【作者】 周宏伟；

【导师】 陈前；

【作者基本信息】 南京航空航天大学 ， 工程力学， 2008， 博士

【摘要】 颗粒阻尼技术是一种振动被动控制新技术。该技术利用结构上现存的或附加的空腔,将颗粒体填入其中,结构振动时颗粒体产生碰撞和摩擦,将机械能转化为热能和声能,产生阻尼效应;同时颗粒体与结构间的动量交换也能起到抑制振动的作用。颗粒阻尼具有应用环境范围广、对原结构改动小、产生的附加质量小、减振效果明显等优点,具有明显的应用前景。目前对颗粒阻尼技术的研究处于起步阶段,理论研究尚不完善。本文根据该项技术的特点,从理论和试验两方面对颗粒阻尼及其控制进行了全面、深入细致的研究。主要工作是:1、在前人研究的基础上,系统讨论了颗粒物质的属性。在假定颗粒体为连续介质的基础上,采用莫尔圆强度理论,对颗粒体在简谐激励作用下的应力状态进行了分析,得到颗粒体处于极限应力状态时所对应的激励加速度理论值,即颗粒产生摩擦效应所需的最小加速度,该值在颗粒阻尼技术当中的地位极其重要。2、对颗粒阻尼器在振动约化加速度Γ小于1和Γ大于1两种情况下的损耗能量进行了研究分析。在约化加速度大于1的情况下,采用完全非弹性蹦球力学模型推导出颗粒阻尼总损耗能量的理论表达式。3、通过试验对颗粒阻尼器的动态特性进行了系统研究。得到颗粒体冲击力受约化加速度控制经历一系列倍周期性分岔的规律,并给出冲击力的统一谐波表达形式。采用统计能量方法对颗粒阻尼产生的损耗功率和附加质量进行了研究,发现颗粒阻尼器的损耗功率和附加质量存在临界点(转捩点)现象,在临界点之前,阻尼颗粒不损耗能量,附加质量变化不明显;临界点之后,损耗功率随激励强度增加而增大,损耗功率值由阻尼器振动速度幅值决定,附加质量随阻尼器加速度幅值的增加而变小,且对激励频率的变化不敏感。提出通过绘制损耗因子等高线图的方式来确定颗粒阻尼器的最佳工作范围,从而对颗粒阻尼减振效果进行预估的方法。4、提出针对颗粒阻尼单自由度系统参数识别的恢复力曲面算法。在窄带随机激励条件下,对不同振动水平、颗粒尺寸和填充率情况下的系统等效阻尼比和等效质量进行了识别,得到了与简谐激励情况类似的结论。5、对直流电磁场作用下的颗粒阻尼器减振效果进行了理论分析和试验研究。结果表明:在一定振动强度下,通过施加直流电磁场的方法,可以加大颗粒体与振动系统间的动量交换,提高对结构振动的抑制作用;同时能够增大磁颗粒之间的接触压力,由此加大摩擦力,提高阻尼器的性能。该方法为颗粒阻尼技术由被动控制发展成为半主动控制,来抑制不同强度的振动提供了有益的探索。更多还原

【Abstract】 Particle damping technology is new vibration passive control approach. It can make use of the structural pre-existing voids or enclosures attached to structure to partially fill with particles. When the structure moves, the particles collide with each other and with the enclosure causing damping through inelastic of nearly collisions, and convert kinetic energy into heat or sound energy. At same time, the momentum conversion between particles and structure can also suppress the dynamic response of primary system. It enjoys a lot of advantages such as: it can be used in a wide range of environment, the structures are modified hardly, additional mass to the system is minimum, and the effect of vibration absorption is notable etc. all of them make it to be used widely in the future.At present, the researches on particle damping are falling to doing, and the theories are not far away from satisfactory. In this paper, some theoretical model and experiments are introduced to study the dynamic characteristics of particle damping, and some technique are used to control and improve the performance of particle damper. The dissertation includes:1. Based on the predecessors’studies, the properties of granular matter are systematically discussed. Presupposing the granular as continuous material, the stress state of particle is analysised with Mohr stress circle under harmonic excitation, and obtains the acceleration theoretics value at which the granular matter is on utmost stress state. The value is very important for particle damping because it can tell us when the granular friction effectiveness act.2. The dissipated energy by the particle damper is analysised on the cases ofΓ<1 andΓ>1, hereΓis the dimensionless reduced acceleration of damper. WhenΓ>1, the model of completely inelastic boucing ball is used to derive the formula of total dissipated energy of particle damper.3. The dynamic characteristics of particle damper are experimentally investigated for thorough understanding its behaviors. It is observed that the impact force between granular bed and container bottom, controlled by the dimensionless reduced vibration acceleration of container, undergoes a series of period doubling bifurcations. Derive a same expression for all of impact forces with different period bifurcations. The Statistical Energy Analysis(SEA)technique is used to estimate the dissipated energy and the dynamic mass of damper. As a result, there is a critical acceleration at which the dissipated energy and the dynamic mass can change suddenly. Below the critical value, the damper can’t dissipate the energy and the additional mass of particles does not change distinctly. Over the point, the dissipated power increases with excitation level and takes some regularity depended on velocity amplitude. However the equivalent mass of damper falls with acceleration amplitude increasing, and is not relative with the vibration frequency. The 3-dimemension contours of loss factor on velocity and frequency is a better way to describe the particle damping performance, by which we can confirm and estimate the best working area of damper.4. Based on the conventional restoring force surface (RFS) method, the paper puts forward a new arithmetic to identify the parameters of particle damping single degree of freedom system by the way of adding acceleration terms into the restoring force equation. And utilize the new method to estimate the equivalent damping ratio and equivalent mass of particle damping system on the cases of different vibration level, different particle sizes and different particle filling ratio under the narrowband random excitation. The results resemble with the case of harmonic excitation.5. The effect of direct current electromagnetic field on ferromagnetic particle damping is theoretically anlysised and experimently investigated for low level vibration case. As a result, the electromagnetic field can significantly increases the momentum conversion between particles and structure, at same time it can also enlarge the contact and friction force between ferromagnetic particles, therefore enhancing its vibration suppression ability. This result suggests that the electromagnetic field could be used to control the energy dissipation performance of a particle damping system in a semi-active way.更多还原