基于面光滑有限元法的三维声传播问题研究

为解决标准有限元方法"过刚"的特性,采用一种基于面的光滑有限元法(FS-FEM)来求解三维声学问题,在FS-FEM模型当中,应用四节点的四面体单元来离散三维声场域,通过与四面体单元面相关的光滑域并运用伽辽金弱形式来建立线性离散系统的控制方程,在面光滑域上进行的梯度光滑操作能够"软化"原来"过刚"的FEM模型,因此能够减少数值离散误差。数值仿真结果表明:运用相同的网格密度,FS-FEM能够得到比FEM更加精确的计算结果。

结构不确定性分析的集合有限元法及其应用

用非概率凸集模型[3,4]反映结构参数的不确定性,结合响应面有限元法和优化理论,提出进行结构不确定性分析的集合有限元方法;该方法能解决不确定性数据信息较少、参数概率统计特性无法给出的结构可靠性问题,对于大型复杂结构不确定性分析有重要的意义;简述了响应面有限元法和非概率凸集模型,并对两种常用的凸集模型进行了比较,然后介绍了集合有限元法及其应用。

基于响应面法的钢拱桥可靠度分析

大型复杂桥梁结构的极限状态函数都是隐式的非线性函数,采用传统的可靠性分析方法可能无法实现,但利用响应面有限元法可以很好地解决这类问题。利用响应面法对一下承式钢拱桥拱肋、主梁在正常使用极限状态下的轴向应力、竖向位移的可靠度进行了分析,并根据拟合出的各极限状态函数显式表达式得出了相应的可靠度指标,说明响应面有限元法是计算下承式钢拱桥构件可靠度的有效方法。

拱形屋盖结构不平衡雪荷载的模拟研究

该文利用基于有限面元(Finite Area Element,FAE)方法对拱形屋面的不均匀积雪荷载进行了研究。首先设计制作了缩尺比为1∶100、矢跨比为0.125的拱形屋面风洞试验模型,通过风洞试验测得屋面平均风速大小,结合CFD数值模拟确定平均风速方向,再基于FAE方法利用风速-雪通量经验公式计算得到屋面的积雪分布系数;并分析了不同风速和不同风向角对屋面积雪分布系数及不平衡雪荷载的影响。其次,对基于FAE方法计算得到的积雪分布系数、基于两相流的CFD数值模拟结果以及我国现行《建筑结构荷载规范》GB 50009-2012的结果进行了比较。最后,总结了屋面雪荷载分布规律,给出了针对这类大跨结构雪荷载设计的一些建议。

Dynamic analysis of pavement on long span steel bridge decks

In order to analyze the dynamic response of pavement on long-span steel bridge decks under random dynamic loads, the irregularities of the pavement surface is simulated with the power spectrum density function, and the random load is calculated according to a vehicle vibration equation of vehicle model. The mechanical responses of three different cases are compared by using a transient dynamic analysis method, i. e., under random dynamic load, constant moving load and dead load respectively. The results indicate that the mid-span of two adjacent transversal diaphragms is the worst load position. The maximum vertical displacement and the maximum transversal tensile stress of the pavement are 1.33 times and 1.39 times as much as those when only considering the impact coefficients. This study not only provides a theoretical basis for the mixture design and structural design of pavement, but also puts forward higher demand on the construction and maintenance for steel deck pavement.

高拱坝的非概率可靠性分析

随着一大批高拱坝将在我国水力资源丰富的西南地区修建,高拱坝的可靠性日益成为了水工研究的焦点。拱坝问题复杂,设计中涉及的不确定参数较多,可利用的统计信息却较少,给出它们准确的概率分布和隶属函数几乎是不可能的,因此传统的可靠性分析方法在应用中遇到较大的困难。为此,采用统计数据需求较少的非概率可靠性分析方法,结合响应面有限元法建立了高拱坝的非概率可靠度计算模型,编制了相关的软件,并依托小湾拱坝进行了高拱坝的应力变形分析和可靠度计算分析。

FAE方法在屋盖结构雪荷载研究中的应用

雪荷载设计是大跨屋盖结构设计中的重要环节,目前国内工程实践中的设计雪荷载通常是采用规范条文,个别重要的工程还会结合CFD数值模拟的结果。由于试验设备和条件的限制,较少采用实验对其进行验证。有限面元法结合了常规风洞试验模拟和计算机仿真技术,是一种研究大跨度屋盖结构雪荷载分布的有效方法。本文对其进行概述和分析,并以高低屋盖结构为例,采用有限面元法研究了风速和风向角对屋面积雪分布系数的影响。结果表明:与我国现行《建筑结构荷载规范》比较,二者整体分布规律基本一致,但在具体分布数值上略有差异;风速、风向亦对高低屋盖的积雪分布系数具有重要影响,就本文研究的高低屋盖结构而言,积雪分布系数随风速增大而增大,在270~337.5°风向角范围内屋盖的雪荷载分布较为不利,但在规范中并不考虑这种斜风向不利分布工况。

Identification of processing window for extrusion of large thick-walled Inconel 625 alloy pipes using response surface methodology

Identifying suitable processing window is necessary but difficult for achieving favorable microstructure and performance in extrusion of large thick-walled pipe with difficult-to-deform Inconel 625 alloy. In this work, a method was established for identifying the extrusion process window considering temperature control using response surface methodology. Firstly, the response surface models, which correlate temperature rise and peak temperature to key extrusion parameters, have been developed by orthogonal regression based on finite element calculated data. Secondly, the coupled effects of the key extrusion parameters on the temperature rise and peak temperature have been disclosed based on the regression models. Lastly, suitable extrusion processing windows, which are described by contour map of peak temperature in the space of extrusion speed and initial billet temperature, have been established for different extrusion ratios. Using the identified process window, a suitable combination of the key extrusion parameters can be determined conveniently and quickly.

NUMERICAL INVESTIGATION OF TOROIDAL SHOCK WAVES FOCUSING USING DISCONTINUOUS GALERKIN FINITE ELEMENT METHOD

A numerical simulation of the toroidal shock wave focusing in a co-axial cylindrical shock tube is inves- tigated by using discontinuous Galerkin （DG） finite element method to solve the axisymmetric Euler equations. For validating the numerical method, the shock-tube problem with exact solution is computed, and the computed results agree well with the exact cases. Then, several cases with higher incident Mach numbers varying from 2.0 to 5.0 are simulated. Simulation results show that complicated flow-field structures of toroidal shock wave diffraction, reflection, and focusing in a co-axial cylindrical shock tube can be obtained at different incident Mach numbers and the numerical solutions appear steep gradients near the focusing point, which illustrates the DG method has higher accuracy and better resolution near the discontinuous point. Moreover, the focusing peak pres- sure with different grid scales is compared.

Reflective cracking viscoelastic response of asphalt concrete under dynamic vehicle loading

In order to investigate the mechanical response of reflective cracking in asphalt concrete pavement under dynamic vehicle loading, a finite element model is established in ABAQUS. The viscoelastic behavior is described by a prony series which is calculated through nonlinear fitting to the creep test data obtained in the laboratory. Based on the viscoelastic theory, the time-temperature equivalence principle, fracture mechanics and the dynamic finite element method, both the Jintegral and the mix-mode stress intensity factor are utilized as fracture evaluation parameters, and a half-sine dynamic loading is used to simulate the vehicle loading. Finally, the mechanical response of the pavement reflective cracking is analyzed under different vehicle speeds, different environmental conditions and various damping factors. The results indicate that increasing either the vehicle speed or the structure damping factor decreases the maximum values of fracture parameters, while the structure temperature has little effect on the fracture parameters. Due to the fact that the vehicle speed can be enhanced by improving the road traffic conditions, and the pavement damping factor can become greater by modifying the components of materials, the development of reflective cracking can be delayed and the asphalt pavement service life can be effectively extended through both of these ways.

Optimal design of butterfly-shaped linear ultrasonic motor using finite element method and response surface methodology

A new method for optimizing a butterfly-shaped linear ultrasonic motor was proposed to maximize its mechanical output. The finite element analysis technology and response surface methodology were combined together to realize the optimal design of the butterfly-shaped linear ultrasonic motor. First, the operation principle of the motor was introduced. Second, the finite element parameterized model of the stator of the motor was built using ANSYS parametric design language and some structure parameters of the stator were selected as design variables. Third, the sample points were selected in design variable space using latin hypercube Design. Through modal analysis and harmonic response analysis of the stator based on these sample points, the target responses were obtained. These sample points and response values were combined together to build a response surface model. Finally, the simplex method was used to find the optimal solution. The experimental results showed that many aspects of the design requirements of the butterfly-shaped linear ultrasonic motor have been fulfilled. The prototype motor fabricated based on the optimal design result exhibited considerably high dynamic performance, such as no-load speed of 873 ram/s, maximal thrust of 27.5 N, maximal efficiency of 43%, and thrust-weight ratio of 45.8.

A Parallel Algorithm for Adaptive Local Refinement of Tetrahedral Meshes Using Bisection

Local mesh refinement is one of the key steps in the implementations of adaptive finite element methods. This paper presents a parallel algorithm for distributed memory parallel computers for adaptive local refinement of tetrahedral meshes using bisection. This algorithm is used in PHG, Parallel Hierarchical Grid Chttp：//lsec. cc. ac. cn/phg/）, a toolbox under active development for parallel adaptive finite element solutions of partial differential equations. The algorithm proposed is characterized by allowing simukaneous refinement of submeshes to arbitrary levels before synchronization between submeshes and without the need of a central coordinator process for managing new vertices. Using the concept of canonical refinement, a simple proof of the independence of the resulting mesh on the mesh partitioning is given, which is useful in better understanding the behaviour of the biseetioning refinement procedure.

Modeling of contact surface morphology and dust particles by using finite element method

The effect of dust particles on electric contacts and a hazardous size range of hard dust particles using a rigid model were discussed before. As further research, elastic-plastic model of finite element analysis was established in this work, which is closer to real condition. In this work, the behavior of large size and small size particles, and the influence of particles hardness were investigated. The calculating result of small-size particles presents a general hazardous size coefficient for different contact surface morphology; for large-size particles, it presents a hazardous size coefficient for complicated composition of the dust. And the effect of the dust shape is also discussed.

Optimization of press bend forming path of aircraft integral panel

In order to design the press bend forming path of aircraft integral panels,a novel optimization method was proposed, which integrates FEM equivalent model based on previous study,the artificial neural network response surface,and the genetic algorithm.First,a multi-step press bend forming FEM equivalent model was established,with which the FEM experiments designed with Taguchi method were performed.Then,the BP neural network response surface was developed with the sample data from the FEM experiments.Furthermore,genetic algorithm was applied with the neural network response surface as the objective function. Finally,verification was carried out on a simple curvature grid-type stiffened panel.The forming error of the panel formed with the optimal path is only 0.098 39 and the calculating efficiency has been improved by 77%.Therefore,this novel optimization method is quite efficient and indispensable for the press bend forming path designing.

圆波导Y结环行器

本文介绍一种Y型波导结环行器———圆波导环行器 ,它由装有铁氧体样品的圆柱形结腔及其侧面连接的三段互成 12 0°的圆波导组成 ,并在Ku波段上利用有限元法对这种Y结环行器的性能进行数值计算和实验测量。所得结果表明这种结构的环行器可以实现环行性能。

Phase Field Simulation of Intragranular Microvoids Evolution Due to Surface Diffusion in Stress Field

Based on the bulk free energy density and the degenerate mobility constructed by the quartic double-well potential function,a phase field model is established to simulate the evolution of intragranular microvoids due to surface diffusion in a stress field.The corresponding phase field governing equations are derived.The evolution of elliptical microvoids with different stressesΛ,aspect ratiosβand linewidths hˉis calculated using the mesh adaptation finite element method and the reliability of the procedure is verified.The results show that there exist critical values of the stressΛc,the aspect ratioβc and the linewidth hˉc of intragranular microvoids under equivalent biaxial tensile stress.When Λ≥Λ_(c),β≥β_(c) or h≤h_(c),the elliptical microvoids are instable with an extending crack tip.WhenΛ<Λ_(c),β<β_(c) or hˉ>h_(c),the elliptical microvoids gradually cylindricalize and remain a stable shape.The instability time decreases with increasing the stress or the aspect ratio,while increases with increasing the linewidth.In addition,for the interconnects containing two elliptical voids not far apart,the stress will promote the merging of the voids.

Stress distributions on crown-luting cement-substrate system with finite element method

The aim of this work is to analyze the stress distributions on a crown-luting cement-substrate system with a finite-element method in order to predict the likelihood of interfacial micro cracks, radial or circumferential cracks, delamination, fracture and delamination with torsion. The contact and layer interface stresses in elastic layered half-space indented by an elastic sphere were examined using finite element method. The model consists of crown, luting cement and substrate. The solutions were carried out for three different elastic moduli of luting cement. It was placed between the cement and the substrate as a middle layer and its elastic module was chosen lower than the elastic module of crown and higher than the elastic module of dentin. An axisymmetric finite element mesh was set up for the stress analysis. Stress distributions on the contact surface and the interfaces of crown-luting cement and luting cement-dentin have been investigated for three different values of luting cement by using ANSYS. The effects of the luting cement which has three different elastic moduli on the pressure distribution and the location of interfacial stresses of the multi-layer model have been examined. The mechanism of crack initiation in the interfaces and interracial delamination was also studied quantitatively. For each luting cement, the pressure distribution is similar at the contact zone. Stress discontinuities occur at the perfect bonding interfaces of the crown-luting cement and the substrate-luting cement. The maximum stress jumps are obtained for the highest and the lowest elastic module of the luting cement. In the crown-luting cement-substrate system, failures may initiate at crown-luting cement region for luting cement with the lowest elastic module value. In addition, failures at luting cement-substrate region may occur for luting cement with the highest elastic module. In the luting cement, the medium elastic module value is more suitable for stress distribution in crown-luting cement-substrate interfaces.

Electrode Design of Cylindrical Coplanar-grid CdZnTe Detector by Finite Element Methods

Cylindrical coplanar-grid configurations,which offer a lot of advantages over established designs,can effectively overcome the problem of poor hole collection.Finite element analysis is utilized for simulating the potential distribution of the cylindrical coplanar-grid detector under different models by varying the widths of grid and pitch of electrodes. In addition, a modified grid pattern has been discussed to improve the weighting potential match between two grids. In this way, the geometry of electrodes for cylindrical coplanar-grid detectors is optimized.

Effects of surface finish and treatment on the fatigue behaviour of vibrating cylinder block using frequency response approach

This paper presents the effects of surface finish and treatment on the high cycle fatigue behaviour of vibrating cylinder block of a new two-stroke free piston engine at complex variable amplitude loading conditions using frequency response approach. Finite element modelling and frequency response analysis was conducted using finite element analysis software Package MSC.PATRAN/MSC.NASTRAN and fatigue life prediction was carded out using MSC.FATIGUE software. Based on the finite element results, different frequency response approach was applied to predict the cylinder block fatigue life. Results for different load histories and material combinations are also discussed. Results indicated great effects for all surface finish and treatment. It is concluded that polished and cast surface finish conditions give the highest and lowest cylinder block lives, respectively; and that Nitrided treatment leads to longest cylinder block life. The results were used to draw contour plots of fatigue life and damage in the worst or most damaging case.

Numerical investigation of temperature gradient-induced thermal stress for steel–concrete composite bridge deck in suspension bridges

A3D finite element model(FEM)with realistic field measurements of temperature distributions is proposed to investigate the thermal stress variation in the steel–concrete composite bridge deck system.First,a brief literaturereview indicates that traditional thermal stress calculation in suspension bridges is based on the2D plane structure with simplified temperature profiles on bridges.Thus,a3D FEM is proposed for accurate stress analysis.The focus is on the incorporation of full field arbitrary temperature profile for the stress analysis.Following this,the effect of realistic temperature distribution on the structure is investigated in detail and an example using field measurements of Aizhai Bridge is integrated with the proposed3D FEM model.Parametric studies are used to illustrate the effect of different parameters on the thermal stress distribution in the bridge structure.Next,the discussion and comparison of the proposed methodology and simplified calculation method in the standard is given.The calculation difference and their potential impact on the structure are shown in detail.Finally,some conclusions and recommendations for future bridge analysis and design are given based on the proposed study.