振动在运动训练中的应用

体育动作是人体与周围环境之间相互作用的结果,人体组织和结构,各种器材和装备都有自身的固有频率和在力作用下产生振动的频率.运动员可以在一定范围内通过改变肌肉紧张度使人体的晃动质量变为硬质量,从而调节动作频率,以适应器械（如跳水跳板,单、双杠等）的振动频率,取得共振的效果.为此,需要测定人体和器械（包括运动鞋等）的固有频率,并通过运动员技术使二者共振.文章介绍了振动在体育训练中的运用,由于人体对振动刺激的反映规律尚不清楚,振动的运用还需要进一步探索和研究.     

Application of hysteresis functions in vibration problems

In the paper, the notion of the hysteresis function introduced by the author is developed further and applied in some vibration problems for hysteretic materials. The stress–strain relation is built on the basis of well-known extended Masing's rules in which the scaled backbone curve used in the second rule is replaced by a more general function called the hysteresis function. This modification allows us to regulate the dependence of the damping ratio on the strain amplitude in the process of cycle deforming of a material with further extending to arbitrary deformation processes. The three cases of hysteretic systems are considered: the system with limited stress when strain increases without bound, the system with linear backbone curve, and the system with the backbone curve having increasing stiffness for increasing strain. For a number of dynamic examples, a comparison of different hysteresis functions is carried out.     

Application of dynamic vibration absorbers in structural vibration control under multi-frequency harmonic excitations

In this research, the response properties of a single-degree-of-freedom system under dual harmonic excitation are analyzed to provide some principles for the choice of time span and step in the simulations. The performances of dynamic vibration absorber (DVA) and state-switched absorber (SSA) are compared. The results indicate that dual DVAs almost have the same performance as the SSA. Moreover, dual DVAs compared with the SSA have some advantages such as lower ratio of tuning frequencies, more rapid optimization process and lower requirement for the anti-fatigue property of the material. Furthermore, the performances of different frequency-tuning methods are investigated. It is shown that the one-one method almost has the same performance as the optimization method and it does not need time-consuming optimization process.     

Application of dynamic vibration absorbers in floating raft system

To improve the isolation performance of the traditional floating raft system, dynamic vibration absorber (DVA) is introduced into floating raft in this research. The mathematical models of floating raft system consisting of beams are implemented by assembling the mobility matrices of the subsystems. Then the power flow transmission characteristics of the coupled system with/without the DVAs are investigated to evaluate the vibration reduction performance of DVAs. Numerical simulations are performed to explore the influence of several parameters, such as the setting positions, damping and mass of the passive DVAs, on the vibration reduction effects of DVAs. Moreover the vibration reduction performance of the semi-active absorber adjusting its stiffness adaptively is analyzed for the case of time-varying frequency excitation. In addition, the vibration reduction effects of semi-active DVAs under multi-frequency excitation are investigated. The results show that DVAs can significantly improve the isolation performance of floating raft system.     

Application of ESPI to three-dimensional vibration measurements

There are many situation in vibration analysis where it is necessary or desirable to make three-dimensional measurements. By using three different illumination geometries around a single imaging system, electronic speckle pattern interferometry (ESPI) can be used to measure the orthogonal components of vibration amplitude independently. These can be combined to determine the three-dimensional amplitude and mode shape. Examples of experimental results are presented for volume vibrations of a thick cylinder, identification of vibration modes of a turbocharger blade, and observation of in-plane modes in a thin plate.     

动力吸振器在斯特林制冷机振动控制中的应用

针对斯特林制冷机的振动模型分析了振动特点,分析了动力吸振器在斯特林制冷机振动控制中的应用,给出了动力吸振器的设计方法.     

对弦振动实验中振源的改进

设计制作了一种振源．将其应用于弦振动实验时,不但能像电动音叉作振源那样,可以验证弦线上驻波波长与弦线张力、密度的关系,而且还可以验证电动音叉作振源所不能验证的弦线上驻波波长与驻波频率的关系．     

Application of gas-fluid atomization technology in ultrosonic vibration cutting titanium alloy workpiece

Acoustical Physics - To further improve machined surface quality of diamond cutting titanium workpiece and reduce diamond tool wear, it puts forward a kind of machining technology with mixture of...     

Application of optimization methods to vibration control of stretched strings

In this paper, non-linear programming techniques are applied to the problem of controlling the vibration pattern of a stretched string. First, the problem of finding the magnitudes of two control forces applied at two points l₁ and l₂ on the string to reduce the energy of vibration over the interval (l₁, l₂) relative to the energy outside the interval (l₁, l₂) is considered. For this problem the relative merits of various methods of non-linear programming are compared. The more complicated problem of finding the positions and magnitudes of two control forces to obtain the desired energy pattern is then solved by using the slack unconstrained minimization technique with the Fletcher-Powell search. In the discussion of the results it is shown that the position of the control force is very important in controlling the energy pattern of the string.     

A model for competitiveness level analysis in sports competitions: Application to basketball

The degree of overall competitiveness of a sport league is a complex phenomenon. It is difficult to assess and quantify all elements that yield the final standing. In this paper, we analyze the general behavior of the result matrices of each season and we use the corresponding results as a probably density. Thus, the results of previous seasons are a way to investigate the probability that each team has to reach a certain number of victories. We developed a model based on Shannon entropy using two extreme competitive structures (a hierarchical structure and a random structure), and applied this model to investigate the competitiveness of two of the best professional basketball leagues: the NBA (USA) and the ACB (Spain). Both leagues’ entropy levels are high (NBA mean 0.983; ACB mean 0.980), indicating high competitiveness, although the entropy of the ACB (from 0.986 to 0.972) demonstrated more seasonal variability than that of the NBA (from 0.985 to 0.990), a possible result of greater sporting gradients in the ACB. The use of this methodology has proven useful for investigating the competitiveness of sports leagues as well as their underlying variability across time.