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71.
桁架结构稳定分析的几何非线性欧拉稳定理论 总被引:3,自引:0,他引:3
目前,桁架结构稳定分析有两个理论:经典的特征值理论和几何非线性临界点理论。前者发展较早,在许多结构力学书中都有叙述。但是经过工程应用检验,它过高地估计了结构抗稳定的能力。后者是20年前提出的,提出者认为适用于所有的扁桁架。经过几年的研究,作者连续提出三个稳定理论:线性与非线性欧拉理论;非线性临界点-欧拉理论和两个计算方法,进行桁架结构的线性和非线性截面优化设计。经过理论研究和对前人文献中数值例题的计算和比较,发现特征值理论不符合实际,临界点理论只适用于大扁度的桁架,而不适用于一切扁桁架。研究结果提供了若干有用的结论,给出了各种稳定理论的适用范围,指出了国际文献中若干例题的正确和错误,补充了桁架结构的稳定分析理论,使之更为完整和实用了。 相似文献
72.
侧柱对串列双柱脉动压力的干扰 总被引:2,自引:0,他引:2
研究了串列双圆柱旁加上一个等直径的圆柱,组成一个等边三角形排列的三圆柱的脉动压力分布.着重研究侧柱对串列双圆柱脉动压力分布的影响.研究的结果表明,绕流等边三角形排列的三圆柱,受影响最严重的是后柱.脉动压力分布出现了严重的不对称,外侧的压力脉动极其强烈,内侧的压力脉动较弱,与时均压力分布,很好的对应关系.另外,侧柱对于串列双圆柱是否达到超过临界间距的绕流流态,有很大的影响 相似文献
73.
74.
AbstractThis article is presenting the common experimental specimen for determining the fracture toughness of the first pure mode and second pure mode. The Notched beam is chosen from a presented common specimen in the form of three-point flexure beam and four-point flexure beam that were built in the concrete laboratory. For prevention of cracks growth, a critical load of first pure mode and the second pure mode of each specimen computed. Obtained results are used for computing the fracture toughness. For the purpose of investigating the effective fracture parameters in the suggested specimen, finite element analysis on the mentioned geometry is performed. Obtained results show that different parameters are effective on the fracture toughness including crack length, cement percentage, water and the thickness of biggest used aggregate in the sand. Also with changing each of these parameters, the fracture mechanic properties are changed. Each of these effects is examined separately in this article and the conclusions presented in tables and figures.Communicated by Dumitru Caruntu. 相似文献
75.
76.
Based on von Karman plate theory, the issue about nonlinear vibration for circular sandwich plates under circumjacent load with the loosely clamped boundary condition was researched. Nonlinear differential eigenvalue equations and boundary conditions of the problem were formulated by variational method and then their exact static solution can be got. The solution was derived by modified iteration method, so the analytic relations between amplitude and nonlinear oscillating frequency for circular sandwich plates were obtained. When circumjacent load makes the lowest natural frequency zero, critical load is obtained. 相似文献
77.
On the use of stretched-exponential functions for both linear viscoelastic creep and stress relaxation 总被引:1,自引:0,他引:1
The use of the stretched-exponential function to represent both the relaxation function g(t)=(G(t)-G ∞)/(G 0-G ∞) and the retardation function r(t) = (J ∞+t/η-J(t))/(J ∞-J 0) of linear viscoelasticity for a given material is investigated. That is, if g(t) is given by exp (?(t/τ)β), can r(t) be represented as exp (?(t/λ)µ) for a linear viscoelastic fluid or solid? Here J(t) is the creep compliance, G(t) is the shear modulus, η is the viscosity (η?1 is finite for a fluid and zero for a solid), G ∞ is the equilibrium modulus G e for a solid or zero for a fluid, J ∞ is 1/G e for a solid or the steady-state recoverable compliance for a fluid, G 0= 1/J 0 is the instantaneous modulus, and t is the time. It is concluded that g(t) and r(t) cannot both exactly by stretched-exponential functions for a given material. Nevertheless, it is found that both g(t) and r(t) can be approximately represented by stretched-exponential functions for the special case of a fluid with exponents β=µ in the range 0.5 to 0.6, with the correspondence being very close with β=µ=0.5 and λ=2τ. Otherwise, the functions g(t) and r(t) differ, with the deviation being marked for solids. The possible application of a stretched-exponential to represent r(t) for a critical gel is discussed. 相似文献
78.
Michel Bouthier 《Comptes Rendus Mecanique》2004,332(12):1019
Universal motions with uniform steady vorticity form a corolla of linear spaces derived from rigid body motions. Closely related to potential flows, they satisfy two extensions of Lagrange theorem, are investigated with the help of complex functions, as stand celebrated when be plane. They take place in hydrodynamics, aerodynamics, geophysics, astrophysics, turbulence, physics of plasmas and superfluid helium. In all the cases, arbitrary unsteady span-wise translations permit to generalise as well as to exhibit helical or 3D universal motions. Three misunderstood periodic flows illustrate our purpose, as they approach shear instabilities in numerous fluids. To cite this article: M. Bouthier, C. R. Mecanique 332 (2004). 相似文献
79.
A technique for stability analysis of stringer shells is proposed. It is used to analyze the minimum critical stresses. The
dependence of the dimensionless parameters σcr/σcl on the number of stringers is plotted. The linear and nonlinear theories of ribbed shells are used to examine the features
of how stringer shells lose stability. It is shown that the minimum critical stresses determined using the theory of ribbed
shells and a structurally orthotropic model are close within the range of stiffness parameters considered
__________
Translated from Prikladnaya Mekhanika, Vol. 42, No. 2, pp. 59–64, February 2006. 相似文献
80.
The paper presents a nonlinear model describing vibration of the landing gear relative to the fuselage. The model is intended
to analyze the dynamic stability of nonswiveling main-gear wheels. The model is used to show that the lateral component of
the fuselage speed has a significant effect on the critical shimmy speed
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Translated from Prikladnaya Mekhanika, Vol. 42, No. 9, pp. 134–142, September 2006. 相似文献