Combined Finite Element Method Research Articles

Study on Numerical Simulation of Seismic Collapse of RC Frame Structure with Infilled Wall

The infilled wall plays an important role in the formation of the survival space and life‐saving passage of the seismic collapse of reinforcement concrete (RC) frame structure. Here, with the numerical modeling method of the infilled wall, the connection between infilled wall and RC frame was primarily investigated. The combined finite element (FE) and finite‐discrete element (F‐DE) method is proposed to simulate the multispan and multistory RC frame structure with infilled wall. The reliability of the numerical simulation method was verified by the shaking table test; the evaluation criterion includes the collapse mechanism and mode. The results show that the numerical simulation is highly consistent with the shaking table test; it is easy for RC frame structure to form short columns due to the influence of the low or half‐height infilled wall, and the structural collapse is caused by the shear failure of columns; the overall structure shows pancake type of collapse; the survival space becomes smaller and smaller on the direction of structural collapse. The proposed numerical simulation method can be valuable in simulating RC frame structure with infilled wall for postearthquake rescue.

Dynamic Phasor Finite Element Modeling of Grid-Connected DFIG Considering Winding Space Harmonics

This paper presents a new technique for quantifying the winding MMF space harmonics of wind-driven Doubly-Fed Induction Generator (DFIG) for power quality assessments. Instead of following the commercial electromagnetic transient programs in modeling electric machines using lumped-parameters models, the paper uses a combined Dynamic Phase modeling and Finite Element Method (FEM) to model the generator accurately while reducing the computational burden and simulation time associated with the conventional time-stepped finite element analysis. The technique has the ability to efficiently model core nonlinearity and stator/rotor MMF space harmonics. The results of a C++ code written by the authors of the new dynamic phasors FEM technique are compared to the conventional time-stepping FEM to show the capability of the method to produce comparable results in shorter simulation time.

Individual Trabecular Bone Demonstrate a Linear Relation between Deteriorated Volume Fraction and Mechanical Properties - a Discovery Come from 3D Printing Combining Finite Element Method

Individual Trabecular Bone Demonstrate a Linear Relation between Deteriorated Volume Fraction and Mechanical Properties - a Discovery Come from 3D Printing Combining Finite Element Method

Study of the Mechanical Properties of Wood under Transverse Compression Using Monto Carlo Simulation-Based Stochastic FE Analysis

Wood is an anisotropic material, the mechanical properties of which are strongly influenced by its microstructure. In wood, grain compression strength and modulus are the weakest perpendicular to the grain compared to other grain directions. FE (finite element) models have been developed to investigate the mechanical properties of wood under transverse compression. However, almost all existing models were deterministic. Thus, the variations of geometry of the cellular structure were not considered, and the statistical characteristic of the mechanical property was not involved. This study aimed to develop an approach to investigate the compression property of wood in a statistical sense by considering the irregular geometry of wood cells. First, the mechanical properties of wood under radial perpendicular to grain compression was experimentally investigated, then the statistical characteristic of cell geometry was extracted from test data. Finally, the mechanical property of wood was investigated using the finite element method in combination with the Monte Carlo Simulation (MCS) techniques using randomly generated FE models. By parameter sensitivity analysis, it was found that the occurrence of the yield points was caused by the bending or buckling of the earlywood axial tracheid cell wall in the tangential direction. The MCS-based stochastic FE analysis was revealed as an interesting approach for assessing the micro-mechanical performance of wood and in assisting in understanding the mechanical behavior of wood based on its hierarchical structure.

Deterministic and probabilistic buckling response of fiber–metal laminate panels under uniaxial compression

PurposeThe purpose of this paper is to study the deterministic elastic buckling behavior of cylindrical fiber–metal laminate panels subjected to uniaxial compressive loading and the investigation of GLAss fiber-REinforced aluminum laminate (GLARE) panels using probabilistic finite element method (FEM) analysis.Design/methodology/approachThe FEM in combination with the eigenvalue buckling analysis is used for the construction of buckling coefficient–curvature parameter diagrams of seven fiber–metal laminate grades, three glass-fiber composites and monolithic 2024-T3 aluminum. The influences of uncertainties concerning material properties and laminate dimensions on the buckling load are studied with sensitivity analyses.FindingsIt is found that aluminum has a stronger impact on the buckling behavior of the fiber–metal laminate panels than their constituent uni-directional or woven composites. For the classical simply supported boundary conditions, it is found that there is an approximately linear relation between the buckling coefficient and the curvature parameter when the diagrams are plotted in double logarithmic scale. The probabilistic calculations demonstrate that there is a considerable probability to overestimate the buckling load of GLARE panels with deterministic calculations.Originality/valueIn this study, the deterministic and probabilistic buckling response of fiber metal laminate panels is investigated. It is shown that realistic structural uncertainties could substantially affect the buckling strength of aerospace components.

Visualization of Ion Fluxes in Nanopipettes: Detection and Analysis of Electro-osmosis of the Second Kind.

Nanopipettes are finding increasing use as nano "test tubes", with reactions triggered through application of an electrochemical potential between electrodes in the nanopipette and a bathing solution (bath). Key to this application is an understanding of how the applied potential induces mixing of the reagents from the nanopipette and the bath. Here, we demonstrate a laser scanning confocal microscope (LSCM) approach to tracking the ingress of dye into a nanopipette (20-50 nm diameter end opening). We examine the case of dianionic fluorescein under alkaline conditions (pH 11) and large applied tip potentials (±10 V), with respect to the bath, and surprisingly find that dye ingress from the bath into the nanopipette is not observed under either sign of potential. Finite element method (FEM) simulations indicate this is due to the dominance of electro-osmosis in mass transport, with electro-osmotic flow in the conventional direction at +10 V and electro-osmosis of the second kind acting in the same direction at -10 V, caused by the formation of significant space charge in the center of the orifice. The results highlight the significant deviation in mass transport behavior that emerges at the nanoscale and the utility of the combined LSCM and FEM approach in deepening understanding, which in turn should promote new applications of nanopipettes.

Dependence of thermogasodynamic parameters of operation of a helicopter gas turbine engine on its operation and dust in the atmosphere

By scanning the blades of the impeller and the guide devices of the full-scale compressor of the helicopter gas turbine engine, a solid-state design model of the compressor with a tunable geometry in the height of the blades was developed. The empirical dependencies of the values of nonlinear wear of the blade of the 1st stage of the compressor on the operating time and the concentration of dust in the air are presented. A block diagram of the procedure for calculating the characteristics and parameters of a helicopter gas turbine compressor is presented. When calculating the flow in the gas–air path of the compressor, the numerical solution of the Navier–Stokes equations averaged by Reynolds, the finite element method in combination with the establishment of patterns of erosive wear of the blades depending on the operating conditions of the engine is used. Mathematical dependencies of the thermogasodynamic parameters of the helicopter gas turbine compressor operation on its operating time and the dustiness of the atmosphere are obtained using modeling. The obtained results can be used in the development of a methodology for automated monitoring of the wear condition of the compressor blades of a helicopter gas turbine engine according to its thermogasodynamic parameters, applied to various climatic operating conditions.

Superposition‐based concurrent multiscale approaches for poromechanics

AbstractSuperposition‐based concurrent multiscale approaches for poromechanical problems aimed at resolving localized fluid flow and deformation of a solid skeleton including its possible fracture are developed. The main departure of the proposed formulation is that the primary unknowns in the coupling zone, the solid displacement u and pore pressure p, are discretized by possibly different numerical models. Two discretization schemes are studied: (i) superposition of two or more finite element (FE) discretizations of the Biot's u‐p model of a porous medium, and (ii) superposition of the peridynamics (PD) discretization of the fractured solid phase on the FE discretization of the Biot's u‐p model of a porous medium. In the latter case, the total stress of the fluid–solid mixture in the coupling domain is derived from the effective stress obtained from the combined PD and finite element method solutions while the pore pressure is obtained from the FE solution. The accuracy of the superposition‐based concurrent multiscale method is studied on several benchmark problems including the classical Terzaghi's one‐dimensional consolidation problem, the two‐dimensional strip footing problem, and the pressure‐ and fluid‐driven fracture propagation problem in saturated porous media. The main hydraulic fracture characteristics, including complex crack paths and fluid flow patterns, have been found to be reasonably well reproduced by the proposed method.

A FDEM 3D moisture migration-fracture model for simulation of soil shrinkage and desiccation cracking

This paper proposes a three-dimensional moisture migration model, which can simulate the moisture migration process in soil. A simple moisture transport example with analytic solutions is given to verify the correctness of the 3D moisture migration model. Combining the moisture migration model with the combined finite discrete element method (FDEM), a moisture migration-fracture model that simulates soil shrinkage and cracking is constructed and implemented in an in-house GPU parallel multiphysics finite element-discrete element software, namely MultiFracs. The calculation process of the three-dimensional moisture migration-fracture model is: first obtain the moisture field distribution of the solution domain through the moisture migration model; then obtain the shrinkage stress in all tetrahedral elements according to the change of the moisture field; finally, apply the shrinkage stress as a load to perform the deformation and fracture calculations of FDEM. The 3D moisture migration-fracture model is used to simulate an experiment of clayey soil shrinkage cracking. Image recognition technology is used to carry out quantitative statistics and analysis of desiccation crack patterns. The simulation results show high consistency with the laboratory experiment. Moreover, the influences of shrinkage parameter, water evaporation rate, and layer thickness on clayey soil desiccation cracking are studied comprehensively.

Numerical Analysis for Dynamic Propagation and Intersection of Hydraulic Fractures and Pre-existing Natural Fractures Involving the Sensitivity Factors: Orientation, Spacing, Length, and Persistence

Pre-existing natural fractures in a fractured reservoir will intersect with the hydraulic fractures and propagate dynamically during the hydrofracturing process, which has a significant impact on the morphology of the fracture network and subsequent gas production. If the representative properties of the natural fractures cannot be accurately extracted and appropriate numerical models are not established to describe the propagation and intersection behaviors of the fractures, it is difficult to determine the fracturing scheme for naturally fractured reservoirs and to obtain the expected fracture network and gas production. In this study, the combined finite element-discrete element method and discrete fracture network model were used to simulate the hydrofracturing process of naturally fractured reservoirs by controlling different sensitivity factors (orientation, spacing, length, and persistence) of natural fractures. To investigate the sensitivity factors, typical numerical cases were carefully designed and established, and the results of the dynamic propagation and intersection of hydraulic fractures and pre-existing natural fractures were derived. Two typical types of fracture network morphologies are detected when hydraulic fractures intersect the natural fractures: center-type (intersection of hydraulic fractures and the crossed cluster of the natural fractures) and edge-type (intersection of hydraulic fractures and the edge of the natural fractures). The quantitative results of the length and volume of the fracture networks and gas production in enhanced permeability fractured reservoirs were analyzed. The mechanisms by which the sensitivities of natural fractures affect and control the optimal fracturing behaviors are well understood; the conditions of small fracture spacing, large fracture length, or small fracture persistence of natural fractures are conducive for hydraulic fractures to intersect with the natural fractures and form a complex center-type fracture network and improve gas production.

DISTRIBUTION AND EVOLUTION OF FREE VOLUME OF ELLIPSOIDAL PARTICLE SYSTEMS DURING SHEARING

Granular material is a complex multi-body interaction system which is composed of a large number of discrete particles and their surrounding free volume. Although the correlation between free volume and the mechanical properties as well as the deformation characteristics of granular materials has been proved, the local free volume of non-spherical particles is not fully understood at present due to the difficulties in characterizing. In this paper, the combined finite and discrete element method (FDEM) is used to simulate the triaxial tests of ellipsoidal particles with different principal axis lengths, and the Set Voronoi tessellation method is applied to construct the Voronoi cells of the particles during shearing. The statistical distribution and evolution of the local free volume of the granular systems during shearing are analyzed, and the influence of particle shape on the evolution of free volume is studied. Our results show the anisotropy of Voronoi cells gradually increases during shearing, and the degree of anisotropy increase will be intensified with the increase of particle shape asphericity, which means the granular assembly with a larger asphericity will experience more intense rearrangement during shearing. The local void ratio of ellipsoidal particle systems with different asphericity statistically complies with a k-gamma distribution, which is controlled by the global void ratio of granular assembly and not affected by particle shape and shear state. The local void ratio fluctuations follow an Asymmetric Laplace Distribution (ALD), and its asymmetric parameter which has a linear relationship with the global void ratio of granular assembly describes the competition between contraction and dilatation of local free volume.

Fully plastic j-integrals for mixed mode fracture induced by inclined surface cracks in pressurized ductile pipes

Surface cracks have been recognized as major causes of their potential failures. This paper intends to determine a normalized fully plastic J-integral solution to mixed-mode fracture caused by inclined surface cracks in pressurized ductile metal pipes. A combined J-integral and finite element method is developed to evaluate the J-integral for inclined surface cracks. A set of predictive formulas for the normalized fully plastic J-integral are developed. It is found in this paper that an increase of strain hardening exponent can increase the difference of normalized fully plastic J-integrals in pipes with different wall thicknesses and the normalized fully plastic J-integral increases with the decrease of crack inclination angle and aspect ratios and the increase of strain hardening exponent. It is also found that the critical locations of crack propagation occur between the surface point and the deepest point of cracks when the inclination angle is relatively small and that the developed formulas can accurately predict the normalized fully plastic J-integrals along the front of inclined surface cracks. The results of this paper enable researchers and practitioners to predict the mixed-mode fracture failure of pressurized pipes subject to inclined surface cracks.

Time-frequency analysis of the spatial distribution for Li<sup>+</sup>concentration in the electrolyte throughout the full battery

<p indent=0mm>Advanced battery management systems can improve the safety, operation efficiency, and service life of the power Li-ion battery. Such a battery management system requires accurate information about the spatial distribution of Li⁺ concentration in the electrolyte. In general, the acquisition of the spatial distribution information of Li⁺ concentration can be described based on the Li battery physicochemical model and its corresponding solution algorithm. In this study, a pseudo-2D electrochemical model is used as the Li battery physicochemical model, which can provide complete information about the spatial distribution of Li⁺ concentration in the electrolyte throughout the full battery. Regarding the solution algorithm, which normally takes considerable time for the traditional finite difference method to discretize the diffusion partial differential equation, a new algorithm combining the finite element and <italic>θ</italic> method is proposed and a simple and efficient linear basis function is introduced into the finite element method in this study, thus aiming at a quick calculation on the spatial distribution of Li⁺ concentration in the electrolyte throughout the complete battery under different charging/discharging modes. The results of numerical calculation show: (1) in the frequency domain, the numerical solution obtained by the finite element method is highly consistent with the analytical solution obtained by the variation-of-parameters method; (2) in the time domain, the numerical solution obtained by the combination of finite element method and <italic>θ</italic> method agrees well with that obtained by the finite difference method. The algorithm proposed in this paper provides a new method for obtaining the spatial distribution of Li⁺ concentration in the electrolyte throughout the full battery with high speed and accuracy.

Design of low-frequency broadband flextensional transducers based on combined particle swarm optimization and finite element method

For designing underwater acoustic transducers, it is usually very difficult and time-consuming to determine multiple parameters simultaneously. Therefore, a novel design method that combines the particle swarm optimization (PSO) and finite element method (FEM) is proposed for low-frequency broadband flextensional transducers (FTs). This method can optimize multiple structural dimensions simultaneously and maximize the bandwidth performance of FTs efficiently. The validity of the PSO-FEM approach was verified by the optimization design and experiments of a class IV FT. Compared with previously reported design methods of FTs, this method is more efficient and avoids tedious operations. This work also provides a powerful and handy tool for the design of other underwater acoustic transducers.

Dynamic Mode Ⅱ fracture behavior of rocks under hydrostatic pressure using the short core in compression (SCC) method

The shear failure of rocks under both a static triaxial stress and a dynamic disturbance is common in deep underground engineering and it is therefore essential for the design of underground engineering to quantitively estimate the dynamic Mode Ⅱ fracture toughness KⅡC of rocks under a triaxial stress state. However, the method for determining the dynamic KⅡC of rocks under a triaxial stress has not been developed yet. With an optimal sample preparation, the short core in compression (SCC) method was designed and verified in this study to measure the dynamic KⅡC of Fangshan marble (FM) subjected to different hydrostatic pressures through a triaxial dynamic testing system. The formula for calculating the dynamic KⅡC of the rock SCC specimen under hydrostatic pressures was obtained by using the finite element method in combination with secondary cracks. The experimental results indicate that the failure mode of the rock SCC specimen under a hydrostatic pressure is the shear fracture and the KⅡC of FM increases as the loading rate. In addition, at a given loading rate the dynamic rock KⅡC is barely affected by hydrostatic pressures. Another important observation is that the dynamic fracture energy of FM enhances with loading rates and hydrostatic pressures.

A novel Z-shaped elastic flange structure for increasing the amplitude output of a piezoelectric ultrasonic transducer

A novel Z-shaped elastic flange structure is presented in this paper, which is used to mount the piezoelectric ultrasonic transducer (PUTs) together with the housing and increase amplitude output of the transducer. Generally, the mounting fixture of the transducer refers to the traditional flat-faced flange structure, which has the advantages of low processing cost and easy installation. However, considering its structural characteristics, the flange structure also exerts a negative influence on the coupling between the transducer and housing and accordingly suppresses the conversion of ultrasonic vibration energy inside the transducer. The novel Z-shaped elastic flange is combined with a traditional flat-faced flange structure and an elastic cylindrical sleeve, and the amplitude output of the transducer is increased by reducing the longitudinal and radial coupling effect between the transducer and the flange. Ultrasonic transducers with different flange structures are designed and manufactured. Through the combination of Finite Element Method and experimental analysis, the decoupling and amplitude increase ability of the novel elastic flange are investigated in detail. The results show that without changing the stiffness of the transducer, the proposed Z-shaped elastic flange structure could significantly increase the amplitude output of the transducer, regardless of whether the transducer was working in a resonance state. Hence, the newly proposed structure serves as a meaningful attempt and can be used as a universal structure for PUTs in different fields.

Numerical simulation based on a combination of finite-element method and proper orthogonal decomposition to prevent the groundwater contamination

Numerical simulation based on a combination of finite-element method and proper orthogonal decomposition to prevent the groundwater contamination

Improved optical properties of perovskite solar cells by introducing Ag nanopartices and ITO AR layers

Embedded noble metal nanostructures and surface anti-reflection (AR) layers affect the optical properties of methylammonium lead iodide (CH3NH3PbI3) perovskite solar cells significantly. Herein, by employing a combined finite element method and genetic algorithm approach, we report five different types of CH3NH3PbI3 perovskite solar cells by introducing embedded Ag nanoparticles within the CH3NH3PbI3 layer and/or top ITO cylinder grating as an AR layer. The maximum photocurrent was optimized to reach 23.56 mA/cm2, which was 1.09/1.17 times higher than Tran’s report/ flat cases. It is also comparable with values (23.6 mA/cm2) reported in the literature. The calculations of the electric field and charge carrier generation rate of the optimized solar cell further confirms this improvement than flat cases. It attributes to the synergistic effect of the embedded Ag nanoparticles and ITO AR layer. The results obtained herein hold great promise for future boosting the optical efficiency of perovskite solar cells.

Stability analysis of wooden arches with account for nonlinear creep

Introduction. The paper deals with the calculation of wooden arches taking into account the nonlinear relationship between stresses and instantaneous deformations, as well as creep and geometric nonlinearity, are considered. The analysis is based on the integral equation of the viscoelastoplastic hereditary aging model, originally proposed by A.G. Tamrazyan [1] to describe the nonlinear creep of concrete. Materials and Methods. The creep measure is taken in accordance with the work of I.E. Prokopovich and V.A. Zedgenidze [2] as a sum of exponential functions. The transition from the integral form of the creep law to the differential form is shown. The relationship between stresses and instantaneous deformations for wood under compression is determined from the Gerstner formula, and elastic work is assumed under tension. The solution is carried out using the finite element method in combination with the Newton-Raphson method and the Euler method according to the scheme that involves a stepwise increase in the load with correction of the stiffness matrix taking into account the change in the coordinates of the nodes with the sequential calculation of additional displacements of the nodes, which are due to the residual forces. The proposed approach for increasing the accuracy of determination of creep deformations at each step provides using the fourth-order Runge-Kutta method instead of the Euler method. Results. Based on the Lagrange variational principle, expressions are obtained for the stiffness matrix and the vector of additional dummy loads due to creep. The method developed by the authors is implemented in the form of a program in the MATLAB environment. Calculation examples are given for parabolic arches simply supported at the ends without an intermediate hinge and with an intermediate hinge in the middle of the span under the action of a uniformly distributed load. The results obtained are compared in the viscoelastic and viscoelastic formulation. The reliability of the results is validated through the calculation in the elastic formulation in the ANSYS software package. Discussion and Conclusions. For the arches considered, it is found that even with a load close to the instant critical, the growth of time travel is limited. Thus, the nature of their work under creep conditions differs drastically from the nature of the deformation of compressed rods.

Reduction of Residual Quenching Stresses in 2A14 Aluminum Alloy Tapered Cylinder Forgings via a Novel Cold Bulging Process

This study combined finite element method (FEM) simulations and physical experiments to develop a novel cold bulging process, with the aim of studying and mitigating the quenching residual stresses in 2A14 tapered cylinder forgings. The samples underwent cold bulging at different ratios (0–4.0%) to evaluate the residual stress reduction performance (via the hole-drilling strain-gauge method) and the improvements in their mechanical properties. The FEM simulation and experimental results revealed that our proposed cold bulging process reduced the quenching residual stresses by up to 85–87%. The density and uniformity of the precipitated phases increased along with the extent of cold bulging, as confirmed by transmission electron microscope (TEM) observations. Furthermore, compared to the unprocessed samples, the tensile and yield strengths, and elongation of the samples with 3% cold bulging were significantly enhanced (65 MPa, 55 MPa, and 1.7%, respectively).