Underwater moving noise source identification based on hybrid near-field acoustical holography

Near-field acoustical holography (NAH) is a powerful tool for identifying noise sources and visualizing acoustic field. By recording the acoustic pressures in the near-field, the acoustic quantities in the whole 3-D field can be reconstructed and predicted. However, the current theory of NAH is not applicable to tracking large scale moving noise sources. Therefore, the hybrid near-field acoustical holography is developed for reconstructing acoustic radiation, which is derived from statistically optimized near-field acoustical holography (SONAH) and moving frame acoustical holography (MFAH). The theoretical formulation is systematically addressed. This method enables us to visualize the noise generated by moving noise sources and the measurement array can be smaller than the source, which improves the practicability and efficiency of this technology. Numerical simulations are presented to demonstrate the advantages of hybrid NAH. Then, two experiments have been carried out with a line array of hydrophones. The results of simulations and experiments support the proposed theory, which shows the advantage of hybrid NAH in the reconstruction of an acoustic field in an underwater holographic measurement.

Underwater patch near-field acoustical holography based on particle velocity and vector hydrophone array

One-step patch near-field acoustical holography(PNAH) is a powerful tool for identifying noise sources from the partially known sound pressure field.The acoustical property to be reconstructed on the surface of interest is related to the partially measured pressure on the hologram surface in terms of sampling and bandlimiting matrices,which cost more in computation.A one-step procedure based on measuring of the normal component of the particle velocity is described,including the mathematical formulation.The numerical simulation shows that one-step PNAH based on particle velocity can obtain more accurately reconstructed results and it is also less sensitive to noise than the method based on pressure.These findings are confirmed by an underwater near-field acoustical holography experiment conducted with a vector hydrophone array.The experimental results have illustrated the high performance of one-step PNAH based on particle velocity in the reconstruction of sound field and the advantages of a vector hydrophone array in an underwater near-field measurement.

Underwater hybrid near-field acoustical holography based on the measurement of vector hydrophone array

Hybrid near-field acoustical holography(NAH) is developed for reconstructing acoustic radiation from a cylindrical source in a complex underwater environment. In hybrid NAH,we combine statistically optimized near-field acoustical holography(SONAH) and broadband acoustical holography from intensity measurements(BAHIM) to reconstruct the underwater cylindrical source field. First,the BAHIM is utilized to regenerate as much acoustic pressures on the hologram surface as necessary,and then the acoustic pressures are taken as input to the formulation implemented numerically by SONAH. The main advantages of this technology are that the complex pressure on the hologram surface can be reconstructed without reference signal,and the measurement array can be smaller than the source,thus the practicability and efficiency of this technology are greatly enhanced. Numerical examples of a cylindrical source are demonstrated. Test results show that hybrid NAH can yield a more accurate reconstruction than conventional NAH. Then,an experiment has been carried out with a vector hydrophone array. The experimental results show the advantage of hybrid NAH in the reconstruction of an acoustic field and the feasibility of using a vector hydrophone array in an underwater NAH measurement,as well as the identification and localization of noise sources.

NEAR-FIELD ACOUSTIC HOLOGRAPHY FOR SEMI-FREE ACOUSTIC FIELD BASED ON WAVE SUPERPOSITION APPROACH

In the semi-free acoustic field, the actual acoustic pressure at any point is composed of two parts： The direct acoustic pressure and the reflected acoustic pressure. The general acoustic holographic theories and algorithms request that there is only the direct acoustic pressure contained in the pressure at any point on the hologram surface, consequently, they cannot be used to reconstruct acoustic source and predict acoustic field directly. To take the reflected pressure into consideration, near-field acoustic holography for semi-free acoustic field based on wave superposition approach is proposed to realize the holographic reconstruction and prediction of the semi-free acoustic field, and the wave superposition approach is adopted as a holographic transform algorithm. The proposed theory and algorithm are realized and verified with a numerical example, and the drawbacks of the general theories and algorithms in the holographic reconstruction and prediction of the semi-free acoustic field are also demonstrated by this numerical example.

Novel Method for Selection of Regularization Parameter in the Near-field Acoustic Holography

Because of the ill-posedness of the near-field acoustic holography（NAH）,the regularization method is required to stabilize the computational process of NAH.The regularization effect is related to how to select the parameter correctly and effectively.However the L-curve method commonly used for the selection of regularization parameters has the disadvantages of wrong selection and incorrect selection,which influences the application of NAH.For the purpose of solving the problems existed in the L-curve method,the （？）-curve method is introduced into the field of NAH,and the performance applied to NAH directly is analyzed on the basis of equivalent source method-based NAH.However,it is found out via investigations that the（？）-curve method in NAH also has the problem of wrong selection and is unable to choose the regularization parameter correctly.In order to select the parameter correctly and effectively,a novel method for selecting regularization parameters is proposed based on the original（？）-curve method,which can be called improved （？）-curve method.In the proposed method the regularization parameters are discretized linearly between the largest singular value and the smallest singular value,and the solution norm and the residual norm corresponding to these regularization parameters are also described in a linear coordinate instead of in a lg-lg coordinate,which are the two main differences compared with the L-curve and with the original（？）-curve method.In linear coordinate and using the linearly discretized regularization parameters,the solution norm is a monotonically decreasing function of the residual norm as the increase of the regularization parameter,moreover the curve is convex everywhere.So the regularization parameters can be selected correctly and effectively based on the improved（？）-curve method.Then a numerical simulation is done with a simply supported plate to verify the validity of the proposed method.Experiments with two actual sources,a clamped plate and the double speakers,are carried out to do a further demonstration.The simulation result as well as the experimental result shows that the improved（？）-curve method is efficacious and has some advantages over the L-curve method and the original（？）-curve method.The proposed novel method is able to avoid the problem of wrong selection and to select the regularization parameter correctly even if the curve is smooth.

High-efficiency prediction method for helicopter global/ground noise based on near-field acoustic holography

Noise reduction program design is an effective approach that relies on efficient noise prediction for reducing ground noise during flight.The existing noise prediction methods have the limitations of being computationally expensive or only applicable to far-fields.In this paper,a High-Efficiency Prediction Method(HEPM)for helicopter global/ground noise based on near-field acoustic holography is proposed.The HEPM can predict the global noise based on acoustic modal analysis and has the advantages of high prediction accuracy and low time cost.The process is given as follows:firstly,the rotor noise on the holographic surface in the specified flight is obtained by simulations or experiments.Secondly,the global noise model,which maps time-domain noise to acoustic modes,is established based on near-field acoustic holography and Fourier acoustic analysis methods.Finally,combined with acoustic modal amplitude,the model established enables efficiently predicting the global/ground noise in the corresponding flight state.To verify the accuracy of the prediction method,a simulation study is conducted in hovering and forward flight states using a model helicopter with a 2-meter rotor and Rotor Body Interaction(ROBIN)fuselage.The comparison of HEPM with numerical results shows that the average prediction errors of the global and ground noise are less than 0.3 dB and 0.2 dB,respectively.For a region containing 100000 observers,the computation time of the HEPM is only one-fifth of that of the acoustic hemisphere method,demonstrating the rapidity of the proposed method.

RECONSTRUCTION STABILITY OF NEARFIELD ACOUSTIC HOLOGRAPHY

The distributed source boundary point method （DSBPM） is used as the spatial transform algorithm for realizing nearfield acoustic holography （NAH）, the sensitivity of the reconstructed solution to the measurement errors is analyzed, and the regularization method is proposed to stabilize the reconstruction process, control the influence of the measurement errors and get a better approximate solution. An oscillating sphere is investigated as a numerical example, the influence of the measurement errors on the reconstruction solution is demonstrated, and the feasibility and validity of the regularization method are validated. Key words： Acoustic holography Boundary point method Inverse problem Regularization

Study on Transient Properties of Levitated Object in Near-Field Acoustic Levitation

A new approach to the study on the transient properties of the levitated object in near-field acoustic levitation （NFAL） is presented. In this article, the transient response characteristics, including the levitated height of an object with radius of 24 mm and thickness of 5 mm, the radial velocity and pressure difference of gas at the boundary of clearance between the levitated object and radiating surface （squeeze film）, is calculated according to severa/velocity amplitudes of radiating surface. First, the basic equations in fluid areas on Arbitrary Lagrange--Euler （ALE） form are numericaJly solved by using streamline upwind petrov gaJerkin （SUPG） finite elements method. Second, the formed a/gebraic equations and solid control equations are solved by using synchronous alternating method to gain the transient messages of the levitated object and gas in the squeeze film. Through theoretical and numerical analyses, it is found that there is a oscillation time in the transient process and that the response time does not simply increase with the increasing of velocity amplitudes of radiating surface. More investigations in this paper are helpful for the understanding of the transient properties of levitated object in NFAL, which are in favor of enhancing stabilities and responsiveness of levitated object.

Nearfield acoustic holography in a moving medium based on particle velocity input using nonsingular propagator

Nearfield acoustic holography in a moving medium is a technique which is typically suitable for sound sources identification in a flow.In the process of sound field reconstruction,sound pressure is usually used as the input,but it may contain considerable background noise due to the interactions between microphones and flow moving at a high velocity.To avoid this problem,particle velocity is an alternative input,which can be obtained by using laser Doppler velocimetry in a non-intrusive way.However,there is a singular problem in the conventional propagator relating the particle velocity to the pressure,and it could lead to significant errors or even false results.In view of this,in this paper,nonsingular propagators are deduced to realize accurate reconstruction in both cases that the hologram is parallel to and perpendicular to the flow direction.The advantages of the proposed method are analyzed,and simulations are conducted to verify the validation.The results show that the method can overcome the singular problem effectively,and the reconstruction errors are at a low level for different flow velocities,frequencies,and signal-to-noise ratios.

基于声全息法和单目视觉技术的柴油机噪声可视化实现

柴油机属于多噪声耦合动力装置,其噪声的识别和控制是内燃机研究领域的难点。为实现柴油机噪声的可视化,本研究结合了近场声全息法与单目视觉技术,开发了基于Labview的声像匹配模块,测试系统人机界面友好,并通过已知声源试验验证了声像匹配模块的正确性。将验证后的测试系统应用于高压共轨柴油机对主/次推力侧声源进行识别,结果表明:在大气压力为80kPa、转速为1800r/min的最大扭矩工况下,主推力侧出现较大辐射噪声的位置为中冷器进气管、曲轴定时齿形带轮、排气管、脚架和涡轮增压器等;次推力侧辐射噪声峰值出现在起动机位置。

基于共同稀疏贝叶斯学习的多频等效源近场声全息方法

现有基于压缩感知的等效源近场声全息方法通常采用基于单频处理的单测量向量模型进行声场重建,此模型存在噪声鲁棒性较差以及重建精度不足的问题。实际中噪声源往往具有宽频特征,同一位置处不同频率的等效源源强聚集从而呈现共同稀疏特性,若充分利用源强的共同稀疏特性,可以改善重建性能。因此,提出一种基于共同稀疏贝叶斯学习的多频等效源近场声全息方法。在该方法中,首先采用多频协同处理,构建多频等效源近场声全息模型;然后为等效源源强施加共同稀疏约束,并使用共同稀疏贝叶斯学习方法求解等效源源强。与单频等效源近场声全息方法相比,所提方法可以获得更高的重建精度和更好的噪声鲁棒性。通过单极子声源仿真和小音箱试验验证了所提方法的优越性。

治疗超声系统中换能器声学性能的声全息法评估

换能器的聚焦特性等声学性能是治疗超声系统的重要参数之一,在出厂前和日常维护中须精确测量。目前常用的水听器测量法结果准确,但受声压幅度及测量效率的限制,高功率量程的声功率计造价较高;而基于声全息的表面振动模式测量法可作为高声压下水听器和声功率计测量法的补充,测量小声压平面并对高幅度声压焦域进行重建。为评估声全息法的准确性,文章研究了在小声压下使用基于声全息的表面振动模式测量法对声场进行测量和重建,分析该方法与水听器测量结果之间的功率和声压误差,以及影响误差的重要参数。结果表明,基于声全息的表面振动模式测量法可重建得到与水听器直接测量相近的结果,有望对高声压下工作的换能器的声场特性进行评估。

基于循环维纳滤波器的声学成像优化方法

针对混响环境中背景噪声干扰导致循环平稳源重建精度不高的问题,基于循环维纳滤波器,结合贝叶斯近场声全息技术,提出了一种声学成像优化方法。通过麦克风阵列在声源的近场测量由声源辐射信号的声压,利用循环维纳滤波器对测量值进行去噪,从而实现对循环平稳信号的盲提取,再应用贝叶斯近场声全息技术在空间上重建循环平稳源。首先,通过仿真分析,系统地评估了盲信号提取算法的有效性。然后,通过开展声源重建实验,进一步验证了该声学成像优化方法的可行性。

基于二级迭代的局部近场声全息研究及实验

为了有效减小传统近场声全息声场重建过程中的“窗效应”和准确利用有限测量孔径测量并定位潜艇的表面声源,提出一种基于二级迭代的局部近场声全息方法。首先,通过改进基于正交球面波的局部近场声全息方法,提出基于二级迭代的局部近场声全息方法;然后,仿真对比上述两种局部近场声全息方法的重构结果,研究外推误差和扩展测点数对重构精度的影响;最后,在消声水池中利用小孔径全息测量面进行基于二级迭代的局部近场声全息的实验研究。结果表明,基于二级迭代的局部近场声全息能大大减小有限测量孔径带来的“窗效应”和“孔径重复效应”误差,验证了该方法的优越性,可为水下大尺寸声源的近场声全息精确测量提供重要参考。

声全息测量架对近场时空频特性影响规律分析

在开展水下声全息测量时,常常忽略测量支架及其他辅助设备引起的测量误差。基于有限元法分析在Benchmark模型周围上加装声全息测量架后对近场声散射测量精度的影响。通过对共形圆环阵测量架提取多路测点的声场数据,分析入射波频率、角度以及测量架材料对近场声全息声场测量误差的影响。研究发现:在散射效应较弱的入射角度区间内加装声全息测量架,测量的散射声压变化较为敏感;分布在靠近声全息测量架处测点接收到的声学数据误差较大,出现较多峰值;材料特性阻抗较大的测量架引起的误差高于特性阻抗较低的测量架。

NEAR-FIELD SOURCE LOCALIZATION METHOD AND APPLICATION USING THE TIME REVERSAL MIRROR TECHNIQUE

In order to develop the acoustic keyboard for Personal Computer(PC),it is necessary to seek high-precision near-field source localization algorithm for identifying the keyboard characters.First of all,the focusing property of Time Reversal Mirror(TRM) is introduced,and then a mathe-matical model of microphone array receiving typing sound is established according to the realization of acoustic keyboard from which the TRM localization algorithm is carried out.The results through computer simulation show that the localization Root Mean Square Error(RMSE) performance of the algorithm can reach 10-3,which demonstrates that the algorithm possesses a high accuracy for the actual near-field acoustic source localization,with potential of developing the computer acoustic keyboard.Furthermore,for the purpose of testing its effect on actual near-field source localization,we organize three experiments for acoustic keyboard characters localization.The experiment results show that the positioning error of TRM algorithm is less than 1 cm within a provided acoustic keyboard region.This will provide theoretical guidance for the further research of computer acoustic keyboard.

Particle Velocity Sensor and Its Application in Near-Field Noise Scanning Measurement

The Particle Velocity Sensor (PVS) is a kind of acoustic transducer which measures the particle velocity directly with figure-of-eight directivity. This paper proposes a near-field noise scanning technology based on the research of PVS, pressure-particle velocity (P-U) probe, and its application in noise source identification. Firstly, the principle and characteristics of PVS are presented. Secondly, a P-U probe is designed on the basis of PVS development. Finally, the noise measurement experiment for a single source is arranged and conducted. The result shows that the proposed P-U probe performs well in near-field noise source identification and localization.

压缩感知等效源法对板件近场重构精度改进的研究

为改进目前板件压缩感知等效源法近场声全息中存在的稀疏基稀疏度不足、适用范围小等问题,提出一种优化等效源面范围的方法。使用板件振动模态与声辐射模态对板件倏逝波分布区域进行联合研究。利用板件振动模态得到高波数倏逝波分布情况,结合声辐射模态得到等效源向量在波数域分布情况,提出减小等效源范围从而达到过滤高波数倏逝波,减小重建误差的效果。数值模拟实验结果表明,该方法增加了等效源向量的稀疏度,对重建精度有大幅度的改善作用,扩大了压缩感知等效源法的使用范围。

联合扩散场激励与近场声全息重建的建筑构件隔声测量方法

提出了一种联合扩散场(DAF)激励与近场声全息(NAH)辐射声强重建的建筑构件空气声隔声测量方法。该方法首先通过DAF激励构件振动并获取入射声功率,然后利用NAH技术从辐射声压场中重建构件表面高空间分辨率的法向声强分布,最后根据声强分布来计算辐射声功率和定位辐射热区,从而实现构件隔声量和隔声缺陷测量。隔声室实验研究表明,在测试距离和采样间距均为0.04 m的条件下,该方法测量的隔声量与声压法的误差在100~5000 Hz频带小于3.3 dB,在250~3150 Hz频带小于1.3 dB,对圆孔(直径8 mm)和矩形缝(长80 mm、宽3 mm)的定位精度高达厘米级;同时,该方法在一定混响和背景噪声影响下的稳定性较强,接收室混响时间从1.0 s增至3.4 s(步长0.6 s)以及信噪比从10 dB降至0 dB(步长5 dB),隔声量测量误差分别在0.8 dB和0.3 dB以内,缺陷定位误差在0.037 m和0.035 m以内。所提方法有助于提高实验室中建筑构件隔声特性的测量能力,同时对接收室测试环境具有较强的鲁棒性。

基于球型传声器阵列的高分辨率低频波束形成算法

球型传声器阵列广泛用于三维空间噪声源定位,其分辨率取决于阵列的尺寸和输入信号的频率,当阵列较小时,不适合对低频噪声源进行定位,此外,为实现实时定位,要求算法的计算过程简单。球谐波束形成算法计算过程简单,但其低频分辨率差,不适合布置在小型阵列上。为使用固定尺寸的小型开口球型阵列对三维空间内的低频噪声源进行定位,并且避免增大计算量,提出一种基于球谐波束形成算法的高分辨率改进算法,该算法首先通过声全息算法对空间声场进行重构,然后将重构声场作为波束形成算法的输入,最后对三维空间进行搜索,实现声源定位。所提算法的声成像图更清晰,分辨率性能指标得到提高,证明重建声场可有效改善球谐波束形成算法的低频分辨率,使其更有利于实际应用。