Active vibration control of beam structures using acceleration feedback control with piezoceramic actuators

In this study, the active vibration control of clamped–clamped beams using the acceleration feedback (AF) controller with a sensor/moment pair actuator configuration is investigated. The sensor/moment pair actuator is a non-collocated configuration, and it is the main source of instability in the direct velocity feedback control system. First, the AF controller with non-collocated sensor/moment pair actuator is numerically implemented for a clamped–clamped beam. Then, to characterize and solve the instability problem of the AF controller, a parametric study is conducted. The design parameters (gain and damping ratio) are found to have significant effects on the stability and performance of the AF controller. Next, based on the characteristics of AF controllers, a multimode controllable single-input single-output (SISO) AF controller is considered. Three AF controllers are connected in parallel with the SISO architecture. Each controller is tuned to a different mode (in this case, the second, third and fourth modes). The design parameters are determined on the basis of the parametric study. The multimode AF controller with the selected design parameters has good stability and a high gain margin. Moreover, it reduces the vibration significantly. The vibration levels at the tuned modes are reduced by about 12 dB. Finally, the performance of the AF controller is verified by conducting an experiment. The vibration level of each controlled mode can be reduced by about 12 dB and this value is almost same as the theoretical result.     

Base impedance of velocity feedback control units with proof-mass electrodynamic actuators

Control units comprising a proof-mass electrodynamic actuator and accelerometer-sensor pair with a time integrator and fixed gain controller are an effective way to implement velocity feedback control on thin flexible structures. These control units produce active damping provided the fundamental resonance frequency of the actuators is well below that of the structure under control. Control stability limits arise from the actuators fundamental resonances which introduce a 180° phase lag in the sensor-actuator frequency response functions, thus causing the feedback loops to be only conditionally stable. In contrast to previous studies, this paper discusses the response of a control unit with electrodynamic proof-mass actuator in terms of the open- and closed-loop base impedance that it exerts on the structure. This allows for a straight-forward physical interpretation of both stability and control performance. Experimental and simulation results show that the base impedance can be described as the sum of passive and active frequency response functions, where the active part of the control unit response depends on the actuator electromechanical response and also on the response function of the analogue controller circuit. The results show that the base impedance formulation can be effectively used to investigate new designs of both the actuator and electronic controller in order to optimise the stability and performance properties of the control unit.     

Rectangular plate with velocity feedback loops using triangularly shaped piezoceramic actuators: experimental control performance

This paper presents experimental results on the implementation of decentralized velocity feedback control on a new smart panel in order to produce active damping. The panel is equipped with 16 triangularly shaped piezoceramic patch actuators along its border and accelerometer sensors located at the top vertex of the triangular actuators. The primary objective of this paper is to demonstrate the vibration and sound radiation control using the new smart panel. Narrow frequency band experimental results highlight that the 16 control units can produce reductions up to 15 dB at resonance frequencies between 100 and 700 Hz in terms of both structural vibration and sound power radiation.     

Expanding amplitude-squeezing bandwidth with off-peak dispersive optical feedback

Weak dispersive optical feedback has been proved both theoretically and experimentally to be able to reduce the intensity noise of semiconductor lasers and allow the generation of amplitude-squeezed states. I propose a novel scheme exploiting the off-peak optical feedback condition that expands the squeezing bandwidth and significantly enhances the repeatability over the most commonly utilized on-peak optical feedback scheme. Using a realistic model, I show that under the zero-frequency-pulling condition the off-peak scheme greatly enhances the squeezing bandwidth.     

双稳系统随机共振的反馈控制

将双稳系统的输出反馈到输入端再作用于系统,提出了采用反馈来控制随机共振的方法.以典型双稳系统为对象,并以信噪比和功率谱放大率作为度量随机共振效应的可观察变量,分别研究了采用线性或非线性反馈函数所产生的随机共振现象.理论分析和数值仿真结果表明随机共振是可控制的.该方法特别适用于系统参数固定或难以改变的系统. 关键词： 双稳系统 随机共振 反馈控制 共振效应     

一种机械谐振下的控制带宽扩展方法

针对系统固有机械谐振影响光电稳定跟踪系统频带宽度的问题,提出了一种机械谐振下的控制带宽扩展方案。该方案借助系统频率特性测量方法,利用最小二乘参数辨识算法实现。试验结果表明,利用本文方案,速度闭环下的谐振峰值减小至原来的1/3,控制带宽提高了接近2倍,证明本文提出的方案能够有效实现机械谐振抑制,提高系统控制带宽,保证系统稳定性能。     

Comparison of decentralized velocity feedback control for thin homogeneous and stiff sandwich panels using electrodynamic proof-mass actuators

Theoretical and experimental work is presented to compare the effect of decentralised velocity feedback control on thin homogeneous and sandwich panels. The decentralised control system consists of five control units, which are composed of a proof-mass electrodynamic actuator with an accelerometer underneath its footprint and an analogue controller. The stability of the feedback loops is analysed by considering the sensor-actuator open-loop frequency response function of each control unit and the eigenvalues of the fully populated matrix of open-loop frequency response functions between the five sensors and five actuators. The control performance is then analysed in terms of the time-averaged total kinetic energy and total sound power radiated by the two panels. The results show that for a stiff sandwich panel higher stable feedback gains can be implemented than on a thin homogeneous panel of comparable weight per unit area. Moreover the implementation of decentralised velocity feedback can offset some of the undesirable sound transmission properties of lightweight sandwich structures by efficiently reducing structural vibration and sound power radiation in the mid audio frequency range.     

Reduction of magnetic field fluctuations in powered magnets for NMR using inductive measurements and sampled-data feedback control

Resistive and hybrid (resistive/superconducting) magnets provide substantially higher magnetic fields than those available in low-temperature superconducting magnets, but their relatively low spatial homogeneity and temporal field fluctuations are unacceptable for high resolution NMR. While several techniques for reducing temporal fluctuations have demonstrated varying degrees of success, this paper restricts attention to methods that utilize inductive measurements and feedback control to actively cancel the temporal fluctuations. In comparison to earlier studies using analog proportional control, this paper shows that shaping the controller frequency response results in significantly higher reductions in temporal fluctuations. Measurements of temporal fluctuation spectra and the frequency response of the instrumentation that cancels the temporal fluctuations guide the controller design. In particular, we describe a sampled-data phase-lead-lag controller that utilizes the internal model principle to selectively attenuate magnetic field fluctuations caused by the power supply ripple. We present a quantitative comparison of the attenuation in temporal fluctuations afforded by the new design and a proportional control design. Metrics for comparison include measurements of the temporal fluctuations using Faraday induction and observations of the effect that the fluctuations have on nuclear resonance measurements.     

Feedback compensator for control units with proof-mass electrodynamic actuators

This paper presents theoretical and experimental work on a velocity feedback control unit with an electrodynamic proof-mass actuator. The study shows that the stability and performance of the feedback control loop can be substantially improved by implementing an appropriate compensation filter, which detunes the passive and active responses of the actuator. The control unit is analysed in terms of the open- and closed-loop base impedance it presents to the structure under control. In this way the analytical expression for the proposed compensator is derived directly from known actuator parameters. The compensation filter provides significant improvement over the uncompensated case, even for considerable variations in the actuator response. One drawback of the compensator is the enhancement of the feedback signal at low frequencies, which may lead to stroke/force saturation effects in the actuator. In this respect the study shows that it can be beneficial to implement an additional high pass filter, which however produces a loss in the phase and gain margins.     

Stochastic resonance in FitzHugh-Nagumo system with time-delayed feedback

The dynamics of a periodically driven FitzHugh-Nagumo system with time-delayed feedback and Gaussian white noise is investigated. The stochastic resonance which is characterized by the Fourier coefficient Q is numerically calculated. It is found that the stochastic resonance of the system is a non-monotonic function of the noise strength and the signal period. The variation of the time-delayed feedback can induce periodic stochastic resonance in the system.     

窄线宽、高光束质量的外腔双反馈激光二极管阵列

设计了一种离轴双反馈外腔能够有效地改善激光二极管阵列的线宽和光束质量。闪耀光栅和高反镜之间形成了一个共振腔。通过调整光栅和高反镜之间的倾角可以选定一个空间模在共振腔中放大。将一个半波片插入外腔中的光栅反馈支路,来控制反馈光的数量,激光从光栅反馈支路输出。运用这项技术,在工作电流16 A,可以把激光二极管阵列的输出线宽压缩到0.15 nm,光束束宽积减小到283 mm·mrad。由于光栅的锁定作用,中心波长几乎不随温度的变化而改变。在工作电流17 A时,输出激光的功率为2.44 W,斜率效率为0.5 W/A。     

脉冲步进调制高压电源远程通讯与反馈控制系统研究

为了满足HL-2A装置二级加热系统的高压电源系统的要求,开发了脉冲步进调制(PSM)高压脉冲电源控制系统.PSM电源控制系统采用数字信号处理器(DSP)和现场可编程门阵列器件(FPGA)组合控制方式,总计输出112路脉冲.DSP芯片实现计算、反馈、远程通信等功能,FPGA主要负责与DSP的数据传输及112路脉冲输出的时...     

基于状态反馈参数激励系统的超谐共振分岔控制

设计了非线性参数控制器，改变了参数激励系统2 倍超谐共振时的稳态响应，减小了系统的响应幅值和消除了超谐共振时的鞍结分岔，从而消 除了跳跃和滞后现象.首先由多尺度法得到参数系统的近似频响方程，再进行分岔分析，从 而实现非线性控制的目标.通过数值模拟，说明状态反馈控制是可行的和有效的. 关键词： 参数激励 鞍结分岔 分岔控制 2倍超谐共振     

Steady control of laminar separation over airfoils with plasma sheet actuators

This work analyzes the effects produced by an EHD actuator on the flow around an airfoil at low Re numbers (Re≈10⁴). The analysis is undertaken from flow visualizations and measurements of the surface pressure distributions. The experiments indicate that, for low Re number, the effects of the actuation depend on the power added to the flow and on the relative distance between the actuator and the separation line.     

Laser stabilization with multiple-delay feedback control

Stabilization of chaotic intensity fluctuations of intracavity frequency-doubled solid-state (Nd: YAG) lasers using multiple-delay feedback control (MDFC) is demonstrated by numerical simulations. It is shown that MDFC not only provides stable (cw) output for constant pump rates but also works with slowly varying pump currents, resulting in corresponding (nonchaotic) intensity modulations.     

Modified split-potential model for modeling the effect of DBD plasma actuators in high altitude flow control

Surface DBD plasma actuators are novel means of actively controlling flow. They have shown promising ability in reducing drag, postponing transition from laminar to turbulent flow, suppression of separation, noise reduction and enhancement of mixing in different applications. The CFD simulation of the effect of plasma actuator in such kind of applications could provide more information, and insight, for optimization and design of close looped flow control systems. However, the fluid models for simulating the formation of the plasma and its effect are computationally expensive such that, although they provide more detailed information about the physics related to the formation plasma, they are still not viable to be used in large scale CFD simulations. In this paper, we present the modified version of a simpler model that predicts the thrust generated by the plasma actuator with acceptable accuracy and can be easily incorporated in CFD calculations. This model is also free of empirical fitting parameters, being based on pure flow physics scaling.     

Forebody asymmetric vortex control with extended dielectric barrier discharge plasma actuators

Plasma control of forebody asymmetric vortices is mostly achieved by means of dielectric barrier discharge(DBD)plasma actuators. However, DBD actuators suffer from some disadvantages such as a weak induced body force, a singledirection induced jet, and an unclear control mechanism. We carry out wind tunnel experiments involving the forebody vortex control of a slender body at high angles of attack using an innovative extended DBD actuator, which has a stronger capacity to induce an electric wind than a DBD actuator. Through synchronous measurements of the pressure distribution and particle image velocimetry(PIV), the spatiotemporal evolution of the dynamic interactions between plasma-actuationinduced vortices and forebody asymmetric vortices is analyzed. The influence of plasma discharge on the boundary layer separation around a slender body and the spatial topological structures of asymmetric vortices are further surveyed, as the optimized actuation parameters. Extended DBD actuators are found to be more capable of controlling asymmetric vortices than DBD actuators, and a linear proportionality of the sectional lateral force versus the duty ratio is achieved.There exists an optimal normalized reduced frequency( f+= 2π fpd/U∞= 2.39) for asymmetric vortex control under the present experimental conditions. The research results can provide technical guidance for the control and reuse of forebody asymmetric vortices.     

Suboptimal control of wall turbulence with arrayed dimple actuators for drag reduction

Direct numerical simulation of a turbulent channel flow with moving dimples at the bottom wall is carried out using the pseudo-spectral method and the curvilinear coordinate system. Suboptimal control based on the spanwise wall shear stress is applied for skin-friction drag reduction, and is implemented by the finite-size sensor-actuator system. The control law is realised in physical space by using a cross-shaped truncation of the wall shear stress information, which can be measured by the sensor. Only the information of wall shear stress inside the sensor area is utilised and that outside the sensor area is obtained by a linear reconstruction from the averaged value over the sensor. To effectively intervene the near-wall coherent structures, low-pass filtering of the spanwise wall shear stress is additionally implemented to eliminate the extra disturbances induced by the presence of dimple actuators, and the filtered stress is used as the control input. Numerical tests on the present control strategy show that the pressure form drag caused by the presence of dimples is reduced significantly as compared with the original suboptimal control, and the reduction of total drag is comparable with that of the opposition control. The underlying mechanism is further analysed by looking into the interaction between the moving dimples and the near-wall coherent structures.