平稳随机激励下随机智能桁架结构振动主动控制中的优化

研究了平稳随机激励下随机智能桁架结构振动主动控制中主动杆的配置位置和闭环控制系统增益的优化问题。考虑结构物理参数、几何尺寸、阻尼同时具有随机性以及作用荷载为平稳随机激励,基于系统最小储存能,构建了具有位移响应均方值、应力响应均方值可靠性约束的主动杆配置和控制增益的优化模型;并对结构平稳随机动力响应的数字特征进行了推导。通过算例,验证了该优化配置模型的合理性和有效性,获得了若干有意义的结论。     

Stochastic optimal active control of a half-car nonlinear suspension under random road excitation

The random response analysis and the stochastic optimal active control of a half-car model with nonlinear suspension stiffness and damping traversing a rough road are studied in this paper. The road roughness height is modeled as the output of a first-order linear filter to Gaussian white noise. Considering the hysteretic nonlinear stiffness and the square damping of the vehicle model, the response statistics of the nonlinear suspension with active control are obtained by using the equivalent linearization method. The performance indexes of the active suspension are evaluated and compared with those of the corresponding passive suspension. It is found that the nonlinear active suspension gives a better vehicle performances like ride comfort, suspension stroke and overall performance. Finally, the theoretical results are verified through Monte Carlo simulation.     

Experiment of active control using electromagnetic force

In the use of the feedback designed by the transfer function method, the experiment on active control, in which an electromagnetic exciter is used as an actuator, is studied in this paper. The experiment has been made using a car model with four degrees of freedom (4 DOF) excited by low frequency sine or wider bandwidth random signal. This shows that the electromagnetic exciter is suitable for active control in the case of low frequency and wider bandwidth random signal because of its short mechanical delay, and the attenuating effect is above 80%.The project was supported by National Natural Science Foundation of China.     

Instability of cylinder wake under open-loop active control

Instability of a wake controlled by a streamwise Lorentz force is investigated through a Floquet stability analysis. The streamwise Lorentz force, which is a two-dimensional control input created by an electromagnetic actuator located on the cylinder surface,adjusts the base flow to affect the three-dimensional wake instability and achieve wake stabilization and transition delay. The instability mode at a Reynolds number Re = 300 can be transformed from B to A with N = 1.0, where N is an interaction number representing the strength of the Lorentz force relative to the inertial force in the fluid. The wake flow is Floquet stable when N increases to 1.3. The spanwise perturbation wavelengths are 3.926 D and 0.822 D in the modes A and B, respectively, where D is the cylinder diameter. In addition, the oscillating amplitudes of drag and lift are reduced with the increase in the interaction number. Particle tracing is used to explore the essential physical mechanism for mode transformation. The path lines show that suppression of flow separation hinders the fluid deformation and rotation, leading to the decrease in elliptic and hyperbolic instability regions, which is the material cause of mode transformation.All of the results indicate that wake stabilization and transition delay can be achieved under open-loop active control via the streamwise Lorentz force.     

Improvement of rotor performance under rubbing conditions through active auxiliary bearings

This paper develops a new concept to enhance the adaptive capability of rotating machinery to the rubbing conditions through active auxiliary bearings. To demonstrate the feasibility of this idea, a model with a Jeffcott rotor and an active auxiliary bearing, which accounts for both the dynamics of the auxiliary bearing and the deformation on the contact surface, is investigated. The dynamics and the stability of the non-linear piecewise-smooth passive rotor/stator (auxiliary bearing) system are first studied. Then, two control approaches are proposed with the aim to reduce the rubbing severity during the rotor/stator rubbing. It is shown that by using an optimal controller, the harmful heavy rubbing between the rotor and the stator can be well stabilized to the mild light rub through the active auxiliary bearing, and the already established rotor-to-stator rubbing can even be released by using PD-controllers.     

Time-delayed feedback control optimization for quasi linear systems under random excitations

A strategy for time-delayed feedback control optimization of quasi linear systems with random excitation is proposed. First, the stochastic averaging method is used to reduce the dimension of the state space and to derive the stationary response of the system. Secondly, the control law is assumed to be velocity feedback control with time delay and the unknown control gains are determined by the performance indices. The response of the controlled system is predicted through solving the Fokker-Plank-Kolmogorov equation associated with the averaged Ito equation. Finally, numerical examples are used to illustrate the proposed control method, and the numerical results are confirmed by Monte Carlo simulation .     

基于模糊神经网络的结构非模型主动控制

本文将模糊人工神经网络运用到结构的主动控制中，用模糊联想记忆（ＦＡＭ）神经网络作为控制器，对在地震力下的结构振动进行主动控制，控制过程中无须引入结构的运动模型和精确参数。数值仿真的结果表明，该控制系统具有适应能力强，消振迅速且效果良好的特点。     

Experimental and numerical investigations into flow features in an intake duct for the waterjet propulsion under mooring conditions

Acta Mechanica Sinica - The waterjet propulsion is widely applied in the marine vessels over 30 knots, and the intake duct is considered as an essential component that strongly relates to the...     

Unsteady transonic aerodynamic loadings on the airfoil caused by heaving,pitching oscillations and control surface

An implicit upwind finite volume solver for the Euler equations using the improved flux-splitting method is established and used to calculate the transonic flow past the airfoils with heaving, pitching oscillations and the control surface. Results are given for the NACA64A-10 airfoil which is in harmonic heaving and pitching oscillation and with the control surface in the transonic flow field. Some computational results are compared with the experiment data and the good agreements are shown in the paper.     

On the generation of yawing moment using active flow control

The generation of control moments without moving control surfaces is of great practical importance. Following a successful flight demonstration of creating roll motion without ailerons using differential, lift oriented, flow control the current study is a first step towards generating yawing motion via differential flow controlled drag.A wind tunnel study was conducted on a 21% thick Glauert type airfoil. The upper surface flow is partially separated from the two-thirds chord location and downstream on this airfoil at all incidence angles. An array of mass-less Piezo-fluidic actuators, located at x/c = 0.65, are capable of fully reattaching the flow in a gradual, controlled manner. The actuators are individually operated such that the boundary layer could be controlled in a 3D fashion.Several concepts for creating yaw motion without moving control surface are examined. The ultimate goal is to generate the same lift on both wings, while decreasing the drag on one wing and increasing the drag on the other, therefore creating a yawing moment. Decreased drag is created by effective part-span separation delay while increased drag can be created by enhanced generation of vortex shedding or by highly localized 3D actuation.Detailed measurements of 3D surface pressure distributions and wake data with three velocity and streamwise vorticity components are presented and discussed along with surface flow visualization images. The data provide evidence that yawing moments can be generated with AFC.     

微重力下Stewart平台的主动减振系统研究分析

Stewart平台是一种并联减振机构,因其具有承载能力强、刚度大、结构稳定、精度高等优点,广泛应用于航天航空和精密仪器领域。采用Cubic构型Stewart平台并对压电陶瓷的力一位移关系线性化后,可简化成单自由度的线性主动控制系统,对六自由度的Stewart平台分散控制,在随机平稳白噪声的激励下考虑时滞影响,并对其解耦后的Stewart平台进行LQR数值分析,用Adams预测公式进行时滞补偿。分析结果表明：Stewart平台具有较好的减振性能,能有效减小平台在微重力干扰下引起的位移反应;时滞因素会降低LOR的控制作用;可通过Adams预测公式对时滞影响进行较好地补偿。     

Investigation of micro-jet active control of a precessing jet using PIV

A circular jet entering an open-ended concentric circular chamber can rotate or precess about the jet axis for certain flow conditions and chamber configurations. Active flow control of a precessing jet provides the ability to influence the flow field inside the chamber and the resulting flow after the chamber exit. Twelve micro-jets surrounding the jet at the chamber inlet are used as actuation. At the chamber exit, four pressure probes and three-component velocity measurement using stereo particle image velocimetry (stereo-PIV) is used to monitor the flow. A phase plane method using signals from the pressure sensors is developed to monitor the location of the jet high-velocity region in real-time. Phase-locked stereo-PIV, triggered by the micro-jet actuation signal, is used to investigate the flow field and validate the pressure phase plane results. The effectiveness of the micro-jet actuation and the validation of the pressure phase plane measurements demonstrate actuation and the sensing needed for future closed-loop control of the precessing jet.     

NMR for equilateral triangular geometry under conditions of surface relaxivity—analytical and random walk solution

We consider analytical and numerical solution of NMR relaxation under the condition of surface relaxation in an equilateral triangular geometry. We present an analytical expression for the Green’s function in this geometry. We calculate the transverse magnetic relaxation without magnetic gradients present, single-phase, both analytically and numerically. There is a very good match between the analytical and numerical results. We also show that the magnetic signal from an equilateral triangular geometry is qualitatively different from the known solution: plate, cylinder, and sphere, in the case of a nonuniform initial magnetization. Nonuniform magnetization close to the sharp corners makes the magnetic signal very fast multiexponential. This type of initial configuration fits qualitatively with the experimental results by Song (Phys. Rev. Lett. 85, 3878 (2000)), Song et al. (Nature 406, 178 (2000)), Song (Mag. Reson. Imag. 19, 417 (2001)) and Lisitza and Song (Phys. Rev. B 65, 172406 (2002)). It should also be noted that the solution presented here can be used to describe absorption of a chemical substance in an equilateral triangular geometry (for a stationary fluid).     

Truss optimization under stiffness, stability constraints and random loading

An actual design of light-weight structures must evaluate strength, stiffness and stability constraints as well as the nature of external loading. A designed structure must satisfy optimality and safety criterions per prescribed maintenance period. One faces the known difficulties when trying to implement several from the above mentioned requirements into optimization problem for further successful numerical realization. A method to formulate the optimization problem, incorporating all above described criterions, the mathematical model and algorithm to solve it numerically, taking into account the stochastic nature of external loading, are presented for elastic–plastic truss-type structure.     

Model reduction and active control of flexible beam using internal balance technique

The internal balance technique is effective for the model reduction in flexible structures,especially the ones with dense frequencies.However,due to the difficulty in extracting the internal balance modal coordinates from the physical sensor readings,research on this topic has been mostly theoretical so far,and little has been done in experiments or engineering applications.This paper studies the internal balance method theoretically as well as experimentally and designs an active controller based on the reduction model.The research works on a digital signal processor (DSP) TMS320F2812-based experiment system with a flexible beam and proposes an approximate approach to access the internal balance modal coordinates.The simulation and test results have shown that the proposed approach is feasible and effective,and the designed controller is successful in restraining the beam vibration.     

Model reduction and active control of flexible beam using internal balance technique

The internal balance technique is effective for the model reduction in flexible structures, especially the ones with dense frequencies. However, due to the difficulty in extracting the internal balance modal coordinates from the physical sensor readings, research on this topic has been mostly theoretical so far, and little has been done in experiments or engineering applications. This paper studies the internal balance method theoretically as well as experimentally and designs an active controller based on the reduction model. The research works on a digital signal processor (DSP) TMS320F2812-based experiment system with a flexible beam and proposes an approximate approach to access the internal balance modal coordinates. The simulation and test results have shown that the proposed approach is feasible and effective, and the designed controller is successful in restraining the beam vibration.     

Projective synchronization between two different time-delayed chaotic systems using active control approach

In this paper, we investigate the projective synchronization between two different time-delayed chaotic systems. A suitable controller is chosen using the active control approach. We relax some limitations of previous work, where projective synchronization of different chaotic systems can be achieved only in finite dimensional chaotic systems, so we can achieve projective synchronization of different chaotic systems in infinite dimensional chaotic systems. Based on the Lyapunov stability theory, we suggest a generic method to achieve the projective synchronization between two different time-delayed chaotic systems. The validity of the proposed method is demonstrated and verified by observing the projective synchronization between two well-known time-delayed chaotic systems; the Ikeda system and Mackey–Glass system. Numerical simulations fully support the analytical approach.     

Parametric active aeroelastic control of a morphing wing using the receptance method

This study proposes the parametric active aeroelastic control of a folding wing, which is a promising concept of morphing wings, by integrating the parameterized aeroservoelastic model and the receptance-based control strategy. It starts with establishing the parameterized aeroservoelastic model of the folding wing with respect to its folding angle and air speed. The transfer functions between the embedded sensors and the actuators of the folding wing are then efficiently obtained using the parameterized aeroservoelastic model. Finally, control gains for varying folding angle and air speed of the wing are synthesized using the receptance method. The results of numerical analyses show that smooth evolutions of the control gains can be obtained over a wide range of folding angles and air speeds, although the dynamic behavior of the folding wing is sensitive to these parameters. In addition, the active aeroelastic control can effectively suppress aeroelastic vibrations and expand flutter boundaries of the folding wing. The benefit of the parametric active aeroelastic control for the folding wing, i.e., smoothly switching among the control laws without exciting undesirable vibrations is highlighted.     

Anti-synchronization between identical and non-identical fractional-order chaotic systems using active control method

This article deals with the anti-synchronization between two identical chaotic fractional-order Qi system, Genesio–Tesi system, and also between two different fractional-order Genesio–Tesi and Qi systems using active control method. The chaotic attractors of the systems are found for fractional-order time derivatives described in Caputo sense. Numerical simulation results which are carried out using Adams–Boshforth–Moulton method show that the method is reliable and effective for anti-synchronization of nonlinear dynamical evolutionary systems.