Model of wind-generated ambient noise in stratified shallow wate

In order to build a rapid ocean ambient noise model adapted for a stratified shallow water, a hybrid model of normal mode method (for far field) and ray method (for near field) is suggested which combines the advantages of both methods. Since the near field of wind-generated noise is not sensitive to the sound speed pro- file, the sound speed profile is regarded as a constant; which makes the model rapid and accurate. The simulation results are in agreement with those of the wave model.

Shallow velocity structure of the Luoyang basin derived from dense array observations of urban ambient noise

Determining the shallow structure of a sediment basin is important when evaluating potential seismic hazards given that such basins can significantly amplify seismic energy. The Luoyang basin is located in the western He’nan uplift and is a Meso-Cenozoic depression basin. To characterize the shallow structure of the basin, we develop a model of the shallow high-resolution three-dimensional(3D)shear-wave velocity structure of the basin by applying ambient noise tomography to a dense array of 107 portable digital seismometers deployed over the basin. More than 1,400 Rayleigh-wave dispersion curves for periods in the range 0.5–5 s are extracted. The 3D variations of shear-wave velocity in the shallow crust are inverted using a direct surface-wave tomographic method with period-dependent ray tracing, with all the surface-wave group-velocity dispersion data being inverted simultaneously. The results show that in the shallow crust of the study area, the velocity distribution corresponds to surface geology and geological features. The Luoyang basin exhibits a low shear-wave velocity feature that is consistent with the distribution of sediment in the region,while the Xiongershan and Songshan uplifts exhibit higher shear-wave velocity structures. The results provide a shallow high-resolution 3D velocity model that can be used as a basis for simulation of strong ground motion and evaluation of potential seismic hazards.

Ambient Noise Tomography, Green’s Function and Earthquakes

Green’s function is well-known, among others, in the application of ambient noise tomography methodologies that may demonstrate the potential of hydrocarbon entrapment in the study area. Here it is also shown to be of key importance in identifying the fractal dimension in the unified scaling law for earthquakes as well as in studying an explicit relationship of a future strong earthquake epicenter to the average earthquake potential score. Such studies are now in progress.

3D Analysis and Investigation of Traffic Noise Impact from Hemmat Highway Located in Tehran on Buildings and Surrounding Areas

This study analyzes and investigates the impact of traffic noise on high rise buildings and surrounding areas by the side of Hemmat Highway that links west of Tehran to the east. In this study, a 3D traffic noise simulation model is applied on a GIS system. Visualized noise levels are formulated by the proposed model for noise mapping on all surfaces of the buildings and surrounding ground in a 3D platform. The investigation shows that there is a high traffic noise impact on the foreground and front facades of buildings, rendering these areas unsuitable for residential purposes. The ground area by the sides of buildings and the building side panels receive a lower noise impact. Most of these areas are still not acceptable for residential and even commercial use, only the back yards and back panels, have the lowest traffic noise impact. It also shows that the building height is not an effective factor for reducing motorway noise on the upper part of the building. Finally, construction cantilever barriers with a height of seven meters, close to the outer edge of the highway was presented as an effective way to reduce noise within the allowable range of noise pollution for commercial and residential purposes.

Experiments on Exploration of Shallow Fine Structures and the Construction of the 1-D Velocity Model in the Pingtan Island,Fujian

112 short-period seismographs were set up in the 400 km^2 area of Pingtan Island and its surrounding areas in Fujian.The combined observations of the airgun source and ambient noise source were carried out using a dense array to receive the 387 airgun signals excited around the island and one month of continuous ambient noise recording.The 1-D P-wave and S-wave shallow velocity model of Pingtan Island is obtained by the inversion of the airgun body wave’s first arrival time data,and the reliability of the velocity model is verified by using the surface wave phase velocity dispersion curve,which can provide initial model for subsequent 3-D imaging.The experimental results show that this experiment is a successful demonstration of local scale green non-destructive detection,which can provide basic data for shallow surface structure research and strong vibration simulation of the Pingtan Island.

Ambient noise near the sea-route

Ambient noise data measured in an experiment conducted in shallow water near a sea-route were analyzed. It was observed that, at low frequency, the horizontal correlation has an obvious difference from that predicted by the classical ambient noise model. The theoretical analyses show that this phenomenon is caused by wind noise together with the discrete shipping noise nearby. An ambient noise model was proposed to include the effects caused by both the noise sources. Data measured at different times verify that the proposed model can be used to forecast the ambient noise field in shallow water near the sea-route.

Joint inversion of Rayleigh group and phase velocities for S-wave velocity structure of the 2021 M_(S)6.0 Luxian earthquake source area,China

On September 16,2021,a MS6.0 earthquake struck Luxian County,one of the shale gas blocks in the Southeastern Sichuan Basin,China.To understand the seismogenic environment and its mechanism,we inverted a fine three-dimensional S-wave velocity model from ambient noise tomography using data from a newly deployed dense seismic array around the epicenter,by extracting and jointly inverting the Rayleigh phase and group velocities in the period of 1.6–7.2 s.The results showed that the velocity model varied significantly beneath different geological units.The Yujiasi syncline is characterized by low velocity at depths of~3.0–4.0 km,corresponding to the stable sedimentary layer in the Sichuan Basin.The eastern and western branches of the Huayingshan fault belt generally exhibit high velocities in the NE-SW direction,with a few local low-velocity zones.The Luxian MS6.0 earthquake epicenter is located at the boundary between the high-and low-velocity zones,and the earthquake sequences expand eastward from the epicenter at depths of 3.0–5.0 km.Integrated with the velocity variations around the epicenter,distribution of aftershock sequences,and focal mechanism solution,it is speculated that the seismogenic mechanism of the main shock might be interpreted as the reactivation of pre-existing faults by hydraulic fracturing.

基于类噪声扰动的电网惯量常态化连续估计方法

精确估计惯量是客观评估电网频率安全稳定性的关键环节,现有方法主要基于有功–频率大扰动的离散事件,无法对电网惯量连续估计。鉴于此,该文研究利用有功–频率类噪声扰动信息连续估计电网惯量的方法。首先以区域为对象,将断面联络功率和区域内负荷扰动作为输入、频率扰动作为输出,应用输出误差(output error,OE)模型对区域惯量进行估计,进而对各区域合并求解全网等效惯量。提出数据分段、移动数据窗的处理方式,对多段类噪声输入的OE模型分范围选阶辨识,并剔除离群值,获取充足的惯量估计样本及其均值,减小随机扰动引起的辨识误差。最后通过算例系统验证所提方法和模型的有效性及精确性。

海洋环境噪声预报建模与算法研究

对海洋环境噪声分布特征进行预报 ,是有利于探索抑制海洋环境噪声的有效方法。本文依据海洋环境噪声谱级的实测数据 ,利用三次样条插值法建立了海洋环境噪声预报模型 ,并对我国北海浅海区的环境噪声谱级进行了预报 ,预报结果与实测功率谱图基本一致。在建立海洋环境噪声预报模型的基础上 ,提出了海洋环境噪声生成算法 ,仿真表明 ,该算法能生成具有任何振幅分布的、谱级曲线满足要求的海洋环境噪声序列。因此 ,本研究在工程上有参考价值。

浅海内波对环境噪声水平方向凹槽的影响

典型夏季海洋环境噪声垂直指向性水平方向经常出现一显著凹槽。采用三维声速场海洋环境噪声理论模型,分析了各阶简正波对垂直指向性的贡献,指出不同阶简正波的贡献不同,高阶简正波是形成水平方向凹槽的主因,低阶简正波起填补环凹槽的主要作用,无内波时海面噪声源激发低号简正波的能量较低,填补能力较差,水平凹槽显著;内波活动期,内波改变了声信号的传播路径,引起不同阶简正波耦合,低号简正波能量增强,其填补噪声水平凹槽的作用明显加强,高阶简正波能量减少,凹槽变浅。还探讨了凹槽填补程度与内波强度之间的关系,以及有内波时环境噪声垂直指向性随时间的变化。

南海南部海域深海环境噪声统计特性分析

针对海洋噪声对声呐信号处理和声呐性能评估的背景干扰问题,本文分析了南海南部海域夏季和冬季实测深海环境噪声的深度分布、经验拟合和概率密度分布等统计特性;利用参数化模型得到了噪声谱曲线及其与风速、波高、1 kHz谱之间的经验拟合结果;提出了基于Weibull和Burr分布噪声谱级概率密度拟合方法。结果表明:400 Hz以下800 m以浅夏季噪声谱级中值比冬季高约6 dB,低频航船噪声谱级概率密度(PDF)服从Burr分布,高频风关噪声PDF近似服从高斯分布,夏冬两季噪声统计特性差异与中尺度涡旋分布、声信道传播损失和航船噪声源密度密切相关。

基于高斯混合模型的敞开式质谱重叠峰解析方法

针对敞开式质谱重叠峰影响待测物特征峰识别的问题,提出了基于高斯混合模型的重叠峰解析方法。根据手肘法和质谱图中各参数意义有效选取模型初始参数,然后研究了该方法在重叠峰不同幅值比、分离度和噪声下的解析效果,并对敞开式质谱实测冰毒碎片离子的重叠峰进行解析。结果表明,模拟数据的各个参数在解析后变化较小,均值和标准偏差的最大相对误差分别为0.4%和2%;实测数据在解析后可有效识别目标谱峰并使信噪比最高可提升10.2%,该方法解析效果好并且具有抗噪声干扰能力,可用于敞开式质谱重叠峰的解析。

混合高斯-指数噪声中水中目标信号的最佳检测

提出一种最佳检测器结构,应用于水中非高斯噪声背景下目标信号的检测。根据海洋环境噪声及水中目标辐射噪声信号特点,建立了海洋环境噪声模型,并研究了该模型下水中目标信号的最佳检测,通过仿真噪声数据以及实测海洋环境数据验证了检测性能。结果表明:文中设计的最佳检测器的性能优于传统的能量检测器,且检测性能的改善随着非高斯性的增强而更加明显。

基于水下滑翔机的海洋声学背景场观测技术

水下滑翔机作为新型水下无人平台,具有对海洋环境噪声进行长时序,大范围稳定观测能力。文中通过开展水听器与水下滑翔机集成应用研究,设计完成了具备海洋环境噪声测量能力的声学观测型水下滑翔机。基于水听器工作原理与水下滑翔机运动约束,并根据商用计算流体力学软件对流体水动力参数的计算结果,优化了水听器在水下滑翔机本体的安装位置。通过建立声学观测型水下滑翔机动力学模型,进行了运动仿真并确定最优运动参数,并于2019年5月在我国南海某海域进行了海上试验应用,获取了大量的水下滑翔机自噪声与海洋环境噪声数据。海上试验数据分析结果验证了声学观测型水下滑翔机的运动稳定性及其海洋声学背景场的观测能力。

基于AR模型的海洋环境噪声仿真预测研究

文章主要介绍了AR模型及其参数确定的基本方法。应用Matlab仿真软件,对海洋环境噪声信号的时间序列进行仿真分析,并对预测值与真实值进行比较。结果表明,应用AR模型预测得到的环境噪声信号很好地逼近了实测值,预测的功率谱也具有较高的精度,模拟的结果较好,为海洋环境噪声的预报提供了一种简单可行的模式。

一种适用于小干扰分析的在线负荷建模方法

负荷模型对小干扰稳定分析影响很大,然而目前的负荷建模方法利用大扰动的响应数据建立负荷模型,由于负荷具有时变性,大扰动时刻建立的负荷模型不能等效于替他时刻的负荷模型,故不适用于其他时刻的小干扰稳定分析。为解决上述问题,基于子空间法提出一种适用于小干扰分析的在线负荷建模方法。首先选择时时存在的类噪声信号作为辨识信号,并采用子空间法在线辨识负荷的状态空间模型,旨在通过在线建模解决由负荷时变性导致负荷模型不准确的问题。但是子空间法建立的负荷状态空间模型并不是实际负荷的状态空间模型,二者存在未知的线性变换,采用解析的方法证明了上述未知线性变换不影响小干扰分析的结果,从而说明所提出的负荷建模方法适用于小干扰分析。最后,在10机39节点系统验证了方法的有效性。

两种非高斯海洋环境噪声统计模型分析

海洋环境噪声是影响声呐工作的主要因素之一,噪声模型的选取十分重要,普遍采用的高斯噪声模型在很多情况下存在局限性。引出两种非高斯噪声模型匹配实际非平稳的海洋环境噪声:广义自回归条件异方差模型(Generalized Autoregressive Conditional Heteroscedasticity,GARCH)和双模模型,通过分析两种噪声的概率密度分布函数,并与高斯模型噪声和实测海洋环境噪声比较得出两种噪声模型的适用性。GARCH(1,1)模型通过调节参数可以吻合大部分浅海和深海海洋环境噪声,双模模型则只对浅海某些情况存在适用性,而对深海吻合性较差。两种噪声模型的统计特性分析表明它们可以适用于高斯噪声模型存在局限的非平稳环境下。

东印度洋海域风和降雨对环境噪声的影响

海面风和降雨对海洋环境噪声影响显著,利用海洋环境噪声模型结合风速和降雨率参数可对环境噪声谱级进行预报.本文研究了东印度洋海域环境噪声特性,分析了海面风速和降雨率对海洋环境噪声的影响规律,结果表明没有降雨时高频段噪声谱级与风速的相关系数可达0.59,存在降雨时高频段噪声谱级和降雨率的相关系数可达0.85,强降雨可使高频段环境噪声谱级增大6 dB以上.同时修正了风生噪声源级公式使其适用于东印度洋深海环境,修正后模型预报强降雨噪声谱级与实验数据整体误差在2 dB以内.利用小范围降雨噪声数据对模型进行验证时发现,在小范围降雨时噪声源模型采用海面非均匀降雨噪声源,比采用均匀噪声源的计算结果更加准确.修正后的风生及降雨噪声模型对东印度洋海洋环境噪声特性预报具有重要意义.

复杂地形对风关海洋环境噪声特性影响

海山/岛礁附近的海底地形往往复杂多变,起伏海底对海洋波导中的声传播具有重要影响,使海底地形多变海域的海洋环境噪声建模和仿真计算的难度增加。本文采用射线理论的N×2D和3D三维算法,依据变化海底地形海域的地形数据,建立了复杂海底地形海域的风关海洋环境噪声模型。模型的计算结果表明:在负梯度声速剖面条件下,接收点各方位扇区的海洋环境噪声级和垂直指向性,在海山/岛礁方位与平坦海底方位的结果明显不同;距海山/岛礁较近接收点的总噪声级略高于较远的接收点;在声速不随距离和方位变化的情况下,N×2D三维近似和3D算法所得到的风关噪声级的深度分布、噪声垂直指向性,以及扇区风关噪声级和垂直指向性虽有所区别,但变化趋势相同,对于复杂地形海域如水平方向声速不发生剧变,当计算时间有限制时,可选用N×2D算法计算风关海洋环境噪声特征。