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981.
In this paper we investigate further the method for controlling the uncertain Lue system via adaptive backstepping.The Lue system is transformed into the so-called general strict-feedback form.Then a novel control method can overcome the sigularity problem.Numerical simulations show the effectiveness and feasibility of this approach. 相似文献
982.
Bhabani K. Satapathy Martin Ganß Roland Weidisch Petra Ptschke Dieter Jehnichen Thomas Keller Klaus D. Jandt 《Macromolecular rapid communications》2007,28(7):834-841
A ductile‐to‐semiductile transition in the crack resistance behaviour of PP/MWNT composites is discussed, using an essential work of fracture approach based on a post yield fracture mechanics concept and its possible interrelation to the structural attributes studied by TEM, SEM, and WAXD. A maximum in the non‐essential work of fracture is observed at 0.5 wt.‐% MWNT content, which demonstrates the enhanced resistance to crack propagation compared to pure PP, followed by a sharp decline with the increase in MWNT content to 1.5 wt.‐%, which reveals a ductile‐to‐semiductile transition. Fracture kinetic studies present a qualitative picture of the nature of such a transition in terms of a) switch over from non‐steady (in pure PP) to steady‐state crack tip opening displacement rate (in nanocomposites), and b) a ductile‐to‐semiductile transition; largely as a result of delayed‐yielding of the nanocomposites.
983.
The paper is concerned with adaptive tracking problem for a class of
chaotic system with time-varying uncertainty, but bounded by norm
polynomial. Based on adaptive technique, it proposes a novel
controller to asymptotically track the arbitrary desired bounded
trajectory. Simulation on the Rossler chaotic system is performed
and the result verifies the effectiveness of the proposed method. 相似文献
984.
An exact solution to paraxial propagation of laser beams in longitudinal inhomogeneous plasmas 下载免费PDF全文
An exact, general solution for laser beams propagating in
longitudinally inhomogeneous plasmas is obtained in the form of
the diffraction integral. The Gaussian beam and the Hermite--Gaussian
beam are taken for example. In the case of an increasing plasma
density along the propagation distance, natural diffraction of the
Gaussian beam is retarded. This retardance has a less effect on the
central part of the Hermite--Gaussian beam while a considerable rise
of the power in bucket (PIB) occurs in the surrounding part of the
beam. 相似文献
985.
986.
By comparison of the characteristics of existing models for long fatigue crack propagation rates, a new model, called the generalized passivation-lancet model for long fatigue crack propagation rates (GPLFCPR), and a general formula for characterizing the process of crack growth rates are proposed based on the passivation-lancet theory. The GPLFCPR model overcomes disadvantages of the existing models and can describe the rules of the entire fatigue crack growth process from the cracking threshold to the critical fracturing point effectively with explicit physical meaning. It also reflects the influence of material characteristics, such as strength parameters, fracture parameters and heat treatment. Experimental results obtained by testing LZ50 steel, AlZnMgCu0.5, 0.5Cr0.5Mo0.25V steel, etc., show good consistency with the new model. The GPLFCPR model is valuable in theoretical research and practical applications. 相似文献
987.
Mihaela Popescu 《Acta Mechanica Sinica》2009,25(3):311-318
This paper presents a computational model for the fluid dynamics in a fractured ductile pipe under high pressure. The pressure profile in front of the crack tip, which is the driving source of crack propagation, is computed using a nonlinear wave equation. The solution is coupled with a one dimensional choked flow analysis behind the crack. The simulation utilizes a high order optimized prefactored compact-finite volume method in space, and low dispersion and dissipation Runge-Kutta in time. As the pipe fractures the rapid depressurization take place inside the pipe and the propagation of the crack-induced waves strongly influences the outflow dynamics. Consistent with the experimental observation, the model predicts the expansion wave inside the pipe, and the reflection and outflow of the wave. The model also helps characterize the propagation of the crack dynamics and fluid flows around the tip of the crack. 相似文献
988.
989.
数值流形方法的粘性边界问题初探 总被引:1,自引:1,他引:0
在实际工程数值流形方法分析中,采用固定约束边界的方法处理无限域或者半无限域的情况,边界处应力波的反射造成模拟结果与实际情况不符.本文基于Lysmer等人提出的粘性边界理论,在边界上设置阻尼器,推导相应粘性边界条件下流形单元刚度矩阵的数值计算格式,经岩石长条中弹性波传播算例,并与有限元结果对比,验证了该粘性边界的有效性,有利于数值流形方法的工程中推广应用. 相似文献
990.