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1.
In this paper are presented the results of a study of synchronous motor oscillations resulting from sudden application of mechanical load. By means of the Differential Analyzer at the Moore School of Electrical Engineering of the University of Pennsylvania, theoretical synchronous machine equations were solved for conditions of suddenly applied load, and the effect on the resulting oscillations of variations in field excitation was determined for the most practical cases. The analyzer results were checked by a number of experimental observations, and it was found that the magnitude and duration of the oscillations could be greatly decreased by using the proper type of excitation variation.  相似文献   

2.
This paper characterizes oscillations found in block pulse function (BPF) domain identification of open loop first-order systems with step input. A useful condition for occurrence of such oscillations is presented mathematically. For any positive value of ‘ah’, oscillations are observed to occur, where h is the width of BPF domain sub-interval and 1/a is the time constant of the first-order system under consideration.  相似文献   

3.
Discrete-scale invariance (DSI) is a phenomenon featuring intriguing log-periodicity that can be rarely observed in quantum systems. Here, we report the log-periodic quantum oscillations in the longitudinal magnetoresistivity (ρxx) and the Hall traces (ρyx) of HfTe5 crystals, which reveal the DSI in the transport-coefficients matrix. The oscillations in ρxx and ρyx show the consistent logB-periodicity with a phase shift. The finding of the logB oscillations in the Hall resistance supports the physical mechanism as a general quantum effect originating from the resonant scattering. Combined with theoretical simulations, we further clarify the origin of the log-periodic oscillations and the DSI in the topological materials. This work evidences the universality of the DSI in the Dirac materials and provides indispensable information for a full understanding of this novel phenomenon.  相似文献   

4.
This award recognizes two specific discoveries that constitute the experimental discovery of neutrino oscillations. In 1998 the Super-Kamiokande group under the leadership of Yoji Totsuka published their paper, “Evidence for Oscillation of Atmospheric Neutrinos” in Physical Review Letters [1]. The paper describes a deficit of muon-type neutrinos from below the detector relative to those from above. It explains this “atmospheric neutrino anomaly” as a result of transformation of some of the muon neutrinos into another type of neutrino. Four years later, the group led by Arthur McDonald described “Direct Evidence for Neutrino Flavor Transformation from Neutral-Current Interactions in the Sudbury Neutrino Observatory” [2] in the same journal. This experiment detected lower energy neutrinos from deep inside the Sun. By measuring all flavors of neutrinos with large rates, the SNO collaboration showed definitively that the long-standing “solar neutrino puzzle” was another manifestation of neutrino oscillations. As a result of these two experiments, we now understand that neutrinos can change identities during propagation and that both the solar and atmospheric neutrino “problems” result from the same underlying phenomenon of oscillations. A consequence of neutrino oscillations is that neutrinos, previously thought to be massless, must have a non-zero rest mass.  相似文献   

5.
Vibrations of an elastic string when the separation between the ends varies randomly are studied. The emphasis is on the evolution of the coherent, or ordered, oscillations of the string. Using a perturbation technique borrowed from quantum field theory and the modified Kryloff–Bogoliuboff method, the “multiple scattering” effect of the random separation between the ends on the linear and nonlinear coherent oscillations are investigated. It is found that due to the random interactions the coherent fundamental oscillation as well as the harmonies are damped. Their frequencies are also modified.  相似文献   

6.
In this paper a tuning procedure is proposed for event based PI controllers with Regular Quantization with Hysteresis (RQH) sampling law. The RQH is a generalization of Symmetric Send on Delta (SSOD) strategy which decreases the robustness requirements to avoid limit cycle oscillations and reduce the number of events needed for control, improving the overall performance of PI controllers in networked control systems. The tuning procedure takes into account not only classical robustness margins but also takes advantage of some specific robustness measures to avoid limit cycle oscillations induced by the sampler. As the robustness analysis depends on the Describing Function (DF) method, a study evaluating the effect of high order harmonics is provided, showing the validity of the tuning procedure. Some examples are included in which the usefulness of the tuning procedure is shown.  相似文献   

7.
In wind power system, low frequency oscillations are observed due to imbalance between mechanical input and electrical output. Hence, variable susceptance controllers are being adopted to mitigate these oscillations. However, improper modulation of control parameters also leads to system instability. Therefore, we propose an optimization methodology for mitigating low frequency oscillations in wind power generation system. To visualize our methodology, we use a lead-lag type variable susceptance controller for fixed speed induction generator (FSIG) based wind generation system. Then, we optimize gain and time constants of lead-lag controller using three optimization algorithms: particle swarm optimization (PSO), genetic algorithm (GA), and flower pollination algorithm (FPA). Later, we perform non-linear time domain simulation and quantitative analysis to find average fitness, standard deviation, run time, and iteration number for these optimization algorithms. Moreover, non-parametric statistical analysis, such as Kolmogorov–Smirnov and Wilcoxon signed-rank tests are employed for identifying statistically significant differences among these algorithms.  相似文献   

8.
The effects of an added mass on the oscillations of a SDOF bluff body, elastically supported, exposed to a steady flow and undergoing galloping oscillations, are investigated. The stability boundaries of the trivial equilibrium position of the 2DOF system are determined in a four parameters space. The occurrence of different types of bifurcation on these boundaries is highlighted, namely, simple Hopf, non-resonant double Hopf and 1 : 1 resonant double Hopf. The perturbation multiple scale method is employed to analyze the system postcritical behavior around the codimension-1 and codimension-2 critical manifolds. The analytical results are compared with numerical solutions obtained through direct integration of the equations of motion. Finally, the effects of the closeness of the critical frequencies on the non-resonant double Hopf manifold, are discussed by using a quasi-resonant asymptotic solutions.  相似文献   

9.
综合分析处理了包括武汉台在内的全球地球动力学(GGP)台站超导重力仪长期、连续重力观测资料,研究和检测了地球液核的动力学效应。系统讨论了在日月引潮力、表面负荷和液核动力学行为引起的核幔边界及内核边界上,压力和重力扰动等不同驱动力作用下,地球的弹性引力形变响应.基于周日重力潮汐观测中的共振放大特征,通过国际超导重力仪观测资料的迭积,研究了地球的自由和章动(FCN),精密确定了FCN参数.采用位移场的变分方法研究了液核的自由振荡,严密推导获得了用于有限元数值计算的本征值 本征向量问题.同时采用GGP台站超导重力仪长期、连续、高质量重力观测数据,研究了固体内核的平动振荡  相似文献   

10.
Gas discharges generate oscillations superimposed on random noise of several megacycles bandwidth.Positive ions oscillate in two distinct regions of the discharge, i.e., the plasma and the potential minimum at the cathode.The disturbances produced by the ion motions appear as voltage variations between the electrodes.Oscillations generated in the plasma are usually below 400 kc./sec., while “cathode” oscillations are about 700 kc./sec.As the discharge current is increased, the amplitude of the plasma oscillation increases while its frequency decreases. The random noise also depends on current, increasing rapidly as the Townsend discharge changes into an are. After arc conditions are fully established, the noise changes slightly with current. Probe studies show that the noise voltage between probe and cathode increases rapidly as space charge conditions change to permit acceleration of electrons to the probe. When the probe collects positive ions, the noise as viewed on an oscilloscope is coarse, i.e., lacking in high frequency components.An explanation of the noise generation may be found in the random fluctuations of space charge at the electrodes. Calculations based on this theory give voltage fluctuations of the observed order of magnitude.  相似文献   

11.
In this work, tuning rules of the PID controller have been developed by categorizing a system's response into distinct classes. The classes are formed using the shapes of the test oscillations induced by the system under the Modified Relay Feedback Test (MRFT) produced by specific system models. It is proposed that a physical system can be categorized into one of the proposed classes and thus the tuning rules for a particular class can apply to any kind of system from this class. The idea of producing tuning rules that are based on the shape of the oscillations induced in the loop containing the process comes from the observations that oscillatory responses of physical systems reveal just a few different shapes depending on system dynamics. For applying the developed optimal tuning rules for an arbitrary system, first, certain system characteristics are determined using a priori knowledge of the class model. Then the system's response with the application of the MRFT is examined to classify the oscillation waveform/shape. In this work, such classification is carried out using a cross-correlation algorithm. Finally, a class tuning rules are applied.  相似文献   

12.
A method has been presented in recent papers for deriving precisely stabilized waveform generators by relating them to second order conservative oscillators. The present paper demonstrates a method for modifying the previous models and in doing so a novel class of applicable oscillator models is established.Conditions that enable the models to sustain oscillations in steady state are described. A precise method for dynamically stabilizing the oscillators waveforms is developed, and practical uses are suggested.  相似文献   

13.
The principal contribution of this note is to avoid the parametric resonance effect and attenuate the payload oscillations in an overhead-crane system subject to periodic variations in the base support. Considering an appropriate sliding output with relative degree one, we present the sliding mode control design based on the Super-Twisting Algorithm (STA), ensuring finite time convergence to the desired sliding surface for the linear periodic system with Lipschitz continuous matched and unmatched uncertainties bounded together by their gradients by known functions. The suggested approach also provides chattering phenomenon attenuation. Obtained results are verified experimentally.  相似文献   

14.
Presented herein is a detailed analysis of the small, free oscillations of pre- stressed rectangular plates in both pre- and post-buckling ranges. The simply supported plate is stressed either thermally or by the uniaxial in-plane loads on two opposite edges, the other two edges are taken to be either freely movable or immovable, and all the edges are restrained to remain straight. Both the symmetrical and anti-symmetrical small vibration modes superimposed upon both primary- and secondary-buckling, and the coupling among these modes, are studied. A criterion for the existence of coupling is given. Some numerical results are then presented.  相似文献   

15.
Numerous relatively simple physical systems give rise under appropriate circumstances to oscillations which obey the equation y″ + ?(1 + k cos t)y = 0 (Mathieu's equation). These oscillations may be either stable, periodic, or unstable, depending upon parameters of the physical system as expressed by the parameters ? and k in the basic equation. It has been customary to distinguish between the stable and unstable states by diagrams of the type of Fig. 1, from which it is possible to tell whether a given set of values of the parameters ?, k will yield a stable or unstable solution. In this paper are given curves which not only present this information, but in addition give for an important part of the stable state the values of the characteristic exponent μ. The solution of the equation y″ + ?(1 + k cos t)y = 0 depends to a large extent on this exponent, and the availability of values of μ should greatly facilitate the practical application of the equation.  相似文献   

16.
采用数值模拟方法 ,研究了外部色噪音对蓝细菌生物钟体系的影响。结果表明,外噪音可以在体系的确定性稳态区诱导产生振荡和相干共振;在确定性振荡区,外噪音对振荡起到了破坏性作用,但是振荡的周期并没有随着外噪音的增加而明显变化,说明体系对外噪音具有鲁棒性;而在右侧分叉点附近的确定性振荡区,也发现了外噪音诱导相干共振现象。另外,研究了噪音相关时间的影响,发现其与噪音强度起相反的作用。  相似文献   

17.
PIO是飞行仿真软件分析的最重要的内容之一。飞行员诱发振荡（PIO）是一种人-机闭环系统的不稳定的动态运动,通常由飞行员试图执行精确的飞行操纵任务所致。目前,已经研发出了大量的PIO理论用于预测PIO的敏感性,本研究仅对3个PIO准则进行理论研究和预测命中率分析,即带宽/俯仰速率超调准则、Smith-Geddes准则和Gibson相位速率准则。  相似文献   

18.
Dynamic problems of axially moving materials as exemplified by strings in textile industry and band saws, belts and chains in mechanical machinery have recently received some attention (1–15). In the present study, the parametric resonance of an axially accelerated beam is investigated. The beam which has encastré ends is subjected to a periodic root force as shown in Fig. 1. The object of the investigation is to identify regions of instability of this system for various combinations of the excitation frequency and amplitude of the axial oscillations.  相似文献   

19.
付兵  刘国华  王振宇  陈龙珠 《科技通报》2006,22(3):372-376,384
采用解析的方法研究了上覆单相弹性层的饱和地基上刚性圆板的摇摆振动.首先运用积分边变换技术分别求解了单相弹性介质和饱和介质情况时的控制方程,然后按混合边值条件建立了部分饱和地基上刚性圆板振动的对偶积分方程,并把对偶积分方程化为易于数值求解的第二类Fredholm积分方程,数值算例给出动力柔度系数和摇摆振动转角幅值随无量纲频率变化的曲线,并与完全饱和介质情况进行了对比.数值结果表明,在共振频率附近,弹性层的存在可减弱其振动.  相似文献   

20.
With the fast development of acoustic systems in clinical and therapeutic applications, acoustically driven microbubbles have gained a prominent role as powerful tools to carry, transfer, direct, and target drug molecules in cells, tissues, and tumors in the expanding fields of targeted drug delivery and gene therapy. The aim of the present study is to establish a biocompatible acoustic microfluidic system and to demonstrate the generation of an acoustic field and its effects on microbubbles and biological cells in the microfluidic system. The acoustic field creates non-linear oscillations of the microbubble-clusters, which results in generation of shear stress on cells in such microsystems. This effectively helps in delivering extracellular probes in living cells by sonoporation. The sonoporation is investigated under the combined effects of acoustic stress and hydrodynamic stress during targeted drug and gene delivery.  相似文献   

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