Real-time acoustic classification of sperm whale clicks and shipping impulses from deep-sea observatories

The automated real-time detection and classification of cetacean and anthropogenic sounds from deep-sea observatories can play a key role to study cetaceans in the field, to quantify the impact of anthropogenic sounds or to initiate mitigation measures during potentially harmful human activities. In the area of the NEMO-ONDE deep-sea observatory, sperm whales are often present together with heavy shipping. The spatial coincidence of both sound sources allows for the long term monitoring of their interaction. Some ships produce impulsive sounds and the automated separation of these impulses from sperm whale clicks is not a trivial task. As part of a detection, classification and localisation system for acoustic data from marine observatories, we present four modules performing the automated real-time classification of clicks from sperm whales and impulsive sounds produced by ships. First, two modules detect segments that contain impulsive sounds within a specifiable frequency band and return the impulses’ positions. Then, two modules classify the detected impulses as sperm whale clicks or ship impulses. Finally, at the level of 22 s segments, the classification outputs from individual impulses are combined into a decision on the presence of sperm whale clicks or ship impulses. The modules’ reliability was tested on data from the NEMO-ONDE observatory. Training and testing data were separated by more than 2 months, enabling to assess the consistency of the predictions over the long term. The automated separation between segments of the two classes was high with area under the ROC curve (AUC) values between 0.94 and 0.98.     

Lower order three-dimensional Burgers equation having non-Maxwellian ions in dusty plasmas

The dust acoustic(DA) shock wave with dust charge fluctuations, non-Maxwellian ions, and non-isothermal electrons is studied theoretically. The perturbation technique is employed to derive the lower order three-dimensional(3D) Burgers equation, and shock wave solution is explored by the tan-hyperbolic method. The effects of flat trapped and trapped electron distributions in the presence of Maxwellian and non-Maxwellian ions on characteristics shock waves are observed. The temperature ratio of non-Maxwellian ion temperature and non-isothermal electron temperature is found to play an important role in forming the shock-like structure.     

Combined wave and ray based room acoustic simulations of audio systems in car passenger compartments,Part I: Boundary and source data

The present series of papers summarizes the results of a three-year research project on the realistic simulation of car audio sound in car passenger compartments using a combined Finite Element (FE) and Geometrical Acoustics (GA) approach. The simulations are conducted for the whole audible frequency range with the loudspeakers of the car audio system as the sound sources. The challenges faced during the project relate to fundamental questions regarding the realistic sound field simulation in small enclosures with strong modal and diffraction effects.The paper denoted here as Part I focuses on boundary and source representations in the FE and GA domain and suggests guidelines for a best-possible acquisition of the required data. Since a straight-forward determination of the boundary and source characteristics is mostly hampered by the immense complexity and inhomogeneity of the materials and loudspeaker configurations inside a car compartment, different measurement and calculation methods have been applied to determine the required data and quantify the corresponding uncertainty. The paper clearly points out the strength and weaknesses of the applied methods depending on the considered frequency range and material characteristics. In order to keep the complexity of the FE simulations at a manageable level, all passive boundaries were considered as locally reacting with impedance conditions.Part II of the study applies the obtained data in combined FE-GA room acoustic simulations and compares the simulated room impulse responses (RIR) with corresponding measurement results. In a final step the observed differences in the RIRs are related to the uncertainty and inherent errors in the boundary and source representation.     

The effects of air temperature and humidity on the acoustic design of voice alarm systems on underground stations

Sound attenuation of air due to climatic conditions is often assumed to be constant and/or negligible in the electro acoustic design of voice alarm (VA) systems. However, air attenuation variations can be significant in large underground spaces and particularly as the frequency increases to the mid to high frequencies which are the most relevant to speech intelligibility. This investigation evaluates and quantifies the impact of the variability of the most influential climatic parameters, air temperature and relative humidity, on the performance of VA systems in underground stations. Computer simulations were employed to predict the effect of varying these climatic parameters on key performance metrics. Results demonstrated a significant increase in the values of reverberation time parameters with both temperature and humidity, at frequencies critical for speech intelligibility. Consequently the values of speech intelligibility related metrics decreased with rising temperatures and humidity. Hence, the study shows how ignoring temperature and humidity effects can lead to calculation errors in the design of VA systems. These errors could cause over-specification of the absorption required of surface materials, and the inaccurate prediction of acoustic and speech intelligibility related parameters.     

Accuracy of speech transmission index predictions based on the reverberation time and signal-to-noise ratio

This paper examines the accuracy of the speech transmission index (STI) calculated from the reverberation time (T) and signal-to-noise ratio (L_SN) of enclosed spaces. Differences between measured and predicted STIs have been analysed in two rooms (reverberant vs. absorbent), for a wide range of absorption conditions and signal-to-noise ratios (sixteen tests). The STI was measured using maximum length sequence analysis and predictions were calculated using either measured or predicted values of T and L_SN, the latter assuming diffuse sound field conditions. The results obtained for all the conditions tested showed that STI predictions based on T and L_SN tend to underestimate the STI, with differences between measured and predicted STIs always lower than 0.1 (on a 0.0–1.0 scale), and on average lower than 0.06. According to previous research, these differences are noticeable and therefore non-negligible, as 0.03 is the just noticeable difference in STI. The use of either measured or predicted values of T and L_SN provided similar STI predictions (i.e. non-noticeable changes), with differences between predictions that are on average lower than 0.03 for the absorbent room, and lower than 0.01 for the reverberant room.     

Numerical simulations of the primary Bjerknes force experienced by bubbles in a standing ultrasonic field: Nonlinear vs. linear

The primary Bjerknes force experienced by a population of multiple bubbles in a liquid set in a nonlinear ultrasonic standing field and their translation are calculated and analyzed by numerical simulations. The force field is evaluated by considering the nonlinear bubble oscillations as well as the nonlinear character of the ultrasonic pressure field (both variables are unknown in the coupled nonlinear differential system). The results at small amplitudes agree with the classical theory on bubble translation, depending on the driving frequency in relation to the bubble resonance. It is shown that, when amplitudes are raised, the force field exhibits important modifications that strongly affect the motion of the bubbles and the way they form agglomerates. An analysis is performed on the importance of the terms in the differential system that provoke (a) the nonlinearity of the bubble oscillations and (b) the nonlinearity of the acoustic wave. This study reveals that both features should be considered to better approximate the primary Bjerknes force field. Simulations of the nonlinear ultrasonic field after the bubbles form agglomerates under the influence of this force are also performed.     

Forces on surface-piercing vertical circular cylinder groups on flooding staircase

Flooding into underground spaces has become a common threat and caused significant damages and casualties in the past decades. To improve the understanding of people walking through the flooding staircase, a 1:2-scale physical model of a staircase with rest platform was assembled. An instrument was developed to measure the hydrodynamic forces acting on individual vertical circular cylinders, as well as cylinder groups arranged side-by-side, in tandem and staggered cylinder arrays on the flooding staircase. The results show that the horizontal hydrodynamic force on a cylinder increases rapidly with the increasing of the inundated depth on the entrance of the staircase. With a side-by-side tight cylinder array, the force on the central cylinder is always larger than an isolated one. The force on the downstream cylinder in tandem cylinder array is always smaller. However, the drag coefficients of both cases are much larger than the corresponding ones in a horizontal bed channel. For the case of staggered cylinder array, the force on the downstream cylinder varies with the change of the transverse spacing and the longitudinal distance between cylinders.     

应用光纤布喇格光栅传感器监测地下管道腐蚀的新方法研究

地下管线工作环境恶劣,腐蚀是引起它破坏和失效的主要原因之一.本文提出了一种应用光纤光栅传感器监测管道腐蚀的新方法.输送石油和天然气等一些物质的管道内部存在的压力会使管道发生膨胀,进而导致管道外壁产生环向变形.假定管道为无限长,管道内部压力导致的管道外壁轴向应变可忽略不计,当管线发生腐蚀时,会导致管壁变薄,管道内部的压力又可以看作基本不变,这样就会增大管道外壁的环向应变.当管道内部压力保持恒定时,管道壁厚与应变之间存在一定的反比例关系,本文方法就是将封装好的光纤光栅传感器粘贴在管道外壁,通过监测外壁环向变形来判断管道腐蚀的情况和程度.通过理论值、模拟值和试验值三者的对比分析来说明了这种新方法是可行的,并且值得被广泛应用,为埋地管道的防灾减灾提供了一种对策.     

上海地铁隧道建设中工程地质条件及主要地质问题研究

随着上海地铁隧道建设大规模的展开,建设中面临的工程地质问题日趋凸现。本文结合上海市特有的地质条件,分析了与地铁隧道建设相关的工程地质条件,包括工程地质结构特征及浅部含水层地下水位特征。在此基础上,对地铁车站基坑开挖以及区间隧道施工可能面临的工程地质问题进行了分析研究,绘制了市中心地区工程地质问题严重性程度分区图,可为工程设计、施工提供从参考依据。     

Noise Shielding Using Acoustic Metamaterials

We exploit theoretically a class of rectangular cylindrical devices for noise shielding by using acoustic metamateriais. The function of noise shielding is justified by both the far-field and near-field full-wave simulations based on the finite element method. The enlargement of equivalent acoustic scattering cross sections is revealed to be the physical mechanism for this function. This work makes it possible to design a window with both noise shielding and air flow.