离心泵叶轮爆裂转速数值仿真和试验

基于SimXpert对某液体火箭发动机离心泵叶轮进行弹塑性有限元分析,计算离心泵叶轮在离心载荷作用下的爆裂转速,并与在超速试验台上得到的爆裂试验结果进行对比.结果表明,考虑材料非线性的弹塑性有限元计算结果与试验结果误差为0.59%,可应用于离心泵叶轮的强度校核和结构优化. 该离心泵叶轮的爆裂转速为2.716倍的工作转速,对其进行结构轻量化或优化十分必要.     

An elastic plastic damage formulation for concrete: Application to elementary tests and comparison with an isotropic damage model

Pure elastic damage models or pure elastic plastic constitutive laws are not totally satisfactory to describe the behaviour of concrete. They indeed fail to reproduce the unloading slopes during cyclic loading which define experimentally the value of the damage in the material. When coupled effects are considered, in particular in hydro-mechanical problems, the capability of numerical models to reproduce the unloading behaviour is essential, because an accurate value of the damage, which controls the material permeability, is needed. In the context of very large size calculations that are needed for 3D massive structures heavily reinforced and pre-stressed (such as containment vessels), constitutive relations ought also to be as simple as possible. Here an elastic plastic damage formulation is proposed to circumvent the disadvantages of pure plastic and pure damage approaches. It is based on an isotropic damage model combined with a hardening yield plastic surface in order to reach a compromise as far as simplicity is concerned. Three elementary tests are first considered for validation. A tension test, a cyclic compression test and triaxial tests illustrate the improvements achieved by the coupled law compared to a simple damage model (plastic strains, change of volumetric behaviour, decrease in the elastic slope under hydrostatic pressures). Finally, one structural application is also considered: a concrete column wrapped in a steel tube.     

铝合金受压板件局部屈曲承载力设计方法

为考察现有铝合金设计规范预测非焊接受压板件承载力的准确性,采用壳单元建立单向受压四边简支板、方形截面管柱和十字形截面轴压柱有限元模型,使用ANSYS计算得到铝合金板件弹塑性屈曲临界应力和极限承载力。数值计算结果与理论分析结果对比发现：现有板件弹塑性屈曲应力理论能够给出铝合金板件屈曲临界应力的下限值,误差较小。中国规范非加劲板件有效厚度预测公式偏保守,因此给出修正的有效厚度预测公式。修正后的非加劲板件有效厚度公式可以提高板件利用率,增强经济性。     

A variational inequality approach to the inelastic stress-unilateral analysis of cable-structures

The present paper deals with the inelastic, stress-unilateral analysis of cable-structures undergoing large displacements. The response of the cable-structures to load- and initial strain-increments is described by a set of equations and inequalities, which are formulated compactly as variational inequalities. Two dual extremum principles—generalizations of the minimum of the potential and complementary energy—with inequalities as subsidiary conditions are derived. The numerical calculation is preformed iteratively by using the decomposition techniques of the multilevel optimization and applying in the resulting substructures the algorithms of non linear optimization. As an example the elastic, elastic-perfectly plastic and workhardening behaviour of a cable-structure is examined and some useful results from the comparison of the solutions are obtained.     

An admissible-behaviour-based analysis of the deadlock in Petri-net controllers

This paper addresses the problem of verifying the discrete control logic that is typically implemented by programmable controllers. Not only are the logical properties of the controller studied during verification, the behaviour of the overall controlled system is also examined. An approach that combines the calculation of the safety-oriented interlock controllers in terms of supervisory control theory (SCT), the corresponding calculation of the admissible behaviour of the system, and the specification of the desired system operation by Petri nets is proposed. A potential deadlock in the controlled system is then verified by taking the admissible-behaviour model as a process model. The analysis of the simultaneously operated supervisory-control-based interlock controller and the Petri-net-based sequential controller is performed with a C-reachability graph. The paper focuses on the calculation of the graph, and the approach is illustrated with an example of a simple manufacturing cell.     

空时分组编码在多入多出系统中的容量分析

研究瑞利衰落信道下正交空时分组编码的信道容量,针对收端已知信道状态信息(CSI)以及收发两端均知CSI的2种情况,给出相应的容量分析及计算公式的推导。在收端已知CSI情况下,采用泰勒级数展开方法,给出一种信道容量的近似表达式,该式可有效简化原有精确公式的计算,获得与真实值非常相似的结果。在收发两端均知CSI情况下,提出一种基于最陡下降算法的简单计算方法,用于求解最优中断门限值,该方法可避免原有求解方法的大量搜索和计算。仿真结果表明,所给出的信道容量精确表达式以及近似表达式均与相应的计算机仿真结果一致,从而验证了所推公式的有效性。     

飞机结构整体优化和细节分析

飞机结构复杂,部件众多,连接形式复杂,传统的单一计算方法已很难满足计算要求,为更好地挖掘飞机的承载能力,还要考虑结构局部进入塑性区应力分布.对飞机结构进行有限元分析,有时需同时考虑整体和局部,大型结构采用较密的网格会耗费大量时间、资源等,甚至会导致计算不收敛;局部结构须划分较细的网格才能得到局部构件的细节应力.以某型飞机机翼为例,简单介绍开展飞机结构整体优化和细节分析的方法与流程.     

Numerical modelling of the cyclic behaviour of the basic components of steel end plate connections

This paper aims at developing a new methodology based on finite element (FE) techniques with a combination of several other methods to extend the component-based design philosophy of EC3 to the cyclic behaviour of end plate connection. In the first part, the experimental procedure for studying the behaviour of an isolated T-stub as the main component of an end plate connection under monotonic and cyclic loading is presented. The second part comprises the four steps necessary to build the analytical model. Firstly the monotonic and secondly the cyclic FE models of these specimens are discussed and validated. Then, a mathematical energy balance model is developed to reproduce the cyclic response. This model is the basis of a mechanical model which predicts the behaviour of a T-stub which constitutes the main component of connections. With these data, a spring model is used to predict the moment rotation curve for an isolated end plate connection.     

Finite element simulation of polymer behaviour using a three-dimensional, finite deformation constitutive model

This paper presents a phenomenological three-dimensional viscoelastic–plastic constitutive model for polymers. The model is based on the assumption that stress can be decomposed into two parts, namely viscoelastic and elastic–plastic. The proposed rate-dependent nonlinear model is then implemented in a finite element program. The validity of the code is assessed by the data from experiments on a specific polymer. The data from three types of tests, namely uniaxial compression, creep, and relaxation, are used to evaluate the validity of the model. Comparisons show that the proposed constitutive model could satisfactorily represent the time-dependent mechanical behaviour of polymers. The model is then used to study the effect of friction in the compression test and the behaviour of polymers under cyclic loading.     

快艇运动系统仿真模型的实现

该文通过对快艇模拟器分析研究,运用回转变换张量法对运动系统数学模型中的三维姿态进行解算。因为回转变换张量法具有方便、简洁、实用的优点,使得整个运动模型的分析计算得到了简化,并且建立的运动模型与实际相符。     

基于Rodrigues参数交互模型航天器相对位姿测量技术

针对传统测量技术测量航天器相对位姿准确度较低的问题,引用Rodrigues参数交互模型研究了一种新的航天器相对位姿测量技术。利用Rodrigues参数建立航天器位姿采集模型,通过原向量、旋转轴、原向量和旋转轴的交叉积等向量作为标架,获得航天器旋转以后得向量组,利用四元数定理来减少计算航天器旋转向量的计算量,在观察三维空间内的坐标系间的向量变化曲线规律后,测量出交互模型的航天器相对位姿,得出基于罗德里格旋转参数交互模型结构图,确定罗德里格旋转参数模型与航天器的距离H和地面接收到的航天器相位位姿的误差。通过Harris角点检测方法计算航天器模拟图像的每个像素和灰度,通过像素和灰度信息进行条件随机场计算,分析航天器相对位姿特征,在多次寻找三维坐标系中查找相似的最近临近点和次临近点后,合理匹配,确定航天器相对位姿。实验结果表明,基于Rodrigues参数交互模型航天器相对位姿测量技术测量的精准度比传统技术高出25.88%,实用性更强。     

A biaxial constitutive law for concrete incorporated in BOEOR5 code

A two-parameter plastic model for concrete behaviour in plane stress is presented and its implementation in BOSOR5 Computer Code for the analysis of shells of revolution is discussed. A numerical example is included.     

混凝土塑性弥散裂缝模型和应用

将塑性弥散裂缝模型在混凝土裂缝研究中进行拓展,将拓展后的模型通过子程序在Abaqus有限元平台中进行实现,并将该模型得出的计算结果与梁的三点弯试验进行对比.计算结果与试验结果吻合.     

Shape optimization of shear panel damper for improving the deformation ability under cyclic loading

This paper presents a shape optimization approach for a low-yield steel shear panel damper to improve the deformation ability. A minimization problem of maximum cumulative equivalent plastic strain, an index of the deformation ability of the shear panel damper is formulated subject to a constraint of total absorbing energy. The response surface methodology as well as the design of experiment technique are applied to the optimization process. In this study, finite element analysis with iso-tropic/kinematic hardening model is adopted to simulate the cyclic elasto-plastic behavior instead of experimental approach, and the numerical solutions are validated by comparing with previous experimental results. With the numerical analysis, the shape parameters effects are investigated and second order polynomials are fitted to obtain the regression equations for the maximum cumulative equivalent plastic strain and the total absorbing energy. The final optimal shape is determined by using the established regression equations. The shape optimization approach can substantially improve the deformation capacity of the shear panel damper.     

Consolidation analysis of elasto-plastic soil

Non-linear consolidation analysis using a finite element formulation based on Biot's consolidation theory has been used to study the behaviour of strip and circular footings resting on an elastic-perfectly plastic soil satisfying the Mohr-Coulomb yield criterion. The initial stress method with a modified Newton-Raphson iterative scheme has been used for this study. Displacement of the footing and pore pressure dissipation in the soil are compared with those of linear analysis. Incorporation of the plastic behaviour of soil increases the consolidation rate and settlement. Effects of flow rule and p₀/c ratio on consolidation behaviour have also been reported.     

Numerical analyses of embankments on PVD improved soft clays

In this paper, three-dimensional behaviour of an embankment on soft soils incorporating prefabricated vertical drains is analysed with finite element method using a recently proposed constitutive model, namely S-CLAY1S. The constitutive model accounts for plastic anisotropy, interparticle bonding and degradation of bonds. The numerical simulations show that neglecting effects of anisotropy and destructuration may lead to inaccurate predictions of soft clay response. The same problem is also analysed under two-dimensional plane strain conditions. Axisymmetric vertical drains are converted into equivalent plane strain conditions using three different numerical matching techniques purposed in the literature. In order to validate these matching techniques, the 2D equivalent plane strain results are compared with the results of 3D analysis. It is shown that these numerical matching techniques accurately predict the consolidation behaviour of an embankment on PVD improved soft clays and provide a useful tool for engineering practice.     

逆变器非线性运行的同步电动机无源性控制研究

通过严格的理论分析和数学计算,建立了同步电动机在同步坐标系中E-L方程形式的数学模型,给出了逆变器的非线性模型。以这些模型为基础,研究并设计了在负载转矩(转速、位置)为任意时变未知情形下同步电动机的无源性渐近跟踪控制器。该控制器在实现机械控制目标的同时实现了对磁场方向和磁场幅值的控制,即同时实现了磁场矢量控制。仿真结果表明,该无源性控制器可以很好地实现转速和位置的跟踪控制,具有很高的动态控制性能和鲁棒特性。     

A nonlinear finite element analysis of an ice-strengthened ship shell structure

Finite element method is used to study the nonlinear behaviour of an ice-strengthened ship shell structure. The main object is the plastification and collapse of a frame. The plastic limit load for this frame is determined using the calculated load-deflection curve. The results of the finite element analysis are compared with well-known formulas of plastic design and also with experimental results. The finite element program used in the analysis is ADINA.     

水库动态库容的建模研究与应用

针对传统的实时调度方法存在的缺陷,特别是静态库容计算方法的不足,根据实时调度的特点和研究现状,本文提出了动态库容计算方法,探索出了壅水跌水模型,并对其进行了求解;运用壅水跌水模型开发出了基于VC++的三峡-葛洲坝梯级水库任意情况下不同调度方案的水量平衡分析计算系统,解决了三峡-葛洲坝梯级电站实时调度中的负荷调整问题。