基于拓扑优化的新型蜂窝结构设计

可变体飞行器若要实现机翼后掠角、面积和前后缘弯度等参数的大幅度变化,机翼蒙皮需要具有光滑的气动外形、大变形、高承载以及驱动力小的特点。针对柔性蒙皮的需求,本文利用拓扑优化方法设计了一种新型零泊松比蜂窝结构,通过有限元仿真与U形蜂窝结构和余弦形蜂窝结构进行对比,验证其变形和承载等性能。以最大应变2%为基准,比较了三种蜂窝结构的变形能力。结果表明,新型蜂窝结构的拉伸变形量高达75%,分别是U形蜂窝结构和余弦形蜂窝结构的1.7倍和2.1倍。在最大位移量相同时,所需驱动力分别是U形蜂窝结构和余弦形蜂窝结构的0.51倍和0.28倍,表明新型蜂窝结构具有很大的易变形能力。当蜂窝结构的橡胶蒙皮受到相同压强载荷且处于初始未拉伸状态/拉伸状态时,新型蜂窝结构橡胶蒙皮的最大法向位移量分别是U形蜂窝橡胶蒙皮和余弦形蜂窝橡胶蒙皮的0.4倍/0.56倍和0.29倍/0.42倍,表明新型蜂窝结构具有良好的面外承载能力。另外,通过适当增加壁厚,可以提高新型蜂窝结构本身的抗弯曲能力。分析结果表明,本文设计的新型蜂窝结构具备大变形、高承载以及驱动力小的优点。     

弹性杆与结构接触冲击的冲击力计算研究

本文提出了一种将杆与结构的接触冲击问题简化为集中力与集中阻尼的常规结构动力学问题的计算模型。对于大型结构，可采用一种特殊的人工边界，只需对人工边界域内的结构用有限元法进行计算。这种人工边界是齐次的，可根据冲击影响区的大小人为地确定     

结构杆件撤除后简化分析一般方法

本文提出结构杆件撤除后简化分析的一般方法,视杆件撤除后新结构的解为原结构的解与原结构上加以关联荷载解的叠加,利用原结构的解及总体刚度矩阵的逆矩陈求解新结构,无需进行结构重分析,使计算量大大减小,文中基于有限元法导出求关联荷载的一般算式。该法适用于空间网格结构和刚架结构一根杆件撤除问题,也适用于多根杆件同时撤除问题。     

Experimental PIV/V3V measurements of vortex-induced fluid–structure interaction in turbulent flow—A new benchmark FSI-PfS-2a

The investigation of the bidirectional coupling between a fluid flow and a structure motion is a growing branch of research in science and industry. Applications of the so-called fluid–structure interactions (FSI) are widespread. To improve coupled numerical FSI simulations, generic experimental benchmark studies of the fluid and the structure are necessary. In this work, the coupling of a vortex-induced periodic deformation of a flexible structure mounted behind a rigid cylinder and a fully turbulent water flow performed at a Reynolds number of Re=30 470 is experimentally investigated with a planar particle image velocimetry (PIV) and a volumetric three-component velocimetry (V3V) system. To determine the structure displacements a multiple-point laser triangulation sensor is used. The three-dimensional fluid velocity results show shedding vortices behind the structure, which reaches the second swiveling mode with a frequency of about 11.2 Hz corresponding to a Strouhal number of St=0.177. Providing phase-averaged flow and structure measurements precise experimental data for coupled computational fluid dynamics (CFD) and computational structure dynamics (CSD) validations are available for this new benchmark case denoted FSI-PfS-2a. The test case possesses four main advantages: (i) the geometry is rather simple; (ii) kinematically, the rotation of the front cylinder is avoided; (iii) the boundary conditions are well defined; (iv) nevertheless, the resulting flow features and structure displacements are challenging from the computational point of view. In addition to the flow field and displacement data a PIV-based force calculation method is used to estimate the lift and drag coefficients of the moving structure.     

基于时域解耦算法的多液舱浮式结构物运动模拟

对于带有多个晃荡液舱的浮式结构物, 浮体的运动、外场水动力以及各舱内的液体晃荡力会实时相互决定, 发生复杂的耦合作用. 为准确模拟多液舱浮式结构物的运动, 本文引入一种有效的时域解耦算法. 该方法以模态分解法为基础, 通过对浮式结构物所受外域水动力和各液舱内非线性晃荡力进行模态分解, 最终形成时域解耦运动方程, 无需迭代求解过程即可显式计算浮式结构物的瞬时加速度. 该方法可避免传统迭代求解方法在迭代次数、截断误差和收敛特性等方面的不足, 减少解耦过程的计算耗时. 本文进一步结合边界元数值方法, 分别对单液舱浮式结构物和多液舱浮式结构物的工况开展数值模拟研究. 通过与单液舱浮式结构物的实验结果对比, 验证了本文时域解耦算法的有效性. 本文详细分析了晃荡力对单液舱浮式结构物运动的影响, 发现存在一个共振影响区间: 当外场波浪频率在该区间之外时, 可以在时域计算结果中观察到稳定的浮体运动; 在比该区间更低频的波况下, 液舱晃荡力与外场波浪力相位相反甚至可以相互抵消, 此时晃荡液舱的存在可以减弱浮体运动; 在比该区间更高频的波况下, 液舱内晃荡力与外场波浪力可以具有相同相位, 此时晃荡液舱的存在会加剧浮体的运动. 本文进一步研究了四液舱浮式结构物在波浪中的纵荡、垂荡和纵摇运动情况, 发现非线性液舱晃荡可对纵荡和纵摇运动产生影响, 但对垂荡运动影响很小.      

等速上仰翼型尾部流动观察及动态失速机理探讨

在尾缘处置氢气泡铂丝,观察了上仰翼型自尾缘流入尾迹的涡层。基于尾涡层及(以往)上翼面分离涡的观察,用涡动力学理论,探讨了动态失速的机理,并解释了新的失速现象。     

Existence of Weak Solutions for the Three-Dimensional Motion of an Elastic Structure in an Incompressible Fluid

We study here the three-dimensional motion of an elastic structure immersed in an incompressible viscous fluid. The structure and the fluid are contained in a fixed bounded connected set Ω. We show the existence of a weak solution for regularized elastic deformations as long as elastic deformations are not too important (in order to avoid interpenetration and preserve orientation on the structure) and no collisions between the structure and the boundary occur. As the structure moves freely in the fluid, it seems natural (and it corresponds to many physical applications) to consider that its rigid motion (translation and rotation) may be large. The existence result presented here has been announced in [4]. Some improvements have been provided on the model: the model considered in [4] is a simplified model where the structure motion is modelled by decoupled and linear equations for the translation, the rotation and the purely elastic displacement. In what follows, we consider on the structure a model which represents the motion of a structure with large rigid displacements and small elastic perturbations. This model, introduced by [15] for a structure alone, leads to coupled and nonlinear equations for the translation, the rotation and the elastic displacement.     

求解含缺陷一维周期结构动力响应的高效算法

基于周期结构的动力特性和群理论,建立了一种高效求解含缺陷一维周期结构动力响应的数值方法。在求解结构动力响应时,高效求解结构对应的线性代数方程组最为关键。采用凝聚技术,可减小结构对应线性代数方程组的规模。基于周期结构动力系统中线性代数方程组的特性,通过一个小规模含缺陷结构和一维周期结构的响应分析,可得到含缺陷一维周期结构的动力响应。同理,一维周期结构的动力响应可通过一系列小规模结构的响应分析得到,且小规模结构的动力响应可基于群理论高效求解。数值算例表明,本文算法有较高的求解效率。     

Mechanical response of a tensegrity structure close to its integrity limit submitted to external constraints

The response to an external constraint of a symmetrical tensegrity structure made of elastic and rigid elements has been studied by numerical experiments. Two non-linear effects have been found when the structure is close to its integrity limit above which it collapses. The first one is that the mechanical power response of the tensegrity structure can be modulated according to the magnitude of the applied force. This effect indicates that the structure may act as a mechanical power amplifier. The second one is that a slightly prestressed tensegrity structure can offer a greater resilience to an applied force than more prestressed equivalent structures. This paradoxical stiffening effect indicates that increasing the prestress may not always be the most efficient way to keep the stability of the structure.     

PIV measurements combined with the motion tracking technique to analyze flow around a moving porous structure

To gain a better understanding of the fluid–structure interaction and especially when dealing with a flow around an arbitrarily moving body, it is essential to develop measurement tools enabling the instantaneous detection of moving deformable interface during the flow measurements. A particularly useful application is the determination of unsteady turbulent flow velocity field around a moving porous fishing net structure which is of great interest for selectivity and also for the numerical code validation which needs a realistic database. To do this, a representative piece of fishing net structure is used to investigate both the Turbulent Boundary Layer (TBL) developing over the horizontal porous moving fishing net structure and the turbulent flow passing through the moving porous structure. For such an investigation, Time Resolved PIV measurements are carried out and combined with a motion tracking technique allowing the measurement of the instantaneous motion of the deformable fishing net during PIV measurements. Once the two-dimensional motion of the porous structure is accessed, PIV velocity measurements are analyzed in connection with the detected motion. Finally, the TBL is characterized and the effect of the structure motion on the volumetric flow rate passing though the moving porous structure is clearly demonstrated.     

电阻应变测试技术中的温度补偿功能辨析

针对基于温度应变补偿的结构电阻应变测试技术,分析了结构温度应变的产生原理与结构温度应变的补偿原理,辨析了结构温度应变与补偿块温度应变二者的相互关联与差异.在此基础上,指出了基于温度应变补偿模式的结构电阻应变测试技术的错误在于:概念上混淆了结构的温度应变与补偿块的温度应变,导致了结构温度应变的错误补偿.同时,给出了正确实现工程结构应变测试的环境条件,以最大限度地保证了结构应变测试数据的客观性与可靠性.     

一种基于附加重力场的铸件拓扑优化方法

针对铸件结构拓扑优化问题,提出了一种新的铸造脱模约束形式.首先,在变密度拓扑优化的框架下,提出了相对密度描述的优化解的逆结构概念;之后,对该逆结构施加附加重力载荷并固定脱模方向的边界;最后,利用该问题的位移解构造铸造约束.通过对逆结构的最大柔顺性施加单一约束,即可避免优化结构出现不可铸造的特征(包括内部孔洞和侧凹),从...     

一维离散结构能带结构与表面态的辛分析方法

本文基于辛几何方法推导了一维离散周期结构、半无穷周期结构和含杂质半无穷周期结构的本征方程,力求建立一个完整的辛分析体系。通过辛分析,将一维离散半无限周期结构转化到一个元胞上求解,大大简化了计算量。对于含杂质半无穷周期结构,结合辛分析和W-W算法,给出求解含杂质半无穷周期结构本征值问题的精确、稳定和高效算法。数值算例说明了本文算法的有效性。     

The analysis of the orientation effect of non-linear flexible systems on performance of the pendulum absorber

In practical applications, many vibration absorbers are used to absorb oscillation of a structure, one of which is pendulum-type vibration absorbers. They are widely used in engineering applications where oscillations of a structure are constrained within a prescribed envelope. In this study, the primary structure consists of a flexible beam which has a single degree of freedom, and is subjected to a vertical sinusoidal base excitation. Non-linearity in the primary structure is due to large deflections. The rotation point of the pendulum-type absorber is attached to the tip of the primary structure. The primary structure and absorber together constitute a couple systems with two degrees of freedom. The primary objective of this study is to determine the effectiveness of pendulum-type passive vibration absorber attached to a primary structure whose orientation varies. In this study, the orientation at which the absorber is effective is established, and the factors that affect performance of the absorber are determined. The results are in good agreement with the experimental ones given in the literature.     

Pressure profiles in detonation cells with rectangular and diagonal structures

Experimental results presented in this work enable us to classify the three-dimensional structure of the detonation into two fundamental types: a rectangular structure and a diagonal structure. The rectangular structure is well documented in the literature and consists of orthogonal waves travelling independently from each another. The soot record in this case shows the classical diamond detonation cell exhibiting ‘slapping waves’. The experiments indicate that the diagonal structure is a structure with the triple point intersections moving along the diagonal line of the tube cross section. The axes of the transverse waves are canted at 45 degrees to the wall, accounting for the lack of slapping waves. It is possible to reproduce these diagonal structures by appropriately controlling the experimental ignition procedure. The characteristics of the diagonal structure show some similarities with detonation structure in round tube. Pressure measurements recorded along the central axis of the cellular structure show a series of pressure peaks, depending on the type of structure and the position inside the detonation cell. Pressure profiles measured for the whole length of the two types of detonation cells show that the intensity of the shock front is higher and the length of the detonation cell is shorter for the diagonal structures. Received 17 May 2000 / Accepted 29 November 2000     

Runup and green water velocities due to breaking wave impinging and overtopping

The present study investigates, through measurements in a 2D wave tank, the velocity fields of a plunging breaking wave impinging on a structure. As the wave breaks and overtops the structure, so-called green water is generated. The flow becomes multi-phased and chaotic as a large aerated region is formed in the flow in the vicinity of the structure while water runs up onto the structure. In this study, particle image velocimetry (PIV) and its derivative, bubble image velocimetry (BIV), were employed to measure the velocity field in front and on top of the structure. Mean and turbulence properties were obtained through ensemble averaging repeated tests. The dominant and maximum velocity of the breaking wave and associated green water are discussed for the three distinct phases of the impingement–runup–overtopping sequence. Initially the flow is mainly horizontal right before the breaking wave impinges on the structure. The flow then becomes primarily vertical and rushes upward along the front wall of the structure right after the impingement. Subsequently, the flow becomes mainly horizontal on top of the structure as the remaining momentum in the wave crest carries the green water through. The distribution of the green water velocity along the top of the structure has a nonlinear profile and the maximum velocity occurs near the front of the fast moving water. Using the measured data and applying dimensional analysis, a similarity profile for the green water flow on top of the structure was obtained, and a prediction equation was formulated. The prediction equation may be used to predict the green water velocity caused by extreme waves in a hurricane.     

模糊随机可靠性分析的统一模型

针对基本变量和状态变量的不确定性可能既有随机性又有模糊性的情况，通过 引入规一化因子和模糊变量隶属函数的等效概率密度函数转换，建立了同时考虑随机和模糊 两种不确定性因素的统一可靠性模型. 由于该模型将模糊变量等价转换成了随机变量，并且 这种等价变换没有改变模糊变量的可能性分布，因而随机可靠性模型的所有方法均可用于统 一模型，并且其可靠度和失效概率的计算将是准确的. 所提模型不仅适用于只有应力和强度 两个基本变量的情况，而且也适用于多个变量的情况. 用算例对所提模型与前人的采 用截集并在截集中引入人为分布的模型进行了对比，结果表明该方法更适于工程应用.     

结构构型与结构间连接方式协同优化设计

通常的结构拓扑优化是在给定外部作用下的构型设计. 然而对于复杂结构,各部件由连接构件相连并通过它传递外部作用,所以连接方式影响部件承受载荷的分布,即连接构件的布局对部件的最优构型有重要影响. 研究结构部件构型与部件之间连接方式的协同优化问题,在连接区域引入一种特殊的材料模型,以材料的分布描述连接方式. 将承力结构与连接构件域的材料密度同时作为设计变量,提出了一种基于拓扑优化思想的连接方式与结构拓扑优化协同设计的优化模型和相应的求解方法. 给出的算例证明了这种设计方法与优化策略的有效性.      

A new method for stress analysis of a cyclically symmetric structure

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考虑车辆随机停放的停车楼减震设计与可靠度分析

在停车楼的设计中通常将车辆荷载以活荷载的方式均匀分布到结构上,实际上受车辆随机停放的影响,停车楼结构整体质量中心偏移,一旦结构遭遇罕遇地震时,车辆的随机停放可能造成停车楼结构发生扭转破坏.本文在传统减震设计方法的基础上考虑车辆活荷载的随机性,并从可靠度的角度验算减震结构在大震作用下的倒塌概率.结果表明,相同的减震设计布...