Feedback Active Control System Research Articles

Active feedback control on acoustic radiation of metastructure shell with low-frequency and broadband characteristics

Due to the tunable characteristics of elastic waves, the vibroacoustic coupling behavior of a mechanical metastructure is a hot topic of underwater vehicles. In this work, a metastructure shell with active feedback control is presented and fabricated. The dynamic effective density and sound pressure level are derived to find the influences of acceleration and displacement feedback control. Different from a single cylinder, a double cylinder structure has both in-phase and anti-phase modes. Numerical results are obtained by Fourier transform and harmonic series expansion. With the introduction of an active feedback control system, the reduction of acoustic radiation shows low-frequency and broadband characteristics. In addition, finite element simulation is applied to support numerical results and present vibroacoustic characteristics. Finally, an experiment is performed in the anechoic chamber to illustrate the quiet metastructure shell, which can be applied to new designs of underwater vehicles.

Nonlocal topological states in elastic wave metamaterials with active feedback control

Topological elastic wave metamaterials provide a new mechanism to tune wave energy and provide engineering applications which are difficult to realize by traditional structures. This work reports topological characteristics of nonlocal elastic wave metamaterials with active feedback control. The effects of nonlocal connection on band structures and dynamic behaviors of rectilinear lattices are studied. Then, the honeycomb lattice with nonlocal interactions is investigated, which realizes interface transmission and hybrid order topological states. The introduction of active feedback control systems can change the Young’s modulus of nonlocal metamaterials, which flexibly tune the topological characteristic of elastic waves. According to finite element simulation and experiment, the interface transmission and hybrid order can be generated by active feedback control, which agrees with theoretical predictions.

Compact Active Vibration Isolation and Tilt Stabilization for a Portable High-Precision Atomic Gravimeter

In high-precision atomic gravimeters, a rest mass is needed to provide a gravity reference, which is typically the retro-reflecting mirror of the Raman laser beams that addresses the two hyperfine ground states of the specific free-falling atomic test mass. We constructed a compact active feedback control system for the retro-reflecting mirror that provides vibration isolation in the vertical axis as well as two rotation stabilization in the horizontal plane. The active feedback control provides vertical vibration reduction of up to a factor of 300 in the frequency range of 0.03 to 10 Hz and tilt stabilization of approximately $\pm$ 1 $\mu$rad in the noisy lab environment. This system has enabled high-precision gravity measurements on a portable gravimeter with sensitivity reaching $6.4\times 10^{-8}$ g/$\sqrt{\text{Hz}}$ and resolution of $2.8\times 10^{-9}$ g after an integration time of 4000 s.

Optimal stochastic compensator for time-delayed active structural control systems subjected to random excitations

Active feedback control systems confront with technical challenges when they are applied in civil engineering structures for vibration mitigation; one of which is the potential instability risk inherent in structure-control systems caused by insufficient compensation of time delay, especially in the scenario considering randomness associated with external excitations. To this end, this paper proposes an optimal stochastic compensator (OSC) to improve time-delayed active structural control systems subjected to random excitations. By extending the state vector, the OSC can be denoted as a linear combination between system state at the present time-step and control forces at the previous time-steps. According to the probabilistic criterion in function of reliability metrics of system state and control force, optimal cost-function weights of the OSC for good trade-off between control gain and control cost can be readily derived by introducing the framework of physically-based stochastic optimal (PSO) control. For verification purposes, randomly base-excited structures controlled by time-delayed active tendon systems, comprising single-degree-of-freedom, multi-degree-of-freedom and nonlinear oscillator systems, are investigated. The analysis and results reveal that the control performance is seriously degraded with increasing time delay; however, a rationally-designed OSC can be used to significantly improve control systems. Moreover, a definite relationship in cubic polynomial functions between optimal control cost-function weight of the OSC and time delay is obtained, by which the problem of time-varying delay compensation can be elegantly solved. In addition, the OSC has a good robustness, and can accommodate a larger effective time delay to linear systems than to nonlinear systems.

Active feedback control of sound radiation in elastic wave metamaterials immersed in water with fluid–solid coupling

Due to their potential properties unlike traditional materials and structures, elastic wave metamaterials have received significant interests in recent years. With the coupling between the acoustic and vibration, their mechanical characteristics can be tuned by the active feedback control system at low frequency ranges in which the traditional passive control is limited. This work illustrates that the superior performances of the effective mass density and sound pressure level (SPL) of an elastic wave metamaterial can be significantly changed by the active control, in which the periodic array of local resonators and orthogonal stiffeners are included. Significantly, based on the locally resonant mechanism, the negative density occurs over a frequency range. Due to the effects of lattice constant, structural damping and other parameters, the SPL with the function of fluid–solid coupling are illustrated and discussed.

Sound Transmission Comparisons of Active Elastic Wave Metamaterial Immersed in External Mean Flow

Using the active feedback control system on the elastic wave metamaterial, this research concentrates on the sound transmission with the dynamic effective model. The metamaterial is subjected to an incident pressure and immersed in the external mean flow. The elastic wave metamaterial consists of double plates and the upper and lower four-link mechanisms are attached inside. The vertical resonator is attached by the active feedback control system and connected with two four-link mechanisms. Based on the dynamic equivalent method, the metamaterial is equivalent as a single-layer plate by the dynamic effective parameter. With the coupling between the fluid and structure, the expression of the sound transmission loss (STL) is derived. This research shows the influence of effective mass density on sound transmission properties, and the STL in both modes can be tuned by the acceleration and displacement feedback constants. In addition, the dynamic response and the STL are also changed obviously by different values of structural damping, incident angle (i.e., the elevation and azimuth angles) and Mach number of the external fluid with the mean flow property. The results for sound transmission by two methods are compared, i.e., the virtual work principle for double plates and the dynamic equivalent method corresponding to a single one. This paper is expected to be helpful for understanding the sound transmission properties of both pure single- and double-plate models.

Sound Transmission Tuned by Active Feedback Control Attached to Elastic Wave Metamaterials Immersed in Water

Abstract Elastic wave metamaterials have been widely exploited with their dynamic superior properties and outstanding acoustic responses. However, it is difficult to directly manipulate sound pressure in low frequencies. In this study, we propose a new kind of elastic wave metamaterial which consists of vertical and lateral resonators as well as orthogonal stiffeners. The active feedback control system is applied to extend to the tunable scope for both lower and higher frequency regions and change the characteristics of acoustic-structure coupling. Its effective mass density is also discussed with different feedback constants. In order to present effects of the fluid–solid interaction, we considered that the elastic wave metamaterial is immersed in different fluid medium and its sound transmission loss (STL) is calculated. This work provides a feasible method for creating mechanical/acoustic models with multi-functional potentials.

A 1.4-kW Mode-Controllable Fiber Laser System

We demonstrated a mode-controllable fiber laser system with output power of 1.4 kW level. The system consists of a kilowatt-scale master oscillator power amplifier and an active feedback control system based on the stochastic parallel-gradient descent algorithm. We can convert the LP01 and LP11 modes by performing an extremum search for power in the bucket of the output beam. Under the same pump power, we obtain the mode conversion of LP11 to LP01, and the efficiency is as high as 99.5%. The maximum output power of LP11 and LP01 mode are 1396 W and 1389 W, respectively, with corresponding slope efficiencies of 85.8% and 84.1%.

Active feedback control of effective mass density and sound transmission on elastic wave metamaterials

With the active feedback control system on elastic wave metamaterials, this research is concentrated on the effective mass density and sound transmission by a harmonic incident sound pressure. The elastic wave metamaterials consist of double plates which are attached by the upper and lower four-link mechanisms being bonded with four lateral resonators. The vertical resonator in every unit cell is jointed by the active feedback control system which is connected by two four-link mechanisms. Using the dynamic effective medium method, the expressions of the effective mass density are obtained and the dynamic responses are presented. Based on the Bloch–Floquet theorem and Poisson summation formula, the sound transmission loss (STL) of this elastic wave metamaterial is shown by the principle of virtual work. This research also shows that the characteristics of the effective mass density and STL can be tuned by the acceleration and displacement feedback in the active control system. Furthermore, it is found that the dynamic response and STL are also changed obviously by different incident angles (including the elevation and azimuth angles), the periodicity spacing of local resonators and the structural damping.

A frequency band constrained filtered-x least mean square algorithm for feedback active control systems.

The generalized leaky filtered-x least mean square (GLFxLMS) algorithm can reduce the noise amplification caused by the waterbed effect in feedback active control systems effectively; however, it suffers from a high computation complexity. Hence, a frequency band constrained filtered-x least mean square algorithm is proposed to reduce the computation complexity of the GLFxLMS algorithm by replacing the penalty term containing a symmetric Toeplitz matrix in the cost function with the mean square of a penalty signal. The simulation results based on the measured transfer functions of an active headrest system show that the proposed algorithm has the same performance as the GLFxLMS algorithm, but with much lower computation complexity.

External Mean Flow on Sound Radiation of Active Mechanical Metamaterials

Sound pressure level (SPL) is one of the significant parameters of the acoustic–structure coupling for the elastic wave metamaterial. This paper presents the use of the external mean flow and the active feedback control system. Based on the locally resonant mechanism, the dynamic effective mass density is also discussed and the negative density appears at a lower frequency region. From the results, it can be seen that both the SPL and the effective mass density can be controlled by the active feedback system. As the frequency region of the negative density increases obviously, it emerges two negative regions with the changing of the displacement feedback control action and leads to the changing of the SPL. Besides the Mach number of the external mean flow, other influences on the SPL are also discussed, such as the structural damping, lattice constants, excitation position, elevation angle, and azimuth angle. Finally, these interesting effects on the elastic wave metamaterial are presented and explored.

Design, preparation and characterization of antireflective coatings using oxynitride films

In present paper, we introduce an investigation of aluminum oxynitride films deposition using one metallic target in various gas mixture. The optimized preparation conditions for such reactive sputtering were found. Non-optimized conditions led to sputtering target poisoning or under-stoichiometric films formation. The reactive deposition process was guided by the active feedback control system. Dependence between gas composition and changes of nitrogen concentration in the films and their optical properties were investigated. The increase of nitrogen content in films leads to increases in extinction coefficient in UV region and refractive index in the whole investigated wavelength range. It was shown the possibility of using oxynitride films for antireflective coating (AR) deposition. The coating composed from three layer of oxynitrides with changing the composition. It has low surface roughness and low compressive stress.

Active Feedback Control on Sound Radiation of Elastic Wave Metamaterials

To show the effects of active feedback control on elastic wave metamaterials, this research is focused on effective mass density and sound radiation by a point force excitation. The expressions of effective mass density and sound-pressure level (SPL) are derived. The elastic wave metamaterials consist of double plates that are attached by the four-link mechanisms. To form the four-link mechanisms, the periodic structures consist of the lateral local resonators and the vertical resonator that is bonded by the active feedback control system. Based on the dynamic effective medium method, the effective mass density is obtained and the acoustic–structural response is presented. With the Fourier transform technique, the SPL of the double-plate model in the far field is shown. Results from a single-plate model with and without the equivalent method are compared. This work shows that the influences of effective mass density and SPL can be tuned by the acceleration and displacement feedback in the active control system. Furthermore, it is found that the acoustic–structural response and SPL can be changed by different active feedback control constants.

Bio-inspired sensing and actuating architectures for feedback control of civil structures

Civil structures, such as buildings and bridges, are constantly at risk of failure due to external environmental loads, such as earthquakes or strong winds. To minimize the effects of these loads, active feedback control systems have been proposed but such systems still face numerous challenges which impede their widespread adoption. In order to overcome many of these challenges, inspiration can be drawn from the signal processing and actuating techniques employed by the biological central nervous system to develop a bio-inspired control algorithm. In this study the front-end, signal processing techniques employed by biological sensory systems, and in particular the mammalian auditory system, are drawn upon in order to alleviate computations at the actuation node. This results in a simplistic control law that is a weighted combination of input information about the structure’s response such that F = WN, where F is the applied control force, W is a pre-determined weighting matrix, and N is a deconstructed representation of the structural response to the applied excitation. There is no empirical solution for deriving an optimal weighting matrix, W, and in this study numerous methods are explored in order to determine values for this matrix that produce the most effective control. These methods include particle swarm optimization, artificial neural networks, and optimal control theory. The various weighting matrices are integrated into the proposed bio-inspired control algorithm and applied in simulation to a five story benchmark structure. These methods are also compared to a traditional linear quadratic regulator (LQR) to gain insight into the overall performance of the bio-inspired control algorithm. Of the three training techniques, the particle swarm optimization technique offers the most effective control which is comparable in performance to the traditional LQR.

Enhancing damping of gas bearings using linear parameter-varying control

Journal bearings can be lubricated through controllable injectors using pressurised fluids, whose viscosity highly determines the dynamic responses of the rotating machine. The use of fluids with low viscosity is attracting a growing interest due to the reduced friction forces and consequent losses when the machine is in operation. However low viscosity also entails poor damping properties, which may lead to degraded performance or even instability when the rotating machine operates at or near one of the modal frequencies. This issue can be properly addressed by employing active feedback control systems to regulate the injection pressure of the fluid. Due to the strong dependencies of system performance on system parameters, the sought controller should be robust over a large range of operational conditions. This paper addresses the damping enhancement of controllable gas bearings through robust control approaches. Through an extensive experimental campaign the paper evaluates two robust controllers, a linear parameter-varying (LPV) controller and H∞ controller, on their capability to guarantee stability and performance of a gas bearing across the large operational envelopes in rotational speed and injection pressure. The control systems are designed applying state-of-the-art methods in the respective areas. The experimental results clearly demonstrate the feasibility of enhancing the damping properties of a gas bearing by means of robust control methods.

State observers and Kalman filtering for high performance vibration isolation systems

There is a strong scientific case for the study of gravitational waves at or below the lower end of current detection bands. To take advantage of this scientific benefit, future generations of ground based gravitational wave detectors will need to expand the limit of their detection bands towards lower frequencies. Seismic motion presents a major challenge at these frequencies and vibration isolation systems will play a crucial role in achieving the desired low-frequency sensitivity. A compact vibration isolation system designed to isolate in-vacuum optical benches for Advanced Virgo will be introduced and measurements on this system are used to present its performance. All high performance isolation systems employ an active feedback control system to reduce the residual motion of their suspended payloads. The development of novel control schemes is needed to improve the performance beyond what is currently feasible. Here, we present a multi-channel feedback approach that is novel to the field. It utilizes a linear quadratic regulator in combination with a Kalman state observer and is shown to provide effective suppression of residual motion of the suspended payload. The application of state observer based feedback control for vibration isolation will be demonstrated with measurement results from the Advanced Virgo optical bench suspension system.

Active toroidal field ripple compensation and MHD feedback control coils in FAST

The Fusion Advanced Study Torus (FAST) has been proposed as a high magnetic field, compact size tokamak providing a flexible integrated environment to study physics and technology issues in ITER and DEMO relevant conditions.FAST has a quite large natural toroidal field ripple (around 1.5%) due to its compactness and to the number of access ports: this ripple must be lowered to an acceptable level to allow safe operations and a good confinement quality. An Active Ripple Compensating System (ARCS) has been designed, based on a set of poloidal coils placed between the plasma chamber and the Toroidal Field Coils (TFCs). These ARCS coils will be fed with adjustable currents, opposite in direction respect to the TFC currents, and will allow lowering the ripple up to zero and beyond.The CAD model of FAST including the ARCS coils has been completed and preliminary electromagnetic and thermal analyses have been carried out.Moreover, a Feedback Active Control System (FACS) composed of two arrays of in-vessel saddle coils has been designed to allow safe high plasma current, low safety factor operation and to mitigate possibly large ELMs effects in FAST. These FACS coils will be fed by a feedback system to control MHD modes: a first engineering assessment of the current requirements has been carried out.

0208 磁性流体の円管内流動特性(OS2 機能性流体とその先進応用,オーガナイズドセッション)

Drag control allows energy saving, noise reduction and thus heat control. However the only mean to attain it is through Active feedback control system. This research focuses on magnetic fluid because its characteristics are dramatically changed by magnetic field control and it is possible to reduce the pipe friction. In this article, a study of the effect of external magnetic field control on magnetic fluid. Pressure difference and flow rate measurements have been conducted under different Reynolds numbers and non-uniform magnetic field. The experiments showed a drop of the pipe friction coefficient which goes up to 9.9 percent in the transition region (Re = 2770). Yet, this phenomenon vanishes at higher Reynolds number.

Incorporation of Feedback Control into a High-Fidelity Aeroservoelastic Fighter Aircraft Model

Flight testing for aeroservoelastic clearance is an expensive and time consuming process. Large degree-of-freedom high-fidelity nonlinear aircraft models using computational fluid dynamics coupled with finite element models can be used for accurately predicting aeroelastic phenomena in all flight regimes including subsonic, supersonic, and transonic. With the incorporation of an active feedback control system, these high-fidelity models can be used to reduce the flight-test time needed for aeroservoelastic clearance. Accurate computational fluid dynamics/finite element models are computationally complex, rendering their runtime ill suited for adequate flight control system design. In this work, a complex, large-degree-of-freedom, transonic, inviscid computational fluid dynamics/finite element model of a fighter aircraft is fitted with a flight control system for aeroelastic oscillation reduction. A linear reduced-order model of the complete aeroelastic aircraft dynamic system is produced directly from the high-order nonlinear computational fluid dynamics/finite element model. This rapid runtime reduced-order model is used for the design of the flight control system, which includes models of the actuators and common nonlinearities in the form of rate limiting and saturation. The oscillation reduction controller is successfully demonstrated via a simulated flight test using the high-fidelity nonlinear computational fluid dynamics/finite element/flight control system model.

Controllable Drogue for Automated Aerial Refueling

This paper presents a new method for controlling and stabilizing an automated refueling drogue. The drogue automatically stabilizes in the presence of winds or receiver forebody effects using drogue canopy manipulation. This paper reports on a characterization and simulation study in which the stability derivatives of a low-speed drogue were calculated based on wind-tunnel data. A simulation was developed using a pendulum-based hose model combined with the aerodynamic drogue model. An active feedback control system is shown to stabilize and control the drogue to hold a commanded steady-state offset.