Passive axial magnetic bearing with Halbach magnetized array in magnetically suspended control moment gyro application

The paper presents a special configuration of passive axial magnetic bearing with segmented Halbach magnetized array in magnetically suspended control moment gyro (MSCMG). Peculiarity of presented passive axial magnetic bearing is its ability to provide angular stiffness so that it can produce gyro moment when it is used in MSCMG. The MSCMG with this passive axial magnetic bearing can efficiently reduce the power loss when it supplies gyro moment compared with the five degrees of freedom (5-DOF) MSCMG. The characteristics of the suspension force and stiffness of the passive axial magnetic bearing are studied using finite element method (FEM). The performance of the presented passive axial magnetic bearing with Halbach magnetized array is verified by a prototyped MSCMG.     

Chaotic dynamic behavior analysis and control for a financial risk system

According to the risk management process of financial markets,a financial risk dynamic system is constructed in this paper.Through analyzing the basic dynamic properties,we obtain the conditions for stability and bifurcation of the system based on Hopf bifurcation theory of nonlinear dynamic systems.In order to make the system’s chaos disappear,we select the feedback gain matrix to design a class of chaotic controller.Numerical simulations are performed to reveal the change process of financial market risk.It is shown that,when the parameter of risk transmission rate changes,the system gradually comes into chaos from the asymptotically stable state through bifurcation.The controller can then control the chaos effectively.     

Electric control of magnetic moment in a ferromagnet/semiconductor hybrid system

It is shown that the exchange coupling in a “ferromagnet/semiconductor quantum well” heterostructure allows the electric control of the orientation of magnetic moment in the ferromagnet. A highly anisotropic exchange interaction between holes in the quantum well and magnetic atoms in the ferromagnet causes the orientational transition: magnetic moment leaves the plane and becomes oriented along the normal. The normal component of magnetization can be inverted by applying voltage pulses to the structure gate.     

Fast time-division color electroholography using a multiple-graphics processing unit cluster system with a single spatial light modulator

We demonstrate fast time-division color electroholography using a multiple-graphics-processing-unit(GPU) cluster system with a spatial light modulator and a controller to switch the color of the reconstructing light. The controller comprises a universal serial bus module to drive the liquid crystal optical shutters. By using the controller, the computer-generated hologram(CGH) display node of the multiple-GPU cluster system synchronizes the display of the CGH with the color switching of the reconstructing light. Fast time-division color electroholography at 20 fps is realized for a three-dimensional object comprising 21,000 points per color when 13 GPUs are used in a multiple-GPU cluster system.     

球状泡群内气泡的耦合振动

振动气泡形成辐射场影响其他气泡的运动, 故多气泡体系中气泡处于耦合振动状态. 本文在气泡群振动模型的基础上, 考虑气泡间耦合振动的影响, 得到了均匀球状泡群内振动气泡的动力学方程, 以此为基础分析了气泡的非线性声响应特征. 气泡间的耦合振动增加了系统对每个气泡的约束, 降低了气泡的自然共振频率, 增强了气泡的非线性声响应. 随着气泡数密度的增加, 振动气泡受到的抑制增强; 增加液体静压力同样可抑制泡群内气泡的振动, 且存在静压力敏感区(1–2 atm, 1 atm=1.01325×10⁵ Pa); 驱动声波对气泡振动影响很大, 随着声波频率的增加, 能够形成空化影响的气泡尺度范围变窄. 在同样的声条件、泡群尺寸以及气泡内外环境下, 初始半径小于5 μm 的气泡具有较强的声响应. 气泡耦合振动会削弱单个气泡的空化影响, 但可延长多气泡系统空化泡崩溃发生的时间间隔和增大作用范围, 整体空化效应增强.     

Direct measurement of moment mobility and a moment excitation system

Over the years, a number of investigators have tried to solve the problems in the direct measurement of moment mobility. However, no one has found a moment excitation system that can produce a pure and sufficiently powerful moment. In the past, most investigators tried to solve the problem of impurity in moment by tackling the problem in unmatched shakers in a moment exciter. Su and Gibbs (Su J, Gibbs BM. Measurement of point moment mobility in the presence of non-zero cross mobility. Applied Acoustics 1998;54(1):9-26) have indicated theoretically that compromise between the purity and the power of a moment generated by the moment exciter is greatly affected by the output force impedance of the moment excitation system. In this paper, experiments have been conducted to investigate the effect of output force impedance on direct measurement of moment mobility from which theory of Su and Gibbs has been verified. Methods of improvements of the moment exciter have been proposed in order that the moment exciter can generate a pure and sufficiently powerful moment.     

Shears band with a large dynamic moment of inertia in 197Bi

High-spin states in ¹⁹⁷Bi were studied with the AFRODITE γ-ray array at iThemba LABS using the ¹⁸¹Ta( ²²Ne, 6n) reaction at a beam energy of 125 MeV. A new shears band was found and linked to the low-lying states in ¹⁹⁷Bi. Its dynamic moment of inertia, , is considerably larger than the of the shears bands in the neighbouring Pb isotopes. This is probably a result of the involvement of an additional high-K h_9/2 proton orbital.     

Active vibration isolation of a system with a distributed parameter isolator using absolute velocity feedback control

This paper is concerned with the active isolation of a system containing a distributed parameter isolator using absolute velocity feedback control. The main differences between this type of system and one with a massless isolator, is that there are isolator resonances. It is shown that the vibration at these resonance frequencies cannot be suppressed using a simple velocity feedback control strategy. Moreover, it is found that the isolator resonances can cause the control system to become unstable, if the isolated equipment is supported on a flexible base. A stability criterion based on the mode shapes of the system is presented. Two techniques to stabilise the system are investigated and compared. The first involves the addition of mass on the base structure, and the second involves an electronic lead compensator. Experimental results are presented to support the theoretical findings. It is shown that even if the instability due to the isolator resonances and flexibility of the base can be prevented, the instability due to the flexibility of the equipment remains a problem.     

The design and dynamic performance of a moment actuator

I.IntroductionMachinenoiseisanenvironmcnta1po11utantanditscontrolremainsamajorunresolvedprob1cm.Inadditiontoair-bornesound,machinesimpartvibrationalenergyintosupportingandconnectedstructuresbybothtrans1ationa1androtationa1motions.Translationa1compo-nentsarerelative1yeasytoestimatesinccnearpureforcescanbegeneratedandmeasured.ThisisnotthecaseforrotationalcomponentSsincemomcntsaremoredifficu1ttogenerateandmeasure.Suchmeasurementswould1eadtoafu11undcrstandingofthis1ittleunderstoodbutoftenimporta…     

力矩激励器的设计和动态特性

人们愈来愈认识到,机器和其它振动源,向支撑和与之相连接的结构发射的结构声,除了平动成份之外,还有转动成份。众所周知,由于转动分量不易于激发和测量,所以很难对它评价。本文介绍一种由两根平行的磁伸缩棒构成的力矩激励器,并利用一个传递函数来研究它的特性和提出一个物理量一\     

Experiment and analysis of a fuzzy-controlled piezoelectric seismic isolation system

Because a conventional seismic isolation system is usually a long-period dynamic system, it may easily incur an excessive seismic response when subjected to near-fault earthquakes, which usually contain strong long-period wave components. In order to alleviate this near-fault isolation problem, this paper investigates the possible use of a fuzzy-controlled semi-active isolation system, called a piezoelectric seismic isolation system (PSIS), whose seismic response is attenuated by a variable friction damper driven by an embedded piezoelectric actuator. The studied PSIS adopts a fuzzy controller whose control logic is similar to that of the anti-lock braking systems (ABS) widely used in the automobile industry. This ABS-type fuzzy controller has the advantages of being simple and easily implemented, because it only requires the measurement of the PSIS sliding velocity. In order to investigate its feasibility and isolation effectiveness, in this work both theoretical and experimental studies were carried out on a prototype PSIS. It is observed that the experimental responses of the PSIS can be well predicted by the theoretical responses simulated by the mathematical model and numerical procedure. Furthermore, both theoretical and experimental results have demonstrated that in either a near-fault or a far-field earthquake, the PSIS with the ABS-type fuzzy controller is very effective in suppressing simultaneously the isolator displacement and the acceleration response of the isolated object.     

Nonlinear analysis of a maglev system with time-delayed feedback control

This paper undertakes a nonlinear analysis of a model for a maglev system with time-delayed feedback. Using linear analysis, we determine constraints on the feedback control gains and the time delay which ensure stability of the maglev system. We then show that a Hopf bifurcation occurs at the linear stability boundary. To gain insight into the periodic motion which arises from the Hopf bifurcation, we use the method of multiple scales on the nonlinear model. This analysis shows that for practical operating ranges, the maglev system undergoes both subcritical and supercritical bifurcations, which give rise to unstable and stable limit cycles respectively. Numerical simulations confirm the theoretical results and indicate that unstable limit cycles may coexist with the stable equilibrium state. This means that large enough perturbations may cause instability in the system even if the feedback gains are such that the linear theory predicts that the equilibrium state is stable.     

Robust control of novel pendulum-type vibration isolation system

A novel pendulum-type vibration isolation system is proposed consisting of three active cables with embedded piezoelectric actuators and a passive elastomer layer. The dynamic response of the isolation module in the vertical and horizontal directions is modeled using the Lagrangian approach. The validity of the dynamic model is confirmed by comparing the simulation results for the frequency response in the vertical and horizontal directions with the experimental results. An approximate model is proposed to take into account system uncertainties such as payload changes and hysteresis effects. A robust quantitative feedback theory (QFT)-based active controller is then designed to ensure that the active control can achieve a high level of disturbance rejection in the low-frequency range even under variable loading conditions. It is shown that the controller achieves average disturbance rejection of ?14 dB in the 2–60 Hz bandwidth range and ?35 dB at the resonance frequency. The experimental results confirm that the proposed system achieves a robust vibration isolation performance under the payload in the range of 40–60 kg.     

Distributed formation control for a multi-agent system with dynamic and static obstacle avoidances

Formation control and obstacle avoidance for multi-agent systems have attracted more and more attention. In this paper, the problems of formation control and obstacle avoidance are investigated by means of a consensus algorithm. A novel distributed control model is proposed for the multi-agent system to form the anticipated formation as well as achieve obstacle avoidance. Based on the consensus algorithm, a distributed control function consisting of three terms(formation control term, velocity matching term, and obstacle avoidance term) is presented. By establishing a novel formation control matrix, a formation control term is constructed such that the agents can converge to consensus and reach the anticipated formation. A new obstacle avoidance function is developed by using the modified potential field approach to make sure that obstacle avoidance can be achieved whether the obstacle is in a dynamic state or a stationary state. A velocity matching term is also put forward to guarantee that the velocities of all agents converge to the same value. Furthermore, stability of the control model is proven. Simulation results are provided to demonstrate the effectiveness of the proposed control.     

Suppression of dynamic instabilities in erbium-doped fiber amplifiers with a combined gain control system

We report an improved transient response of an Er(3+) -doped fiber-optic amplifier with combined electronic feedforward (EFF) and optical feedback (OFB) control systems. We find, theoretically and experimentally, that the time delay of an EFF response leads to control instabilities in the form of erbium-doped fiber amplifier gain auto-oscillations, which can be suppressed by an appropriate choice of OFB wavelength and control system design.     

Feedback control of a single atom in an optical cavity

We discuss feedback control of the motion of a single neutral atom trapped inside a high-finesse optical cavity. Based on the detection of single photons from a probe beam transmitted through the cavity, the position of the atom in the trap is estimated. Following this information, the trapping potential is switched between a high and a low value in order to counteract the atomic motion. This allowed us to increase the storage time by about one order of magnitude. Here, we describe the technical implementation of the feedback loop and give a detailed analysis of its limitations as deduced from Monte-Carlo simulations. We also discuss different strategies to further improve the performance of the feedback.     

Coherent control of a V-type three-level system in a single quantum dot

In a semiconductor quantum dot, the IIx and IIy transitions to the polarization eigenstates, |x> and |y>, naturally form a three-level V-type system. Using low-temperature polarized photoluminescence spectroscopy, we have investigated the exciton dynamics arising under strong laser excitation. We also explicitly solved the density matrix equations for comparison with the experimental data. The polarization of the exciting field controls the coupling between the otherwise orthogonal states. In particular, when the system is initialized into \Y>, a polarization-tailored pulse can swap the population into |x>, and vice versa, effectively operating on the exciton spin.     

Aeroelastic dynamic response and control of an airfoil section with control surface nonlinearities

Nonlinearities in aircraft mechanisms are inevitable, especially in the control system. It is necessary to investigate the effects of them on the dynamic response and control performance of aeroelastic system. In this paper, based on the state-dependent Riccati equation method, a state feedback suboptimal control law is derived for aeroelastic response and flutter suppression of a three degree-of-freedom typical airfoil section. With the control law designed, nonlinear effects of freeplay in the control surface and time delay between the control input and actuator are investigated by numerical approach. A cubic nonlinearity in pitch degree is adopted to prevent the aeroelastic responses from divergence when the flow velocity exceeds the critical flutter speed. For the system with a freeplay, the responses of both open- and closed-loop systems are determined with Runge-Kutta algorithm in conjunction with Henon’s method. This method is used to locate the switching points accurately and efficiently as the system moves from one subdomain into another. The simulation results show that the freeplay leads to a forward phase response and a slight increase of flutter speed of the closed-loop system. The effect of freeplay on the aeroelastic response decreases as the flow velocity increases. The time delay between the control input and actuator may impair control performance and cause high-frequency motion and quasi-periodic vibration.     

Oscillation control of a multimode chaotic system with an asymmetric characteristic

A mathematical model of a controlled chaotic system is studied that is based on a differential-difference equation widely used in various fields of science and technology. Numerical methods are applied to study the feasibility of controlling the oscillations of a delayed system using a filter inserted into a feedback circuit that converts chaotic oscillations into quasi-harmonic ones, and the asymmetric amplitude characteristic typical of real systems is used. The transition to chaos is considered under the conditions when the filter resonance frequency falls into the interval between the eigenfrequencies of the system. Relevant experimental data are presented.     

Generation of attosecond pulses in a system with permanent dipole moment

The generation of attosecond pulses in a two-level system with permanent dipole moment is investigated. It is shown due to the presence of permanent dipole moments, that the plateau of the high-order harmonic generation spectrum can be extended to X-ray range. Moreover, attosecond pulses with higher intensity can be synthesized by using both even and odd harmonics because of their quantum interference.