共查询到20条相似文献,搜索用时 31 毫秒
1.
C.R. HALKYARDB.R. MACE 《Journal of sound and vibration》2002,254(1):117-141
This paper concerns the real-time estimation of wave amplitudes and their subsequent use as a cost function in adaptive active control of bending vibrations in a beam. The amplitude of the wave propagating downstream from the control location is estimated by filtering the outputs of an array of sensors. Minimizing this wave amplitude has significant advantages over the more conventional approach in which velocity at some point is minimized. Expressions for the ideal frequency responses of the wave filters are found for the case of an array comprising two sensors in the far field. These filters are non-causal. FIR implementations designed using direct and time-delay methods are described, the latter offering some substantial advantages. Practical performance considerations are discussed, including filter length, frequency range, effects of near fields, group delays, accuracy and cross-sensitivity. Simulations and experimental measurements are performed and compared. 相似文献
2.
V. M. Tkachenko A. V. Smol’yakov V. A. Kolyshnitsyn V. P. Marshov 《Acoustical Physics》2008,54(1):109-114
The methods proposed earlier for measuring the wave number-frequency spectrum of wall pressure fluctuations beneath a turbulent boundary layer are considered: the spatial filtering of the pressure field components by special-purpose transducers (wave filters) and the digital processing of signals obtained from an array of transducers. It is shown that, for the wave filters, transducers with a rectangular shape of sensitive surface rather than those with a circular one are necessary. Results of measuring the wave number-frequency spectrum of turbulent pressure fluctuations in a low-noise wind tunnel are presented. The measurements are performed with the use of four wave filters consisting of rectangular transducers with a constant sensitivity distribution over their surfaces. The mathematical model of the wave number-frequency spectrum proposed earlier by the authors is compared with the measurement data reported by Abraham and Keith. The model is used for processing the results of measurements in the wind tunnel. The measured spectra are compared with the data obtained by Martin and Leehey. 相似文献
3.
基于二阶锥规划的任意传感器阵列时域恒定束宽波束形成 总被引:12,自引:5,他引:7
提出了基于FIR滤波器的适用于任意几何形状和阵元方向性的传感器阵列的时域恒定束宽波束形成方法。首先将设计频带分成若干窄带,采用优化方法,通过对各窄带波束施加约束,设计出具有设定主瓣形状要求的各窄带波束。然后针对每个传感器,根据其各频率波束形成加权向量,采用约束优化方法,设计出具有要求幅度和相位响应的FIR滤波器。各滤波器输出相加即得到时域恒定束宽波束输出时间序列。波束图主瓣形状设计与期望频率响应FIR滤波器的设计问题都可以转化为二阶锥规划(Second-Order Cone programming)的形式,然后利用已有的内点方法(Interior-Point,Methods)求出其数值解。计算机仿真结果显示,设计出的各子带波束主瓣宽度比较接近,FIR滤波器设计精度高。湖上实验数据处理结果表明,该方法可以适用于实际水声系统,时域宽带波束能够满足恒定束宽要求。 相似文献
4.
Yun Hwa Hong 《Journal of sound and vibration》2010,329(23):4980-5003
This paper presents two types of finite impulse response (FIR) filters to reconstruct dynamic displacement induced by structural vibration from measured acceleration. The governing equation for the reconstruction is derived by taking the variation of a minimization problem, which defines an inverse problem on displacement. A regularization function for overcoming the ill-posedness of the inverse problem is included in the minimization problem. The governing equation of the inverse problem becomes the same type of differential equation as that of a beam on an elastic foundation. The conventional FIR (CFIR) filter directly approximates the transfer function of the governing equation, while the FEM-based FIR (FFIR) filter is formulated by the discretization of the minimization problem with the finite element method. For the finite element discretization, the Hermitian shape function is utilized. The proposed FFIR filter is capable of reconstructing displacement and velocity simultaneously. The fundamental characteristics of the proposed filters are investigated in the frequency domain using the transfer and accuracy functions. It is shown that the proposed FIR filters suppress low frequency noise components in measured accelerations effectively, and reconstruct physically meaningful displacement accurately. The validity of the proposed filters is demonstrated through a numerical simulation study, a field experiment and an evaluation of flutter derivatives using measurements taken from a wind tunnel test. 相似文献
5.
线性嵌套阵可以很好地在很宽的频率(N个倍频程,N=7)上实现恒定束宽。这种方法设计简单,又节省线阵阵元。本文给出了线性嵌套阵具体的数字化实现方法,解决了FIR滤波器设计,滤波器时间延迟等问题。由于数字化实现过程中使用了很多组FIR滤波器,计算量很大,文章采用了DSP信号处理板实现数字化算法,利用DSP处理板可以多任务同时处理优势,解决了计算量大的问题。经过实验验证,在DSP上实现的数字化的线性嵌套阵宽带恒定束宽方法满足了工程上实时处理的需要。 相似文献
6.
The problem of measuring the radiation directivity pattern of a moving source in a horizontal plane is considered. It is shown experimentally that the angular dependence of radiation can be reconstructed at discrete frequencies in detecting an acoustic signal by a linear array positioned in the near field of the source followed by signal processing. The technique described in this work and its technical implementation can be used in developing and creating a measurement system for monitoring ship fields in the horizon plane.
相似文献7.
宽带低旁瓣时域波束形成 总被引:11,自引:3,他引:8
针对有源和无源声呐中的宽带波束形成,提出了一种低旁瓣时域实现方法。声阵列各个阵元的输出首先经过数字延迟线实现数倍采样间隔的时延补偿,然后由FIR数字滤波器来补偿剩余的时延,并实现低旁瓣波束所需的频率加权,最后再把滤波器输出相加得到时域波束输出。FIR数字滤波器的设计采用改进的自适应方法,其期望响应由工作频带划分成的等间隔窄子带上的低旁瓣波束形成权系数构成。各个子带上的低旁瓣波束则采用基于MVDR波束形成原理的波束优化设计方法得到。针对圆弧阵的计算机仿真设计结果和湖上实验验证了本文方法的正确性和有效性。 相似文献
8.
GUO qili SUN Chao YANG Yixin 《声学学报:英文版》2006,25(3):258-266
A method for designing broadband beamformers based on an expected response interpolation technique was proposed, with the aim of reducing the heavy optimization burden in the broadband beamformer design problem. In the method, some typical frequencies in the designing frequency band are selected and the optimal array weights are designed on these typical frequencies, based on which a broadband expected response function is constructed. Then, FIR filters are designed to realize the broadband beamforming over the whole designing frequency band, via the interpolation technique which is utilized to the expected responses of the FIR filters. Broadband beamforming can be fulfilled by applying these filters to each of the sensors in the array. By using the proposed method, designers need not to divide the whole designing frequency band into narrow subbands so as to make the narrow band assumption valid, which not only reduces the heavy designing burden, but also releases the requirement for measurements at fine frequency grids in the robust beamformer design. Results of both computer simulations and watertank experiments verify the effectiveness of the proposed method. 相似文献
9.
E. B. Kudashev 《Acoustical Physics》2007,53(5):629-637
Methods of experimental spatial filtering of wall pressure fluctuations beneath a turbulent boundary layer are developed with the aim of obtaining information on the wave number-frequency spectrum. The spatial filtering of the pressure field components by wave-vector filters is studied. The method of spatial filtering of pressure fluctuations by an acoustic array, i.e., a periodic structure with a finite number of elementary transducers, is analyzed. The relation between the wave number characteristic of the acoustic array and the wave number spectrum of the amplitude distribution of transducer’s local sensitivity is determined. Quantitative estimates are obtained for the sensitivity of the array to the wave number spectrum of turbulent boundary-layer pressures, which is necessary for measuring the wall pressure fluctuations in a turbulent boundary layer by wave-vector filters. 相似文献
10.
在以往窄带波束优化设计研究工作的基础上,提出了一种基于期望响应内插技术的宽带波束优化设计方法,目的在于避免宽带问题中由于频带划分过细带来的过重的设计负担,并使之可应用于稳健波束优化设计当中。该方法首先在设计频段内选取几个频率点,在每个频率点上设计得到相应的窄带波束优化权系数,并且根据每个阵元在不同频率点上的权系数构造一个宽带期望响应函数;然后用基于期望响应内插的FIR滤波器设计方法设计合适的FIR滤波器组,以使整个频段上的宽带波束优化得以实现。采用这种方法可以避免宽带波束优化设计中繁重的设计负担,并且在对实际声呐基阵进行宽带波束优化设计时只需少数几个频率点的测量值即可获得好的效果。仿真设计结果和实验研究表明了本文方法的有效性。 相似文献
11.
Shefeng Yan Author Vitae 《Applied Acoustics》2006,67(6):511-528
Two approaches to the optimal design of FIR beamformers with frequency invariant patterns using second-order cone programming (SOCP) are proposed. The first approach is a two-step method, which is implemented via separately optimal array pattern synthesis and optimal FIR filters design. The array weights for each frequency bin within the working frequency band are designed to insure that the array patterns approximate the reference ones. And the FIR filter corresponding to each sensor is designed to insure that the frequency responses approximate the array weights. The second approach is a direct method, in which the beam response is expressed as a linear function of FIR filter tap weights and the filters are designed by jointly optimizing the spatial and frequency responses to achieve the desired array patterns. All the optimal design problems (array pattern synthesis, FIR filter design and joint optimization) are formulated as the SOCP, which can be solved efficiently using the well-developed interior-point methods. Results of computer simulations and lake experiment for a twelve-element semicircular array confirm satisfactory performance of the two approaches proposed in this paper. 相似文献
12.
A O Santillán 《The Journal of the Acoustical Society of America》2001,110(4):1989-1997
The results of a theoretical study on global sound equalization in rectangular rooms at low frequencies are presented. The zone where sound equalization can be obtained is a continuous three-dimensional region that occupies almost the complete volume of the room. It is proved that the equalization of broadband signals can be achieved by the simulation of a traveling plane wave using FIR filters. The optimal solution has been calculated following the traditional least-squares approximation, where a modeling delay has been applied to minimize reverberation. An advantage of the method is that the sound field can be estimated with sensors placed in the limits of the equalization zone. As a consequence, a free space for the listeners can be obtained. 相似文献
13.
V. V. Tyutekin 《Acoustical Physics》2011,57(3):305-310
14.
A method for generation of a wave-field that is a plane wave is described. This method uses an array of loudspeakers phased so that the field in the wave-number domain is nearly concentrated at a point, this point being at the wave-number vector of the desired plane wave. The method described here for such a wave-number concentration makes use of an expansion in spherical harmonics, and requires a relatively small number of measurement points for a good approximate achievement of a plane wave. The measurement points are on a spherical surface surrounding the array of loudspeakers. The input signals for the individual loudspeakers can be derived without a matrix inversion or without explicit assumptions about the loudspeakers. The mathematical development involves spherical harmonics and three-dimensional Fourier transforms. Some numerical examples are given, with various assumptions concerning the nature of the loudspeakers, that support the premise that the method described in the present paper may be useful in applications. 相似文献
15.
16.
This paper revisits a nearfield microphone array technique termed nearfield equivalent source imaging (NESI) proposed previously. In particular, various issues concerning the implementation of the NESI algorithm are examined. The NESI can be implemented in both the time domain and the frequency domain. Acoustical variables including sound pressure, particle velocity, active intensity and sound power are calculated by using multichannel inverse filters. Issues concerning sensor deployment are also investigated for the nearfield array. The uniform array outperformed a random array previously optimized for far-field imaging, which contradicts the conventional wisdom in far-field arrays. For applications in which only a patch array with scarce sensors is available, a virtual microphone approach is employed to ameliorate edge effects using extrapolation and to improve imaging resolution using interpolation. To enhance the processing efficiency of the time-domain NESI, an eigensystem realization algorithm (ERA) is developed. Several filtering methods are compared in terms of computational complexity. Significant saving on computations can be achieved using ERA and the frequency-domain NESI, as compared to the traditional method. The NESI technique was also experimentally validated using practical sources including a 125 cc scooter and a wooden box model with a loudspeaker fitted inside. The NESI technique proved effective in identifying broadband and non-stationary sources produced by the sources. 相似文献
17.
《中国科学:物理学 力学 天文学(英文版)》2010,(8)
This paper deals with the computational simulation of both scalar wave and vector wave propagation problems in infinite domains. Due to its advantages in simulating complicated geometry and complex material properties, the finite element method is used to simulate the near field of a wave propagation problem involving an infinite domain. To avoid wave reflection and refraction at the common boundary between the near field and the far field of an infinite domain, we have to use some special treatments to this boundary. For a wave radiation problem, a wave absorbing boundary can be applied to the common boundary between the near field and the far field of an infinite domain, while for a wave scattering problem, the dynamic infinite element can be used to propagate the incident wave from the near field to the far field of the infinite domain. For the sake of illustrating how these two different approaches are used to simulate the effect of the far field, a mathematical expression for a wave absorbing boundary of high-order accuracy is derived from a two-dimensional scalar wave radiation problem in an infinite domain, while the detailed mathematical formulation of the dynamic infinite element is derived from a two-dimensional vector wave scattering problem in an infinite domain. Finally, the coupled method of finite elements and dynamic infinite elements is used to investigate the effects of topographical conditions on the free field motion along the surface of a canyon. 相似文献
18.
T. Maniv B. Rosenstein I. Shapiro B.Ya. Shapiro R.F. Hung 《Physica C: Superconductivity and its Applications》2010,470(19):744-746
Dynamics of the flux lattice in the mixed state of strongly type-II superconductor near the upper critical field subjected to AC field and interacting with a periodic array of short range pinning centers is considered. The superconductor in a magnetic field in the absence of thermal fluctuations on is described by the time-dependent Ginzburg–Landau equations. For a special case of the δ-function shaped pinning centers and for pinning array commensurate with the Abrikosov lattice (so that vortices outnumber pinning centers) an analytic expression or the AC conductivity is obtained. It is found that below a certain critical pinning strength and for sufficiently low frequencies there exists a sliding Abrikosov lattice, which vibrates nearly uniformly despite interactions with the pinning centers. At very small frequencies the conductivity diverges at the critical pinning strength. 相似文献
19.
用时阈有限差分方法研究光纤微探针近场分布特性 总被引:9,自引:7,他引:2
采用三维时间域有限差分(FDTD)方法研究了扫描近场光学显微镜中光纤微探针的近场分布特性,研究结果表明,锥形裸光纤探针的近场光中,以从探针锥变区侧面泄露的光即传播场为主,当在探针的侧面镀上一层金属膜对于从侧面泄露的光具有较好屏蔽效果,因而比裸光纤探针具有更好的空间束缚能力,无论是裸光纤探针还是金属膜探针,入射偏振光从针尖出射手发生了退极化现象,近场分布中产生与入射光偏振方向垂直的其它两个电场分量,而且金属膜探针的退极化分量对近场分布的影响比裸探针显著得多,如果在近场成像中接收退极化分量而不是总场则可以提高近场成像的对比度,还详细地分析了微探针的近场分布特征与退极化之间的关系。 相似文献
20.
A. I. Lomtev 《Technical Physics》2014,59(3):438-440
The ponderomotive force acting on a variable-charge granule in a dusty plasma from an intense ion-sound wave is considered. Allowance for oscillations of the granule charge in the field of an ion-sound wave makes it possible to reveal new components of this force that are proportional to the wave vector of the field and the cube of its amplitude. These components do not vanish in the case of a uniform field and also lead to a directed transport of the dust plasma fraction. 相似文献