不对称滞回振动系统频率俘获情况下的同步现象

对具有不对称滞回性的自同步振动系统在频率俘获情况下的同步特性进行研究。建立不对称滞回模型和具有不对称滞回特性的自同步振动系统的非线性动力学模型,利用Matlab/Simulink仿真呈现频率俘获情况下的系统双激振电机的同步运行和系统的同步运行稳定特性。通过仿真分析系统可实现频率俘获现象以及在频率俘获情况下仍能实现同步特性。研究表明具有不对称滞回性的非线性振动系统仍能实现频率俘获情况下的双激振电机的同步运转和系统的同步稳定性。     

反向回转双机驱动振动系统的自同步理论

利用异步电动机电压同步坐标系,得出电动机稳态运行时电磁转矩与转速的关系。运用动力学理论分析反向回转双机驱动振动系统的动力学特性,建立系统频率俘获的方程,得到实现频率俘获的条件及俘获频率和两偏心转子相位差的理论计算方程。利用非线性动力学理论,建立了频率俘获的稳定方程。利用Routh-Hurwitz准则获得系统稳定性条件。     

非线性振动系统基于频率俘获现象的谐振同步分析

基于单质体非线性振动系统的机电耦合动力学模型,在对非线性振动系统起动过程中出现的频率俘获现象定量描述的基础上,考虑非理想振动系统的激振源与系统非线性振动运动的相互影响,研究了双激振源非线性振动系统基于频率俘获作用,实现谐振同步的理论条件。并依据激振电动机驱动系统与振动机械系统之间的耦合动力学模型及试验测定的试验台机械特性参数,通过数值仿真及试验,验证和解释了非线性振动系统频率俘获现象下,系统双激振源的谐振同步问题,指出非理想非线性振动系统的频率俘获现象,以及该现象下的多激振源谐振同步运动与振动系统的非线性强度、刚度、阻尼等参数之间的关系。研究结果对多激振源激励非线性振动系统的谐振同步运动现象分析,提供一定的理论支持和试验依据。     

在振动筛上实现振动同步传动及试验研究

在自同步理论研究中,存在着一种现象,无直接驱动源的激振器仍能跟随另外一个或多个有源驱动的激振器同步运转,即称振动同步传动。针对直线振动筛的振动机构,应用Lagrange能量方程建立动力学模型,根据线性叠加原理得到系统稳态时的响应,利用时间双尺度法获取频率俘获方程,并给出直线振动筛实现"振动同步传动"的同步性判据及同步状态下的稳定性判据。在供电频率50Hz的试验条件下,测量得到电机2断电前后稳态时系统的响应及两激振器的相位差和转速,验证了理论方法的正确性,为直线振动筛在振动同步传动理论方面的应用提供了依据。     

手持式振动机械的同步问题

提出了一种双电机驱动的手持式振动机模型,研究了该振动系统的自同步理论.首先,利用拉格朗日公式,推导出振动系统的运动微分方程;然后,引入两个扰动小参数,对激振器的角速度和相位差进行平均.通过对两激振器的运动方程在平均周期内进行积分平均计算,推导出了系统频率捕获方程.该方法将两激振器的自同步问题转换成了频率捕获方程零解的存在性和稳定性问题,进而推导出了实现频率捕获和两电机稳定同步运行的条件,还提出频率捕获转矩概念来解释两激振器自同步的特性.结果表明,两激振器之间存在一个频率捕获力矩,对两电机同步运行和稳定性有影响.     

反向回转双机驱动振动系统基于频率俘获的控制研究

建立了反向回转双机驱动振动系统的动力学模型和感应电机的数学模型,运用动力学理论分析了振动系统的动力学特性,得到了反向回转双机驱动振动系统实现频率俘获的条件．根据振动系统的频率俘获条件,分析了对2个2偏心转子相位差的控制策略．分别运行自同步条件下的系统仿真程序和基于振动系统频率俘获条件的相位差控制仿真程序,计算机仿真结果表明对振动系统施加控制后,该系统能够快速实现速度同步和相位同步,验证了控制策略的有效性．     

自同步振动系统的动力学耦合特性及实验

为了研究双机驱动自同步振动系统的动力学耦合特性,引入两个激振器的平均角速度和相位差两个参数,对振动系统的参数进行无量纲化处理,得到振动系统的同步性条件和稳定性条件。定量分析了振动系统两个激振器的动力学耦合特性,发现系统的频率俘获力矩与相位差正弦值乘积的一半以阻力矩形式加在相位超前的电动机上以降低其角速度,另一半则以驱动力矩形式加在相位滞后的电动机上以增加其角速度。同步实验台振动系统的实验验证了该理论分析的正确性。     

三激振器振动系统的振动同步传动

在振动同步理论研究中,存在着一种特殊现象,无直接驱动源的激振器仍能跟随其他有源驱动的激振器进行同步运转,称之为振动同步传动。针对三机驱动水平放置的振动试验台,应用Lagrange能量方程建立动力学模型,根据线性叠加原理得到系统稳定时的响应,利用时间双尺度法获取系统的平均力矩平衡方程,并给出了系统实现振动同步和振动同步传动的同步性判据及同步状态与振动同步传动状态下的稳定性判据。在供电频率50Hz的试验条件下,测得电机2及电机3断电前后系统稳态时的激振器相位差,验证了理论推导的正确性,为振动同步传动理论在多机振动同步机械上的应用提供了依据。     

双机驱动振动系统的定速比控制同步研究

针对相同频率激励振动系统不利于筛分多样性物料以及不同频率激励振动系统不能实现任意定速比同步运动的问题，提出了一种双激励振动系统的定速比控制同步方法。利用拉格朗日方程建立反向回转双机驱动振动系统的动力学方程，推导出振动系统定速比响应方程。应用Matlab/Simulink软件设计出模糊比例积分微分（proportional-integral-derivative，简称PID）控制方法，基于主从控制方式设计了定速比控制器，使两激励反向驱动定速比振动系统能够实现控制同步运动。选择定速比参数为1.2和1.5，通过仿真验证了振动系统振动同步不能实现给定的定速比，而控制同步可以实现；通过实验验证了定速比控制同步理论对两激励驱动振动系统的有效性。     

双机振动系统振动方向角动态调节仿真及实验

振动方向角是影响振动机械筛分效率和输送速度等性能的关键参数,为了实现振动方向角的动态调节,针对双轴椭圆振动系统研究了两激振电机供电频率对振动方向角的影响。首先,采用拉格朗日方法建立系统动力学模型,经过理论推导得到两激振电机在不同供电频率下能够实现稳定同步状态,但相比于同供电频率而言,椭圆轨迹的振动方向角发生改变;其次,利用数值方法建立振动系统仿真模型,计算得到系统椭圆轨迹并分析得出振动方向角随供电频率的变化规律;最后,通过搭建双轴椭圆实验样机进行实验验证。研究结果表明:在系统保持同步运转下改变两激振电机的供电频率,振动系统稳定同步状态发生改变且振动方向角能够实现大幅度(0～90°)调节。     

Vibratory synchronization transmission of two exciters in a super-resonant vibrating system

In this study, vibratory synchronization transmission (VST) of two exciters is investigated in a super-resonant vibrating system to save energy. First, the frequency capture equation of two exciters (FCETE) is deduced by the average method of small parameters. The criterion of VST being the equivalent effective residual torque of motor with power supply should be smaller or equal to the frequency capture torque of the system by setting the disturbance parameters of angular velocities in FCETE to zero. The stability criterion of synchronous states is derived by complying with the generalized Lyapunov equations. Lastly, experiment and computing simulation on VST are conducted. The VST regime of two exciters is discussed in detail from coupling characteristic, current change, visual picture, phase relation, and direct verification of parameters, respectively by comparison and analyses of corresponding data. Results indicate that the key factor in VST implementation is the torque of frequency capture, which serves as the ‘vehicle’ in transferring energy. Thus, the distance between rotational centre of each exciter and mass centre of the rigid frame should be far enough to enhance the ability of VST and ensure energy saving. The theory, experiment, and computing simulation prove that the theoretical approach used in this study is useful and feasible.     

Synchronization of two non-identical coupled exciters in a non-resonant vibrating system of plane motion

In the average method of modified small parameters, the synchronization of two coupled exciters is converted to a problem on the existence and stability of zero solutions for the average differential equations of small parameters over the average period of two exciters. To implement frequency capture, the torque of frequency capture should be greater than or equal to the absolute value of the difference between the residual electromagnetic torques of the two motors. Because each exciter is involved in the motion of the vibrating system it has excited, its relative moment of inertia is reduced. The reduction is proportional to half its coefficient of cosine effect of phase angles (CCEPA). Because one of the exciters is involved in the motion excited by the other, a coupled moment of inertia exists for the two exciters. The stability of the synchronization of the two exciters is affected by the reduction of their relative moments of inertia and their moment of coupling inertia. For the synchronization to be stable, two conditions must be satisfied: (1) the non-dimensional relative moments of inertia of the two exciters are all greater than zero, and (2) four times the product of their non-dimensional relative moments is greater than the square of the coefficient of coupled cosine effect (CCCPA). The stability of synchronization depends solely on the ratios of the masses of the two exciters to the mass of the vibrating system and the ratio of the distance between one exciter and the centroid of the rigid frame to the equivalent rotating radius of the vibrating system about its centroid of the rigid frame, and is independent of the parameters of the two induction motors.     

Frequency capture characteristics of vibration system with two degrees of freedom

In this study, the dynamical model of the vibration of the wind power system was established according to the Lagrange’s principle for investigating the phenomenon of frequency capture. The system response of the vibration of wind power device in the horizontal and vertical directions of tower was analyzed by numerical simulation. At the same time, the paper analyzed the characteristics of the vibration model comparing with the traditional model. Then the conditions of frequency capture were studied through the analysis of mathematical model. In particular, the effects that five key parameters had on the frequency capture characteristics were analyzed. Finally, the research reveal that reducing the eccentric mass and eccentricity of the blade, increasing the support stiffness and displacement damping coefficient, and increasing the torque of the input shaft can reduce vibration and avoid the phenomenon of frequency capture. The simulation results provide the theory basis for the design and installation of wind power device.     

Time-dependent identification of a bridge-like structure with crossing loads

Time-variant systems must be treated with those algorithms that can take into account the variation of the system with time. In this article, we consider the case of a slender pinned–pinned plate carrying a moving load, simulating the well-known example of a bridge crossed by vehicles or trains.We propose two different methods to extract dynamic parameters from such a system. The identification is evidently more complex because the system input is unknown (output-only measures).To simulate such a system and to control the system parameters, a scaled train bridge excited by a crossing train has been built keeping with realistic conditions.The model described is very useful because of its simplicity and the repeatability of measurements; the goal of this article is to look at the different information given by two alternative tools, developed by two main groups involved in the research.This system is “almost” linear and it varies with time. In addition, its dynamic parameters change due to the varying position of the load, crossing the system at constant speed. Accelerations are measured along the beam, at different locations.One of the two methods proposed is a time–frequency approach (CWT) and the other is a modified version of the SSI method, referred to here as short-time stochastic subspace identification (ST-SSI).Time–frequency maps allow one to follow the instantaneous frequency variations along the bridge crossing and, by adopting the appropriate techniques, these instruments can follow the frequency skeleton and the damping along time, as for the case of the proposed ST-SSI method.     

Monitoring mechanical impedance of the thorax with compression and decompression cardiopulmonary resuscitation device

To reduce the complications of cardiopulmonary resuscitation (CPR) and increase its effectiveness, the quality of CPR must be measured and feedback provided to the CPR practitioner. Although CPR ancillary devices that attach sensors to measure the compression frequency and depth have been used, these devices did not previously capture the parameters necessary to determine whether the compression position was appropriate, or whether the thorax was deformed by fracture or other causes. In this study, we proposed a system for measuring the mechanical impedance of a patient’s thorax using a load cell and an accelerometer, incorporated into a CPR ancillary device; the mechanical impedance measurements enabled monitoring of the characteristics and deformations of the thorax during in vitro experiments using dummies, and in an animal experiment using two pigs. When CPR was performed, sensors attached to the CPR assist device measured the compression force and movement, and then the single frequency elements of force and velocity at chest compression frequency were calculated. The mechanical impedance can be determined by calculating the ratio of the obtained force to the velocity. Dummies with different elastic moduli show differences in mechanical impedance. In the animal experiment using pigs, the mechanical impedance of the pig’s thorax steadily decreased in response to successive chest compressions. The mechanical impedance system proposed in this study may be useful in the development of new methods to rapidly measure the mechanical properties of the human body or other complex structures.

     

基于光纤局域网的远距离多路视频监控系统的研究

在武器试验的安全监控中,为了解决数字视频监控系统的远距离视频采集和实时设置视频设备各种参数的问题,提出了一种基于光纤局域网(LAN)的远距离多路视频监控系统,并利用第三方SDK软件包的二次开发实现视频采集和相机参数控制,最后进行了实验测试.结果表明:该系统具有网络负担小、界面友好、参数设置灵活、使用维护方便等优点,从而...     

空间充气展开绳网捕获系统动力学建模与分析

空间充气展开绳网系统在空间捕获中具有自身特殊的优势：占用体积小,展开后捕获范围大,且绳网由充气杆支撑,结构更加稳固,比空间飞网系统更加具有应用潜力。基于绝对节点坐标法（Absolute node coordinate method,ANCF）建立空间充气展开绳网捕获系统动力学模型,应用Hertz理论建立柔性体碰撞动力学模型,对系统进行动力学仿真分析。仿真表明,静力学和振动分析能够为机构力学参数选型提供参考,相比充气杆末端激励,绳网中部受到激励时对捕获机构振动影响更大;机构收口拉力随着充气杆刚度的增加而增大,对充气杆的放气处理可以降低其刚度,从而减小收口拉力,约为原来的10%,易于收口机构的设计。通过对期望目标的捕获仿真,分析了影响收口过程的关键指标,证明了捕获策略的合理性和动力学模型的准确性。研究结果能够对空间充气展开绳网捕获系统设计提供有效的依据。     

子结构界面连接参数识别的波传播法

提出一种基于波传播法识别子结构连接界面刚度和阻尼的新方法。以子结构在平面内的弯曲振动为例,将单元的状态变量与波模式联系起来。通过单元波幅系数的识别,得到连接界面的位移和力向量,再由结点上位移连续及力平衡条件,求得连接界面各个自由度上的动刚度。在识别过程中,将动刚度分离为实部和虚部,以便于连接刚度和阻尼的独立识别。为了提高识别精度,选择一定的频率范围,在每一频率下求得连接界面的刚度和阻尼,最后求出统计平均值作为界面的连接参数。数值仿真算例表明本方法具有良好的识别精度和数值稳定性,是一种极有潜力的参数辨识方法。