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41.
In some previous geometric nonlinear finite element formulations, due to the use of axial displacement, the contribution of
all the elements lying between the reference node of zero axial displacement and the element to the foreshortening effect
should be taken into account. In this paper, a finite element formulation is proposed based on geometric nonlinear elastic
theory and finite element technique. The coupling deformation terms of an arbitrary point only relate to the nodal coordinates
of the element at which the point is located. Based on Hamilton principle, dynamic equations of elastic beams undergoing large
overall motions are derived. To investigate the effect of coupling deformation terms on system dynamic characters and reduce
the dynamic equations, a complete dynamic model and three reduced models of hub-beam are prospected. When the Cartesian deformation
coordinates are adopted, the results indicate that the terms related to the coupling deformation in the inertia forces of
dynamic equations have small effect on system dynamic behavior and may be neglected, whereas the terms related to coupling
deformation in the elastic forces are important for system dynamic behavior and should be considered in dynamic equation.
Numerical examples of the rotating beam and flexible beam system are carried out to demonstrate the accuracy and validity
of this dynamic model. Furthermore, it is shown that a small number of finite elements are needed to obtain a stable solution
using the present coupling finite element formulation. 相似文献
42.
Flexible-body modeling with geometric nonlinearities remains a hot topic of research by applications in multibody system dynamics
undergoing large overall motions. However, the geometric nonlinear effects on the impact dynamics of flexible multibody systems
have attracted significantly less attention. In this paper, a point-surface impact problem between a rigid ball and a pivoted
flexible beam is investigated. The Hertzian contact law is used to describe the impact process, and the dynamic equations
are formulated in the floating frame of reference using the assumed mode method. The two important geometric nonlinear effects
of the flexible beam are taken into account, i.e., the longitudinal foreshortening effect due to the transverse deformation,
and the stress stiffness effect due to the axial force. The simulation results show that good consistency can be obtained
with the nonlinear finite element program ABAQUS/Explicit if proper geometric nonlinearities are included in the floating
frame formulation. Specifically, only the foreshortening effect should be considered in a pure transverse impact for efficiency,
while the stress stiffness effect should be further considered in an oblique case with much more computational effort. It
also implies that the geometric nonlinear effects should be considered properly in the impact dynamic analysis of more general
flexible multibody systems. 相似文献
43.
Atsushi Kawamoto 《Structural and Multidisciplinary Optimization》2009,37(4):429-433
This paper deals with the design of compliant mechanisms in a continuum-based finite-element representation. Because the displacements
of mechanisms are intrinsically large, the geometric nonlinearity is essential for designing such mechanisms. However, the
consideration of the geometric nonlinearity may cause some instability in topology optimization. The problem is in the analysis
part but not in the optimization part. To alleviate the analysis problem and eventually stabilize the optimization process,
this paper proposes to apply the Levenberg–Marquardt method to the nonlinear analysis of compliant mechanisms. 相似文献
44.
Vimal Singh 《Automatica》2008,44(1):282-285
A novel criterion for the global asymptotic stability of a class of digital filters utilizing single saturation nonlinearity is presented. An example showing the effectiveness of the present criterion is given. 相似文献
45.
46.
第五代移动通信系统新空口(5G NR)的信号带宽、调制度和峰均比相比4G信号高很多。用于小蜂窝或微蜂窝基站组网的光载无线通信(Radio-over-Fiber, RoF)前传系统的非线性失真也更加严重。为了使5G NR信号线性传输,采用记忆多项式(Memory Polynomial, MP)和广义记忆多项式(Generalized Memory Polynomial, GMP)模型构建数字预失真器,矫正5G RoF前传系统的非线性。在实验中搭建了2 km光纤的RoF前传系统,并采用100 MHz带宽5G NR信号作为测试信号对其进行线性化测试。实验结果表明,采用MP和GMP数字预失真器进行线性化时,5G RoF前传系统的邻信道功率比(Adjacent Channel Power Ratio, ACPR)可分别改善13 dB和17 dB以上。这说明MP和GMP数字预失真器对5G RoF前传系统的非线性具有显著的抑制作用。因此基于MP和GMP两个模型的数字预失真器均可用于5G RoF前传系统的线性化,而且GMP预失真器比MP预失真器对该系统线性化的能力更强。 相似文献
47.
具有硬边界的动基座双自由度动力学系统在受到基座周期性激励与随机冲击扰动时,振子与边界碰撞后的强非线性特性导致系统产生复杂的混沌行为.本文基于Soft Actor-Critic强化学习框架,构建了同时实现振动控制与基座运动跟随的智能算法,研究了宽频域范围内含有硬边界约束的动基座双自由度系统的动力学控制效果.通过构建包含相对位移、控制力的复合奖励函数,实现动力学系统精度较高的轨迹跟踪与振动抑制.结果表明,该算法可以实现频率范围跨2个数量级(0.01Hz到1Hz)的有效振动控制,并通过与PID控制方法的比较,展现了该方法在复杂环境中的稳定性与泛化性. 相似文献
48.
Cong Viet Phan Hervé Di Benedetto Cédric Sauzéat Josselin Dayde Simon Pouget 《Fatigue & Fracture of Engineering Materials & Structures》2017,40(12):2169-2182
Quantification of different effects (nonlinearity, heating, thixotropy, and fatigue) occurring during fatigue tests on bituminous mixtures is presented in this paper. A focus is given on the nonlinearity phenomenon. Continuous fatigue tests and a test with specific protocol (called fatigue tests to estimate biasing effects) were performed in tension/compression mode on cylindrical samples of the same material. The analysis of results reveals that reversible effects (nonlinearity, heating, and thixotropy) are important (more than 90% decrease at 100,000 cycles for a strain amplitude of 100 μm/m at 10 Hz) and cannot be ignored when interpreting classical fatigue tests. The nonlinearity effects respect the time‐temperature superposition principle, and they are more pronounced at “high” temperature (at the same frequency). Direction of nonlinearity curve in the Cole‐Cole axes is shown to be independent of temperature and frequency for the considered range. 相似文献
49.
50.
The rth order nonlinearity of a Boolean function is an important cryptographic criterion in analyzing the security of stream as well as block ciphers. It is also important in coding theory as it is related to the covering radius of the Reed-Muller code R(r,n). In this paper we deduce the lower bounds of the second order nonlinearities of the following two types of Boolean functions:
- 1.
- with d=22r+2r+1 and , where n=6r.
- 2.
- , where x,y∈F2t,n=2t,n?6 and i is an integer such that 1?i<t,gcd(2t-1,2i+1)=1.