radial stress. The algorithm was implemented in the Wolfram Mathematica computer algebra system for two liner materials. The obtained results demonstrate the influence of the radial component on the stress-strain state, which can be significant for materials with low yield and tensile strengths.

A mathematical model and a numerical method are proposed for solving Maxwell’s equations in structures with inhomogeneous waveguide ports based on a system of combined field integral equations. The model supports both perfect electric conductors and dielectric regions of arbitrary shape. In contrast to approaches requiring a special basis of the port’s eigenmodes, the proposed method allows the use of standard basis functions for currents (RWG and higher-order functions). This enables correct accounting of complex port cross-sections with various dielectrics and allows for seamless integration of such ports calculation into existing software packages for solving diffraction problems without modifying their core (including fast algorithms, e.g., MLFMM). The possibility of using second-order basis functions to achieve higher accuracy in S-parameter calculation is illustrated on model problems. Verification of the method was performed using examples of a waveguide with inhomogeneous dielectric filling and a horn antenna, showing good agreement with calculations in commercial software packages (HFSS, CST, FEKO) and with experimental data.

The use of structurally sensitive thermal protection materials with a high degree of thermal conductivity anisotropy allows for the redistribution of heat fluxes across the entire surface of the thermal protection coating. As a result, the thermal protection layers heat up significantly during descent. Often, due to mass minimization and consequently, the reduction of thermal protection thickness these layers operate at the limit of their materials' operational capabilities, both in terms of reached temperatures and the induced thermal stresses. At such temperature levels at the internal layer interfaces, besides conduction, radiative heat transfer begins to play a substantial role if any of the layers are semi-transparent. Neglecting the radiative heat flux can lead to significant inaccuracies and erroneous conclusions regarding the suitability of the thermal protection shield.

This paper presents the application of vortex particle methods for simulating external flows around engineering structures using the VM2D code, which has been enhanced with a hybrid fast algorithm that combines the Barnes–Hut method and the Fast Multipole Method. This approach reduces computational costs preserving physical accuracy, thereby enabling long-duration simulations of problems that were previously prohibitive with direct algorithm. The capability of the fast algorithm is demonstrated through three test cases, confirming its suitability for practical engineering applications.

Solvers of systems of linear algebraic equations based on domain decomposition and multigrid methods demonstrate high efficiency in solving two-dimensional problems using cell-centered methods with a 5-point discretization stencil. In the 3D case, such methods utilize a 7-point stencil, requiring modification of the solvers. The aim of this work is to develop similar solvers for systems arising from the solution of three-dimensional problems using cell-centered methods with a 7-point discretization stencil. Formulas for computing the elements of the system matrices in three-dimensional subdomains and on interface planes, considering the 7-point stencil, are derived. It is shown that the structure of the interface system matrix coincides with the two-dimensional case. Therefore, the same direct solver used for 2D can be applied. Solving systems within subdomains is performed using the FGMRES method with preconditioning. When using the multigrid method as a preconditioner, certain parts of the algorithm require modifications for the transition from 2D to 3D. An algorithm for 3D ADLJ-smoother is presented. Since the considered system is derived from cell-centered grid methods where unknowns are located at cell centers rather than grid nodes, non-standard projection and prolongation operators are required for transferring between grid levels. The general principle for their constructing is demonstrated for 1D. Based on these formulas, three-dimensional operators are constructed for all possible cases. The developed solvers were verified on systems formed when solving three-dimensional hydrodynamics problems using the LS-STAG-3D immersed boundary cell-centered method with a 7-point stencil. For comparison, similar solvers for the two-dimensional case were also considered, applied to systems of the same dimension but formed from solving two-dimensional hydrodynamics problems using the LS-STAG method. Computational experiments show that the required accuracy is achieved in a comparable number of iterations for 2D and 3D problems of the same system dimension.