基于动响应约束的结构材料优化设计

针对于随机荷载作用下动响应为约束的结构材料优化问题,基于结构拓扑优化思想,提出了一种变动响应约束的结构材料优化方法。采用分式有理式和幂函数识别结构材料单元特性参数,以微观单元拓扑变量倒数为设计变量,导出了频率及振型对微观单元设计变量的一阶导数,进而得到了随机荷载作用下结构均方响应的一阶近似展开式。结合变约束限的思想,建立了以结构质量作为目标函数,均方响应作为约束条件的连续体微结构拓扑优化近似模型,并采用对偶方法进行求解。对典型结构进行了考虑单个和多个动响应约束的结构材料优化设计,优化所得结果验证了该方法的有效性和可行性。     

高频变流诱发的电主轴高次谐波振动及其抑制方法

高速电主轴已在超高速磨削中获得成功应用,但由高频变流诱发的高次谐波机电耦合振动严重影响磨削系统的稳定性和磨削质量,而其动力学机理尚不明确.利用传统的砂轮转子机械模型尚不能定量解释高频变流诱发高次谐波机电耦合振动的原因.在传统砂轮转子机械模型的基础上建立了"逆变器-电主轴-砂轮-磨削载荷"系统的机电耦合数学模型.利用该模型研究了启动、升速及突变磨削载荷等条件下磨削系统的几类典型非平稳过渡过程,并在超高速平面磨床上进行了试验研究.揭示了功率开关高频变流诱发超高速磨削系统机电耦合振动的物理机理,提出了通过优化逆变器工作参数抑制机电耦合振动的具体策略.     

简谐激励下板壳结构加强筋仿生布局降噪方法

分析叶脉脉序形态的形成机理及构型规律,提取叶脉脉序生长的结构力学准则。以最小弹性应变能与抑制最大剪应力为主及次脉生长准则、以矢量平衡方程为脉序分歧准则建立具有叶脉分枝结构特征的板壳加强结构仿生设计模型。以降低谐振结构声辐射为目标,利用相似原理提出适合板壳结构加强筋布局设计的仿生脉序生长算法。并用典型薄板结构进行加强筋分布设计,验证板壳加强结构仿生布局方法在降噪中的可行性及有效性。     

Topology optimization in magnetic fields using the homogenization design method

To improve the performance of electric machinery, it is necessary to obtain the optimal topology of a structure in magnetic fields. The homogenization design method is applied to obtain the optimal topology. In the method, the change of inner hole size and rotational angle of unit cell determines the optimal material distribution in a design domain and this distribution defines an optimal topology. The objective function is defined as maximizing magnetic mean compliance (MMC). This is the same as maximizing magnetic vector potential and effective to improve the performance of electomagnet. The analysis and optimization is performed based on three‐dimensional hexahedral elements. This design method is applied to the H‐shaped electromagnet (H‐magnet). Copyright © 2000 John Wiley & Sons, Ltd.     

Topology optimization for unsteady flow

A computational methodology for optimizing the conceptual layout of unsteady flow problems at low Reynolds numbers is presented. The geometry of the design is described by the spatial distribution of a fictitious material with continuously varying porosity. The flow is predicted by a stabilized finite element formulation of the incompressible Navier–Stokes equations. A Brinkman penalization is used to enforce zero‐velocities in solid material. The resulting parameter optimization problem is solved by a non‐linear programming method. The paper studies the feasibility of the material interpolation approach for optimizing the topology of unsteady flow problems. The derivation of the governing equations and the adjoint sensitivity analysis are presented. A design‐dependent stabilization scheme is introduced to mitigate numerical instabilities in porous material. The emergence of non‐physical artifacts in the optimized material distribution is observed and linked to an insufficient resolution of the flow field and an improper representation of the pressure field within solid material by the Brinkman penalization. Two numerical examples demonstrate that the designs optimized for unsteady flow differ significantly from their steady‐state counterparts. Copyright © 2011 John Wiley & Sons, Ltd.     

低振动旋翼桨尖代理优化设计

为探索直升机低振动旋翼的工程设计方法,将代理优化与旋翼气弹耦合分析相结合,开展了旋翼桨尖几何外形设计,推导了非平直桨叶气弹动力学方程,训练了旋翼功率、模态阻尼以及振动载荷预测的Kriging代理模型.以气动性能与气弹稳定性为约束,以桨毂振动载荷最小化为目标,采用自适应加点准则设计了优化流程.以某旋翼为例,计算了其气动性...     

Topology optimization of a magnetic field in a three-dimensional finite region

This article describes the method of magnetic field topology optimization in an axisymmetric three-dimensional finite region. It is assumed that the region of interest is surrounded by a cylindrical solenoid with an electrical current. The solenoid’s inner and outer surfaces are built-up by rotating plane Bezier curves around the symmetry axis. As a global minimizer a genetic algorithm method is used. Optimal configurations are provided under given constraints.     

地铁致某近代建筑振动分析及减隔振措施研究EI北大核心CSCD

地铁运行引起的振动通过土层传播,会对邻近建筑物产生不利影响。以某地铁沿线近代历史保护建筑为背景,依据建筑结构参数及土层实测数据建立“隧道⁃土体⁃保护建筑”精细化三维数值模型,并结合振动响应预测分析方法对地铁运行时建筑物振动响应进行评估。从振源减振及过程阻振两方面对其减振效果进行量化分析和参数优化研究。结果表明:在未采取减隔振措施的情况建筑物振动超限,优化轨道类型的减振效果最为显著,使用弹性长枕轨道时结构Z振级可降低8.2~11.2 dB;使用钢弹簧浮置板轨道可使结构Z振级降低14.9~18.9 dB。过程阻振措施中,隔振墙的隔振性能对墙体材料特性最为敏感,深度及厚度其次;其中EPE泡沫材质墙体隔振效果最优,可使结构Z振级降低10.6~11.5 dB,水平速度峰值约75%;增加隔振墙厚度及埋深在一定程度上提升了隔振性能,但隔振效果增量不显著。提出了一种快速计算隔振墙隔振效果的预测方法,该研究可为类似工程的振动分析以及减隔振措施设计提供参考依据。     

Topology optimization for submerged buoyant structures

This paper presents an evolutionary structural topology optimization method for the design of completely submerged buoyant modules with design-dependent fluid pressure loading. This type of structure is used to support offshore rig installation and pipeline transportation at all water depths. The proposed optimization method seeks to identify the buoy design that has the highest stiffness, allowing it to withstand deepwater pressure, uses the least material and has a minimum prescribed buoyancy. Laplace's equation is used to simulate underwater fluid pressure, and a polymer buoyancy module is considered to be linearly elastic. Both domains are solved with the finite element method. Using an extended bi-directional evolutionary structural optimization (BESO) method, the design-dependent pressure loads are modelled in a straightforward manner without any need for pressure surface parametrization. A new buoyancy inequality constraint sets a minimum required buoyancy effect, measured by the joint volume of the structure and its interior voids. Solid elements with low strain energy are iteratively removed from the initial design domain until a certain prescribed volume fraction. A test case is described to validate the optimization problem, and a buoy design problem is used to explore the features of the proposed method.     

Topology optimization for reinforcement of no-tension structures

In the paper, the reinforcement of no-tension structures by the application of superposed high-strength sheets, or by the insertion of tensile bars, has been considered with the purpose to set up a design path aiming at the positioning of the new material according to some optimal criterion. In detail, no-tension models are adopted which are recognized as an effective tool for analyzing a wide class of structures (e.g., masonry and reinforced concrete members), and the equilibrium and the failure analysis of the reinforced body are developed with particular reference to its ultimate limit state of collapse. Finally, an approach through the “topologic optimization” is proposed for the identification of the optimal distribution of the reinforcement, and some of the obtained results are shown.     

Topology optimization with geometric uncertainties by perturbation techniques

The aim of this paper was to present a topology optimization methodology for obtaining robust designs insensitive to small uncertainties in the geometry. The variations are modeled using a stochastic field. The model can represent spatially varying geometry imperfections in devices produced by etching techniques. Because of under‐etching or over‐etching parts of the structure may become thinner or thicker than a reference design supplied to the manufacturer. The uncertainties are assumed to be small and their influence on the system response is evaluated using perturbation techniques. Under the above assumptions, the proposed algorithm provides a computationally cheap alternative to previously introduced stochastic optimization methods based on Monte Carlo sampling. The method is demonstrated on the design of a minimum compliance cantilever beam and a compliant mechanism. Copyright © 2012 John Wiley & Sons, Ltd.     

Topology optimization of metallic devices for microwave applications

In electromagnetic optimization problems of metallic radio‐frequency devices, such as antennas and resonators for wireless energy transfer, the volumetric distribution of good conductors, e.g. copper, has been known to cause numerical bottlenecks. In finite element analysis the limiting factor is the skin depth, which calls for highly refined meshing in order to capture the physics. The skin depth problem has therefore prohibited the application of topology optimization to this class of problem. We present a design parameterization that remedies these numerical issues, by the interpolation of Maxwell's equations and a fictitious element impedance condition. The validity of the proposed design parameterization is confirmed by several numerical examples. Copyright © 2010 John Wiley & Sons, Ltd.     

Golay-encoded excitation for dual-frequency harmonic detection of ultrasonic contrast agents

Golay-encoded excitation in combination with the third harmonic (3f?) transmit phasing is examined for both signal-to-noise ratio (SNR) and contrast-to-tissue ratio (CTR) improvements in harmonic imaging of contrast microbubbles. To produce the cancellation pair of tissue harmonic signal in 3f? transmit phasing, the phase of the bit waveform is properly designed for both the fundamental and the 3f? transmit signals to provide the Golay encoding of the received harmonic responses. Results indicate that the proposed Golay excitation can effectively suppress the tissue harmonic amplitude to increase CTR. Meanwhile, the SNR of the contrast harmonic signal also improves because of the elongated waveform of Golay excitation. Nevertheless, the generation of marked range side-lobes of the bubble region would degrade the achievable SNR improvement and the image contrast, especially when the bit of Golay excitation increases. The range side-lobes could result from the nonlinear resonance of the microbubbles that interferes with the phase modulation of the Golay encoding.     

Design of chirp excitation waveform for dual-frequency harmonic contrast detection

Tissue background suppression is essential for harmonic detection of ultrasonic contrast microbubbles. To reduce the tissue harmonic amplitude for improvement of contrast-to-tissue ratio (CTR), the method of third harmonic (3f₀) transmit phasing uses an additional 3f₀ transmit signal to provide mutual cancellation between the frequency-sum component and the frequency-difference component of tissue harmonic signal. Chirp excitation can further improve the SNR in harmonic imaging without requiring an excessive transmit pressure and thus reduce potential bubble destruction. However, for effective suppression of tissue harmonic background in 3f₀ transmit phasing, the 3f₀ chirp waveform has to be carefully designed for the generation of spectrally matched cancellation pairs over the entire second harmonic band. In this study, we proposed a chirp waveform suitable for the method of 3f₀ transmit phasing, the different-bandwidth chirp signal (DBCS). With the DBCS waveform, the frequency-difference component of tissue harmonic signal becomes a chirp signal similar to its frequency-sum counterpart. Thus, the combination of the DBCS waveform with the 3f₀ transmit phasing can markedly suppress the tissue harmonic amplitude for CTR improvement together with effective SNR increase of contrast harmonic signal. Our results indicate that, as compared with the conventional Gaussian pulse, the DBCS waveform can provide 6-dB improvement of SNR in 3f₀ transmit phasing with a CTR increase of 3 dB. Nevertheless, the limitation of available transmit bandwidth and the frequency-dependent attenuation can degrade the performance of the DBCS waveform in tissue suppression. The design of the DBCS waveform is also applicable to other dual-frequency imaging techniques that rely on the harmonic generation at the difference frequency.     

Topology optimization of unconstrained damping treatments for plates

A finite element model for composite plates consisting of an elastic isotropic base layer covered with viscoelastic treatment is presented. The composite plate undergoes bending vibrations in the lateral direction. In contrast to many previous publications, the viscoelastic treatment is not constrained from the top in order to better simulate real cases. The objective is to find the optimum distribution of viscoelastic treatment which maximizes the modal damping ratio (MDR) for a certain volume of treatment. Topology optimization is performed with two strategies: optimizing the whole domain of viscoelastic treatment and optimizing a unit cell of the periodic treatment. Numerical examples show that the presented model is able to increase the MDR by an order of magnitude compared to plain treatments.     

Potentials induced on magnetic reeds by excitation

Mating magnetic reeds produces an electrical potential upon excitation. These potentials arise from two causes and have two distinct waveforms. The observation results of the polarities of the potentials are described.     

拓扑与形状优化用于有效的产品设计

 介绍了基于有限元法(FEM)的计算机辅助结构优化方法． 拓扑优化有助于设计新零件的形状，形状优化则通过表面几何形状的局部调整改善零件的刚度或使用寿命．     

负泊松比微结构拓扑优化设计

在构建负泊松比结构拓扑优化模型时,直接用负泊松比的数学表达式构造目标函数,将使得目标函数高度非线性,迭代过程敏度分析困难。采用线性拟合法,构建了具有线性特征的负泊松比微结构拓扑优化目标函数,基于能量法和均匀化方法,结合拓扑优化理论,构建了一种可以快速准确求解负泊松比的拓扑优化设计模型,求解该模型得到了一种优化的拓扑构型及相应的负泊松比值。根据优化求解得到的结构模型,参考国家标准GB/T 22315-2008《金属材料弹性模量和泊松比试验方法》,利用有限元软件对其泊松比进行仿真计算,然后采用激光加工方式制造试样,并测试其泊松比,经过与优化模型求解得到的泊松比值对比分析,验证了所构建优化模型的正确性。本文方法既避免了以负泊松比表达式为优化函数时会出现的高度非线性问题,也降低了求解的复杂程度,为负泊松比微结构的设计提供了一种参考方法。     

结构减振设计的协同优化分析

建立一种适用于工程结构减振设计的协同优化模型。在学科级优化子模型中,分别使用了不同的目标函数;在系统级优化子模型中,以如何获得尽可能接近于子学科独立优化的最优解为目标函数。系统级目标函数消除了量纲和数量级的影响。该模型采用分布协同的双层结构,允许在每一级优化中使用不同的优化策略。以减速器和板梁柱混合结构为例,对其进行了单学科和多学科优化分析。实例结果表明,在结构减振设计时,采用协同优化模型进行优化设计,不仅可以有效的降低结构动力特性参数,而且优化后结构的综合性能更佳,说明该模型能应用于实际工程结构的减振设计。     

多载荷多工位转盘拓扑优化设计

基于拓扑优化理论,以结构总质量最小为目标,利用SIMP材料插值方法,结合HyperWorks/Optistruct拓扑优化功能对自动化组装设备中常用的多工位转盘进行了拓扑优化．根据优化后的重构模型与原始结构模型的静力学对比分析知,优化后降低了多工位转盘的总质量,提高了多工位转盘的刚度,同时减小了多工位转盘的局部最大应力．数据结果表明本方法对多工位转盘优化设计是有效的．