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表面能对纳米颗粒的晶格收缩和固有频率的影响 总被引:6,自引:0,他引:6
由于纳米颗粒具有很大的比表面积,因此,表面能对它的力学性能有着不可忽略的影响.本文给出了由表面能所导致的纳米颗粒晶格收缩效应的解析结果,与试验观察定量上相当一致;计算了表面能对纳米颗粒固有频率的影响,预测了由于表面能的影响,纳米颗粒出现的“振动软化”现象. 相似文献
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We study a two-dimensional analog of the Helmholtz resonator with walls of finite thickness in the critical case, for which there exists a frequency which is simultaneously the limit of poles generated both by the bounded component of the resonator and by a narrow communication channel. Under the assumption that the limit frequency is a simple frequency for the bounded component, by using the method of matched asymptotic expansions, we construct asymptotics for the two sequences of poles converging to this frequency. We obtain explicit formulas for the leading terms of the asymptotics of poles and for the solution of the scattering problem. 相似文献
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弹簧质量对振动的影响 总被引:18,自引:9,他引:9
给出了弹簧质量不可忽略的弹簧振子系统的振动解,导出了弹簧的有效质量的渐近级数表达式、指出振动呈拟周期性。 相似文献
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在超声速或高超声速绕流中,一种很严重的脉动压力环境是由激波边界层相互作用引起的激波振荡.这种高强度的振荡激波可能诱发结构共振.因这一现象非常复杂,已发表的文章都采用经验或半经验方法.本文首次从基本流体动力学方程出发,给出了由湍流剪切层引起的激波振荡频率的理论解,得到了振荡频率随气流Mach数M∞和压缩折转角θ的变化规律,计算结果与实验值是相符的.本文为激波振荡导致的气动弹性问题提供了一种有价值的理论方法. 相似文献
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Summary The paper proposes a method in finite element analysis for estimating natural frequencies of a disk tensioned by rolling,
without the use of eigenvalue analysis. The natural frequencies of a disk vary when the localized plastic deformation caused
by roll-tensioning induces residual stresses. Tensioning is used for improving the dynamic stability of circular saws; the
optimal condition of rolling can be predicted from natural frequency characteristics. In the proposed method, the natural
frequencies after rolling are easily estimated from the mode shapes of the disk before rolling and the stress distribution
after rolling. The method is based on ideas similar to thermal stress and sensitivity analysis rather than on eigenvalue analysis.
The effectiveness of the method is shown by comparing the natural frequency characteristics obtained by this method with those
by eigenvalue analysis.
Received 18 June 1998; accepted for publication 8 April 1999 相似文献
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主要对上海光源(SSRF)束流位置监视器(BPM)支撑的机械稳定性进行了研究.受有限元计算与初始设计方案的振动测试结果不一致的启发,对BPM支撑与地面的连接考虑了三种方案:膨胀螺母、半灌浆与全灌浆连接.通过采用改进的全灌浆连接来代替初始设计的膨胀螺母连接,BPM支撑的横向最低共振频率由20.2Hz增加到50.2Hz,支撑顶部与地面的横向均方根位移(4-50Hz)之比由4.36降低到1.32,机械稳定性能得到大大的提高. 相似文献
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In this paper, how to compute the eigenfrequencies of the structures composed of a series of inclined cables is shown. The physics of an inclined cable can be complicated, so solving the differential equations even approximately is difficult. However, rather than solving the system of 4 first-order equations governing the dynamics of each cable, the governing equations are instead converted to a set of equations that the exterior matrix satisfies. Therefore, the exterior matrix method (EMM) is used without solving the original governing equations. Even though this produces a system of 6 first-order equations, the simple asymptotic techniques to find the first three terms of the perturbative solution can be used. The solutions can then be assembled to produce a 6 × 6 exterior matrix for a cable section. The matrices for each cable in the structure are multiplied together, along with the exterior matrices for each joint. The roots of the product give us the eigenfrequencies of the system. 相似文献