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Due to the dielectric film with charges from corona discharge of high-voltage direct current (HVDC) overhead lines, the electric field near the greenhouses covered by the dielectric film can be distorted. The electric field at some position on the ground level can be measured under the dielectric film. However, the distribution characteristics of the electric field cannot be obtained. In this article, based on the measurement results of some defined points, an algorithm to calculate the ion flow field with the presence of a dielectric film is proposed. Poisson’s equation and the current continuity equation are iteratively solved by the finite-element method (FEM) and the divergence theorem, respectively. The experiment validates the validity of the hybrid method. The research is helpful to understand the influence of charged dielectric film fully. [ABSTRACT FROM AUTHOR]

The coupling model of temperature-phase transformation-mechanics is constructed in this paper. The effect of solid state phase transformation and different hardening models on the residual stress distribution of S355J2W welded joints have been studied with finite element method (FEM) simulation. The microstructure, micro hardness and residual stress of welded joints are also studied. It has been shown that the microstructure of weld seam is composed of bainite structure with little martensite, while the base metal is ferrites and pearlites. The simulation results by FEM were in good accordance with the X-ray results. The maximum tensile residual stress is 463 MPa in the weld. The tensile residual stress was decreased with the larger distance to the weld. [ABSTRACT FROM AUTHOR]

Based on the KGD scheme, this paper investigates, with both analytical and numerical approaches, the propagation of a hydraulic fracture with a fluid lag in permeable rock. On the analytical aspect, the general form of normalized governing equations is first formulated to take into account both fluid lag and leak-off during the process of hydraulic fracturing. Then a new self-similar solution corresponding to the limiting case of zero dimensionless confining stress (T=0) and infinite dimensionless leak-off coefficient (L=∞) is obtained. A dimensionless parameter R is proposed to indicate the propagation regimes of hydraulic fracture in more general cases, where R is defined as the ratio of the two time-scales related to the dimensionless confining stress T and the dimensionless leak-off coefficient L. In addition, a robust finite element-based KGD model has been developed to simulate the transient process from L=0 to L=∞ under T=0, and the numerical solutions converge and agree well with the self-similar solution at T=0 and L=∞. More general processes from T=0 and L=0 to T=∞ and L=∞ for three different values of R are also simulated, which proves the effectiveness of the proposed dimensionless parameter R for indicating fracture regimes. [ABSTRACT FROM AUTHOR]

The stainless steel-carbon steel clad plate was investigated using the theoretical analysis of various factors influencing the high-temperature interfacial bonding during its rolling. Phenomenological prediction analysis model of interfacial bonding strength at high temperature which considers the vacuum depth, rolling temperature, and rolling reduction, was established. The specific thermal simulation experiment was designed. The bonding strengths of carbon steel and stainless steel at 1000~1200°C and compression degree of 10~30% were measured by a Gleeble 3500 thermal simulator, as a result, the interfacial bonding ratio was obtained. The results show that the bonding ratio is 0.5-0.65 at the experimental temperature and compression degree. The numerical simulation method was used to analyze the influence of the compression degree of the first pass for a 2000 × 1500 × 100 mm stainless steel clad plate under the interfacial bonding conditions. The simulation results show that the optimum compression degree of the first pass is 15-20% at the rolling temperature of 1200°C. [ABSTRACT FROM AUTHOR]

Mechanical remote centre of motion (RCM) mechanisms are often used to construct robotic minimally-invasive surgical manipulators, such that potential damage on the incision ports is eliminated. Current parallelogram-based RCM linkages (PB-linkage) typically have large footprints that compromise optimal surgical operations. A novel cable system with remote centre of motion is proposed to reduce the footprint. The RCM function of the cable system is proven mathematically. A new approach based on constraint analysis is conducted to determine the magnitudes of tension. The results are validated by finite element analysis, hence proves the use of constraint approach and the functioning of the cable system. Upon verification, the footprint of the cable linkage is compared to that of a PB-linkage in a simplified surgical scenario through three approaches. The quantitative analysis shows that the cable linkage has a smaller footprint in more than half of the design points in all approaches. A prototype is built for proofing the concept of the cable linkage. [ABSTRACT FROM AUTHOR]

This paper presents a new method suitable for modelling multiple discontinuities within a finite element. The architecture of the proposed method is similar to that of the phantom node method (which is equivalent to XFEM with Heaviside enrichment), and the solution of it is equivalent to local remeshing within the cracked element. The new method shows several advantages over the phantom node method, such as avoiding errors in the mapping of the crack geometry from the physical to the natural space and avoiding performing integrations over only part of an element. Compared to remeshing, the proposed method enables the representation of discontinuities through relatively closed FE codes (such as user-defined elements) without modifying the initial mesh and geometry, thus making it computationally more efficient. Additionally, the proposed method is particularly suited for modelling weak and cohesive discontinuities and for the representation of complex crack networks; it can model multiple plies and interfaces of a composite laminate, and both matrix crack and delamination, within a user-defined element; the information is shared between the plies and interfaces within such an element, allowing the direct implementation of interactive mechanisms. Verification examples show that the floating node method can predict stress intensity factors and crack propagation accurately. An application example shows that the proposed method can predict well the transition from matrix cracking to delamination and the subsequent saturation of matrix crack density in a cross-ply laminate. [ABSTRACT FROM AUTHOR]

This paper presents an approach for measuring weld-induced initial distortions in plated structures, allowing also for the possibility for transferring that information directly to finite element models. Photogrammetry, which employs a three-dimensional measurement technique and central projection imaging as a fundamental mathematical model, has been used to generate the displacement field from sets of digital images of box girders. Three-dimensional deformation models of box girders were obtained before and after a buckling collapse test. A comparison between the photogrammetric result and Smith's initial imperfection classifications has been performed. A new equation to predict the initial imperfections of very-thin-walled structures has been developed. It is demonstrated that the output of the photogrammetry analysis can be used as a direct input to a finite element model of the deformed structure. The procedure was validated against direct measurements of the deflections, and statistical analyses of the error between measurements and photogrammetric evaluations are presented. [ABSTRACT FROM AUTHOR]

Abstract: The stress and strain distributions in a ring strain sensor, subjected a pair of pressing loadings at its upper and lower top points, are investigated with Finite Element Method (FEM). The investigated results show that there are maximum stresses/strains and distinct stress/strain concentrations at its upper and lower top points, which are not appropriate locations for sticking strain gauges. The investigated results also show that there are second-larger stresses/strains and without stress/strain concentrations at the left and right top points of the sensor, which are the most appropriate locations for sticking strain gauges. The precision of the strain sensor with the strain gauges at its left and right top points are tested and compared with that of the sensor with the strain gauges at its upper and lower top points. The compared result shows that the test precision of the former is distinctly better than that of the latter, which verifies the validity of the results obtained with FEM. [Copyright &y& Elsevier]

This paper, a continuation of our previous work, is a presentation of the effect of the morphology and the average thickness of the deformed coating films on the slow diffusional release characteristics analyzed numerically under the constraints of the constant volume of the drug matrices and the coating films, if the films have the same average thickness. Increasing the average thickness of the coating films slows down the fractional release and the average release rate of the drug and smoothen the initial burst of the drug, as well as increase the initial lag time. The effect due to deformation of the coating films on these diffusional release characteristics are found to be less significant with the increasing average thickness of the coating films. Interestingly initial lag times are found to be the same for the coated particles having the same smallest thickness but different average thickness of coating films. The effect due to the change in the average thickness of the coating films on the characteristics of the slow controlled-release is discussed to shed light on the design of a better controlled-release device. [Copyright &y& Elsevier]

A new multiscale shape and topology optimization method is presented to design closed liquid cell materials based on the extended multiscale finite element method, which directly captures the small scale features to the large scale computation. The multiscale optimization method firstly focuses on seeking the optimum geometrical parameters and volume expansion of the fluid in the closed liquid cells in the microscale level in terms of maximizing the macroscale mechanical response of the structure. Furthermore, a new hierarchical multiscale optimization method is developed to optimize the macroscale distributions of closed liquid cells and the microscale shape of the fluid inclusion in the cells. In the macroscale level of the multiscale optimization method, the macroscale design domain is discretized by the multiscale coarse elements, while the shape of the fluid inclusions is set to be the design parameters in the microscale level. This method is firstly utilized to minimize the system compliance of the closed liquid cell structure. Moreover, due to the fact that non-uniform volume expansions of the fluid in cells can induce the elastic action, the multiscale optimization method is further extended to design biomimetic compliant actuators of the closed liquid cell materials. The multiscale optimization methods developed are implemented in the FE-package SiPESC, and the numerical examples are carried out to validate the accuracy of the methods proposed. [ABSTRACT FROM AUTHOR]

The objective of this paper is to develop a finite element model for 3D elastic-plastic frictional contact problem of Cosserat materials. Because 3D elastic-plastic frictional contact problems belong to the unspecified boundary problems with nonlinearities in both material and geometric forms, a large number of calculations are needed to obtain numerical results with high accuracy. Based on the parametric variational principle and the corresponding quadratic programming method for numerical simulation of frictional contact problems, a finite element model is developed for 3D elastic-plastic frictional contact analysis of Cosserat materials. The problems are finally reduced to linear complementarity problems (LCP). Numerical examples show the feasibility and importance of the developed model for analyzing the contact problems of structures with materials which have micro-polar characteristics. [ABSTRACT FROM AUTHOR]

Abstract: Assuming the voids in a pearlitic steel are cylindrical, a cylindrical void-cell model is presented. From the analysis of the void-cell model a void evolution equation is obtained. Defining a new intrinsic time and the softening function related to the void evolution, and introducing them into an endochronic constitutive equation, the constitutive equation involving void evolution is derived. The corresponding numerical algorithm and the finite element approach are offered, which are applied to analyse the stress and porosity distributions of the unnotched and notched cylindrical specimens of a pearlitic steel. The analytical result of the unnotched specimen shows that the porosity of the specimen increases with the increase of its plastic deformation, which is consistent with the experimental data. The analytical result of the notched specimen reveals that the stress of considering void evolution is larger than that of no considering void evolution. Both the stress and porosity reach their maximum at the notch root. The latter agrees with the experimental result. [ABSTRACT FROM AUTHOR]

Abstract: This paper proposes an artificial neural network based element extraction method for automatic finite element mesh generation. A finite element mesh is a discretized representation of a geometric domain. A domain is discretized into elements, which may be triangles, quadrilaterals, tetrahedron, or hexahedron. The element extraction method repeatedly generates element (s) within the domain using some predefined ‘if-then’ rules until the whole domain is filled with required elements. This method has an advantage of creating meshes for domains with complex boundaries. However, the ‘if-then’ rules for element extraction are usually difficult to acquire, because these rules not only generate elements but also change the problem they are designed to solve. In this paper, a Back-Propagation (BP) neural network is used to represent the ‘if-then’ element extraction rules and to train the relationship behind these rules. The input for this network includes the coordinates of some boundary points while the output defines the parameters for extracting an element. In order to generate good quality element while keeping the updated problem still solvable, the design and definition of the neural network is more complex than those in the traditional classification problems. This paper discusses issues related to the design of the neural network for element extraction. Numerical experiments on quadrilateral mesh generation have shown that this method is effective. [Copyright &y& Elsevier]

The accuracy of fatigue life assessment for the welded joint in a steel bridge is largely dependent on an appropriate S - N curve. In this paper, a master S - N curve-based fatigue life assessment approach for the welded joint with an open-rib in orthotropic steel bridge deck is proposed based on the finite element model (FEM) and field monitoring data from structural health monitoring (SHM) system. The case studies on fatigue life assessment by use of finite element analysis (FEA) for constant-amplitude cyclic loading mode and field monitoring data under variable-amplitude cyclic loading mode are addressed. In the case of FEA, the distribution of structural stress at fatigue-prone weld toe is achieved using 4-node shell element model and then transformed into equivalent structural stress by fracture mechanics theory. The fatigue life of the welded joint is estimated with a single master S - N curve in the form of equivalent structural stress range versus the cycles to failure. In the case of monitoring data-based fatigue life assessment, the daily history of structural stress at diaphragm to U-rib is derived from the raw strain data measured by the instrumented fiber Bragg grating (FBG) sensors and transformed into equivalent structural stress. The fatigue life of the investigated welded joint is calculated by cyclic counting method and Palmgren–Miner linear damage cumulative rule. The master S - N curve method provides an effective fatigue life assessment process, especially when the nominal stress is hard to be defined. A single master S - N curve will facilitate to solve the difficulty in choosing a proper S - N curve which is required in the traditional fatigue life assessment methods. [ABSTRACT FROM AUTHOR]

The numerical simulation was conducted to analyse the fatigue crack growth in gear with the finite element codes ansys (ANSYS, Inc. Canonsburg, Pennsylvania, USA.) and franc3 d (Fracture Analysis Consultants, Inc. Ithaca, New York, USA.), and the corresponding fatigue test was also carried out. During the simulation, the location of maximal stress induced by the external force was first determined by the code ansys, and then the obtained results were imported into the franc3 d to analyse the crack growth. The analysed results were input into the codes ansys and franc3 d again to compute the stress and the stress intensity factor in the following steps. After several rounds of analysis, the results of the fatigue crack propagation were obtained. The investigations show that the crack mode I is dominant during the crack growth and the stress intensity factor KI raises with increase of crack growth length and a series of quarter-elliptical cross sections of the ruptured gear tooth are obtained. The simulation results are in good accordance with experimental findings. [ABSTRACT FROM AUTHOR]

A fast scheme based on the multi-level substructure technique is proposed for the band structure and transmission characteristics calculation of phononic crystals uniformly. The main idea is that finite element models of phononic crystals are divided into several domains by a special multi-level decomposition. For the band structure calculation, the upscaling calculation is employed to condense the internal stiffness matrix of the unit cell into the Bloch boundary. Due to the internal stiffness matrix does not change along with reduced wave vectors in an iteration process, the scheme can reduce the computational scale and improve the efficiency greatly, meanwhile it does not introduce approximation into the traditional finite element model. For the transmission characteristics calculation, the unit cell of the phononic crystal is periodic which is taken as a substructure with the same coefficient matrix. Moreover, the downscaling calculation of internal displacements can be selected flexibly. Some closely watched examples of the three-dimensional locally resonant, defect state of Lamb wave and Bragg waveguide are analyzed. Numerical results indicate that the proposed scheme is efficient and accurate, which may widely be applicable and suitable for complex phononic crystal problems, and provides a reliable numerical tool to optimize and design crystal devices. [ABSTRACT FROM AUTHOR]

The band structure of a nacreous composite material is studied by two proposed models, where an ultrawide low frequency band gap is observed. The first model (tension-shear chain model) with two phases including brick and mortar is investigated to describe the wave propagation in the nacreous composite material, and the dispersion relation is calculated by transfer matrix method and Bloch theorem. The results show that the frequency ranges of the pass bands are quite narrow, because a special tension-shear chain motion in the nacreous composite material is formed by some very slow modes. Furthermore, the second model (two-dimensional finite element model) is presented to investigate its band gap by a multi-level substructure scheme. Our findings will be of great value to the design and synthesis of vibration isolation materials in a wide and low frequency range. Finally, the transmission characteristics are calculated to verify the results. [ABSTRACT FROM AUTHOR]

Extended multiscale finite element method (EMsFEM) has been proved to be an efficient method for the mechanical analysis of heterogeneous materials. The key factor for efficiency and accuracy of EMsFEM is the numerical base functions (NBFs). The paper summarizes the general method for constructing NBFs and proposes a generalized isoparametric interpolation based on the rigid displacement properties (RDPs) of NBFs. We prove that the NBFs constructed by linear, periodic and rotational angle boundary conditions satisfy the RDPs, which is independent with the shape and material properties of unit cells. The properties of NBFs for oversampling technique are also comprehensively discussed. The algorithm complexity is discussed in theoretical and numerical aspects, which concludes that the computation quantity of EMsFEM is much smaller than the direct solutions. The algorithm is validated by linear analysis of the materials with random impurities and holes and the efficiency is improved further by parallel computing. [ABSTRACT FROM AUTHOR]