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.

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%.

Influence of finite element mesh size on the carrying capacity analysis of single-row ball slewing bearing

Slewing bearings are widely used in industry to provide rotary support and carry heavy load. The load-carrying capacity is one of the most important features of a slewing bearing, and needs to be calculated cautiously. This paper investigates the effect of mesh size on the finite element (FE) analysis of the carrying capacity of slewing bearings. A local finite element contact model of the slewing bearing is firstly established, and verified using Hertz contact theory. The optimal mesh size of finite element model under specified loads is determined by analyzing the maximum contact stress and the contact area. The overall FE model of the slewing bearing is established and strain tests were performed to verify the FE results. The effect of mesh size on the carrying capacity of the slewing bearing is investigated by analyzing the maximum contact load, deformation, and load distribution. This study of finite element mesh size verification provides an important guidance for the accuracy and efficiency of carrying capacity of slewing bearings.

Creating the finite element mesh of non-periodic masonry from the measurement of its geometrical characteristics: a novel automated procedure

This paper presents an automated procedure that enables the creation of a finite element mesh directly from the image file representing the rasterized sketch of a generic masonry element. This procedure goes under the name “pixel strategy” if a 2D finite element mesh is needed, where the elements are planar and rectangular; conversely, its extension in the 3D case is named “voxel strategy”, and there the resulting finite elements are solid bricks. The finite element meshes so obtained are then used for extracting homogenized in-plane failure surfaces for historical masonry cells, which display a non-periodic arrangement of units. These surfaces are consistent with the expected results, and their shapes suggest that the behavior of such type of masonry may range between orthotropic (if bed mortar joints are clearly noticeable) and quasi-isotropic (if some units spread over two or more masonry layers).