Wavelet analysis of the structure of point processes

The structure of point processes generated by a threshold system can reflect interactions of the intrinsic dynamics of this system and that caused by an external action, in particular, in the form of frequency modulation. A new method based on the double wavelet transform is proposed for the detection of such changes in the structure of nonstationary point processes.     

Forecasting point and continuous processes: Prequential analysis

Summary The problem considered in this paper is that of evaluating the performance of a forecaster who predicts the intensity of a point process or the dirft and diffusion rates of a continuous process. It is shown that we can evaluate this performance in a “prequential” manner, without the usual assumption that the forecasts are generated in accordance with some probability distribution. Technically, the results in this paper are prequential counterparts of the Dambis-Dubins-Schwarz reduction of a continuous martingale, via a change of time, to a Wiener process, and the Papangelou-Meyer reduction of a counting process to a Poisson process.     

Estimating the predictability time of noisy chaotic dynamics from point sequences

Technical Physics Letters - A method for increasing the accuracy of estimation of the predictability time of noisy chaotic dynamics from system-related point sequences is proposed. General laws...     

Dynamic analysis of three point bend specimens under impact

A simple one dimensional inertial model is presented for transient response analysis of notched beams under impact, and extracting dynamic initiation toughness values. The model includes the effects of striker mass interactions, and contact deformations of the beam. Displacement time history of the striker mass is applied to the model as forcing function, The model is validated by comparison with the experimental investigation on ductile aluminium 6061 alloy and brittle polymer, PMMA.     

滚动轴承测振点的动力学响应分析

为了有效捕捉轴承局部损伤后的故障特征,需要对传感器的测量位置进行合理配置和优化。考虑到滚动轴承结构的复杂性,本文采用数值仿真技术研究缺陷轴承工作状态下的动力学响应特征。基于故障轴承的有限元模型,分析各部件运动规律及相应的应力分布,获得不同部位缺陷诱发的冲击脉冲分布形态;建立附加轴承座的整体装配模型,故障冲击作为激励载荷施加到该模型上,同时考虑结构内部的非线性接触特性,仿真获得缺陷激励下的滚动轴承各节点动力学响应;将轴承座表面节点的响应波形与实测的轴承振动信号进行比较分析,保证仿真结果的真实性;进而深入研究振动信号在轴承外圈及轴承座之间的传递特性;基于上述动力学分析结果,对轴承故障状态下的测振点位置及测量方向进行优化选择。     

牛津型斯特林制冷机的动力特性分析

为了提高牛津型斯特林制冷机的制冷效率,提出了一种应用数值软件进行动力特性研究的方法。总结分析了压缩机、膨胀机的板弹簧刚度和活塞质量,充气压力,膨胀机位移相位角,膨胀机活塞行程以及制冷温度对制冷机动力特性的影响规律。优化了制冷机的动力系统,实验验证了该方法的可行性。研究结果表明,优化后制冷机的压缩机电机效率和整机效率均有所提高。     

同轴对转行星齿轮传动系统动态特性分析

本文以同轴对转行星齿轮传动系统为研究对象,基于齿轮系统动力学和Lagrange方程,采用集中参数法建立了同轴对转系统的耦合动力学模型,模型中考虑了轮系的支撑刚度、弹性耦合和功率流向。在各个齿轮副的偏心误差、齿频误差和时变啮合刚度共同作用下,用数值分析方法得到了同轴对转系统的位移响应和速度响应等时域动态特性,并对比了定轴轮系与差动轮系的载荷分配,为同轴对转传动系统的动态性能优化与振动噪声研究提供了依据。     

切削振动加速度时间历程演化过程的动力学特征

取自刀架的振动加速度时间历程被分为三大部分：无颤振切削状态,过渡切削状态和颤振状态。这里分别从热力学角度和几何角度描述了切削系统的动力学行为,给出了与无颤振切削状态和颤振状态相对应的振动加速度时间序列的概率密度分布和三维重构吸引子。并计算了各阶段的Lyapunov 指数和 Kolmogrov 熵。同时绘制并讨论了Lyapunov 指数和 Kolmogrov 熵与切削加工参数的关系曲线。研究表明： Lyapunov 指数和 Kolmogrov 熵与切削加工参数的关系曲线变化趋势相同,看起来象稳定阈图,这些曲线对切削加工参数的选择具有指导作用。并且,当切削状态从无颤振状态过渡到颤振状态时,Lyapunov 指数和 Kolmogrov 熵将随振动幅值的增大而增大。     

一种挤压油膜阻尼器的动力特性分析*

摘要：挤压油膜阻尼器对旋转机械的减振具有重要作用。不同挤压油膜阻尼器的工作特性也不相同。本文首先介绍了挤压油膜阻尼器动力特性计算方法,比较了数值求解的迭代计算法和曲线交点法的优缺点;其次设计了一种挤压油膜阻尼器试验台,介绍了所设计的实验条件和方法,并进行了动力特性试验研究,得到了3种激振力幅值下的位移导纳曲线。然后对位移导纳的幅频特性和相频特性,进行了计算与试验结果的对比分析,最后得出了有实用价值的结论。     

对转圆柱滚子轴承动态特性分析

针对内外圈对转圆柱滚子轴承内部复杂的运动特性及相互作用力,通过分析轴承径向游隙的影响因素以及考虑滚子与滚道的接触变形和热效应对油膜厚度的影响,利用拟静力学法建立了轴承的分析模型,并采用NewtonRaphson法进行求解;同时,利用该模型对滚子打滑率进行计算,以验证所采用分析方法的正确性和可靠性。然后,进一步探讨了不同工况下对转圆柱滚子轴承内部组件的转速变化规律与接触特性。结果表明：滚子的自转转速、滚子与滚道的接触载荷均随径向载荷的增大而增大;内、外圈转速变化会使受载区滚子与滚道的接触载荷以一定的规律重新分配,且转速对最小油膜厚度的影响较径向载荷更为明显。研究结果可为对转圆柱滚子轴承的结构优化和生热机理分析提供理论依据。     

动态镦粗过程的动力显式有限元分析

为了研究金属的三维动态锤锻成形过程,基于连续介质力学及有限变形理论,建立了一种有限元模型.采用动力分析方法,在运动方程中加入惯性力项考虑锤锻中显著的惯性效应;根据设备的工作原理按照能量守恒定律计算变形期间的锤头速度;同时,将变形视为一个绝热过程计算变形期间试样内部的温度升高.基于建立的模型开发了动力显式有限元分析程序,模拟了铅块试样在落锤打击下的动态镦粗过程,给出了试样内部的位移、等效应变、等效应力和温度分布规律.将变形后试样几何形状、成形载荷-时间曲线和锤头速度-时间曲线的计算结果与实验结果相对比,表明了开发程序计算结果的准确性.     

弹丸惯性卡膛冲击问题动力学研究

基于弹塑性有限元接触理论对弹丸惯性卡膛过程进行了理论分析,建立了弹丸惯性卡膛过程的有限元模型.对弹丸在1 m/s -4 m/s卡膛速度下的惯性卡膛过程进行了分析计算,明确了卡膛过程中弹带的弹塑性形变规律和弹丸的动力学响应,并通过计算分析了摩擦系数对卡膛过程计算结果的影响.     

金鳌洲塔动力测试与特性的研究

结构的动力特性是评价古塔抗震性能和损伤状态的重要指标。基于金鳌洲塔保护技术的研究,介绍了应用环境随机激振技术测试砖石古塔动力特性的要点和方案,并将测试结果与有限元分析软件Strand7计算分析的结果进行了对比,获得的试验结果是较为理想的,进一步讨论了实测结果与有限元计算结果之间的异同,并分析了原因。这些将为古塔的永久性保护、适度的开发利用及测试提供有益的参考。     

橡胶轴承-转轴系统碰摩响应动力学特性研究

将橡胶轴承支撑的转轴/轴承系统简化为非线性弹性支撑的转轴/轴承系统。基于非线性动力学及分叉理论进行分析、研究,确定周期无碰摩响应边界、碰摩运动边界、稳定性边界。结果表明,同频全周碰摩、跳跃现象及碰摩响应在周期、非周期运动间过渡;通过对阻尼比、偏心率等系统参数对系统动态响应特性影响分析获得参数平面内不同碰摩响应区域边界。因而可较好理解系统参数与不同系统响应特性间关系。     

一种压缩空气驱动的武器发射过程动力学分析

气动发射武器以弹药结构简单和发射能量可控的优势在反恐防暴领域有着巨大应用前景,提出了一种以压缩空气作为动力源的气动发射武器的工作原理;基于气体动力学理论和赫兹接触理论,建立了其变质量热力学模型和摩擦力模型,从而建立了发射过程的动力学模型。采用MATLAB/Simulink对模型进行了数值仿真,得到了恒压气源条件下的膛内气体状态参数和弹丸运动参数的变化规律;并在此基础上分析了结构参数和动力源参数变化对气动发射武器发射过程的影响。研究结果对压缩空气驱动的气动发射武器的研发和设计具有理论指导意义。     

Dynamic analysis of the multi-link five-point suspension system using point and joint coordinates

Summary In this paper the transient dynamic analysis of a quarter car model with a multi-link five-point suspension is presented. The equations of motion are formulated using a two step transformation. Initially, the formulation is written in terms of a dynamically equivalent system of particles. The equations of motion are then transformed to the relative joint variables. For open chains, this process automatically eliminates all of the non-working constraint forces and leads to an efficient solution and integration of the equations of motion. For closed chains, suitable joints should be cut and few cut joints constraint equations should be included for each closed chain. The model includes four closed chains together with the necessary elements such as the leaf springs and shock absorbers. The tire is modelled simply by a spring-damper element that imposes constraint forces on the motion of the system. The results of the, simulation indicate the simplicity and generality of the dynamic formulation.     

新型机枪枪架及其动态特性分析

以某型重机枪为研究对象,在不改动枪身的前提下设计了一种新型弹性三角枪架。通过建立机枪有限元模型,分析计算了其固有特性;建立基于刚柔耦合多体系统动力学的机枪虚拟样机模型,求解出其在连发状态下的动力响应。所得结果与原有三脚架进行了分析比较,证明了新型三脚架的优越性。     

High-frequency resonant characteristics of triple-layered piezoceramic bimorphs determined using experimental measurements and theoretical analysis

This is an experimental, theoretical, and numerical investigation of vibration characteristics in high-frequency resonance, which are studied for parallel- and series-type piezoelectric bimorphs. In the experimental measurements, the full-field optical technique known as electronic speckle pattern interferometry (ESPI) is used to measure the transverse (out-of-plane) and planar (in-plane) resonant frequencies and corresponding mode shapes for piezoelectric bimorphs. In addition, in-plane resonant frequencies are obtained from impedance analysis and the response curves of the frequency spectra show different vibration characteristics of the piezoelectric bimorphs with different electrical connections. Piezoelectric bimorphs with normal connections have three-dimensional coupled vibration characteristics and the out-of-plane vibration dominates the motion. However, only in-plane vibration motions can be excited in the high-frequency range for abnormal connections, and the resonant characteristics are similar to the single-layered piezoelectric plate. The triple-layered piezoelectric bimorphs with abnormal connection are also analyzed using theoretical analysis. The resonant frequencies, mode shapes, and normalized displacements are calculated based on the analytical solution. The experimental results and the theoretical analysis are in good agreement with the numerical calculations using the finite element method. From the discussion of the results for the parallel- and series-type piezoelectric bimorphs with normal and abnormal connections, the vibration characteristics at high frequencies are completely analyzed in this study.     

约束阻尼管动态特性分析方法与应用

建立具有支撑功能的减振约束阻尼管的力学模型,采用解析分析得到该类型阻尼管位移、动刚度和损耗因子等关于各项几何及物理参数的表达式。通过计算发现,阻尼胶填充长度对元件的损耗因子有比较显著的影响,在给定的结构参数条件下,存在最优填充长度。为阻尼管结构设计提供了快速、简便的优化设计方法。     

Magnetron sputtering modes during pulsed deposition process determined by the analysis of power supply parameter

The goal of this paper is to present a new control method of reactive magnetron sputtering. The processes of reactive magnetron sputtering of aluminum target in Ar + O₂ atmosphere in high efficiency deposition and low efficiency deposition mode were studied. The mode of magnetron operation — metallic, transient, reactive (compound) — was determined by the analysis of medium frequency (MF) magnetron voltage and current waveforms and a circulating power (power supply parameter). This parameter enables monitoring of any mismatch between plasma-magnetron impedance and the resonant circuit of power supply. The experiments show that the Al_xO_y layer formation conditions could be determined by use of the power supply parameters. Conclusions were supported by the refractive index and dielectric constant measurements.