共查询到20条相似文献,搜索用时 46 毫秒
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已有的非保守大变形虚位移原理表达式在形式上是完美的,但其非保守载荷的虚功项并不能直接用于有限元数值计算。本文对此项的计算作了进一步的推导,给出了能用于实际计算的公式。对常见的非保守法向载荷,公式十分简单。对小应变大转动变形,公式也有非常简单的形式。 相似文献
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在大变形弹塑性本构理论中,一个基本的问题是弹性变形和塑性变形的分解.通常采用两种分解方式,一是将变形率(或应变率)加法分解为弹性和塑性两部分,其中,弹性变形率与Kirchhoff应力的客观率通过弹性张量联系起来构成所谓的次弹性模型,而塑性变形率与Kirchhoff应力使用流动法则建立联系;另一种是基于中间构形将变形梯度进行乘法分解,它假定通过虚拟的卸载过程得到一个无应力的中间构形,建立所谓超弹性-塑性模型.研究了基于变形梯度乘法分解并且基于中间构形的大变形弹塑性模型所具有的若干性质,包括:在不同的构形上,塑性旋率的存在性、背应力的对称性、塑性变形率与屈服面的正交性以及它们之间的关系.首先,使用张量函数表示理论,建立了各向同性函数的若干特殊性质,并导出了张量的张量值函数在中间构形到当前构形之间进行前推后拉的简单关系式.然后,基于这些特殊性质和关系式,从热力学定律出发,建立模型在不同构形上的数学表达,包括客观率表示的率形式和连续切向刚度等,从而获得模型所具有的若干性质.最后,将模型与4种其他模型进行了比较分析. 相似文献
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针对带有弹性支撑的超静定结构的位移计算问题, 对利用虚功原理得到的位移计算一般公式进行了进一步推导, 提出了该类结构位移的简化计算方法. 文中计算公式表达形式简洁, 且与一般刚性支撑超静定结构的位移计算方法一致. 通过与有限元分析结果的对比,证明了该公式的正确性. 相似文献
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空间曲线索平衡方程可在理想柔索假定的基础上进行推导,也可以由空间曲线梁平衡方程退化得到。本文给出后者的连续化分析过程并进行了初步的讨论,目的在于将空间曲线索的各种力学模型统一起来。采用理想柔索假定后单索只能是平面曲线,自然坐标系和整体直角坐标系下平面曲线索的平衡方程是等价的。同时,针对以往单索连续化分析中几何判定的不足,基于空间曲线的弧长独立参数概念,指出单根理想柔索本质上为静不定和动不定体系。 相似文献
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张景瑞 《应用数学和力学(英文版)》2008,29(8):1013-1021
The steering laws of single gimbal control moment gyros (SGCMGs) are analyzed and compared in this paper for a spacecraft attitude control system based on singular value decomposition (SVD) theory. The mechanism of steering laws escaping singularity, especially how the steering laws affect singularity of gimbal configuration and the output torque error, is studied using SVD theory. Performance of various steering laws are analyzed and compared quantitatively by simulation. The obtained results can be used as a reference for designers. 相似文献
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陈至达 《应用数学和力学(英文版)》1991,12(3):247-253
Living system is a non-equilibrium open system having the function of self-organizationand self-control.The study of energy principle of living system involves two principal parts:mechanics and thermodynamics.The classical infinitesimal deformation theory andthermodynamics of equilibrium state are not sufficient to explain the complex motion ofliving system.We aim in this paper to describe the mechanical energy principle ofmacroscopic motion of living body based on large deformation non-symmetry stress fieldtheory.The principle of irreversible thermodynamics applied to living system will be left inanother paper. 相似文献
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In this paper,the problem of large axisymmetric deformation of hyperelasticmembrane is reformulated on the basis of the general theory of finite elasticity.From thefundamental equations derived here,the tensile instability of toroidal rubberlike membranewith Mooney-Rivlin’s model constitutive relation is solved by using the shooting method.The upper and lower limit loads and the response curve of the displacement to the load aregiven. 相似文献
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In this paper,determination of the characteristics of futures market in China is presented by the method of the phase-randomized surrogate data.There is a significant difference in the obtained critical values when this method is used for random timeseries and for nonlinear chaotic timeseries.The singular value decomposition is used to reduce noise in the chaotic timeseries.The phase space of chaotic timeseries is decomposed into range space and null noise space.The original chaotic timeseries in range space is restructured.The method of strong disturbance based on the improved general constrained randomized method is further adopted to re-deternination.With the calculated results,an analysis on the trend of futures market of commodity is made in this paper.The results indicate that China's futures market of commodity is a complicated nonlinear system with obvious nonlinear chaotic characteristic. 相似文献
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An optimizing reduced implicit difference scheme (IDS) based on singular value decomposition (SVD) and proper orthogonal decomposition (POD) for the two‐dimensional unsaturated soil water flow equation is presented. An ensemble of snapshots is compiled from the transient solutions derived from the usual IDS for a two‐dimensional unsaturated flow equation. Then, optimal orthogonal bases are reconstructed by implementing SVD and POD techniques for the ensemble of snapshots. Combining POD with a Galerkin projection approach, a new lower dimensional and highly accurate IDS for the two‐dimensional unsaturated flow equation is obtained. Error estimates between the true solution, the usual IDS solution, and the reduced IDS solution based on POD basis are derived. Finally, it is shown by means of a numerical example using the technology of local refined grids that the computational load is greatly diminished by using the reduced IDS. Also, the error between the POD approximate solution and the usual IDS solution is proved to be consistent with the derived theoretical results. Thus, both feasibility and efficiency of the POD method are validated. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
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针对捷联式惯导系统多位置对准可观测性的问题,以捷联式惯导十状态误差方程为研究对象,利用卡尔曼滤波分别得到固定位置对准与二位置对准以及二位置对准与三位置对准时的方位失准角估计误差收敛情况。在分段线性定常系统理论的基础上,利用奇异值分解的方法,分别对固定位置对准以及二位置对准时的系统各状态变量的可观测性进行分析。仿真结果表明,三位置对准和二位置对准时的方位失准角估计误差达到的稳态误差是一致的,并且多位置对准能够改善捷联惯导系统各状态变量的可观测度。该研究结果不仅为确定并提高捷联惯导系统各状态的可观测度提供了途径,而且为捷联式惯导系统的可观测性达到最佳以及捷联惯导系统对准精度的快速提高提供了理论基础。 相似文献
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基于余能原理的有限变形问题有限元列式 总被引:1,自引:0,他引:1
利用基面力概念,推导了一种基于余能原理的有限变形问题显式有限元列式,可应用于结构的大位移、大转动问题。以基面力为状态变量来表达单元的余能,将有限变形情况下的单元余能分解为变形余能部分和转动余能部分,利用Lagrange乘子法推导出余能原理有限元的控制方程,编制了相应的非线性有限元程序。通过算例分析,说明该列式和程序的可靠性和精确性。 相似文献