Stability and accuracy of central difference method for real-time dynamic substructure testing considering mass participation coefficient

For real-time dynamic substructure testing(RTDST),the influence of the inertia force of fluid specimens on the stability and accuracy of the integration algorithms has never been investigated.Therefore,this study proposes to investigate the stability and accuracy of the central difference method(CDM)for RTDST considering the specimen mass participation coefficient.First,the theory of the CDM for RTDST is presented.Next,the stability and accuracy of the CDM for RTDST considering the specimen mass participation coefficient are investigated.Finally,numerical simulations and experimental tests are conducted for verifying the effectiveness of the method.The study indicates that the stability of the algorithm is affected by the mass participation coefficient of the specimen,and the stability limit first increases and then decreases as the mass participation coefficient increases.In most cases,the mass participation coefficient will increase the stability limit of the algorithm,but in specific circumstances,the algorithm may lose its stability.The stability and accuracy of the CDM considering the mass participation coefficient are verified by numerical simulations and experimental tests on a three-story frame structure with a tuned liquid damper.

Delay-dependent stability and added damping of SDOF real-time dynamic hybrid testing

It is well-recognized that a transfer system response delay that reduces the test stability inevitably exists in real-time dynamic hybrid testing （RTDHT）. This paper focuses on the delay-dependent stability and added damping of SDOF systems in RTDHT. The exponential delay term is transferred into a rational fraction by the Pad6 approximation, and the delay-dependent stability conditions and instability mechanism of SDOF RTDHT systems are investigated by the root locus technique. First, the stability conditions are discussed separately for the cases of stiffness, mass, and damping experimental substructure. The use of root locus plots shows that the added damping effect and instability mechanism for mass are different from those for stiffness. For the stiffness experimental substructure case, the instability results from the inherent mode because of an obvious negative damping effect of the delay. For the mass case, the delay introduces an equivalent positive damping into the inherent mode, and instability occurs at an added high frequency mode. Then, the compound stability condition is investigated for a general case and the results show that the mass ratio may have both upper and lower limits to remain stable. Finally, a high-emulational virtual shaking table model is built to validate the stability conclusions.

Simulation of large-scale numerical substructure in real-time dynamic hybrid testing

A solution scheme is proposed in this paper for an existing RTDHT system to simulate large-scale finite element （FE） numerical substructures. The analysis of the FE numerical substructure is split into response analysis and signal generation tasks, and executed in two different target computers in real-time. One target computer implements the response analysis task, wherein a large time-step is used to solve the FE substructure, and another target computer implements the signal generation task, wherein an interpolation program is used to generate control signals in a small time-step to meet the input demand of the controller. By using this strategy, the scale of the FE numerical substructure simulation may be increased significantly. The proposed scheme is initially verified by two FE numerical substructure models with 98 and 1240 degrees of freedom （DOFs）. Thereafter, RTDHTs of a single frame-foundation structure are implemented where the foundation, considered as the numerical substructure, is simulated by the FE model with 1240 DOFs. Good agreements between the results of the RTDHT and those from the FE analysis in ABAQUS are obtained.

Geographically distributed hybrid testing & collaboration between geotechnical centrifuge and structures laboratories

Distributed Hybrid Testing（DHT） is an experimental technique designed to capitalise on advances in modern networking infrastructure to overcome traditional laboratory capacity limitations. By coupling the heterogeneous test apparatus and computational resources of geographically distributed laboratories, DHT provides the means to take on complex, multi-disciplinary challenges with new forms of communication and collaboration. To introduce the opportunity and practicability afforded by DHT, here an exemplar multi-site test is addressed in which a dedicated fibre network and suite of custom software is used to connect the geotechnical centrifuge at the University of Cambridge with a variety of structural dynamics loading apparatus at the University of Oxford and the University of Bristol. While centrifuge time-scaling prevents real-time rates of loading in this test, such experiments may be used to gain valuable insights into physical phenomena, test procedure and accuracy. These and other related experiments have led to the development of the real-time DHT technique and the creation of a flexible framework that aims to facilitate future distributed tests within the UK and beyond. As a further example, a real-time DHT experiment between structural labs using this framework for testing across the Internet is also presented.

Real-time modular dynamic modeling for compression system of altitude ground test facilities

Modeling of a centrifugal compressor is of great significance to surge characteristics and fluid dynamics in the Altitude Ground Test Facilities(AGTF).Real-time Modular Dynamic System Greitzer(MDSG)modeling for dynamic response and simulation of the compression system is introduced.The centrifugal compressor,pipeline network,and valve are divided into pressure output type and mass flow output type for module modeling,and the two types of components alternate when the system is established.The pressure loss and thermodynamics of the system are considered.An air supply compression system of AGTF is modeled and simulated by the MDSG model.The simulation results of mass flow,pressure,and temperature are compared with the experimental results,and the error is less than 5%,which demonstrates the reliability,practicability,and universality of the MDSG model.

搭接-叠片式箔片气体动压轴承转子动力学特性实验研究

本文研制了由搭接式径向轴承和叠片式推力轴承组成的一套搭接-叠片式箔片气体动压轴承,同时设计并搭建了相应的箔片气体动压轴承转子实验台,通过多组转子降速对比实验研究了所提出箔片气体动压轴承的起飞特性,分析了转子不平衡量和外部载荷对该轴承-转子系统的转子动力学影响。起飞实验结果表明,本文所研制的搭接式径向箔片气体动压轴承的起飞转速约为7500 r/min,最大起飞转矩约为220 N·mm。转子降速实验研究结果表明,随着转子不平衡量的增加,转子系统1X频振动幅值逐渐增大、二阶临界转速逐渐降低、次频振动发生频率逐渐提前;随着转子转速的增加,转子系统1X频振动呈现先增大后减小的趋势、次频振动幅值整体逐渐增大;在减小顶箔结构的圆心距后,转子系统稳定性增加。不平衡量与外部载荷加载耦合实验结果表明,不平衡量与外部载荷都会激起系统的次频振动,次频振动幅值随转速升高而增大;并且在激起次频振动方面,不平衡量与外部载荷之间存在着相互放大作用。

卫星大型旋转载荷动平衡控制应用研究

卫星携带的转动体的动不平衡对星体产生非期望的干扰力矩,进而影响卫星姿态,为此在卫星高品质运动控制中必须对转动体的动平衡特性进行控制。本文在建立卫星多挠性体姿态动力学模型的同时,分析了动平衡检测在转动体残余干扰力矩分析中的应用,提出了大型旋转载荷动平衡控制方法和流程,最后通过实际工程应用情况,验证了该动平衡控制方法和流程的实用性和有效性。

人体失衡性实时测试系统研究

采用测试平台及计算机系统建立了人体失衡性实时测试系统 ,通过失衡性指数提出评价体系。对不同年龄组 4 0名受试者进行失衡性动态检测。测试状态包括 :睁眼状态、闭眼状态、平台倾斜 10度、平台倾斜 2 0度、平台倾斜 30度、横向视跟踪、纵向视跟踪、矢向视跟踪。结果表明

网络空间拟态防御研究

本文扼要分析了网络安全不平衡现状及本源问题,重点阐述了动态异构冗余架构以及如何利用不可信软硬构件组成高可靠、高安全等级信息系统的原理与方法,概略的给出了拟态防御的基本概念。最后,介绍了拟态防御原理验证系统的测试评估情况和初步结论。

自适应重复控制抑制测试台动不平衡扰动研究

通过分析三轴测试台的动不平衡因素,得出测试台存在周期扰动力矩。该周期扰动力矩主要是由加速度力矩、哥氏耦合力矩、离心耦合力矩组成,与测试台三轴的转动惯量、位置角和转动速度有关,影响测试台的定位精度和速率精度。为抑制三轴测试台动不平衡引起的不确定性频率周期性扰动力矩,提出一种用于消除带有的周期性扰动的自适应有限维重复控制。采用自适应算法在线辨识扰动频率,并调整有限维重复控制器参数消除该扰动,用平均方法证明算法的收敛性和系统的稳定性。同时该算法可以通过调整自适应多周期有限维重复控制器的结构来消除不同频率的多个周期的扰动。仿真结果表明该方法能有效的抑制三轴测试台动不平衡引起的周期性扰动,提高测试台系统的定置精度和速率精度。

基于瞬时功率理论的静止无功补偿新算法

在总结已有的研究成果基础之上,将瞬时无功功率理论应用于提高功率因数和补偿三相不平衡的静止无功功率补偿装置控制之中,简化了瞬时无功功率算法,提出了更为高效的滤波器结构,并推导出补偿电抗的表达公式、动态模拟试验和仿真试验,证明了算法的有效性和可行性。

基于Ansys的汽轮机转子动平衡一次加准法研究

针对目前汽轮机转子动平衡技术需要多次加重试车的不足,提出了一种基于Ansys的一次加准动平衡方法。建立有限元模型时,考虑到油膜刚度和阻尼的影响,以COMBI214单元模拟滑动轴承支撑结构,运用Ansys的瞬态动力学分析功能,在转子上施加虚拟不平衡质量,通过转子的幅频、相频响应图,根据动平衡理论得到转子的影响系数,为一次加准法提供一定的依据。最后,通过计算影响系数的相对误差率并与设计参数进行对比,证明本方法的可行性与有效性。

刚性转子动平衡现场检测系统的硬件设计

基于传感器-计算机的设计思想,通过系统硬件的选型和信号处理电路的设计,组成以PCL-818L数据采集卡为核心的刚性转子动平衡现场检测系统。检测系统软件使用Visual C++编写,可在Win32环境下运行。与传统检测方法相比较,该系统不仅人机交互性强、操作简便,而且具有工作效率高、生产成本低等优势,比较适用于单件转子拆装比较困难的场合。

分离摆式积分陀螺加速度计外环摩擦试验研究

为分离摆式积分陀螺加速度计外环摩擦力,提出一种在高精度三轴转台上测试摆式积分陀螺加速度计的新试验方法。该试验采用三轴转台中环转动速度随动摆式积分陀螺加速度计外环进动角速度,从而分离仪表外环轴摩擦力的方案。为研究三轴转台存在的动不平衡对摆式积分陀螺加速度计测试试验的影响,建立了三轴转台的动不平衡模型,分析了三轴转台的动不平衡对转台定位精度的影响,并通过提高三轴转台的带宽和改变工作点来获得高的定位精度,消除三轴转台的动不平衡扰动影响,完成分离摆式积分陀螺加速度计的外环摩擦力的试验。通过对试验数据进行分析,得出外环摩擦力的存在影响了摆式积分陀螺加速度计精度,为进一步改进仪表结构以提高仪表的精度提供了试验研究基础。

新型滚子动不平衡量测量装置振动系统的模态特性分析

圆柱滚子有质量小和不平衡量微小等特点,不平衡量的测量难度较大,目前的测量方法为接触式测量,对滚子表面有损伤且测量结果不精确。设计了一种新型小质量圆柱滚子动不平衡量无损测量装置,构建了振动系统动力学模型,分别用理论、仿真计算和试验定量测量了4种刚度系数下的振动系统模态参数。理论、仿真与试验得出的固有频率极差最高为2.4%,验证了振动系统动力学模型的准确性。

不平衡量的测试与应用

介绍了机械平衡的原理及分类,以及机械制造过程中允许的不平衡量和平衡精度,并对回转件的平衡实验法及原理、动平衡测试系统以及数字信号处理技术作了介绍,根据动平衡理论分析了平衡测试技术在生产中的应用.

载重子午线轮胎动平衡检测原理及应用

分析轮胎动平衡试验机的检测原理,研究测量轮辋宽度和生产过程控制对载重子午线轮胎动平衡检测结果的影响。试验结果表明:测量轮辋宽度对上、下不平衡质量影响较大,轮胎冠部材料的不均匀性对轮胎平衡性影响较大;双面配重修补法对不平衡质量减小效果较明显。

基于动态检测法的提升机钢丝绳在线监测系统

为解决现有方法对多绳摩擦提升机钢丝绳张力不平衡的诊断和调整不准确的问题,深入分析影响钢丝绳张力不平衡的主要因素,按照动态监测法测钢丝绳张力的基本原理,提出了基于动态监测法对钢丝绳张力不平衡进行诊断的新方法。通过现场试验表明该方法简单易操作,并且能够准确反映出钢丝绳张力不平衡的原因。

轴段可调节式双转子结构动力特性模拟试验台设计与优化

为了解航空发动机双转子的动力学特性,搭建了轴段可调节式双转子结构动力特性模拟试验台,其主要包括高速电机、低压转子、高压转子、模拟盘、支架、齿轮箱、基座等。采用有限元法和变换哈默斯利算法相结合的联合仿真方法,对试验台进行了临界转速的计算及优化;计算了双转子系统的稳态不平衡响应,分析了临界转速变化对转子系统振动特性的影响。结果表明:优化后试验台前4阶临界转速与原型机实测临界转速的误差在5%以内,试验台能较好的模拟原型机动力学特性;优化后各轴承处最大响应幅值中的最大值明显减小,试验台具有良好的振动特性。

基于全相位FFT不平衡分析的转子现场动平衡

为了对地面转子试验器进行动平衡,降低其振动量值,掌握转子系统现场动平衡技术,基于全相位快速傅里叶变换(fast Fourier transform,简称FFT)建立了转子不平衡量的计算模型,并在地面转子试验器上搭建了不平衡测试系统。试验表明,当转速高于1 kr/min后,计算模型可准确地分析出转子不平衡响应。对转子试验器进行了现场动平衡,结果表明,所建立计算模型在较轻的试重条件下(三圆法无法计算出配平方案),经单次配平可使转子不平衡振动降低77.3%,证明了所建立的不平衡计算模型的有效性与准确性。该模型可用于对其他复杂转子机械的现场动平衡计算。