ST-LSTM-SA:A New Ocean Sound Velocity Field Prediction Model Based on Deep Learning

The scarcity of in-situ ocean observations poses a challenge for real-time information acquisition in the ocean.Among the crucial hydroacoustic environmental parameters,ocean sound velocity exhibits significant spatial and temporal variability and it is highly relevant to oceanic research.In this study,we propose a new data-driven approach,leveraging deep learning techniques,for the prediction of sound velocity fields(SVFs).Our novel spatiotemporal prediction model,STLSTM-SA,combines Spatiotemporal Long Short-Term Memory(ST-LSTM) with a self-attention mechanism to enable accurate and real-time prediction of SVFs.To circumvent the limited amount of observational data,we employ transfer learning by first training the model using reanalysis datasets,followed by fine-tuning it using in-situ analysis data to obtain the final prediction model.By utilizing the historical 12-month SVFs as input,our model predicts the SVFs for the subsequent three months.We compare the performance of five models:Artificial Neural Networks(ANN),Long ShortTerm Memory(LSTM),Convolutional LSTM(ConvLSTM),ST-LSTM,and our proposed ST-LSTM-SA model in a test experiment spanning 2019 to 2022.Our results demonstrate that the ST-LSTM-SA model significantly improves the prediction accuracy and stability of sound velocity in both temporal and spatial dimensions.The ST-LSTM-SA model not only accurately predicts the ocean sound velocity field(SVF),but also provides valuable insights for spatiotemporal prediction of other oceanic environmental variables.

Flow and sound fields of scaled high-speed trains with different coach numbers running in long tunnel

Segregated incompressible large eddy simulation and acoustic perturbation equations were used to obtain the flow field and sound field of 1:25 scale trains with three,six and eight coaches in a long tunnel,and the aerodynamic results were verified by wind tunnel test with the same scale two-coach train model.Time-averaged drag coefficients of the head coach of three trains are similar,but at the tail coach of the multi-group trains it is much larger than that of the three-coach train.The eight-coach train presents the largest increment from the head coach to the tail coach in the standard deviation(STD)of aerodynamic force coefficients:0.0110 for drag coefficient(Cd),0.0198 for lift coefficient(Cl)and 0.0371 for side coef-ficient(Cs).Total sound pressure level at the bottom of multi-group trains presents a significant streamwise increase,which is different from the three-coach train.Tunnel walls affect the acoustic distribution at the bottom,only after the coach number reaches a certain value,and the streamwise increase in the sound pressure fluctuation of multi-group trains is strengthened by coach number.Fourier transform of the turbulent and sound pressures presents that coach number has little influence on the peak frequencies,but increases the sound pressure level values at the tail bogie cavities.Furthermore,different from the turbulent pressure,the first two sound pressure proper orthogonal decomposition(POD)modes in the bogie cavities contain 90%of the total energy,and the spatial distributions indicate that the acoustic distributions in the head and tail bogies are not related to coach number.

Extension of sound field reconstruction based on element radiation superposition method in a sparsity framework

Nearfield acoustic holography(NAH)is a powerful tool for realizing source identification and sound field reconstruction.The wave superposition(WS)-based NAH is appropriate for the spatially extended sources and does not require the complex numerical integrals.Equivalent source method(ESM),as a classical WS approach,is widely used due to its simplicity and efficiency.In the ESM,a virtual source surface is introduced,on which the virtual point sources are taken as the assumed sources,and an optimal retreat distance needs to be considered.A newly proposed WS-based approach,the element radiation superposition method(ERSM),uses piston surface source as the assumed source with no need to choose a virtual source surface.To satisfy the application conditions of piston pressure formula,the sizes of pistons are assumed to be as small as possible,which results in a large number of pistons and sampling points.In this paper,transfer matrix modes(TMMs),which are composed of the singular vectors of the vibro-acoustic transfer matrix,are used as the sparse basis of piston normal velocities.Then,the compressive ERSM based on TMMs is proposed.Compared with the conventional ERSM,the proposed method maintains a good pressure reconstruction when the number of sampling points and pistons are both reduced.Besides,the proposed method is compared with the compressive ESM in a mathematical sense.Both simulations and experiments for a rectangular plate demonstrate the advantage of the proposed method over the existing methods.

The diffracted sound field from the transition region of an axisymmetric body in water

Understanding the physical features of the diffracted sound field on the surface of an axisymmetric body is important for predicting the self-noise of a sonar mounted on an underwater platform. The diffracted sound field from the transition region of an axisymmetric body was calculated by the geometrical theory of diffraction. The diffraction ray between the source point and the receiving point on the surface of an axisymmetric body was calculated by using the dynamic programming method. Based on the diffracted sound field, a simulation scheme for the noise correlation of the conformal array was presented. It was shown that the normalized pressure of the diffracted sound field from the transition region reduced with the increases of the frequency and the curvature of the ray. The flow noises of two models were compared and a rather optimum fore-body geometric shape was given. Furthermore, it was shown that the correlation of the flow noise in the low frequencies was stronger than that in the high frequencies. And the flow noise received by the acoustic array on the curved surface had a stronger correlation than that on the head plane at the designed center frequency, which is important for sonar system design.

High-stability electrostatic field micro sensor for sounding thunderstorm applications

In this paper,the design and experimental results for a novel high-stability sounding electrostatic field micro sensor are presented.By means of hermetic chip sealing,digital weak signal demodulation unit,and probe sensor structure design,harsh environmental adaptation problems such as low temperature,high humidity,low air pressure,waterfall are solved.The sensor has a high resolution of 14 V/m,a wide measurement range of±100 kV/m,and is proved to have superior stability and performance in sounding electric field experiments than traditional sensors under different kinds of weather.

A Sound Field Separation and Reconstruction Technique Based on Reciprocity Theorem and Fourier Transform

We show a method to separate the sound field radiated by a signal source from the sound field radiated by noise sources and to reconstruct the sound field radiated by the signal source. The proposed method is based on reciprocity theorem and the Fourier transform. Both the sound field and its gradient on a measurement surface are needed in the method. Evanescent waves are considered in the method, which ensures a high resolution reconstruction in the near field region of the signal source when evanescent waves can be measured. A simulation is given to verify the method and the influence of measurement noise on the method is discussed.

Theoretical and Experimental Research on the Sound Field in A Finite Duct

Based upon the theoretical analysis of the sound field in a finite duct and the spatialsampling principle,this paper applies the adaptive filtering technique to the measurement of thesound field in the duct with the distribution patterns of standing waves in the direction of thewaveguide and high—order wavefront on the cross section of the duct measured and the acousticmode theory proved by experimental results.

An Investigation on Feasibility of Pure Tone Sound Field Audiometry

It′s generally believed that the appropriate stimuli for sound field tests are warble tones and narrow band noise, while pure tone can only be a signal used in the free field and earphone listening conditions. In this study, we take a measurement of sound pressure distribution, sound field variability, and effects of frequency shifting on sound pressure levels (SPLs) at reference points of pure tone in an audiometric test room. It was found that the pure tone SPLs were also distributed uniformly at some sound field areas although it was not so well as warble tones. This indicated that the test results were relatively stable to head movement and/or frequency shifting in those regions, which was confirmed by the clinical measurements on 20 subjects with severe sensorineural hearing loss. Our study concluded that pure tones could also be suitable for sound field audiometry if subjects were seated at a proper location on the basis of the sound field calibrations.

Aerodynamic Sound and Flow Field Generated from Combinational Inclined Tapered Cylinder

This study deals with the aerodynamic sound, especially the Aeolian tone. One of the problems with the aerodynamic sound, noise reduction along a railway line is significant engineering issue for further speed-up of a high-speed train. In particular, a pantograph is one of the main aerodynamic noise sources of a high-speed train. As one of the methods for the aerodynamic noise reduction, this study proposes the tapered cylinder by a pantograph. In this paper, the aerodynamic sound and the wake flow of the combinational inclined circular cylinder and tapered cylinder are experimentally and numerically investigated in knuckle upstream and knuckle downstream. Also, we suggest that the surface of grooves such as wood grain interacts with the aerodynamic sound generated from the model. Here, it is considered that the comparison of aerodynamic sound between the model with grooves and without grooves. Consequently, reduction of the maximum aerodynamic sound is possible for the tapered cylinder in the case of knuckle downstream. Furthermore, the noise reduction method is effective that the model surface with grooves such as wood grain.

Wave Superposition Based Sound Field Reconstruction

In order to overcome the obstacle of singular integral in boundary element method （BEM）, we presented an efficient sound field reconstruction technique based on the wave superposition method （WSM）. Its principle includes three steps： first, the sound pressure field of an arbitrary shaped radiator is measured with a microphone array; then, the exterior sound field of the radiator is computed backward and forward using the WSM; at last, the final results are visualized in terms of sound pressure contours or animations. With these visualized contours or animations, noise sources can be easily located and quantified; also noise transmission path can be found out. By numerical simulation and experimental results, we proved that the technique are suitable and accurate for sound field reconstruction. In addition, we presented a sound field reconstruction systern prototype on the basis of this technique. It makes a foundation for the application of wave superposition in the sound field reconstruction in industry situations.

A simple algorithm to calculate the pulsed sound field of a wide-band linear phased array

A simple algorithm using an impulse response for a rectangular piston element is discussed. The impulse response of linear phased array is obtained hv stumming the impulse responses of rectangular piston elements with different delay times. The output response of the linear wide-band array is equal to the convolution of impulse response functions with wide-band pulse exeiting signal. Sound field distributions and impulse responses of three kinds of transducers are compared. The results can be used to optimize the parameters of the linear phased array transducers used in uhrasonie imaging in nondestructive testing （NDT）.

Improvement of Low-Frequency Sound Field Obtained by an Optimized Boundary

An approach based on the finite element analysis was introduced to improve low-frequency sound field. The optimized scatters on the wall redistribute the modes of the room and provide effective diffusion of sound field. The obtained through a 1：5 scaled set up. The results show that the optimized treatment has a positive effect on sound field and the improvement is obvious.

A Novel Algorithm for the Sound Field of Rectangular-Shaped Transducers

An alternative extension to the Gaussian-beam expansion technique is provided to simplify the computation of the ~esnel field integral for rectangular symmetric sources. From a known result that the circle or rectangle function is approximately decomposed into a sum of Gaussian functions, the cosine function is similarly expanded by the Bessel Fourier transform. Two expansions are together inserted in this field integral, it is then expressible in terms of the simple algebraic functions. As examples, the numerical results for the sound pressure field are presented for the uniform rectangular piston transducer, in a good agreement with those directly evaluated from the Fresnel integral. A wide applicability of this approach is discussed in treatment of the ultrasonic field radiation problem for a large and important group of piston sources in acoustics.

Experimental Validation and Application of a Phased Array Ultrasonic Testing Model on Sound Field Optimization

In safety dominant industries, nondestructive evaluation (NDE) is crucial in quality assurance and assessment. Phased array ultrasonic testing (PAUT) as one of the NDE methods is more promising compared with conventional ultrasonic testing (UT) method in terms of inspection speed and flexibility. To incorporate PAUT, the techniques should be qualified, which traditionally is performed by extensive physical experiments. However, with the development of numerical models simulating UT method, it is expected to complement or partly replace the experiments with the intention to reduce costs and operational uncertainties. The models should be validated to ensure its consistency to reality. This validation work can be done by comparing the model with other validated models or corresponding experiments. The purpose of current work focuses on the experimental validation of a numerical model, simSUNDT, developed by the Chalmers University of Technology. Validation is conducted by comparing different data presentations (A-, B- and C-scan) from experimental and simulated results with some well-defined artificial defects. Satisfactory correlations can be observed from the comparisons. After the validation, sound field optimization work aiming at retrieving maximized echo amplitude on a certain defect can be started using the model. This also reveals the flexibility of parametric studies using simulation models.

以声场测听方法评估插入式耳机和头戴式耳机的衰减值

目的研究在声场测试中,头戴式耳机和插入式耳机对不同频率声音的衰减作用。方法选取40名健听人,在声场条件下测试双耳裸耳听阈及双耳分别佩戴头戴式和插入式耳机双耳听阈,耳机均不给声。比较在声场条件下不同类型耳机对不同频率声音的衰减作用。结果头戴式耳机在0.25~8 kHz每倍频程的声音衰减值分别为6.13±2.40 dB HL、7.00±3.36 dB HL、12.50±3.92 dB HL、18.75±5.03 dB HL、28.25±6.56 dB HL、17.50±5.99 dB HL;插入式耳机在0.25~8 kHz每倍频程的声音衰减值分别为16.88±5.27 dB HL、18.13±5.27 dB HL、22.38±4.08 dB HL、31.25±4.49 dB HL、36.13±5.49 dB HL、35.50±6.68 dB HL。结论两种不同类型耳机对不同频率声音的衰减均有显著效果,对声音的衰减值随着频率的升高而增加,在1~8 kHz范围内效果更显著,插入式耳机的衰减效果明显优于头戴式耳机。

联合收割机滚动轴承故障诊断系统研究--基于声场空间分布特征

首先,介绍了联合收割机滚动轴承振动机理和故障特征,并研究了基于声场空间分布特征的故障诊断流程;然后,对联合收割机滚动轴承的声音信号采集及特征提取进行了深入研究;最后,利用神经网络算法的模式识别对联合收割机滚动轴承的故障进行诊断。验证结果表明:系统对联合收割机滚动轴承故障的综合诊断率为91.67%,系统具有可行性。

湘南坪宝矿田岩浆热液成矿系统深部探测与地球化学约束

湘南是我国乃至世界最重要的钨锡多金属矿集区之一,发育了坪宝、柿竹园、骑田岭等多个大型矿床(田)。随着浅部资源逐渐枯竭,成矿系统深延与探测成为找矿突破的重点,尤其是覆盖层下隐伏成矿岩体、流体运移通道与矿体赋存空间的准确识别。本文以湘南坪宝矿田为例,采用广域电磁、构造解析与地球化学等方法揭示了成矿系统的空间结构与物质组成:(1)矿田深部(<5 km)存在4个隐伏的燕山期花岗岩体,包括宝山、黄沙坪、大坊、野鹅塘,岩体呈现不规则形态;(2)岩体侵位受NNE走向、NE走向与NW走向的区域断裂交汇联合控制,其岩体接触带与次级断裂为主要的控矿构造;(3)断层破碎带中方解石、石英、赤铁矿等热液矿物为成矿流体活动留下的痕迹,可用来识别成矿流体的源区与路径;(4)科学钻探证实了矿体与成矿运移通道深延稳定,且可能与深部隐伏岩体导通;(5)宝山矿区西部、黄沙坪矿区东部、大坊与野鹅塘矿区深部应为该区未来找矿勘查的重点。通过广域电磁、构造解析与矿物地球化学分析可以深入认识隐伏岩体的空间形态与形成时代,构建成矿物质与流体的“源-运-储”模型,开展成矿系统的深部探测与成矿潜力评价。

论电场近区双频测深的可行性

非平面波区测深是频率域电磁勘探方法理论发展的重要动力。广域电磁法不对非平面波区电磁场表达式做简化,通过迭代求解获取全区视电阻率,极大拓展了人工源频率域电磁法的观测空间范围与探测深度。E-Ex模式是现今最为常用的广域电磁法观测模式,但其近区测深能力有限。本文探讨了两种广域电磁法E-Ex模式近区双频测深方案的可行性。首先,简述了高阶近似和低阶近似两种近区电场双频测深视电阻率计算方案的基本原理;然后采用一维模型进行数值模拟,对比了半空间模型中E-Ex模式不同场成分的强度与感应数的关系,计算了典型地电模型的视电阻率,分析了频率间隔及观测误差等对计算结果的影响。结果表明:高阶近似方案基本不具备可行性;低阶近似双频测深方案在理想条件下可以获得近区地电介质的变化信息,对地下低阻层反映更为灵敏,受观测角度、接地导线偶极长度及观测频率间隔等因素影响均较小,但对观测数据误差极为敏感,观测总场中较小的误差也将导致近区视电阻率信息提取失败。因此,广域电磁法E-Ex模式近区双频测深方案实际应用的关键在于控制观测精度。

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。

基于正则化声压匹配法的舱室声场复现

舱室噪声控制、声品质设计等研究通常需开展大量的声场测试试验,由于舱室实际试验成本较高,因此通过声场复现的方式在舱室模拟舱中复现所需求的声学环境,对于降低研究成本、开展重复性试验具有重要意义。本文面向舱室声环境复现需求,以经典声压匹配法为基础,建立了基于扬声器阵列输出的多目标点位协同复现算法,通过引入正则化技术,使算法对实际测试中的各类噪声具有更强的鲁棒性。在一个实际舱室模拟舱环境中搭建了复现系统,复现试验表明,本文算法可在指定舱内的多个点位上协同复现目标频响曲线,在宽频范围内相对误差小于5%,具有良好的精度,在舱室声环境复现应用中具有良好的前景。