Use Of Active Control Research Articles

360841 ACTIVE CONTROL OF AIRSPRING SECONDARY SUSPENSION TO IMPROVE RIDE COMFORT IN PRESENCE OF RANDOM TRACK IRREGULARITY(Vehicle,Technical Session)

Aim of this paper is to explore the possible benefits brought by the use of active control of the airspring secondary suspension for high speed railway vehicles. The concept of the active suspension is developed and a prototype is tested. Then, the benefits of active suspension control are assessed by means of multi-body simulation.

Intelligent interfaces for sound insulation: Numerical and experimental optimisation

Sound insulation is actually achieved thanks to passive multilayers. These ones are classically made of elastic, acoustic and poroelastic media. Good results are obtained in medium and high frequencies, but low frequencies disturbances still remain a problem. Indeed, local and global resonant behaviours of the panel, such as plate bending mode or the double-leaf phenomenon, occur and lower the performances. An active concept has already been proposed and validated. Piezoelectric components are added to the interface and act a secondary source aiming at minimising the sound transmitted. In this contribution, a double-plate system is studied. A reduced finite element model of an elementary cell is presented. This one relies on modal projection and classical component mode synthesis (CMS) procedures. This model is first updated and validated thanks to measurements performed on a dedicated test bench. The use of active control allows a 15 dB enhancement of sound insulation at low resonant frequencies. Numerical experiments are designed. Response surfaces are obtained thanks to kriging procedures. Finally, the configuration of the optimal interface is discussed in a physical point of view.

Pantograph Dynamics and Control of Tilting Train

The modeling methodology of tilting train is studied. The vehicle and pantograph are considered as nonlinear multiple rigid body systems, and the catenary is modeled by FEM method. The electrical mechanical actuators for carbody and pantograph tilting control are also considered in the tilting train model. The method of on-line curving detection, filtering and control is adopted for the tilting train. The passive and active controls for the pantograph lateral motions during tilting train curve negotiation are analyzed. The pantograph guideway on top of the carbody is designed, and the control strategy for the pantograph active control is investigated. It is known that the pantograph lateral and vertical displacement and the fluctuation of pantograph-catenary contact force can be minimized by the use of active control.

Comparison of Strategies for the Active Control of Buzz-Saw Tones

The results are presented of a feasibility study into the use of active control to reduce the low-engine-order components of buzz-saw noise produced in an aeroengine. It is shown that effective control performance can be achieved using a single ring of circumferentially spaced control actuators and a single ring of error sensors. Two control approaches are investigated: the minimization of the sum of the squared pressures at the error sensors, and the minimization of the sum of weighted squared spinning mode amplitudes. A comparison is made between the performance obtained by these control objectives. It is shown that pressure minimization and minimization of spinning mode amplitudes at the duct walls yields identical control performance. It is also shown that the amplitude of the evanescent modes excited by the control actuators is the fundamental factor in limiting control performance when noise and extraneous modes are absent at the error sensors. The variation of sound power reduction vs tip speed is investigated in detail. It is shown that, following control, a new set of resonances arise because of standing waves set up between the secondary sources and the duct exhaust termination and between the sensors and the duct inlet termination. Considerable improvements in control performance can be achieved by weighting the modal control objective such that control is focussed on the buzz-saw mode.

Active‐controlled, non‐inferiority trials in oncology: arbitrary limits, infeasible sample sizes and uninformative data analysis. Is there another way?

In oncology, it may not always be possible to evaluate the efficacy of new medicines in placebo-controlled trials. Furthermore, while some newer, biologically targeted anti-cancer treatments may be expected to deliver therapeutic benefit in terms of better tolerability or improved symptom control, they may not always be expected to provide increased efficacy relative to existing therapies. This naturally leads to the use of active-control, non-inferiority trials to evaluate such treatments. In recent evaluations of anti-cancer treatments, the non-inferiority margin has often been defined in terms of demonstrating that at least 50% of the active control effect has been retained by the new drug using methods such as those described by Rothmann et al., Statistics in Medicine 2003; 22:239-264 and Wang and Hung Controlled Clinical Trials 2003; 24:147-155. However, this approach can lead to prohibitively large clinical trials and results in a tendency to dichotomize trial outcome as either 'success' or 'failure' and thus oversimplifies interpretation. With relatively modest modification, these methods can be used to define a stepwise approach to design and analysis. In the first design step, the trial is sized to show indirectly that the new drug would have beaten placebo; in the second analysis step, the probability that the new drug is superior to placebo is assessed and, if sufficiently high in the third and final step, the relative efficacy of the new drug to control is assessed on a continuum of effect retention via an 'effect retention likelihood plot'. This stepwise approach is likely to provide a more complete assessment of relative efficacy so that the value of new treatments can be better judged.

Modelling and control of growing slugs in horizontal multiphase pipe flows

In this paper, the use of active control to restrict the length of growing slugs in horizontal pipelines is investigated. Specifically, the paper attempts to determine if such control can be attained with realistic measurements and actuators. Simulations in OLGA2000 show that a feedback controller can use measurements or estimates of slug length to control the growth of a slug in a horizontal pipeline by partially closing inlet or outlet chokes. A control-volume approach is used to develop a low-order model of inlet choke-slug growth dynamics based on mass- and impulse balances. The resulting model is a system of nonlinear differential-algebraic equations, which is suitable for observer-design. The tuned model is found to be in good agreement with experiments and OLGA2000-simulations. Linearizations of the model are found to be observable around realistic trajectories when rates and pressures at the inlet and outlet are measured. An extended Luenberger-observer is shown to give good estimates of slug length and -position in simulations even under model uncertainty.

A Numerical Study on Active Control for Tiltrotor Whirl Flutter Stability Augmentation

The use of active control to augment whirl flutter stability of tiltrotor aircraft is studied by means of a multibody simulation. The numerical model is based on a 1/5 scale semi-span aeroelastic wind tunnel model of a generic tiltrotor concept and possesses a gimballed, stiff-in-plane rotor that is windmilling. A single-input single-output controller and two types of multi-input multi-output algorithms, Linear Quadratic Gaussian Control and Generalized Predictive Control, are studied. They are using measured wing deflections in order to calculate appropriate swashplate input. Results on the closed-loop behavior of three wing and two gimbal natural modes are given. Robustness analyses with respect to major parameters like wing natural frequencies or structural damping are also briefly discussed. The rotor shear force is shown in the uncontrolled condition and in presence of a controller in order to illustrate the whirl flutter mechanism. The single-input single-output controller yielded substantial gain in stability and turned out to be most suitable for industrial application, whereas the Linear Quadratic Gaussian Regulator yielded even higher damping and still had good robustness characteristics.

Quantum locking of mirrors in interferometric measurements

We discuss the use of active control to reduce mirror position fluctuations at the quantum level. We have shown in a recent experiment that it is possible to reduce the thermal noise of a mirror by measuring and controlling its motion with an optomechanical sensor based on a high-finesse optical cavity. This approach can be extended to lock the mirror motion at the quantum level, and to suppress the quantum effects of radiation pressure in interferometric measurements such as gravitational-wave detectors. The sensitivity improvement is furthermore independent of losses in the interferometer.

Controlledinteractions of two microparticle clouds in a dc glow dischargedusty (complex) plasma

The control of the confinement of charged microparticles in aplasma is an important topic for the dusty plasma community.Earlier experiments have used control over individual microparticles or a single particle cloud to obtain informationabout the potential structure of the surrounding plasma. Inthis paper, experiments that make use of active control of twomicroparticle clouds suspended in a plasma are discussed. Here,an array of three electrodes is used to modify the potentialbetween the two clouds. Through the application of an applied perturbation on one of the array elements, the two clouds areallowed to interact. Particle image velocimetry techniques areused to obtain spatial maps of the interaction process. Theexperimental measurements show that an apparent recoil occursbetween the two particle clouds as a result of the interaction.A simple model is used to show that a recoil may be a possible outcome of the interaction process.

Active control of fan noise from high-bypass ratio aeroengines: a numerical study

AbstractUnder the national research project, dubbed Turbotech II, in which MTU Aero Engines, DLR Institute of Propulsion Technology and EADS Corporate Research Centre participate, active noise control (ANC) has been tested with a scale model fan of one metre diameter for a high bypass ratio aeroengine. MTU’s task in this project was to develop a computer code to predict the sound field in the intake duct of the fan-rig by the use of active control. The primary objective of the numerical study was to specify numbers of actuators (loudspeakers) and error sensors (microphones) and their positioning to control the harmonic sound power, radiated upstream to the duct intake. The computer model is based on the geometry of an annular or circular duct of rigid walls and infinite length, containing a subsonic axial uniform flow. The modal amplitudes of the primary sound field are input data. The actuators are modelled by acoustic monopoles. Two control algorithms have been used for achieving the control objective. The first consists simply in the reduction of the in-duct mean squared pressures. The second, so called modal control, is designed to cancel dominant modes selectively. Numerical results are presented using a typical configuration of wall mounted actuators and error sensors in the form of a number of rings uniformly distributed along the length of the intake duct. Guidelines have also been derived to design a favourable configuration of actuators and sensors. The findings of the numerical study are compared with the results of the ANC tests.

FRICTION CONTROL FOR VIBRATION SUPPRESSION

Friction damping in bolted joint connections of large space structures turned out to be a major source of damping. For vibration suppression, the joints are designed such that the normal force in a frictional interface is controlled which improves the damping performance. The use of active control to vary the normal contact force in a joint by means of a piezoelectric element is explored. A model consisting of two elastic beams connected by a single active joint is considered. A friction model with velocity-dependent dynamics is used to describe the friction phenomena. A control law for friction dampers which maximises energy dissipation instantaneously by controlling the normal force at the friction interface is proposed. The effect of displacement- and velocity-induced friction dynamics is considered for the design of the control law. We arrive at a controller which prevents frictional energy stored as potential energy in a bristle model from being returned to the system.

A finite element approach to the position problems in open-loop variable geometry trusses

The present paper looks at some kinematic and static-equilibrium problems that arise with variable-geometry trusses (VGTs). The first part of the paper looks at the use of active controls in the correction of static deformations, the second part at the position problems. The separation between deformable- and rigid-body displacements makes it possible to consider separately the corrections in each component of the structure. VGTs are considered as open-loop linkages with redundant rigid-body degrees of freedom. Owing to this redundancy, possible solutions to the inverse problem are in general infinite, for which reason it is necessary to use some optimization criteria. To tackle the problem an optimization procedure with constraints is developed for the purpose of minimizing the displacements of the actuators. Suitable use of the constraints allows us to solve the direct position problem using the same optimization procedure.

FEEDBACK CONTROL OF COMBUSTION OSCILLATIONS

Combustion oscillations are excited by a feedback mechanism which results from the coupling between the flame instability and an acoustic resonance mode of the combustion chamber. The most important event of this mechanism is believed to be the upstream feedback from the acoustic resonance to the initial region of the flame, where new disturbances are generated. A control system has been implemented into a commercial household burner to counteract this upstream feedback. This is achieved by means of pulsating either the fresh air for combustion or the fuel. The actuators are activated by the signal of a sensor measuring the pulsation inside either the combustion chamber or the fresh air supply pipe. Combustion oscillations of this burner have been eliminated altogether, also when two modes were simultaneously excited, without destabilizing other acoustic modes. This results in 35dB reduction in the amplitude of the pressure pulsation. Furthermore, when the combustion process was stable, i.e. no resonances were excited, the use of active control has reduced the broad-band noise by 4dB. The effect of the input sensor location on the control system performance has also been investigated.

Active control in passively base isolated buildings subjected to low power excitations

The use of active control on a passively base isolated building model is proposed, to counteract vibrations due to a low power excitation. The base isolated building is modeled as a three degree freedom rigid body. The rotation at the centroid of this rigid building model is controlled with the help of vertical synchronized actuators. The control methods which are applied to the base isolated model and compared are: (i) optimal control; (ii) eigenvalue assignment using state feedback; and (iii) eigenvalue assignment using output feedback. One of the disadvantages of the state feedback method is the requirement that all components of the state at every instant of the control be known. For the optimal control method difficulties may arise in making choices for the weighting matrices. Upon comparison, the eigenvalue assignment technique using output feedback appears to be more feasible than the other two methods for controlling vibrations in the passively base isolated building subjected to low power excitation.

Combustion Oscillation Control by Cyclic Fuel Injection

A number of recent articles have demonstrated the use of active control to mitigate the effects of combustion instability in afterburner and dump combustor applications. In these applications, cyclic injection of small quantities of control fuel has been proposed to counteract the periodic heat release that contributes to undesired pressure oscillations. This same technique may also be useful to mitigate oscillations in gas turbine combustors, especially in test rig combustors characterized by acoustic modes that do not exist in the final engine configuration. To address this issue, the present paper reports on active control of a subscale, atmospheric pressure nozzle/combustor arrangement. The fuel is natural gas. Cyclic injection of 14 percent control fuel in a premix fuel nozzle is shown to reduce oscillating pressure amplitude by a factor of 0.30 (i.e., −10 dB) at 300 Hz. Measurement of the oscillating heat release is also reported.

A Reduced Order Model of Unsteady Flows in Turbomachinery

A novel technique for computing unsteady flows about turbomachinery cascades is presented. Starting with a frequency domain CFD description of unsteady aerodynamic flows, we form a large, sparse, generalized, non-Hermitian eigenvalue problem that describes the natural modes and frequencies of fluid motion about the cascade. We compute the dominant left and right eigenmodes and corresponding eigenfrequencies using a Lanczos algorithm. Then, using just a few of the resulting eigenmodes, we construct a reduced order model of the unsteady flow field. With this model, one can rapidly and accurately predict the unsteady aerodynamic loads acting on the cascade over a wide range of reduced frequencies and arbitrary modes of vibration. Moreover, the eigenmode information provides insights into the physics of unsteady flows. Finally we note that the form of the reduced order model is well suited for use in active control of aeroelastic and aeroacoustic phenomena.

Silencers: The impact of active control

Over the past decade, powerful new adaptive techniques have been developed for the active control of sound and vibration. One of the areas that has received the most attention is the application of active control to enhance the performance of silencers used on ducts or pipes. Active silencing is often combined with passive silencing to create a new form of hybrid silencer. These silencers can be used as intake or discharge silencers for heating, ventilating, and air conditioning (HVAC) fans, industrial fans, rotary blowers, compressors, internal combustion engines, gas turbines, pumps, and related equipment. This paper will review the use of active control for these applications with particular emphasis on the different reasons generating the interest in active control for each application. Among the potential advantages of active control for silencers are improved low frequency performance, reduced flow restriction, and decreased size and cost. The degree to which these potential advantages can be realized in specific applications can vary considerably as well as the ultimate impact of the improvement for the end user. These issues will be discussed using a number of actual examples and implications for the future use of active control will be suggested.

Active control of acoustic impedance with a multi‐element system

The use of active control of acoustic impedance is of general interest due to a variety of potential defense and civilian applications. These include control systems to minimize aircraft and rocket payload section interior acoustic levels. Control of impedance at a boundary is one of the most challenging in active control due to the collocation of sensors and actuators (implicit in this is feedback control). Some of the technical issues include—the selection of the appropriate physical control law, the degree of inter‐connectivity (local versus global control), device linearity, component and processor delays, system identification, nonminimal phase‐zero constraints the coupling matrix, and performance versus robustness tradeoffs. Recently, new active boundary control (ABC) experiments were carried out at NRL’s Laboratory for Structural Acoustics on a 15‐tile array system. The results of these experiments will be discussed with a focus on the application of H∞ control engineering techniques and the physics involved.

Formation and Sustaining Conditions of High-Voltage Ultrashort Pulse Plasma for CVD Processing.

Formation and sustaining conditions and the structure of high-voltage ultrashort pulse plasma of CH4 diluted with H2 and Ar gases have been studied for the use of active control of CVD processing. Using square-wave pulsed high voltage with 50∼1000 ns pulse width, voltage-current characteristics, timelag of current rise from that of voltage and emission intensity profiles of the plasma have been investigated. Very high voltages up to several kilovolts can be successfully applied without any plasma nonuniformity on the electrode surface because the pulsed high voltage drops before the transition to arcing. During the pulse period, very large current of more than 102∼103 times as that of usual DC plasma can enter into the plasma field. For the formation of stable pulse plasma, the pulse width should be longer than the timelag, which has been comprehensively expressed by the parameters of pressure, applied voltage and distance between anode and cathode. Through the measurement of potential profiles in the positive column of the plasma, it has been found that the stratified plasma structure can be controlled simply through the parameters of current and pressure.

Characterization of ultra-short pulsed discharge plasma for CVD processing

Characteristics of pulsed discharge plasma of methane-hydrogen gas mixture and Ar gas are studied for use in active control of plasma chemical vapor deposition (CVD) processing. Voltage-current characteristics, time lag of the current pulse, and the photon emission intensity profile investigated using high-voltage pulses of 50-1000 ns duration. In such a pulsed discharge, voltages much higher than those in a DC glow discharge can be applied without any plasma nonuniformity or arcing because voltage amplitude falls to zero before the glow-to-arc transition. A current value of more than 10/sup 3/ times those in a flow discharge can be established. Very high photon emission intensity from CH radicals and H ions are observed near the anode in a pulsed plasma. This is different in DC plasma, where the negative glow region near the cathode is the brightest. >