塔式多绳摩擦提升机整体振动的计算机模拟

对离散化后链状系统在某一主振型下的振动即主振动进行了研究 ,提出了用计算机模拟提升机整体振动的某一主振动的方法 ,从而可直观地了解该系统主振动的情况 ,为研究塔式多绳摩擦提升机的主振动特性提供了一个切实可行的方法 ,并给出了计算机程序流程图     

微波电路中的光子带隙结构

介绍了微波电路中的光子带隙结构。光子带隙结构是具有带阻特性的周期结构,最初应用于光学领域,近几年被引入微波波段。光子带隙结构可以采用金属或介质材料周期排列而成,由于一维和二维平面带隙结构易于实现,所以在微波电路中得到了广泛的应用。     

地铁列车运行诱发地面邻近建筑振动的数值模拟研究

为研究城市地铁运行产生的振动波在地面邻近建筑物中的传播规律,以地铁沿线邻近建筑为研究对象,参数取值参考实际工程量值范围,建立地铁列车-轨道-隧道-地层-建筑物整体有限元数值模型,重点研究地面邻近建筑中同楼层和不同楼层间振动响应的传递分布规律和频谱特性。结果表明：地铁运行对建筑的振动激励以中低频1~50 Hz为主;房间面积越大,楼板自振频率位于激励荷载优势频段范围越多,越易引起楼板共振;楼板跨中点的振动强度通常大于边角点的振动强度,角点的振动会在低频段1.25~2.0 Hz超过楼板跨中点;随着楼层的升高,三向振动加速度响应均呈波动性变化。通过多工况的计算,分析了运行车速、隧道埋深和振中距对邻近地铁建筑物振动响应的影响规律。     

张紧式荫罩微振动的分析测量

分析了不同类型的张紧式荫罩在受激后产生的各种近似振动模式,通过光机转换技术,采用非接触式的单光纤强度反射法测量荫罩的振动特性.实验证明,该测量系统能够准确、客观地反映荫罩振动的各项参数,包括各振动模的振动频率、振幅和衰减时间.对于荫罩这种振幅极小的振动,本方法具有简单、方便、快速和精确的特点,是分析测量荫罩振动的有力工具.     

Structural safety criteria for blasting vibration based on wavelet packet energy spectra

Given multi-resolution decomposition of wavelet packet transforms, wavelet packet frequency band energy has been deduced from different bands of blasting vibration signals. Our deduction reflects the total effect of all three key elements (intensity, frequency and duration of vibration) of blasting vibration.We considered and discuss the dynamic response of structures and the effect of inherent characteristics of controlled structures to blasting vibration. Frequency band response coefficients for controlled structures by blasting vibration have been obtained. We established multi-factor blasting vibration safety criteria, referred to as response energy criteria. These criteria reflect the total effect of intensity,frequency and duration of vibration and the inherent characteristics (natural frequency and damping ratio) of dynamic responses from controlled structures themselves. Feasibility and reliability of the criteria are validated by an example.     

结构随机风振响应分析的复模态法

对单自由度结构的随机风振响应问题进行了研究。首先建立运动方程，并用线性滤波过程生成脉动风谱，用复模态理论和扩阶法进行解耦，获得了等效风谱对应的结构风振响应的解析解，从而建立了结构风振响应分析的复模态法，该方法可用于带TMD和TLD结构的风振分析和优化设计。     

摩擦系数对轴向推力作用下碰摩转子振动特性的影响

推导建立了轴向推力作用下的碰摩转子非线性动力学方程。以转定子间摩擦系数为控制参数,对碰摩转子系统横向振动和轴向振动行为进行了数值仿真。分析表明:转子与定子间摩擦系数对转子系统横向振动和轴向振动特性的影响非常明显,摩擦系数越大,转子系统振动越复杂。随着摩擦系数的增加,转子系统由简单的周期振动突变为拟周期振动。增大摩擦系数,以转速比为控制参数的系统轴向振动的复杂运动区范围变大,且复杂运动区的振动幅值也有增大趋势。分析结果对旋转机械碰摩故障的识别提供了理论依据。     

Source model for blasting vibration

By analyzing and comparing the experimental data, the point source moment theory and the cavity theory, it is concluded that the vibrating signals away from the blasting explosive come mainly from the natural vibrations of the geological structures near the broken blasting area. The source impulses are not spread mainly by the inelastic properties (such as through media damping, as believed to be the case by many researchers) of the medium in the propagation pass, but by this structure. Then an equivalent source model for the blasting vibrations of a fragmenting blasting is proposed, which shows the important role of the impulse of the source's time function under certain conditions. For the purpose of numerical simulation, the model is realized in FEM, The finite element results are in good agreement with the experimental data.     

二维蜂窝晶格钢/水声子晶体能带结构

利用平面波展开法研究了钢柱按蜂窝晶格周期排列水中构成二维钢/水声子晶体的能带结构,并详细推导了蜂窝晶格的2种结构因子.基于超声浸水透射技术,沿着第一简约布里渊区2个高对称方向测试声子晶体的带隙.实验结果表明,第一完全带隙频率范围与理论计算结果相吻合.     

Acoustic band gaps in two-dimensional square arrays of semi-hollow circular cylinders

Concave surfaces focus sound while convex surfaces disperse sound. It is therefore interesting to know if it is possible to make use of these two opposite characteristics to enhance the band gap performance of periodic arrays of solid cylinders in air. In this paper, the band gap characteristics of a 2-D square array of semi-hollow circular cylinders embedded in air are investigated, both experimentally and theoretically. In comparison with the types of inclusion studied by previous researchers, a semi-hollow circular cylinder is unique in the sense that it has concave inner surfaces and convex outer surfaces. The finite difference time domain (FDTD) method is employed to study the propagation behavior of sound across the new phononic crystal of finite extent, and the influences of sample size and inclusion orientation on band gap characteristics are quantified in order to obtain the maximum band gap. For reference, the band gap behaviors of solid circular cylinder/air and hollow circular cylinder/air systems are considered and compared with those of semi-hollow circular cylinder/air systems. In addition to semi-hollow circular cylinders, other inclusion topologies such as semi-hollow triangular and square cylinders are also investigated. To validate the theoretical predictions, experimental measurements on square arrays of hollow Al cylinders in air and semi-hollow Al cylinders in air are carried out. The results demonstrate that the semi-hollow circular cylinder/air system has the best overall band gap performance.     

钢轨底部动力吸振器对钢轨振动与噪声的影响

为分析钢轨底部动力吸振器对钢轨振动特性和声辐射特性的影响,建立钢轨振动-声辐射模型.首先,根据铁路板式轨道实际拓扑结构建立三维实体有限元模型,采用直接法求解钢轨结构的特征值问题;其次,计算分析了钢轨在垂向单位力激励下的导纳特性与振动衰减率;再次,利用轮轨滚动噪声预测模型计算分析了动力吸振器对钢轨声辐射功率的影响;最后,对轨底动力吸振器的参数影响进行了分析.结果表明:轨底动力吸振器的减振频段为750～1 650 Hz,降噪频段为800 Hz以上;吸振器的质量比越大其减振降噪水平越高,但减振降噪水平的提高效率越低;在一定范围内适当增大吸振器刚度可略微提高降噪水平,但是刚度过大会加剧钢轨的振动及其纵向传播;阻尼系数影响减振降噪作用频率的带宽,需要保证足够大且与吸振器质量、刚度相匹配.对钢轨底部动力吸振器减振降噪作用和参数影响的计算分析可以为钢轨轨底动力吸振器的参数设计以及低噪声钢轨的选型提供一定的参考.     

方柱流致横向振动的CFD数值模拟

为对弹性支撑方柱的流致横向驰振与涡激振动现象进行研究,利用Fluent软件求解Re=500下的粘性不可压流场,方柱振动模型简化为质量-弹簧-阻尼体系,将Newmark-β方法写入用户自定义函数(UDF)来求解柱体运动方程,方柱和流场之间的非线性耦合作用通过动网格实现.考虑了质量比和折合阻尼对方柱振动的影响,结果得到了低频率比下方柱的驰振现象,方柱的最大驰振位移达到2.5倍边长,观察到方柱由驰振到涡激振动的转化.详细分析不同频率比下柱体的升阻力系数、横向位移特征值和尾流涡结构,获得"拍"和"相位开关"等现象.工程中对自振频率较低的方形结构进行设计时需考虑驰振作用的影响,优先采用不易发生驰振的截面形式.     

直升机旋翼振动主动控制方法研究进展

直升机特有的旋翼动力学结构使其拥有极高的战略发展价值,但旋翼在工作过程中产生的振动问题也对直升机的飞行性能造成了严重影响,因此,研究旋翼振动控制方法对直升机性能提升有重大意义。针对由直升机主旋翼工作而引发的机身振动控制问题,首先,从旋翼引起机身振动的原因以及振动的频率特征出发,分析了主动振动控制的原理。其次,基于直升机振动的周期性质,将振动控制方法划分为频域控制和时域控制,并对频域方法以及时域方法中的时域高阶谐波方法、鲁棒方法、智能方法以及其相关试验成果展开综述及总结。另外,针对振动传递抑制技术进行了简单介绍,并对国内研究机构的主动振动控制试验进行了梳理。最后,归纳了振动控制方法存在的不足,并在此基础上指出了直升机主动控制方法的未来发展方向,应进一步深入针对稳定飞行状态的鲁棒自适应控制和针对全飞行状态的智能自学习控制方法研究,并开展面向性能提升的综合主动控制系统设计。     

二阶效应的压弯构件振动分析

采用结构振动理论和二阶理论对压弯构件的振动进行了分析,求解构件的二阶自振频率和主振型,并对均匀简谐荷载作用下压弯构件的强迫振动进行了讨论。结果表明,二阶效应将对构件的位移和内力产生极为不利的影响。     

Characteristics of ultrasonic vibration transmission in bonding process

The transmitting models of ultrasonic vibration in ultrasonic transducer and capillary were presented according to the propagating mechanism of ultrasonic wave in elastic body. The coupling characteristics of ultrasonic longitudinal-complex transverse vibration system were simulated by Matlab software. The ultrasonic vibration displacement and the velocity of high frequency were measured by using the PSV-400-M2 （1.5 MHz） laser Doppler vibrometer. The vibration locus shapes driven by the same frequency and different frequencies were tested by using GDS-820S dual channel digital oscilloscope. The microstructures at bonding interface were observed by means of KYKY2800 scanning electron microscope. The results show that ultrasonic vibration displacement or velocity and energy density increase with the decrease of section area in the transmitting process. The vibration locus shapes driven simultaneously by the same frequency and different frequencies are elliptical （or circular） loci and rectangular （or square） loci, respectively. And the characteristics at bonding interface are improved by coupling loci.     

含共振单元的单相3维声子晶体设计及其带隙特性研究

局域共振型声子晶体具有低频段的弹性波带隙特性,在振动与噪声控制工程领域有着重要的应用前景。三维局域共振型声子晶体的结构形式目前主要是基于多组元材料体系,在面向工程实际的制造和应用方面存在局限。对此,本文提出一种可实现低频局域共振带隙的单相三维声子晶体结构,利用有限元方法计算了声子晶体的能带结构、振动模态和传输特性。结果表明：该结构在具有高频带隙的同时,可在归一化频率低于0.1的范围内打开相对带隙宽度超过20%的低频弹性波带隙。结构中球形质量单元和连接体的局域共振是该低频带隙产生的主要原因。结构材料属性的变化影响带隙频率值的实际大小,而结构几何参数决定带隙在整个能带结构中出现的相对位置。通过改变结构材料参数和几何参数,可以实现对低频带隙边界和带隙宽度的调控。带隙的进一步拓宽可以通过构造几何参数渐变的组合结构来实现。本文所提出的单相三维声子晶体结构可用于低频减振降噪材料和器件的设计开发。     

汽车驾驶员脑氧参数的振动响应特性分析

应用近红外光谱法,研究分析汽车驾驶员在振动状态下的脑部血氧参数变化,探讨车辆振动对脑氧参数的影响。实验过程中应用近红外光谱法监测试验人员脑氧参数。经方差分析发现实验人员经车辆振动后脑部各血氧参数有显著性变化。实验结果表明汽车振动对脑部血氧参数还原血红蛋白的浓度(c_Hb)、氧合血红蛋白的浓度(c_HbO2)、血红蛋白总量的浓度(c_tHb)有显著性影响,且不同频率振动的影响显著性不同,其中4.5Hz的振动对脑氧参数影响最大;但振动对脑部组织血氧饱和度(tissue oxygen index,TOI)的影响极小。     

Simultaneous investigation of blast induced ground vibration and airblast effects on safety level of structures and human in surface blasting

The significance of studying, monitoring and predicting blast induced vibration and noise level in mining and civil activities is justified in the capability of imposing damages, sense of uncertainty due to negative psychological impacts on involved personnel and also judicial complaints of local inhabitants in the nearby area. This paper presents achieved results during an investigation carried out at Sungun Copper Mine, Iran. Besides, the research also studied the significance of blast induced ground vibration and airblast on safety aspects of nearby structures, potential risks, frequency analysis, and human response. According to the United States Bureau of Mines (USBM) standard, the attenuation equations were developed using field records. A general frequency analysis and risk evaluation revealed that: 94% of generated frequencies are less than 14 Hz which is within the natural frequency of structures that increases risk of damage. At the end, studies of human response showed destructive effects of the phenomena by ranging between 2.54 and 25.40 mm/s for ground vibrations and by the average value of 110 dB for noise levels which could increase sense of uncertainty among involved employees.     

阻尼振动的傅里叶分析

实际上的阻尼振动不可能是单一频率的振动,本文对阻尼振动的傅里叶分析,一方面表明了阻尼振动是无穷多个正弦振动和余弦振动所组成,另一方面通过傅里叶强度分析,证明了对固有圆频率ω0相同的不同振动系统,阻尼因子β愈小,单色性就愈好,文章为力学教学提供了一个很好的教学背景。     

双模态耦合系统的振动耗能特性研究

以固有频率处于1／3倍频程内的一个双振子耦合系统为例,研究了双模态耦合系统的振动耗能特性,通过分别改变激励外力的频率和幅度,振子的基本特性,耦合元素特性等诸要素,对系统损耗因子进行了分析,研究发现,耦合系统的损耗因子总是介于两个模态损耗因子之间,并且这两个模态一个从振动能量的角度占主导地位,而另一个从能量损耗的角度占主导地位,系统的损耗因子是两平衡的结果。