Dynamic interaction of moving vehicles and structures

A procedure is developed for simulating the dynamic interaction between traversing vehicles and structures. Lagrange multipliers are employed in time to satisfy constraint conditions between the systems. Illustrative examples are presented. The results are shown to compare very well with analytical and experimental results. The importance of often overlooked terms in the constraint equations is demonstrated.     

Response of a continuous guideway on equally spaced supports traversed by a moving vehicle

An algorithm is developed to analyze the dynamic response of a continuous guideway resting on equally spaced supports being traversed by a moving vehicle. A critical speed, one at which the amplitude of the guideway displacement becomes large, is determined. The critical speed corresponds to the slowest possible speed at which a transverse wave can propagate longitudinally in the guideway structure. A parametric study is also presented.     

Stability of vehicles moving on an elastic foundation

Few studies have been made of the stability of a dynamic system moving on an infinite continuum. Here a general method of analysis of such coupled systems is presented. It shows that vehicles possessing a single point of contact with the foundation become unstable above a velocity always higher than the critical speed defined in the classical constant moving force problem. Flutter speeds lower than this critical speed have been obtained in the case of vehicles with two points of contact. This destabilizing effect is due to the damping of the foundation. The evolution of the flutter boundaries as a function of the characteristics of the foundation is described for a typical vehicle.     

动载体成像系统底座无角位移减振器的设计

详细分析了由动载体振动引起的角位移和线位移对成像系统的影响。角位移是影响成像质量的主要因素。对成像底座减振系统的要求既要满足减振效率,又要控制减振过程中产生的角位移。设计了一种三向等刚度无角位移减震器,它既能满足减振要求,又能控制减振过程中产生的角位移,从而提高了动载体摄像系统的清晰度,同时又不影响视轴的指向精度,是一种比较理想的减振器。     

Disk model for wheels moving over highway bridges with rough surfaces

In most previous analyses of vehicle-bridge interaction (VBI) problems in highways involving surface roughness, the wheels of vehicles have been treated as points, referred to as the point model, and the tracks as a series of hills and valleys. The point model is unrealistic for wheels, as they are of finite size and cannot touch the bottom of valleys. In this study, each wheel will be modeled instead as a rigid disk of finite size, referred to as the disk model, neglecting the tire deformations. The VBI element will be modified accordingly for computing the vehicle and bridge responses. Numerical examples are prepared to illustrate the effect of wheel size on the dynamic responses of the bridge and passing vehicles. It is concluded that the point model tends to introduce some unrealistic high-frequency vibrations on the system responses, while underestimating the amplitude of vehicle frequency in the vehicle response. The disk model should be adopted, if the velocity and acceleration responses of the bridge and the dynamic responses of the moving vehicle are of major concern.     

Terahertz radiation from a nonlinear slab traversed by an optical pulse

We report on the theoretical calculations considering collinear electromagnetic radiation at the propagation of an optical pulse through a slab of nonlinear material. Calculated waveforms of the radiated field fit well to the experimental dependencies showing the remarkable similarities between the radiation at nonlinear wave interaction and the radiation phenomena of moving external charges, similarly to discussed in the Tamm Problem and transition radiation of moving external charges.     

Development and calibration of acoustic video camera system for moving vehicles

In this paper, a new acoustic video camera system is developed and its calibration method is established. This system is built based on binocular vision and acoustical holography technology. With binocular vision method, the spatial distance between the microphone array and the moving vehicles is obtained, and the sound reconstruction plane can be established closely to the moving vehicle surface automatically. Then the sound video is regenerated closely to the moving vehicles accurately by acoustic holography method. With this system, the moving and stationary sound sources are treated differently and automatically, which makes the sound visualization of moving vehicles much quicker, more intuitively, and accurately. To verify this system, experiments for a stationary speaker and a non-stationary speaker are carried out. Further verification experiments for outdoor moving vehicle are also conducted. Successful video visualization results not only confirm the validity of the system but also suggest that this system can be a potential useful tool in vehicle's noise identification because it allows the users to find out the noise sources by the videos easily. We believe the newly developed system will be of great potential in moving vehicles' noise identification and control.     

On the dynamic interaction between moving dislocations

Received: 25 August 1997/Accepted: 23 October 1997     

Suspended bridges subjected to moving loads and support motions due to earthquake

The paper deals with the vibration of suspended bridges subjected to the simultaneous action of moving loads and vertical support motions due to earthquake. The basic partial integro-differential equation is applied to the vertical vibration of a suspended beam. The dynamic actions of traffic loads are modelled as a row of equidistant moving forces, while the earthquake is considered by vertical motions of supports. The governing equation is solved first analytically to receive an ordinary differential equation and next numerically. Moreover, the designed world's largest suspended bridge—Messina Bridge—is investigated (central span of length 3.3 km). The paper studies the effect of various lags of the earthquake arrival because the earthquake may appear at any time when the train moves along a large-span bridge. The modified Kobe earthquake records have been applied to calculations. The results indicate that the interaction of both the moving and seismic forces may substantially amplify the response of long-span suspended bridges in the vicinity of the supports and increase with the rising speed of trains.     

Vacuum magnetic moment of an electron moving in a uniform magnetic field

The methods of quantum electrodynamics are used to study the dependence of the vacuum magnetic moment of the electron on its energy and on the magnetic field intensity. This dependence is most important in the case of strong magnetic fields. For an ultrarelativistic electron, the vacuum magnetic moment turns out to depend on the electron energy, even in a weak magnetic field.Translated from Izvestiya VUZ. Fizika, Vol. 11, No. 11, pp. 17–22, November, 1968.     

Effects of surface irregularities upon the dynamic response of bridges under suspended moving loads

The effects of surface irregularities upon the dynamic response of bridges under suspended moving loads is analyzed by means of a theoretical study. The paper deals with geometrical imperfections of two types, global and local ones. The former may represent irregularities due to permanent loads, creep process or deflections produced by prestressing forces acting on young concrete. The local ones may represent the initial joint or local defects. The vehicle dynamics model is a simple degree of freedom oscillator and the method of analysis used is a Rayleigh-Ritz one. In some cases the amplification factors are found to be much greater than those given by current international design codes and the dynamic effects can no longer be neglected.     

Amplification of electromagnetic pulses in graphene with Hubbard interaction by a uniform high-frequency alternating field

The Maxwell equations for an electromagnetic field propagating in graphene in which electrons with different spin projections experience a strong Coulomb repulsion at a single node are considered. An effective equation analogous to the classical (1+1)-dimensional sine-Gordon equation is derived. Electrons are treated within the framework of the quantum formalism with allowance for changes in the dispersion law in the presence of Coulomb interaction. The effective equation is solved numerically, and the effect of Coulomb repulsion is identified. The amplification of an ultrashort pulse is observed when an external uniform electromagnetic field with a period shorter than the pulse duration is applied.     

动载体成像模糊的振动被动控制技术

动载体成像模糊的振动被动控制技术是解决无人机在高空飞行时,振动加速度为5g(20 500Hz)条件下引起的成像模糊问题。介绍了动载体成像模糊的机理、动载体成像模糊的容限。为了提高动载体光电系统的动态分辨能力,提出了解决动载体成像模糊的措施———振动被动控制技术。分析了振动被动控制的基本原理和设计原则,给出一些相关的典型设计实例。     

Planar nearfield acoustical holography in moving fluid medium at subsonic and uniform velocity

Nearfield acoustical holography (NAH) data measured by using a microphone array attached to a high-speed aircraft or ground vehicle include significant airflow effects. For the purpose of processing the measured NAH data, an improved nearfield acoustical holography procedure is introduced that includes the effects of a fluid medium moving at a subsonic and uniform velocity. The convective wave equation along with the convective Euler's equation is used to develop the proposed NAH procedure. A mapping function between static and moving fluid medium cases is derived from the convective wave equation. Then, a conventional wave number filter designed for static fluid media is modified to be applicable to the moving fluid cases by applying the mapping function to the static wave number filter. In order to validate the proposed NAH procedure, a monopole simulation at the airflow speed of Mach=-0.6 is conducted. The reconstructed acoustic fields obtained by applying the proposed NAH procedure to the simulation data agree well with directly-calculated acoustic fields. Through an experiment with two loudspeakers performed in a wind tunnel operating at Mach=-0.12, it is shown that the proposed NAH procedure can be also used to reconstruct the sound fields radiated from the two loudspeakers.     

带电粒子在相互垂直的匀强电场和磁场中的运动轨迹

推导出带电粒子在相互垂直的匀强电场和磁场中普遍情况下的运动方程,给出了几种典型情况下的轨迹,并对轨迹的形状和性质,结点的出现进行了讨论.     

Peculiarities of the interaction of a structure with moving ice

A new model describing the vibration caused by the interaction between the moving ice cover and a structure attached to the bottom is proposed. The equations obtained estimate the forces affecting the structure under its interaction with ice. The influence of the velocity of ice movement on different vibration conditions is analyzed.     

W波段扩展互作用器件均匀磁聚焦电子光学系统

扩展互作用器件,采用三个线圈和一个磁极实现均匀磁场分布。根据理论计算采用有限元法磁学(FEMM)仿真软件对所求磁场进行了建模分析,依据FEMM计算的磁场结合静电电子枪,采用CST仿真软件对高电流密度、高压缩比的电子注在均匀聚焦磁场的作用下传输进行优化。经过计算得出,在工作电压为17 kV、阴极发射电流密度小于10 A/cm2的条件下,由皮尔斯电子枪发射的电子注在均匀磁场的聚焦作用下传输良好,通过率为100%,得到了导流系数为0.175μP的电子枪,在均匀磁场区形成了高电流密度、高压缩比的电子注,平均电流密度达到343.17 A/cm2,压缩比为32,电子注横纵速度比为7.2%。     

W波段扩展互作用器件均匀磁聚焦电子光学系统

扩展互作用器件,采用三个线圈和一个磁极实现均匀磁场分布。根据理论计算采用有限元法磁学（FEMM）仿真软件对所求磁场进行了建模分析,依据FEMM计算的磁场结合静电电子枪,采用CST仿真软件对高电流密度、高压缩比的电子注在均匀聚焦磁场的作用下传输进行优化。经过计算得出,在工作电压为17 kV、阴极发射电流密度小于10 A/cm2的条件下,由皮尔斯电子枪发射的电子注在均匀磁场的聚焦作用下传输良好,通过率为100%,得到了导流系数为0.175 P的电子枪,在均匀磁场区形成了高电流密度、高压缩比的电子注,平均电流密度达到343.17 A/cm2,压缩比为32,电子注横纵速度比为7.2%。     

Ultracold neutrons and the interaction of waves with moving matter

The present review is focused on the problem of interaction of neutron waves with moving matter. The validity of the 1/v law for ultracold neutrons and the possibility to characterize the interaction of neutrons with matter using the effective potential were verified in the so-called null Fizeau experiments. A neutron wave in such experiments propagates through a flat sample that moves parallel to its edges. The observation of effects caused by this motion provides evidence that the concept of constant effective potential is not correct. The second part of the review deals with the prediction and the first observation of the accelerated matter effect (a change in the energy of neutrons in passing through a refractive sample that moves with an acceleration directed along or opposite the direction of neutron propagation). The characteristic features of this phenomenon in the case of birefringent material are considered. In conclusion, the problem of propagation of neutron waves in matter moving with giant acceleration is discussed.