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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. 相似文献
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V. G. Vovk 《TEST》1993,2(1-2):189-217
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. 相似文献
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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... 相似文献
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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. 相似文献
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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。 相似文献
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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。 相似文献
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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。 相似文献
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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. 相似文献
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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。 相似文献
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Dr. H. A. Attia 《Acta Mechanica》1996,119(1-4):221-228
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. 相似文献
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Huang YH Ma CC Chao CK 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2012,59(6):1219-1232
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. 相似文献
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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 AlxOy layer formation conditions could be determined by use of the power supply parameters. Conclusions were supported by the refractive index and dielectric constant measurements. 相似文献