一种磁流变阻尼器动态阻尼力模型

磁流变阻尼器用于汽车悬架,可以实现理想的半主动控制,控制算法要求准确刻画阻尼力,针对有关学者提出的磁流变阻尼器的Bingham粘塑性模型、双粘性塑性模型及双粘性滞后模型,建立了基于反正切函数的磁流变阻尼器动态阻尼力模型,该模型是前三种模型的推广,其参数具有明显的物理意义,且其动态阻尼力为光滑函数,与实验象一至,最后对新模型进行了实验验证。     

一种可应用于小阻尼力领域的新型磁流变液阻尼器

在总结现有磁流变液阻尼器的结构形式和特点的基础上,提出一种可应用于地面小型机械结构或空间微重力环境下减振系统等小阻尼力领域的新型磁流变液阻尼器.对该新型磁流变液阻尼器进行结构设计、液体分析、磁路分析、力学分析、理论结果分析和误差分析,验证了它的有效性,说明它能够应用在小阻尼力领域,拓展了磁流变液阻尼器的应用范围.     

阻尼力双向调节磁流变阻尼器的性能测试与滞回模型

基于概念设计和理论分析,制作了4个阻尼力双向调节磁流变阻尼器的模型,并测试了模型阻尼器在不同输入电流状态下阻尼通道内的磁场分布以及力-位移和力-速度等性能曲线;通过对改进型Sigmoid模型的参数识别,建立了模型阻尼器的动力滞回模型。研究表明:模型阻尼器的磁路结构能够较好地实现阻尼力的双向调节,且阻尼通道内的磁场分布基本满足设计要求;模型阻尼器在零、最大正向和最大负向电流状态分别实现中等出力、最大出力和最小出力,且零电流状态的中等出力既能保证阻尼器的故障安全性能,又能防止磁流变液沉降;所建立的滞回模型简单、实用,且精度高。     

磁流变阻尼器在多维减振平台上的应用

 自行设计并制作了一款磁流变阻尼器，通过对实验数据和特征曲线的分析，研究了该阻尼器的磁场强度和阻尼性能，验证了该阻尼器应用于半主动控制的优越性。根据减振平台主体机构的并联机构机型的选择原则，以三平移减振平台为例，提出了将磁流变阻尼器应用于多维减振平台上的设想，并构思了初步方案，为此类阻尼器应用于多维减振平台提供了数据基础和技术支持。     

磁流变阻尼器参数辨识方法研究

应用修正的Dahl模型,通过能量积分分批识别出不同电流下的参数,确定参数与电流的关系。提出的参数辨识方法,将含有滞迟环节的非线性参数识别转化为线性识别问题,达到了较高的识别精度。     

剪切阀式磁流变阻尼器动态特性实验研究

介绍了剪切阀式磁流变阻尼器的结构和工作原理,基于平板模型得出了其阻尼力的计算公式。对自行研制的剪切阀式磁流变阻尼器的阻尼力、电流、位移、速度和频率等动态特性进行了实验研究。结果表明剪切阀式磁流变阻尼器的阻尼力随控制电流的增大呈非线性增加,阻尼力可调系数随电流变化连续可调。在相同振幅下,阻尼器的可调倍数随频率增大而降低,阻尼力随振动频率的增大而增大。通过深入分析该型阻尼器的动力特性,为其在车辆悬挂系统半主动控制中的应用奠定了基础。     

火炮磁流变阻尼器试验分析与动态模型

火炮磁流变阻尼器工作在高速高冲击条件下,其动力特性及其力学模型与常用的磁流变阻尼器存在较大不同。针对某型号火炮设计了反后坐用磁流变阻尼器,并进行了5种不同电流下的动态测试,验证了该阻尼器对反后坐控制的可行性。由试验分析得,火炮磁流变阻尼器的输出力不仅与控制电流和后坐速度有关,还与高冲击条件下的磁流变效应的复杂性、惯性力、腔体内气体压力等因素有关。提出了用改进的多项式模型描述火炮磁流变阻尼器,该模型具有形式简洁,易于求解逆模型,便于实时控制等优点。通过参数辨识后的模型能较好的描述火炮反后坐过程中阻尼器的输出力。     

全通道有效磁流变阻尼器的性能测试与滞回模型

传统剪切阀式磁流变阻尼器在活塞上缠绕励磁线圈,导致1/2以上长度阻尼通道无效,影响阻尼器的最大出力。为了克服上述缺陷,在前期概念设计和理论分析的基础上,制作了2个全通道有效的磁流变阻尼器模型,测试了其在不同电流输入状态下阻尼通道处的磁场分布以及力-位移、力-速度等力学性能曲线,并通过对改进型Sigmoid模型的参数识别建立了模型阻尼器的动力滞回模型。研究表明,模型阻尼器阻尼通道处的磁场分布与有限元分析结果基本符合,其磁路结构可较好地实现全通道有效;全通道有效磁流变阻尼器的最大阻尼力比传统剪切阀式磁流变阻尼器的最大阻尼力提高一倍以上,阻尼力调节系数提高70%以上;改进型Sigmoid模型结构形式简单,识别精度高,可作为全通道有效磁流变阻尼器的动力滞回模型。     

基于遗传算法的磁流变阻尼器Bouc_Wen模型参数辨识

在除试验数据外无任何先验知识的条件下如何识别Bouc_Wen模型的参数是一个亟待解决的问题。本文在对磁流变阻尼器进行力学特性试验的基础上,采用遗传算法对磁流变阻尼器Bouc_Wen模型进行参数辨识,并采用缩小参数取值范围的方法逐渐提高遗传算法的识别精度。通过分析参数值与电流间的特征曲线,采用曲线拟合的方法确定它们之间的函数关系,再利用遗传算法得到具体的函数表达式。最后用不同幅值和频率的激励试验数据对识别结果和拟合结果进行了验证。结果表明：利用缩小取值范围的方法得到的Bouc_Wen模型参数识别结果在全局最优解的附近,拟合结果和辨识出的模型均能满足要求     

旋转剪切式磁流变液阻尼器设计及力学模型

设计、制作了阻尼力可调范围大、位移不受限制的旋转剪切式MR阻尼器,进行了MR阻尼器力学性能试验,提出了MR阻尼力库仑摩擦阻尼力峰值与输入电流的玻尔兹曼函数关系。分析了MR阻尼力时程,MR阻尼力与位移、速度关系,以及振动频率、幅值和电流对MR阻尼力的影响。对比MR试验值与基于玻尔兹曼函数Bingham模型值的关系,证明了基于玻尔兹曼函数的Bingham模型是合理的。     

被动式电磁阻尼器的原理和实验研究

为了简单可靠地增加系统的稳定性、抑制转子的共振峰值 ,提出了一种新型的被动式电磁阻尼器 ,它的结构类似于电磁轴承 ,但无需闭环控制 ,采用直流电工作。通过分析发现 ,电磁阻尼器线圈内由于转子涡动时变化的磁场而产生的波动电流与转子位移间的相位差是产生阻尼的原因 ,推导了波动电流、阻尼系数的计算公式。实验结果显示该阻尼器提供的阻尼能够有效地抑制共振振幅     

Analytic solution for flow of a micropolar fluid

Summary The time-independent equations for the two dimensional incompressible micropolar fluid have been considered. Using group method the equations have been reduced to ordinary differential equations and then solved analytically. Finally the boundary value problem has been discussed, and the graphical results are in good agreement with the numerical solution.     

Modeling and experimental validation of a new type of tuned liquid damper

This paper introduces a new type of tuned liquid damper (TLD) having a relatively simple, easy-to-model behavior and high effectiveness in controlling structural vibrations. It consists of a traditional TLD with addition of a floating roof. Since the roof is much stiffer than water, it prevents wave breaking, hence making the response linear even at large amplitudes. The roof also facilitates the incorporation of supplemental devices with which the level of damping of the liquid vibration can be substantially augmented. This newly proposed TLD, denoted as tuned liquid damper with floating roof (TLD-FR), maintains the traditional advantages of TLDs (low cost, easy installation and tuning), but its numerical characterization is much simpler because the floating roof suppresses higher sloshing vibration modes, resulting in a system that can be represented by a single-degree-of-freedom model. An efficient numerical scheme, where the dynamic behavior of the TLD-FR is expressed as a second-order lineal system of equations, is discussed and validated by scaled experimental tests. The equations of motion of a structure equipped with a TLD-FR are then derived and manipulated to offer a unifying representation dependent upon only four model characteristics of the TLD-FR: The first three (mass, frequency and damping ratios) are common for all type of mass dampers, whereas the final one, termed efficiency index, is related to a similar parameter used to characterize liquid column dampers. Through this approach, the behavior of the proposed TLD-FR can be easily correlated with the behavior of other well-known linear mass damper devices. The relationship between these parameters and the geometrical characteristics of the TLD-FR is also examined. Finally, the identification of the optimal characteristic of the TLD-FR (natural frequency and damping) under stationary stochastic excitation is discussed.     

Using MR elastography to image the 3D force chain structure of a quasi-static granular assembly

We have developed a magnetic resonance elastography (MRE) technique to experimentally investigate the force chain structure within a densely packed 3D granular assembly. MRE is an MRI technique whereby small periodic displacements within an elastic material are measured. We verified our MRE technique using a gel phantom and then extended the method to image the force carrying chain structure within a 3D granular assembly of particles under an initial pre-stressed condition, on top of which is superimposed a small-amplitude vibration. We find that significant coherent displacements form along force chains, where spin phase accumulates preferentially, allowing visualization. This work represents the first time that the internal force chain structure of a dry assembly of granular solids has been fully acquired in three dimensions.     

板式剪切型铅阻尼器的试验研究及有限元分析

提出一种新型的剪切型铅阻尼器,该装置中铅块直接嵌于滑动钢板与固定钢板的凹槽之间,构造简单。基于性能试验和有限元分析对该装置的滞回性能及关键参数进行了研究,研究结果表明:该阻尼器的滞回性能可以采用双线性模型加以模拟;阻尼器屈服阻尼力由铅块的剪切面积决定;加载曲线中弹性阶段与完全塑性阶段之间的过渡弧段的曲率半径与剪切铅块的长厚比成反比。     

Influence of the valve lubricant on the aerodynamic particle size of a metered dose inhaler

Presented in this work are the results of a study designed to investigate the impact of valve lubricant (i.e., silicone oil) on the aerodynamic particle size distribution (PSD) of a steroid suspension metered dose inhaler (MDI) containing propellant HFA-227. The objective of this study was to explore whether the valve lubricant, which is often used in MDI products to prevent valve sticking, can enter an MDI product and potentially impact the aerosol spray dynamics. The results of this work have shown that samples containing valves with high silicone levels produced a larger aerodynamic particle size (by cascade impaction) than samples with low-silicone or silicone-free valves. It is postulated that the presence of silicone in the product may increase the propensity for drug aggregation, thereby leading to an increase in the aerodynamic particle size of the emitted aerosol. These findings stress the importance of evaluating the effects of valve lubricant on the aerodynamic PSD in the early formulation development stage of an MDI.     

一种剪切式磁流变车削减振器的设计与减振试验

将智能材料——磁流变液应用于外圆车削振动控制的研究中。针对普通CA6140车床的结构,通过结构设计、磁路设计研制了一种剪切模式的磁流变车削减振器。建立了基于磁流变减振器的车削系统动力学模型,并通过仿真验证了减振效果。利用有限元法对减振器的磁路进行了优化,优化后磁路面积相对初始设计减小24%,使减振器结构更紧凑,且磁场在非磁流变区域的损耗减小,从而提高了减振器的工作效率。建立外圆车削减振试验系统来对磁流变减振器的减振效果进行试验研究,结果表明减振器可以对车削振动进行有效地控制。     

管式变摩擦阻尼器的减振性能试验与数值模拟

提出了一种具有变刚度特征的管式变摩擦阻尼器,该阻尼器的主要部件包括套筒和装于其内并可来回移动的摩擦环。摩擦环外径略大于套筒内径,当摩擦环装入套筒后将产生装配应力,因而当摩擦环左右移动时接触面上将产生摩擦力。变摩擦的功能是通过在套筒壁中摩擦环初始所在部位适当开缝的方式实现的。由于在套筒壁中部开了缝,在其初始状态阻尼器套筒对内环几乎没有约束应力,这样在非工作状态套筒对内环之间的摩擦力就很小了。研究表明,在结构中安装这类变摩擦阻尼器以后,可以使得系统具有半主动变刚度的特征：即在结构偏离平衡位置时,阻尼器的套筒提供越来越大的围束力,导致套筒和内部摩擦环之间产生越来越大的摩擦力,从而能阻止结构位移增加;在结构返回平衡时,阻尼器提供反向摩擦力,其幅值逐渐减小,使结构在复位过程中振动速度得到抑制。对此种被动变摩擦阻尼器的性能试验和有限元数值模拟都证明在工程结构中应用该阻尼器能够达到主动变刚度控制效果,装置非常简单,而变刚度控制系统则是需要计算机和伺服反馈阻尼器支持的。由于该阻尼器构造简单,出力大,价格低廉,能够适应各种结构和机械工程减振控制的需求,因此具有很好的推广应用前景。     

Analytic solution for rotating flow and heat transfer analysis of a third-grade fluid

Summary The present work examines the flow of a third grade fluid and heat transfer analysis between two stationary porous plates. The governing non-linear flow problem is solved analytically using homotopy analysis method (HAM). After combining the solution for the velocity, the temperature profile is determined for the constant surface temperature case. Graphs for the velocity and temperature profiles are presented and discussed for various values of parameters entering the problem.