Response of concrete gravity dam by damage model under seismic excitation

The aim of this study is to investigate the earthquake damage response of the concrete gravity dam. It is well known that simulation of concrete structures up to rupture requires nonlinear behavior of the models. The material behavior whose principle is based on the damage mechanics has been implemented in a finite element program. This model takes into account the dissymmetry of the behavior of concrete and considers cracking in tension and rupture in compression. The dynamic equilibrium equations of motion are solved by using the explicit central difference method which is based on approximation of velocities and accelerations with quotients of finite difference of known values of displacements with regular time step. For numerical application, two dimensional seismic analysis of Koyna gravity dam is performed by using the 1967 Koyna earthquake records. The results obtained are shown in the time history graphs of the horizontal and vertical displacements of the nodal point located at the crest of the dam. These are the stresses, the strains and the cumulated damage at the integration points respectively.     

Free vibrations of inflatable dams

Summary Inflatable dams are used for various purposes in a number of countries. They are cylindrical membrane structures which are attached to a rigid foundation along two of their generators and are inflated with water, air, or a combination of water and air. Some studies of their cross-sectional static profiles have been carried out in the past, both for cases when the dam impounds water and when overflow occurs. Experiments on scale models also have been reported. Vibrations have been observed on actual dams and on the physical models, but a theoretical analysis of the dynamic behavior of inflatable dams has not been published previously. In this paper, two-dimensional linear vibrations are considered. The dam is inflated with water and is used to impound water. Its material is assumed to be inextensible. Vibration modes and frequencies are obtained with the use of the finite difference and boundary element methods. The effects of the membrane density, internal head, and upstream head on the frequencies are determined.     

薄膜充气环动态特性试验研究

充气环是新一代大型空间薄膜结构的主要支撑部件,它具有轻质柔性、局部抗弯刚度低、几何非线性、高阻尼等特点。本文针对薄膜充气环动态特性,建立了一套柔性结构的动态测试系统。由于采用普通力锤极易引起结构的局部变形,本文改进了激励方式,得到薄膜充气环的面内和面外振动频响函数。通过复模态指示函数识别极点数目,采用多项式拟合识别出结构的固有频率,阻尼比和振型。分析不同充气压力下结构动态特性的变化规律,并对薄膜充气结构动态特性测试相关问题进行讨论,实验结果为空间薄膜结构有限元模型有效性验证提供依据。     

Inertia effects in axisymmetrically deformed cylindrical shells under axial impact

The axisymmetric buckling of elastic–plastic cylindrical shells subjected to axial impact are studied using a finite element analysis. This study reveals that shells, subjected to axial impact, are both velocity and mass sensitive, so that larger energies can be absorbed by a shell for high-velocity impacts when decreasing the striking mass. It is shown that the inertia characteristics of the shell, together with the material properties, determine particular patterns of the axial stress wave propagation, thus, causing either dynamic plastic or dynamic progressive buckling to develop during the initial phase of the shell response. Domains of the load parameters, where the different buckling phenomena develop, are obtained for two particular shells. Strain rate effects are also considered when discussing the energy absorbing properties of the shells.     

Stochastic design sensitivity in structural dynamics

A method to analyse stochastic design sensitivity for problems of structural dynamics is presented. A combination of the adjoint variable approach and the second order perturbation method is used in the finite element context. An alternative form of the constraint functional that holds for all times is introduced to consider the time response of dynamic sensitivity. The terminal problem of the adjoint system is solved using equivalent homogeneous equations exicited by initial velocities. The numerical procedures are shown to be much more efficient when based on the fold superposition technique: the generalized co-ordinates are normalized and the correlated random variables are transformed to uncorrelated variables, whereas the secularities are eliminated by the fast Fourier transform of complex valued sequences. Numerical algorithms have been worked out and proved to be accurate and efficient; they can be readily adapted to fit into the existing finite element codes whose element derivative matrices can be explicitly generated. A number of numerical results for the deterministic and stochastic sensitivity analysis of beams and shells illustrates the paper.     

Rigid plastic model of incremental sheet deformation using second‐order cone programming

This paper describes a method for numerically modelling the incremental plastic deformation of shells and applies the method to incremental sheet forming (ISF). An upper bound finite element shell model is developed based on sequential limit analysis under the rigid plastic assumption, which is solved by manipulating the problem into the form of a second‐order cone program (SOCP). Initially, the static upper bound plate problem is investigated and the results are compared with the existing literature. The approach is then extended to a shell formulation using a linearized form of the Ilyushin yield condition and two methods for treating the Ilyushin condition are presented. The model is solved efficiently using SOCP software. The resulting model shows good geometric agreement when validated against an elasto‐plastic model produced using existing commercial software and with measurements from a real product produced using ISF. Copyright © 2008 John Wiley & Sons, Ltd.     

钢质圆柱壳在侧向局部冲击荷载下的变形及失效破坏

基于动力有限元程序LS-DYNA及随动塑性Cowper-Symonds模型,对两端固支钢质薄壁圆柱壳经受半球头弹体侧向局部冲击的非线性动力响应问题进行数值模拟,获得了不同冲击条件下圆柱壳的变形及破坏模态,并研究了弹体在不同周向冲击倾角时壳壁产生穿透性破裂的最小速度（临界破裂速度）。研究表明,圆柱壳破坏模式与弹体冲击倾角θ0、冲击速度V等因素密切相关,将发生局部凹陷、碟形变形及穿透现象,且临界破裂速度随冲击倾角的增大而增大。研究结果可应用于圆柱壳在侧向局部冲击作用下的毁伤预测,从而为圆柱壳结构的安全防护设计提供理论依据。     

Dynamic response of shear-deformable axisymmetric orthotropic circular plate structures solved by the DQEM and EDQ based time integration schemes

The dynamic response of shear-deformable axisymmetric orthotropic circular plate structures is solved by using the DQEM to the spacial discretization and EDQ to the temporal discretization. In the DQEM discretization, DQ is used to define the discrete element model. Discrete dynamic equilibrium equations defined at interior nodes in all elements, transition conditions defined on the inter-element boundary of two adjacent elements and boundary conditions at the structural boundary form a dynamic equation system at a specified time stage. The dynamic equilibrium equation system is solved by the direct time integration schemes of time-element by time-element method and stages by stages method which are developed by using EDQ and DQ. Numerical results obtained by the developed numerical algorithms are presented. They demonstrate the developed numerical solution procedure.     

厚截锥壳结构的自由振动

本文对基于Mindlin理论所导出的厚截锥壳的一阶基本微分方程组采用了子结构离散变量法,求解了这类结构的固有频率和相应的振型。文中给出了算例,其结果与试验结果和有限无法计算结果相比是令人满意的。     

A static and dynamic finite element shell analysis with experimental verification

A system of finite element shell analysis codes, called SABOR/DRASTIC, is used to analyse a complex two-layered shell of revolution under static and dynamic asymmetric loads. The dynamic analysis is compared with experimentally measured response. In this linear elastic analysis, emphasis is placed on the inherent flexibility of the finite element method in modelling the complex structural geometry of a given test specimen. Static studies, which involve variations in important shell parameters, and dynamic studies, which provide a successful correlation with experiment, are used to illustrate both the detail and the generality with which shell analyses may now be performed with confidence.     

Multimaterial topology design for optimal elastic and thermal response with material-specific temperature constraints

We present an original method for multimaterial topology optimization with elastic and thermal response considerations. The material distribution is represented parametrically using a formulation in which finite element–style shape functions are used to determine the local material properties within each finite element. We optimize a multifunctional structure that is designed for a combination of structural stiffness and thermal insulation. We conduct parallel uncoupled finite element analyses to simulate the elastic and thermal response of the structure by solving the two-dimensional Poisson problem. We explore multiple optimization problem formulations, including structural design for minimum compliance subject to local temperature constraints so that the optimized design serves as both a support structure and a thermal insulator. We also derive and implement an original multimaterial aggregation function that allows the designer to simultaneously enforce separate maximum temperature thresholds based upon the melting point of the various design materials. The nonlinear programming problem is solved using gradient-based optimization with adjoint sensitivity analysis. We present results for a series of two-dimensional example problems. The results demonstrate that the proposed algorithm consistently converges to feasible multimaterial designs with the desired elastic and thermal performance.     

薄壁扁球壳结构在撞击载荷下的变形控制方法研究

对薄壁扁球壳结构撞击刚性板的变形特性和控制方法进行了研究。使用LS—DYNA软件建立了薄壁扁球壳结构撞击刚性板的有限元模型，并通过试验结果对模型的有效性进行了验证。利用数值仿真方法，对薄壁球壳结构撞击刚性板的变形特性和动态响应特点进行了分析。针对薄壁扁球壳结构一种典型撞击性能的要求，利用变形控制和局部弱化等方法得到了符合要求的变形模式和加速度响应曲线。最后的试验结果验证了设计结构方案的正确性．该变形控制方法可应用于工程实际。     

沉管隧道结构有限元建模及模型有效性研究

对不同的沉管隧道结构建模方法进行对比,研究采用两种不同类型的单元对沉管隧道结构计算模型有效性的影响,并通过试验进行验证。结果证明采用板壳单元进行建模时可得到较高精度的结果。结论可用于结构和周围介质较为复杂的沉管隧道这类大型地下工程动力特性分析与计算,将有效提高计算结果的准确性和效率。     

考虑接触效应的具轴对称脱层层合圆柱壳的非线性动力响应分析

基于非线性弹性壳理论,建立了考虑脱层接触效应的具轴对称脱层层合圆柱壳的运动控制方程。引入假想弹簧计算接触力,然后对系统的横向运动控制方程进行修正,从而有效地避免了脱层之间的相互贯穿。整个问题采用有限差分法进行求解,算例中,详细讨论了脱层的大小、深度、位置以及载荷等因素对具脱层轴对称层合圆柱壳非线性动力响应的影响。数值计算结果表明,在脱层结构动力响应分析中考虑接触效应是非常重要的,它可避免脱层结构出现物理上不可能的相互贯穿。     

Numerical modelling of the boundary conditions on beams stuck transversely by a mass

In this paper, numerical results of a drop weight impact test examining the dynamic response of a clamped steel beams struck transversely at the centre by a mass with a rectangular indenter are presented. The numerical simulation showed that the results are very sensitive to the way in which the supports are modelled and thus this paper studies the modelling of the structural supports used to clamp the specimen beam in the experiment. The first approach simplifies the structural support as boundary condition on the nodes; the second model represents the entire support as the real approximation; the last approach uses simplified support plate model acting with the beam to simulate the experimental set up. The complete force-displacement curve is used to compare the plastic deformation of the impacted beams, thus the best approximation is selected for further calculations. The finite element model was performed using the LS-DYNA non-linear, dynamic finite element software. The numerical calculations can predict accurately the response of deflections, forces and absorbed energies, when proper boundary conditions are applied, in this case with shell elements representing the support plates.     

变速超空泡航行体壳结构的动力响应分析

通过对变速超空泡水下航行体壳结构受力模型的分析,建立了恒定推力下航行体的平面运动方程,确定了变速过程中的阻力和冲击力。利用有限元方法,进行了结构响应计算,分析了减速过程中节点时域上的最大应力值在轴向的分布情况及典型节点处的响应。结果表明：航行体所需推力和所受应力较大,对其结构强度要求较高;运动过程中,节点时域上的最大应力在空间域上的极大值主要分布在首尾端部和柱壳中部;存在一些振动频率对航行体结构响应影响显著。结果对超空泡航行体壳结构受力和强度分析以及优化设计有着重要的指导意义。&;#61472;     

矿石冲击下自卸汽车车箱底板纵横梁开裂和断裂原因分析

针对重型自卸汽车车箱在装载矿石过程中出现的车箱底板纵横梁异常开裂和断裂问题,应用HyperMesh有限元软件建立了以板壳单元为基本单元的车箱有限元分析模型,并针对装载矿石的特点建立了矿石有限元模型,采用显式动态有限元法,以ANSYS/LS-DYNA为求解器,求解了不同质量的矿石从不同高度下落对车箱底板的冲击响应。结果表明：车箱底板纵横梁异常开裂和断裂是底板纵横梁连接部位冲击应力值大于材料的最小抗拉强度产生的,这与实车车箱底板纵横梁开裂和断裂情况相吻合。当车箱底板厚度为16mm,下落矿石质量超过0.3t之后,开裂和断裂处最大应力已大于底板材料的屈服强度（345 MPa）或最小抗拉强度（470 MPa）。为避免出现车箱底板大梁异常开裂和断裂现象,在确定的车箱底板厚度条件下,应限制装载矿石的质量和下落高度。     

弹性支撑模型对火箭发射过程结构振动响应影响研究EI北大核心CSCD

固体火箭从发射筒发射过程中,采用弹性支撑降低火箭结构与发射筒内壁接触引起的冲击,弹性支撑力学模型对火箭发射过程中结构振动响应计算存在影响。利用多体动力学建立包含火箭、发射筒、弹性支撑在内的发射动力学模型,在火箭发射物理过程分析基础上,利用ANSYS/LS-DYNA软件建立火箭壳体与弹性支撑局部有限元模型,获得了火箭壳体与弹性支撑接触面积变化对支撑刚度影响规律,在此基础上,提出了用于火箭发射多体动力学建模的弹性支撑改进模型,求解弹性支撑模型改进前后火箭发射过程结构振动响应与弹性支撑支反力,分析了弹性支撑模型改进对结构振动响应的影响及其原因。结果表明:提出的弹性支撑改进模型可以准确描述火箭尾部结构脱离弹性支撑过程中接触面积逐渐变化到零的物理过程;与弹性支撑模型改进前相比,改进后结构弯矩响应峰值显著减小。该成果有助于准确评估火箭发射过程结构响应水平,对于火箭结构精细化设计具有工程意义。     

鸡蛋品质特性的有限元分析方法

目的研究鸡蛋品质物性参数与结构动力学响应特征参数间的关联特性,构建鸡蛋品质检测的动力学相关性模型。方法以敲击响应检测技术为基础,引入结构动力学分析方法,应用有限元仿真技术定量分析鸡蛋品质物性参数(蛋形参数、蛋壳厚度、蛋壳刚度、蛋液密度)与其一阶共振频率间的对应变化规律,获取鸡蛋品质相关的动力学特征参数。结果鸡蛋品质物性参数中蛋形参数、蛋壳厚度、蛋壳刚度、蛋液密度与其结构一阶共振频率关联性显著;蛋壳厚度与蛋体结构一阶共振频率间符合较好的线性规律。相较而言,蛋壳密度、气室高度对结构一阶共振频率的影响较小。结论鸡蛋品质特性相关参数(蛋形参数、蛋壳厚度、蛋壳密度和蛋液密度)与其结构动力学响应特性具有较强的关联性。     

Non‐linear random response of laminated composite shallow shells using finite element modal method

This paper investigates the large‐amplitude multi‐mode random response of thin shallow shells with rectangular planform at elevated temperatures using a finite element non‐linear modal formulation. A thin laminated composite shallow shell element and the system equations of motion are developed. The system equations in structural node degrees‐of‐freedom (DOF) are transformed into modal co‐ordinates, and the non‐linear stiffness matrices are transformed into non‐linear modal stiffness matrices. The number of modal equations is much smaller than the number of equations in structural node DOF. A numerical integration is employed to determine the random response. Thermal buckling deflections are obtained to explain the intermittent snap‐through phenomenon. The natural frequencies of the infinitesimal vibration about the thermally buckled equilibrium positions (BEPs) are studied, and it is found that there is great difference between the frequencies about the primary (positive) and the secondary (negative) BEPs. All three types of motion: (i) linear random vibration about the primary BEP, (ii) intermittent snap‐through between the two BEPs, and (iii) non‐linear large‐amplitude random vibration over the two BEPs, can be predicted. Copyright © 2006 John Wiley & Sons, Ltd.