Solid State Phenomena Vol. 248

Abstract: The aim of this paper is to present a method of nonparametric and parametric secondary path model identification for adaptive active noise control systems with low-power non-Gaussian excitations of the form of a higher-order discrete-time multisine random process and data processing based on cross-higher-order spectra. Properties of the discussed method are illustrated by simulation experiments devoted to secondary path identification for feedforward and feedback active noise control systems. Its robustness to nonlinear distortions implied by data acquisition system and adaptation procedure is proved.

Abstract: An active casing made of appropriately controlled vibrating plates can be used to reduce noise propagating from the mechanism enclosed in the casing. Since a practical vibrating casing can behave in a nonlinear way, the performance quality strongly depends on the ability of control filters to compensate for the nonlinearity. The classical approach to nonlinear active control, e.g. based on the Volterra filters, can deal with harmonics generated by the nonlinearity. However, when a complex structure is considered, neural networks have a higher potential. Although, they are much more computationally demanding, for some cases they can be simplified and still provide acceptable performance.In this paper, results of control obtained for a real casing with multiple actuators exciting each wall are presented and discussed.

Abstract: This paper presents a method for the active noise and vibration control (ANC/AVC) of harmonically related nonstationary disturbances using varying-sampling-time linear parameter-varying (LPV) controller. The frequencies are assumed to be known and varying within given ranges and they are multiples of one fundamental frequency.

Abstract: The idea of active casing is an approach to reduce device and machinery noise by controlling vibration of casing walls. The sound insulation efficiency of this technique for a single-plate casing was confirmed by the authors in previous publications. However, under specific circumstances, a dedicated double-panel structure can yield even higher noise reduction. The aim of this paper is to propose and evaluate by means of laboratory experiments the performance of a double-panel casing in comparison with a single-panel casing. An adaptive control strategy based on the Least Mean Square (LMS) algorithm is used to update control filter parameters. A low-frequency noise in the range up to 250 Hz is considered. Obtained results are reported, discussed, and conclusions for future research are drawn.

Abstract: High acoustic insulation windows are common mean to decrease sound transmission to closed spaces. Hence, the improvement of sound insulation of windows is very important research issue. In this paper partial results of research project aimed at synthesis of the window panel with actively controlled sound transmission are presented. Recent stage of the project is focused on the development of multichannel Active Structural Acoustic Control algorithm. High amplitude excitation produces nonlinear vibration effects. Using feedforward control strategy it is convenient to control not only the reference signal spectrum, but also additional frequencies generated as the cause of nonlinearity. Therefore neural network based algorithm is considered. To lower the computational burden of the algorithm, round robin based error backpropagation learning is employed. The results of numerical simulations are presented. Major conclusion of presented part of the research is that the algorithm is capable of controlling a wide-band noise efficiently. Reduction of the computational complexity leads to increased convergence time, not influencing the final value of mean square error.

Abstract: The article deals with the problem of a space with vibroacoustical source generating inside specific conditions, which form a field of some values. All applies to an acoustic field in particular, characterized by an acoustic pressure or field of displacements in vibration problems. In general the field is described by specific dependent variable w(t) in all points of space, whose location are defined by coordinates r. The first aspect of this work relates to the modeling of an induced field, which can be alternative to finite element method (FEM) or boundary element method (BEM) in a low range of frequency. The second aspect is connected with minimization of some significant factor level related to dependent variable w(t) and subsequently to control field inside bounded space in order to get required state. In this work, it is assumed that the field distribution can be described by using modal analysis assumptions. Therefore, the dependent variable w(t) is defined by a modal expansion i.e. the sum over a set of a space’s eigenfunctions Ψ(r) (normal modes, characteristic functions) and time components (modal amplitudes, generalized coordinates). If the assumption of the highest values of acoustical or mechanical impedance of the space boundaries (damping properties of boundaries) is made, the modal coupling can be neglected. Such approach results in the vibroacoustical model being faster than alternative FEM or BEM models and suitable for the optimization procedure by using genetic algorithms, in the case when a computational cost is high. Thereafter, the topology optimization problem is formulated, where the influence of boundaries, represented by their impedance and the shape of space, represented by eigenfunctions are considered as the design variables. The genetic algorithm method is applied in order to find a minimum of objective function. In this case the function returns some functional value. As the result of the optimization a topology of the investigated space is obtained in the form of its shape and simultaneously configuration of damping properties of the space’s boundaries

Abstract: A hybrid active-passive noise control system for a HVAC duct combines both a physicalnoise absorber and an active system. Due to the presence of the passive component, requirements forthe active system can be relaxed, removing the need for detecting and suppressing noise in the frequencyrange already covered by the passive elements. A typical noise measurement system adaptedto working in airflow usually uses a microphone with a housing designed to reduce the noise generateddue to local turbulent flow introduced by the housing itself. Alternatively, there are microphonesspecifically designed to work in the airflow.During work on the hybrid active-passive noise control system both a microphone designed forairflow and a microphone with special housing were tested. While these solutions can be used forresearch, both have issues making them impractical when designing a commercial product. This, alongwith the required narrow frequency range motivated the authors to consider vibration measurementsperformed by appropriately installed accelerometers. An audio signal is then synthesized using thosemeasurements and it is confronted with signals obtained at the same time with microphones.In the paper the proposed method is presented and validated with a laboratory HVAC installation ofa large cross-section and an originally designed passive absorber. Obtained results encourage further research.

Abstract: An active noise-canceling casing is very attractive for reduction of sound generated bydevices. Such casing can provide good noise reduction for low frequencies, where a passive barrierwould be too thick for practical use. The classical active noise control approach, where the goal is tominimize the sound pressure level around multiple microphones outside the casing can be used. However,it requires placing external microphones, what makes the overall technical solution not acceptedfor many applications. The active vibration control, where the goal is to minimize vibrations of allplates, requires only sensors on the plates. However, in this solution, in turn, noise reduction resultsare worse. This paper presents employment of the idea of the virtual microphone-based approach toimprove results from the system based on vibration sensors only, which are used to estimate acousticpressure at specific locations in the acoustic field. By using a two-stage structure, the system is tunedto reconstruct the same vibrations of the plates, which were present when the acoustic pressure wereminimized directly in the square sense. A laboratory active noise-canceling casing used for experimentsis made of 5 actively controlled aluminum plates mounted on a steel frame. It is passivelyisolated from the floor. On each plate, three electrodynamical actuators are installed. The controlsystem is experimentally verified and obtained results are reported.

Abstract: The essence of the undertaken topic is the problem of estimation of state vector in the model of 2S1 tracked vehicle suspension system through the use of Extended Kalman Filter. The use of non-linear filter has become necessary due to the magnetorheological damper located at suspension system, which has been described by hyperbolic model. Application of the damper caused the tested suspension system has become a semi-active structure in which the hybrid control was applied. The choice of this type of control stems from the fact that in the case of tracked combat vehicles in addition to the advantageous conditions of work of vehicle crew also cornering stability and the possibility of sudden acceleration or braking is important. The hybrid control allows to determine a compromise between ride comfort and stability of 2S1 platform.