1,720,965 research outputs found
Experimental multimode traveling waves identification in an acoustic waveguide
No full textAn essential part of nondestructive testing and experimental modeling of waveguides is the decomposition of propagating wave patterns. The traveling wave ratio is a measure of partial reflections assisting in quantifying the pureness of a single traveling wave from a power flow perspective. This paper expands the notion of traveling wave ratio for multimode systems and outlines several schemes capable of decomposing the waves into their different traveling modes while quantifying their traveling and standing proportions individually. A method to strike an optimal balance between increasing model order and to maintain low uncertainty is proposed. An experimental study performed on an acoustic wave tube, which utilizes the various methods while assessing their accuracy and performance, is reported. The results described here emphasize the importance of including additional propagating modes. In addition, the results illustrate the capability of using the recursive multichannel least-mean-squares method for both a fast decomposition and as a basis to formulate closed-loop schemes controlling the wave’s propagation patterns
The use of a digital twin to reconfigure a nonlinear internal model controller
No full textA reconfigurable feedback controller based on a digital twin is illustrated using simulations of a system with a time-varying nonlinear backlash. The control system consists of a motor driving the position of a flexible structure through a lead screw subject to backlash, whose gap angle changes over time. An internal model control (IMC) approach is utilised as the feedback path to increase the linear controller robustness. When a backlash is considered in the model, it is shown that although the linear IMC remain asymptotically stable, its performance deteriorates. A nonlinear IMC (NIMC) approach improves the closed-loop system’s transient behaviour. When the backlash model used in the NIMC is exact, the NIMC can follow the reference model. However, residual vibrations are observed if the backlash model is not estimated precisely. A digital twin of the system is used to estimate the backlash gap angle and to re-design the backlash model for the NIMC via asynchronous communication, thus ensuring the stability of the feedback system
Determining the underwater acoustic properties of materials, with a fluid-filled impedance tube and two spatial-modes reduced-order model
No full textNonlinear control of boundary impedance in an acoustic waveguide
No full textWavetubes are employed for measurements of acoustic properties in various fluids. The ability to manipulate and control the frequency-dependent boundary impedance of the tube improves the estimation accuracy. Passive solutions, which use composite materials to change the boundary impedance, enable one to realize a finite combination of boundary impedances. In this paper, the tube boundary impedance is tuned at will by using two loudspeakers. The suggested method operates in the presence of dispersion by estimating, in real-time, a parametric reduced-order model using a multichannel least mean square algorithm. The identified model is fed to a nonlinear, adaptive control algorithm to realize modal traveling wave ratio (TWR) control. It has been noted that the TWR is smooth and parabolic across closed regions in the parameter space, thus assuring the convergence of the nonlinear control. Several methods to estimate the TWR gradient are considered and compared based on an analytical model of a rigid impedance tube. An experimental case study utilizing an air-filled impedance tube with two loudspeakers is presented. The results demonstrate the ability to control the dynamics of the principal acoustic mode at will, thus enabling one to set the desired tube's boundary impedance.</p
A parallel analog and digital adaptive feedforward controller for active noise control
No full textDigital adaptive controllers are widely used for feedforward active noise control, especially in headphones. In such applications, the secondary path delay, including the sampling and reconstruction effects, must be shorter than the primary path delay to maintain good broadband performance. A mixed analog and digital adaptive feedforward controller is developed to eliminate the added delay of the sampling and reconstruction. The analog controller is based on a state-filtered adaptive linear combiner, while the digital one uses an adaptive finite-impulse-response filter. It is shown that both filters can be adapted using the normalized filtered-reference LMS algorithm but with different secondary path models. A method to design the analog state-filter based on Padé's approximation is described. The performance of the proposed controller with two analog states, the direct feedthrough and a 0.3 milliseconds delay, is assessed and compared to the separate analog or digital controllers in a controlled environment. The results highlight that adding the analog delay improves the digital controller performance by about 5 dB in this application, regardless of the primary noise direction.</p
The use of digital twins to remotely update feedback controllers for the motion control of nonlinear dynamic systems
No full textThe use of a digital twin to update a feedback controller is considered, and this is illustrated using simulations of a position-controlled dynamical system with a time-varying nonlinear element. The feedback control system consists of a dc motor driving the displacement of a three degree of freedom structure through a lead screw that is subject to backlash, whose gap angle changes over time due to wear for example. The backlash is shown to destabilise the feedback loop when using a PID controller designed for the linear system. However, stability can then be re-established by including a dead zone within the controller. The design of the dead zone depends on the extent of the gap angle in the backlash and is a trade-off between stabilising the system and avoiding excessive steady-state errors and undesired transient behaviour. When the backlash gap angle changes significantly from the one used to design the dead zone, both performance and stability are affected. Therefore, a digital twin of the system is used to estimate the backlash gap angle as it changes with time and this estimate is used to re-design the dead zone, which is then communicated back to update the controller. The digital twin and controller-design process can be implemented offline and remotely from the physical twin and the real-time controller via an asynchronous link with variable time delays. As a result of combining the feedback loop and digital twin, good performance and stability are maintained at all times.</p
Experimental Dispersion identification using a fitted state-space model
No full textAn identification method that can estimate the dispersion relation of waveguides experimentally using an efficient and accurate procedure is presented. The method fits a linear state-space model before resorting to a kinematic wave model in the frequency region near the pre-identified natural frequencies. The eigenvectors, or mode-shapes, are computed at the sensor locations, and based on the reduced-Bloch mode expansion method, the propagation modes are fitted to match the identified vibration mode-shape at these frequencies. Classical methods to identify the dispersion relation from measured data can be computationally expensive and time-consuming, with limited accuracy in cases of multimode propagation. Results show that the fitted dynamic model expands the frequency range of obtained dispersion curves and enhances the speed of computation and accuracy. The method is derived and verified for both lumped and distributed systems, using numerical finite element simulation. Experimental verification is carried out on two acoustical waveguides. The first is a circular ring-shaped array of coupled Helmholtz resonators, modeled using a lumped parameter model. The second is an air-filled acoustic wave-tube that is modeled as a distributed acoustic-elastic coupled waveguide. The method's strengths and weaknesses are discussed from the experimentally obtained dispersion curves, and its main feature, the ability to fit the dispersion model of weak modes, is highlighted.</p
Adaptive model-based control of boundary impedance in an acoustic impedance tube
No full textImpedance tubes are employed for measurements of acoustic properties in various fluids. The ability to manipulate and control the frequency-dependent boundary impedance of the tube improves the accuracy of the estimation. Passive solutions, which use composite materials to change the boundary impedance, have been used in the past, and these enable one to realize a finite combination of boundary impedances. In this paper, the tube boundary impedance is being tuned at will by using two loudspeakers, one at each tube’s end. The suggested method operates in the presence of dispersion by estimating, in real-time, a parametric reduced-order model using a multichannel least mean square algorithm. The identified model is fed to a nonlinear, adaptive control algorithm to realize modal traveling wave ratio control. It has been noted that the traveling wave ratio is smooth and parabolic with respect to a second actuator’s complex amplitude across closed regions in the parameter space, thus assuring the convergence of the nonlinear control. An experimental case study utilizing an air-filled impedance tube with two loudspeakers is presented. The results demonstrate the ability to control the dynamics of the principal acoustic mode at will. Thus, enabling one to set the desired tube’s boundary impedance.</p
Active detection of small imperfections in structures with cyclic symmetry
No full textStructures possessing cyclic symmetry such as turbine bladed disks, ultrasonic motors, and toothed gear wheels can experience elevated vibration levels when small deviations from circumferential periodicity exist. Detection of these perturbations via classical system identification approaches is time-consuming, indirect, and exhibits low sensitivity to defects and are affected by measurement noise. The present work utilizes low-level forces that automatically lock onto a weighted rotating projection of the system modes at resonance frequency to enhance the detectability of small structural imperfections. The spatial localization of defects is exploited to identify multiple, localized, isolated defects' locations. The defects' severities are estimated based on the deviation from the circular structure's analytical mode shapes. Fast and enhanced precision of defect identification is obtained by employing the modal filtered Autoresonance technique. To validate the presented method, an experimental system consisting of a ring of coupled Helmholtz acoustic resonators was developed. Experimental results show good agreement with numerical simulations, verifying the method's capabilities to identify the location and severity of multiple defects. Thus, implementation of the suggested method provides fast and precise structural health monitoring of cyclic symmetric systems
Dispersion based reduced-order model identification and boundary impedance control in a weakly coupled impedance tube
No full textImpedance tubes are commonly employed for non-destructive measurement methods of the acoustic properties of materials. Most physical models neglect the elastic nature of the tube resulting in a single mode propagation up to the cut-off frequency and are thus unable to accurately predict the propagati patterns in the case of liquidfilled tubes. An understanding of the dispersion pattern in the latter case is crucial for the success of the acoustic properties estimation procedure. Furthermore, a model-based control can be implemented on the basis of the dispersion relation which is able to enhance the existing methods. This work presents a case study of an air-filled impedance tube. A novel, two-actuators phase-perturbations technique was developed to identify the tube dispersion curves and to compare to analytical models. The accurate identification of dispersion curves was utilized in a successful effort to formulate a reduced-order model used to control a single mode traveling wave’s ratio by employing a feedforward control algorithm. The success of the case study in the case of a weak acoustic coupling mechanism such as the air-filled impedance tube emphasizes the capabilities when considering a stronger acoustic coupling such as in the liquid-filled impedance tube
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