Finite Element Method Calculations Research Articles

Challenges in the Design of a New Centrifugal Fan with Variable Impeller Geometry

Abstract This article presents a description of design work for newly created centrifugal fans. This was done based on the example of an innovative solution that uses a change in impeller geometry. In the described solution, this is achieved by shortening and lengthening the impeller blades. The development of a technical solution with such properties requires a change of approach in the design process compared with classic solutions. Therefore, the following text describes this process from the concept stage to demonstrator tests. The principle of operation of such a solution is presented and the assumptions made based on analytical calculations are also described. The text also shows a 3D model of the centrifugal fan with variable impeller geometry, made with the help of computer aided design (CAD) tools. In the further part, numerical calculations were made on its basis. The finite element method (FEM) calculation made it possible to verify the structural strength of the project and its modal properties as well as to verify flow parameters, thanks to the use of computational fluid dynamics (CFD) calculations. The next step describes the procedure for testing centrifugal fans with variable rotor geometry, which is different from that of fans without this feature. The next part presents the results of research from the tests carried out.

Constructive and technological solutions for underground space safety amidst dense historical buildings and weak foundation soils

The article considers the issues of geotechnical substantiation and application of constructive and technological measures for the construction of underground space up to 4.4 m deep in the closed courtyard of the Palace built in the 18th century in conditions of weak water-saturated soils in the historical center of St. Petersburg. The underground space of 18.4 x 29.4 m was arranged in close proximity to the enclosing structures of civil buildings built in the 18th - 19th centuries. The article presents design solutions based on the finite element calculation method for strengthening the foundations of existing buildings, enclosing the pit and the foundations of the new structures, which comprehensively ensure compliance with the required safe additional deformations of the surrounding buildings. The results of geotechnical monitoring are presented in comparison with the results of a numerical calculation of the main load-bearing structures of new and existing buildings of the surrounding development during the construction process.

Numerical and experimental study of porous NiTi anisotropy under compression

Porous NiTi samples were obtained by self-propagating high-temperature synthesis (SHS) and cut to specific dimensions by electrical discharge machining. Quasi-static compression of the porous SHS-NiTi alloy demonstrated that the deformation was elastic-plastic. Three characteristic types of fracture surfaces of bridges can be distinguished. 1) Ductile fracture of the austenite phase in the form of a cup and cone relief. 2) Brittle fracture with the formation of cleavage steps. 3) Large areas of plastic shear, where cup and cone, and cleavage facets are nucleated. An algorithm for obtaining a porous framework model suitable for finite element method calculations has been developed. The effective moduli of elasticity and shear for the porous volume of the material were determined. It is shown that the studied porous volume has orthotropic elastic properties due to the geometry of the porous framework.

ANN-Based Assessment of Soft Surface Soil Layers’ Impact on Fault Rupture Propagation and Kinematic Distress of Gas Pipelines

Large-scale lifelines in seismic-prone regions very frequently cross areas that are characterized by active tectonic faulting, as complete avoidance might be techno-economically unfeasible. The resulting Permanent Ground Displacements (PGDs) constitute a major threat to such critical infrastructure. The current study numerically investigates the crucial impact of soil deposits, which usually cover the ruptured bedrock, on the ground displacement profile and the kinematic distress of natural gas pipelines. For this purpose, a decoupled numerical methodology, based on Finite Element Method (FEM), is adopted and a detailed parametric investigation is performed for various fault and soil properties. Moreover, the advanced capabilities of Artificial Neural Networks (ANNs) are utilized, aiming to facilitate the fast and reliable assessment of soil response and pipeline strains due to seismic faulting, replacing time-consuming FEM computations. An extensive sensitivity analysis is performed to select the optimal architecture and training algorithm of the employed ANNs for both the geotechnical and structural parts of the decoupled approach, with suitable input and target values related to bedrock offset, fault and soil properties, surface PGDs, and pipeline strains. The proposed ANN-based approach can be efficiently applied by practice engineers in seismic design and route optimization of natural gas pipelines.

Processing of experimental current-voltage characteristics of single tip emitters taking into account the functional dependence of the emission area on the applied voltage

The work addresses the question of the field-dependence of the notional emission area for a field-emitter tip using computer simulation and experimental data. Based on finite-element method calculations, it was determined that for single field emitters having a given shape, there is a stable and characteristic shift of the degree of voltage in the pre-exponential voltage exponent of the field emission equation relative to the “planar” case. A power-law fit to the 3D-data was applied so as to use it in the analysis of the current-voltage data using a k-power plot (KP-plot) of semilogarithmic type. A comparison of effective emission parameters obtained from the model current-voltage characteristic with the classical Fowler–Nordheim plot, modern Murphy–Good plot, and new KP-plot is carried out. The KP-plot is subsequently used to analyze the experimental data of Tungsten emitters having a scanning emission microscope determined apex radius. The new semilogarithmic analysis reveals that the apex radius of curvature is within the observed range.

Подход к определению коэффициента теплообмена между породой и смесью флюидов при моделировании процессов неизотермической многофазной фильтрации

The paper presents an approach to calculation of the coefficient determining the rate of heat transfer between a fluid mixture in oil reservoir and a matrix-rock. This coefficient is necessary for further joint modeling of hydrodynamic and thermal processes that occur in the field reservoir during its development using, for example, thermal methods for enhanced oil recovery. To model the processes of a non-isothermal multiphase flow, an approach based on implicit pressure calculation using the finite element method and explicit calculation of phase saturations is used. The approach to determining the heat transfer coefficient is based on solving the thermal problem in an area corresponding to a channel of a porous medium and a part of the matrix-rock around it. In this case, a fluid mixture with a known temperature value, different from the initial temperature in the channel and matrix-rock, enters the channel at a given rate. A two-dimensional problem is solved in an axisymmetric formulation by the finite element method.Numerical experiments to determine the heat transfer coefficient were carried out on models for various values of the channel size, porosity, initial temperatures of the medium, temperature of the mixture entering the channel, thermal properties of the fluid mixture and rock. As a result of the study, it was found that the channel size and porosity have the most significant effect on the value of the heat transfer coefficient, since these characteristics determine the volume of the matrix-rock, which should “warm up / cool down” when the temperature of the fluid mixture in the channel changes. Also, the coefficient values obtained were quite large, since the heat exchange between the rock and the mixture in the channel occurs in minutes, which practically corresponds to instantaneous heat transfer when it comes to modeling field development processes, where time steps are days and months.

Rotation patterns of a mangle-type magnetic field source optimized via covariance matrix adaptation evolution strategy with 3D finite element method

Mangle-type magnetic field sources offer high accessibility to the interior and ease of fabrication and operation. The rotation pattern of such magnetic field sources with four magnets has been investigated using a covariance matrix adaptation evolution strategy; however, the use of 2D finite element method (FEM), which assumes an infinite magnet length, results in significant differences between the FEM calculations and experimental results. Thus, this study has adopted the 3D FEM; the optimization results were compared with those of 2D FEM. This optimization aimed to generate a homogeneous magnetic field with the required magnitude and direction. The magnet angles for the highest field were uniquely determined, which were the same as those of 2D FEM. The magnet angles for zero field were different between 2D and 3D FEMs; although infinite variation was obtained via 2D FEM, only two sets of angles were obtained via 3D FEM. The angles discovered with 3D FEM were spiral, wherein the magnetic flux from the north pole of the magnet enters the south pole of the next magnet without straying into the central region. By measuring the surface magnetic flux densities of the magnets and using them in 3D FEM calculations, the results were found to be in good agreement with those of the experiments.

Effect of electrode design and dust particle size on electrodynamics dust shield procedure

In order to reduce water consumption (especially in remote areas) for the self-cleaning dust removal systems, the efficiency of a three-phase traveling electromagnetics wave for some designed Electrodynamics Dust Shield (EDS) setups are simulated and also experimentally tested. The designed Fresnel rings electrodes EDS system showed about 25% enhancement on light collecting power and a substantial improvement on dust removal efficiency, as well. On the other hand, for the fabricated EDS systems the dust removal efficiency has been tested as a function of the dust particle size, respectively. In this study, the removal dust particles has been sampled from three different Iran's desserts with a vast size ranges, which matches with many of the remote areas in the world. It was confirmed that the sweeping frequency range from 5 to 100 Hz improved the cleaning efficiency and also the sweeping time lasting reduced about half for the zigzag electrode EDS system in comparison to a simple parallel bar one. For designing the different EDS systems, the well-known Finite Element calculation method (COMSOL Multiphysics software) has been employed, respectively.

Natural vibration of cantilever porous twisted plate with variable thickness in different directions

In this paper, the blade is assumed to be a rotating variable thickness cantilever twisted plate structure, and the natural vibrations of variable thickness cantilever twisted plate made of metal porous material are studied. It is assumed that the thickness of the plate changes along spanwise direction and chordwise direction, respectively, and it changes in both directions. The classical thin shell theory, the first and second fundamental forms of surface and von Karman geometric relationship are employed to derive the total potential energy and kinetic energy of the cantilever twisted plate, in which the centrifugal force potential due to high rotational speed is included. Then, according to the Rayleigh-Ritz procedure and applying the polynomial functions which satisfy the cantilever boundary conditions, the dynamic system expressed by equations of motion is reduced to an eigenvalue problem. By numerical simulation, the frequency curves and the mode shapes of the twisted plate can be obtained to reveal the internal connection between natural vibration and the parameters. A series of comparison studies are performed to verify the accuracy of the present formulation and calculations, in which compared data come from experimental, finite element method and theoretical calculation, respectively. The influence of pre-twist angle, three different forms of thickness taper ratio and rotational speed on natural vibration, mode exchange and frequency veering phenomenon of the system is discussed in detail. In addition, the approach proposed here can efficiently extract analytical expressions of mode functions for rotating variable thickness cantilever twisted plate structures.

Quadruple perovskite CaCu3Fe2Re2O12: A potential actuator based on a multiscale model

In this study, the magnetic structure of CaCu 3 Fe 2 Re 2 O 12 is analyzed combined on a macro to micro-scale. To combine first-principles calculations and finite element methods, the magnetic properties, Young's modulus and Poisson's ratio are used as input parameters in the finite element methods calculations. As a function of applied magnetic field and actuator structure, the energy loss and magnetostrictive coefficient of an magnetostrictive actuator are identified. When the voltage and frequency are specified, a small bar radius and narrow air gap are preferred for a high magnetostrictive coefficient. The total range of simulation parameters results in a large magnetostrictive coefficient of 2700 ppm, which is higher than the one for Tb-Dy-Fe alloys. According to our results, CaCu 3 Fe 2 Re 2 O 12 can be designed to be used as actuators by controlling the structures and applying magnetic fields.

Effect of Mg remelting and mechanical hooks of steel on the mechanical and fatigue responses of resistance element welded AZ31/DP780 joints: Experimental, FEM and thermodynamic calculation studies

This study focuses on the fatigue fracture response and microstructure behavior of a resistance element weld (REW) in assembling AZ31B magnesium alloy and dual phase (DP) 780 plates. With the increase of the welding current the prior austenite grain size (PAGS) increased, which resulted in a decrease in the fraction of an alpha prime martensite at the welding interface and had little influence on the dual phase at the welding interface. It is clear that the formation of a suitable hook accompanied by the phase transformation between S20C elements and DP780 steels at the interface can have a positive effect on the mechanical properties. However, the Mg melting and the formation of a partially melted zone (PMZ) affected the elongation decrease significantly. Furthermore, the insufficient penetrations of the welding interface, the severe melted Mg and the formation of porosities in the PMZ were fatal to the strength and fatigue performance. Morphologies and microstructure characteristics including phases of the REWed joint were quantitatively analyzed by electron back-scatter diffraction (EBSD) and thermodynamic calculation by coupling the phase diagrams (CALPHAD) method, respectively. The experiment results were incorporated into the finite element method (FEM) to numerically elucidate their effects against mechanical responses including fatigue behaviors. The results explained why the mechanical strength, fatigue endurance, and fracture modes are radically different for joint morphologies and microstructure developments.

Multiscale Optimization of 3D‐Printed Beam‐Based Lattice Structures through Elastically Tailored Unit Cells

Herein, a numerical multiscale tool is developed to design 3D periodic lattice structures. The work is motivated by the high design freedom of additive manufacturing technologies, which enable complex multiscale lattice structures to be printed. A finite‐element‐based free‐material optimization method is used to determine the ideal orthotropic material properties of a 3D macrostructure space. Subsequently, a population‐based algorithm is established to design optimized microscopic lattice unit cells with the desired structural properties. The design variables are the coordinates of lattice skeleton nodes defined within the 3D lattice unit cell space, and the connectivities between them resulting in a truss skeleton. For the calculation of the mechanical properties of the individual lattice cells, an effective Timoshenko beam‐based finite element calculation method is developed. The macroscale structure can be constructed by periodically filling the domain with the customized unit cell representing a metamaterial. The method is demonstrated by 3D beam problems with compliance constraints. These macroscopic demonstrators of the developed lattice structures were also 3D‐printed. The benefit regarding the weight‐specific structural performance is validated through benchmarking with periodic lattice design solutions using well‐known standard lattice cells.

On the pressure decline analysis for hydraulic fractures in elasto-plastic materials

In this paper the problem of a plane strain hydraulic fracture in elasto-plastic material is analyzed. The analysis is based on Finite Element Method computations of crack propagation and closure to simulate the Mini-Frac calibration test. The basic trends of fracture evolution are identified for both, the propagation and the closure stage in elasto-plastic materials and compared with the results obtained for purely elastic deformation of rock. Pressure decline analysis is conducted to identify the closure stress and leak-off coefficient. The results show that the standard techniques of pressure decline analysis can be adopted also for the case where the fractured material deforms inelastically.

Simulation of the Kinematic Condition of Radial Shear Rolling and Estimation of Its Influence on a Titanium Billet Microstructure.

The finite element method (FEM) computer simulation of the three-high radial shear rolling of Ti-6Al-4V alloy round billets was conducted using QForm software. The simulation was performed for the MISIS-100T rolling mill's three passes according to the following rolling route: 76 mm (the initial billet diameter) →65 mm→55 mm→48 mm (the final billet diameter). The change in the total velocity values for the points on the radius of the 48 mm diameter billet was estimated while passing the rolls' draft. The relative increase in the accumulated strain was estimated for the same points. Then, experimental shear rolling was performed. Grain sizes of the α- and β-phases were estimated in the cross section of the final billet at the stationary stage of rolling. The grain size distribution histograms for different phases were plotted. An area was found in the billet's cross section in which the trend of change in the total velocity of the points changed. This area represented a neutral layer between the slowing peripheral segments of the billet and the accelerating central segments of the billet. Inside this neutral layer, the limits of the cylindrical surface radius value were estimated. Experimental radial shear rolling was performed to compare the experimental rolling results (the billet microstructure investigation) with the computer simulation results. The computer simulation obtained two estimations of the radius limits: 8-16 mm (based on the analysis of the total velocity change) and 12-16 mm (based on the accumulated strain's relative increment change). The experimental rolling obtained two more estimations of the radius limits: 8.4-19.5 mm and 11.3-19.7 mm-based on the results of the microstructure investigation. It was confirmed that varying the kinematic and deformation parameters of radial shear rolling allows regulation of the thickness of the peripheral fine-grain layer and the diameter of the central coarse-grain layer of the rolled billets.

Influence of the internal solitary waves on the deep sea mining system

The South China Sea is rich in mineral resources, and the prospect of developing seabed mineral resources in the South China Sea is bright. However, the South China Sea is also famous for the active internal solitary waves, the researchers detected an internal solitary waves with an amplitude of 240 m and a peak velocity of 2.55 m/s in this area, which may severely impact the deep sea mining system. In this paper, we first simplify the vector finite element method's calculation process. Then the improved vector form intrinsic finite element method is used to simulate the installation process and normal working state of the deep sea mining systems under the action of internal solitary waves. The influence of the internal solitary waves on the deep sea mining systems in the installed state is limited, and its displacement and internal force changes are controllable. Still, the internal solitary waves may cause extensive movement or 180° bends in deep sea mining systems during installation. Necessary measures must be taken during installing deep sea mining systems to reduce the effects of internal solitary waves.

A safety assessment approach to pressure vessels based on machine learning

The safety assessment of a pressure vessel with a surface crack is an important part of the safety assessment of engineering equipment. However, the existing methods are mostly based on the assumption of plane specimens and the K criterion applicable to brittle fracture, which may lead to unacceptable errors when applied to a fracture problem in an elastoplastic pressure vessel. In this article, based on the finite element method (FEM) and artificial neural network (ANN), the elastic-plastic three-dimensional J-integral of a crack tip in a pressure vessel with an axial semi-elliptic crack on the surface under the loading of internal pressure is studied. First, the influence of the vessel geometry, the crack size, and internal pressure on the three-dimensional J-integral is analyzed. Second, the machine learning dataset is constructed based on the results of 1,200 cases of FEM calculation; then ANNs are used to discover the potential relationship between multiple parameters and the three-dimensional J-integral. The results show that the neural network constructed in this article can well predict the elastoplastic three-dimensional J-integral of a pressure vessel surface crack.

Dead Load Allocation in Triple-Cable Suspension Bridges by Adjusting the Unstrained Lengths of Hangers: A Novel Analytical Approach

Triple-cable design of suspension bridges with an ultrawide main girder can improve their mechanical properties, making it lucrative for numerous engineering scenarios. However, its realization requires assigning an appropriate share of the dead load of the main girder supported by three main cables to avoid the middle main cable overload by the main girder’s dead load since the latter would impair the mechanical behavior of the upper transverse beams in the towers and deteriorate the whole bridge’s torsional stiffness. Therefore, this study proposes an analytical approach for dead load allocation to the suspension bridge with three main cables, which adjusts the share of the main girder’s dead load supported by three main cables via changing the unstrained lengths of the hangers. The main advantage of the proposed approach is that it can consider both uniform and nonuniform allocations. The spatial model for the suspension bridge with three cable planes is first converted into a plane model. The relationship between unstrained lengths of the three hangers in the same cross section is determined via the deformation compatibility conditions and one of the following options: (1) equality of stiffness of the two side hangers in the case of a symmetrical plane model; or (2) energy conservation conditions in case of an asymmetrical one. The proposed method was applied to an example of a triple-cable suspension bridge with a main span of 2,100 m and a width of 75 m, and its analytical solutions were compared against finite-element method calculation results. An increase in the share of the main girder’s dead load supported by the two side main cables increased the torsional stiffness of the whole bridge and reduced the vertical load exerted by the middle main cable on the top transverse beam of each tower. Meanwhile, variation of the share of the main girder’s dead load supported by the side and middle main cables only slightly influenced the whole bridge’s vertical and lateral stiffness values. The aforementioned adjustment by the proposed method could be accomplished without increasing the steel consumption of the bridge cables. The results could provide references for the design, static, and dynamic response analysis of similar triple-cable ultrawide suspension bridges.

A study on ultra-thin and ultra-broadband acoustic performance of micro-perforated plate coupled with coiled-up space structure

The sound wave of low-frequency noise has strong penetration, consumes less energy in the propagation process, and is not easy to be consumed by traditional materials. In order to solve this problem, the micro-perforated plate (MPP) coupling a coiled-up space structure (MPCS) has been proposed. The MPCS is composed of an MPP and a coiled-up space structure, and its overall thickness is only 30 mm. The finite element method (FEM) and theoretical calculation were used to predict the sound absorption performance of a single MPCS. Results show that this structure is 100 % effective at absorbing sound at the resonance frequency. Moreover, the effects of the perforation ratio, aperture, and cavity length L of the MPCS have been studied in this paper. We constructed a sound-absorbing unit (MPCSs) consisting of three coiled-up space channels and six micro-perforated plates, then a broadband sound absorbing body (Bi-MPCSs) was constructed, which has two absorbing units with different parameters in parallel. Its sound absorption achievable reached more than 50 % in the range of 415 Hz–905 Hz, and the average sound absorption was more than 75.6 %. Next, the theoretical calculation results verify the accuracy of the simulation results. To further broaden the sound absorption performance of Bi-MPCS, a low-frequency and ultra-wide frequency sound absorption body (F-MPCSs) composed of four different parameters absorbing units (MPCSs) were constructed. Interestingly, the sound absorption of the absorber achieved more than 50 % in the range of 350 Hz–1150 Hz, and an average sound absorption reached 66.7 %.

Scattering properties of protoplanetary dust analogs with microwave analogy: Aggregates of fractal dimensions from 1.5 to 2.8

Context. The growth of dust grains in protoplanetary disks is not understood in detail. Several studies have proposed the presence of aggregates and irregular grains to overcome the physical barriers in grain growth models. In order to understand the scattering properties of these aggregates, laboratory measurements of light scattering and microwave scattering have been developed over the last 50 years. Aims. We aim to measure the scattering properties of different protoplanetary analog aggregates with fractal dimensions of 1.5, 1.7, 2.0, 2.5, and 2.8. Methods. We used the microwave scattering technique (microwave analogy) for the measurements. The analog particles were virtually generated and fabricated by 3D printing with a controlled size (scaling factor), geometry, and refractive index. The seven analogs were measured at wavelengths ranging from 16.7 mm to 100 mm, leading to aggregate size parameters ranging from Xagg = 1 to Xagg = 20. The results were compared to finite element method calculations of the same analogs for cross-validation. Results. The phase function and the degree of linear polarization were deduced from the scattered field measurements of the different aggregates. These scattering properties are compared and discussed as a function of the fractal dimension. Conclusions. The scattering properties of aggregates with different fractal dimensions are different. Three different realizations of aggregates with the same fractal dimension but different monomer configurations yield the same phase functions. We verified that the maximum degree of linear polarization is higher for porous aggregates than for compact aggregates. Furthermore, the maximum polarization occurs at larger scattering angles for high fractal dimensions, while the half width at half maximum of the phase functions present larger values for small fractal dimensions.

Study on Low-Loss and High-Energy Density Coil Structure of a Wireless Power Transmission System Using High Temperature Superconducting Coils for Railway Vehicle

We have been investigating a wireless power transmission (WPT) system using a high-temperature superconducting (HTS) coil for a railway vehicle. In the previous research, we investigated the conceptual design of the WPT system using the HTS coils for the railway vehicle. However, in order to suppress the AC loss per HTS coil below the cooling power of a cryocooler, it was necessary to install multiple HTS coils in parallel on the vehicle and ground sides. Therefore, we investigated the low-loss and high-energy density coil structure in the WPT system for the railway vehicle. In this study, we analyzed the AC loss and the coupling coefficient of various HTS coil structures using the narrow REBaCuO (RE: Rare Earth elements, REBCO) wires in parallel by finite element method (FEM) calculation, and evaluated the power transmission characteristics of the WPT system using the HTS coil structures using the narrow REBCO wires in parallel for the railway vehicle. As a result, we found that the AC loss of the HTS coil structure using the narrow REBCO wires in parallel was lower than that using the wide REBCO wire. The coupling coefficient between coils using a single pancake coil structure was higher than that using a double pancake coil structure. Also, the receiving power density of the WPT system was improved by the HTS coil structures using the narrow REBCO wires. Particularly, the receiving power density of the single pancake coil using the twisted narrow wire in parallel in the coil radial direction increased to about 1.5 times that of the single pancake coil using the wide wire.