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991.
垂直参数激励表面波研究进展 总被引:3,自引:1,他引:3
受外激励的充液刚性容器中流体的波动问题有实际的工程应用背景.竖直方向的受周期性外激励的充液容器的自由表面波问题--Faraday波问题是流体力学三大不稳定性难题之一(另外两个不稳定性问题是Rayleigh-B\'enard对流和Taylor-Couette流).本文综述了在理想流体中和弱粘性流体中Faraday波的研究成果;介绍了作者在底部垂直激励的圆柱形容器中流体表面波图谱的实验研究和理论分析的结果.最后提出有待进一步研究的问题.图13,参74 相似文献
992.
993.
黏性阻尼模型存在每周期耗散能量与外激励频率相关的缺陷, 复阻尼模型时域计算结果存在发散现象. 为克服上述两种阻尼模型的不足, 在复阻尼模型基础上, 依据时频域转化原则推导了频率相关黏性阻尼模型. 频率相关黏性阻尼模型不仅具有每周期耗散能量与外激励频率无关的优点, 还保证了结构位移时程的稳定收敛. 混合结构由具有不同阻尼特性的材料组成, 其阻尼矩阵为非比例矩阵, 无法直接采用实模态叠加法. 根据频率相关黏性阻尼模型与复阻尼模型的转换关系, 提出了适用于混合结构的基于频率相关黏性阻尼模型的复模态叠加法. 算例分析结果表明, 与基于黏性阻尼模型的复模态叠加法相比, 基于频率相关黏性阻尼模型的复模态叠加法不仅计算结果唯一, 且不增加矩阵维度, 具有较高的计算效率. 小阻尼情况下, 两种方法的计算结果近似相等, 且与复阻尼模型的频域计算结果一致. 当阻尼比较大时, 两种方法的计算结果差异增大, 但频率相关黏性阻尼模型的复模态叠加法与复阻尼模型的频域计算结果仍保持一致. 相似文献
994.
Tatsuhiro Takahashi Jun Watanabe Keiji Minagawa Jun-ichi Takimoto Kenji Iwakura Prof. Kiyohito Koyama 《Rheologica Acta》1995,34(2):163-171
The effect of ionic interaction on linear and nonlinear viscoelastic properties was investigated using poly(ethylene-co-methacrylic acid) (E/MAA) and its ionomers which were partially neutralized by zinc or sodium. Dynamic shear viscosity and step-shear stress relaxation studies were performed. Stress relaxation moduli G(t, y) of the E/MAA and its sodium or zinc ionomers were factorized into linear relaxation moduli G°(t) and damping functions h(y). The relaxation modulus at the smallest strain in each ionomer agreed with the linear relaxation modulus calculated from storage modulus G and loss modulus G. In the linear region, the ionic interaction shifted the relaxation time longer with keeping the same relaxation time distribution as E/MAA. In the nonlinear region, the ionic interaction had no influence on h(y) when the ion content was low. At higher ion content, however, the ion bonding enhanced the strain softening of h(y). 相似文献
995.
Ding Xie-ping 《应用数学和力学(英文版)》2003,24(5):499-508
A new class of constrained multiobjective games with infinite players in noncompact locally convex H-spaces without linear
structure are introduced and studied. By applying a Fan-Glicksberg type fixed point theorem for upper semicontinuous set-valued
mappings with closed acyclic values and a maximum theorem, several existence theorems of weighted Nath-equilibria and Pareto
equilibria for the constrained multiobjective games are proved in noncompact locally convex H-spaces. These theorems improve,
unify and generalize the corresponding results of the multiobjective games in recent literatures.
Contributed by Ding Xie-ping
Foundation items: the National Natural Science Foundation of China (19871059); the Natural Science Foundation of Education Department of Sichuan
Province ([2000]25)
Biography: Ding Xie-ping (1938-) 相似文献
996.
针对非线性动力学方程,通过Taylor展开和Duhamel积分,得到一个具有待定参数的逐步积分求解公式;通过数学变换,将原动力学方程转换为一个能确定待定参数的能量校准方程;最后将该参数回代入逐步积分公式,得到数值解.数值算例的结果说明了该方法的有效性,可以消除算法阻尼和抑制数值解发散,同时,在大步长的条件下也得到了非常准确而且稳定的结果,可以对系统长期性态进行仿真. 相似文献
997.
组合结构振动的等效阻尼比 总被引:8,自引:0,他引:8
本文采用滞后阻尼的假定,在获得组合结构含有滞后阻尼系数的复频率方程后,进而导出了一种分析组合结构体系效阻尼比的方法,只要在实数范围内,采用通常的特征值方法或所选用2的软件。便可获得各种组合结构任一阶等铲阻尼比,简单且实用,本文最后给出了一个组合悬臂结构和组合高层建筑筒体结构的实例。 相似文献
998.
This study presents a practical, fieldable active controller applicable to shallow, slack cables. The controller is based upon an underlying theory that does not assume that the inertial forces are negligible in the direction of the cable chord. The theoretical framework is developed, and an experimental verification is presented. The experiments utilized a TV camera to track a small number of LED targets on the controlled cable, a commercial X-Y tracker and a PC to compute the cable's present position and velocity, and a linear actuator to vary the cable's tension. A Kalman filter was employed to smooth the position estimates and provide least-squares estimates of the cable velocity. The stability limits for the phase and amplitude of the control signal were established. An analytical estimate of the induced damping expected from the control algorithm is derived. Experimental measurements of the cable frequency and induced damping compared well with theoretical predictions. It is shown that he proposed active control approach is a simple, reliable, as well as an effective, method for vibration attenuation in lightly damped, shallow, slack cables. 相似文献
999.
Water surface wave radiation generated by multiple cylinders oscillating with identical frequency 总被引:3,自引:0,他引:3
贺五洲 《应用数学和力学(英文版)》1999,20(10):1150-1159
IntroductionAfundamentalsubjectinthestudyofinteractionbetweenwavesandbodyistosolvethetwo_dimensionalradiationproblemgeneratedbycylindersoscillatinginorbelowthefreewatersurface,whichhasattractedwideattention.EversinceUrsellpublishedthepaper[1]involvin… 相似文献
1000.
Nylon-6 is an important engineering polymer that, in its fully spherulitic (bulk) form, has many applications in gears, rollers,
and other long life cycle components. In 1993, Toyota commercialized a nylon-6/clay nanocomposite out of which it produced
the timing belt cover for the Camry. Although these hybrid nanocomposites show significant improvements in their mechanical
response characteristics, including yield strength and heat distortion temperature, little is known about the degradation
of these properties due to environmental pollutants like NO
x
. Nylon-6 fibers are severely degraded by interaction with NO
x
and other pollutants, showing a strong synergy between applied load and environmental degradation. While the nanocomposites
show a significant reduction in permeability of gases and water due to the incorporation of lamellar clay, their susceptibility
to nondiffusional mechano-chemical degradation is unknown. The fracture toughness of these nylon-6/clay nanocomposites increases,
not as a function of clay content, but as a function of the volume of nylon-6 polymer chains influenced by the clay lamellae
surfaces. Both the clay and the constrained volume offer the nanocomposites some protection from the deleterious effects of
NO
x
. The time-to-failure at a given stress intensity factor as a function of clay content and constrained volume is discussed
along with fracture toughness of the materials. 相似文献