共查询到19条相似文献,搜索用时 93 毫秒
1.
教学经常使用固有频率表达式不显含弹簧静变形和重力加速度的振子;但也能找到相反的情形.本研究探讨前者的充要条件.分析发现如果弹簧轴线在质点通过静平衡位置时沿其轨迹的切向,则弹簧静变形从固有频率表达式中消失.在满足这一前提下,进一步要求质点轨迹在静平衡位置的曲率为0,或沿铅垂方向,则重力也无回复力的效果,从而重力加速度在固有频率表达式中不出现.该结论不仅有助于理解重力与固有频率之间的关系,也可指导振动例题编制和选用. 相似文献
2.
关于弹簧振子固有频率的进一步讨论 总被引:7,自引:3,他引:4
近年来,国内外的一些研究生入学试题中,常见的一个题目是,在不能忽略弹簧质量的前题下计算弹簧振子的固有频率。这个问题本质上牵涉到弹性介质中波的传播问题,比较复杂.但是,在某些简化假设下,可以用计算固有频率的能量法──雷利法[1]来近似求解,并证明在此情况下弹簧振子的固有(圆)频率为[2]:式中k为弹簧的倔强系数,m为弹簧的质量,M为振动物体的质量. 现在,我们证明(1)式只是精确解在一定程度下的近似,同时讨论(1)式的应用条件和因而引起的误差,以便对(1)式有个较深入的理解. 我们仍然需要作一些简化处理,即把弹簧简化为一根均匀的弹性杆… 相似文献
3.
4.
弹簧振子系统振动的周期 总被引:2,自引:2,他引:0
本文分析了弹簧质量不可忽略时,对振子周期的影响.引用瑞利法讨论系统振动的基频,最后按多自由度理论对精确求解进行了讨论;通过比较,阐明瑞利法的适用范围及精度.文中还提到计算振动周期的简捷方法──能量法. 相似文献
5.
6.
本文在处理对力的粒子数守恒方法的基础上,提出了处理长程力的一个方法,利用此方法分析了重变形核的振动态的微观机构.变形核的振动态被看成是在长程力(四极力、八极力等)的影响下,K~π相同的若干“对拆散态”和“对激发态”的某种相干混合.给出了长程力在各“对拆散态”和“对激发态”之间的矩阵元公式.在此方法中,避免了通常在BCS方法基础上处理振动时所碰到的粒子数不守恒、假态、波函数不正交等困难.也没有采用RPA方法中那些近似假定.而且基态或激发态的不同的堵塞效应已自动考虑在内。np力对导致振动态的出现起了重要作用.作为例子,我们分析了稀土偶偶核的γ振动和锕系偶偶核的b振动态的内部结构.具体说明了以下事实:(l)振动带位置随不同核的变化规律(图1,3);(2)从基态到振动态的跃迁几率有显著加强;(3)讨论了重变形核中什么区域可以出现低能级的振动带.本文还分析了奇A核的γ振动态,它们被看成是K~π相同的三粒子态和单粒子态的相干混合.以Ho~(165)为例,分析了奇A核γ振动的各种特点.在这里堵塞效应起了很重要的作用. 相似文献
7.
8.
9.
10.
11.
Camera calibration from vanishing points in a vision system 总被引:1,自引:0,他引:1
Camera calibration has been studied for many years and there are many methods available to find the parameters precisely. However, most existing methods require information of the known scene points in general three-dimensional positions for the calibration. A simple, geometrically intuitive method is proposed. The intrinsic parameters of the camera are determined by using the vanishing points in each image. The rotation matrix of the projection matrix is computed from the vanishing and image edges and the translation matrix are obtained with additional translation motion between the viewpoints. Our approach does not need any a priori information about the cameras being used. Computer simulations and real data experiments are carried out to validate our method. 相似文献
12.
13.
14.
It is proved that the Kubo formula for the conductivity σ(ω) is valid at real frequencies ω. On this basis, an exact relation is derived for the static conductivity σst of the Coulomb system. It is shown that the static conductivity is determined by the time correlation function in the limit t→∞. It is proved that the permittivity ε(ω) satisfies the Kramers-Kronig relations which take into account a singularity associated with static conductivity. 相似文献
15.
A dyadic shell model for the Navier-Stokes equations is studied in the context of turbulence. The model is an infinite nonlinearly coupled system of ODEs. It is proved that the unique fixed point is a global attractor, which converges to the global attractor of the inviscid system as viscosity goes to zero. This implies that the average dissipation rate for the viscous system converges to the anomalous dissipation rate for the inviscid system (which is positive) as viscosity goes to zero. This phenomenon is called the dissipation anomaly predicted by Kolmogorov’s theory for the actual Navier-Stokes equations. 相似文献
16.
Resonance response of a single-degree-of-freedom nonlinear vibro-impact system to a narrow-band random parametric excitation 下载免费PDF全文
The resonant response of a single-degree-of-freedom nonlinear vibro-impact oscillator with a one-sided barrier to a narrow-band random parametric excitation is investigated. The narrow-band random excitation used here is a bounded random noise. The analysis is based on a special Zhuravlev transformation, which reduces the system to one without impacts, thereby permitting the applications of random averaging over "fast" variables. The averaged equations are solved exactly and an algebraic equation of the amplitude of the response is obtained for the case without random disorder. The methods of linearization and moment are used to obtain the formula of the mean-square amplitude approximately for the case with random disorder. The effects of damping, detuning, restitution factor, nonlinear intensity, frequency and magnitude of random excitations are analysed. The theoretical analyses are verified by numerical results. Theoretical analyses and numerical simulations show that the peak response amplitudes will reduce at large damping or large nonlinear intensity and will increase with large amplitude or frequency of the random excitations. The phenomenon of stochastic jump is observed, that is, the steady-state response of the system will jump from a trivial solution to a large non-trivial one when the amplitude of the random excitation exceeds some threshold value, or will jump from a large non-trivial solution to a trivial one when the intensity of the random disorder of the random excitation exceeds some threshold value. 相似文献
17.
Nicolai Reshetikhin 《Letters in Mathematical Physics》1992,26(3):167-177
It is shown that the Knizhnik-Zamolodchikov (KZ) equation (and corresponding vector bundle) can be viewed as a quantization of the isomonodromy problem for differential equations with several singular points. 相似文献
18.
This paper provides an approximate method to determine the stiffness and the fundamental frequency of a cracked beam. The cracked beam is first represented as an un-cracked beam with equivalent reduced sections around the cracks. The effect of the cracks is explained, visualised and quantified using the equivalence concept developed for stepped beams with periodically variable cross-sections. Then an alternative expression of the improved Rayleigh method is provided to calculate the natural frequencies of a beam with a variable stiffness distribution along its length. As the method is insensitive to the assumed mode shapes, it avoids the difficulty in choosing appropriate mode shapes and yields accurate results. This is shown using several examples to compare the results determined using the proposed method and the Finite Element method (FEM). The method greatly simplifies the calculation of cracked beams with complicated configurations, such as a beam with several cracks, a cracked beam with concentrated masses, a beam with cracks close to each other, and a beam with periodically distributed cracks. 相似文献
19.
《Physics letters. [Part B]》1987,197(4):500-504
Ground state spins of odd-A nuclei in the region just beyond 208Pb are compiled. They are compared with the theoretically predicted spins of an axially symmetric, reflection asymmetric nucleus with octupole deformation ϵ3 = 0.08 to determine the region of static quadrupole-octupole deformation. Coexistence of different shapes and the corresponding spectra in the same nucleus are predicted in the transition regions. 相似文献