压力罐中水声材料声学特性的参量源测量法

设计了一种原波频率500 kHz、差频范围1~30 kHz的截断宽带参量阵,作为水声材料测量系统的声源。通过分析典型频率下的宽带参量源指向性理论计算和实际测量结果,发现两者结果的曲线基本吻合,证明计算模型是正确的。应用钟形短时脉冲实现水声材料声特性的宽带测量,有益于降低样品边缘衍射干扰。并建立了测量水声材料大面积板状样品声压反射系数、声压透射系数和吸声系数的压力罐测量系统,罐体内尺寸Φ4 m×12 m,最高静水压4.5 MPa,测量频率范围1~30 kHz。对标准样品(尺寸1m×1m)进行了测量实验,其测量结果和理论曲线有很好的吻合,参量源测量法得到了验证;之后,通过对一块橡胶板样品在不同静压力下的吸声性能进行了测量和有效评估,进一步确认了参量源测量法在压力罐这样有限水域中的潜在应用价值。     

水声材料横波声速和衰减系数参量源法测量系统

提出了测量10-100 kHz频段水声材料平均横波声速和衰减系数的测量系统,系统具有低频、小尺寸、窄波束的特点。测量装置应用截断参量源作为声源,结合了精密的坐标系统。在对平板声压透射系数的平面波模型进行理论修正和实验研究的基础上,测量平板样品的透射系数(插入损失)的频谱和角谱,并采用曲线拟合方法来估计样品在测量频段的平均横波声速和衰减系数。在2 m×1 m×1.5 m消声水槽中,对一些典型样品(尺寸500 mm×600 mm)进行了测量实验,结果表明,水声材料样品在声波不同入射角时的声学性能有较大差异,不能用声波垂直入射时的声学性能数据代替;横波声速和衰减系数是评定水声材料声学性能的重要参数,尤其在声波斜入射情况下;在研究材料构件或复杂器件的声学性能时它们也是必不可少和不能不考虑的。实验还验证了测量方法和系统的可行性,也表明仅在这一频段的测量还远不能满足水声工程的实际需求,有必要将测量方法应用扩展到更低或更高的频段。     

水声材料构件声学特性自由场宽带测量装置

介绍一套新建的水声材料构件声学特性自由场宽带测量装置,在开放消声水池中测量水声材料构件大面积样品的复声压反射系数(回声降低)、复声压透射系数(插入损失)和吸声系数,为研究和评定声纳水下声系统、潜艇声隐身等项目所用的水声材料构件设备声学特性提供了标准测试/校准系统.装置应用了宽带压缩脉冲叠加法和宽带指向性声源,最低测量频...     

水声材料透声性能测量技术的改进

本文对传统的水声无源材料透声性能测量技术提出了几点改进,以便在小型消声水池中测量有限尺寸的大面积材料的插入损失（透射系数）随频率的变化规律。材料样品的典型尺寸为 １×１ｍ２左右,测量频率范围为 ２－２０ ｋＨｚ．文中对标准样品进行了声学性能测量,测量结果和平面波理论模型计算值有较好的吻合。     

一种新的水声无源材料声学性能测量装置

阐述了一种新的水声无源材料声学性能实验室测量装置,测量频率范围10-100kHz,最大静水压至3.0MPa,被测材料样品典型尺寸为300×300mm²。装置应用多基元平面换能器基阵,大面积声透明PVDF薄膜水听器以及宽带窄脉冲信号和现代信号处理技术,在小型压力罐中建立近似的平面波自由声场,测量材料声学性能随频率、静水压的变化规律。测量参数包括复反射系数(口声降低)、复透射系数(插入损失)、衰减系数、复声阻抗和纵波声速。通过对多种不同性能材料样品的测量分析,验证了本装置的测量能力,装置的稳定性考核表明其反射测量扩展不确定度为1.2dB,透射测量扩展不确定度为0.8dB。     

In search of a noncontact underwater acoustic source

The history of studies of the photoacoustic effect in liquids and its applications to the development of a “virtual” source of underwater acoustic signals is briefly reviewed. The problem of the efficiency of the photoacoustic conversion is considered. The modes of laser generation of sound, i.e., the thermooptical, nonlinear surface, and nonlinear bulk modes of operation, are discussed taking into account the real features of the marine environment, the most important of them being the surface waves. A review of the publications concerned with the problem of a moving photoacoustic source is presented. Advances in the photoacoustic underwater remote sensing technology are described.     

水声无源材料插入损失虚拟聚焦测量方法

提出了一种适合在有限尺寸水池中测量水声材料插入损失的方法,称为\     

A mixed method for measuring low-frequency acoustic properties of macromolecular materials

A mixed method for measuring low-frequency acoustic properties of macromolecular materials is presented. The dynamic mechanical parameters of materials are first measured by using Dynamic Mechanical Thermal Apparatus(DMTA) at low frequencies, usually less than 100 Hz; then based on the Principles of Time-Temperature Superposition (TTS), these parameters are extended to the frequency range that acousticians are concerned about, usually from hundreds to thousands of hertz; finally the extended dynamic mechanical parameters are transformed into acoustic parameters with the help of acoustic measurement and inverse analysis. To test the feasibility and accuracy, we measure a kind of rubber sample in DMTA and acquire the basic acoustic parameters of the sample by using this method. While applying the basic parameters to calculating characteristics of the sample in acoustic pipe, a reasonable agreement of sound absorption coefficients is obtained between the calculations and measurements in the acoustic pipe.     

水声目标识别中一种轴频提取方法

针对水声目标解调谱轴频提取中信噪比低和本舰干扰的问题,分析了最大似然比准则下的本舰干扰和目标的轴频检测问题,提出了基于模糊系统的采用累加处理改善信噪比和利用Doppler扩展抑制本舰干扰的轴频提取方法,对实录海上数据进行的试验表明本处理方法有效提高了检测性能。     

水下等离子体声源的冲击波负压特性

基于修正的Rayleigh气泡脉动方程对水下等离子体声源放电产生的 强声冲击波的传播过程进行了分析; 利用Euler方程作为控制方程组, 建立了水下等离子体声源的聚束声场模型, 通过仿真计算获得的传播云图对冲击波负压的形成机理进行了直观的理论分析. 结果表明: 经过聚能反射罩反射汇聚得到的聚束波在反射稀疏波和水的惯性作用下, 聚束波周围水域产生了拉伸, 形成负压区, 如果拉伸力大于水的抗拉上限, 就会使得水中形成不连续现象, 即出现空化气泡; 此外聚能罩边缘处产生的衍射波进一步加剧了负压的产生, 边缘衍射波最终与拉伸波叠加, 使冲击波负压达到最大值; 通过对比仿真波形和实验波形, 从而验证和进一步揭示了冲击波负压的形成原因. 研究结果对认识水下冲击波的传播规律和进一步改进等离子体声源的设计具有指导意义. 关键词： 等离子体声源 冲击波负压 聚束声场模型 气泡     

Direct regressions for underwater acoustic source localization in fluctuating oceans

In this paper, we show the potential of machine learning regarding the task of underwater source localization through a fluctuating ocean. Underwater source localization is classically addressed under the angle of inversion techniques. However, because an inversion scheme is necessarily based on the knowledge of the environmental parameters, it may be not well adapted to a random and fluctuating underwater channel. Conversely, machine learning only requires using a training database, the environmental characteristics underlying the regression models. This makes machine learning adapted to fluctuating channels. In this paper, we propose to use non linear regressions for source localization in fluctuating oceans. The kernel regression as well as the local linear regression are compared to typical inversion techniques, namely Matched Field Beamforming and the algorithm MUSIC. Our experiments use both real tank-based and simulated data, introduced in the works of Real et al. Based on Monte Carlo iterations, we show that the machine learning approaches may outperform the inversion techniques.     

水声材料性能的自由场宽带压缩脉冲叠加法测量

水声材料的许多声学特性一般可以通过对复反射系数和透射系数计算得到。本文提出一种新的自由场测量方法,即应用宽带脉冲压缩技术在消声水池中测量有限尺寸的大面积材料样品的性能参数,从而使这种标准测量的低频限被明显降低。除传统的回声降低和插入损失参数等外,两个新的参数——消声系数和去耦系数也在评价之列。文中对两块平板样品进行了实验测量,其尺寸约为1m×1m,测量频率范围为 2~20kHz。     

水声构件材料动态切变模量测量方法研究

阐述了一种新的水声构件材料动态切变模量测量方法,该方法利用宽带参量声源、精密坐标装置和信号处理技术,在小型消声水槽中可以准确测量频率范围20~100kHz、典型尺寸500×500mm²材料样品的动态切变模量。文中先后介绍了测量基本原理、实验装置,给出并分析了测量结果。     

海洋声学环境下水中声源的时延估计法定位精度分析

水中声源的定位精度受到海洋声学环境的重要影响。结合海上试验的实际应用,分析了水下观测平台采用时延估计法对声源的定位精度问题。根据理论分析,计算了时延估计误差、海洋中声速不均匀、平台非稳性、及声传播起伏等因素引起的俯仰角和方位角误差。利用误差传递公式,获得了上述因素引起的不同平台深度下,不同距离声源的定位误差。比较了采用平面阵与立体阵、是否补偿声线弯曲效应等条件下定位误差的变化,并通过海上试验结果进行了部分验证。研究结果表明,海洋声速不均匀对定位误差的贡献最大。采用立体阵代替平面阵、测量海洋声速剖面并补偿声线弯曲引起的定位误差,在1000m距离上可使定位相对误差从最大30%降低到约10%,有效提高了较远距离上的定位精度。研究结果对于采取措施提高水中声源的定位精度有指导意义。     

水声材料插入损失测量中的声波多途效应抑制方法

提出了一种在非自由声场中测量水声材料插入损失时抑制多途效应的方法,称为\     

A restraining multipath effect method for the measurement of insertion loss of underwater acoustic materials

A method suppressing multipath effect when measuring the underwater acoustic materials in a reverberant field is proposed, which is called "virtual end-fire array method".To weaken the coherence of the same-frequency reflection interference of each path, signal of different phases at different positions was transmitted by a single transducer in the simulation design, and a sharp directionality in the direction of the array length was formed. All signals at the above positions were superimposed t...     

水声材料低频声性能的行波管测量

发展了一种测量水声材料声学性能的行波管测量技术,能够在实验室充水管中模拟海洋水温水压环境,对样品的声学参数实施低频范围的测量。被测样品置于声管中央,声管两端配置一对发射器。应用主动消声技术使样品的透射声波在声管次发射器表面的反射可忽略,在管中建立起行波声场。然后,通过分别计算样品两边声场中每一对水听器的传递函数,得到样品的反射系数和透射系数。测量系统声管的内径为Φ208 mm,工作频率范围为100~4000 Hz,最高静水压为5 MPa。对水层和层状不锈钢样品的反射系数和透射系数进行了实际测量和理论计算,结果表明,测量值和计算值有较好的吻合,测量不确定度不大于1.5 dB。     

Traveling wave tube measurements for low-frequency properties of underwater acoustic materials

A traveling wave tube measurement technique for measuring acoustic properties of underwater acoustic materials was developed.Water temperature and pressure environments of the ocean can be simulated in a water-filled tube,and the acoustic parameters of samples of underwater acoustic materials are measured in the range of low-frequency.A tested sample is located at central position of the tube.A pair of projectors is separately located at both ends of the tube.Using an active anechoic technique,the sound wave transmitting the tested sample is hardly reflected by the surface of secondary transducer.So the traveling sound field is built up in the tube.By separately calculating the transfer functions of every pair of double hydrophones in the sound fields from the both sides of the sample,its reflection coefficients and transmission coefficients are obtained.In the measurement system,the inside diameter of the tube isΦ208 mm,the working frequency range is from 100 to 4000 Hz,the maximum pressure is 5 MPa.The reflection coefficients and transmission coefficients of a water layer and a stainless steel layer samples are measured actually and calculated theoretically.The results show that the measured values are in good agreement with the values calculated,and the measurement uncertainty is not greater than 1.5 dB.     

The measurement of acoustic properties of limited size panels by use of a parametric source

A method of measuring the acoustic properties of limited size panels immersed in water, with a truncated parametric array used as the acoustic source, is described. The insertion loss and reflection loss of thin metallic panels, typically 0·45 m square, were measured at normal incidence by using this technique. Results were obtained for a wide range of frequencies (10 to 100 kHz) and were found to be in good agreement with the theoretical predictions for plane waves. Measurements were also made of the insertion loss of aluminium, Perspex and G.R.P. panels for angles of incidence up to 50°. The broad bandwidth available from the parametric source permitted detailed measurements to be made over a wide frequency range using a single transmitting transducer. The small spot sizes obtainable with the parametric source also helped to reduce the significance of diffraction from edges of the panel under test.     

Wideband acoustic absorption characteristics of rubberized coir for underwater applications

Reflection and transmission coefficients of rubberized coir pads over the frequency band 200 kHz to 4 MHz are presented in this Paper. These results are compared with those reported for neoprene, paraffin wax, rubber car mat and plastic door mat¹. The rubberized coir pads were found to possess wideband absorption characteristics. It has been experimentally found that 0.05 m thick coir pads have almost 100% absorption in the frequency range 800 kHz-3 MHz with a maximum at 2.35 MHz. We have used this material for lining the water tank for underwater acoustic studies.