旋转层化二维海洋波动连续谱的波包特征分析

对旋转层化二维海洋波动中重力惯性波和涡旋波连续谱波包的结构以及演变特征作了计算和分析,并得到以下结论:这两类波动的结构与演变各不相同。连续谱波包的演变不但依赖基本场的分布,而且还依赖初始扰动的结构。根据初始场的不同,扰动可衰减,也可先增长、再衰减,有时增长还很大,但其最终是衰减的。连续谱波包的结构随时间变化,然而构成该波包的连续谱其结构则不随时间变化,这是两者的最大差异。连续谱波包的上述演变特性表明,在有限时段扰动的演变中连续谱是不能被忽略的,在海洋波动演变中连续谱和离散谱的作用均须予以考虑和重视。     

大黄鱼噪声谱分析

一、序言海洋中自然噪声是水声探测仪器的水下主要干扰源之一。这些噪声源中起主要作用的有海水运动噪声,包括因风速变化引起海面扰动产生的噪声、船只噪声、以及生物噪声等。它们在不同频率上有不同的特性,而且在谱的任一区域中,这些源中的一个或几个将超过其他源起主导作用。显然,自然噪声是由海洋中各种声源组合的结果,这种不同组合构成了自然噪声谱特性随着不同海区和时间而不同。Wenz,G、M、[3]、     

大功率超低频膜结构电磁声源振动特性研究

膜结构电磁式声源具有体积位移大、超低频声场可控、适装性佳等显著优势,在扫雷声源方面具有广阔的应用前景。辐射膜是声源核心振动部件,研究辐射膜的振动特性对于电磁声源的设计及应用具有重要意义。研究了一种膜结构电磁声源振动特性的解析方法。首先,建立真空中电磁声源圆环膜自由振动的解析模型。其次,采用分离变量法求解得到真空中圆环膜自由振动的固有频率和振型,通过与文献数据对比及有限元仿真验证了理论解的正确性。然后,分析了不同边界条件下和圆环膜半径的变化对膜在真空中的振动特性的影响。最后,考虑声源实际水下工况粘性液体负载与内部填充压力的影响,得到了电磁声源实际工况中不同尺寸圆环膜低频强迫振动的幅频特性与声源振动体积位移。所提方法可较准确地反映实际工况下电磁声源振动特性与声辐射能力,可为大功率电磁声源的设计和结构优化提供重要参考。     

基于粘性流模型的筒型基础防波堤波浪力数值分析

筒型基础防波堤是一种新型港口海岸工程结构,其基础上部是由连续排列的圆筒构成的直立防浪墙.采用粘性流数值模型,研究连续圆筒防波堤上波浪力竖向分布、水平(沿圆筒环向)分布和波浪力合力特性,并对粘性流数值模型计算的平面直墙波浪力与海港水文规范方法计算结果;粘性流数值模型计算的连续圆筒墙面波浪力与平面直墙波浪力;无限长连续圆筒墙面波浪力与有限长连续圆筒墙面波浪力进行比较分析.针对所选工程算例,建议按<海港水文规范>中平面直墙波浪力计算方法确定连续圆筒防波堤上的波浪力时,波峰时考虑0.90左右的折减系数,波谷时考虑0.95左右的折减系数.     

浅海双跃层脉冲声传播

利用在东海测量的双跃层声速剖面和修改的单跃层声速剖面,数值模拟了2种跃层条件下不同收发深度声脉冲传播的波形。模拟结果表明,当声源或接收器位于上混合层时,信号波形在2种条件下都出现梳状多途结构。当声源和接收器都位于下混合层时,信号波形在2种条件下均相似。当声源位于中间均匀层时,信号波形在除上混合层以外的4层都有显著差异。用简正波的深度-简正波号域的幅度和相应的群速度解释了双跃层和单跃层声速剖面条件下信号波形特点以及异同的原因。     

深海海面目标单水听器被动测距方法与验证

基于射线理论分析了在深海情况下海面声源产生声场的频率-距离干涉结构,给出了影区内声场频率-距离干涉结构的近似理论表达式,分析得到影区内声场频域干涉周期随收发距离的增加而增大、随着接收水听器深度的增加而减小。因此由单水听器记录的声场干涉结构即可实现被动声源距离估计。在南海深海实验中观测到海面宽带噪声源在声场影区形成的声场干涉结构,对实验获得声场干涉结构的处理结果验证了深海声场影区干涉结构用于被动声源距离估计的有效性。与传统的匹配场被动定位方法相比,该方法不需要已知海底声学参数和大规模的拷贝场计算。     

电火花和气枪声源在深层剖面仪中应用分析

本文介绍了深地层剖面仪中应用的两种声源——电火花和气枪声源,分析了这两种声源的特性及其在应用上的差异,导出了在测试时存在虚源效应的声能计算表达式,并给出某些典型的海上探测地层剖面图。     

海底、海面的边界反射对浅海环境噪声场的影响

关于海洋噪声谱级的理论,测量和分析以及相应噪声源的机理探讨已经有大量的工作;例如Knudson[6];EcKarf[2];Weng[10]和Piyyof[7]的工作.文〔1〕采用分层介质中的传播算子,推广了EcKarf的工作,建立了一般情况下由源特性及传播算子所表达的噪声场表示.目前关于传播条件--在浅海中特别是海底的反射特性--对环境噪声场特性的影响还较少有具体的结果.     

水下打桩和船舶噪声对斑海豹听觉影响的初步分析

通过测定水下打桩和船舶噪声,利用Matlab软件对两类典型海洋噪声的时-频统计特性进行分析,结合斑海豹听阈和发声频域特性,分析水下打桩和船舶噪声对斑海豹的影响.结果表明:水下打桩及船舶噪声的主要能量分布频段(0～4.0 kHz)与斑海豹听阈敏感频段(0.1～ 100.0 kHz)及发声频段(0.4 ～ 1.5 kHz)相重叠;水下打桩噪声所产生的强噪声声源级(206 dB)会高于斑海豹可忍受的最高声源级(190 dB).由此推断,两类噪声会对斑海豹的生境产生严重干扰,轻者可能导致斑海豹的习性改变及感知和交流能力减弱,重者则会造成斑海豹的听阈丧失.本研究为斑海豹的声学保护提供声学参数依据,并为进一步深入研究提供参考.     

表面噪声源的噪声场时空相关函数

噪声场的时空相关数由于在抗干扰应用上的重要性,已引起人们的注意,并已做了一些理论和实验的研究。 噪声场时空相关函数的较早期工作是厄卡特作的,他建立了所讨论的空间内无噪声源时的时空相关函数所满足的微分方程组,从而导出了均匀各向同性噪声场的时空相关函数的表式。1962年,柯罗尼与谢曼就海水介质是均匀和无吸收的情况,计算了两种噪声模型的单频归一化空间相关函数。1966年,许祯镛采用传播网络算子工具,建立了所讨论区域内     

A study on propeller noise source localization in a cavitation tunnel

Localizing noise sources in cavitation experiments is an important research subject along with predicting noise levels. A cavitation tunnel propeller noise localization method is presented. Propeller noise measurement experiments were performed in the MOERI cavitation tunnel. To create cavitating conditions, a wake-generating dummy body was devised. In addition, 10 hydrophones were put inside a wing-shaped casing to minimize the unexpected flow inducing noise around the hydrophones. After measuring both of the noises of the rotating propeller behind the dummy body and acoustic signals transmitted by a virtual source, the data were processed via three objective functions based on the ideas of matched field processing and source strength estimation to localize noises on the propeller plane. In this paper, the measured noise analysis and the localization results are presented. Through the experiments and the analysis, it was found that the source localization methods that have been used in shallow water applications could be successfully adapted to the cavitation tunnel experiments.     

Deep-ocean vertical noise directionality

The structure of beam noise measured at the output of a vertical array in a range dependent ocean basin was investigated using the modified wide-angle parabolic equation (PE). Noise sources were distributed throughout the basin, and the field due to each noise source at an array located in the midbasin was calculated. The response of the array to the superposition of the noise sources was found by beamforming. An efficient and direct approach that superimposes the noise sources on the PE field as the field is marched toward the array was developed. Downslope calculations of the midbasin vertical directionality were made between 50 and 400 Hz with this technique. Use of a geoacoustic model shows that the bottom behaves as a low-pass filter     

Parameterization of ocean wave-induced mixing processes for finite water depth

Three dimensional wave-induced mixing plays an important role in shallow water area. A quite direct approach through the Reynolds average upon characteristic length scale is proposed to parameterize the horizontal and vertical shallow water mixing. Comparison of finite depth case with infinite depth results indicates that the difference of the wave-induced mixing strength is evident. In the shallow water condition, the infinite water depth approximation overestimates the mixing strength in the lower layers. The nonzero horizontal wave-induced mixing presents anisotropic property near the shore. The Prandtl’s mixing length theory underestimated the wave-induced mixing in the previous studies.     

海洋表面偶极子辐射模型的噪声场时空相关函数的计算

由于海面噪声源都可以抽象成偶极子辐射源,因此,研究海水表面偶极子辐射模型的噪声場的时空相关函数是有实际意义的。 设偶极子辐射源均勻而独立地分布在海水表面上,其辐射谱为S,则具有时延为的两点     

安达曼海内孤立波的潜标观测分析研究

安达曼海是内孤立波生成最多的海域之一,目前对其研究大多基于卫星遥感,缺乏基于现场观测资料的相关研究。本文通过2016年至2017年布放在安达曼海中部的锚系潜标对该海域内孤立波的方向和强度进行研究,结果表明在研究区域内孤立波主要向东北方向传播,最大振幅可达100 m。应用彻体力理论预测了研究海域内孤立波波源的分布,与遥感统计结果基本一致,并且波源位置更精确,可直观地给出不同波源激发内孤立波的能力。本文分别用浅水方程、深水方程和有限深方程对安达曼海中部内孤立波相速度进行模拟,结合卫星遥感分析发现该海域内孤立波的产生符合Lee波机制,在三种方程中有限深方程的模拟效果与潜标观测最相符。     

Nonlinear saturation-based whitecapping dissipation in SWAN for deep and shallow water

This study investigates the effectiveness of a revised whitecapping source term in the spectral wind wave model SWAN (Simulating WAves Nearshore) that is local in frequency space, nonlinear with respect to the variance density and weakly dependent on the wave age. It is investigated whether this alternative whitecapping expression is able to correct the tendency towards underprediction of period measures that has been identified in the default SWAN model. This whitecapping expression is combined with an alternative wind input source term that is more accurate for young waves than the default expression. The shallow water source terms of bottom friction, depth-induced breaking and triad interaction are left unaltered. It is demonstrated that this alternative source term combination yields improved agreement with fetch- and depth-limited growth curves. Moreover, it is shown, by means of a field case over a shelf sea, that the investigated model corrects the erroneous overprediction of wind-sea energy displayed by the default model under combined swell-sea conditions. For a selection of field cases recorded at two shallow lakes, the investigated model generally improves the agreement with observed spectra and integral parameters. The improvement is most notable in the prediction of period measures.     

基于小型三维阵列的瞬态声源快速被动定位方法

重物在落水和着底过程中都会产生瞬态声信号,这类信号可被运用于浅水区域水下目标定位。 针对浅水区域目标定位的问题,提出了一种基于小型立体五元基阵的瞬态声源快速被动定位算法。 在分析重物落水信号特征的基础上,选取合适的广义互相关加权函数求得传声器之间的声程差,运用快速最小二乘搜索算法进行声源定位。 结果表明:运用 5 传声器阵列可以同时兼顾定位精度和鲁棒性,且满足实时性要求,该方法可运用于浅水区域瞬态声源定位等领域。     

台风期间南海北部岛礁及下坡海底对水下噪声的影响研究

The correlation of ambient noise with wind speed, and the depth dependence of ambient noise are both investigated, where the ocean noise data were recorded by a vertical line array in the northern South China Sea. It is shown that the correlation coefficients increase with increasing hydrophone depth during typhoon periods when the frequency ≥ 250 Hz, which opposes the generally accepted knowledge that the correlation coefficients of noise level and wind speed decrease with increasing depth during non-typhoon periods. Particularly at frequencies of 250 Hz, 315 Hz and 400 Hz, the correlation coefficients increase by more than 0.05 at depths ranging from 155 m to 875 m. At the three frequencies, the average noise levels also increase with increasing depth during typhoon periods. It is suggested that these differences are attributed to the wind-generated noise in shallow waters and the effect of "downslope enhancement" to sound propagation. During typhoon periods, the surf breaking and surf beat upon the shores and reefs are strengthened, and the source levels are increased. The wind-generated noise in shallow waters interacts with the downslope sea floor, with the noise-depth distribution changed by a "downslope enhancement" effect promoting noise propagation.     

Robust source localization in shallow water based on vector optimization

Owing to the multipath effect, the source localization in shallow water has been an area of active interest. However, most methods for source localization in shallow water are sensitive to the assumed model of the underwater environment and have poor robustness against the underwater channel uncertainty, which limit their further application in practical engineering. In this paper, a new method of source localization in shallow water, based on vector optimization concept, is described, which is highly robust against environmental factors affecting the localization, such as the channel depth, the bottom reflection coefficients, and so on. Through constructing the uncertainty set of the source vector errors and extracting the multi-path sound rays from the sea surface and bottom, the proposed method can accurately localize one or more sources in shallow water dominated by multipath propagation. It turns out that the natural formulation of our approach involves minimization of two quadratic functions subject to infinitely many nonconvex quadratic constraints. It shows that this problem (originally intractable) can be reformulated in a convex form as the so-called second-order cone program (SOCP) and solved efficiently by using the well-established interior point method, such as the software tool, SeDuMi. Computer simulations show better performance of the proposed method as compared with existing algorithms and establish a theoretical foundation for the practical engineering application.     

利用浅水地形及其SAR影像确定海面风向的一种方法

利用浅水地形的SAR影像以及基于浅水地形SAR仿真模型计算得到的仿真SAR影像,基于仿真SAR影像与真实SAR影像之间的相关性提出了一种确定海面风向的方法——最大相关系数法.以南沙双子礁海域为例,利用最大相关系数法确定出了一幅RADARSAT SAR影像成像时刻的海面风向,通过对结果的比较分析可以看出对于包含浅水地形的SAR影像应用该方法探测海面风向是可行的.