A nonlinear analytical model for the squeeze-film dynamics of parallel plates subjected to axial flow

In this paper, we develop a theoretical model to predict the nonlinear fluid-structure interaction forces and the dynamics of parallel vibrating plates subjected to an axial gap flow. The gap is assumed small, when compared to the plate dimensions, the plate width being much larger than the length, so that the simplifying assumptions of 1D bulk-flow models are adequate. We thus develop a simplified theoretical squeeze-film formulation, which includes both the distributed and singular dissipative flow terms. This model is suitable for performing effective time-domain numerical simulations of vibrating systems which are coupled by the nonlinear unsteady flow forces, for instance the vibro-impact dynamics of plates with fluid gap interfaces. A linearized version of the flow model is also presented and discussed, which is appropriate for studying the complex modes and linear stability of flow/structure coupled systems as a function of the average axial gap velocity. Two applications of our formulation are presented: (1) first we study how an axial flow modifies the rigid-body motion of immersed plates falling under gravity; (2) then we compute the dynamical behavior of an immersed oscillating plate as a function of the axial gap flow velocity. Linear stability plots of oscillating plates are shown, as a function of the average fluid gap and of the axial flow velocity, for various scenarios of the loss terms. These results highlight the conditions leading to either the divergence or flutter instabilities. Numerical simulations of the nonlinear flow/structure dynamical responses are also presented, for both stable and unstable regimes. This work is of interest to a large body of real-life problems, for instance the dynamics of nuclear spent fuel racks immersed in a pool when subjected to seismic excitations, or the self-excited vibro-impact motions of valve-like components under axial flows.     

非线性失真对场倒置加扰信号的影响

文章通过分析非线性失真对场倒置加扰信号的影响，指出了非线性失真是引起解忧后图象色度闪烁的一个不容忽视的原因。它的大小，将直接影响此类加扰方式的效果。     

Gas bubble dynamics—experiment and fractal analysis

In the paper, nonlinear features of the air bubbling from a submerged glass nozzles are discussed. The air bubbles were emitted from glass nozzles of different diameters submerged in distilled water at a depth of 15 cm in a cylindrical tank of 30 cm in diameter and 37 cm height. The air volume flow rate was changed from 1 l/h to 45 l/h. A laser-photodiode and an acoustic technique system have been used. Also photographic study of bubbles departure has been carried out. Measured data have been analysed using the fractal analysis method. It has been shown that bubbles dynamics is of deterministic chaos nature and behaviours of such system can be chaotic or periodic depending on the volume flow rate. The map of chaos appearance has been constructed. Data recorded by acoustic system has been used to analysis of bubble wall movement.     

自主机器人直线行进过程的数字PID控制

针对自主机器人的直线行进过程，提出一种通过硬件电路确定直流电机模型的方法，即利用光电编码器测得机器人驱动轮电机转速信号，经硬件电路将每个周期时间内的脉冲数记录下来，从而得到电机输出转速响应曲线，确定电机的数学模型。在电机模型确定的基础上，实现了自主机器人直线行进过程的数字PID控制。数字PID参数的确定采用Ziegler—Nichols法，同时借助Matlab／Simulink仿真软件对所得PID参数进行了进一步的整定，取得了良好的控制效果。     

RAPID APPROXIMATE SOLUTIONS FOR ADSORPTION BED CONCENTRATION PROFILE AND BREAKTHROUGH CURVE BEHAVIOR: FAVORABLE ISOTHERMS AND BOTH PHASE RESISTANCES IMPORTANT

A simple method is presented for determining fluid-phase and solid-phase solute concentration profiles, and solute breakthrough curves, for fixed bed adsorbers when both the fluid-phase and solid-phase mass transfer resistances are important. The method applies to any nonlinear isotherm of the “favorable” type. Freundlich and Langmuir isotherms are used as specific examples in the present paper. Constant-pattern behavior and linear-driving-force rate laws are assumed.     

A survey on nonlinear analog-to-digital converters

This paper presents a survey on Nonlinear Analog-to-Digital converters (ADC). This class of converters is extremely relevant in applications where there is a need for non-uniform quantization characteristic, for example, some specific applications in the areas of light detection, hearing aid, nuclear physics, image acquisition, communication systems, etc. This survey outlines the state-of-the-art Nonlinear ADC topologies, such as, floating point, logarithmic, piecewise linear and oversampled nonlinear converters, and discusses their performance and advantages in terms of their applications.     

无人机空中加油自主会合导引律研究

针对自主空中加油技术中的会和阶段的理论研究,提出一种带有终端偏航角约束的导引问题。通过对三维空间中重新设计偏置项,来同时约束俯仰与偏航角,将期望的会合点作为跟踪目标,并在制导末端结合纯追踪法,实现终端航向的控制。最后,以匀速直线运动和作U型机动的加油机为例,对无人机（UAV）选取不同的初始位置和航向来检验所提出的制导律实现会合的能力。仿真结果表明,所设计的自主会合制导律有效实现无人机空中加油自主会合,解决了现有一类自主会合制导律设计复杂、需预先已知加油机轨迹及大量在线规划计算的问题。     

Circuit-limited oscillations at the onset of impurity breakdown in ultrapure p-Ge with an S-shaped current-field characteristic

Ultrapure p-Ge with doping concentration as low as 10¹¹ cm⁻³ is considered to investigate self-pulsating oscillations at the onset of impurity breakdown with respect to an S-shaped current-field characteristic. The associated nonlinear dynamics is computed within the two-impurity-level model with more convincing parameterization. The system undergoes a single Hopf bifurcation in the presence of a sufficiently large circuitry capacitance. As the operating point is controlled towards the breakdown threshold, no further bifurcations but a changeover of the periodic oscillation occurs from being sinusoidal to pulsating. Our approach also obtains agreeable results for n-GaAs with typically higher doping.     

Multisoliton complexes in fiber lasers

The formation of stationary and non-stationary pulse groups is regularly observed in multiple pulse soliton fiber lasers. The environment developed in this study for the flexible investigation of this phenomenon is based on the cavity comprising a semiconductor saturable absorber mirror (SESAM) with complex dynamics of absorption recovery and all-fiber dispersion management. The detailed experimental and theoretical considerations show that multiple pulsing in fiber systems offers numerous embodiments ranging from stationary bound states to chaotic bunches. The pulse interaction through the dispersive waves was found to produce a principal impact on the bound state formation. The stability and transformation of stationary bound states and bunch propagation have been also addressed.     

Low threshold and tunable all-optical switch using two-photon absorption in array of nonlinear ring resonators coupled to MZI

In this paper a novel structure based on Mach-Zehnder Interferometer (MZI) and an array of nonlinear ring resonators for all-optical switching including very low threshold, fast and all-optically tunable is presented. In this proposal, an array including N ring resonators is coupled to one arm of MZI to introduce the required nonlinear phase shift to switching. Also, two-photon absorption phenomenon is used and will be proposed as another alternative for manipulation of optical switching properties. The proposed idea needs small chip area (∝1/Ntraditional cases) for implementation. We show that the switching threshold intensity can be decreased with increase of N, decrease of the coupling coefficient and increase of the two-photon absorption coefficient. In this structure with traditional optical fibers with the low nonlinear index of refractions and using an array including 15 ring resonators with 6 mm diameter for each rings only 3 mW for the switching threshold power is required. Also, using erbium-doped fiber for implementation of the rings with the high nonlinear index of refractions and five ring resonators including 0.3 mm diameter, the switching threshold power can be reduced to μW level. If the nonzero two-photon absorption coefficient is considered, the switching threshold will be very smaller than the above-mentioned values. We show that with changing the optical amplifier gain the switching threshold can be tuned. So, the proposal can be used as a functional block for the integrated optical switch with very small and tunable threshold.