Assessment of acoustic iterative inverse method for bubble sizing to experimental data

Comparative study was carried out for an acoustic iterative inverse method to estimate bubble size distributions in water. Conventional bubble sizing methods consider only sound attenuation for sizing. Choi and Yoon [IEEE, 26(1), 125–130 (2001)] reported an acoustic iterative inverse method, which extracts the sound speed component from the measured sound attenuation. It can more accurately estimate the bubble size distributions in water than do the conventional methods. The estimation results of acoustic iterative inverse method were compared with other experimental data. The experimental data show good agreement with the estimation from the acoustic iterative inverse method. This iterative technique can be utilized for bubble sizing in the ocean.     

A model for variations in the range and depth dependence of thesound speed and attenuation induced by bubble clouds under wind-drivensea surfaces

When modeling sound propagation through the uppermost layers of the ocean, the presence of bubble clouds cannot be ignored. Their existence can convert a range-independent sound propagation problem into a range-dependent one. Measurements show that strong changes in sound speed and attenuation are produced by the presence of swarms of microbubbles which can be depicted as patchy clouds superimposed on a very weak background layer. While models suitable for use in acoustic calculations are available for the homogeneous bubble layer (which results from long time averages of the total bubble population), no similar parameterizations are available for the more realistic inhomogeneous bubble layer. Based on available information and within the framework of a classification scheme for bubble plumes proposed by Monahan, a model for the range and depth dependence of the bubbly environment is developed to fill this void. This model, which generates a possible realization of the bubbly environment, is then used to calculate the frequency-dependent change in the sound speed and attenuation induced by the presence of the bubble plumes. Time evolution is not addressed in this work     

A comparison of four methods for bubble size and void fractionmeasurements

We compare the performance of four different bubble-sensing techniques in a range of environment from the surf zone to the open ocean: a remote sensing method using high-frequency backscatter, two in situ methods using an acoustical resonator and a pulse propagation sensor, and a bulk method using electrical conductivity. Comparisons between the techniques show general consistency within the appropriate operational bubble density ranges, although spatial variability in bubble clouds introduces substantial variance. Each technique has its strengths and limitations. Our acoustical resonator is suitable for bubble concentrations with air fractions greater than approximately 10 ^-9 and the pulse propagation sonar for air fractions from 10 ^-6; the upper limit for both is constrained by attenuation and the validity of the Foldy scattering approximation. Both sensors can be implemented to encompass a wide frequency range with high resolution, corresponding to resonant bubble radii of 10~1200 μm. For air fractions higher than ~5×10^-4, bulk measurement using electrical conductivity provides a measure of air fraction. Sufficient overlap in operational air-fraction range exists between in situ acoustical techniques and conductivity measurement to permit comparison and demonstrate consistency in the measurement. Single- and multi-frequency backscatter sonars may be used for low air fractions (<1×10^-5) and provide a continuous vertical profile from a deployment beneath the active surface zone, but are subject to masking by dense bubble clouds and are unable to resolve high air fractions close to the surface. This study suggests that the best approach is to use a combination of sensors to probe the bubble field     

Attenuation Measurements Across Surface-Ship Wakes and Computed Bubble Distributions and Void Fractions

A surface ship's wake is composed of several hydrodynamic phenomena. A large part of that wake contains a mixture of air bubbles of various sizes in turbulent water. Eventually, as the wake ages, the turbulence subsides and bubbles begin to rise at rates that are determined by their sizes. These bubbles of various sizes and concentrations control the propagation of acoustic signals inside and across a wake. To further our understanding of these phenomena, a series of three continuous-wave (CW)-pulsed signals were transmitted across a wake as the wake aged. Each transmission contained a set of four 0.5-ms-long pulses. The 12 pulses ranged over frequencies from 30 to 140 kHz in 10-kHz steps. The acoustic attenuations across wakes that were due to varying bubble-size densities within the wakes were determined experimentally. From those data, estimates of the bubble densities as functions of the speed of the wake-generating ship, the wake's age, and acoustic frequency were calculated. From the bubble-density results, power-law fits and void fractions are calculated. The attenuation measurements were taken at 7.5-m intervals behind the wake-generating ship and continued for about 2 km. The experiment was run for wakes generated at ship speeds of 12- and 15-kn wakes, and the 15-kn run was repeated for consistence determination. The bubble densities were observed to have power-law forms with varying parameters with the strongest, for early ages, having an exponent of ${-}$3.6 and a void fraction of 4 $times$ 10$^{-7}$ , and with both diminishing for older wakes, as might be expected.      

Fine-scale acoustic tomographic imaging of shallow water sediments

In acoustic tomographic system capable of performing in situ two-dimensional (2D) acoustic imaging of shallow water sediments is described. This system is capable of resolving inhomogeneities greater than 10 cm and differentiating sound-speed variations greater than 2%, A tomographic inversion is performed in a 2D vertical slice of about 1 m ² (1 m×1 m) using three identical probes, with each consisting of 70 evenly distributed transducers. In normal deployments, two of the probes are oriented vertically and are separated by about 1 meter, and the third is positioned horizontally right above the two vertical probes. The additional horizontal probe greatly improves the horizontal resolution of the system compared to conventional crosshole tomographic setups. Numerical simulations are performed to evaluate the influences of arrival time detection error and transducer position error on the performance of the tomography system. For an arrival time of 500 ns (standard deviation) and a position error of 4 mm (standard deviation), sound-speed anomalies of greater than 0.8% can be correctly predicted near the upper portion (close to the horizontal probe) and are resolvable near the lower portion. A controlled laboratory experiment was conducted to evaluate the performance of the system. The location of a polyurethane block (Conap EN22) used as a known target is correctly predicted while the inverted sound speed is about 9% lower than that from its actual value. Field data taken from a saturated muddy site are presented and analyzed. The inverted mean sound speed and attenuation are about 1480 ms^-1 and 20 dBm^-1, respectively     

深圳湾浮游细菌生物量的时空动态及影响因素

自2015年5月至2016年3月在深圳湾布设了3个站位,对该海域进行了每季至少1次共7个航次的浮游细菌生物量调查。结果表明:(1)深圳湾浮游细菌生物量季节均值的变化范围为(4.90~86.90)×10^-2μg·mL^-1,总均值为3.14×10^-1μg·mL^-1;(2)深圳湾浮游细菌生物量的季节变化模式为:冬季(5.98×10^-1μg·mL^-1)>秋季(3.02×10^-1μg·mL^-1)>夏季(2.79×10^-1μg·mL^-1)>春季(7.52×10^-2μg·mL^-1);(3)从空间分布来看,浮游细菌生物量湾中含量最高,湾口其次,湾顶最低;(4)深圳湾浮游细菌生物量与亚硝氮含量呈极显著的正相关(P<0.01),与氨氮含量呈显著正相关(P<0.05);(5)深圳湾水体中浮游细菌丰度季节均值变化范围为(2.45~43.50)×10⁶个·mL^-1,年均值达1.57×10⁷个·mL^-1;(6)从整体的细菌丰度及生物量来看,深圳湾海域呈现富营养化状态,湾中最严重,湾口次之,湾顶最轻。     

Research on the sediment acoustic properties based on a water coupled laboratory measurement system

Abstract

The high-frequency acoustic properties of seafloor sediments are very significant in seafloor study and underwater acoustic study field. In order to measure the sound speed and the attenuation for the small-scale sediment cores more accurately, this study developed a water coupled acoustic laboratory measurement system based on Richardson-Briggs technique. This method used the correlation comparison of waveforms received in sediment core and in identical reference tubes filled with water to measure sound speed and attenuation. The sound speed and attenuation of a clayey silt sediment sample were measured using the water coupled acoustic laboratory measurement system. This frequency dependence of the sound speed and attenuation showed that the clayey silt sediment has a weak positive sound speed dispersion, while the attenuation increases with a strong positive gradient within the measurement frequency range. This study also noted that the measured sound speed ratio match well with the empirical equations from literature. The measured attenuation factor data can fall in the Hamilton’s empirical prediction range.     

南极普里兹湾海域湍流扩散系数估计

基于Thorpe尺度方法,利用CTD数据,计算了南极普里兹湾海域的Thorpe尺度和湍流扩散系数,分析了观测区域(64°～69°S,66°～80°E)湍流翻转现象的强弱及分布。结果表明,在海底和地形粗糙区存在较大的Thorpe尺度(较强湍流翻转)和湍流扩散系数,湍流扩散系数最大值能达到10^-2m²/s量级,比平坦开阔海洋高2～3个数量级,部分观测站位的湍流扩散系数和湍动能耗散率表现出大-小-大的垂向分布结构,总水深较深的区域尤为明显;深水区域的浮力频率在海表面到500 m层比较大,浅水区域该现象不明显;湍动能耗散率在(67.25°S,73°E)周围和经度为78°E的各站位都表现相对较大,能达到10^-6 w/kg量级,个别站位甚至能达到10^-5 w/kg量级。     

原位测量技术在黄海沉积声学调查中的应用

介绍了最新研制的基于液压驱动贯入的自容式海底沉积声学原位测量系统及其在南黄海中部海底沉积声学调查中的应用。该系统可以实现对海底沉积物声速和声衰减系数进行原位测量,通过液压驱动装置将四根声学探杆匀速贯入到海底沉积物中,减少了对沉积物的扰动,可按照预设的工作参数在海底全自动工作,无需甲板上人员实时控制,采集的声波信号自容式存储于存储单元。系统工作水深为500 m,测量深度为1 m,测量频率为30 kHz,采样频率为10 MHz。使用该系统在南黄海中部获得了40个站位不同类型沉积物的声学特性原位测量数据,并使用CTD剖面仪对该系统声速测量进行了标定,相对误差均小于0.5%,表明该系统测量数据准确、可靠。     

Experiments investigating the use of fiber-optic probes formeasuring bubble-size distributions

An experimental investigation was conducted in the laboratory in order to evaluate the use of fiber-optic probes for measuring the size distribution of large transient bubbles entrained beneath breaking ocean waves. Measurements were made in a unidirectional flow cell using two-fiber Optoflow fiber-optic probes (Photonetics Inc.). It was found that the rise times of the signal pulses created when bubbles crossed the probe tip were closely correlated with the bubble velocities. Therefore, bubble velocities and hence bubble sizes could be estimated using a single probe. It was observed that the correlation between the rise time and the bubble velocity varied significantly between probes but was only a weak function of water type (i.e., freshwater or seawater) and the bubble impaction angle. Estimates of the bubble-size distributions and void fraction made using the fiber-optic probes and video image data were compared. It was found that the fiber-optic probes could be used to obtain fairly accurate estimates of the void fraction. The bubble-size distributions estimated from the probe signals compared favorably with those estimated from video images. It was concluded that the probes could be used to make reasonably accurate measurements of the bubble-size distributions beneath breaking ocean waves     

Numerical investigation on the gas entrainment of ventilated partial cavity based on a multiscale modelling approach

Ventilated cavitation which is acknowledged as an efficient drag reduction technology for underwater vehicle is characterised by the very disparate length and time scales, posing great difficulty in the application of this technology. A multiscale numerical approach which integrates a sub-grid air entrainment model into the two-fluid framework is proposed in this paper to resolve the complex flow field created by ventilated cavity. Simulations have been carried out for the partially ventilated cavity underneath flat plate, with special efforts putting on understanding the gas entrainment at the cavity tail and the bubble dispersion process downstream. The flow parameters including the void fraction, the bubble velocity and the bubble size distributions in and downstream of the ventilated cavity are fully investigated. Comparisons between the numerical results with the experimental data are in satisfactory agreement, demonstrating the potential of the proposed methodology. The ventilation rate effect on the cavity shape and bubbly flow parameters are further investigated, obtaining the law of bubble dispersion and the bubble size evolution. This research not only provide a useful method for the investigation on the multiscale multiphase flow, but also give insight on understanding the combined drag reduction mechanism resulted from large-scale cavity and microbubbles.     

苏禄—苏拉威西海内孤立波动力参数时空变化特征

基于弱非线性理论及再分析同化数据,计算了苏禄—苏拉威西海冬季及夏季内孤立波动力参数,包括内孤立波线性速度、一阶和二阶非线性参数及线性色散参数,并研究了这些参数的时空变化特征。我们发现,虽然苏拉威西海域受到更加显著的西北太平洋水入侵,但苏禄海内孤立波动力参数的时空变化特征却比苏拉威西海更为显著。夏季苏禄海内孤立波线性速度总体上比冬季约大0.1m·s^–1;与此相反,夏季苏拉威西海内孤立波线性速度却比冬季约小0.05m·s^–1。无论是一阶或二阶非线性动力参数,其在苏拉威西海的时空变化均比较微弱,但在苏禄海则较为显著。苏禄海夏季一阶非线性动力参数比冬季高出约3×10^–3s^–1,但是夏季二阶非线性动力参数却比1月份低约3×10^–5m^–1·s^–1。此外,相比冬季,夏季苏禄海和苏拉威西海的色散动力参数均有所减弱,但其在苏禄海减弱的幅度更大。综上,苏禄—苏拉威西海环流引起的水体层化最大浮力频率所在深度的时空变化是造成上述内孤立波动力参数时空变化的根本...     

Calibration of a Seawater Sound Velocimeter

We calibrated a sound velocimeter to a precision of plusmn0.034 m/s using Del Grosso's sound-speed equation for seawater at temperatures of 2, 7.2, 11.7, and 18degC in a tank of seawater of salinity 33.95 at one atmosphere. The sound velocimeter measures the time-of-flight of a 4-MHz acoustic pulse over a 20-cm path by adjusting the carrier frequency within a 70-kHz band until the pulse and its echo are inphase. We used the adjustable carrier frequency to determine the internal timing characteristics of the sound velocimeter to nanosecond precision. Similarly, sound-speed measurements at four different temperatures determined the acoustic pathlength to micrometer precision. The velocimeter was deployed in the ocean from the surface to 4500 dbar alongside conductivity, temperature, and pressure sensors (CTD). We demonstrated agreement of plusmn0.05 m/s (three parts in 10⁵) with CTD-derived sound speed using Del Grosso's seawater equation from 500 to 4500 dbar after removing a bias and a trend     

小球藻EC04产胞内多糖条件优化及抗氧化活性研究

小球藻胞内多糖等活性物质具有多种重要生物活性和生理功能。为提高小球藻EC04胞内多糖的产率, 采用单因素实验和L₉(3 ⁴)正交实验优化对其培养条件进行优化。在暗光比12∶12、温度24±1℃和2000Lux光照条件下, EC04产胞内多糖的最佳条件为: MgSO₄·7H₂O浓度112.5mg·L ^-1, K₂HPO₄浓度60mg·L ^-1, NaNO₃浓度1.2g·L ^-1, 维生素B₁浓度0.5mg·L ^-1, 维生素B₁₂浓度0.1μg·L ^-1。在此条件下, EC04产糖率为271.74mg·g ^-1, 细胞密度为48.027×10 ⁶cells·mL ^-1, 与基础培养基相比分别提高了97.49%和34.91%。添加VB₁、VB₁₂等也在不同程度上影响小球藻胞内多糖产率。对所提取胞内多糖进行抗氧化活性初探, 结果表明其具有一定的自由基的清除能力, 对DPPH·(1-二苯基-2-三硝基苯肼)和·OH(羟自由基)的最大清除率分别达到了82.32%和64.27%。     

基于精细温度观测的南海东北部陆坡-深海盆底层湍流混合*

南海是存在强湍流混合的边缘海之一, 但前人对南海湍流混合的研究更多关注的是中上层, 对底层则鲜有关注。本文基于高分辨率温度传感器于2019年5月在南海东北部22个站位海底上方0.5m处持续观测4.4d的温度数据, 分析了2216~3200m深度范围内底层海水温度的时间变化特征, 并探讨了地形粗糙度和内潮对底层湍流混合的影响。分析结果表明, 南海东北部各站位底层海水的温度变化量级约为10^-4~10^-3℃; 温度变化趋势与正压潮变化趋势不同, 温度能谱显示多数站位在全日和半日频带区间出现谱峰, 温度变化更多地受斜压潮影响, 全日、半日内潮起主要调制作用。陆坡-深海盆过渡区及深海盆底层的湍动能耗散率量级为10^-10~10^-9m²∙s^-3, 涡扩散系数量级为10^-4~10^-3m²∙s^-1。观测数据未能显示底层湍流混合与地形粗糙度存在明显的相关性。底层湍流混合的空间分布与过去观测到的南海北部深海盆内潮的南北不对称性分布一致。     

First arrival cycle-based calculation methods of in situ sound speed and attenuation in sediments

The acoustic properties of seafloor sediments are of great importance in geoacoustic modeling, detecting, and oceanic engineering. The methods based on the first arrival cycle are investigated to calculate sound speed and attenuation of sediment more precisely in in situ measurements. The comparison of different data analysis methods based on the first arrival cycle approach for in situ measurement results in the following conclusions: (1) the calculated methods can help find the effective cycles and reduce the errors in calculating sound speed and attenuation; (2) using this approach, the point judgment method-based data analysis has the same effectiveness as the cross-correlation method-based data analysis in calculating group sound speed and has the same effectiveness in calculating attenuation in the time domain as the spectrum analysis method-based data analysis has in calculating attenuation in frequency domain; and (3) measurement in water can help not only calibrate the transmitting distance but also can calculate the time delay for the sound speed and the attenuation loss in the transmitting process. Finally, theoretical calculation was used to calculate the measured results, indicating a good agreement, which supports that first arrival cycle-based calculated methods can be used to analyze the measured data and the effective density fluid model can be used to analyze more acoustic properties and invert several physical properties in this experiment.     

中国西沙群岛底栖甲藻热带库里亚藻(Coolia tropicalis)的形态学、系统发育及毒性研究

库里亚藻(Coolia)是一类广泛分布且具有生物毒性的海洋底栖甲藻。本研究对近年来在中国南海西沙群岛海域采集分离的4株库里亚藻, 通过光镜及电镜下的形态学观察, 并结合基于核糖体大亚基(large subunit, LSU)rDNA(D1-D3)和内部转录间隔区(internal transcribed spacer, ITS)的序列进行系统发育分析, 鉴定该4个株系为热带库里亚藻(Coolia tropicalis)。在卤虫(Artemia salina)生物毒性试验中, 热带库里亚藻不同株系毒素提取液对卤虫幼虫表现出了毒性差异, XS554株系的48h半致死浓度(LC50)为1.42mg·mL ^-1(约相当于1.1×10 ⁵cells·mL ^-1), 5XS15株系的LC50为1.92mg·mL ^-1(约相当于1×10 ⁵cells·mL ^-1)。     

利用高分辨率水体反射地震资料研究吕宋海峡以东黑潮区混合

混合过程是海洋中普遍存在的一种形式, 对气候变化、物质分布等起到了重要作用。地震海洋学是近十多年发展起来的一门新兴学科, 被广泛应用到物理海洋学问题的研究中, 具有高空间分辨率的突出优点。文章利用反射地震资料, 通过斜率谱方法, 分别获得了吕宋海峡以东黑潮区湍流段与内波段的耗散率及扩散率。结果显示, 在剖面深度200~800m的平均耗散率为10 ^-7.0W·kg ^-1, 平均扩散率为10 ^-3.3m ²·s ^-1, 比大洋统计均值10 ^-5.0m ²·s ^-1高约1~2个量级, 与前人在吕宋海峡的观测结果相一致。湍流段和内波段的扩散率空间分布差异较大: 湍流段扩散率高值区对应强流区域, 推测这里是中尺度涡边缘, 其次中尺度不稳定过程引起扰动增强, 进而引起湍流混合的加强; 内波段扩散率高值区出现在吕宋岛弧附近, 推测是内波遇到岛弧地形发生破碎, 进而引起强的内波混合。     

Mid- to High-Frequency Acoustic Penetration and Propagation Measurements in a Sandy Sediment

During the recent 2004 Sediment Acoustics Experiment (SAX04), a buried hydrophone array was deployed in a sandy sediment near Fort Walton Beach, FL. The array was used to measure both the acoustic penetration into the sediment and sound speed and attenuation within the sediment while a smaller, diver-deployed array was also used to measure sound speed and attenuation. Both of these systems had been deployed previously during the 1999 Sediment Acoustics Experiment (SAX99). In that experiment, the buried array was used to make measurements in the 11–50-kHz range while the diver-deployed array made measurements in the 80–260-kHz range. For the SAX04 deployment, the frequency range for the measurements using the buried array was lowered to 2 kHz. The diver-deployed array was also modified to cover the 40–260-kHz range. Unlike the SAX99 deployment, there were no obvious sand ripples at the SAX04 buried array site at the time of the measurements. To examine the role of sand ripples in acoustic penetration over this new frequency range, artificial ripple fields were created. For the high frequencies, the penetration was consistent with the model predictions using small-roughness perturbation theory as in SAX99. As the frequency of the incident acoustic field decreased, the evanescent field became the dominant penetration mechanism. The sound speed measured using the buried array exhibits dispersion consistent with the Biot theory while the measured attenuation exceeds the theory predictions at frequencies above 200 kHz.      

珠江磨刀门河口水位分布演变特征及其对人类活动的响应*

河口区水位受径流、潮汐、地形、人类活动等多因素影响, 其空间分布结构及变化复杂。作为河口动力结构的重要参数, 水位分布演变特征及机制的研究对水资源高效开发利用和河口治理具有重要指导意义。文章基于珠江磨刀门河口沿程马口、甘竹、江门、竹银、灯笼山和三灶6个测站1965—2016年月均余水位数据及马口站的月均流量数据, 分析人类活动影响下水位空间分布的异变, 采用双变量线性回归模型定量辨识水位分布异变的主要影响因素, 并初步讨论人类活动、动力结构、地形变化之间的相互耦合关系。结果表明, 基于平均水面形态变化参数(即曲率)可较好地指示河床冲淤变化趋势, 河段平均曲率为正, 指示河床趋于淤积, 曲率为负, 河床趋于冲刷侵蚀; 围垦、大规模挖沙、河道疏浚等强人类活动前, 磨刀门河口上、下段坡降大于中段(江门—甘竹段), 即中段存在一个水位坡降变缓的区域, 枯季低流量时中段水位坡降出现由海向陆方向的倒坡降, 强人类活动后, 余水位空间分布结构发生异变, 中段坡降增大、低流量时的逆坡降消失; 强人类活动引起的河床地形变化是磨刀门河口沿程水位空间形态发生变化的主要原因, 使口门段(三灶—竹银)和河口上段(甘竹—马口)水位曲率分别减小0.41×10^-4m·km^-2和1.04×10^-4m·km^-2, 河口中段(竹银—甘竹)水位曲率增大0.21×10^-4m·km^-2, 沿程曲率由正(下凹)-负(上凸)-正转变为负-正-负, 沿程河床也随之由淤积-冲刷-淤积趋势转变冲刷-淤积-冲刷趋势。