水电站压力钢管外压稳定问题的数值仿真研究

水电站压力钢管因失稳屈曲破坏过程的复杂性及影响失稳因素的多样性,导致对该问题的研究很难进行.目前该问题的传统计算方法存在一定的局限性,有时甚至计算结果相差较大.本文用神经网络模型结合模拟退火算法对该问题进行数值仿真求解,并通过测试样本验证了算法的可行性,为压力钢管外压稳定问题的分析方法开拓了一条新的研究思路.     

有限空间爆炸静态压力的温度补偿方法

为改善压阻式压力传感器的温度漂移特性,构建了基于遗传算法和小波神经网络的压力传感器温度补偿模型。针对小波神经网络收敛速度慢且易陷入局部最优解的问题,采用遗传算法对小波神经网络的连接权值、伸缩参数和平移参数进行优化。基于压力传感器的标定数据,分别采用BP神经网络、小波神经网络和遗传小波神经网络对其进行温度补偿研究,结果表明:遗传小波神经网络兼容了小波分析的时频局部特性和神经网络的自学习能力,表现出良好的收敛速度和补偿精度,经补偿后传感器的输出值更接近于标定值,其最大误差由?17.44 kPa变至0.38 kPa,最大相对误差由?14.0%变至0.38%。将该模型应用于有限空间爆炸静态压力的温度补偿中,取得了较好的实际应用效果。     

铝基复合材料高速干摩擦行为的遗传神经网络预测模型

对4种SiC颗粒增强铝基复合材料在5种速度和4种压力条件下进行了销-盘摩擦磨损试验,运用遗传神经网络技术建立了铝基复合材料在高速干滑动过程中的摩擦行为预报模型,并用该模型对铝基复合材料进行预报.结果表明,蓄热能力较大的铝基复合材料在服役条件下具有较高的摩擦系数,与实际情况相一致.用遗传神经网络建立的铝基复合材料摩擦行为预测模型为服役条件下提供了简便、可靠的优选材料方法.     

弯曲及拉伸荷载作用下的钢管抗压溃性能研究

钢管在海洋油气资源开发中应用广泛,一般依据在位应用时的荷载进行设计,设计理论较为成熟。但在某些安装工况中的拉伸和弯曲荷载与在位荷载具有相同的量级,此时钢管的设计需要考虑安装荷载的影响。本文针对钢管在承受拉伸和弯曲荷载下的抗外压压溃性能开展研究。基于商业软件ABAQUS建立有限元模型,开展钢管压溃实验与带有弯曲荷载下的钢管压溃实验验证有限元模型的正确性,进而利用验证后的数值模型讨论拉伸、弯曲荷载和两者联合作用下对管道抗外压压溃性能的影响。结果表明,弯曲荷载是影响抗压溃性能的重要因素,弯曲荷载的增加都会使极限压溃值显著下降。管道所受拉伸荷载对抗压溃性能有一定的影响,但影响很小,在两者共同作用下极限压溃值随弯曲荷载的增加都出现先增大后减小的现象,而且极值的位置与拉伸荷载的大小和弯曲荷载有关。因此,在抗压溃设计中应重点考虑弯曲荷载对压溃的影响,可忽略拉伸荷载的影响。本文可为海洋管道的安装起到指导作用。     

滑移爆轰驱动钢管的层裂

将VG损伤模型推广到二维情况,考虑了最大主应力方向对损伤演化的影响,并使用显式断裂算法对20钢管在GI-920炸药滑移爆轰驱动下层裂的问题进行二维数值模拟。分析了一维内爆和滑移爆轰两种加载方式下作用于钢管外表面的压力及钢管内部受力状态的区别,考察了滑移爆轰加载方式下钢管外表面的受力随炸药厚度变化的规律,进而研究了钢管内损伤的分布和演化,以及裂纹的产生和扩展现象。计算得到的层裂片初始厚度随炸药厚度的变化规律与实验结果符合较好。     

基于双剪统一强度理论的复式钢管混凝土轴压承载力计算

考虑内、外钢管对混凝土的双重约束作用, 分析复式钢管混凝土的轴压应力状态, 采用双剪统一强度理论分析混凝土和钢管各自的极限轴压强度, 得出复式钢管混凝土轴压承载力公式; 通过推导钢管在极限状态的强度折减系数及钢管与混凝土之间的紧箍力值, 计算出的轴压承载力与试验数据进行对比, 吻合较好, 验证了双剪统一强度理论在复式钢管混凝土轴压承载力计算中的适用性; 并给出了内圆钢管的径厚比和直径与轴压承载力提高系数的关系, 为复式钢管混凝土的优化设计提供理论依据.     

边坡稳定性预测的模糊神经网络模型

根据边坡稳定问题具有的模糊性,提出了一种判定边坡稳定性的模糊神经网络模型。该系统仅从期望输入输出数据集即可达到获取知识、确定模糊初始规则基的目的。再利用神经网络学习能力便不难修改规则库中的模糊规则以及隶属函数和网络权值等参数,这样大大减少了规则匹配过程,加快了推理速度,从而极大程度地提高了系统的自适应能力。最后用收集到的边坡数据样本训练和测试模糊神经网络模型,结果表明该模糊神经网络预测边坡稳定性是可行的、有效的。     

基于神经网络的惯性平台温度场仿真模型修正方法

针对目前平台系统仿真方法计算效率低且精度不高的问题,提出了一种基于神经网络算法且考虑真实壁面条件的惯性平台系统仿真模型修正方法。从惯性平台三维仿真模型入手,使用神经网络算法修正后的对流换热系数作为惯性平台与外界的换热条件,建立系统与无限大空间进行热交换的仿真模型,利用该仿真模型得到了更高精度的系统内部温度分布。仿真与试验结果表明,修正后的仿真模型中网格数量减小24.61%,仿真精度提高了15.95%。所得到的对流换热系数修正系数可用于具有相似外壁面惯性平台的温度场仿真分析。     

蜂窝钢管约束混凝土靶的准静态球形空腔膨胀模型及其应用

基于空腔膨胀理论建立工程模型是研究侵彻问题的常用方法。针对射弹侵彻蜂窝钢管钢管约束混凝土靶问题,考虑被打击单元钢管及其外围混凝土的综合约束作用,粉碎区混凝土采用Hoek-Brown (H-B) 准则,建立了蜂窝钢管约束混凝土靶的准静态球形空腔膨胀模型和刚性弹侵彻深度预测公式,并分析了综合约束刚度对侵彻过程的影响。算例表明：蜂窝钢管约束混凝土靶不同于半无限混凝土靶,侵彻过程中的扩孔压力不为常数;综合约束刚度越大,扩孔压力越大;侵彻深度预测公式计算结果与文献侵彻试验吻合较好。     

遗传优化小波神经网络在组合导航系统中的应用

实时性是组合导航系统的一个重要指标，而神经网络的优化学习问题是决定网络效率的关键技术。遗传优化小波神经网络不仅继承了小波分析良好的局部性及其神经网络的学习和推广能力，而且具有遗传算法全局寻优的特点，是多层前向神经网络学习的一种理想算法。将它应用于组合导航系统中并进行了仿真，结果表明，该算法能够根据实际情况自适应确定网络结构，实时性好，精度与常规方法相当。     

Experimental Identification Technique of Nonlinear Beams in Time Domain

In previous papers, the authors proposed a new experimental identification technique applicable to elastic structures. The proposed technique is based on the principle of harmonic balance and can be classified as a frequency domain technique. The technique requires the excitation force to be periodic. This is, in some cases, a restriction. So another technique free from this restriction is of use. In this paper, as a first step for developing such techniques, a technique applicable to beams is proposed. The proposed technique can be classified as a time domain technique, two variations of which are proposed. The first method is based on the usual least-squares method. The second is based on solving a minimization problem with constraints. The latter usually yields better results. But in this method, an iteration procedure is used which requires initial values for the parameters. To obtain the initial values, the first method can be used. So both methods are useful. Finally, the applicability of the proposed technique is confirmed by numerical simulation as well as experiments.     

岩土的一种强度准则及其变换应力法

基于岩土摩擦性,假设岩土破坏是由其物理空间内特征面上的应力比决定,提出了等效应力比的概念,即物理空间特征面上的剪应力合力与正应力合力的比值.在二维条件下,等效应力比可表示为σ-τ坐标系下与摩尔圆相切的直线扣除截距正切值;在三维条件下,假设在XYZ空间内存在一三维物理空间平面,此三维空间特征平面的等效应力比为影响材料强度特性的决定性因素,基于上述三维空间特征面建立了强度准则并称之为a准则.SMP准则以及广义Mises准则都是a准则的特例,当二维坐标中的截距为零时,则强度准则退化为SMP(spatially mobilized plane)强度准则,而当正切角为零时,则强度准则退化为广义Mises准则.而当截距与外切角均不为零时,则强度准则为介于上述两者之间的一种强度准则,在偏平面上为介于SMP曲边三角形与广义Mises圆形之间的曲边三角形.在子午面上,采用考虑岩土压剪耦合的屈服准则,破坏准则采用幂函数表达式.在偏平面上提出了基于a准则的形状函数,并采用真三维应力状态表示的破坏强度准则表示在三轴压缩路径下以p,q二维应力变量表达的准则公式,推导得到了基于a准则的变换应力公式,可简单地将一般以p,q为基本变量的二维模型转变为三维应力模型.通过强度以及多种应力路径的测试对比,验证了a准则及基于该准则的变换应力公式的合理性.     

结构损伤诊断的改进灵敏度方法

提出一种改进的灵敏度方法用于工程结构损伤检测中.通过在迭代算法中引入一个“加速”公式来迅速获得足够精确的识别结果,避免了多次迭代,可以大大减少计算花费.用文献[8]和文献[10]中的两个数值算例对所提方法进行了验证,并把结果和原文中的计算结果进行比较.结果表明:采用改进的方法一般只需经过一次计算即可获得精度更高的识别结果,避免了多次迭代,显著减少了计算花费,显示了改进方法突出的优越性.     

Momentum/continuity coupling with large non‐isotropic momentum source terms

Pressure‐based methods such as the SIMPLE algorithm are frequently used to determine a coupled solution between the component momentum equations and the continuity equation. This paper presents a colocated variable pressure correction algorithm for control volumes of polyhedral/polygonal cell topologies. The correction method is presented independent of spatial approximation. The presence of non‐isotropic momentum source terms is included in the proposed algorithm to ensure its applicability to multi‐physics applications such as gas and particulate flows. Two classic validation test cases are included along with a newly proposed test case specific to multiphase flows. The classic validation test cases demonstrate the application of the proposed algorithm on truly arbitrary polygonal/polyhedral cell meshes. A comparison between the current algorithm and commercially available software is made to demonstrate that the proposed algorithm is competitively efficient. The newly proposed test case demonstrates the benefits of the current algorithm when applied to a multiphase flow situation. The numerical results from this case show that the proposed algorithm is more robust than other methods previously proposed. Copyright © 2009 John Wiley & Sons, Ltd.     

发动机流道气动分析的上下游边界替代降阶模型

为了解决航空发动机流道内上下游干涉带来的计算量大的问题,提出了一种边界替代降阶模型方法。该方法辨识出研究流域与相邻的上下游流域交界面的气动力降阶模型,并耦合到该研究流域仿真模型的交界面上,用以表征上下游对该流域的影响,由此将多流域计算转化为单流域计算,同时又考虑了上下游的影响。采用一阶Volterra级数降阶模型实现了该方法。结果表明,采用本文方法和所有流域都采用CFD得到的压力和速度一致;本文方法所用的网格更少,可以加速收敛和提高计算速度。     

Parametric variational solution of linear-quadratic optimal control problems with control inequality constraints

A parametric variational principle and the corresponding numerical algo- rithm are proposed to solve a linear-quadratic （LQ） optimal control problem with control inequality constraints. Based on the parametric variational principle, this control prob- lem is transformed into a set of Hamiltonian canonical equations coupled with the linear complementarity equations, which are solved by a linear complementarity solver in the discrete-time domain. The costate variable information is also evaluated by the proposed method. The parametric variational algorithm proposed in this paper is suitable for both time-invariant and time-varying systems. Two numerical examples are used to test the validity of the proposed method. The proposed algorithm is used to astrodynamics to solve a practical optimal control problem for rendezvousing spacecrafts with a finite low thrust. The numerical simulations show that the parametric variational algorithm is ef- fective for LQ optimal control problems with control inequality constraints.     

A novel Volume-Compensated Particle method for 2D elasticity and plasticity analysis

A novel Volume-Compensated Particle model (VCPM) is proposed for the modeling of deformation and fracture in solids. In this proposed method, two potentials are introduced to model the interactions between material particles, i.e., a local pair-wise potential and a non-local multi-body potential. The local pair-wise potential is utilized to account for the constitutive relationship within the connecting bonds between particles while the non-local multi-body potential is employed for considering the volumetric effects under general mechanical loadings. The potential coefficients are determined by matching the potential energy stored in a discrete unit cell to the strain energy at the classical continuum level. A volume conservation scheme is proposed to model the plastic deformation. The validity of the proposed model is tested against the classical elasticity and elasto-plasticity benchmarks before its application to fracture problems. Several conclusions are drawn based on the proposed study.     

可靠性灵敏度函数及其特征指标的条件概率模拟求解方法

可靠性分析中基本变量分布参数为区间均匀变量时,失效概率为分布参数的函数。基于条件概率马尔科夫链模拟,提出了一种可靠性灵敏度函数的求解方法,并提出了一种新的可靠性灵敏度度量指标,它为参数可靠性灵敏度函数在参数空间上的期望。文中推导了线性极限状态正态变量下全局灵敏度函数及新指标的计算式.并提出了高效的基于条件概率马尔科夫链...     

Study on spline wavelet finite-element method in multi-scale analysis for foundation

A new finite element method （FEM） of B-spline wavelet on the interval （BSWI） is proposed. Through analyzing the scaling functions of BSWI in one dimension, the basic formula for 2D FEM of BSWI is deduced. The 2D FEM of 7 nodes and 10 nodes are constructed based on the basic formula. Using these proposed elements, the multiscale numerical model for foundation subjected to harmonic periodic load, the foundation model excited by external and internal dynamic load are studied. The results show the pro- posed finite elements have higher precision than the tradi- tional elements with 4 nodes. The proposed finite elements can describe the propagation of stress waves well whenever the foundation model excited by extemal or intemal dynamic load. The proposed finite elements can be also used to con- nect the multi-scale elements. And the proposed finite elements also have high precision to make multi-scale analysis for structure.     

Modified Adams-Moulton Predictor-Corrector Method in Solving Multibody Dynamical Systems

A modified Adams-Moulton predictor-corrector method is proposed to solve multibody dynamical systems. The proposed method is obtained by combining an Adams-Bashforth predictor method and an Adams-Moulton corrector method with derived weighting coefficients. With the modification, the accuracy of the proposed method is almost one order of magnitude better than the Adams-Moulton predictor-corrector method with the same step size. Stability limits of the proposed method are also studied. Because the present method has greater stability limits than Adams-Moulton predictor-corrector methods, the proposed method has good robustness during the process of time integration. A crank-slider mechanism is used as an example to investigate the capability of the proposed method in solving multibody dynamic systems.