This article reports our explorations for solving interface problems of the Helmholtz equation by immersed finite elements (IFE) on interface independent meshes. Two IFE methods are investigated: the partially penaliz...This article reports our explorations for solving interface problems of the Helmholtz equation by immersed finite elements (IFE) on interface independent meshes. Two IFE methods are investigated: the partially penalized IFE (PPIFE) and discontinuous Galerkin IFE (DGIFE) methods. Optimal convergence rates are observed for these IFE methods once the mesh size is smaller than the optimal mesh size which is mainly dictated by the wave number. Numerical experiments also suggest that higher degree IFE methods are advantageous because of their larger optimal mesh size and higher convergence rates.展开更多
The smoothed finite element method (S-FEM) was originated by G R Liu by combining some meshfree techniques with the well-established standard finite element method (FEM). It has a family of models carefully designed w...The smoothed finite element method (S-FEM) was originated by G R Liu by combining some meshfree techniques with the well-established standard finite element method (FEM). It has a family of models carefully designed with innovative types of smoothing domains. These models are found having a number of important and theoretically profound properties. This article first provides a concise and easy-to-follow presentation of key formulations used in the S-FEM. A number of important properties and unique features of S-FEM models are discussed in detail, including 1) theoretically proven softening effects;2) upper-bound solutions;3) accurate solutions and higher convergence rates;4) insensitivity to mesh distortion;5) Jacobian?free;6) volumetric-locking-free;and most importantly 7) working well with triangular and tetrahedral meshes that can be automatically generated. The S-FEM is thus ideal for automation in computations and adaptive analyses, and hence has profound impact on Al-assisted modeling and simulation. Most importantly, one can now purposely design an S-FEM model to obtain solutions with special properties as wish, meaning that S-FEM offers a framework for design numerical models with desired properties. This novel concept of numerical model demand may drastically change the landscape of modeling and simulation. Future directions of research are also provided.展开更多
Abstract Recently, pH-sensitive hydrogels have been utilized in the diverse applications including sensors, switches, and actuators. In order to have continuous stress and defor- mation fields, a new semi-analytical a...Abstract Recently, pH-sensitive hydrogels have been utilized in the diverse applications including sensors, switches, and actuators. In order to have continuous stress and defor- mation fields, a new semi-analytical approach is developed to predict the swelling induced finite bending for a functionally graded (FG) layer composed of a pH-sensitive hydrogel, in which the cross-link density is continuously distributed along the thickness direction under the plane strain condition. Without considering the intermediary virtual reference, the initial state is mapped into the deformed configuration in a circular shape by utilizing a total deformation gradient tensor stemming from the inhomogeneous swelling of an FG layer in response to the variation of the pH value of the solvent. To enlighten the capabil- ity of the presented analytical method, the finite element method (FEM) is used to verify the accuracy of the analytical results in some case studies. The perfect agreement con- firms the accuracy of the presented method. Due to the applicability of FG pH-sensitive hydrogels, some design factors such as the semi-angle, the bending curvature, the aspect ratio, and the distributions of deformation and stress fields are studied. Furthermore, the tangential free-stress axes are illustrated in deformed configuration.展开更多
Hot air producing is one of the most important engineering applications in recent years.It is a technique used in various thermodynamic systems,such as home heating systems,food dryers.One of the main problems impedin...Hot air producing is one of the most important engineering applications in recent years.It is a technique used in various thermodynamic systems,such as home heating systems,food dryers.One of the main problems impeding the spread of hot air producing technology is the lack of homogeneity of the heat flow coming from hot air generators as well as an inadequate flow rate.The most of the existing hot air generators require to be supported by systems that can increase the low volumetric flow and the air temperature of these generators,through increasing the speed of the flow of air emitted or lifting the drawer Heat,which contributes to raising the overall cost.However,to improve the thermal and dynamic quality of the hot air flow produced by the generator,a numerical investigation of the free convection flow inside two different configurations is presented in this thesis.The primary objective of this work is to predict the behavior of the flow inside tow configurations,the first one consists of a vertical cylinder with heated walls,and the second configuration is an open-ended vertical cylinder with a hot disc placed at the entrance(configuration A,configuration B).This work characterizes through the examination of this flow,the variables that control an air emission with high flow rate and a high and homogeneous temperature to represent the appropriate criteria that should be respected to obtain a hot air generator overcoming the previously mentioned constraints.Furthermore;the results of this work show the influence the boundary conditions and Rayleigh number on the resulting flow.展开更多
Elastic critical buckling load of a column depends on various parameters,such as boundary conditions,material,and crosssection geometry.The main purpose of this work is to present a new method for investigating the bu...Elastic critical buckling load of a column depends on various parameters,such as boundary conditions,material,and crosssection geometry.The main purpose of this work is to present a new method for investigating the buckling load of tapered columns subjected to axial force.The proposed method is based on modified buckling mode shape of tapered structure and perturbation theory.The mode shape of the damaged structure can be expressed as a linear combination of mode shapes of the intact structure.Variations in length in piecewise form can be positive or negative.The method can be used for single-span and continuous columns.Comparison of results with those of finite element and Timoshenko methods shows the high accuracy and efficiency of the proposed method for detecting buckling load.展开更多
The first objective of this paper is to study the influence of the orthotic device on the maximum values of stresses in knee cartilages by using Ansys Workbench 14.5 software and applying the Finite Element Analysis (...The first objective of this paper is to study the influence of the orthotic device on the maximum values of stresses in knee cartilages by using Ansys Workbench 14.5 software and applying the Finite Element Analysis (FEA) on a virtual assembly composed by an orthotic device and osteoarthritic knee (OAK). The second objective consists into quantifying and investigating the nonlinear motion of the human knee joint for OAK patients, with and without the orthotic device mounted on OAK, using tools of dynamics stability analysis. The short Lyapunov Exponents (LEs) are calculated, as measures of human knee and ankle joints stability, based on the experimental time series collected by using the biometrics acquisition system during walking on horizontal and inclined treadmills from a sample of healthy subjects and a sample of patients suffering by OAK disease. The values of LEs obtained for OAK patients are larger on the inclined treadmill than on horizontal treadmill and are larger than those obtained for healthy knees, being associated with more divergence and less stability. The results confirm that the influence of an orthotic device mounted on OAK on its stability is significant, the values obtained for LEs being smaller than those calculated for OAK, and closer to the values of normal knees of patients and of healthy subjects.展开更多
Objective To establish finite element models of skull, fronto-orbital advancement and fronto-orbital distraction osteogenesis of craniosynostosis, to analyze the mechanical characteristics of skull base and fronto-orb...Objective To establish finite element models of skull, fronto-orbital advancement and fronto-orbital distraction osteogenesis of craniosynostosis, to analyze the mechanical characteristics of skull base and fronto-orbital operation area, so as to guide the later app lication of distractors. Methods One 6-year-old male patient with unilateral coronal synostosis was enrolled in October 2015. Three-dimensional (3D) computed tomography (CT) scan of skull was performed. DICOM data was imported into Mimics 17.0 for contour extraction and cranial 3D reconstruction. The skull model was processed by Mimics, Geomagic Studio 12.0, Hypermesh 12.0 and other software to establish a three-dimensional finite element model. The unilateral and bilateral fronto-orbital anterior osteotomy models were simulated respectively. The mechanical analysis was performed at point A in forehead area and point B in temporal area. Three different groups of traction forces were loaded:(1) 50 Newton for point A, 50 Newton for point B;(2) 80 Newton for point A and 50 Newton for point B;(3) 100 Newton for point A and 50 Newton for point B, to obtain the optimized traction force.. Results Stress analysis was performed on established cranial finite element model, as well as unilateral and bilateral fronto-orbital advancement procedures. The stress distribution of the anterior and middle cranial fossae was found to be concentrated. After unilateral fronto-orbital advancement, the stress of anterior cranial fossa, especially the affected side, was decreased. The stress on both side in anterior cranial fossa was decreased after bilateral fronto-orbital advancement. After force was applied to point A and point B, the optimum deviation result at supraorbital notch point, midpoint of supraorbital margin, frontal temporal point and frontal zygomatic suture point in 3D (Deviation result of X value:-29.4%,-20.5%,-8.6%,-9.3%, Deviation result of Y value: 20.9%, 31.5%, 73.0%, 539.4%;Deviation result of Z value: 4.4%, 1.9%, 0.1%, 11.8) demonstrated the applicatio展开更多
In this paper, we present an optimal 3-point finite difference scheme for solving the 1D Helmholtz equation. We provide a convergence analysis to show that the scheme is sixth-order in accuracy. Based on minimizing th...In this paper, we present an optimal 3-point finite difference scheme for solving the 1D Helmholtz equation. We provide a convergence analysis to show that the scheme is sixth-order in accuracy. Based on minimizing the numerical dispersion, we propose a refined optimization rule for choosing the scheme’s weight parameters. Numerical results are presented to demonstrate the efficiency and accuracy of the optimal finite difference scheme.展开更多
A method for dynamic alignment calculation of a large turbogenerator shafting is proposed. The method can analyze bearing load and bearing load sensitivity. Shafting alignment is made up of two parts:static alignment ...A method for dynamic alignment calculation of a large turbogenerator shafting is proposed. The method can analyze bearing load and bearing load sensitivity. Shafting alignment is made up of two parts:static alignment and dynamic alignment. Static alignment forms the basis of dynamic alignment, its mathematical model is deduced by transfer matrix method, the shafting static characteristic parameters under specific alignment installation requirements were obtained afterwards. Based on superposition method, bearing sensitivity analysis is performed to find the impact of slight bearing elevation change of the static alignment result. Above static alignment, dynamic shafting alignment considers the internal geometry of bearing under rotating state, static Reynolds equation is solved by the finite difference method and the relative position relationship of the center of journal and bearing are obtained. For static characteristic parameters calculated by static alignment and bearing sensitivity analysis, the calculation accuracy is verified by finite element software. The alignment model and codes in this paper can be a tool for the installation and safety analysis of large-scale shafting with three-point or four-point supports.展开更多
In this study,numerical optimisation and experimental validation of a divided rail freight brake disc crown made of grey cast iron EN-GJL-250 is presented.The analysed brake disc is used in rail freight wagons and pos...In this study,numerical optimisation and experimental validation of a divided rail freight brake disc crown made of grey cast iron EN-GJL-250 is presented.The analysed brake disc is used in rail freight wagons and possesses a load capacity of 22.5 tons per axle.Two of the divided rail freight brake discs are mounted on each axle.With the aid of numerical analysis,the thermal dissipation properties of the brake disc were optimised and ventilation losses were reduced,and the numerical results were compared with experimental results.A one-way fluid–structure interaction analysis was performed.A computational fluid dynamic model of a divided rail freight brake disc,used to predict air flow properties and heat convection,was incorporated into a finite element model of the disc and used to evaluate the temperature of the disc.A numerical parametrical optimisation of cooling ribs of the brake disc was also performed,and novel optimised cooling ribs were developed.A transient thermal numerical analysis of the brake disc was validated using temperature measurements obtained during a braking test on a test bench.The ventilation losses of the brake disc were measured on a test bench specifically designed for the task,and the losses were compared to the simulation results.The experimentally obtained ventilation losses and temperature measurements compared favourably with the simulation results,confirming that this type of simulation process may be confidently applied in the future.Through systematic optimisation of the divided rail freight brake disc,ventilation losses were reduced by 37% and the mass was reduced by 21%,resulting in better thermal performance that will bring with it substantial energy savings.展开更多
Let G be a finite group of Lie type E6 over Fq (adjoint or simply connected) and W be the Weyl group of G. We describe maximal tori T such that T has a complement in its algebraic normalizer N(G, T). It is well known ...Let G be a finite group of Lie type E6 over Fq (adjoint or simply connected) and W be the Weyl group of G. We describe maximal tori T such that T has a complement in its algebraic normalizer N(G, T). It is well known that for each maximal torus T of G there exists an element w ∈ W such that N(G, T )/T ■ CW(w). When T does not have a complement isomorphic to CW(w), we show that w has a lift in N(G, T) of the same order.展开更多
1 Introduction and main contributions Finite automata are dynamical systems with discrete inputs and outputs, which belong to the domain of logical systems and have a wide range of applications. In engineering, due to...1 Introduction and main contributions Finite automata are dynamical systems with discrete inputs and outputs, which belong to the domain of logical systems and have a wide range of applications. In engineering, due to the excellent hardware qualities of simple structure, low power consumption and low electromagnetic noise, etc., finite automata are used in avionics and nuclear engineering, where the environment is bad and require strict safety. In science, finite automata serve as one of the main molding tools for discrete event dynamic systems (DEDS)(others are Petri nets, Markov chains and queuing networks, etc.). Studying DEDS is one of the major ways to study the cyber physical systems (CPS) which is the core content of Industry 4.0.展开更多
Solving the advection-diffusion equation in irregular geometries is of great importance for realistic simulations. To this end, we adopt multi-patch parameterizations to describe irregular geometries. Different from t...Solving the advection-diffusion equation in irregular geometries is of great importance for realistic simulations. To this end, we adopt multi-patch parameterizations to describe irregular geometries. Different from the classical multi-patch parameterization method, C 1- continuity is introduced in order to avoid designing interface conditions between adjacent patches. However, singularities of parameterizations can’t always be avoided. Thus, in this paper, a finite volume method is proposed based on smooth multi-patch singular parameterizations. It is called a singular parameterized finite volume method. Firstly, we present a numerical scheme for pure advection equation and pure diffusion equation respectively. Secondly, numerical stability results in L2 norm show that the numerical method is not suffered from the singularities. Thirdly, the numerical method has second order accurate in L2 norm. Finally, three numerical tests in different irregular geometries are presented to show efficiency of this numerical method.展开更多
The correlation between crystal rotation and redundant shear strain in rolled single crystals was investigated by using the crystal plasticity finite element(CPFE) model in this paper. The deformation in aluminium sin...The correlation between crystal rotation and redundant shear strain in rolled single crystals was investigated by using the crystal plasticity finite element(CPFE) model in this paper. The deformation in aluminium single crystals of four representative orientations(rotated-Cube, Goss, Copper, and Brass) after rolling and plain strain compression was simulated, and the predictions have been validated by the experimental observations. In the rotated-Cube and Goss, the redundant shear strain and crystal rotation were in the same pattern, alternating along the thickness, while the relation between them was not obvious for the Copper and Brass due to their asymmetrical distributions of activated slip systems. The relations between slip system activation, crystal rotation, and shear strain were investigated based on the CPFE model, and the correlation between shear strain and crystal rotation has been built.展开更多
A mixed finite element method combining an iso-parametric Q 2-P 1 element and an isoparametric P^-Pi element is developed for the computation of multiple cavities in incompressible nonlinear elasticity. The method is ...A mixed finite element method combining an iso-parametric Q 2-P 1 element and an isoparametric P^-Pi element is developed for the computation of multiple cavities in incompressible nonlinear elasticity. The method is analytically proved to be locking-free and convergent, and it is also shown to be numerically accurate and efficient by numerical experiments. Furthermore, the newly developed accurate method enables us to find an interesting new bifurcation phenomenon in multi-cavity growth.展开更多
Compression tests on twenty unidirectional(UD) carbon fibre reinforced plastic(CFRP) specimens are conducted, the statistics on the measured compressive strength is calculated, and the fracture surface is characterize...Compression tests on twenty unidirectional(UD) carbon fibre reinforced plastic(CFRP) specimens are conducted, the statistics on the measured compressive strength is calculated, and the fracture surface is characterized. Two types of different fracture surface are experimentally observed, and they are corresponding to very different values on the compressive strength. A finite element(FE) analysis is conducted to investigate the influence of random fibre packing on the compressive strength. And a riks method(provided in ABAQUS software) is applied in FE model to analyze fibre buckling behaviour in the vicinity of compressive failure. The FE analysis agrees well with the experimental observation on the two types of buckling modes and also the partition of compressive strength. It is clearly shown that the random fibre packing lays a significant influence on the random variability of compressive strength of CFRP.展开更多
The human tricuspid valve, one of the key cardiac structures, plays an important role in the circulatory system. However, there are few mathematical models to accurately simulate it.In this paper, firstly, we consider...The human tricuspid valve, one of the key cardiac structures, plays an important role in the circulatory system. However, there are few mathematical models to accurately simulate it.In this paper, firstly, we consider the tricuspid valve as an elastic shell with a specific shape and establish its novel geometric model. Concretely, the anterior, the posterior and the septal leaflets of the valve are supposed to be portions of the union of two interfacing semi-elliptic cylindrical shells when they are fully open.Next, we use Koiter’s linear shell model to describe the tricuspid valve leaflets in the static case, and provide a numerical scheme for this elastostatics model. Specifically, we discretize the space variable, i.e., the two tangent components of the displacement are discretized by using conforming finite elements(linear triangles) and the normal component of the displacement is discretized by using conforming Hsieh-Clough-Tocher triangles(HCT triangles).Finally, we make numerical experiments for the tricuspid valve and analyze the outcome. The numerical results show that the proposed mathematical model describes well the human tricuspid valve subjected to applied forces.展开更多
This paper focuses on performance of several efficient and accurate numerical methods for the long-wave short-wave interaction equations in the semiclassical limit regime. The key features of the proposed methods are ...This paper focuses on performance of several efficient and accurate numerical methods for the long-wave short-wave interaction equations in the semiclassical limit regime. The key features of the proposed methods are based on:(i) the utilization of the first-order or second-order time-splitting method to the nonlinear wave interaction equations;(ii) the ap-plication of Fourier pseudo-spectral method or compact finite difference approximation to the linear subproblem and the spatial derivatives;(iii) the adoption of the exact integration of the nonlinear subproblems and the ordinary differential equations in the phase space. The numerical methods under study are efficient, unconditionally stable and higher-order accurate, they are proved to preserve two invariants including the position density in L^1. Numerical results are reported for case studies with different types of initial data, these results verify the conservation laws in the discrete sense, show the dependence of the numerical solution on the time-step, mesh-size and dispersion parameter ε, and demonstrate the behavior of nonlinear dispersive waves in the semi-classical limit regime.展开更多
Let σ={σi | i ∈ I} be some partition of the set of all primes P. A set H of subgroups of G is said to be a complete Hall σ-set of G if every member ≠ 1 of H is a Hall σi-subgroup of G, for some i ∈ I, and H con...Let σ={σi | i ∈ I} be some partition of the set of all primes P. A set H of subgroups of G is said to be a complete Hall σ-set of G if every member ≠ 1 of H is a Hall σi-subgroup of G, for some i ∈ I, and H contains exactly one Hall σi-subgroup of G for every σi ∈σ(G). A subgroup H of G is said to be:σ-permutable or σ-quasinormal in G if G possesses a complete Hall σ-set H such that HAx= AxH for all A ∈ H and x ∈ G:σ-subnormal in G if there is a subgroup chain A = A0≤A1≤···≤ At = G such that either Ai-1■Ai or Ai/(Ai-1)Ai is a finite σi-group for some σi ∈σ for all i = 1,..., t.If Mn < Mn-1 <···< M1 < M0 = G, where Mi is a maximal subgroup of Mi-1, i = 1, 2,..., n, then Mn is said to be an n-maximal subgroup of G. If each n-maximal subgroup of G is σ-subnormal(σ-quasinormal,respectively) in G but, in the case n > 1, some(n-1)-maximal subgroup is not σ-subnormal(not σ-quasinormal,respectively) in G, we write mσ(G)= n(mσq(G)= n, respectively).In this paper, we show that the parameters mσ(G) and mσq(G) make possible to bound the σ-nilpotent length lσ(G)(see below the definitions of the terms employed), the rank r(G) and the number |π(G)| of all distinct primes dividing the order |G| of a finite soluble group G. We also give the conditions under which a finite group is σ-soluble or σ-nilpotent, and describe the structure of a finite soluble group G in the case when mσ(G)=|π(G)|. Some known results are generalized.展开更多
The crystallization characteristics of a ubiquitous T-shaped phase change memory (PCM) cell, under SET current pulse and very small disturb current pulse, have been investigated by finite element modelling. As analyze...The crystallization characteristics of a ubiquitous T-shaped phase change memory (PCM) cell, under SET current pulse and very small disturb current pulse, have been investigated by finite element modelling. As analyzed in this paper, the crystallization region under SET current pulse presents first on the corner of the bottom electron contact (BEC) and then promptly forms a filament shunting down the amorphous phase to achieve the low-resistance state, whereas the tiny disturb current pulse accelerates crystallization at the axis of symmetry in the phase change material. According to the different crystallization paths, a new structure of phase change material layer is proposed to improve the data retention for PCM without impeding SET operation. This structure only requires one or two additional process steps to dope nitrogen element in the center region of phase change material layer to increase the crystallization temperature in this confined region. The electrical-thermal characteristics of PCM cells with incremental doped radius have been analyzed and the best performance is presented when the doped radius is equal to the radius of the BEC.展开更多
文摘This article reports our explorations for solving interface problems of the Helmholtz equation by immersed finite elements (IFE) on interface independent meshes. Two IFE methods are investigated: the partially penalized IFE (PPIFE) and discontinuous Galerkin IFE (DGIFE) methods. Optimal convergence rates are observed for these IFE methods once the mesh size is smaller than the optimal mesh size which is mainly dictated by the wave number. Numerical experiments also suggest that higher degree IFE methods are advantageous because of their larger optimal mesh size and higher convergence rates.
文摘The smoothed finite element method (S-FEM) was originated by G R Liu by combining some meshfree techniques with the well-established standard finite element method (FEM). It has a family of models carefully designed with innovative types of smoothing domains. These models are found having a number of important and theoretically profound properties. This article first provides a concise and easy-to-follow presentation of key formulations used in the S-FEM. A number of important properties and unique features of S-FEM models are discussed in detail, including 1) theoretically proven softening effects;2) upper-bound solutions;3) accurate solutions and higher convergence rates;4) insensitivity to mesh distortion;5) Jacobian?free;6) volumetric-locking-free;and most importantly 7) working well with triangular and tetrahedral meshes that can be automatically generated. The S-FEM is thus ideal for automation in computations and adaptive analyses, and hence has profound impact on Al-assisted modeling and simulation. Most importantly, one can now purposely design an S-FEM model to obtain solutions with special properties as wish, meaning that S-FEM offers a framework for design numerical models with desired properties. This novel concept of numerical model demand may drastically change the landscape of modeling and simulation. Future directions of research are also provided.
文摘Abstract Recently, pH-sensitive hydrogels have been utilized in the diverse applications including sensors, switches, and actuators. In order to have continuous stress and defor- mation fields, a new semi-analytical approach is developed to predict the swelling induced finite bending for a functionally graded (FG) layer composed of a pH-sensitive hydrogel, in which the cross-link density is continuously distributed along the thickness direction under the plane strain condition. Without considering the intermediary virtual reference, the initial state is mapped into the deformed configuration in a circular shape by utilizing a total deformation gradient tensor stemming from the inhomogeneous swelling of an FG layer in response to the variation of the pH value of the solvent. To enlighten the capabil- ity of the presented analytical method, the finite element method (FEM) is used to verify the accuracy of the analytical results in some case studies. The perfect agreement con- firms the accuracy of the presented method. Due to the applicability of FG pH-sensitive hydrogels, some design factors such as the semi-angle, the bending curvature, the aspect ratio, and the distributions of deformation and stress fields are studied. Furthermore, the tangential free-stress axes are illustrated in deformed configuration.
文摘Hot air producing is one of the most important engineering applications in recent years.It is a technique used in various thermodynamic systems,such as home heating systems,food dryers.One of the main problems impeding the spread of hot air producing technology is the lack of homogeneity of the heat flow coming from hot air generators as well as an inadequate flow rate.The most of the existing hot air generators require to be supported by systems that can increase the low volumetric flow and the air temperature of these generators,through increasing the speed of the flow of air emitted or lifting the drawer Heat,which contributes to raising the overall cost.However,to improve the thermal and dynamic quality of the hot air flow produced by the generator,a numerical investigation of the free convection flow inside two different configurations is presented in this thesis.The primary objective of this work is to predict the behavior of the flow inside tow configurations,the first one consists of a vertical cylinder with heated walls,and the second configuration is an open-ended vertical cylinder with a hot disc placed at the entrance(configuration A,configuration B).This work characterizes through the examination of this flow,the variables that control an air emission with high flow rate and a high and homogeneous temperature to represent the appropriate criteria that should be respected to obtain a hot air generator overcoming the previously mentioned constraints.Furthermore;the results of this work show the influence the boundary conditions and Rayleigh number on the resulting flow.
文摘Elastic critical buckling load of a column depends on various parameters,such as boundary conditions,material,and crosssection geometry.The main purpose of this work is to present a new method for investigating the buckling load of tapered columns subjected to axial force.The proposed method is based on modified buckling mode shape of tapered structure and perturbation theory.The mode shape of the damaged structure can be expressed as a linear combination of mode shapes of the intact structure.Variations in length in piecewise form can be positive or negative.The method can be used for single-span and continuous columns.Comparison of results with those of finite element and Timoshenko methods shows the high accuracy and efficiency of the proposed method for detecting buckling load.
文摘The first objective of this paper is to study the influence of the orthotic device on the maximum values of stresses in knee cartilages by using Ansys Workbench 14.5 software and applying the Finite Element Analysis (FEA) on a virtual assembly composed by an orthotic device and osteoarthritic knee (OAK). The second objective consists into quantifying and investigating the nonlinear motion of the human knee joint for OAK patients, with and without the orthotic device mounted on OAK, using tools of dynamics stability analysis. The short Lyapunov Exponents (LEs) are calculated, as measures of human knee and ankle joints stability, based on the experimental time series collected by using the biometrics acquisition system during walking on horizontal and inclined treadmills from a sample of healthy subjects and a sample of patients suffering by OAK disease. The values of LEs obtained for OAK patients are larger on the inclined treadmill than on horizontal treadmill and are larger than those obtained for healthy knees, being associated with more divergence and less stability. The results confirm that the influence of an orthotic device mounted on OAK on its stability is significant, the values obtained for LEs being smaller than those calculated for OAK, and closer to the values of normal knees of patients and of healthy subjects.
基金This study is currently receiving the grant (Capital Clinical Medicine Special Project No. Z181100001718187 ) from Beijing Municipal Science and Technology Commission and the grant (CAMS Initiative for Innovative Medicine 2016-I2M-1-018) from Chinese Academy of Medical Sciences.
文摘Objective To establish finite element models of skull, fronto-orbital advancement and fronto-orbital distraction osteogenesis of craniosynostosis, to analyze the mechanical characteristics of skull base and fronto-orbital operation area, so as to guide the later app lication of distractors. Methods One 6-year-old male patient with unilateral coronal synostosis was enrolled in October 2015. Three-dimensional (3D) computed tomography (CT) scan of skull was performed. DICOM data was imported into Mimics 17.0 for contour extraction and cranial 3D reconstruction. The skull model was processed by Mimics, Geomagic Studio 12.0, Hypermesh 12.0 and other software to establish a three-dimensional finite element model. The unilateral and bilateral fronto-orbital anterior osteotomy models were simulated respectively. The mechanical analysis was performed at point A in forehead area and point B in temporal area. Three different groups of traction forces were loaded:(1) 50 Newton for point A, 50 Newton for point B;(2) 80 Newton for point A and 50 Newton for point B;(3) 100 Newton for point A and 50 Newton for point B, to obtain the optimized traction force.. Results Stress analysis was performed on established cranial finite element model, as well as unilateral and bilateral fronto-orbital advancement procedures. The stress distribution of the anterior and middle cranial fossae was found to be concentrated. After unilateral fronto-orbital advancement, the stress of anterior cranial fossa, especially the affected side, was decreased. The stress on both side in anterior cranial fossa was decreased after bilateral fronto-orbital advancement. After force was applied to point A and point B, the optimum deviation result at supraorbital notch point, midpoint of supraorbital margin, frontal temporal point and frontal zygomatic suture point in 3D (Deviation result of X value:-29.4%,-20.5%,-8.6%,-9.3%, Deviation result of Y value: 20.9%, 31.5%, 73.0%, 539.4%;Deviation result of Z value: 4.4%, 1.9%, 0.1%, 11.8) demonstrated the applicatio
基金The Key Project (2018Z02) of Jilin University of Finance and Economics, the NSF (11701209) of China.
文摘In this paper, we present an optimal 3-point finite difference scheme for solving the 1D Helmholtz equation. We provide a convergence analysis to show that the scheme is sixth-order in accuracy. Based on minimizing the numerical dispersion, we propose a refined optimization rule for choosing the scheme’s weight parameters. Numerical results are presented to demonstrate the efficiency and accuracy of the optimal finite difference scheme.
基金Supported by the National Natural Science Foundation of China (51506072)the National Science and Technology Major Project (2012ZX06002-017-01-04-02).
文摘A method for dynamic alignment calculation of a large turbogenerator shafting is proposed. The method can analyze bearing load and bearing load sensitivity. Shafting alignment is made up of two parts:static alignment and dynamic alignment. Static alignment forms the basis of dynamic alignment, its mathematical model is deduced by transfer matrix method, the shafting static characteristic parameters under specific alignment installation requirements were obtained afterwards. Based on superposition method, bearing sensitivity analysis is performed to find the impact of slight bearing elevation change of the static alignment result. Above static alignment, dynamic shafting alignment considers the internal geometry of bearing under rotating state, static Reynolds equation is solved by the finite difference method and the relative position relationship of the center of journal and bearing are obtained. For static characteristic parameters calculated by static alignment and bearing sensitivity analysis, the calculation accuracy is verified by finite element software. The alignment model and codes in this paper can be a tool for the installation and safety analysis of large-scale shafting with three-point or four-point supports.
基金the European Union’s Horizon 2020 research innovation programme FUTURA under Grant Agreement No.700985.
文摘In this study,numerical optimisation and experimental validation of a divided rail freight brake disc crown made of grey cast iron EN-GJL-250 is presented.The analysed brake disc is used in rail freight wagons and possesses a load capacity of 22.5 tons per axle.Two of the divided rail freight brake discs are mounted on each axle.With the aid of numerical analysis,the thermal dissipation properties of the brake disc were optimised and ventilation losses were reduced,and the numerical results were compared with experimental results.A one-way fluid–structure interaction analysis was performed.A computational fluid dynamic model of a divided rail freight brake disc,used to predict air flow properties and heat convection,was incorporated into a finite element model of the disc and used to evaluate the temperature of the disc.A numerical parametrical optimisation of cooling ribs of the brake disc was also performed,and novel optimised cooling ribs were developed.A transient thermal numerical analysis of the brake disc was validated using temperature measurements obtained during a braking test on a test bench.The ventilation losses of the brake disc were measured on a test bench specifically designed for the task,and the losses were compared to the simulation results.The experimentally obtained ventilation losses and temperature measurements compared favourably with the simulation results,confirming that this type of simulation process may be confidently applied in the future.Through systematic optimisation of the divided rail freight brake disc,ventilation losses were reduced by 37% and the mass was reduced by 21%,resulting in better thermal performance that will bring with it substantial energy savings.
基金Russian Science Foundation (project no. 14-21-00065).
文摘Let G be a finite group of Lie type E6 over Fq (adjoint or simply connected) and W be the Weyl group of G. We describe maximal tori T such that T has a complement in its algebraic normalizer N(G, T). It is well known that for each maximal torus T of G there exists an element w ∈ W such that N(G, T )/T ■ CW(w). When T does not have a complement isomorphic to CW(w), we show that w has a lift in N(G, T) of the same order.
基金This work was supported by the National Natural Science Foundation of China (Grant Nos. U 1804150, 61573199)the 2018 Henan Province Science and Technique Foundation (182102210045).
文摘1 Introduction and main contributions Finite automata are dynamical systems with discrete inputs and outputs, which belong to the domain of logical systems and have a wide range of applications. In engineering, due to the excellent hardware qualities of simple structure, low power consumption and low electromagnetic noise, etc., finite automata are used in avionics and nuclear engineering, where the environment is bad and require strict safety. In science, finite automata serve as one of the main molding tools for discrete event dynamic systems (DEDS)(others are Petri nets, Markov chains and queuing networks, etc.). Studying DEDS is one of the major ways to study the cyber physical systems (CPS) which is the core content of Industry 4.0.
基金The authors are grateful to the anonymous reviewers for their useful comments and suggestionsThe authors are supported by the NSF of China (No. 11601114, No.11401138)the Anhui Provincial Natural Science Foundation (No. 1608085QA14).
文摘Solving the advection-diffusion equation in irregular geometries is of great importance for realistic simulations. To this end, we adopt multi-patch parameterizations to describe irregular geometries. Different from the classical multi-patch parameterization method, C 1- continuity is introduced in order to avoid designing interface conditions between adjacent patches. However, singularities of parameterizations can’t always be avoided. Thus, in this paper, a finite volume method is proposed based on smooth multi-patch singular parameterizations. It is called a singular parameterized finite volume method. Firstly, we present a numerical scheme for pure advection equation and pure diffusion equation respectively. Secondly, numerical stability results in L2 norm show that the numerical method is not suffered from the singularities. Thirdly, the numerical method has second order accurate in L2 norm. Finally, three numerical tests in different irregular geometries are presented to show efficiency of this numerical method.
文摘The correlation between crystal rotation and redundant shear strain in rolled single crystals was investigated by using the crystal plasticity finite element(CPFE) model in this paper. The deformation in aluminium single crystals of four representative orientations(rotated-Cube, Goss, Copper, and Brass) after rolling and plain strain compression was simulated, and the predictions have been validated by the experimental observations. In the rotated-Cube and Goss, the redundant shear strain and crystal rotation were in the same pattern, alternating along the thickness, while the relation between them was not obvious for the Copper and Brass due to their asymmetrical distributions of activated slip systems. The relations between slip system activation, crystal rotation, and shear strain were investigated based on the CPFE model, and the correlation between shear strain and crystal rotation has been built.
基金The research was supported by the NSFC projects 11171008 and 11571022.
文摘A mixed finite element method combining an iso-parametric Q 2-P 1 element and an isoparametric P^-Pi element is developed for the computation of multiple cavities in incompressible nonlinear elasticity. The method is analytically proved to be locking-free and convergent, and it is also shown to be numerically accurate and efficient by numerical experiments. Furthermore, the newly developed accurate method enables us to find an interesting new bifurcation phenomenon in multi-cavity growth.
文摘Compression tests on twenty unidirectional(UD) carbon fibre reinforced plastic(CFRP) specimens are conducted, the statistics on the measured compressive strength is calculated, and the fracture surface is characterized. Two types of different fracture surface are experimentally observed, and they are corresponding to very different values on the compressive strength. A finite element(FE) analysis is conducted to investigate the influence of random fibre packing on the compressive strength. And a riks method(provided in ABAQUS software) is applied in FE model to analyze fibre buckling behaviour in the vicinity of compressive failure. The FE analysis agrees well with the experimental observation on the two types of buckling modes and also the partition of compressive strength. It is clearly shown that the random fibre packing lays a significant influence on the random variability of compressive strength of CFRP.
基金the National Natural Science Foundation of China(Nos.11571275,11572244,11471261,11871399)the Natural Science Foundation of Shaanxi Province(Nos.2018JM1014,2017JM1005).
文摘The human tricuspid valve, one of the key cardiac structures, plays an important role in the circulatory system. However, there are few mathematical models to accurately simulate it.In this paper, firstly, we consider the tricuspid valve as an elastic shell with a specific shape and establish its novel geometric model. Concretely, the anterior, the posterior and the septal leaflets of the valve are supposed to be portions of the union of two interfacing semi-elliptic cylindrical shells when they are fully open.Next, we use Koiter’s linear shell model to describe the tricuspid valve leaflets in the static case, and provide a numerical scheme for this elastostatics model. Specifically, we discretize the space variable, i.e., the two tangent components of the displacement are discretized by using conforming finite elements(linear triangles) and the normal component of the displacement is discretized by using conforming Hsieh-Clough-Tocher triangles(HCT triangles).Finally, we make numerical experiments for the tricuspid valve and analyze the outcome. The numerical results show that the proposed mathematical model describes well the human tricuspid valve subjected to applied forces.
基金the the National Natural Science Foundation (Grant No. 11571181)the Natural Science Foundation of Jiangsu Province (Grant No. BK20171454)Qing Lan project, thank the reviewers for their many valuable suggestions. This work was partially done while the first author was visiting Beijing Computational Science Research Center from October 3, 2013 to March 3, 2014.
文摘This paper focuses on performance of several efficient and accurate numerical methods for the long-wave short-wave interaction equations in the semiclassical limit regime. The key features of the proposed methods are based on:(i) the utilization of the first-order or second-order time-splitting method to the nonlinear wave interaction equations;(ii) the ap-plication of Fourier pseudo-spectral method or compact finite difference approximation to the linear subproblem and the spatial derivatives;(iii) the adoption of the exact integration of the nonlinear subproblems and the ordinary differential equations in the phase space. The numerical methods under study are efficient, unconditionally stable and higher-order accurate, they are proved to preserve two invariants including the position density in L^1. Numerical results are reported for case studies with different types of initial data, these results verify the conservation laws in the discrete sense, show the dependence of the numerical solution on the time-step, mesh-size and dispersion parameter ε, and demonstrate the behavior of nonlinear dispersive waves in the semi-classical limit regime.
基金National Nature Science Foundation of China (Grant No. 11771409)Wu Wen-Tsun Key Laboratory of Mathematics of Chinese Academy of Sciences.
文摘Let σ={σi | i ∈ I} be some partition of the set of all primes P. A set H of subgroups of G is said to be a complete Hall σ-set of G if every member ≠ 1 of H is a Hall σi-subgroup of G, for some i ∈ I, and H contains exactly one Hall σi-subgroup of G for every σi ∈σ(G). A subgroup H of G is said to be:σ-permutable or σ-quasinormal in G if G possesses a complete Hall σ-set H such that HAx= AxH for all A ∈ H and x ∈ G:σ-subnormal in G if there is a subgroup chain A = A0≤A1≤···≤ At = G such that either Ai-1■Ai or Ai/(Ai-1)Ai is a finite σi-group for some σi ∈σ for all i = 1,..., t.If Mn < Mn-1 <···< M1 < M0 = G, where Mi is a maximal subgroup of Mi-1, i = 1, 2,..., n, then Mn is said to be an n-maximal subgroup of G. If each n-maximal subgroup of G is σ-subnormal(σ-quasinormal,respectively) in G but, in the case n > 1, some(n-1)-maximal subgroup is not σ-subnormal(not σ-quasinormal,respectively) in G, we write mσ(G)= n(mσq(G)= n, respectively).In this paper, we show that the parameters mσ(G) and mσq(G) make possible to bound the σ-nilpotent length lσ(G)(see below the definitions of the terms employed), the rank r(G) and the number |π(G)| of all distinct primes dividing the order |G| of a finite soluble group G. We also give the conditions under which a finite group is σ-soluble or σ-nilpotent, and describe the structure of a finite soluble group G in the case when mσ(G)=|π(G)|. Some known results are generalized.
基金support of the "Strategic Priority Research Program" of the Chinese Academy of Sciences (No. XDA09020402)the National Integrate Circuit Research Program of China (No. 2009ZX02023-003)+2 种基金the National Natural Science Foundation of China (Nos. 61261160500,61376006, 61401444, 61504157)the Science and Technology Council of Shanghai (Nos. 14DZ2294900, 15DZ2270900,14ZR1447500)the National Natural Science Foundation of China (61874178).
文摘The crystallization characteristics of a ubiquitous T-shaped phase change memory (PCM) cell, under SET current pulse and very small disturb current pulse, have been investigated by finite element modelling. As analyzed in this paper, the crystallization region under SET current pulse presents first on the corner of the bottom electron contact (BEC) and then promptly forms a filament shunting down the amorphous phase to achieve the low-resistance state, whereas the tiny disturb current pulse accelerates crystallization at the axis of symmetry in the phase change material. According to the different crystallization paths, a new structure of phase change material layer is proposed to improve the data retention for PCM without impeding SET operation. This structure only requires one or two additional process steps to dope nitrogen element in the center region of phase change material layer to increase the crystallization temperature in this confined region. The electrical-thermal characteristics of PCM cells with incremental doped radius have been analyzed and the best performance is presented when the doped radius is equal to the radius of the BEC.