基于广义可靠性的随机模糊杆系结构优化设计

研究了随机参数杆系结构的广义可靠性优化设计问题。导出了随机荷载作用下以模糊许用值为条件的结构广义可靠度计算公式;建立了以杆截面为设计变量、结构重量均值为目标函数、结构模糊位移和单元模糊强度广义可靠度为约束条件的优化数学模型;通过引入罚函数,将原广义可靠性约束优化问题转化为无约束优化问题,利用遗传算法求解。设计结果表明:文中提出的模型和计算公式是可行有效的。     

模糊-区间参数连续体结构的拓扑优化设计

研究位移可靠性约束下的模糊-区间参数连续体结构的拓扑优化问题.利用3σ准则和信息熵分别将区间变量和模糊变量近似转换为随机变量,构建了随机参数平面连续体结构的拓扑优化模型,以结构的形状拓扑信息为设计变量,结构总质量均值极小化为目标函数.以满足位移可靠性为约束条件;利用代数综合法导出了位移响应的数字特征的计算表达式;通过单位虚载荷求得位移灵敏度然后采用双方向渐进结构优化方法求解.通过两个算例验证了文中模型的合理性和求解策略的有效性.     

含模糊变量和区间变量的结构可靠性优化设计方法

提出了基于能度可靠性理论的含模糊变量和区间变量的结构优化设计方法.运用能度可靠性理论建立了含模糊变量和区间变量的结构混合可靠性模型,采用结构的最大失效可能度作为混合模型的可靠性度量,给出最大失效可能度的计算方法,并以混合可靠性模型的最大失效可能度为约束条件建立了混合结构优化设计模型.实例计算表明了本文方法的有效性.     

基于高阶矩的稳健优化设计研究

采用随机响应量的前四阶统计矩来度量目标函数和概率约束条件的稳健性, 通过引入“权重因子”来确定新构造的目标函数中原 函数和敏感系数的比重, 利用加权组合法将稳健优化设计这一多目标优化问题转化为单目标问题, 从而建立新的基于高阶矩的稳健优化设计数学模型. 矩估计方法可高效地评估目标函数和概率约束条件的统计矩, 且不需要搜索技术, 因此不构成嵌套循环(即稳健优化过程是单循环的), 从而可以大大降低优化的计算工作量. 对多个桁架结构进行了确定性优化设计、可靠性优化设计、传统的和该文所提的稳健优化设计, 验证了所建立的基于高阶矩的稳健优化设计数学模型的合理性和正确性, 比较并解释了计算所得的优化结果.     

考虑频率和应力约束的索网式天线多目标优化设计

为确保天线的表面精度和工作性能,综合考虑了天线结构重量、频率、布局等诸多因素,提出了基于优化的设计方法来平衡这些因素.以绳索预张力大小、纵向调整索数目、辐射单元数目为设计变量,结构重量和网状反射面的均方根误差最小为目标函数,应力和频率为约束条件,建立了索网式可展开天线设计的多目标优化数学模型.并将多目标化为单目标用遗传算法进行了求解,结果表明:在结构表面精度达到约2mm 的条件下,结构重量能减轻12%.这表明文中所提出的优化设计方法是有效可行的,对网状天线结构的设计具有一定的指导意义.     

桁架结构概率-非概率混合可靠性拓扑优化

研究了桁架结构概率-非概率混合可靠性拓扑优化问题。建立了以结构重量为目标函数、混合可靠性指标为约束条件的拓扑优化数学模型,针对强度为随机变量和应力为区间变量、强度为区间变量和应力为随机变量两种情况推导了可靠性指标对设计变量的灵敏度计算公式。实例结果表明：混合可靠性拓扑优化的截面尺寸和结构重量相对于非概率可靠性优化都更大,使得结构除了能够容许载荷存在一定变异程度外,也允许位移和强度存在一定变异程度。     

基于区间模型结构稳健性优化设计

采用区间变量描述结构不确定性参数,对不确定变量进行标准化,借用超椭球模型分析思路,对优化过程中的变量进行分类,突出稳健性优化设计特点,重点描述基于区间模型稳健性优化的基本思想方法.采用目标性能分析方法,强调指定可靠性指标的唯一性,将变量划分为两类,考虑约束条件从特殊到一般,给出了稳健性优化的具体算法、求解步骤和迭代收敛准则.对实际算例进行了分析与求解,与已有结果比较,验证了论文方法的正确性和有效性.     

基于变位移约束的结构材料优化设计

针对质量最小化、位移为约束条件的结构材料优化问题,提出了一种变位移约束的结构材料拓扑优化方法。采用分式有理式识别结构材料单元特性参数,以细观单元拓扑变量倒数为设计变量,结合均匀化方法求出宏观结构单元的等效刚度矩阵以及其对细观单元设计变量的导数,进而得到位移的一阶近似展开式。结合变约束限的思想,得到了以结构质量作为目标函数、位移作为约束条件的连续体细观结构拓扑优化近似模型;并采用对偶方法进行求解。对几种典型结构,进行了考虑单个和多个位移约束的结构材料优化设计,所得结果验证了本文方法的有效性和可行性。     

渐进结构优化在离心机吊篮结构设计中的应用

根据离心机吊篮的最大外形尺寸、连接边界、载荷以及离心机最大加速度值等参数确定了结构拓扑优化的设计区域、载荷条件和边界条件,采用ANSYS软件,以整体质量最小为目标,根据吊篮实际工作载荷和要求施加拓扑优化约束条件,建立吊篮拓扑优化模型,采用基于应力水平删除材料的渐进结构优化方法进行优化设计.优化后吊篮结构满足约束条件,质...     

一种含混合变量结构的可靠性优化设计方法

提出了一种含模糊变量和区间变量的混合模型结构可靠性优化设计方法.基于模糊可靠性理论建立了含混合变量结构的可靠性模型,给出了混合模型可靠度计算方法.进而,以混合模型可靠度为约束务件建立了可靠性优化设计模型,并针对该模型为两级优化嵌套问题,采用序列线性规划法进行了求解.实例计算表明文中方法是有效可行的.     

Ground thermal response to heat conduction in a power transmission tower foundation

An analytical formulation is developed to predict transient heat conduction in a semi-infinite medium with a vertical finite line heat source, which represents a buried tower of a power transmission line foundation. Unlike past studies with a constant line heat source, the current model develops a time-dependent variable heating strength, as well as a time varying surface temperature of the ground. An approximate VHS model (variable heating strength) is developed for sinusoidal variations of the line source strength and surface temperature, in order to simulate seasonal variations of ground temperatures. The VHS model reduces computational time and exhibits good accuracy, when compared against a full exact solution. The model is applied to heat conduction in a tower foundation, with time-varying ground surface temperatures. Effects of ground thermal conductivity and diffusivity, as well as variations of the line source strength, are investigated in this article.     

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在海冰试验研究的基础上 建立了一个海冰的数学模型,根据此模型推导出海冰的本构关系,并通过试验验证了此本 构关系的正确性. 根据海冰的本构关系拟合出海冰的最大抗压强度和应变率的关系曲线并推 导出海冰最大抗压强度和应变率关系的公式,并用试验数据验证了此公式的正确性.     

Characterization of story-level seismic damage using an energy-based damage model

An energy-based damage model currently used for seismic analysis of structures is modified to ensure a positive value in the damage index at all levels of inelastic response. At the ultimate limit state, the modified model gives the same plastic strain energy capacity as the previous damage model. Testing of small-scale cantilever specimens showed different strength deterioration parameters for coldrolled and hot-rolled steel and composite systems of double cantilevers. The strength deterioration parameter for the composite system is smaller than that of the individual cantilevers. Various weighted-average rules for combining local member damage indices into story-level damage indices are compared with measured story-level damage indices. Based on testing of small-scale steel cantilevers, the current combination rules predict the story-level damage reasonably well near the ultimate limit state but tend to underestimate the story-level damage in the less severely damaged states. A combination rule based on best fitting of the experimental data obtained in this study is presented.     

考虑纤维断裂特征的Nb3Sn股线统计拉伸强度和失效概率

Nb₃Sn 超导复合股线在强磁场工程中有着重要的应用,其拉伸强度为保证和评估其长期服役安全的一个关键参数。本文从 “剪滞”理论出发,利用基于Weibull/Possion统计理论的复合材料纤维断裂的Curtin-Zhou模型,较好地描述复合股线中Nb₃Sn超导纤维碎片化过程,建立了分析超导复合股线统计拉伸强度和失效概率的模型。计算结果表明,青铜法Nb₃Sn超导复合股线的拉伸强度随着初始损伤参数的增大而迅速减小;在4.2K服役温度下,当Weibull模量为8时,随着初始损伤参数的增加,股线的拉伸强度约从900MPa衰减至480MPa,与已有实验结果吻合良好;初始损伤参数约为1时,正规化方差最大。初始损伤和Weibull模量对Nb₃Sn复合股线统计拉伸强度和失效概率函数的分布有着显著影响。     

Modelling of dynamic ductile fracture and application to the simulation of plate impact tests on tantalum

A model of dynamic damage by void nucleation and growth is proposed for elastic-viscoplastic materials sustaining intense loading. The model is dedicated to ductile materials for which fracture is caused by microvoiding. The material contains potential nucleation sites where microvoids are generated when the local pressure overcomes the nucleation pressure. A probability density function is adopted to describe the fluctuation of the nucleation pressure within the material. The void growth is described by using a hollow sphere model where micro-inertia effects are accounted for. The matrix weakening due to void growth is also included.The model has been first tested under uniaxial deformation. When the strain rate is assumed constant, the pressure inside the material has nearly a linear response up to a maximum. An analytical expression for the maximum pressure is proposed.Finite element simulations of plate impact tests have been carried out and compared to experiments on tantalum. From simulations based on the proposed model, an increase of the spall strength is observed with higher shock intensities. Therefore, the relationship between the velocity pullback and spall strength usually assumed in the literature (based on the acoustic approach) seems to be inadequate. Velocity profiles are simulated for different flyer thicknesses and different impact velocities with close agreement with experiments.     

基于静强度分布参数的复合材料剩余强度及寿命预测

为探讨剩余强度及疲劳寿命与初始静强度分布参数之间的关系,构建基于初始静强度分布参数的剩余强度和疲劳寿命计算模型。在模型构建过程中未涉及复合材料结构的层数、铺层厚度和铺层方向,适应性强。模型参数可通过静力试验和剩余强度试验获得,试验成本相对疲劳试验较低。剩余强度和疲劳寿命与初始静强度变异系数及其分布参数有关,当初始静强度服从威布尔分布时,疲劳寿命亦服从威布尔分布,可为开展疲劳可靠性提供借鉴和参考。算例表明,基于建立的模型,剩余强度计算结果最大误差为-1.58%,疲劳寿命与试验数据吻合较好。     

双钢板混凝土组合板抗爆性能分析

钢-混凝土-钢组合板是一种新型的组合结构,与传统钢筋混凝土板相比,具有抗剪强度高、延性大、耗能能力强等特点,目前已经被广泛应用于核反应堆安全壳、海洋平台及储油罐等结构。本文中,设计并制作了缩尺的普通钢筋混凝土板和钢-混凝土-钢组合板,开展了在接触爆炸荷载作用下的实验研究,通过损伤分析、跨中最大挠度对比研究不同板的抗爆性能。基于ANSYS/LS-DYNA非线性有限元程序,研究了钢-混凝土-钢组合板的损伤模式、跨中最大挠度等,并与实验结果进行了对比分析,验证了有限元分析模型的准确性和适用性。参数化分析了炸药量、混凝土强度和钢板厚度等参数对钢-混凝土-钢组合板抗爆性能的影响规律。利用多参数回归分析方法,提出钢-混凝土-钢组合板跨中挠度的预测公式。结果表明:提高混凝土强度可以降低结构的塑性损伤, 增加钢板厚度可以有效降低钢-混凝土-钢组合板的跨中最大挠度。相对于普通钢筋混凝土板,钢-混凝土-钢组合板保持了良好的整体性,且具有继续承载的能力。拟合公式能够较好地预测钢-混凝土-钢组合板跨中挠度与药量和钢板厚度的关系。     

Strength of orthotropic cylindrical panels with account for geometric nonlinearity

This paper describes the influence of geometric nonlinearity in the analysis of the strength of orthotropic cylindrical panels. The values of maximum permissible loads in the linear and nonlinear versions of calculations of structures made of unidirectional carbon plastics are given, and the loads at which stability loss occurs are determined. The mathematical model accounts for transverse shifts and geometric nonlinearity and stated as the full potential strain energy functional. The calculations are carried out on the basis of the method of solution continuation with respect to the parameter. The strength is estimated by using the maximum stress criterion.     

Qualitative properties of plasticity equations for porous media in plane deformation

The instantaneous stress-strain state of a porous rigid-plastic material obeying the cylindrical yield condition and the associated flow rule is considered in the case of plane deformation. It is shown that the type of the system of equations depends on the stress state. In the hyperbolic case, the equations of characteristics and relations along them are derived. An exact solution to the model boundary-value problem with the maximum friction law taken into account is obtained. An asymptotic analysis near the maximum friction surface is performed.