Probabilistic-Ellipsoid Hybrid Reliability Multi-Material Topology Optimization Method Based on Stress Constraint

This paper proposes a multi-material topology optimization method based on the hybrid reliability of the probability-ellipsoid model with stress constraint for the stochastic uncertainty and epistemic uncertainty of mechanical loads in optimization design.The probabilistic model is combined with the ellipsoidal model to describe the uncertainty of mechanical loads.The topology optimization formula is combined with the ordered solid isotropic material with penalization(ordered-SIMP)multi-material interpolation model.The stresses of all elements are integrated into a global stress measurement that approximates the maximum stress using the normalized p-norm function.Furthermore,the sequential optimization and reliability assessment(SORA)is applied to transform the original uncertainty optimization problem into an equivalent deterministic topology optimization(DTO)problem.Stochastic response surface and sparse grid technique are combined with SORA to get accurate information on the most probable failure point(MPP).In each cycle,the equivalent topology optimization formula is updated according to the MPP information obtained in the previous cycle.The adjoint variable method is used for deriving the sensitivity of the stress constraint and the moving asymptote method(MMA)is used to update design variables.Finally,the validity and feasibility of the method are verified by the numerical example of L-shape beam design,T-shape structure design,steering knuckle,and 3D T-shaped beam.

Stress tensor determination by modified hydraulic tests on pre-existing fractures:Method and stress constraints

The hydraulic testing of pre-existing fractures(HTPF)is one of the most promising in situ stress measurement methods,particularly for three-dimensional stress tensor determination.However,the stress tensor determination based on the HTPF method requires at least six tests or a minimum of 14-15 tests(under different conditions)for reliable results.In this study,we modified the HTPF method by considering the shear stress on each pre-existing fracture,which increased the number of equations for the stress tensor determination and decreased the number of tests required.Different shear stresses were attributed to different fractures by random sampling;therefore,the stress tensors were obtained by searching for the optimal solution using the least squares criterion based on the Monte Carlo method.Thereafter,we constrained the stress tensor based on the tensile strength criterion,compressive strength criterion,and vertical stress constraints.The inverted stress tensors were presented and analyzed based on the tensorial nature of the stress using the Euclidean mean stress tensor.Two stress-measurement campaigns in Weifang(Shandong Province,China)and Mercantour road tunnel(France)were implemented to highlight the validity and efficiency of the modified HTPF(M-HTPF)method.The results showed that the M-HTPF method can be applied for stress tensor inversion using only three to four tests on pre-existing fractures,neglecting the stress gradient.The inversion results were confined to relatively small distribution dispersions and were significantly reliable and stable due to the shear stresses on the fractures and the stress constraints employed.The M-HTPF method is highly feasible and efficient for complete stress tensor determination in a single borehole.

APPROACH FOR LAYOUT OPTIMIZATION OF TRUSS STRUCTURES WITH DISCRETE VARIABLES UNDER DYNAMIC STRESS, DISPLACEMENT AND STABILITY CONSTRAINTS

A mathematical model was developed for layout optimization of truss structures with discrete variables subjected to dynamic stress, dynamic displacement and dynamic stability constraints. By using the quasi-static method, the mathematical model of structure optimization under dynamic stress, dynamic displacement and dynamic stability constraints were transformed into one subjected to static stress, displacement and stability constraints. The optimization procedures include two levels, i.e., the topology optimization and the shape optimization. In each level, the comprehensive algorithm was used and the relative difference quotients of two kinds of variables were used to search the optimum solution. A comparison between the optimum results of model with stability constraints and the optimum results of model without stability constraint was given. And that shows the stability constraints have a great effect on the optimum solutions.

A METHOD FOR TOPOLOGICAL OPTIMIZATION OF STRUCTURES WITH DISCRETE VARIABLES UNDER DYNAMIC STRESS AND DISPLACEMENT CONSTRAINTS

A method for topological optimization of structures with discrete variables subjected to dynamic stress and displacement constraints is presented. By using the quasistatic method, the structure optimization problem under dynamic stress and displacement constraints is converted into one subjected to static stress and displacement constraints. The comprehensive algorithm for topological optimization of structures with discrete variables is used to find the optimum solution.

THE TOPOLOGICAL OPTIMIZATION FOR TRUSS STRUCTURES WITH STRESS CONSTRAINTS BASED ON THE EXIST-NULL COMBINED MODEL

A new exist-null combined model is proposed for the structural topology optimization. The model is applied to the topology optimization of the truss with stress constraints. Satisfactory computational result can be obtained with more rapid and more stable convergence as compared with the cross-sectional optimization. This work also shows that the presence of independent and continuous topological variable motivates the research of structural topology optimization.

THE ANALYSES OF THE THREE-DIMENSIONAL STRESS STRUCTURE NEAR THE CRACK TIP OF MODE I CT SPECIMENS IN ELASTICPLASTIC STATE(Ⅰ)—THE ANALYSES OF CONSTRAINT PARAMETERS AND FRACTURE PARAMETERS

In the present paper, three dimensional analyses of some general constraint parameters and fracture parameters near the crack tip of Mode I CT specimens in two different thicknesses are carried out by employing ADINA program. The results reveal that the constraints along the thickness direction are obviously separated into two parts: the keeping similar high constraint field (Z1) and rapid reducing constraints one(Z2). The two fields are experimentally confiremed to correspond to the smooth region and the shear lip on the fracture face respectively. So the three dimensional stress structure of Mode I specimens can be derived through discussing the two fields respectively. The distribution of the Crack Tip Opening Displacement (CTOD) along the thickness direction and the three dimensional distribution of the void growth ratio (Vg) near the crack tip are also obtained. The two fracture parameters are in similar trends along the thickness direction, and both of them can reflect the effect of thickness and that of the loading level to a certain degree.

考虑湿度应力的深部软岩隧道大变形控制研究

为探明深部高地应力软岩隧道大变形产生机理,制定适应大变形控制措施,以月直山隧道为工程依托,首先明确求解围岩形变压力与松动压力的Kastner与Caquot公式,基于岩体弹塑性力学与连续介质理论建立围岩湿度应力解析解,采用收敛-约束法绘制出3种围岩应力作用下围岩与初期支护特征曲线,分析断面变形过程中围岩与支护结构相互作用规律及3种应力占比演化规律。分别以混凝土与型钢钢架作为二衬支护结构对月直山隧道围岩稳定性进行计算分析,明确考虑湿度应力与松动压力条件下隧道二衬最优支护时机与支护参数,以支护结构安全系数FS评判出最优支护方案并对隧道软岩大变形进行治理。结果表明:当围岩径向位移达到550 mm时,仅考虑形变压力Pi时围岩对支护结构的压力P仅为0.813 MPa,考虑湿度应力Pw与松动压力Pa时P增大为1.372 MPa,湿度应力与松动应力总占比达40.7%,仅考虑形变压力而设计的支护结构不满足围岩稳定性要求;根据“卸压支护”理念,确定以“位移释放峰值upeak=0.325 m”与“间距d=0.7 m”作为增设第二层钢架的最佳支护时机与支护参数,现场二次钢架设置24天后使围岩变形收敛于50.8 mm,围岩大变形得到控制,研究成果可为今后相关隧道工程设计与施工提供参考。

约束状态下的有机玻璃零件的加工方法探讨

在生产实践中发现有机玻璃零件处于约束状态时,其所在环境存在较大温差变化,容易产生塑性变形,从而使产品不合格以致报废。该文对处于约束状态下的有机玻璃零件加工工艺进行了研究,重点对托盘组件加工过程中受约束状态下的有机玻璃盘形件加工工艺过程进行了改进、优化和实验验证,得出了约束状态下的有机玻璃零件加工工艺方案,并在实际加工生产中验证了此加工工艺方案的可行性。此方案对有机玻璃零件在自由状态和约束状态下的加工均具有指导意义,具有一定的推广价值。

周向约束对木材压缩吸能特性的影响

通过准静态压缩试验,考察轻木、泡桐、杉木、毛白杨4种木材在周向约束条件时,顺纹和横纹的压缩力学行为、破坏形态、吸能特性,并利用t检验分析其差异显著性。结果表明:①周向约束木材的顺纹压缩应力-应变曲线仍表现为“三阶段”特征,周向约束可抑制木材剪切扩展、大幅屈曲变形等非稳态破坏,曲线平台阶段应力基本与破坏强度持平。②泡桐、杉木、毛白杨顺纹压缩的吸能能力、平台阶段平稳性显著提高,其单位体积吸能值分别提高了15.51%、53.02%、48.15%,理想吸能率增大了35.93%、24.24%、86.00%。③周向约束木材的径向与弦向压缩力学行为、吸能特性相似,木材压头侧边纤维受试样中部拉伸和剪切作用发生竖向剥离,并沿压缩方向产生裂纹。④与无约束压缩相比,周向约束轻木、泡桐横纹压缩应力-应变曲线形状无明显变化,径向压缩单位体积吸能值分别提高了325.51%、182.60%,弦向压缩单位体积吸能值分别提高了430.57%、255.66%;杉木、毛白杨周向约束时横纹压缩应力-应变曲线变为无平台区的“两阶段”形式,理想吸能率均显著降低。

基于物理约束的分布式神经网络三维地应力预测模型

地应力是油气藏全生命周期中井壁稳定分析、水力压裂设计、地层出砂预防、套损预测防治和油气开采措施制定的重要基础参数.针对缺乏三维地震资料情况下的三维地应力场预测问题,以工区已钻井地应力测井解释结果为基础,建立了一种基于物理约束的分布式神经网络三维地应力预测模型.首先,采用测井解释方法获得工区已钻井地应力单井剖面,并通过Kriging插值构建三维地质模型;其次,将测井数据和三维地质模型的三维空间坐标喂入3个并行的全连接神经网络,引入地应力物理约束条件,提出了数据和物理双约束的条件,进而通过三维空间坐标实现三维地应力场的预测;再次,优选了数据和物理双约束的权重参数,与人工神经网络、支持向量回归、随机森林等三种机器学习模型以及克里金插值模型进行了对比;最后,评价了不同机器学习模型预测地应力的效果.研究结果表明:(1)研究区域的地应力满足潜在正断层应力状态,即垂向地应力>最大水平地应力>最小水平地应力;(2)数据和物理双约束权重参数取值对预测结果有显著影响,当权重参数λ=0.2时,三维地应力预测效果最优;(3)与人工神经网络、支持向量回归、随机森林、克里金插值等模型相比,本文模型预测得到的地层三维地应力和孔隙压力更准确,在工区内测试集预测得到的垂向地应力、最大水平地应力、最小水平地应力和地层孔隙压力的最大相对误差分别为0.63%、7.59%、7.16%、3.21%,而且,本文模型能够更加准确捕捉地应力梯度的三维变化特征,水平井段地应力和地层孔隙压力参数的正态分布特征明显.结论认为,物理约束的分布式神经网络模型能有效融合地形构造与地应力之间的联系,提高三维地应力预测的准确性和可解释性,为油田三维地应力场的预测提供了一种新的思路.

Dys-psychological Stress Effect on Expressions of P53 and NFκBp65 in Human Ovarian Carcinoma In Vivo

Objective： To investigate the dys-psychological stress effect on the growth of subcutaneous xenotransplanted tumor in nude mice bearing human epithelium ovarian carcinoma, and the influence on P53 and NFκBp65 expressions. Methods： The subcutaneous tumor xenografts were established by implanting human epithelium ovarian carcinoma tissues into nude mice and the dys-psychological stress model was established with restraint. The mice were randomized into the following four treatment groups with each group six mice respectively： tumor group （group A）, normal saline intraperitoneal injection; tumor with stress group （group B）, normal saline intraperitoneal injection; tumor therapy group （group C）, cisplatin intraperitoneal injection; and tumor therapy with stress group （group D）, cisplatin intraperitoneal injection. The expressions of P53 and NFκBp65 in tumor tissues were determined by Western blotting. Results： The expressions of P53 and NFκBp65 in each restraint group were enhanced compared with the control groups （P0.05）. Conclusion： The dys-psychological stress may induce the high expressions of P53 and NFκBp65 proteins and further promote tumor growth.

残余应力与拘束对GH4169合金疲劳及蠕变-疲劳裂纹扩展速率影响研究

为深入理解残余应力与拘束在疲劳载荷下的交互作用,以镍基高温合金GH4169为研究对象,选用紧凑拉伸(CT)试样,对不同拘束CT试样的上方施加不同大小的预加载荷从而在裂尖产生不同应力。将该应力作为残余应力,系统研究残余应力和拘束交互作用下GH4169合金的疲劳和蠕变–疲劳裂纹扩展速率。结果表明:随着裂尖残余压应力的增加,不同拘束下GH4169合金的疲劳和蠕变–疲劳裂纹扩展速率均降低。与低拘束试样相比,高拘束试样的疲劳和蠕变–疲劳裂纹扩展速率对残余应力的变化更加敏感,这主要与裂尖Mises应力和垂直于裂纹扩展方向的正应力有关。与疲劳裂纹扩展速率相比,蠕变-疲劳裂纹扩展速率对残余应力的变化更加敏感。

ALTERNATING OPTIMIZATION METHOD FOR ISOGEOMETRIC TOPOLOGY OPTIMIZATION WITH STRESS CONSTRAINTS

Topology optimization (TO) has developed rapidly recently. However, topology optimization with stress constraints still faces many challenges due to its highly non-linear properties which will cause inefficient computation, iterative oscillation, and convergence guarantee problems. At the same time, isogeometric analysis (IGA) is accepted by more and more researchers, and it has become one important tool in the field of topology optimization because of its high fidelity. In this paper, we focus on topology optimization with stress constraints based on isogeometric analysis to improve computation efficiency and stability. A new hybrid solver combining the alternating direction method of multipliers and the method of moving asymptotes (ADMM-MMA) is proposed to solve this problem. We first generate an initial feasible point by alternating direction method of multipliers (ADMM) in virtue of the rapid initial descent property. After that, we adopt the method of moving asymptotes (MMA) to get the final results. Several benchmark examples are used to verify the proposed method, and the results show its feasibility and effectiveness.

圆环非线性恢复力的梁约束模型建模

圆环隔振器是一种以圆环结构为基础的非线性隔振器,圆环结构在压缩变形过程中会受到压力和环面拉伸的耦合作用,从而产生非线性恢复力,对圆环结构非线性恢复力的精确建模是研究隔振器性能的关键。将圆环结构等分为多段曲梁,利用梁约束模型对每段曲梁建立计及几何非线性的力-位移关系模型,结合曲梁间的力传递关系和几何约束关系,建立了圆环整体在压缩过程中的非线性恢复力模型,并计算了圆环变形过程中所有分段点处的正应力。通过电子伺服疲劳试验机对圆环结构在压缩过程中的恢复力进行了测量,验证了梁约束模型的建模精度。研究结果表明,利用梁约束模型可以表征圆环结构非线性恢复力特性,其建模精度与椭圆积分法相当,而模型表达式和求解过程都比椭圆积分法简洁。圆环在压缩量最大时正应力最大,此时最大正应力在圆环的上下端点。梁约束模型的建模精度随着分段数的增加而提高,当分段数大于12时,梁约束模型的恢复力计算误差小于2%。

混凝土构件温度与收缩应力敏感参数筛选方法

混凝土温度与收缩应力受多种因素影响,随着构件尺寸和浇筑龄期等改变,敏感参数会发生转化。在混凝土温度及收缩裂缝的理论计算、数值分析和裂缝控制工艺研究方面,若敏感参数判断不当,得到的分析结果会偏差较大,制定的裂缝控制工艺较难具有针对性。文中提出主导约束概念,即2种以上约束同时存在时,最大拉应力基本由主导约束决定,影响混凝土温度与收缩应力的敏感参数也存在于主导约束相关参数中。按照材料构成、温度梯度和外部约束3个不同约束形式建立混凝土构件模型,通过有限元数值计算,分析各个参数值在不同约束中的敏感特性,获得常见混凝土构件温度收缩应力的敏感参数。在此基础上结合参数取值及变化范围,形成影响常见混凝土构件温度收缩应力敏感参数的筛选方法。

水封隧道内天然气管道受力问题研究

长输天然气管道是我国能源发展的生命线,国内先后建成投用了西气东输一线、西气东输二线等长输管道。不可避免要与黄河、长江等发生交叉穿越,形成控制性穿越隧道。其中一些为水封隧道。因为管道在水中会产生浮力。造成注水前后管道的受力情况发生变化,水封隧道中的管道约束成为一个棘手的课题。根据某处水封隧道内管道的现场检测过程,对隧道内管道在注水前后的受力情况进行了研究。

超长结构温度应力问题分析与探讨

超长结构的温度应力是超长结构设计中必须解决的重要问题。本文以某大型综合体为例,系统介绍了超长结构温差计算方法,以及YJK软件温度应力分析的成果,并提出了控制超长结构裂缝的相应措施,可供工程设计参考。分析结果表明,温度应力与结构约束状况有直接关系,楼板所受约束越大,楼板温度应力就越大。

考虑地基弹性约束的地下超长混凝土顶板裂缝控制研究

对于地下超长混凝土结构,顶板的裂缝控制显得尤为重要。论文针对地下超长混凝土结构的底板施加弹簧约束,分析了不同弹簧刚度约束情况下的温度应力变化情况。结果表明,通过减小地基土对筏板的摩擦约束,可以显著减小温度应力,同时,对地下超长混凝土结构裂缝控制措施进行了总结归纳。

某空间螺旋塔斜拉桥合理结构体系研究

某斜拉桥方案采用反对称螺旋形桥塔,空间四索面,造型较为新颖。由于桥梁结构较为复杂,为选用适宜的结构体系,基于桥梁结构的受力形态,在综合比较了漂浮体系、半漂浮体系、半固结体系的优劣后,确定半漂浮体系为最佳方案,并进一步讨论了地震作用下该桥合理的约束体系。这一流程对解决类似复杂结构桥梁合理结构体系的问题有一定参考价值。

Topology Optimization with Aperiodic Load Fatigue Constraints Based on Bidirectional Evolutionary Structural Optimization

Because of descriptive nonlinearity and computational inefficiency,topology optimization with fatigue life under aperiodic loads has developed slowly.A fatigue constraint topology optimization method based on bidirectional evolutionary structural optimization(BESO)under an aperiodic load is proposed in this paper.In viewof the severe nonlinearity of fatigue damagewith respect to design variables,effective stress cycles are extracted through transient dynamic analysis.Based on the Miner cumulative damage theory and life requirements,a fatigue constraint is first quantified and then transformed into a stress problem.Then,a normalized termination criterion is proposed by approximatemaximum stress measured by global stress using a P-normaggregation function.Finally,optimization examples show that the proposed algorithm can not only meet the requirements of fatigue life but also obtain a reasonable configuration.