THE RATIONALISM THEORY AND ITS FINITE ELEMENT ANALYSIS METHOD OF SHELL STRUCTURES

In this paper, a kind of rationalism theory of shell is established which is of different mechanic characters in tension and in compression, and the finite element numerical analysis method is also described.

Numerical Simulation of Stress-Strain State for Nonhomogeneous Shell-Type Structures Based on the Finite Element Method

Projective-iterative version of finite element method has developed for numerical simulation of the stress-strain state of nonhomogeneous shell-type structures (shells with openings). Plastic deformation of the material is taken into account when using the method of elastic solutions that reduce the solution of elastoplastic problems to solution of elastic problems. Developed PIV’s significant savings of computer calculation has been compared with the calculation on a fine mesh of traditional FEM. Designed scheme allows analysis of the mutual influence of openings. Analysis of the transformation zone of plastic deformation is developed. For definiteness, the cylindrical shell structures with several rectangular openings are considered.

BOUNDARY ELEMENT METHOD FOR ARBITRARY ELASTIC THIN SHELL

In this paper,a boundary element scheme for arbitrary elastic thin shells is elaborated,Based on BEM of 3D linear elasticity and Kirchhoff's hypothesis,boundary integral equations for shells are deduced. As a result,only Kelvin's solution is used,the difficulty,in finding a fundamental solution of arbitrary shells is successfully avoided.

THE CONSTRUCTION OF WAVELET-BASED TRUNCATED CONICAL SHELL ELEMENT USING B-SPLINE WAVELET ON THE INTERVAL

Based on B-spline wavelet on the interval （BSWI）, two classes of truncated conical shell elements were constructed to solve axisymmetric problems, i.e. BSWI thin truncated conical shell element and BSWI moderately thick truncated conical shell element with independent slopedeformation interpolation. In the construction of wavelet-based element, instead of traditional polynomial interpolation, the scaling functions of BSWI were employed to form the shape functions through the constructed elemental transformation matrix, and then construct BSWI element via the variational principle. Unlike the process of direct wavelets adding in the wavelet Galerkin method, the elemental displacement field represented by the coefficients of wavelets expansion was transformed into edges and internal modes via the constructed transformation matrix. BSWI element combines the accuracy of B-spline function approximation and various wavelet-based elements for structural analysis. Some static and dynamic numerical examples of conical shells were studied to demonstrate the present element with higher efficiency and precision than the traditional element.

ANALYSES ON NONLINEAR COUPLING OF MAGNETO-THERMO-ELASTICITY OF FERROMAGNETIC THIN SHELL—II:FINITE ELEMENT MODELING AND APPLICATION

Based on the generalized vaxiational principle of magneto-thermo-elasticity of a ferromagnetic thin shell established （see, Analyses on nonlinear coupling of magneto-thermo- elasticity of ferromagnetic thin shell--I）, the present paper developed a finite element modeling for the mechanical-magneto-thermal multi-field coupling of a ferromagnetic thin shell. The numerical modeling composes of finite element equations for three sub-systems of magnetic, thermal and deformation fields, as well as iterative methods for nonlinearities of the geometrical large-deflection and the multi-field coupling of the ferromagnetic shell. As examples, the numerical simulations on magneto-elastic behaviors of a ferromagnetic cylindrical shell in an applied magnetic field, and magneto-thermo-elastic behaviors of the shell in applied magnetic and thermal fields are carried out. The results are in good agreement with the experimental ones.

Stochastic Finite Element Analysis of Plate and Shell Construction

The response of random plate and shell construction is analyzed with the stochastic finite element method (SFEM). Random material properties and geometric dimensions of construction are involved in this paper. A simplified isoparametric local average model is used to describe the random field. Numerical results of the examples indicate that the approach presented herein is an economical and efficient solution for such an analysis compared with Monte Carlo simulation (MCS).

超协调元

该文提出一类超协调的单元理论。不同于在普通协调元中采用的线位移协调插值格式,超协调元的单元插值函数首先引入转角自由度等线位移导数的高阶协调假设,并通过积分推导,进而获得超协调的线位移模型。基于超协调元理论,该文构造了一类新型的三结点三角形平板壳元SCT。数值算例表明:与其他类型单元相比,基于超协调元理论的单元具有计算精度高和计算效率好的优势。该文所提出单元理论构造简单,超协调元理论可以成为构造高性能数值算法的一种新的通用理论。

舰船舷间双层声桥声振传递特性研究

[目的]双层壳之间的舷间结构是声振动从耐压壳向轻外壳传递的重要桥梁,为降低对舰船振动声辐射水平的影响,提出一种双层声桥的舷间结构形式并开展声振传递特性研究。[方法]采用有限元方法建立舷间双层声桥的有限长双层圆柱壳振动声辐射模型,对比分析双层声桥与传统单层声桥结构的声振传递特点,揭示双层声桥结构形式、结构参数以及轴向分布间距等因素对声辐射和振动传递特性的影响规律。[结果]对比结果表明:双层圆柱壳间的双层声桥连接结构比传统单层声桥结构的降噪效果更好;双层圆柱壳间“2-1”型双层声桥结构模型的振动传递降低效果优于“1-2”型和“2-2”型,而3种不同的“1-1”型双层声桥连接结构的振动传递降低效果则较为相近;底层声桥肋板间距和横铺板宽度对双层壳体结构的振动传递降低效果的影响较大,而声桥层高的影响则较小;双层圆柱壳间双层声桥的轴向分布越紧密,其振动传递降低的效果越差。[结论]研究成果可为舰船舷间结构的减振降噪设计提供参考。

钛合金室温受压蠕变损伤本构模型

为了解决工程上在评估深潜器耐压壳体安全可靠性时不考虑拉压蠕变破坏机理产生的差异,会导致较大计算误差问题,本文提出了适用于室温蠕变的蠕变损伤本构模型。通过分析钛合金材料蠕变特性,考虑了室温环境下位错堆积造成的蠕变阻力,并且位错堆积的现象与时间有关。基于微分自洽法提出了适用于室温环境下的钛合金蠕变本构模型,得到受压情况下TC4ELI的相关材料参数,并将该模型用USDFLD和CREEP子程序进行定义。研究表明:对于受压结构而言,使用通过拉伸蠕变实验得到的本构模型的计算结果会过于保守,对于含V型缺口平板受压时等效蠕变应变的相对误差为168.20%。本文所提出的模型适用于环肋耐压壳结构的蠕变损伤分析。

液态金属堆内小长径比同轴双层薄壁结构的流固耦合试验研究

池式液态金属堆的主容器与热屏之间具有狭窄的流体间隙,该结构属于含窄缝间隙的小长径比同轴双层柔性壳体。窄缝间隙中流体与结构之间相互作用产生的流固耦合效应在抗震分析时必须加以考虑。现有研究主要针对长径比较大和流体间隙相对较大的圆柱壳体,对于小长径比和极小流体间隙的同轴柔性壳体研究较为缺乏。本文参考液态金属反应堆的结构设计了三种不同尺寸的窄缝间隙,开展窄缝间隙条件小长径比同轴双层壳体模型的振动试验,测量结构在不同间隙尺寸下的加速度,得到模态频率和主要振型。然后,使用有限元法进行模态分析,通过与试验结果的对比,验证了有限元法的准确性。最后,计算出不同间隙尺寸下模型的附加质量;且随着间隙尺寸的减小,模型附加质量随之增大。本研究可为类似的含窄缝小长径比同轴双层柔性壳体结构的抗震设计提供数据支持,对于液态金属堆的抗震分析具有重要意义。

基于杆系离散元理论考虑构件断裂的单层网壳结构倒塌破坏模拟研究

塑性铰模型计算效率高,可快速获得结构宏观破坏模式,韧性断裂损伤模型从微观机制揭示钢材的断裂机理,可较准确预测钢材的断裂行为。为此,该文基于杆系离散元理论,将两者联合建立构件断裂模拟算法,既具有计算效率高的优势又保证构件断裂模拟的精度。首先介绍杆系离散元法的基本理论,以及宏观塑性铰模型和微观韧性断裂损伤模型具体计算流程;然后给出将两者联合分析的具体实施策略,即以接触截面边缘最不利点处的应力作为整个截面的应力状态,进而调用韧性断裂损伤模型。最后采用Fortran语言编制相应的分析程序,并通过悬臂梁断裂算例和单层网壳振动台倒塌试验,验证该算法对模拟杆件断裂行为的可行性和有效性。杆系离散元法模拟构件断裂时,截面发生开裂,颗粒间发生脱离是一个自然的过程,无需其他任何修正即可实现结构由连续体状态向断裂后非连续体状态过渡,与有限元方法相比,不存在网格畸变重划分、迭代不收敛的问题,更具计算优势,为大跨空间网壳结构倒塌破坏分析提供新的计算手段。

基于有限元模型的永磁同步电机结构振动特性研究

对电机模态固有频率的精确计算及准确分析是电机低噪声驱动设计的一个重要环节。由于用于电动汽车的永磁同步电机(PMSM)属于小型电机,机壳和端盖等装置对振动噪声的影响不容忽略,因此对不同电机结构部件以及耦合系统固有频率进行计算分析具有重要意义。基于一台12槽8极PMSM,利用有限元软件,考虑了铁心材料的各向异性、弹性模量、浸漆、机壳和端盖连接方式等影响,精确建立了定子铁心结构的计算模型,并用锤击法模态实验验证了有限元仿真模型的精确性。

内压无折边斜锥壳与筒体连接结构应力分析

采用有限元结合应力分类方法对受内压无折边斜锥壳与筒体连接结构的应力分布进行分析,结果表明:内压作用下斜锥壳的大端和小端均存在较大的局部应力,其中大端应力强度最大值发生在斜锥壳与大端连接处锥角最大的位置,小端应力强度最大值发生在斜锥壳与小端连接处靠近下部锥角较小的位置。斜锥壳大、小端处应力主要为弯曲应力,但斜锥壳小端处弯曲应力高于大端处。为便于对不同尺寸斜锥壳和筒体连接处的应力分布情况进行对比,文中引入了应力增值系数并通过此系数的变化研究此处应力的变化规律。

基于Workbench的导管架吊装分析

为对导管架整体吊装安全性进行数值模拟分析,采用有限元法。利用ANSYS Workbench对导管架进行整体建模。模型中全部采用壳单元进行模拟。有限元网格划分过程中对不同的板厚和位置设置不同的偏移方向。利用力质量单元向导管架模型赋值,利用重力加速度施加场力。导管架起吊的吊点采用远程点的方式进行模拟,远程点与吊点之间的控制方程简化钢丝绳的建模。对吊点等关键部位进行细化网格处理。在导管架吊装受力后处理时,检查结构的整体应力情况,并重点检查吊点的应力情况。检查远程点反力并与导管架重量进行比对。检查导管架整体位移避免发生翻转。

基于谱元法的加肋圆柱壳设备位置声学设计

加肋圆柱壳是水下航行器的重要结构形式,内部安装有大量机械设备,设备运行产生的低频振动通过基座等结构传递至壳体,引起壳体振动并产生低频辐射噪声,严重影响水下航行器的隐蔽性。通过开展机械设备安装位置声学优化设计研究,建立基于谱元法的加肋圆柱壳振动响应理论计算方法,得到不同安装位置设备振动引起的加肋圆柱壳振动响应,并以加肋圆柱壳整体法向振动响应最小为目标函数,提出加肋圆柱壳内设备位置声学设计方法。数值计算及实验结果验证了该声学优化方法的有效性,对水下航行器机械噪声控制具有重要意义。

内压薄壁圆柱壳电阻凸焊接头疲劳寿命研究

为提高凸焊接头在使用过程中的安全性能,笔者采用有限元法和等效结构应力法,对内压薄壁圆柱壳电阻凸焊接头疲劳寿命预测方法进行了研究。提出了一种考虑预压载荷对圆柱壳形状影响的建模方法,计算了不同预压载荷下的筒体变形和凸焊接头疲劳寿命。研究结果表明薄壁圆柱壳在凸焊接头处的变形对凸焊接头疲劳寿命有显著影响。建议在制造中采取措施减小焊接过程对圆柱壳在开孔区的变形的影响,从而使凸焊接头获得较高的疲劳寿命。

F E M ANALYSIS OF DELAMINATION BUCKLING IN COMPOSITE PLATES AND SHELLS

The purpose of the present study is to develop a new finite element method far analyzing buckling of delaminated composite plates and shells. This is achieved by establishing a new finite element called the reference-surface element. By use of the compatibility condition under Mindlin assumptions, the formulation of the reference-surface element was derived from whichever plate-element or shell-element being capable of analyzing composite plates and shells. This method assures a reasonable description of displacement field and the satisfaction of compatibility conditions for delamination problem. Numerical results for linear delamination buckling of axially compressed shells are presented to validate the method.

A MODIFIED HELLINGER-REISSNER VARIATIONAL FUNCTIONAL INCLUDING ONLY TWO INDEPENDENT VARIABLES FOR LARGE DISPLACEMENT OF THIN SHALLOW SHELL

The variational functional of the Hellinger-Reissner variational principle for the large displacement problem of a thin shallow shell with an arbitrary shape is first established. Then the functional of the modified principle suitable for the finite element method is derived. In the functional only two independent variables, the deflection w and the stress function F are included. The displacement expressions in the middle surface on the boundary of the shell is also derived by means of the previous two variables.

基于DEM-MFBD双向耦合技术的采煤机摇臂壳体疲劳寿命预测

采煤机摇臂壳体是采煤机的重要部件及薄弱环节,其寿命直接影响采煤机的工作性能。为研究采煤机截割复杂煤层时滚筒所受载荷对其摇臂壳体寿命的影响,以MG325型采煤机截割兖州矿区杨村煤矿17层含夹矸煤壁为工程背景,通过虚拟样机技术和离散单元法-多柔体动力学(Discrete Element Method-Multi Flexible Body Dynamics,DEM-MFBD)双向耦合技术,利用离散元仿真软件EDEM和多体系统动力学仿真软件RecurDyn,基于实际工况获得采煤机螺旋滚筒的外负载。在RecurDyn仿真平台中,建立采煤机摇臂三维实体模型并进行边界条件的设置及摇臂壳体的柔性化,通过软件本身的Durability疲劳耐久分析模块,计算摇臂壳体的疲劳寿命。利用专业绘图软件Origin绘制2个软件后处理的载荷曲线图,发现其走势较为一致,其后处理数据均值,标准差等相接近,证明两者耦合效果较好。结果表明:MG325型采煤机以滚筒转速83.5 r/min,截深600 mm,牵引速度5 m/min截割复杂煤层时,滚筒所受载荷具有较为强烈的载荷波动现象,由等效应力云图可得摇臂壳体的最大等效应力为230.51 MPa,且应力较大处集中位于壳体的各个齿轮轴孔处、凹槽处以及上下耳过渡处,经应力疲劳分析后得其最小寿命位于壳体的齿轮轴孔处,循环次数为8.3215×10~6次。本研究方法可为复杂条件下工矿装备大型结构件的优化设计提供参考。

基于离散元法的皂荚壳籽分离仿真与试验

针对打击式壳籽分离过程中存在皂荚壳破碎率低,以及皂荚壳易堵塞筛孔,造成壳籽分离效率低等问题,研究滚筒转速对皂荚壳籽分离的影响。通过对皂荚壳力学特性进行研究,基于离散元法建立皂荚壳离散元模型(Hertz-Mindlin with bonding),并对皂荚壳离散元模型进行粘结参数标定;得到皂荚壳粘结模型法向刚度、切向刚度、临界法向应力、临界切向应力为1.8 MPa、1.35 MPa、1.41 MPa、0.59 MPa。采用EDEM软件对皂荚壳籽分离过程进行仿真分析,仿真结果表明,在滚筒转速为200、360、400、500、1 000 r/min时,皂荚壳破碎率分别为41.7%、65.96%、88.3%、94.52%、94.8%,滚筒转速在500 r/min和1 000 r/min时,破碎率无明显变化,皂荚壳主要破碎形式为冲击破碎和挤压破碎,破碎后物料形态包括粉尘、丝状、未完全破碎3种。样机试验亦表明滚筒转速为500 r/min时,皂荚壳破碎率较高,且易于形成丝状物料,有利于皂荚壳籽分离和减小筛孔堵塞。