共查询到19条相似文献,搜索用时 234 毫秒
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结构动力分析的随机变分原理及随机有限元法 总被引:7,自引:1,他引:7
将结构动力系统的参数及激励的随机性直接引入结构的动力泛函变分表达式中,基于瞬时最小势能原理,应用小参数摄动法,建立了随机结构动力分析的随机变分列式及相应的确机有限元法。算例表明,应用此法分析随机结构动力响应,具有程序实施简便,计算效率高的优点。 相似文献
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埋地管道随机振动的摄动分析 总被引:2,自引:0,他引:2
埋地管道的材料特性和沿线的土壤性质存在差异,对这种差异性采用随机参数描述有一定的合理性,因此在管道的随机振动分析中考虑结构参数的随机性是必要的,对于管道的抗震设计具有现实意义。对于在空间相关的地震地面随机激励下的埋地管道,将结构参数看作是随机变量,采用摄动分析法,推导了随机响应的相关函数和功率谱密度函数的解析表达式,大大方便了工程应用。针对某输油管道,给出了计算结果。 相似文献
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饱和土体中圆柱形孔洞的动力分析 总被引:5,自引:0,他引:5
本文采用工程通用的土力学模型,利用积分变换法推导了置于饱和土体中的圆柱形孔洞瞬态动力响应解答的一般解析表达式,并将其与经典弹性动力学中圆柱形空腔问题的解答作了有价值的比较,文末利用一种十分有效的数值反变换方法给出了有意义的算例。本文为进一步分析岩土工程、地震工程中隧道、管道等地下结构的动力响应提供了有效途径,具有理论与应用价值。 相似文献
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阐述了基于蛋白质晶体结构的残基势能函数的研究进展, 从平均作用力场势能函数的基本物理假设、势能函数性质和影响势能函数准确性的因素3个方面出发, 分析了导出残基相互作用势能的方法, 给出了残基对之间和3个残基之间的平均作用力势能函数计算过程, 并介绍了残基势能函数在蛋白质结构研究领域的应用. 基于蛋白质晶体结构的残基相互作用势能研究表明, 蛋白质结构稳定是多种作用力相互竞争、相互协调进而达到平衡状态的结果. 未来对于残基团簇及其相互作用网络能量分布的研究, 能够建立介于原子尺度和蛋白质整体结构尺度之间的作用力物理模型, 为蛋白质结构宏观尺度研究提供重要的微观力学机理. 相似文献
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管道超声纵向导波裂纹检测数值模拟 总被引:11,自引:0,他引:11
简述了近年来超声导波技术的发展现状及其检测原理,并用有限元程序ANSYS对管道超声纵向导波裂纹检测进行了数值模拟。管道模型中,删除单元模拟管道周向裂纹,通过对管道一端端部周向各节点施加轴向瞬时位移载荷模拟纵向入射应力波,同端接收反射应力波,根据裂纹纵波回波信号到达时间和反射系数能较为精确地判断裂纹位置、周向开口裂纹长度、管壁减薄程度及裂纹截面积,但反射系数对管道轴向裂纹宽度不十分敏感。数值模拟结果与前人实验结果及理论计算结果吻合较好。 相似文献
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给出载流无限大薄板在形成半无限长裂纹的瞬间,尖端附近的温度和应力的具体表达式。通过算例表明:在电流所产生的焦耳热源的作用下,裂尖区域处的温度将瞬时升高,并伴有压应力的产生,从而可达到阻裂纹扩展的目的。 相似文献
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结构误差造成的半球谐振陀螺闭环检测误差分析 总被引:3,自引:1,他引:3
半球谐振陀螺是一种具有广阔应用前景的高精度陀螺。由于制造工艺和装配过程中的因素,其结构难免会出现误差。根据闭环检测机理,推导出结构误差的数学表达式,分析了它对测量结果的影响,这对于编制软件算法以补偿结构误差具有一定的指导意义。 相似文献
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H. Bergkvist 《Journal of the mechanics and physics of solids》1974,22(6):491-502
The analysis of the motion of a crack of finite length extending in an infinite isotropic elastic sheet loaded in the extensional mode forms the basis for the treatment of the motion and the arrest of a brittle crack in a more general two-dimensional structure of finite size. The energy flow to the cracktip is expressed in terms of the value of the static J-integral times a dynamic function depending on the instantaneous crack-tip velocity. This energy flow is equal to the fracture energy which is supposed to be a specific function only of the crack-tip velocity for a given material. If the energy release (calculated as described) becomes less than the fracture energy in some segment along the prospective fracture path, then additional energy will be needed for the crack to be propagated. Such additional energy is available owing to the kinetic state of the structure. An upper limit to the amount of additional energy is determined. A conservative crack-arrest condition is given by the assumption that all this additional energy is consumed in a continued slow extension of the crack. Experimental results for edge-cracked sheets of polymethylmethacrylate conform well with the crack-arrest condition suggested. 相似文献
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提出一种利用结构振动响应和HILBERT-HUANG变换(HHT)技术检测结构小损伤的时域方法,研究了基于HHT的悬臂机翼盒段结构的损伤特征量的提取方法,给出了所提取特征量与结构损伤程度之间的关系。用HHT技术处理完好盒段与损伤盒段在信号激励下的结构动力响应信号,得到信号的希尔波特谱;然后求出希尔波特谱对应的瞬时能量,从中提取出结构损伤信息—瞬时能量变化量,作为损伤特征参数;并研究了将之作为损伤特征参数的抗噪声干扰能力。最后给出了瞬时能量变化量最大值与结构损伤程度之间的关系。 相似文献
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YangJialing LiuXuhong 《Acta Mechanica Solida Sinica》2004,17(2):140-149
I. INTRODUCTION The dynamic plastic response of free-free beams subjected to intense dynamic loading is a subject ofinterest for aerospace engineering applications. For example, when a rocket is attacked by a missile, itslarge plastic deformation behav… 相似文献
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《Journal of Fluids and Structures》2002,16(3):295-316
A delta wing is subjected to both static and dynamic variations of angle-of-attack; the vortices from the wing impinge upon a stationary plate. A technique of high-image-density particle image velocimetry is employed to compare the patterns of vortex development with and without the impingement plate. For the limiting case of static variations of angle-of-attack, the presence of the plate exerts a large influence on the onset of vortex breakdown. In contrast, dynamic (unsteady) variation of angle-of-attack yields changes of breakdown location that are generally similar for cases with and without the impingement plate. The detailed structure of the vortex breakdown-plate interaction is represented by patterns of instantaneous velocity and vorticity, which serve as the origin of buffet-induced loading of the surface of the plate. 相似文献
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On the basis of the Euler-Bernoulli hypothesis, nonlinear static and dynamic responses of a viscoelastic microbeam under two kinds of electric forces [a purely direct current (DC) and a combined current composed of a DC and an alternating current] are studied. By using Taylor series expansion, a governing equation of nonlinear integro-differential type is derived, and numerical analyses are performed. When a purely DC is applied, there exist an instantaneous pull-in voltage and a durable pull-in voltage of which the physical meanings are also given, whereas under an applied combined current, the effect of the element relaxation coefficient on the dynamic pull-in phenomenon is observed where the largest Lyapunov exponent is taken as a criterion for the dynamic pull-in instability of viscoelastic microbeams. 相似文献
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In this paper,based on the mathematical theory of classical mechanics and Chen‘s theorem,the variational method is used in the study of large deformation symmetrical elasticity problems.The generalized variational principles of potential energy and complementary energy,based on the instantaneous configuration are obtained,and the equivalence between the two principles is proved.Besides,the generalized variational principles of dynamical problems based on the instantaneous configuration are also given. 相似文献
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当前在运用渐进结构优化(ESO)时,大多仅设定了单一的静力或动力目标,难以满足工程结构设计的需求。为此,将单目标优化常用的应变能灵敏度和频率灵敏度进行无量纲处理,再与多目标优化理论结合,开发出静动力双目标ESO。通过多个不同边界条件的深受弯构件数值算例,证实了新方法的运行稳定性和普遍适用性,同时还得到了静力优化与动力优化间的权重系数比取值建议。有限元对比分析结果表明,该新方法相较于传统的单目标优化,能够兼顾结构的静动力性能,使结构耗材减少但静力刚度基本维持,同时材料利用率和一阶固有频率还能不断提升。 相似文献
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Velocity profile measurement by ultrasonic doppler method 总被引:11,自引:0,他引:11
Yasushi Takeda 《Experimental Thermal and Fluid Science》1995,10(4):444-453
The ultrasonic velocity profile measuring method has been developed at PSI for application in fluid mechanics and fluid flow measurement. It uses pulsed ultrasonic echography together with the detection of the instantaneous Doppler shift frequency. This method has the following advantages over the conventional techniques: (1) an efficient flow mapping process, (2) applicability to opaque liquids, and (3) a record of the spatiotemporal velocity field. After a brief introduction of its principle, the characteristics and specifications of the present system are given. Then examples in fluid engineering for oscillating pipe flow, T-branching flow of mercury, and recirculating flow in a square cavity are described that confirm the method's advantages. Several other works under way by other investigators are introduced. A potential for in-depth study of fluid dynamics is demonstrated by several examples from an investigation of modulated wavy flows in a rotating Couette system. The position-averaged power spectrum and the time-averaged energy spectral density were used to study the dynamic characteristics of the flow, and subsequently the velocity field was decomposed into its intrinsic wave structure based on two-dimensional Fourier analysis. 相似文献