Abstract
Feedback tracking control for dynamic morphing of piezocomposite actuated flexible wings
Aerodynamic properties of flexible wings can be improved via shape morphing using piezocomposite materials. Dynamic shape control of flexible wings is investigated in this study by considering the interactions between structural dynamics, unsteady aerodynamics, and piezo-actuations. A novel antisymmetric angle-ply bimorph configuration of piezocomposite actuators is presented to realize coupled bending-torsional shape control. The active aeroelastic model is derived using finite element method and Theodorsen unsteady aerodynamic loads. A time-varying linear quadratic Gaussian tracking control system is designed to enhance aerodynamic lift with predefined trajectories. Proof-of-concept simulations of static and dynamic shape control are presented for a scaled high-aspect-ratio wing model. Vibrations of the wing and fluctuations in aerodynamic forces are caused using the static voltages directly in dynamic shape control. The lift response has tracked the trajectories well with favorable dynamic morphing performance via feedback tracking control.
Experimental feedback linearization of a vibrating system with a nonsmooth nonlinearity
Input–output partial feedback linearization is demonstrated experimentally for the first time on a system with nonsmooth nonlinearity, a laboratory three degrees of freedom lumped mass system with a piecewise-linear spring. The output degree of freedom is located away from the nonlinearity so that the partial feedback linearization possesses nonlinear internal dynamics. The dynamic behavior of the linearized part is specified by eigenvalue assignment and an investigation of the zero dynamics is carried out to confirm the stability of the overall system. A tuned numerical model is developed for use in the controller and to produce numerical outputs for comparison with experimental closed-loop results. A new limitation of the feedback linearization method is discovered in the case of lumped mass systems—that the input and output must share the same degrees of freedom.
Acoustic characterization of a nonlinear vibroacoustic absorber at low frequencies and high sound levels
A nonlinear vibroacoustic absorber (nonlinear energy sink), involving a clamped thin membrane made of latex, is assessed in the acoustic domain. This nonlinear energy sink is considered here as a one-port acoustic system, analyzed at low frequencies and for increasing excitation levels. This dynamic and frequency range requires a suitable experimental technique, which is presented first. It involves a specific impedance tube able to deal with samples of sufficient size, and reaching high sound levels with a guaranteed linear response thanks to a specific acoustic source. The identification method presented here requires a single pressure measurement, and is calibrated from a set of known acoustic loads. The nonlinear energy sink reflection coefficient is then estimated at increasing source levels, showing its strong level dependency. This is presented as a means to understand energy dissipation. The results of the experimental tests are first compared with a nonlinear viscoelastic model of the membrane absorber. In a second step, a family of one degree of freedom models, treated as equivalent Helmholtz resonators is identified from the measurements, allowing a parametric description of the nonlinear energy sink behavior over a wide range of levels.
An analytical model of a curved beam with a T-shaped cross section
This article derives a comprehensive analytical dynamic model of a closed circular beam that has a T-shaped cross section. The new model includes in-plane and out-of-plane vibrations derived using continuous media expressions, which produces results that have a valid frequency range above those available from traditional lumped parameter models. The web is modeled using two-dimensional elasticity equations for in-plane motion and the classical flexural plate equation for out-of-plane motion. The flange is modeled using two sets of Donnell shell equations: one for the left side of the flange and one for the right side of the flange. The governing differential equations are solved with unknown wave propagation coefficients multiplied by spatial domain and time domain functions which are inserted into equilibrium and continuity equations at the intersection of the web and flange and into boundary conditions at the edges of the system resulting in 24 algebraic equations. These equations are solved to yield the wave propagation coefficients and this produces a solution to the displacement field in all three dimensions. An example problem is formulated and compared with results from finite element analysis.
Relationship between speech-evoked neural responses and perception of speech in noise in older adults
Speech-in-noise perception involves neural encoding of temporal acoustic cues. Cues include temporal fine structure and envelopes that modulate at syllable and fundamental frequency rates. Here, the relationship between speech-evoked neural responses to these cues and speech-in-noise perception was investigated in older adults. Theta-band phase-locking values that reflect cortical sensitivity to slow-rate ENV and peripheral/brainstem frequency-following responses phase-locked to F0-rate ENV (FFRENV_F0) and temporal fine structure (FFRTFS) were measured from scalp-electroencephalography responses to a repeated speech syllable in steady-state speech-shaped noise and 16-speaker babble noise. The results showed that (1) speech-in-noise performance and phase-locking values were significantly higher under speech-shaped noise than babble noise, implying differential cortical encoding may serve as the neural mechanism of speech-in-noise performance that varies as a function of noise types; (2) phase-locking values and FFRTFS at resolved harmonics were significantly related to good speech-in-noise performance, supporting the importance of phase-locked neural encoding of slow-rate ENV and temporal fine structure of resolved harmonics during speech-in-noise perception; (3) FFRENV_F0 was not associated to speech-in-noise performance until audiometric threshold was controlled for, indicating that hearing loss should be carefully controlled when studying the role of neural encoding of F0-rate ENV. Implications are drawn with respect to fitting auditory prostheses.
Investigating the status of a rare cross-linguistic contrast: the case of Romanian palatalized postalveolars
This study examines a rare cross-linguistic contrast, between plain and secondarily palatalized postalveolar fricatives, through (1) an acoustic analysis of the production of 31 Romanian speakers and (2) a perception experiment with a different group of 31 native speakers. Evidence of acoustic separation between plain and palatalized forms was found for 27 of the subjects, suggesting that the contrast is produced by the majority. This is consistent with previous reports of native speakers collected in 1961. These findings were supported by the results of the perceptual experiment, which showed that native speakers exhibit moderate sensitivity to this contrast. An examination of each of the two genders’ production separately suggests that a process of neutralization may be in progress, more strongly realized by males compared with females. Aside from documenting this phenomenon in Romanian, an explanation is sought for its longevity, and it is proposed that grammatical restructuring offers the best account for the observed facts.
Active room compensation for sound reinforcement using sound field separation techniques
This work investigates how the sound field created by a sound reinforcement system can be controlled at low frequencies. An indoor control method is proposed which actively absorbs the sound incident on a reflecting boundary using an array of secondary sources. The sound field is separated into incident and reflected components by a microphone array close to the secondary sources, enabling the minimization of reflected components by means of optimal signals for the secondary sources. The method is purely feed-forward and assumes constant room conditions. Three different sound field separation techniques for modeling of the reflections are investigated based on plane wave decomposition, equivalent sources, and the spatial Fourier transform. Simulations and an experimental validation are presented, showing that the control method performs similarly well at enhancing low frequency responses with the three sound separation techniques. Resonances in the entire room are reduced, although the microphone array and secondary sources are confined to a small region close to the reflecting wall. Unlike previous control methods based on the creation of a plane wave sound field, the investigated method works in arbitrary room geometries and primary source positions.
Low-frequency band gap of locally resonant phononic crystals with a dual-base plate
To achieve a wider band gap and a lower cut-on frequency, a locally resonant phononic crystal with a dual-base plate is investigated in this article. Comparing the locally resonant phononic crystal with a single plate, the band structure of the locally resonant phononic crystal with a dual-base plate is calculated using the method of plane wave expansion and verified by the finite element method. According to the analysis of the band curves of the locally resonant phononic crystal with a dual-base plate, the mechanisms are explained. Next, the influences of the thickness of the plates, the stiffness of the springs, the mass of resonators, and the lattice constant are also investigated. The results show that the structural asymmetry between the upper and the lower plate is conducive to reducing the cut-on frequency and broadening the band gap effectively. The results indicate a different approach for the application of locally resonant phononic crystal in vibration and noise control.
Active control of viscoelastic systems by the method of receptance
Viscoelastic materials have frequency and temperature-dependent properties and they can be used as passive controlling devices in a wide range of vibration applications. In order to design active control for viscoelastic systems, an accurate mathematical modeling is needed. In practice, various material models and approximation techniques are used to model the dynamic behavior of viscoelastic systems. These models are then transformed into approximating state-space models, which introduces several challenges such as introduction of nonphysical internal state variables and requirement of observer/state estimator design. In this article, it is shown that the active control for viscoelastic structures can be designed accurately by only utilizing the available receptance transfer functions and hence eliminating the need for state-space modeling for control design. Using the recently developed receptance method, it is shown that active control for poles and zeros assignment of the viscoelastic systems can be achieved. 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 receptance transfer functions and solution of the set of linear system of equations.
Nonlinear parametric reduced-order model for the structural dynamics of hybrid electric vehicle batteries
Battery packs used in electrified vehicles exhibit high modal density due to their repeated cell substructures. If the excitation contains frequencies in the region of high modal density, small commonly occurring structural variations can lead to drastic changes in the vibration response. The battery pack fatigue life depends strongly on their vibration response; thus, a statistical analysis of the vibration response with structural variations is important from a design point of view. In this work, parametric reduced-order models are created to efficiently and accurately predict the vibration response in Monte Carlo calculations, which account for stochastic structural variations. In addition, an efficient iterative approach to handle material nonlinearities used in battery packs is proposed to augment the parametric reduced-order models. The nonlinear structural behavior is explored, and numerical results are provided to validate the proposed models against full-order finite element approaches.
Experimental application of time-domain transmissibility identification to fault detection and localization in acoustic systems
This article considers a technique for fault detection and localization based on time-domain transmissibility identification. This technique takes the advantage of unknown external (ambient) excitation to identify a sensor-to-sensor model, which is independent of the excitation signal and the initial conditions of the underlying system. In the presence of unknown external excitation, the identified transmissibility operator is used to compute the sensor-to-sensor residual, which is the discrepancy between the predicted sensor output (based on the transmissibility operator) and the actual measurements. The sensor-to-sensor residuals are used to detect, diagnose, and localize faults in sensors and system dynamics. We consider an experimental setup consisting of an acoustic system with three speakers and six microphones. Each speaker is an actuator, and each microphone is a sensor that measures the acoustic response at its location. Measurements from the six microphones are used to construct transmissibility operators, which in turn are used to detect and localize changes in the dynamics of the acoustic system or the microphones by computing the resulting one-step residuals.
Trailing edge perforation for interaction tonal noise reduction of a contra-rotating fan
This study focuses on a passive noise abatement technique in a small contra-rotating fan, aiming at reducing the interaction noise between the two rotors through porous trailing edge treatment to the forward rotor. A preliminary design with fixed perforation parameters is experimentally investigated, and 6–7 dB overall noise reduction is achieved compared with baseline design under the same aerodynamic output. A three-dimensional (3D), full-wheel, unsteady-flow numerical simulation of the acoustic design is carried out to better understand the noise reduction mechanism. Comparisons of monitored unsteady forces acting on both the forward and the aft rotor between baseline and perforated fan indicate that such treatment reduces all the unsteady forces. Thus, it can be concluded that the noise reduction would be due to not only the mitigation of viscous wake of forward rotor before impinging upon the downstream blades but also the reduction of the response of the upstream rotor to the potential flow interaction with the downstream rotor. Furthermore, a parametric study in a selected range is conducted to minimize the adverse effect of aerodynamic unloading due to trailing edge perforation and to improve the acoustic benefit. The parameters in the parametric study include perforation ratio, aperture diameter, and perforation distribution. Trends are deducted from this, and it is recommended that there exists an optimal perforation ratio; the smallest possible aperture diameter and the decreasing perforation ratio distribution away from the blade trailing edge should be selected in consideration of both aerodynamic and acoustic effects.
A research on acoustic characteristics of gas pressure regulator with silencer
Results of calculations and experimental studies of the acoustic characteristics of the gas pressure regulator with a silencer are reported here. A mathematical model and a method for obtaining a stable solution of the original system of equations were developed. The possibility of reducing the noise of the pressure regulator, when one orifice plate is installed, is presented here. We obtained a good convergence of theoretical and experimental data. The optimization of the flow area silencer consisting of several orifice plates was developed.
Identification of nonlinear behavior of an electromechanical loudspeaker; experimental approach
The performance of common linear algorithms in active noise control applications can be degenerated mainly due to the unmodeled nonlinearities of loudspeakers as actuators in noise attenuation process. The aim of this article is to propose different methods such as prediction error method, nonlinear autoregressive network with exogenous input, and series-parallel nonlinear autoregressive network based on neural network to experimentally identify the nonlinear behavior of a loudspeaker. A model of loudspeaker is being used in noise cancelation and control algorithms; hence, its validity and robustness to input amplitude and frequency plays a crucial role in noise control. The results of this article, which are completely based on real and experimental data, demonstrate that neural network-based series-parallel nonlinear autoregressive model is the best estimator for the fully nonlinear behavior of the loudspeaker. The capability and robustness of this estimator in comparison with other methods is examined by different test inputs with different amplitudes and frequencies.
Investigations on effect of notch on performance evaluation of cantilever beams
It is required that any structure must work properly during its service lifetime. However, due to the internal damage of structures, there may be a chance of breakdown. Therefore, structures require regular costly inspection. During the past few decades, vibration-based fault detection methods are mostly used due to their simplicity of implementation. During operation, all structures are subjected to degenerative effects that may cause initiation of structural fault such as cracks or notch that lead to the disastrous failure or collapse of the structure. It is seen that as a crack or notch starts generating, there is a change in natural frequencies. This research work focuses on the examination of these changes, which is useful for identification of the notch position. In this article, the detailed analysis of cantilever beam with and without notch has been done using finite element method with the help of ANSYS and using modern national instruments LabVIEW software. This method provides information regarding the detection, location, and characterization of the damage in the structure. This article includes the study of dynamic properties of cantilever beams subjected to free vibration under the influence of notch at different positions along the length.
Free vibration analysis of rhombic plate with central crack
In this article, free vibration analysis of rhombic plate with pre-existing central crack has been done using the finite element method. The Mindlin theory of plate has been used in the process of investigation. The following six boundary conditions at the edges of the plate have been considered. They are simply supported at all edges, clamped at all edges, free at all edges, clamped-simply supported, clamped-free, and clamped-free-simply supported. Effects of crack length on natural frequencies of rhombic plate with different skew angles, that is, 15°, 30°, 45°, 60° have been studied. It is observed that percentage drop in fundamental frequency due to presence of central crack in the rhombic plate increases with an increase in skew angle for clamped at all edges, supported at all edges, and clamped-simply supported edge conditions at a given crack ratio (nondimensional crack length). Under the clamped-free, clamped-free-simply supported, and free at all edges edge conditions, percentage drop in natural frequency of rhombic plate is very small for crack ratio of 0.2 at different skew angles. In case of the clamped-free edge condition of the rhombic plate, percentage drop in fundamental frequency is within 0.7% at all skew angles and with all crack ratios considered. Some of the results obtained by the present method have been compared with the published results. Most of the results obtained are novel for rhombic crack plate.
Quantification of preference relevant sound characteristics of multi-tone sounds based on the differences between loudness judgments and preference evaluations
The aim of this study is to quantify the impact of the ratio between fundamental frequencies and the contribution of the sound elements on the loudness and preference for intricate multi-tone sounds, consisting of two complex tones and additional combination tones. Preference evaluations and loudness judgments were determined in the form of levels at two points of subjective equality compared with a fixed, common reference sound. The level difference between the two points of subjective equality is attributed to additional perceptual aspects of the multi-tone sounds, which in turn become tangible and quantifiable in the form of decibel values. In this article, the entirety of these additional perceptual aspects, apart from the loudness perception, is subsumed under the term sound character. The results show a clear differentiation between loudness judgments and preference evaluations by the participants and stable mean values for the level difference attributed to the sound character were obtained. The results demonstrate that a combination of two complex tones can be beneficial, whereas the addition of the combination tones has no adverse impact on the evaluation of this type of sound. For the evaluation of combined sounds, also the ratio between the fundamental frequencies affects the perception.
Influence of the lip horn on acoustic pressure distribution pattern of sibilant /s/
Influence of the lip horn on the acoustic pressure distribution of the sibilant /s/ was experimentally studied using a vocal tract replica to which a rectangular baffle was added to represent a human face. The sound was generated by a sweep sound source (frequency: 2–15 kHz) positioned at the inlet of the pharynx or by air flowing through the replica. The sound generated by the sweep source was measured along two semicircles of radius 4 cm at every 2° (near-field) and radius of 48 cm at every 15° (far-field), whereas the sound generated by the flow was measured along semicircles of radius 10 cm at every 2°. From the normalized pressure distributions, it was observed that the lip horn enhances the pressure amplitude up to 15 dB at the center of the lips in both transverse and sagittal planes in the frequency range above 5 kHz. The pressure distribution patterns measured with the acoustic source were similar to those measured with the flow supply. This indicates that the pressure pattern of sibilant /s/ is affected by the vocal tract geometry rather than by the source characteristics.
Human ability to judge relative size and lateral position of a sound reflecting board using click signals: influence of source position and click properties
In human echolocation, acoustic signals provide information enabling people to perceive the physical environment. Little is known about the relation between properties of click signals used for echolocation purposes and the effect of source position on the resulting echolocation performance. In this work, echolocation performance is studied for two different echolocation tests: board size identification and board lateralization. The used artificial source is placed in front of the mouth and in front of the chest. Three different synthesized test signals are used: two narrow band signals and one broadband click signal. Impulse responses were recorded in an anechoic room for each individual participant, and listening tests were carried out afterwards by playing post-processed individualized signals using headphones. The results show better performance with the sound source at the chest position in both the experiments, with the difference in performance most prominent in the board size identification test. In the board lateralization test, the broadband click results in eminent better performance over the narrow band click signals. This suggests that broadband and chest positioned signals seem favorable over narrow band and mouth positioned signals.
Identification error in airport noise assessment
The unattended monitoring of the airport noise is assessed in terms of the time average sound level L Aeq T with the time interval T, for example, 1 h of early night (22:00–23:00). Airport noise is composed of aircraft noise events. Each of them is quantified by the sound exposure level. Due to identification errors the noise monitoring unit misrecognizes both the sound exposure level of aircraft sound events and the sound exposure level of non-aircraft sound events. This is one of the reasons for the differences between the true and the measured value of L Aeq T. The annual mean of the identification error is estimated.