Empirical approaches to estimate the nonlinear dynamic responses of earth-core rockfill dams subjected to earthquake ground motions

This study investigates three aspects of the dynamic response of earth-core rockfill dams (ECRDs) under earthquake loadings, including induced shear strain, increased fundamental period, and shear modulus reduction. A database of the recorded ground motions of ECRD cases in Japan is analyzed to carry out this study. The required response parameters as mentioned above are extracted by analyzing the acceleration time histories recorded at the dams’ crests and foundations. Subsequently, statistical analyses are performed to achieve the objectives of this study. A graph is developed describing the change in the dam’s fundamental period with the induced shear strain, and it is observed that the increase of the dam’s period is dependent on the increase in the shear strain levels. A relationship is established to estimate the anticipated levels of shear strain from the intensity measure (IM) of the earthquake signals. In the proposed predictive relationship, a new IM is used that can adequately characterize the severity of an earthquake. Finally, a curve and a range are suggested for the average shear modulus degradation of the ECRD’s core materials. The presented empirical graphs and relationships in this study are valuable tools to obtain an appropriate perception of dams’ nonlinear behaviour under strong earthquake excitations.     

超声振动对Al-17Si-xFe合金富铁相形貌的影响

用直接超声振动法处理了Al-17Si-xFe(x=2,3,4,5,质量分数)合金,利用光学显微镜、XRD及EDS等手段分析了传统铸造工艺和超声半固态成形合金的微观组织。结果表明,在无超声振动时,Fe含量为2%的铸态合金组织中的富Fe相以长针状β-Al5FeSi相为主,伴有少量板条状δ-Al4FeSi2相。随着Fe含量的增加,合金组织中长针状β-Al5FeSi相逐渐减少,针片状δ-Al4FeSi2相逐渐增多,Fe含量为5%时以粗大针片状δ-Al4FeSi2相为主。在液相线附近对上述不同Fe含量的合金熔体施加一定时间的超声振动后浇注到金属型,富Fe相均以块状和短条状δ-Al4FeSi2相为主,其晶粒平均等效直径在18～46μm之间,明显细化,此外还伴有少量针状β-Al5FeSi相。初步探讨了超声振动影响富Fe相形貌的作用机理。     

Modified liquid column damper for vibration control of structures

A modified version of the traditional tuned liquid column damper (TLCD) absorber is proposed as a passive vibration control device for structures vibrating at low frequencies. This new version, denoted as tuned liquid column ball damper (TLCBD), is equipped with a coated steel ball, in place of the orifice in TLCD, immersed inside the horizontal column of the damper. The current study examines the performance of TLCBD for a harmonic excitation which is a simplified model for the vortex shedding forces on structures in the cross wind direction. A parametric study to investigate the effect of the ball size and absorber mass on the suppression capacity is carried out. The absorber damping characteristics is identified experimentally using a single point laser vibrometer system and the measured damping factor is used in the mathematical model. Intensive numerical simulations were conduced and the results are compared with the traditional TLCD with optimum parameters. The results revealed an improvement of the vibration suppression capability of the proposed version that exceeds around 66% reduction.     

第三十章 基于WIA技术的滚动轴承振动监测与故障诊断系统

在分析现有的振动信号分析与故障诊断技术的基础上,提出了一个基于工业无线网络wIA技术的滚动轴承振动监测与故障诊断系统,详细介绍了该方案的系统运行原理、系统结构及系统功能。     

冒落矿震强度预测试验研究

冒落矿震可能诱发一定范围内地下工程失稳,导致更大范围内采空区大面积冒落。基于振速来衡量矿震强度,通过室内岩石块落物冲击试验,总结了下落岩块位势能与诱发基座振动速度的关系;在此基础上,通过在井下特定环境下的抛掷岩石块测振试验,探讨了岩石冲击底板引发的振动效应,并研究了岩层中振速的衰减规律,建立了采空区冒落矿震强度的预测模型。     

超高速电梯横向振动控制策略的探讨

介绍了国内外超高速电梯横向振动的一些控制方式;提出采用多目标、系统级的集成设计方法,对主动被动控制方法进行优化设计,可能会取得较为满意的控制效果。     

地铁隧道内浮置板整体道床施工技术

浮制板整体道床是通过设置在道床下面及两侧的橡胶支座来阻隔轨道结构与主体结构之间的刚性连接,吸收列车冲击能量,从而达到减振和消音的目的。本文着重介绍了浮制板道床的施工工艺流程、关键施工技术和相关参数。     

Designing unity magnitude input shaping by using PWM technique

This paper proposes a method for reducing vibrations in flexible systems by using the input shaping. A new input shaper technique based on Pulse Width Modulation (PWM) is used to shape the input.Since unity magnitude (UM) input shaping is easy to implement and provides less control duration, it has been preferred for many application areas. An analytical solution to time locations of the UM shaper requires very complex mathematical expressions due to involving in dependent constraint equations. This paper presents a simple PWM based input shaping method. The proposed technique allows designing UM shapers without analytical solution especially for the shapers having higher order impulse sequence. The method requires only the estimated value of system natural frequency and damping ratio. Desired numbers of impulses can be obtained by comparing reference signal amplitude and carrier wave frequency of a PWM. Analysis and experimental results demonstrate the effectiveness of the proposed method.     

Support vector machine with genetic algorithm for machinery fault diagnosis of high voltage circuit breaker

Based on empirical mode decomposition (EMD) method and support vector machine (SVM), a new method for the fault diagnosis of high voltage circuit breaker (CB) is proposed. The feature extraction method based on improved EMD energy entropy is detailedly analyzed and SVM is employed as a classifier. Radial basis function (RBF) is adopted as the kernel function of SVM and its kernel parameter γ and penalty parameter C must be carefully predetermined in establishing an efficient SVM model. Therefore, the purpose of this study is to develop a genetic algorithm-based SVM (GA-SVM) model that can determine the optimal parameters of SVM with the highest accuracy and generalization ability. The classification accuracy of this GA-SVM approach is tried by real dataset and compared with the SVM, which has randomly selected kernel function parameters. The experimental results indicate that the classification accuracy of this GA-SVM approach is more superior than that of the artificial neural network and the SVM which has constant and manually extracted parameters.     

Decomposition of non-stationary signals into varying time scales: Some aspects of the EMD and HVD methods

The Empirical Mode Decomposition has become very popular since its first introduction. Its suitability and expected performance for specific signal processing task is however somewhat open ended.Addressed are basic questions concerning the decomposition of signals according to different time scales, from noise sensitivity to frequency resolution. Comparing it to the recently introduced Hilbert Vibration Decomposition, signals simulating moving mechanical systems are analyzed. It is argued that in spite of signal adaptive properties, a universal fully automatic decomposition is still beyond our capabilities.