基于分布式体积速度传感的结构声辐射有源控制实验研究

以简支矩形薄板为研究对象,首先在波数域内对结构振动体积速度与辐射声功率的关系进行分析,推导出反映结构模态对体积速度贡献规律的数学表达式。在此基础上,结合PVDF (Polyvinylidene Fluoride)压电薄膜的电荷输出方程,利用三角函数的正交性,给出一种方法来设计体积速度传感器,并针对具体模型进行了结构体积速度测量实验。结果表明,所设计的分布式体积速度传感器具有较好的传感精度。在此基础上,利用所设计的传感器进行了结构声辐射有源控制实验研究,分别针对单频和带宽信号激励情况下的有源控制实验取得了满意的控制效果,从而验证了本文PVDF体积速度传感器设计方法的正确性以及通过PVDF膜传感结构声辐射并作为误差传感器进行有源控制的有效性。      

The design of synthesized structural acoustic sensors for active control of interior noise with experimental validation

In this paper, the feasibility of using synthesized structural acoustic sensors (SSAS) for active noise control inside irregularly shaped enclosures is investigated. A SSAS consists of a cluster of inter-connected discrete PVDF elements, located on the surface of a vibrating structure enclosing a sound field. An optimal design ensures the sensor output to be directly related to the acoustical potential energy inside the enclosure. Hence, synthesized structural acoustic sensors can provide error signals for an active noise control system, and the use of microphones inside the enclosure can be avoided. A cylindrical shell with a floor partition, which can be used to model an aircraft cabin, is used as a test case. PZT actuators are used as control actuators. Both SISO (single input and single output) and MIMO (multi-input and multi-output) control systems are optimally designed using Genetic Algorithms and implemented with a Filtered-X Feedforward LMS (least-mean-square) controller. Their control performances are evaluated with different types of disturbances. To show the effectiveness of the optimal design approach, some non-optimal control systems are also tested and compared with the optimal one. It is shown that with optimally designed SSAS, an active structural acoustic control system can effectively reduce noise inside the enclosures without using any acoustic transducers.     

Secondary actuation and error sensing for active acoustic structure

A typical approach to active control of sound radiation or transmission from vibrating structures involves active structural acoustic control (ASAC) and active noise control (ANC), which introduce respectively force input and compacted sound source to apply on or be close to the vibrating structure. However, for the ASAC approach, arrangement for secondary force and error sensor is heavily dependent upon the properties of the primary structure and acoustical space; for the ANC approach, a large number of compacted secondary sources are required. Hence, in this paper, based on distributed secondary sound source and near-field error sensor, active acoustic structure is proposed to construct adaptive or smart structure as a versatile module or element for controlling sound radiation or transmission at low frequencies. First, a theoretical model based on a minimization of the total sound radiation from the primary and secondary panel is established, after which, taking into consideration the relationship between the vibration modes pattern and sound radiation characteristics for secondary panels, optimal arrangement for the secondary panels is examined in detail. Finally, a near-field pressure-based error sensing approach is presented, based on two kinds of object function, and active control of sound radiation is performed.     

Reduction of radiated exterior noise from the flexible vibrating plate of a rectangular enclosure using multi-channel active control

This study attempted to control the radiated exterior noise from a rectangular enclosure in which an internal plate vibrates by acoustic excitation and noise is thus radiated from that plate. Multi-channel active control was applied to reduce the vibration and external radiation of this enclosed plate. A piezoelectric ceramic was used as a distributed actuator for multiple mode control of the vibration and radiated noise in the acoustically excited plate. To maximize the effective control, an approach was proposed for attachment the piezoelectric actuator in the optimal location. The plate and internal acoustic space in the enclosure are coupled with each other. This will change dominant frequency characteristics of the plate and, thus, those of the externally radiated noise. Active noise control was accomplished using an accelerometer attached to the plate and a microphone placed adjacent to that plate as an error sensor under acoustic excitation of sine wave and white noise. It was found that the control of radiated external radiation noise requires a microphone as an error sensor, a sound pressure sensor due to vibration of the plate, differences in the dominant frequency of externally radiated noise, and complex vibration modes of the plate.     

基于声辐射模态的有源结构声传入及其辐射控制

从辐射模态的概念和角度研究利用结构误差传感方法对弹性封闭空间结构声辐射进行传感和有源控制。首先分析了辐射模态的数学和物理意义并揭示了辐射模态与声腔模态之间的内在耦合关系。通过声辐射模态建立了弹性封闭空间结构声辐射传感和有源控制模型,并提出了通过传感器阵列测量结构表面有限点的振速分布和设计特定的辐射模态空间滤波器来获得控制所需的误差信号。在此基础上对封闭空间结构声辐射有源控制和误差传感策略进行了深入的理论和数值仿真分析,重点讨论了传感器的数量和布放对辐射模态传感及其有源控制效果的影响。结果表明:辐射模态与声腔模态的耦合具有严格的选择性,各阶辐射模态的形状和与相耦合的主导声模态在耦合面上的形状非常相似;利用结构传感技术传感封闭空间的辐射模态时测点不足或空间采样不足将可能产生较严重的模态泄漏问题,使得不希望的结构模态泄露进所测的辐射模态当中来。在低频范围内,一般只需传感并最小化前三阶有效辐射模态声势能,在更低频和空间声模态频率附近,只需最小化前一阶最有效辐射模态声势能,便能和总声势能最小化策略控制效果基本一样。      

Controllability and observability measures of structural vibration and acoustic radiation

This paper studies the controllability and observability measures of structural vi?bration and acoustic radiation and proposes a measure of modal observability based on acoustic pressure outputs and measures of controllability and observability of acoustic radiation by combining the measures of modal controllability and observability of vibration modes with corresponding modal acoustic radiation efficiencies. A plate with control force inputs and vibrational response outputs and acoustic pressure outputs is involved to show the modal controllability and observability measures of vibration modes and measures of controllability and observabil?ity of structural vibration and acoustic radiation. Observability measures based on vibrational response outputs and acoustic pressure outputs are compared and the emphasis is on the mea?sures based on the acoustic pressure outputs. Finally the application and usefulness of the controllability and observability measures to active control of structural vibration and acous?tic radiation are illustrated and compared. It shows that the controllability and observability measures provide useful guidance for active control design especially in optimal actuator and sensor placement.     

结构振动和声辐射的可控性和可观性指标

结构振动和声辐射的可控性和可观性指标对有源控制系统作动器/传感器的布置具有重要意义。对结构振动和声辐射的可控性和可观性指标进行了研究,提出了基于声压输出的振动模态可观性指标,在振动模态可控性和可观性指标的基础上,结合振动模态的声辐射效率,提出了结构声辐射的可控性和可观性指标和基于声压输出的可观性指标。以板结构为例,对结构振动和声辐射的可控性和可观性指标进行了计算分析和讨论,比较了基于声压输出和基于振动响应输出的振动模态可观性,重点研究了基于声压输出的振动模态可观性和结构振动及声辐射的可观性特点,最后对指标值在结构声有源控制中输入(输出)位置选择上的应用进行了讨论和比较,通过数值仿真对指标的有效性进行了验证。      

Virtual sensors for active noise control in acoustic-structural coupled enclosures using structural sensing: part II--Optimization of structural sensor placement

The work proposed an optimization approach for structural sensor placement to improve the performance of vibro-acoustic virtual sensor for active noise control applications. The vibro-acoustic virtual sensor was designed to estimate the interior sound pressure of an acoustic-structural coupled enclosure using structural sensors. A spectral-spatial performance metric was proposed, which was used to quantify the averaged structural sensor output energy of a vibro-acoustic system excited by a spatially varying point source. It was shown that (i) the overall virtual sensing error energy was contributed additively by the modal virtual sensing error and the measurement noise energy; (ii) each of the modal virtual sensing error system was contributed by both the modal observability levels for the structural sensing and the target acoustic virtual sensing; and further (iii) the strength of each modal observability level was influenced by the modal coupling and resonance frequencies of the associated uncoupled structural/cavity modes. An optimal design of structural sensor placement was proposed to achieve sufficiently high modal observability levels for certain important panel- and cavity-controlled modes. Numerical analysis on a panel-cavity system demonstrated the importance of structural sensor placement on virtual sensing and active noise control performance, particularly for cavity-controlled modes.     

海洋声场中分布式无源定位系统的节点配置方法

为了提高海洋声场中分布式无源定位系统的定位精度,提出一种基于自适应遗传算法的节点配置方法。首先,基于到达时间TOA(Time of Arrival)定位算法推导出均匀物理场与海洋声场中定位误差的CRLB(Cramer Rao Lower Bound)。之后,利用BELLHOP模型对海洋声场进行建模,获得任意位置处目标声源与节点接收信号相关的传递函数并对等效声速进行计算.以目标声源在观测区域内服从均匀分布为例,将定位误差的平均CRLB最小为优化准则,采用自适应遗传算法对节点进行优化配置。结果表明,该方法能够有效降低海洋声场中分布式无源定位系统的定位误差,并给出定位误差随节点个数增加呈非线性递减的变化趋势,可为工程应用提供理论指导。      

Local sensing/control or global error sensing/control in structural acoustics: A comparison of two techniques influence over sound power

The active control of radiation from large structures is a difficult, though important practical problem. The major reason for the difficulty is the ‘system’ size, as a large number of sensors and actuators are required for successful implementation, thus making it hard to design a robust, efficient system that integrates all sensors and actuators. This work examines the active attenuation of the global error, sound power, from the point of view of two sensing/control strategies that seek to be generalised; thus are applicable to a wide range of applications and are independent of knowledge of structural dynamics. In each approach the idea is that the required hardware can simply be attached, turned on, and immediately being to attenuate global noise. The two strategies are compared based on the level of attenuation of the global error sound power, the attenuation per total control force, and attenuation per actuator (in a structural-acoustic situation). The first strategy is the collocated-decentralised approach, which is built on measuring and controlling local vibration in an attempt to influence the global acoustic error. An alternative approach, termed the hybrid approach is firstly developed. The approach is termed ‘hybrid’ because it is a mix between a fully ‘centralised’ and ‘decentralised’ approach; but still measuring and controlling the global acoustic error directly. The attenuation of sound power is compared for both strategies on two structural sources; using 16 identically placed velocity sensors and 16 secondary point sources, in simulation in an attempt to suggest efficient sensing and control approaches for the global control of sound radiation from large structural sources.     

An improved algorithm for detecting point of impact in anisotropic inhomogeneous plates

Conventional triangulation techniques fail to correctly predict the acoustic source location in anisotropic plates due to the direction dependent nature of the elastic wave speeds. To overcome this problem, Kundu et al. [1] proposed an alternative method for acoustic source prediction based on optimizing an objective function. They defined an objective function that uses the time of flight information of the acoustic waves to the passive transducers attached to the plate and the wave propagation direction (θ) from the source point to the receiving sensors. Some weaknesses of the original algorithm proposed in Ref. [1] were later overcome by developing a modified objective function [2]. A new objective function is introduced here to further simplify the optimization procedure and improve the computational efficiency. A new algorithm for source location is also introduced here to increase the source location accuracy. The performance of the objective function and source location algorithm were experimentally verified on a homogeneous anisotropic plate and a non-homogeneous anisotropic plate with a doubler patch. Results from these experiments indicate that the new objective function and source location algorithm have improved performance when compared with those discussed in Refs. [1] and [2].     

Noise transmission from a curved panel into a cylindrical enclosure: analysis of structural acoustic coupling

Much of the research on sound transmission through the aircraft fuselage into the interior of aircraft has considered coupling of the entire cylinder to the acoustic modes of the enclosure. Yet, much of the work on structural acoustic control of sound radiation has focused on reducing sound radiation from individual panels into an acoustic space. Research by the authors seeks to bridge this gap by considering the transmission of sound from individual panels on the fuselage to the interior of the aircraft. As part of this research, an analytical model of a curved panel, with attached piezoelectric actuators, subjected to a static pressure load was previously developed. In the present work, the analytical model is extended to consider the coupling of a curved panel to the interior acoustics of a rigid-walled cylinder. Insight gained from an accurate analytical model of the dynamics of the noise transmission from the curved panels of the fuselage into the cylindrical enclosure of an aircraft is essential to the development of feedback control systems for the control of stochastic inputs, such as turbulent boundary layer excitation. The criteria for maximal structural acoustic coupling between the modes of the curved panel and the modes of the cylindrical enclosure are studied. For panels with aspect ratios typical of those found in aircraft, results indicate that predominately axial structural modes couple most efficiently to the acoustic modes of the enclosure. The effects of the position of the curved panel on the cylinder are also studied. Structural acoustic coupling is found to not be significantly affected by varying panel position. The impact of the findings of this study on structural acoustic control design is discussed.     

Acoustic-based damage detection method

Most of the structural health monitoring (SHM) methods is either based on vibration-based and contact acoustic emission (AE) techniques. Both vibration-based and acoustic emission techniques require attaching transducers to structure. In many applications, such as those involving hot structural materials for thermal protection purposes or in rotating machines, non-contact measurements would be preferred because the operating environment is prohibitive leading to potential damage in contact sensors or their attachments. In this paper, a new non-contact, acoustic-based damage detection method is proposed and tested with an objective that the proposed method is able to detect the location and extend of damage accurately. The proposed acoustic-based damage detection method is a direct method. In this proposed method, changes in vibro-acoustics flexibility matrices of the damage and health structure are used to predict the location and extend of damage in the structure. A case study involving actual measured date for the case of a fixed–fixed plate structure is used to evaluate the effectiveness of the proposed method. The results have shown that the proposed acoustic-based damage detection method can be used to detect the location and extend of the damage accurately.     

Vibro-acoustic control with a distributed sensor network

The purpose of this work is to demonstrate the ability of a distributed control system, based on a smart sensor network, to reduce acoustic radiation from a vibrating structure. The platform from which control is effected consists of a network of smart sensors, each referred to as a node. Each node possesses its own computational capability, sensor, actuator and the ability to communicate with other nodes via a wired or wireless network. The primary focus of this work is to employ existing group management middleware concepts to enable vibro-acoustic control with such a distributed network. Group management middleware is distributed software that provides for the establishment and maintenance of groups of distributed nodes and that provides for the network communication among such groups. The control objective is met by designing distributed feedback compensators that take advantage of node groups in order to effect their control. The node groups are formed based on physical proximity. The global control objective is to minimize the radiated sound power from a rectangular plate. Results of this investigation demonstrate that such a distributed control system can achieve attenuations comparable to those achieved by a centralized controller.     

Broadband control of plate radiation using a piezoelectric, double-amplifier active-skin and structural acoustic sensing

The potential of a piezoelectric, double-amplifier active-skin with structural acoustic sensing (SAS) is demonstrated for the reduction of broadband acoustic radiation from a clamped, aluminum plate. The active-skin is a continuous covering of the vibrating portions of the plate with active, independently controllable piezoelectric, double-amplifier elements and is designed to affect control by altering the continuous structural radiation impedance rather than structural vibration. In simulation, acoustic models are sought for the primary and secondary sources that incorporate finite element methods. Simulation indicates that a total radiated power attenuation in excess of 10 dB may be achieved between 250 and 750 Hz with microphone error sensing, while under SAS the radiated power is reduced by nearly 8 dB in the same frequency range. In experiment, the adaptive feed forward filtered-x LMS (least mean square) algorithm, implemented on a Texas Instruments C40 DSP, was used in conjunction with the 6I6O control system. With microphone error sensing, 11.8-dB attenuation was achieved in the overall radiated power between 175 and 600 Hz, while inclusion of SAS resulted in a 7.3-dB overall power reduction in this frequency band.     

Equivalent constitutive model-based design of wave-absorbing material system and controller

A design methodology for wave-absorbing active material system is reported. The design enforces equivalence between an assumed material model having wave-absorbing behavior and a set of target feedback controllers for an array of microelectro-mechanical transducers which are integral part of the active material system. The proposed methodology is applicable to problems involving the control of acoustic waves in passive-active material system with complex constitutive behavior at different length-scales. A stress relaxation type one-dimensional constitutive model involving viscous damping mechanism is considered, which shows asymmetric wave dispersion characteristics about the half-line. The acoustic power flow and asymptotic stability of such material system are studied. A single sensor non-collocated linear feedback control system in a one-dimensional finite waveguide, which is a representative volume element in an active material system, is considered. Equivalence between the exact dynamic equilibrium of these two systems is imposed. It results in the solution space of the design variables, namely the equivalent damping coefficient, the wavelength(s) to be controlled and the location of the sensor. The characteristics of the controller transfer functions and their pole-placement problem are studied.     

一种光学层析图像的多准则重建方法

光学层析成像是一个病态重建问题,为克服重建过程的病态性,提出将多准则优化理论引入到图像重建中。利用了三个用于光学层析图像重建的准则:平方误差函数、图像熵函数和局部平滑函数。采用向量优化方法将多准则优化问题转化为单准则优化问题求解。为了确定各个目标函数间的权重系数,提出一种动态权重系数求解方法。重建过程目标函数关于光学参量的梯度计算是关键,因此提出一种基于梯度树的计算方法。实验过程中对多准则重建结果和基于平方误差函数的单准则重建结果做了比较,证明该方法能够克服传统的偏重单一目标的单准则重建的不足,有效地重建光学层析图像,提高图像重建质量。     

Comparison of laser interferometry and radiation force method of measuring ultrasonic power

The aim of this paper is to compare two different methods for the calculation of the ultrasonic output power of underwater transducers: the radiation force balance, which is the standard method, and the laser heterodyne interferometry, which is rather used to depict displacement or velocity distributions of the acoustic field. Here it is shown that the latter can also be used to calculate the acoustic time-average power with an uncertainty of about 22%, the radiation force balance giving an uncertainty of 12% (with 95% confidence). The interferometry experiments performed with two transducers working at 2.25 MHz and 8.25 MHz showed that they produce different acoustic fields (respectively Gaussian and Lorentz-sigmoidal distributions). Taking into account the acoustic field profiles, the acoustic time-average power from interferometry was calculated. It was found very similar to the time-average power measured with the radiation force balance in the plane-wave assumption.     

Experimental validation of a collocated PVDF volume velocity sensor/actuator pair

The active control of sound transmission through a rectangular panel is experimentally verified. The control system is based on a collocated volume velocity sensor/actuator pair which measures and excites the first radiation mode of the panel. Suppression of the first radiation mode is an efficient strategy to control the low frequency sound radiation from the panel. This configuration leads to a simple single-input single-output control system, to which feedback control can be applied.Two implementations of the volume velocity sensor/actuator pair are tested. First, a polyvinyledene fluoride polymer (PVDF) volume velocity actuator foil with shaped electrodes is used in combination with an identical PVDF volume velocity sensor foil. Due to the mechanical coupling between the PVDF sensor and actuator foil, it is shown that a direct velocity feedback control scheme is not feasible because higher order structural modes will be destabilized. Instead integral force feedback is applied, such that the open-loop transfer function has a roll-off towards higher frequencies. Experiments show that this control strategy results in a reduction of the sound pressure in the receiving room of 10 dB at the first structural resonance without spillover to higher order modes. Due to the roll-off towards high frequencies, the control over higher order modes remains limited. Second, a discrete volume velocity sensor is constructed by summing the signals from 12 point sensors placed on the panel. The volume velocity actuator consists of two PVDF foils, glued on each side of the panel and driven in opposite phase. Direct volume velocity feedback is applied to this system, which is minimum phase. This control system is capable of reducing the sound pressure in the receiving room below 300 Hz by 10-15 dB without spillover to higher order modes.     

Locating point of impact in anisotropic fiber reinforced composite plates

The conventional triangulation technique cannot predict the point of impact in an anisotropic composite plate because the triangulation technique assumes that the wave speed is independent of the direction of propagation which is not the case for anisotropic plates. An alternative method based on the optimization scheme was proposed by Kundu et al. [T. Kundu, S. Das, K.V. Jata, Point of impact prediction in isotropic and anistropic plates from the acoustic emission data, J. Acoust. Soc. Am. 122, 2007, 2057-2066] to locate the point of impact in plates by analyzing the time of arrival of the ultrasonic signals received by the passive sensors attached to the plate. In this paper, that objective function is modified further to overcome the inherent difficulties associated with multiple singularities and to maximize the efficiency of the acoustic emission data for multiple receiving sensors. With this modified objective function the impact point on an anisotropic composite plate is predicted from the acoustic emission data. Experiments are carried out by dropping steel and ping pong balls on a graphite-epoxy composite plate and recording acoustic signals by passive transducers adhesively bonded to the plate at three different locations. The impact point is predicted by the proposed method and compared with the actual location of impact.