汤加火山喷发所产生的次声波

2022年1月15日汤加火山发生了剧烈的喷发。在火山喷发后的8 h 39 min,距离火山喷发位置10151 km的昆明次声台阵记录到很强的次声波信号。次声波波列前几个周期平均为443 s,传播速度约为321 m/s,其波形幅度与频率随时间变化与核爆炸产生的次声波形相似。采用相关检测方法估计次声信号的方位角为119°。在持续监测中,还观测到了火山喷发产生的次声信号沿反方向绕地球到达的信号和沿正方向绕地球一周后再次到达的信号。      

碎片云超高速撞击声发射信号特征分析

为了掌握带防护屏的航天器结构受空间碎片超高速撞击时的声发射信号特征,利用二级轻气炮发射球形弹丸撞击铝合金双层板结构,获取了碎片云撞击铝合金板舱壁产生的声发射信号,并利用小波包技术和能量熵理论对信号进行了分析。实验结果表明:弹丸初始速度、防护屏厚度及弹丸直径是决定二次碎片云形态及声发射信号特征的重要因素;在本实验工况范围内,小波包能量熵值能够描述声发射信号频率的复杂程度;当弹丸初始速度处于破碎段(3~7km/s)时,随着初始速度的增大,二次碎片云进一步细化,撞击产生的声发射信号幅值趋于减小、频率成分趋于复杂化,其小波包能量熵值逐渐增大;防护屏厚度对声发射信号的小波包能量熵值影响较大,弹丸直径对其影响较小。研究结果有助于实现对碎片云撞击舱壁结构的损伤模式识别。     

一种声发射信号方位角自适应监测算法*

四阶累积量可用于声发射信号处理,结合盲波束形成算法可对声发射信号的方位角进行估计。由于四阶累积量的计算量较大,采用迭代计算的思想,提出一种基于四阶累积量的自适应声发射信号方位角监测算法。与改进前的算法相比,自适应算法的计算复杂度和所需存贮空间均显著降低,可用于声发射信号的方位估计和监测。计算机仿真及实测数据分析均验证了算法的有效性。     

激冲次声信号简正波的分离

由于大气层的不均匀性,次声波分解成不同的简正方式来传播,它们有各自的相速度和群速度。当由一个声学阵接收次声波时,不同的简正波在声阵上产生不相同的时间延迟。本文根据各个简正波的主要能量分布在不同的频率区间,从理论上导出计算简正波相速度的平均数值和平均方位的方法,利用速度滤波估算出各个简正波的频谱,通过Weiner-Hopf滤波,从一个声阵接收到的数据中,估算出空间任何一点某个简正波的波形。最后给出了计算机模拟计算,其结果与理论上设定的十分接近。     

美国航天飞机“挑战者号”爆炸时所产生的次声波

1986年1月28日美国航天飞机“挑战者号”在离地面约15km的高空爆炸后约13h,在大约14300km以外的地面上用灵敏微气压计记录到很强的次声波列,其周期约为400—700s,振幅约为30Pa,传播速度约为300m/S,特征与核爆炸所产生的次声波相类似。 根据波列的各项特征估计,这次爆炸的当量约相当于140Mt TNT。这一估计当量由于爆炸高度远高于核爆炸而机构不同于一般大气中核爆炸的情况而偏高。     

南海夏季沿岸内波与定点声起伏特征分析

利用2020年6月海南岛沿岸试验数据,分析内波及声能量起伏特征。试验海域以全日潮内波为主,并伴随有高频内波活动。内波活动引起360 Hz单频信号20 km定点声起伏峰峰值超过30 dB, 320～400 Hz线性调频信号起伏峰峰值超过15 dB。利用测量数据结合数值仿真,讨论了内波引起单频信号和线性调频信号呈现不同起伏特征的原因。结果表明:试验海域内波活动导致单频声场模态间干涉条纹出现移动,进而导致接收位置处特定频率的声能量出现大幅度的快速起伏;由于带宽内的平均作用,宽带信号的能量起伏远小于单频信号的能量起伏。当内波传播速度变化时,各内波成分在声传播路径上出现的时间和位置发生了变化,使得声场出现剧烈起伏的时间也随之变化。     

火箭发射过程中助推作用的研究

假设火箭发射过程中采用助推手段, 我们计算了恒定力助推和弹簧力助推两种情况下火箭离开发射 塔时的速度和经历的时间, 比较了无助推情况下达到相同速度所需要的时间和飞行的高度, 由此得到了助推可以 节省燃料1% 以上的结论     

单轴压缩条件下岩石样品声发射信号的频谱分析

本文对单轴压缩条件下大理岩和辉长岩样品变形过程中的声发射信号进行了频谱分析,分析的范围从25—387kHz。应用高速数字化数据采集系统记录了岩石变形各阶段产生的声发射波形。对32个声发射信号进行了快速傅里叶变换处理(FFT),得到它们的振幅谱。比较了不同种类岩石的频谱以及频谱随应力的变化,找出了声发射信号的频谱分布范围。本文选取声发射信号振幅谱的主频f_Amax,峰个数n和单个声发射释放的能量IE三个参量对岩石声发射振幅谱作了统计分析,主要结果如下:(1)在岩石样品表面探测到的声发射信号包含多种频谱成份,并且频谱具有谐波特性。对本实验所使用的岩石样品尺度(直径2.5—5cm;长度5—10cm的圆柱形),声发射的主要能量分布在40—110kHz的频率范围内。(2)大理岩和辉长岩的主频分布没有明显的差异,但与样品大小有关。(3)岩石样品声发射频谱随压力的变化具有随机性质,没有显著的随应力增加而增大或减小的现象。     

大地震前出现的异常次声波观测研究

研究了一种在大地震前出现的异常次声波,揭示其与地震发生的空间、时间、强度的对应关系.利用CASI-ICM-2011型次声测量传感器在一系列Ms6.0级以上大地震发生前2周以内检测到的一种频率范围0.001 Hz至0.01 Hz的次声波,其特征有:幅值范围50 Pa至200 Pa,持续时间0.5 h至4 h,传播速度10 m/s至30 m/s,震级越高信号越强.通过建立广域次声传感器网络,成功定位了芦山地震前4天出现的异常次声波,以及巴基斯担地震前12天出现的异常次声波.通过对8年时间连续监测数据的分析,研究了这类次声波的出现规律.同时,对其产生机理提出了大地起伏激发次声波的假设,进行了理论论证,并用智利地震测量信号和玉树地震测量信号证明S波可以激发出本地同振的次声波.文中所列举的数个震前异常次声信号的观测结果对于地震预测的信息获取具有参考价值.     

流化床风帽故障的声发射检测

针对气固流化床中风帽故障影响流化质量问题,本文提出一种能够快速精确地检测出风帽故障位置和类型的声发射检测方法;声发射技术是一种实时、在线、非侵入流场的声波检测方法,利用均匀安装在流化床分布板下方的声发射传感器进行定位测量;采集气固流化床内颗粒撞击分布板产生的声信号,对该信号进行多尺度小波包分解,找出特征频段,由各个测点声发射信号总能量对比可以直观反应风帽故障存在位置,而各尺度能量分率的变化能进行故障类型判断;这种实时测量方法能更早,更精确的对风帽破损情况进行准确的判断。     

Field measurements of sonic boom penetration into the ocean

Six sonic booms, generated by F-4 aircraft under steady flight at a range of altitudes (610-6100 m) and Mach numbers (1.07-1.26), were measured just above the air/sea interface, and at five depths in the water column. The measurements were made with a vertical hydrophone array suspended from a small spar buoy at the sea surface, and telemetered to a nearby research vessel. The sonic boom pressure amplitude decays exponentially with depth, and the signal fades into the ambient noise field by 30-50 m, depending on the strength of the boom at the sea surface. Low-frequency components of the boom waveform penetrate significantly deeper than high frequencies. Frequencies greater than 20 Hz are difficult to observe at depths greater than about 10 m. Underwater sonic boom pressure measurements exhibit excellent agreement with predictions from analytical theory, despite the assumption of a flat air/sea interface. Significant scattering of the sonic boom signal by the rough ocean surface is not detected. Real ocean conditions appear to exert a negligible effect on the penetration of sonic booms into the ocean unless steady vehicle speeds exceed Mach 3, when the boom incidence angle is sufficient to cause scattering on realistic open ocean surfaces.     

基于小波分解的岩石破坏次声信息特征研究

次声探测是近年来在自然灾害临灾预警领域兴起的一种新方法,具有广阔的前景。为了研究岩石破坏次声信息特性,在室内试验的基础上采集了砂岩试件破坏前的次声信号,借助小波分析方法对信号的能量特征进行了分析。结果表明:岩石变形破坏次声信号能量主要集中在4～8 Hz的中频带和8～16 Hz的高频带两个频率范围内,中频带能量大于高频带能量,同时在低频带0～4 Hz内也存在一定的能量分布。随着岩石变形破坏程度的增加,次声信号的中低频带能量在相对减少,在岩石临近破坏前,次声信号的中低频带能量与高频带能量的比值接近1。上述特征的发现,为岩石破坏次声信号识别以及破坏前兆预警提供了重要依据。     

Infrasonic waves generated from the volcano eruption in Tonga

The Hunga-Tonga-Hunga-Ha'apai volcano in Tonga erupted violently on January 15, 2022. After 8 hours and 39 minutes, an infrasound array in Kunming at a distance of 10151 km away from the volcano recorded a sequence of strong infrasonic waves. The average period of the first four infrasonic waves is 443 s with propagation speed of 321 m/s. The azimuth angle of this event has been estimated by applying the progressive multi-channel correlation(PMCC) method to process the received signals. During continuous monitoring, the infrasonic waves propagating along and opposite to the direction towards the Kunming array around the earth are recorded respectively.     

Collective bubble oscillations as a component of surf infrasound

Plunging surf is a known generator of infrasound, though the mechanisms have not been clearly identified. A model based on collective bubble oscillations created by demise of the initially entrained air pocket is examined. Computed spectra are compared to infrasound data from the island of Kauai during periods of medium, large, and extreme surf. Model results suggest that bubble oscillations generated by plunging waves are plausible generators of infrasound, and that dynamic bubble plume evolution on a temporal scale comparable to the breaking wave period may contribute to the broad spectral lobe of dominant infrasonic energy observed in measured data. Application of an inverse model has potential to characterize breaking wave size distributions, energy, and temporal changes in seafloor morphology based on remotely sensed infrasound.     

Topographic effects on infrasound propagation

Infrasound data were collected using portable arrays in a region of variable terrain elevation to quantify the effects of topography on observed signal amplitude and waveform features at distances less than 25 km from partially contained explosive sources during the Frozen Rock Experiment (FRE) in 2006. Observed infrasound signals varied in amplitude and waveform complexity, indicating propagation effects that are due in part to repeated local maxima and minima in the topography on the scale of the dominant wavelengths of the observed data. Numerical simulations using an empirically derived pressure source function combining published FRE accelerometer data and historical data from Project ESSEX, a time-domain parabolic equation model that accounted for local terrain elevation through terrain-masking, and local meteorological atmospheric profiles were able to explain some but not all of the observed signal features. Specifically, the simulations matched the timing of the observed infrasound signals but underestimated the waveform amplitude observed behind terrain features, suggesting complex scattering and absorption of energy associated with variable topography influences infrasonic energy more than previously observed.     

Sound, infrasound, and sonic boom absorption by atmospheric clouds

This study quantifies the influence of atmospheric clouds on propagation of sound and infrasound, based on an existing model [Gubaidulin and Nigmatulin, Int. J. Multiphase Flow 26, 207-228 (2000)]. Clouds are considered as a dilute and polydisperse suspension of liquid water droplets within a mixture of dry air and water vapor, both considered as perfect gases. The model is limited to low and medium altitude clouds, with a small ice content. Four physical mechanisms are taken into account: viscoinertial effects, heat transfer, water phase changes (evaporation and condensation), and vapor diffusion. Physical properties of atmospheric clouds (altitude, thickness, water content and droplet size distribution) are collected, along with values of the thermodynamical coefficients. Different types of clouds have been selected. Quantitative evaluation shows that, for low audible and infrasound frequencies, absorption within clouds is several orders of magnitude larger than classical absorption. The importance of phase changes and vapor diffusion is outlined. Finally, numerical simulations for nonlinear propagation of sonic booms indicate that, for thick clouds, attenuation can lead to a very large decay of the boom at the ground level.     

A computational analysis of sonic booms penetrating a realistic ocean surface

The last decade has seen a revival of sonic boom research, a direct result of the projected market for a new breed of supersonic passenger aircraft, its design, and its operation. One area of the research involves sonic boom penetration into the ocean, one concern being the possible disturbance of marine mammals from the noise generated by proposed high-speed civil transport (HSCT) flyovers. Although theory is available to predict underwater sound levels due to a sonic boom hitting a homogeneous ocean with a flat surface, theory for a realistic ocean, one with a wavy surface and bubbles near the surface, is missing and will be presented in this paper. First, reviews are given of a computational method to calculate the underwater pressure field and the effects of a simple wavy ocean surface on the impinging sonic boom. Second, effects are described for the implementation of three additional conditions: a sonic boom/ocean "wavelength" comparison, complex ocean surfaces, and bubbles near the ocean surface. Overall, results from the model suggest that the realistic ocean features affect the penetrating proposed HSCT sonic booms by modifying the underwater sound-pressure levels only about 1 decibel or less.     

超声速全机带动力短舱对近场压力信号和地面声爆的影响

新一代环保高效的超声速商用飞机是近年来研究的热点, 低声爆技术是关键技术之一。研究声爆的影响因素有助于推进低声爆设计技术的发展。就超声速飞机整机而言, 发动机对近场和远场压力信号及地面声爆的影响颇为重要。国内外众多学者和研究单位对此进行了研究。中国商飞北研中心针对超声速带动力对近场压力信号和声爆的影响展开了一系列研究, 选取美国AIAA声爆预测会议提供的低声爆验证标模NASA C25D, 针对通气短舱和动力短舱构型进行了数值模拟和分析研究, 采用基于Euler方法和基于RANS方法的定常计算, 通过波形参数法由近场压力信号计算地面声爆信号, 并转化为可感知强度值, 与部分参会者的结果进行了对比。总结了黏性、是否带动力对超声速飞机近场压力信号和声爆的影响, 为未来超声速商用飞机的低声爆设计储备技术基础。      

Effect of the supersonic transport configuration on the sonic boom parameters

Results of numerical and experimental investigations of the sonic boom parameters for two configurations of civil supersonic transport are presented. Numerical modelling is performed by a combined method based on calculating the spatial flow in the near zone of the aircraft configuration and subsequent determination of disturbed flow parameters at large distances from the examined model. Numerical results are compared with experimental sonic boom parameters measured in the near zone and with results of their recalculation to large distances within the framework of the quasi-linear theory. This validation allows the degree of adequacy of the inviscid Euler model for solving the posed problem to be determined. Reasons for certain disagreement between the calculated and experimental data are discussed. The analysis confirms the possibility of attenuating the sonic boom generated by supersonic transport with an unconventional configuration based on a tandem arrangement of two wings on the fuselage.