Experimental and modeling approaches of MR behaviors under large step strains

Rheological properties of MR fluids under large step strain shear are presented in this paper. The experiments were carried out using a rheometer with parallel-plate geometry. Under the large step strain shear, MR fluids behave as nonlinear viscoelastic properties, where the stress relaxation modulus, G(t, γ), shows a decreasing trend with step strain. The experimental results indicate that G(t, γ) obeys time-strain separability. Thus, a mathematical form based on finite exponential serials is proposed to predict MR behavior. In this model, G(t, γ) is represented as the product of a linear stress relaxation, G(t), and the damping function, h(γ), i.e. G(t, γ)=G(t) h(γ). G(t) is simply represented as a three-parameter exponential serial and h(γ) has a sigmoidal form with two parameters. The parameters are identified by adopting an efficient optimization method proposed by Stango et al. The comparison between the experimental results and the model-predicted values indicates that this mathematical model can accurately predict MR behavior.     

自动线性跟踪Butterworth有源滤波器研究

滤波是通信、测试、数据采集和实时控制等领域至关重要的环节。通常的模拟滤波器，由于截止频率固定，在某些宽频率动态范围且有实时性要求的应用场合，往往达不到预期的滤波效果，有时甚至影响整个系统的正常运行。本文从有源滤波器的机理分析入手，提出了一种由单片机参与的滤波系统，它能自动跟踪输入信号频率，线性地选择合适的滤波器截止频率，弥补了原有滤波器的不足。     

Control of Wind-Induced Self-Excited Oscillations by Transfer of Internal Energy to Higher Modes of Vibration. II: Application to Taut Cables

In Part I of this paper, a theoretical basis is presented using a two-degrees-of-freedom model. In this second part of the study, the passive control and the two types of semiactive controls introduced in Part I are examined numerically for a taut cable experiencing wind-induced galloping motion. The passive and the semiactive control schemes for taut cables show a good similarity with the results obtained for the two-degrees-of-freedom model. The potential of using these control schemes in practical applications to flexible structures is demonstrated.     

二阶系统变阻尼技术研究

本文基于测速反馈原理，针对二阶系统提出了两种改变系统阻尼的方法。通过适当改变测速反馈系数，可使闭环系统的阻尼比按期望的规律变化（阻尼比可以为负），从而可显著地加快系统的输出响应，使系统的动态性能大为改善。文中提供了仿真算例。     

船舶管系减振材料的应用研究

为适应我国舰船减振降噪的需要，试制出ＱＧＤ－１和ＱＧＤ－２两种穿孔型隔振垫，主要用于管路马脚，也可用于基座等振动部位。对两种隔振垫的阻尼性能、阻燃性能、耐油性能与国外同类产品进行了比较。经管路模型试验和水泵机组试验证明，这两种隔振垫可使管路系统振动加速度级明显下降。     

飞行器火工装置的冲击隔离结构方案实验研究

飞行器由于采用了××炸药索作为级间分离及壁板减重的火工装置，当火工品引炸时，对周围的仪器支架和脱拔插头产生高达３００００ｇ的冲击加速度。为保护仪器支架和脱拔插头，本文，总结了多种隔冲击结构方案的试验结果，选出了一种最佳方案，即二级硅橡胶缓冲器与阻尼复合结构的结合形式。该方案可使冲击加速度衰减至１６０ｇ以下。测的是周向过载。４结语粘弹阻尼复合结构用于高频响、高过载的冲击衰减系统尚是一种新的尝试。由于本课题所设计的缓冲支架采用了多级隔冲方式，冲击载荷传递的环节多，而且是三维冲击响应，载荷的波形复杂，不确定因素多，无法采用理论分析的方法进行研究。虽然如此，缓冲器的隔冲特性以及粘弹阻尼复合结构的减振性能还是可以估算的。这方面的理论问题有待于进一步研究。从试验角度而言，本次试验已解决了飞行器的仪器盒及脱拔插头的隔冲击振动问题，证明所设计的隔冲击支架满足使用要求。通过对不同支承界面联接方式的研究，选出了较佳的支承结构形式，即文中的标准状态。该结构形式隔冲击性能好，衰减倍数大，安装和更换方便，防热性能好。试验数据表明，仪器架的衰减倍数大于４００倍，脱拔插头支架大于２９０倍；在最大过载约３００００ｇ，最大响应频率约２２．４     

宽带钢冷轧机颤振控制的数值模拟

本文以较为准确的轧机振动状态下的轧制压力模型为基础，对宽带钢冷轧机干摩擦阻尼减振进行了数值模拟的研究。研究结果与实际观测值相等。     

稀土对ZA27合金阻尼性能的影响

研究了稀土对ZA27合金阻尼性能的影响规律。结果表明：稀土变质可提高ZA27合金的阻尼性能，经稀土变质后的试样，其内耗是未变质的试样的1．4倍。ZA27合金为发挥其阻尼作用，在频率高于70Hz时，效果明显，且经稀土变质后的试样强迫振动衰减效果比未变质的试样强。     

Curing behavior and mechanical behavior of fully and semi-interpenetrating polymer networks based on polyurethane and acrylics

Polyurethane (PU) was made by reacting stoichiometric equivalent of trimethylol propane (TMP) and desmodur L. Fully interpenetrating polymer networks (fully IPN's) of various compositions based on PU and poly(ethylene glycol) diacrylate (PEGDA) were prepared by blending various ratios of PU/PEGDA, and cured by benzoyl peroxide (BPO). Semi-interpenetrating polymer networks based on PU and poly(ethylene glycol) monomethyl ether of acrylate (PEGMEA) were prepared in a similar way. Shift of exothermic peaks during IPN formation were examined with dynamic DSC. Viscosity increases were investigated with a Brookfield RVT type viscometer. Dynamic mechanical properties were probed via a rheometric dynamic spectroscopy (RDS).Expermintal results revealed a good compatibility of both IPN systems, as evidenced from the single damping peak of the RDS curves for each composition. Shifts of exothermic peaks to higher temperatures during the formation of fully IPN were observed, especially for the composition of PU/PEGDA = 50/50, which showed an exothermic peak at the highest temperature. Experimental results also revealed delayed viscosity increases and decreased gel fractions for all fully IPN's. On the contrary, the semi-IPN did not exhibibt similar phenomena. All these findings supported an effect of network interlock during fully IPN formation. The existence of a network not only provided a sterically hindered environment, but also restrained the chain mobility of the growing network, and vice versa, thus retarding the curing rates of both networks. Network interlock also broadened the width of the half damping peak, T_1/2, and subsequently led to improved mechanical properties such as the impact resistance and Young's modulus of fully IPN material.     

Boundary feedback stabilization of the telegraph equation: Decay rates for vanishing damping term

We study a semilinear mildly damped wave equation that contains the telegraph equation as a special case. We consider Neumann velocity boundary feedback and prove the exponential stability of the closed loop system. We show that for vanishing damping term in the partial differential equation, the decay rate of the system approaches the rate for the system governed by the wave equation without damping term. In particular, this implies that arbitrarily large decay rates can occur if the velocity damping in the partial differential equation is sufficiently small.