Optimizing frequency noise calibration and manipulation in an active feedback control loop

Viscoelastic materials both stores and dissipate energies and have frequency and temperature dependent properties and hence by tuning and optimizing their damping (viscous) and stiffness (elastic) properties they can be used as passive controlling devices in wide range of vibration applications. If the control of viscoelastic systems (viscoelastic structures or structures composed of viscoelastic elements) to be realized by active means, then an accurate mathematical modeling of the viscoelastic system is needed. In practice, various material models and approximation techniques such as Biot model, Golla-Hughes-McTavish (GHM) model and Anelastic Displacement Field (ADF) methods are used to model the dynamic behavior of viscoelastic systems. These models are then transformed into approximating state space models which introduces several challenges: (i) they increase the size of the related eigenvalue problems, (ii) state space realization introduces non-physical internal state variables, and, (iii) the feedback control implementation poses practical challenges such as observer and state estimator design. In this research it is shown that the active control for viscoelastic structures can be designed accurately by only utilizing the available transfer functions. These transfer functions can be obtained from dynamic experiments and the active feedback control is designed without having the knowledge of approximated state-space system matrices. The problem associated with the active control for viscoelastic system is formulated as feedback control problems in frequency domain by using the receptance method. Active control for poles and zeros assignment of the viscoelastic systems is demonstrated using numerical examples associated with the multi-degree-degree of freedom systems. It is also shown that a nested active controller can also be designed for continuous structures (beams/rods) supported by viscoelastic elements. It is highlighted that such a controller design requires modest size of transfer functions and solution of the set of linear system of equations.

Nonlocal topological states in elastic wave metamaterials with active feedback control

Active feedback control was applied to suppress oscillations in thermocapillary convection in a half-zone liquid bridge. The experiment is on a unit-aspect-ratio liquid bridge where the most unstable azimuthal mode has wavenumber 2 when control is absent. Active control was realized by locally modifying the surface temperature using the local temperature measured at different locations fed back through a simple control law. The performance of the control process was quantified by analysing local temperature signals, and the flow structure was simultaneously identified by flow visualization. With optimal placement of sensors and heaters, proportional control can raise the critical Marangoni number by more than 40%. The amplitude of the oscillation can be suppressed to less than 30% of the initial value for a wide range of Marangoni number, up to 90% of the critical value. The proportional control was tested for a period-doubling state and it stabilized the oscillation to a periodic state. Weakly nonlinear control was applied by adding a cubic term to the control law to improve the performance of the control and alter the bifurcation characteristics.

This paper deals with a theoretical analysis and experiments of a non-contact active feedback control, which is based on flow and aero-dynamical control, to suppress a leakage-flow-induced vibration of translational 1DOF system. In the proposed active feedback control method, the leakage-flow-induced vibration is suppressed by using a movable plate, as an actuator, set at inlet and outlet of the passage to control fluid force acting on the controlled target and fluid flow in the passage actively. The strategy of this active control method is based on active flow and aero-dynamical control which cancels the exciting fluid force acting on the rigid body. The root locus and critical flow velocity with and without control are calculated with changing the controller gain and phase-shift to evaluate the control performance, and experiments are conducted to verify the theoretical calculations. As a result, it is indicated that the leakage-flow-induced vibration is effectively suppressed by the proposed non-contact active control method and the suppression effect is very sensitive to the phase-shift and actuator position. For the inlet flow control, the vibration is effectively suppressed when the phase-shift is positive, and for the outlet flow control, the vibration is suppressed when the phase-shift is negative. The suppression effect of the inlet flow control is greater than that of outlet flow control.

With the development of active sonar technology, the poor performance of anechoic tiles in avoiding low-frequency detection has emerged. Then tunable mechanical metamaterials with active control systems have extended applications. This work proposes active metamaterial plates composed of two plates and periodic four-link mechanisms with local resonators. By coils and magnets as well as external voltage, active feedback control is used to regulate the dynamic effective density. Based on the Fourier transform and Wiener–Hopf method, a theoretical model is derived to study the scattering of sound waves from active metamaterial plates. The fluid–structure interaction between the acoustic medium and metamaterial plates is considered. Then the vibroacoustic coupling is investigated to achieve the invisible design of submarines. Results show that the scattered sound pressure within a negative density region is effectively reduced with proper acceleration and displacement feedback coefficients. Furthermore, the finite element simulation and acoustic scattering experiment are performed to support the theoretical derivation. This research is expected to provide further insights for improving invisible effects of underwater vehicles.

This paper investigates the design of active feedback controllers for achieving generalized projective synchronization (GPS) of hyperchaotic systems viz. identical hyperchaotic Qi systems (Chen, Yang, Qi and Yuan, 2007), and non-identical hyperchaotic Lorenz system (Jia, 2007) and hyperchaotic Qi system. Lyapunov stability theory has been used to establish the synchronization results (GPS) derived in this paper using active feedback control. Since the Lyapunov exponents are not required for these calculations, the active feedback control method is very effective and convenient for achieving the general projective synchronization (GPS) of hyperchaotic Qi and hyperchaotic Lorenz systems. Numerical simulations are presented to demonstrate the effectiveness of the synchronization results derived in this paper.

Event-driven intermittent feedback control is a form of feedback control in which the corrective control action is only initiated intermittently when the variables of interest exceed certain threshold criteria. It has been reported in the literature that the CNS uses an event-driven intermittent control strategy to stabilize the human upright posture. However, whether the threshold criteria may change under different postural task conditions is not yet well understood. We employ a numerical study with inverted pendulum models and an experimental study with 51 young healthy individuals (13 females and 38 males; age: 27.8 ± 6.5 years) with stabilogram-diffusion, temporal and spectral analysis applied to COP (Center of Pressure) trajectories measured from these experiments to examine this aspect. The present study provides compelling evidence that inducing a natural arm swing during quiet stance appears to lead to higher sensory dead zone in neuronal control reflecting higher intermittency thresholds in active feedback control and a corresponding lower sensory dependence. Beyond the obvious scientific interest in understanding this aspect of how CNS controls the standing posture, an investigation of the said control strategy may subsequently help uncover insights about how control of quiet stance degrades with age and in diseased conditions. Additionally, such an understanding will also be of interest to the humanoid robotics community as it may lead to insights leading to improving control strategies for posture control in robots.

: Active feedback control is applied to cantilever forward-swept wings (FSW) providing significant increases in the critical airspeeds of aeroelastic flutter and divergence. Feedback compensation improves the critical airspeed for a divergence critical FSW by 25% and improves the critical airspeed for a flutter critical FSW example by 30%. These improvements are limited by the emergence as most critical, instabilities that were only secondary without feedback. The method of analysis is linear control theory in the Laplace domain. A significant improvement is made in the Pade Approximant method for calculating damped unsteady aerodynamic forces in the Laplace domain. Keywords: Aeroelasticity, Swept forward wings, Aerodynamics, Feedback control. (Theses)

Stable plasmas with surface elongations of up to 1.8 (aspect ratio ≅ 3.4) have been produced in the upper lobe of Doublet III with the use of both passive and active controls. The growth rate of the vertical instability has been measured at various values of elongation by disabling the feedback circuit of the vertical position control power supply. A rigid-shift analysis of growth rates indicates that the passive stabilization effect of the field-shaping coils plays a key role in achieving a high elongation of 1.8. Experiments have demonstrated that the maximum stable elongation is determined by the strength of the passive stabilization effect even with active feedback control. The dee-shape is found to be preferable to an elliptical shape because the triangularity reduces the absolute value of the decay index required to produce a given elongation.

Lightweight shell structures stiffened by different core layers are widely used and analysed among various industries including aerospace, marine and ocean engineering. In this work, the vibroacoustic coupling and sound transmission of a metastructure shell is studied. Both reinforced by orthogonal rib-stiffeners and local resonators with active control are considered. Cascaded proportional integral (PI) control is applied to reduce steady-state errors and illustrate superior stability. The space harmonic expansion method and principle of virtual work are employed to derive the dynamic effective parameter and sound transmission loss (STL). Results show that the dynamic effective density is affected by the resonator and negative density can be extended as the unit cell increases. STL can be significantly tuned by cascaded PI active control near the resonant frequency of the local resonator. Moreover, finite-element simulation and vibroacoustic experiments are performed to support theoretical predictions and the comparisons exhibit good agreement. This research provides useful vibroacoustic coupling structures for vibration and noise reduction of engineering applications.

Recently, a new six-term 3-D chaotic system with an exponential nonlinearity was discovered (Sundarapandian, 2013). This novel chaotic system has two saddle focus nodes and hence they are unstable. The maximal Lyapunov exponent (MLE) for the six-term Sundarapandian chaotic system was found as 3.2827 and the Lyapunov dimension of the Sundarapandian chaotic system was found as D <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> = 2.1668. Complete synchronization of chaotic systems deals with the problem of asymptotically synchronizing the states of a pair of chaotic systems called as master and slave systems with the help of controllers attached to the slave system. Complete synchronization of chaotic systems has applications in many engineering areas such as secure communications, secure data encryption, cryptosystems, etc. This paper addresses the design of active and adaptive feedback controllers for completely synchronizing the states of identical six-term Sundarapandian chaotic systems with exponential nonlinearity. Active controllers are used when the system parameters a, b and c are available for measurement and the synchronization result is established using Lyapunov stability theory. Numerical simulations using MATLAB have been shown to demonstrate the proposed active and adaptive synchronization results for the novel chaotic system discussed in this paper.

This research has focused on quantitative prediction of the stability, control, and equilibrium state evolution in toroidal burning plasmas. The stability of long pulse burning plasmas is highly sensitive to the physics of resonant layers in the plasma, sources of momentum and flow, kinetic effects of energetic particles, and boundary conditions at the wall, including feedback control and error fields. In ITER in particular, the low toroidal flow equilibrium state, sustained primarily by energetic alpha particles from fusion reactions, will require the consideration of all of these key elements to predict quantitatively the stability and evolution. The principal investigators on this proposal are leading experts in the relevant theoretical and computational areas, and aimed to perform computations guided by analytic modeling, to address this physics in realistic configurations. The overall goal is to understand the key physics mechanisms that describe resistive toroidal burning plasmas, surrounded by a resistive wall, under active feedback control. With the physics of the energetic ions, resonant layers, resistive wall, and toroidal momentum transport included, this study will extend from recent publications in theory and simulation of individual effects and move toward predictive modeling for burning plasmas.

This paper describes a wireless data transmission system for a large-scale rotating experiment to investigate the heat transfer in a three-passage serpentine test section. Patterned after the NASA HOST program, the current experiment extends the data set to larger aspect ratios including 1:2, 1:4 and 1:6. As with HOST, heat transfer is measured using the heated conducting segments technique, and the serpentine test section spins at rotation numbers representative of engine conditions. Rotating experiments are essential for capturing the representative operating conditions and complicated flow physics that must be understood to advance internal cooling technology for these high aspect ratio configurations. There are challenges associated with controlling the operating parameters and collecting accurate data for high measurement-density rotating experiments. This experiment requires that 140 copper panels be held at a constant temperature by independently controlling and recording the power supplied to a separate heater on each panel. This means there must be 140 temperature measurements, 140 pairs of heater power leads, enough power to drive all of these heaters, and data recording capacity left over to measure fluid temperatures and pressures. Traditional methods of transferring rotating signals to the stationary frame of reference (such as slip rings) are widely implemented but have practical limitations in the quantity of transferrable signals and the electrical current capacity of the individual channels. Alternatively, wireless transmission techniques were first developed decades ago, but their practical use has been limited by onboard power delivery requirements and cost. This paper describes the development of a new data transmission and control system that takes advantage of improvements in low-cost off-the-shelf electronics to create a battery powered and microprocessor controlled system for acquisition, storage, control, and wireless communication. These components are assembled to form an integral part of the rotating mechanical hardware. By handling high-fidelity microcircuit signal conditioning, data acquisition, feedback control, and data storage in the rotating frame and transmitting the results with two-way wireless communication, this system provides high measurement density and active feedback control that would have been impractical with a conventional slip-ring approach. The design and construction of the wireless control system for one full sidewall of the three-serpentine passage is described in detail. Its capability and functionality is demonstrated with operational data. It will be demonstrated that while all of the components in this system are readily available, the unique combination of this technology opens up a new world of measurement capabilities.

Resistive wall mode (RWM) instabilities are found to be a limiting factor in advancedtokamak regimes with low internal inductance. Even small amplitude modes can affect therotation profile and the performance of these ELMing H mode discharges. Although completestabilization of the RWM by plasma rotation has not yet been observed, several dischargeswith increased beam momentum and power injection sustained good steady state performancefor record durations. The first investigation of active feedback control of the RWM hasshown promising results: the leakage of radial magnetic flux through the resistive wall canbe successfully controlled and the duration of the high beta phase can be prolonged. Theresults provide a comparative test of several approaches to active feedback control, andare being used to benchmark the analysis and computational models of active control.

The recent attention given to the feedback control of human brain-wave activity and the implications of such control prompts a careful analysis of this phenomenon. Particular emphasis is placed on the learned control of the alpha rhythm. A review of possible factors that might influence the density of alpha rhythms led to the differentiation of three general sources of influence: constitutional, physiological, and cognitive-attentional factors. Each of these factors is discussed as a possible mediator of the learned control of the alpha rhythm. The view is advanced that increases in alpha density during feedback training arise from a diminution of those factors that block this rhythm, and some implications of such a view arc discussed. Several of the issues raised appear generalizable to the whole question of the operant control of autonomic activity.KeywordsOperant ConditioningAlpha ActivityClinical NeurophysiologyAlpha RhythmSensory DeprivationThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.