附加约束阻尼层对星箭系统动特性的影响分析

在星箭连接支架外表面附加约束阻尼层可抑制星箭对接界面的振动,从而降低卫星在发射过程中所承受的振动和噪声载荷.本文将有限元技术与矩阵特征值摄动分析方法相结合,就卫星支架局部修改(附加约束阻尼层)对星箭系统动态特性的影响进行了分析.以已有星箭系统结构的模态信息为基础,给出了支架部位附加约束阻尼层后星箭系统动态特性变化的定量计算方法,并证明了该减振技术能够不明显的改变原星箭系统的固有特性.     

Effects of anti-symmetric nonlinear viscous damping on the force transmissibility of multi-degree of freedom structures

In the present study, the concept of the output frequency response function is applied to theoretically investigate the force transmissibility of multi-degree of freedom (MDOF) structures with a nonlinear anti-symmetric viscous damping. The results reveal that an anti-symmetric nonlinear viscous damping can significantly reduce the transmissibility over all resonance regions for MDOF structures while it has almost no effect on the transmissibility over non-resonant and isolation regions. The results indicate that the vibration isolators with an anti-symmetric damping characteristic have great potential to overcome the dilemma in the design of linear viscously damped vibration isolators where an increase of the damping level reduces the force transmissibility over resonant region but increases the transmissibility over non-resonant regions.     

Effect of viscous damping on power transmissibility for the vibration isolation of building services equipment

Vibration isolation plays an important role in both the vibration and noise control of building services equipment. To evaluate vibration isolation performance, the force transmissibility method is commonly adopted. However, increasing the damping effect in the force transmissibility method reduces both the resonance peak value and the isolation performance in the “isolation region”. The limitation of the method is that the transmitted displacement of a floor structure and the interaction of mounting points are neglected. To include the floor displacement and the interaction of mounting points, Mak and Su recently proposed the power transmissibility method to assess the performance of vibration isolation. In this paper, the effect of viscous damping on power transmissibility is investigated. A practical procedure for experimentally determining the damping ratio is also given.     

TRANSMISSIBILITY OF TRANSVERSE BENDING VIBRATION OF ELASTIC STRUCTURES 1)

振动的传递是振动理论的重要组成部分。在振动力学的教材中,对于离散结构的积极隔振和消极隔振,振动的传递率已有明确的定义。由于弹性结构的振动不止通过一个点传递,尚需讨论如何定义传递率。通过两端弹性支撑梁,定义了弹性结构横向弯曲振动的各支撑端点的振动传递表达式,及支撑点合力的振动传递率表达式。结果显示三种传递率可能存在较大的差别。建议将这一基本振动理论问题收录于教材,并早日进人本科生和研究生的教学课堂。     

A quasi-zero-stiffness isolator with a shear-thinning viscous damper

Quasi-zero-stiffness(QZS) vibration isolators have been widely studied,because they show excellent high static and low dynamic stiffnesses and can effectively solve low-frequency and ultralow-frequency vibration. However, traditional QZS(T-QZS)vibration isolators usually adopt linear damping, owing to which achieving good isolation performance at both low and high frequencies is difficult. T-QZS isolators exhibit hardening stiffness characteristics, and their vibration isolation performance is e...     

A study of power transmissibility for the vibration isolation of coherent vibratory machines on the floor of a building

Vibration isolation is commonly adopted by engineers to reduce the vibratory effect caused by building services equipment. However, the relationship between the amount of sound power transmitted to the floor and the interaction between the mounting points of several machines is uncertain, as it is common to install several coherent machines on the same floor, for example, two water pumps of the same type in a plant room. We conduct an analytical study of the effects of the interaction between two coherent vibratory sources on the power transmitted to the floor. The study is based on two simple vibratory sources with a single contact point, two rectangular machine models of even-mass distribution with four symmetrical supports and the calculated mobilities of a simply supported concrete floor. We find that the total power obtained from coherent sources (point sources or machine models) differs considerably from that obtained from independent sources at some frequencies in a vibration isolation region. To predict the performance of isolators more accurately, the power transmissibility method proposed previously by Mak and Su should consider not only the effect of effective floor mobility and the interactions of the mounting points of the same sources, but also the interactions of the mounting points of different sources on the floor.     

固有模态函数振动传递率损伤识别实验研究

针对风荷载、地震荷载等存在但难以精确量测的问题,提出一种无需量测外荷载的新的损伤识别方法。将经验模态分解(Empirical Mode Decomposition,EMD)应用于结构损伤识别,通过求振动响应信号固有模态函数(Intrinsic Mode Function,IMF)的振动传递率,构建了一种新的结构损伤识别参数。对预置不同程度开胶损伤的玻璃幕墙试件进行动态测试,得到不同损伤程度下玻璃幕墙的固有模态函数振动传递率,与无损伤条件下的固有模态函数振动传递率进行比较来识别和评估玻璃幕墙开胶损伤程度。研究表明:此方法无需量测外荷载也能识别结构损伤,损伤参数值能反映损伤大小。     

几何非线性摩擦阻尼隔振系统动力学行为研究

非线性隔振系统由于具有较线性系统更优的隔振性能,因此在工程中应用广泛.本文通过配置与被隔振对象的运动方向相垂直的库伦摩擦阻尼器,构建了几何非线性摩擦阻尼模型.由于引入了几何非线性,因此其摩擦力与位移正相关,这与传统与位移无关摩擦力模型有显著不同.首先,建立了具有几何非线性摩擦阻尼的数学模型以及隔振系统的受迫振动方程;然后,使用谐波平衡法求解了动力学方程,并使用数值仿真方法验证了谐波平衡法求解的准确性;最后,研究了几何非线性摩擦阻尼隔振器的绝对位移传递率和相对位移传递率.研究结果表明,在库伦摩擦阻尼选择适当,非线性摩擦阻尼系统可以在保持高频振动衰减效果的前提下,显著降低系统共振峰,其性能优于传统的恒定摩擦阻尼隔振模型.同时,几何非线性摩擦阻尼系统能够避免传统摩擦阻尼系统中的“锁定”现象,从传递率角度来说,不利于共振峰控制;但从激励环境改变引发隔振系统失效的角度来看,几何非线性摩擦阻尼系统可以拓宽系统对激励幅值的适应范围,避免隔振系统失效.本文的研究结果对此类隔振系统的设计和摩擦阻尼参数的选择具有通用的指导意义.      

改性聚酯异形中空微孔纤维性能研究

利用不同的异形喷丝板,将聚对苯二甲酸乙二酯(PET)与不同间苯二甲酸- 5- 磺酸基团摩尔含量的共聚酯(HCDP)共混纺丝,制得一系列改性聚酯纤维.改性纤维的断裂强度随共混HCDP中磺酸基团摩尔含量的增加呈现下降趋势,但该趋势在磺酸基团含量达到一定数量后出现回升.纤维对阳离子染料的吸收率随磺酸基团摩尔含量的增加而增加,但对分散染料而言此差异较小,并且不论何种染料,纤维横截面的变化对上染率的影响均不明显.碱处理对纤维上染率影响巨大.纤维保水率与纤维碱处理后形成的具有毛细效应的微孔结构以及异型纤维本身形成的毛细结构有密切关系,而且纤维对水分的传输性能在很大程度上取决于纤维的横截面形状,纤维碱处理后形成的微孔特别是透孔结构有助于输水性能的改善.