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101.
Keith W. Buffinton 《Nonlinear dynamics》1990,1(5):359-377
Studied in this work are the formulation of equations of motion and the response to parametric excitation of a uniform cantilever beam moving longitudinally over a single bilateral support. The equations of motion are generated by using assumed modes to discretize the beam, by regarding the support as a kinematic constraint, and by employing an alternate form of Kane's method that is particularly well suited to systems subject to constraints. Instability information is developed using the results of perturbation analysis for harmonic longitudinal motions of small amplitude and with Floquet theory for general periodic motions of any amplitude. Results demonstrate that definitive instability information can be obtained for a beam moving longitudinally over supports based on the frequencies of free transverse vibration of a beam that is longitudinally fixed. 相似文献
102.
An Optimal Nonlinear Feedback Control Strategy for Randomly Excited Structural Systems 总被引:16,自引:0,他引:16
A strategy for optimal nonlinear feedback control of randomlyexcited structural systems is proposed based on the stochastic averagingmethod for quasi-Hamiltonian systems and the stochastic dynamicprogramming principle. A randomly excited structural system isformulated as a quasi-Hamiltonian system and the control forces aredivided into conservative and dissipative parts. The conservative partsare designed to change the integrability and resonance of the associatedHamiltonian system and the energy distribution among the controlledsystem. After the conservative parts are determined, the system responseis reduced to a controlled diffusion process by using the stochasticaveraging method. The dissipative parts of control forces are thenobtained from solving the stochastic dynamic programming equation. Boththe responses of uncontrolled and controlled structural systems can bepredicted analytically. Numerical results for a controlled andstochastically excited Duffing oscillator and a two-degree-of-freedomsystem with linear springs and linear and nonlinear dampings, show thatthe proposed control strategy is very effective and efficient. 相似文献
103.
斜拉桥中拉索承受着多种端部激励,可激发大幅空间振动.以斜拉索为对象,探究不同端部激励间相位差对其非线性振动的影响.首先,推导斜拉索无量纲离散控制方程,引入考虑相位的三向端部激励得到一般化模型;然后,针对拉索下端存在的纵桥向、竖向和横桥向激励的两两组合,受大幅或小幅激励,及其在主共振区或主参数共振区几组因素,共计12种工况,采用数值分析法分别研究了各工况下不同激励相位差时的斜拉索稳态响应.研究发现:激励相位差能加剧与激励频率相近的面内、外模态振动;在任意端部激励组合下,激励相位差不仅可使斜拉索非线性振动出现定量变化,还可改变内共振的表现形式.面内、外激励组合下,相位差对拉索响应幅值的影响以π为周期变化,且当相位差趋于π/2 + kπ (k = 0, 1, 2…)时影响最为突出;而面内激励组合下,以2π为变化周期,当相位差为π + 2kπ (k = 0, 1, 2, …)时其对稳态幅值的影响最显著.其原因是:面外激励关于拉索所在的竖直面对称,故其本质上以π为周期;而面内激励无此对称性,仍以2π为周期.因此,有无面外激励参与决定了激励间相位差对斜拉索响应的影响规律. 相似文献
104.
105.
在中性原子的磁囚禁实验中,磁阱线圈的电流噪声会激发磁阱中的原子运动,势必对原子团的温度和寿命产生不可忽视的影响。对于非简谐阱,这种激发具有能量选择特性,它又取决于电流噪声的频谱分布。选择了实验中常用的四极阱为研究对象,用直接模拟蒙特卡罗方法来模拟四极阱中原子运动的参变激发现象,得到了原子温度与原子数损失随激发频率的变化关系,并进一步计算了两个共振峰处原子温度随调制时间和调制深度的变化曲线。此外,还研究了弹性碰撞速率对参变激发过程中原子温度上升的影响。这些结果对四极阱参变激发的实验有较好的参考价值。 相似文献
106.
107.
介孔分子筛Al-MCM-41的合成与催化异构化性能 总被引:1,自引:0,他引:1
采用正硅酸乙酯(TEOS)为硅源,九水硝酸铝为铝源,十六烷基三甲基溴化胺(CTMABr)为模板剂,在室温条件下合成了介孔Al-MCM-41分子筛.通过XRD、N2等温吸附、SEM、FTIR等分析测试手段表征了分子筛的介孔结构和表面性质.结果表明所合成的分子筛有良好的介孔结构和较高的有序度,并且有较高的比表面积(达到816 m2·g-1)和窄的孔径分布.采用程序升温的焙烧方式、凝胶Al/Si比最大范围控制在0.06~0.13有利于合成高度有序的介孔Al-MCM-41分子筛.评价结果表明,所合成的Al-MCM-41分子筛对桥式四氢双环戊二烯(endo-TCD)异构化反应合成挂式异构体exo-TCD及金刚烷具有较高的催化活性和极高的选择性. 相似文献
108.
Shyjumon Ibrahimkutty Daniel Issenmann Stefan Schleef Anke‐Susanne Müller Yves‐Laurent Mathis Biliana Gasharova Erhart Huttel Ralph Steininger Jörg Göttlicher Tilo Baumbach Albrecht Bartels Christof Janke Anton Plech 《Journal of synchrotron radiation》2011,18(4):539-545
A high‐repetition‐rate pump–probe experiment is presented, based on the asynchronous sampling approach. The low‐α mode at the synchrotron ANKA can be used for a time resolution down to the picosecond limit for the time‐domain sampling of the coherent THz emission as well as for hard X‐ray pump–probe experiments, which probe structural dynamics in the condensed phase. It is shown that a synchronization of better than 1 ps is achieved, and examples of phonon dynamics of semiconductors are presented. 相似文献
109.
A new crystalline octahedral hexaaqua Ni(II) bis(o-tolylazo-citrazinate)hexahydrate complex was synthesized. The analytical data proved the formation of 1:2 stoichiometry. An X-ray structure investigation has been carried out. The triclinic space group is p and the unit cell parameters are a = 585.5 pm, b = 993 pm, c = 1139.4 pm, α = 101.6°, β = 97.4°, γ = 102.4°. Evaluation of intensity data revealed the structure with an R-value of 0.03 (2316 observed independent reflections). The compound consists of hexaaqua nickel(2+) ions, univalent anions of the carboxylic acid and six additional water molecules per 相似文献
110.
V. S. Gorelik A. A. Esakov A. N. Morozov P. P. Sverbil’ S. D. Tyves 《Journal of Russian Laser Research》2008,29(1):71-89
We developed a method for detecting traces of foreign components in water and analyzing the microstructure of water. The method
is based on studies of the characteristics of secondary emission arising in aqueous media under excitation by radiation of
ultraviolet lasers and light emitting diodes. A new type of cuvette (capillary cuvettes) for studying the secondary emission
in molecular media was elaborated. The cuvettes enable the study of aqueous solutions at small concentrations of the components;
they enable one to recognize the type of molecular compound present in aqueous media, in view of the photoluminescence spectra. 相似文献