A Finite Element Mesh Regrouping Strategy-Based Hybrid Light Transport Model for Enhancing the Efficiency and Accuracy of XLCT

X-ray luminescence computed tomography (XLCT) is an emerging hybrid imaging modality in optical molecular imaging, which has attracted more attention and has been widely studied. In XLCT, the accuracy and operational efficiency of an optical transmission model play a decisive role in the rapid and accurate reconstruction of light sources. For simulation of optical transmission characteristics in XLCT, considering the limitations of the diffusion equation (DE) and the time and memory costs of simplified spherical harmonic approximation equation (SPN), a hybrid light transport model needs to be built. DE and SPN models are first-order and higher-order approximations of RTE, respectively. Due to the discontinuity of the regions using the DE and SPN models and the inconsistencies of the system matrix dimensions constructed by the two models in the solving process, the system matrix construction of a hybrid light transmission model is a problem to be solved. We provided a new finite element mesh regrouping strategy-based hybrid light transport model for XLCT. Firstly, based on the finite element mesh regrouping strategy, two separate meshes can be obtained. Thus, for DE and SPN models, the system matrixes and source weight matrixes can be calculated separately in two respective mesh systems. Meanwhile, some parallel computation strategy can be combined with finite element mesh regrouping strategy to further save the system matrix calculation time. Then, the two system matrixes with different dimensions were coupled though repeated nodes were processed according to the hybrid boundary conditions, the two meshes were combined into a regrouping mesh, and the hybrid optical transmission model was established. In addition, the proposed method can reduce the computational memory consumption than the previously proposed hybrid light transport model achieving good balance between computational accuracy and efficiency. The forward numerical simulation results showed that the proposed method had better transmission accuracy and achieved a balance between efficiency and accuracy. The reverse simulation results showed that the proposed method had superior location accuracy, morphological recovery capability, and image contrast capability in source reconstruction. In-vivo experiments verified the practicability and effectiveness of the proposed method.

Determination of the response surface by strength and vibration parameters of the steam turbine blade

The work is devoted the definition of the function of limiting the geometric parameters of the steam turbine blade at given external loads. For this, a geometric model of a steam turbine blade was created, consisting of a blade body, a shank, and a shroud. The variable parameters were the angle of rotation of the middle section relative to the center of mass (which varied from 87 degrees to 92 degrees), as well as the length of the blade (varied from 495 mm to 525 mm). At the next stage, a finite element mesh was created. For the constructed model, an ordered finite element mesh was created in the area of the blade. Determined the stress-strain state of the blade during the operating mode. When carrying out the static analysis, an rotation velocity of 50 Hz was used as a load, and at the point of attachment of the disk in the shank, fixed displacement of all directions were used. The equivalent von Mises stresses and displacement in the structure are obtained. The zone of maximum stresses is located at the point where the blade is attached to the shank, but they do not exceed the limits. To determine the vibration characteristics of a steam turbine blade, its modal analysis was carried out taking into account the prestressed state from the action of static loads. The first six eigen modes of a steam turbine blade are obtained under the indicated initial conditions. The eigen frequency corresponding to the first form coincides with the rotational velocity (equal to 49 Hz), and the subsequent ones correspond to the multiplicities, respectively. At the next stage, a series of calculations was carried out to determine the response surface for the given parameters. The response surface for the maximum von Mises stresses and the first 4 modes of natural vibrations are determined. On the basis of the obtained results of studies of oscillations and deformed state of the blades with varying input parameters, it is possible to obtain a constraint for solving the optimization problem.

Three-Dimensional Bending Analysis of Multi-Layered Orthotropic Plates by Two-Dimensional Numerical Model

The paper presents effective numerical modelling of multi-layered plates with orthotropic properties. The method called the FEM23 is employed to construct the numerical model. The approach enables a full 3D analysis to be performed while using a 2D finite element mesh. The numerical model for a multi-layered plate is constructed by an assembling procedure, where each layer with orthotropic properties is added to the global numerical model. The paper demonstrates that the FEM23 method is very flexible in defining the multilayered plate, where the thickness of each layer as well as its mechanical orthotropic properties can be defined independently. Several examples of three-layered or nine-layered plates are analyzed in this paper. The results obtained by the FEM23 method coincide with the ones taken from the published papers or calculated with the standard 3D FEM approach. The orthotropic version of the FEM23 can be quite easily applied for other kinds of problems including thermo-mechanics, free vibrations, buckling analysis, or delamination.

Refinement of arrangement of purifying elements of integrated air treatment device for gas transmission systems and power generation based on computational fluid dynamics

Gas pumping units with gas turbine units (GTU) are widely used in gas transmission systems. In recent decades, GTUs are increasingly used in power generation at thermal power plants. The efficiency and reliability of a gas turbine plant largely depend on the quality of air preparation. Integrated air cleaning devices (KVOU) as part of the air intake duct of the GTU have stages of coarse and fine air purification and rather large dimensions. The possibility of using a battery cyclonefilter with cleaning elements, in which both stages of cleaning are combined, in the design of the KVOU is considered. Numerical studies of the movement of a two-phase flow in a multicyclone, which is a model of the first 2 rows of a serial multicyclone, have been carried out. The first two rows of the serial multicyclone TsB-16 of the Biysk boiler plant, consisting of 16 cyclone elements 245 mm in diameter with a semi-coil gas supply, were taken as the initial geometric model. The geometric model was built using the Gambit preprocessor: a two-dimensional 2D model and a finite element mesh based on square elements were built. The finite element mesh of the numerical model generated in the Gambit program was exported to the solver of the ANSYS Fluent software package. Using the methods of computational hydrodynamics, the nature of the movement of a dusty flow in a battery cyclone with a corridor arrangement of cyclone elements has been investigated, their most effective placement has been determined, which provides the maximum inertial capture of suspended particles, in accordance with which a localization scheme for semi-coil entrances to treatment elements has been determined. In numerical studies, the aerodynamic characteristics of the dispersed flow in the multicyclone body are obtained. In accordance with the results of numerical studies, the efficiency of inertial sedimentation of suspended particles from the flow in the first row of elements was 36%, in the second row — 99%.

On the issue of modeling a high-voltage insulator in the COMSOL Multiphysics 5.6 soft package

The article discusses the main aspects of modeling suspended polymer high-voltage insulation of overhead power lines (PTL) in the COMSOL Multiphysics 5.6 software package. Analytical expressions of the mathematical model of the electromagnetic field around the insulator are given, on the basis of which a numerical solution is formed within the software package that allows you to build a model of the electric field in two-dimensional and three-dimensional space. There are three main stages of working with the program interface. At the first stage, the task of the geometric dimensions of the model and the surrounding area is considered, attention is paid to the formation of the design features of polymer insulators. In the second stage, the physical properties of the structural materials of the insulator, as well as the surrounding space, are described. The third stage is reduced to the determination of boundary conditions for solving the Poisson differential equation. Recommendations for finite element mesh density are given. A gradient picture of the distribution of the electric potential near the surface of the insulator is presented. The graphs of the distribution of the normal component of the electric field strength along the surface of the insulator are also plotted. On the basis of the obtained results, the influence of external factors on the properties of the polymer insulator is studied. A possible variant of modeling influencing factors, such as pollution and moisture, by making changes in the description of the physical properties of the insulator surface, namely by including a uniform and continuous layer with a given conductivity, is described. The distribution of the normal component of the electric field strength along the surface of the insulator with contamination is obtained. The results of modeling the electric field distribution with the presence of contamination on the surface of the insulator and its absence are summarized in the table where the electric field strength is indicated depending on the distance to the traverse. Based on the analysis of the results obtained, an assumption is made about the overestimated level of the maximum electric field on the insulators recommended by the manufacturers. The convergence of the considered models with the experimental data obtained in the course of long-term observation of the dynamics of the degradation and aging processes of the surface of polymer suspended insulators of overhead transmission lines is discussed.

Transient Thermo-Mechanical Stress Analysis of Hot Surface Probe Using Sequentially Coupled CFD-FEA Approach

Energy addition using a hot surface probe is required for reliable ignition of aircraft compression ignition engines running on fuel variations and at altitude conditions. Thus, durability of the hot surface probe is crucial for application in these engines. Thermo-mechanical stress is one of the key parameters that determine durability, which requires an accurate prediction of the transient temperature field based on well-defined boundary conditions representing the dynamic and complex fluid flow inside engines. To meet this requirement, the present study focuses on transient thermo-mechanical stress analysis using a sequentially coupled CFD-FEA approach to understand transient thermo-mechanical responses of the hot surface probe. A 3D transient reacting flow simulation was conducted first using CONVERGE software, the results of which were exported to map thermal and pressure boundary conditions onto a structural finite element mesh. Transient thermo-mechanical stress analysis was performed sequentially using ABAQUS software utilizing the mapped boundary conditions. The results such as transient temperature history, resultant thermo-mechanical stress, displacement, potential failure modes, etc. were critically reviewed, which can provide helpful information for further design improvement.

An Analysis Method of Carrying Capacity Accuracy of Three-Row Roller Slewing Bearing

Three-row roller slewing bearings are the core components of large-scale rotating equipment. It has a large structural size and is subjected to heavy loads, which requires extremely high carrying capacity. The effect of finite element mesh size on the carrying capacity accuracy of three-row roller slewing bearing is investigated. A local finite element model is established to analyze the contact area between the roller and the raceway, which is compared with the Hertz contact theory to verify the reasonable mesh size of the finite element model. The local spring finite element model is established, and the effect of the mesh size on the offset and the declination of the upper and lower raceway is investigated; The overall finite element model of the slewing bearing is established to analyze the effect of the mesh size and the nonlinear spring stiffness on the carrying capacity accuracy. The whole circle deformation of the ring and the load distribution is investigated to determine the reasonable mesh size. This article provides a method and idea for the verification of the three-row roller slewing bearing finite element model, which is beneficial to improve the calculation accuracy of the bearing capacity of the three-row roller slewing bearing.