连续体结构拓扑优化改进的敏度修正方法研究

为了消除拓扑优化中的棋盘格现象,在对常用敏度过滤方法的研究基础上,提出了一种新型敏度修正方法来解决数值不稳定性的问题。该方法通过设置中心单元过滤权重对拓扑优化结果进行控制。利用经典的柔度最小化数值算例研究了新型敏度修正方法对拓扑优化结果的影响,数值分析结果表明,该方法能达到消除棋盘格、网格依赖性现象以及避免边界过度磨平的目的。     

一种考虑密度补偿的变过滤半径敏度过滤方法

固定过滤半径的敏度过滤方法可以有效解决棋盘格现象和网格依赖性,但处理后拓扑优化结果普遍存在边界扩散现象,图形边缘存在大量的灰度单元。提出了一种考虑密度补偿的变过滤半径敏度过滤方法,即正向补偿相对密度为0.5~1的单元,反向补偿相对密度为0~0.5的单元,同时在拓扑优化计算的后期逐步缩小过滤半径至1。结合固体各向同性惩罚微结构模型,利用经典结构柔度最小化算例验证可行性。研究结果表明,考虑密度补偿的变过滤半径敏度过滤方法能够消除棋盘格现象,体现了网格无关性,拓扑优化结果具有清晰的边界,且优化效率和优化效果明显提升。     

连续体结构拓扑优化敏度修正方法研究

针对敏度过滤法拓扑优化结果存在边界扩散现象和过滤半径过大时图形过度磨平问题,提出一种新的敏度修正方法,将中心单元周围8个单元根据位置的不同分为两类,采用不同的加权系数,保持中心单元原目标函数敏度值的权重固定,三类单元加权求和。利用经典柔度最小化算例验证新的敏度修正方法的有效性。研究结果表明,新的敏度修正方法可有效消除棋盘格现象,体现较好的网格无关性,拓扑优化结果边界清晰,优化效果优于敏度过滤法。     

一种改进的密度过滤拓扑优化方法

目前拓扑优化的密度过滤是基于单元距离的卷积算法解决有限元的棋盘格问题，但其产生大量灰色模糊区域（非0-1解），不利于后续实际工程应用，往往需要后处理才能得到清晰的结果特征。为提高拓扑优化效率，同时减少灰色区域的影响，提出一种各向异性的密度过滤算法。基于图像存在不连续特征的概念，拓扑优化结果得到的边界也应该保留一定的不连续性，因此各向异性的密度过滤将有限元之间密度差值和距离作为权重系数，有效减少边界的单元生成灰色区域的可能性，减少拓扑优化的后处理工作。利用各种常见的拓扑优化模型进行验证。结果表明：所提方法可有效解决拓扑优化常见的棋盘格、网格依赖性以及灰色模糊区域的情况；与传统的密度过滤方法相比，所提方法仅用15%的时间即可得到目标柔度降低10%的拓扑优化结果。     

基于扩散张量偏微分方程的拓扑优化过滤方法

为了有效抑制拓扑优化结果中出现的数值不稳定现象,提出了基于扩散张量偏微分方程的初边值模型,考虑Neumann边界条件,实现边界扩展,并采用有限差分法求解。将有限差分模型与拓扑优化循环相融合,分别实现单元密度和目标函数灵敏度的过滤处理。算例验证了方法的有效性与灵活性,结果表明：目标函数灵敏度过滤方法能保持边界清晰度,但需要较多的过滤迭代次数;单元密度过滤方法的计算效率较高,但结果边界模糊。     

双向插值模式连续体结构拓扑优化设计

针对传统拓扑优化中对中间密度单元处理的单向(惩罚)性,提出一种由阈值决定中间密度单元处理方式的双向插值模型(Bi-Directional Interpolation Model,BDIM),建立基于BDIM模式的优化模型。利用拓扑优化梯度投影法,结合算例,对比分析传统插值模型、只对敏度进行双向插值模型和同时对刚度和敏度双向插值模型优化。结果表明,只对敏度进行双向插值模型具有无需过滤、全局收敛、边界清晰的多重优点。     

基于双向插值模式的空间扩张拓扑优化

针对传统拓扑优化中对中间密度单元处理的单向性及初始设计域选择过裕而使求解规模增大的问题,提出一种基于双向插值模式的空间扩张拓扑优化。建立了双向插值模式拓扑优化问题的数学模型,构建了基于边界单元敏度信息的空间扩张策略,并提出降低空间扩张拓扑优化问题求解规模的技术,最后通过算例验证了其可行性。算例表明,利用空间扩张策略仅对敏度进行插值的模式相对于基于刚度和敏度进行双向插值的模式和传统带惩罚指数的固体各向同性微结构模式,在优化设计中更具有全局性,不用过滤便可以高效地得到边界清晰的拓扑优化结果,且具有较小的目标设计值和较少的迭代步数。     

基于不同过滤函数的ICM拓扑优化混合建模方法

基于独立连续映射（ICM）法中设计变量独立性的特点，提出一种混合插值建模方法。该方法基于两类常见插值函数分别对单元体积、单元刚度阵进行过滤识别，通过两两组合，得到四种不同的拓扑优化模型。四种模型中，除体积目标函数一、二阶导数表达式不同外，它们的结构响应量的敏度分析和优化建模方法相同，从而保证了优化求解算法的一致性。通过拓扑优化数值算例对比分析了不同模型参数下的拓扑优化结果，结果表明，混合建模方法在连续体结构拓扑优化建模中具有可行性和有效性。     

稳态热传导下的连续体结构拓扑优化

在稳态热传导连续体拓扑优化中,提出单元总热能、节点温度、区域内节点温度平方和三类不同性能指标,推导三类指标的伴随法敏度分析公式。基于独立连续映射法建立以三类指标为约束的体积最小化模型,应用过滤技术克服拓扑优化的数值不稳定性问题,实现了稳态热传导下的连续体拓扑优化设计。通过数值算例对优化结果进行讨论,其结果验证了方法和模型的可行性和有效性。     

基于节点密度插值的多材料柔顺机构拓扑优化

基于弹簧模型和节点密度插值的固体各向同性材料惩罚模型(Solid isotropic material with penalization,SIMP)方法,给出了一种用于多材料柔顺机构拓扑优化设计的分层优化方法.首先,以输出端位移最大化为目标以各种材料相应的体积占比为约束,建立了多材料柔顺机构拓扑优化模型;其次,采用节点密度插值,构造了设计区域内具有C0连续性的密度场函数,给出了目标函数和约束的敏度解析表达式,使用过滤半径自适应迭代的敏度过滤方案,消除了节点密度插值法中的层化现象;再次,给出了一种分层优化策略用于求解多材料柔顺机构拓扑优化问题;最后,分别用典型的二维和三维柔顺机构拓扑优化问题验证了所提出方法的有效性,并分析了设计参数对优化结果的影响机制.     

Minimal Realization of Linear Graph Models for Multi-physics Systems

An engineering system may consist of several different types of components,belonging to such physical"domains"as mechanical,electrical,fluid,and thermal.It is t...     

INTEGRAL EQUATION METHOD＇S APPLICATION IN HOLE-EDGE STRESS OF COMPOSITE MATERIAL PLATE WITH DIFFERENT SHAPED HOLES

The strength of composite plate with different hole-shapes is always one of the most important but complicated issues in the application of the composite material. The holes will lead to mutations and discontinuity to the structure. So the hole-edge stress concentration is always a serious phenomenon. And the phenomenon makes the structure strength decrease very quickly to form dangerous weak points. Most partial damage begins from these weak points. According to the complex variable functions theory, the accurate boundary condition of composite plate with different hole-shapes is founded by conformal mapping method to settle the boundary condition problem of complex hole-shapes. Composite plate with commonly hole-shapes in engineering is studied by several complex variable stress fimction. The boundary integral equations are founded based on exact boundary conditions. Then the exact hole-edge stress analytic solution of composite plate with rectangle holes and wing manholes is resolved. Both of offset axis loadings and its influences on the stress concentration coefficient of the hole-edge are discussed. And comparisons of different loads along various offset axis on the hole-edge stress distribution of orthotropic plate with rectangle hole or wing manhole are made. It can be concluded that hole-edge with continuous variable curvatures might help to decrease the stress concentration coefficient; and smaller angle of outer load and fiber can decrease the stress peak value.     

Non-monotonic material contrast in scanning ion and scanning electron images

30 keV Ga⁺ focused ion beam induced secondary electron (iSE) imaging was used to determine the relative contrast between several materials. The iSE signal compared from C, Si, Al, Ti, Cr, Ni, Cu, Mo, Ag, and W metal layers does not decrease with an increase in target atomic number Z₂, and shows a non-monotonic relationship between contrast and Z₂. The non-monotonic relationship is attributed to periodic fluctuations of the stopping power and sputter yield inherent to the ion–solid interactions. In addition, material contrast from electron-induced secondary electron (eSE) and backscattered electron (BSE) images using scanning electron microscopy (SEM) also shows non-monotonic contrast as a function of Z₂, following the periodic behavior of the stopping power for electron–solid interactions. A comparison of the iSE and eSE results shows similar relative contrast between the metal layers, and not complementary contrast as conventionally understood. These similarities in the contrast behavior can be attributed to similarities in the periodic and non-monotonic function defined by incident particle–solid interaction theory.     

Application of Feature Extraction through Convolution Neural Networks and SVM Classifier for Robust Grading of Apples

This paper proposes a novel grading method of apples,in an automated grading device that uses convolutional neural networks to extract the size,color,texture,an...     

分布动态载荷识别的抗噪处理

针对正交多项式频域法在用多种响应对矩形薄板进行载荷识别中抗噪性较差的问题,综合运用平均法、矩阵预处理和奇异值截断法等方法对之进行改善,并引入空间映射的思想,将该方法的应用范围拓展为复杂的模型.利用仿真算例,证实了该方法具有较好的抗噪性.     

基于MELTAC-N平台的核电厂安全级DCS环网研究与测试

针对工程实践中环网通讯相关问题的处理缺乏理论基础及国产化安全级DCS平台的开发缺乏成熟经验借鉴问题,对基于MELTAC-N平台核电厂安全级DCS环网的软硬件实现进行了研究。提出了安全级DCS环网双环网冗余设计、光切换开关设计等硬件设计方法,以及以RPR协议为基础,采用全数据收发策略的软件设计方法。在CPR1000安全级DCS平台上对安全级DCS环网的可靠性及实时性进行了评价,并进行了容错能力、响应时间及响应时间稳定性测试验证实验。结果表明,基于MELTAC-N平台安全级DCS环网软硬件设计具有较好的容错能力及响应时间稳定性。     

Short-Term Relay Quality Prediction Algorithm Based on Long and Short-Term Memory

The fraction defective of semi-finished products is predicted to optimize the process of relay production lines, by which production quality and productivity ar...     

End-to-End Multiview Gesture Recognition for Autonomous Car Parking System

The use of hand gestures can be the most intuitive human-machine interaction medium.The early approaches for hand gesture recognition used device-based methods....     

The laboratory simulation of abrasive wear

Abrasive wear has long been recognised as one of the most potentially serious tribological problems facing the operators of many types of plant and machinery; several industrial surveys have indicated that wear by abrasion can be responsible for more than 50% of unscheduled machine and plant stoppages. Locating the operating point of a tribological contact in an appropriate operational ‚map’︁ can provide a useful guide to the likely nature and origins of the surface degradation experienced in use, though care must be exercised in choosing the most suitable parameters for the axes of the plot. Laboratory testing of materials and simulations of machine contacts are carried out for a number of purposes; at one level for the very practical aims of ranking candidate materials or surface hardening treatments in order of their wear resistance, or in an attempt to predict wear lives under field conditions. More fundamentally, tests may be aimed at elucidating the essential physical mechanisms of surface damage and loss, with the longer term aim of building an analytical and predictive model of the wear process itself. In many cases, component surface damage is brought about by the ingress of hard, particulate matter into machine bearing or sealing clearances. These may be running dry although, more usually, a lubricant or service fluid is present at the interface. A number of standardised wear test geometries and procedures have been established for both two- and three-body wear situations, and these are briefly described. Although abrasive wear is often modelled as following an ‚Archard’︁ equation (i.e. a linear increase in material loss with both load and time, and an inverse dependence on specimen hardness) both industrial experience and laboratory tests of particularly lubricated contacts show that this is not always the case: increasing the hardness differential in an abrasively contaminated lubricated pair may not always reduce the rate of damage to the harder surface.     

ANGULAR DISTORTION ALLOWABLE VALUE AND ASSESS METHOD OF WELD ON COKE TOWER

A graph as the new engineering method for estimate the safety of bulging deformation of coke tower is proposed. Through stresses analysis of circumferential weld of coke tower and comparing the stresses produced by pressure with heat stress of steady state, residual stress, bending stress produced by both itself weight and wind loads, it showed that the stresses produced by pressure on the angle distortion are the main factor of equivalent stress of the combined stress. After comparing four kinds of stress controlling conditions, the relation to stress with depth of angular distortion, grade of curvature of angular distortion and half of region of angular distortion has been inferred. Graph of deformation allowable value of coke tower for different condition by angular distortion and half of region of angular distortion has been plotted. The five steps for its engineering use have been explained. The lighter the grade of curvature is, the larger of bulge allowance, may be, and the bigger of depth of angular distortion may pose too. For the coke tower with a popular structure of Dg 5 400 mm×28 mm, the result by graph is nearly more than the result of two formulas formed by other research, the error is less than 7.0%. But, the graph can be easily applied to different size of angular distortion.