结构频带激励下的整体动响应优化

结合频响函数的性质,采用目标频带内各模态峰值响应的 -范数作为整体响应水平的衡量指标,将等效目标函数的灵敏度表示为固有频率和振型灵敏度的函数,进而采用基于梯度的迭代方法求解,实现结构在宽频激励下的整体动响应优化,该方法适合于多频带的响应控制。此外,在频带响应优化模型的基础上,提出了通过增加频率约束,使之能应用于密集频率结构,避免迭代过程中的密频和重频现象。最后通过桁架截面优化和形状优化的数值算例,表明了本文提出方法的合理性和有效性。     

考虑结构稳定性的变密度拓扑优化方法

将稳定性问题引入传统变密度法中,可实现包含稳定性约束的平面模型结构拓扑优化。以单元相对密度为设计变量,结构柔度最小为目标函数,结构体积和失稳载荷因子为约束条件建立优化问题数学模型,提出了一种考虑结构稳定性的变密度拓扑优化方法。通过分析结构柔度、体积、失稳载荷因子对设计变量的灵敏度,并基于拉格朗日乘子法和Kuhn-Tucker条件,推导了优化问题的迭代准则。同时,利用基于约束条件的泰勒展开式求解优化准则中的拉格朗日乘子。通过推导平面四节点四边形单元几何刚度矩阵的显式表达式,得到了优化准则中的几何应变能。最后,通过算例对提出的方法进行了验证,并与不考虑稳定性的传统变密度拓扑优化方法进行对比,结果表明该方法能显著提高拓扑优化结果的稳定性。研究结果对细长受压结构的优化设计有重要指导意义,对结构的稳定性设计有一定参考价值。     

基于模态柔度矩阵的结构损伤识别

基于模型修正技术的结构损伤识别方法,无需事先知晓结构的损伤位置,比仪器直接探测更具优势。模型修正大多以模态频率和振型为修正目标。然而,结构损伤对系统的模态频率和振型影响较小,采用模态频率和振型为目标的传统修正方法,难以识别出结构的损伤。为此,引入对结构损伤极为灵敏的模态柔度矩阵,研究以模态柔度矩阵为目标函数的损伤识别方法。选取某带孔的矩形长铁片为研究对象,沿其纵向等分为31块,计算模态柔度矩阵关于各等效模量相对量的灵敏度。结合灵敏度矩阵,利用实测和有限元模型间的柔度矩阵残差建立目标函数,并引入正则化方法求解目标函数的超定方程组。经过9次迭代目标函数收敛,损伤识别结果与实际值保持高度一致,从而验证该方法的正确性和实用性。     

以动柔度为目标的结构阻尼材料层拓扑优化

为讨论附加阻尼材料层壳体结构在受简谐激励作用时阻尼材料最优分布,采用类似SIMP方法的人工阻尼材料模型构造拓扑优化模型。设计目标为给定阻尼材料用量最小化的结构动柔度,以阻尼材料相对密度作为设计变量。对结构呈现非比例阻尼特性,采用在状态空间下降阶后的复模态叠加法计算结构稳态响应及动柔度。优化过程中用伴随变量法对动柔度进行灵敏度分析。通过拓扑优化算例,验证所提模型及方法的合理性与有效性。     

基于局部静力测试的约束子结构修正法

针对局部子结构为修正对象的情况,提出只利用整体结构中局部子结构部分的静力位移即可精确修正子结构模型的约束子结构方法。首先利用静力测试获得局部子结构所对应的局部柔度矩阵,通过在子结构边界处施加虚拟固定支座,把子结构从整体结构中隔离出来成为约束子结构,同时构造出该约束子结构相应的柔度矩阵。然后利用柔度扰动新方法优化修正约束子结构,即等同于修正相应的子结构模型,从而可对该子结构的损伤状况作出评估。以一个平面桁架结构为例对所提方法进行了验证。结果表明,所提方法合理可靠,计算简单快捷且精度良好。     

基于整体应变的柔顺机构多目标拓扑优化设计

针对传统方法在拓扑优化中会出现局部应变集中的缺陷,提出了一种基于整体有效应变的柔顺机构多目标拓扑优化方法.该方法不再以应变能最小作为目标函数,而是以整体有效应变最小来表征机构的刚度最大,从而将应变均匀地分布在整个系统中.考虑到柔顺机构对刚度和柔度的要求,以整体有效应变最小化和互应变能最大化为目标建立了多目标拓扑优化模型,在变密度法的基础上,利用妥协规划法研究了柔顺机构的多目标优化问题.其中,目标函数的灵敏度分析采用伴随矩阵求解方法,并采用移动渐进算法求解拓扑优化问题.最后,通过柔顺夹钳设计的数值算例来说明该方法的有效性和先进性.结果表明,该方法能够减少基于传统优化方法的结构中的局部大应变,从而有效提升柔顺机构的可靠性.     

基于动柔度变化的结构损伤检测

采用一个四自由度的弹簧－质量系统。通过数据计算表明以动柔度作为损伤识别参数比单独用固有频率或振型时的灵敏度高。本文提出了以动柔变化矢量为损伤识别参数,采用神经网络方法建立了动柔度变化矢量与损伤位置和损伤量的关系,解决了结构的损伤定位和定量识别问题,用一个混凝土简支梁模型对该方法进行了验证,说明该方法是切实可行的。     

基于多分辨率-多边形单元建模策略的多材料结构动刚度拓扑优化方法

利用多边形有限单元的高精度求解优势,融合多分辨率拓扑优化方法,实现粗糙位移网格条件下的高分辨率构型设计,由此提出多材料结构动刚度问题的拓扑优化方法。将多边形单元(位移场求解单元)劈分为精细的小单元,构造设计变量与密度变量的重叠网格,形成多分辨率-多边形单元的优化建模策略;以平均动柔度最小化为目标和多材料的体积占比为约束,建立多材料结构的动力学拓扑优化模型,通过HHT-α方法求解结构动响应,采用伴随变量法推导目标函数和约束的灵敏度表达式,利用基于敏度分离技术的ZPR设计变量更新方案构建多区域体积约束问题的优化迭代格式;通过典型数值算例分析优化方法的可行性和动态载荷作用时间对优化结果的影响机制。     

指定频带简谐激励下约束阻尼结构拓扑优化

针对指定频带简谐激励下约束阻尼结构拓扑优化问题,建立以共振峰值平方最小为优化目标,约束阻尼材料用量为约束条件的约束阻尼板拓扑优化模型。优化过程中考虑约束阻尼结构改变对结构阻尼影响较大,将模态阻尼比灵敏度引入优化目标的灵敏度计算中,使优化目标灵敏度计算更准确合理。用渐进优化算法求解拓扑优化模型。给出数值算例,并实验验证优化模型及灵敏度分析方法的有效性。     

基于双值参数化方法且考虑制造约束的炭纤维复合材料铺层优化

基于梯度的优化方法对炭纤维复合材料层合板的铺层数量和顺序进行优化。优化问题中以铺层质量为目标,并以刚度和制造约束为约束。采用改进双值参数化方法对铺层的材料性能进行插值,并基于凸规划对偶算法对优化问题进行求解。为了适应凸规划对偶算法的特点,将关于铺层角度的制造约束表述为少量非线性约束。同时引入离散度约束和惩罚指数以消除优化结果中的中间变量。算例结果验证了该优化方法的有效性。     

基于普通光纤的螺旋缠绕式准分布光纤传感器的研究

针对用传统测试方法难以有效实现大型结构应力状态的分布测试问题,提出采用螺旋缠绕式光纤应变传感器进行测试的新方法。建立了此种光纤传感器的理论模型,对其传感原理进行了理论分析,并进行了实验研究,证明了其可行性。该传感测试方法为大型结构特别是预应力混凝土结构中预应力筋的应力分布测试提供了新的解决思路。     

Evaluation of film adhesion to substrates by means of surface acoustic wave dispersion

For thin film structures acoustically classified as slow-on-fast systems, modeling and evaluation of their interfacial condition are known to be very complex and difficult due to dispersion and multi-mode excitation of acoustic waves. This paper presents a quantitative model and a reliable measurement procedure established for adhesion evaluation of such film structures. An effective interface model employing a virtual intermediate layer is utilized for the dispersion prediction of the surface acoustic wave, which is affected by various interfacial conditions. Through acoustic microscopy experiments, this model presents a potential method to classify the bonding condition. Comparisons with a destructive scratch test and an acoustic imaging verify the failure mode of the film structure.     

Finite Element Computation of Woven Ply Laminated Composite Structures up to Rupture

For unidirectional ply laminates, the great diversity of the damage mechanisms and their patterns of evolution make it extremely difficult to estimate the strength margins. In the case of woven ply laminates, the number of damage mechanisms is fairly small (no transverse rupture occurs and the material has a greater resistance to delamination) and the behaviour of the material is fairly simple to model up to rupture. In this study, a numerical model for woven ply laminated composite structures up to rupture is developed. The implementation is performed in a Euler Backward scheme and the consistent tangent stiffness matrix is calculated. Comparison with some experiments on structures are made and the model predicts these experiments well.     

Design and optimization of symmetric laminated composites using a variable neighbourhood search-based model

The development of society is still marked by the need for lighter and stronger structures. The materials that respond best to these needs are composite materials. Designing composite materials is difficult as it involves designing the geometry and their composition. Traditionally, the design tasks have been based on approximate methods; the possibility for creating composite materials is almost unlimited, characterization by testing is very expensive and it is difficult to apply the results to other contexts. This article proposes a variable neighbourhood search-based model for the design of symmetric laminated composites, a general encoding for the design of composites, an evaluation function that has taken into consideration cost and safety criteria in design, the neighbourhood structures and a set of local search operators. The proposed model has been applied to different real-world problems and the results have been compared with other well-known design methods.     

Model-Based Estimation of Thin Multi-Layered Media Using Ultrasonic Measurements

In ultrasonic measurement situations, when dealing with media of multi-layered structures consisting of 1 or more thin layers, analysis of the measured ultrasonic waveform can be difficult because of overlapping and reverberant echoes. Information from the individual layers is then difficult to extract because the individual echoes cannot be detected. In this study, we use a parametric layer model to analyze the multi-layered material in a system identification approach. The parameters of the model are connected to physical properties of the investigated material, e.g., the reflection coefficients, the time-of-flight, and the attenuation. The main advantage using this model is that the complexity of the model is connected to the number of layers rather than the number of observable echoes in the received ultrasonic waveform. A system of linear equations is presented, giving the opportunity to find the model for both pulse-echo and through-transmission measurements. A thorough effort is made on the parameter estimation and optimization algorithm. The model is validated with practical measurements on a 3-layered structure using both pulse-echo and through-transmission techniques. The 3-layered material consists of a thin embedded middle layer with the time-of-flight in that layer shorter than the emitted signal?s time support, giving rise to overlapping echoes. Finally the relation between the model parameters and physical properties of the material is established.     

Mathematical modelling of structural behaviour during earthquakes

The dynamical behaviour of structures can be modelled and simulated satisfactorily in the linear and slightly nonlinear ranges using finite elements and other analytical models in conjunction with modern computers. However, the highly nonlinear behaviour of structures remains to be studied further. The nonlinear response of complex structures which have been damaged by strong-motion earthquakes lies in this area. It is extremely difficult to collect sufficient field or laboratory data for the construction of accurate mathematical models of such structures for practical applications. This is partly due to the fact that the failure behaviour of a given structure is highly load-history dependent. In the absence of reliable analytical tools, system identification techniques may occasionally be applied to verify and/or update the mathematical model of a structure. The development of mathematical models useful for analysis of structural behaviour to earthquake excitation is an area too large to be covered in detail by a single review. In this paper, an attempt is made to critically review available mathematical models in the random earthquake response analysis of structures. By random, we refer to the excitation, to the properties of the structure itself, or to both. We are especially interested in those models dealing with slightly to highly nonlinear behaviour. Some recent work which utilizes these analytical techniques is highlighted. Also included is a review of system identification techniques as applied to structures. The concept of damage accumulation is mentioned, and a damage index is discussed which may be used in conjunction with an analytical model. A selective bibliography is also given for a more complete introduction into the areas discussed herein.     

基于应用程序交互访问技术的桥梁有限元模型修正研究

传统的有限元模型修正方法对于具有复杂多自由体系的大型桥梁结构显得束手无策,其中一个重要的原因是大型桥梁结构体系很难用有限元编程精确地表达,难以建立完整的或者缩聚的质量矩阵和刚度矩阵。该文开发了基于应用程序交互访问的有限元模型修正模式,首先在Strand7软件中建立初始的有限元模型,然后利用MATLAB建立迭代程序并调用Strand7软件,通过读写Strand7中的物理参数来更新模型,实现了大型桥梁结构有限元模型修正。该文对一座实桥进行多参考点脉冲锤击法模态试验和静载试验,基于获得的静动力试验数据和Strand7有限元模型分析结果,引入损伤函数的概念识别得到了该桥各梁的分段刚度,成功地实现了单元层次的参数识别。     

应用Deeplab V3+网络实现小儿髋关节超声图像识别

利用Graf法进行发育性髋关节发育不良(Developmental Dysplasia of the Hip, DDH)诊断时主要依靠骨-软骨交界面、股骨头、滑膜皱襞、关节囊及软骨膜、盂唇、软骨顶、骨性顶这7个解剖结构进行解剖验证,而初级医生对上述结构识别困难,因此文章提出了一种基于DeeplabV3+的网络模型用于7个结构的分割识别。首先对纳入的106例图像进行手动标记和预处理,之后将其分别输入DeeplabV3+和U-Net两种网络模型中,最终对其预测图表现和分割性能进行比较。与目前DDH图像分割中常用且表现优越的U-Net网络相比,DeeplabV3+网络的预测图包含的结构较多,边界分割也较清晰,其图像分割评价指标如相似性系数、豪斯多夫距离和平均豪斯多夫距离平均值的表现也优于U-Net网络。文章利用DeeplabV3+网络实现了DDH超声图像的7个结构分割,对临床医生进行后续图像的角度测量和分型诊断具有重要意义。     

可展开薄膜结构折叠方式和展开过程研究

薄膜材料广泛运用于太空可展开航天器,薄膜的折叠和展开分析是其中的关键技术。从树叶的仿生学出发,提出薄膜结构的几种折叠方式。建立弹簧-质点系统描述薄膜材料,模拟薄膜结构的展开过程。薄膜展开过程中薄膜不可避免地发生自身的接触碰撞,提出了自接触对的判别准则,采用罚函数法有效地解决薄膜自接触问题。分析了三种折叠方式的薄膜的展开过程,并进行比较,叶外折叠方式和Miura折叠法比较适合平面薄膜的折叠。