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S. Bonanos 《General Relativity and Gravitation》1998,30(4):653-658
A new spinor identity of third order in the Ricci spinor is presented and is shown to be the reason for the vanishing of certain mixed Riemann tensor invariants found recently by Zakhary and McIntosh. Some further identities satisfied by the different 4-index spinors defined in that paper are also given. 相似文献
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The Newtonian theory of spatially unbounded, self-gravitating, pressureless continua in Lagrangian form is reconsidered. Following a review of the pertinent kinematics, we present alternative formulations of the Lagrangian evolution equations and establish conditions for the equivalence of the Lagrangian and Eulerian representations. We then distinguish open models based on Euclidean space R3 from closed models based (without loss of generality) on a flat torus T3. Using a simple averaging method we show that the spatially averaged variables of an inhomogeneous toroidal model form a spatially homogeneous background model and that the averages of open models, if they exist at all, in general do not obey the dynamical laws of homogeneous models. We then specialize to those inhomogeneous toroidal models whose (unique) backgrounds have a Hubble flow, and derive Lagrangian evolution equations which govern the (conformally rescaled) displacement of the inhomogeneous flow with respect to its homogeneous background. Finally, we set up an iteration scheme and prove that the resulting equations have unique solutions at any order for given initial data, while for open models there exist infinitely many different solutions for given data. 相似文献
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结构可靠度分析FORM迭代算法的混沌控制 总被引:1,自引:1,他引:0
利用混沌控制原理对FORM收敛失败进行控制. 理清了全局性和局部性两类混沌反馈
控制各种方法的内在联系,说明稳定转换法和自适应调节法属于全局混沌反馈控制
方法,自适应调节法可视为稳定转换法的特例. 参
数调节混合法不过是松弛牛顿法的另一种表达形式,它们都属于局部混沌反馈控制方法. 阐
明了混沌反馈控制表达式与工程力学收敛控制迭代算法的对应关系. 也揭示了这些迭代算法
收敛控制措施的功效和局限性. 提出了一个以稳定转换法为主联合松弛牛顿法的混
沌反馈控制方法,对可靠度分析FORM迭代算法实现了周期振荡、分岔和混沌控制. 相似文献
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复合材料层合板的率模可靠度研究 总被引:2,自引:0,他引:2
传统的结构可靠性分析是基于二值状态假设的,即结构要么处于失效状态,要么处于安全状态,但在许多工程实际中,在失效和安全之间有一系列中间状态,因此判断结构是否失效,引用模糊状态的概念更为合理.该文将失效(或安全)的模糊状态假设引入到复合材料层合板的可靠度分析和计算中,建立了复合材料层合板的率模可靠度模型和相应的计算模型.在该模型中,考虑了单层复合材料强度指标的随机性,以及极限状态的模糊性.由层合板结构可靠性分析的具体算例,说明了该文模型和计算方法的合理性及有效性.同时,对参数的影响也进行了分析和讨论.结果表明,强度参数的均值以及失效准则的选取对可靠度有较大的影响. 相似文献
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提出了一种针对一般非线性极限状态方程的时变结构可靠度分析方法. 该方法首先将时变功能函数中的随机过程进行离散,获得多个不同时间段的静态功能函数. 之后,将各功能函数在最大可能点处进行线性化,并运用全概率公式将其化简为一新的静态可靠度分析模型,该模型可运用传统的一次二阶矩方法进行高效求解.最后通过管状悬臂梁、十杆桁架、汽车发动机主轴3 个算例验证了该方法的有效性. 相似文献
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Reliability analysis of FRP laminated plates with consideration of both initial imperfection and failure sequence 总被引:13,自引:0,他引:13
A probabilistic progressive failure analyzing method is applied to estimating the reliability of a simply supported laminated
composite plate with an initial imperfection under bi-axial compression load. The initial imperfection and the strength parameters
are considered as random variables. Ply-level failure probability is evaluated by the first order reliability method (FORM)
together with the Tsai-Wu strength criterion and Tan criterion. Current stresses in the laminated structure are calculated
by the classical lamination theory with the stiffness modified based on the last step ply failure. Probabilistically dominant
ply-level failure sequences leading to overall system failure are identified, based on which the system failure probability
is estimated. A numerical example is presented to demonstrate the methodology proposed. Through parameter studies it is shown
that the deviation of the initial imperfection and some of the strength parameters largely influence the system reliability.
Project supported by the Scientific Research Foundation for Returned Overseas Chinese Scholars, State Education Ministry,
and the Research Foundation of Huazhong University of Science and Technology. 相似文献
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M. Ulanovskii 《General Relativity and Gravitation》1999,31(12):1813-1820
We show that to any convex function f:
n
there correspondinfinitely many geodesically complete metricsds2 such that Ric() 0 for anynonspacelike vector . These metrics are constructedas the warped products of the natural metric in and the inner metric of a convexhyperface (the graph of f) in
n + 1. 相似文献
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