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61.
Here, the large amplitude free flexural vibration behaviors of thin laminated composite skew plates are investigated using finite element approach. The formulation includes the effects of shear deformation, in-plane and rotary inertia. The geometric non-linearity based on von Karman's assumptions is introduced. The non-linear governing equations obtained employing Lagrange's equations of motion are solved using the direct iteration technique. The variation of non-linear frequency ratios with amplitudes is brought out considering different parameters such as skew angle, number of layers, fiber orientation, boundary condition and aspect ratio. The influence of higher vibration modes on the non-linear dynamic behavior of laminated skew plates is also highlighted. The present study reveals the redistribution of vibrating mode shape at certain amplitude of vibration depending on geometric and lamination parameters of the plate. Also, the degree of hardening behavior increases with the skew angle and its rate of change depends on the level of amplitude of vibration. 相似文献
62.
63.
重庆“朝天扬帆”钢结构工程风振研究 总被引:1,自引:0,他引:1
“朝天扬帆”是位于重庆朝天间广场的钢结构雕塑工程,该工程建筑型体复杂、结构布局不规则,通过该雕塑工程缩尺模型的几洞试验,确定其风载计算的体型系数;用时程法计算结构的风振响应,且在模拟作用于结构上的脉动风时程曲线时考虑结构的高度相关性,应用ALGOR93软件对结构进行风振时程分析,并自编程序加以前、后处理。通过对比该结构在脉动风和平均风作用下的杆件内力、节点位移响应,约定结构风振系数,为该雕塑工程抗风设计参数的确定提供理论依据。 相似文献
64.
Liu Rongmei 《力学与实践》1979,42(4):442
建立了扁担挑物的动力学模型和动力学方程,并进行了数值求解。扁担挑物时存在三种频率,即重物类似于单摆的振动频率、挑运者的步行频率和扁担-重物系统铅垂方向的振动频率。计算结果表明,为了获得较好的挑担体验,三种频率应该相互协调。当人挑担行走的频率为扁担-重物系统铅垂方向振动频率的70%,$\sim$,80%时,肩部铅垂附加动反力为重物重力的30%左右且与肩部铅垂运动同相,当重物类似于单摆的振动频率为人步行频率的25%,$\sim$,30%时,重物的摆角和肩部受到的水平附加动反力均较小,从而有利于人挑担行走。 相似文献
65.
66.
以子结构模态综合分析为基础,提出一种求解大型结构特征值问题的并行解法.采用子结构模态综合算法,结构特征模态采用子空间迭代方式并行求解.这种子空间迭代法的子结构并行计算的实施是利用子结构的刚度阵和质量阵而不必完全组集系统刚度阵和质量阵求解综合系统的特征值问题.数值结果表明这种求解大型结构特征值问题的并行算法是可行有效的. 相似文献
67.
P. Z. Lugovoi V. F. Meish B. P. Rybakin G. V. Sekrieru 《International Applied Mechanics》2006,42(5):536-540
Dynamic problems for cylindrical shells reinforced with discrete ribs are examined. A numerical algorithm based on Richardson
extrapolation is developed. Specific problems are solved, and the results are analyzed
__________
Translated from Prikladnaya Mekhanika, Vol. 42, No. 5, pp. 50–56, May 2006. 相似文献
68.
讨论螺旋细杆的特殊形式扭转振动,即均匀扭转振动.以非圆截面杆和有原始曲率的圆截面杆为研究对象.杆作均匀扭转振动时各截面有相同的扭角变化规律,且杆中心线的几何形状不受振动过程的影响.研究表明,扭振来源于杆截面的非对称性及杆的原始曲率.杆的扭振规律与单摆运动相似,其动力学方程存在精确解.圆环杆的均匀扭振为螺旋杆的倾角为零时的特例. 相似文献
69.
J. Náprstek 《Meccanica》1998,33(3):267-277
Abstract. The paper presents the solution to the properties of stochastic response of a system with random parametric noises, which is prone to the loss of aerodynamical stability. The system is described by an equation of van der Pol type with the negative linear, and with the positive cubic dampings. The coefficients of the linear damping and of the stiffness include the multiplicative random perturbations, the external excitation being given as a sum of a deterministic function and of an additive perturbation. All three input random processes are supposed to be Gaussian and centered, with the non-zero mutual stochastic parameters, as it corresponds to the properties of real systems. The solution has been based on the method of stochastic linearisation and of the subsequent solution of the Fokker–Planck–Kolmogorov equation in the sense of the first and second stochastic moments for the transient and stationary states. There have been demonstrated several effects, which are typical for systems with parametric noises, differentiating them from the systems with constant coefficients. The principal attention has been devoted to the properties of the spectral density of the response, the character of which changes abruptly with the degree of non-linearity of the damping and of the level of random perturbations.Sommario. La presente memoria studia le proprietà della risposta stocastica di un sistema con eccitazione casuale parametrica, che tende alla perdita della stabilità aerodinamica. Il sistema è descritto mediante un'equazione del tipo di van der Pole con il termine lineare dello smorzamento negativo e il termine cubico positivo. Poichá l'eccitazione esterna è la somma di una funzione deterministica e di una perturbazione additiva, i coefficienti dello smorzamento lineare e della rigidezza comprendono le perturbazioni casuali moltiplicative. I tre processi stocastici di eccitazione sono assunti gaussiani e a media nulla con parametri stocastici incrociati diversi da zero, come si verifica per le proprietà dei sistemi reali. La soluzione è basata sul metodo della linearizzazione stocastica e della successiva soluzione dell'equazione di Fokker-Planck-Kolmogorov studiando i primi e i secondi momenti statistici per gli stati transitori e stazionari. Vengono mostrati diversi effetti, tipici dei sistemi con eccitazione parametrica, differenziandoli dai sistemi a coefficienti costanti. Particolare attenzione è rivolta alle proprietà della densità spettrale della risposta le cui caratteristiche cambiano bruscamente con il grado di non linearità dello smorzamento e del livello di casualità delle perturbazioni. 相似文献
70.
Theoretical analysis of the mode coupling induced by heat of large-pitch micro-structured fibers 下载免费PDF全文
In this paper,a theoretical model to analyze the mode coupling induced by heat,when the fiber amplifier works at high power configuration,is proposed.The model mainly takes into consideration the mode field change due to the thermally induced refractive index change and the coupling between modes.A method to predict the largest average output power of fiber is also proposed according to the mode coupling theory.The largest average output power of a large pitch fiber with a core diameter of 190 μm and an available pulse energy of 100 mJ is predicted to be 540 W,which is the highest in large mode field fibers. 相似文献