表层声速对多波束测深影响的研究

在多波束测深系统中,表层声速是线型接收换能器基阵对接收波束进行束控的重要参数。表层声速误差会直接造成接收波束的指向误差,也通过归算导致多波束脚印位置误差和回波图像的失真。在分析多波束信号处理流程和接收波束束控原理基础上,探讨表层声速对多波束指向和测深影响规律。     

深水黑匣子声信标快速搜寻定位方法研究

为了在深水海域快速地搜索黑匣子声信标信号,采用拖曳式声信标探测仪是目前采用的主要手段之一。分析了黑匣子声信标搜寻探测仪的国内外发展现状,研究了声信标搜寻定位的两种测量方法,在此基础上设计了多元圆型基阵的换能器,研制了拖曳式的搜寻声纳系统。提出了自远而近、逐步推进的快速搜寻三步走策略,使搜寻工作可以更加科学合理,对实际工作具有重要的指导意义。     

一种水下磁场测量基阵的设计

针对水下被测磁场目标,根据磁场测量的要求,分析计算了测量单元的布置方式和基阵的受力,设计了一种用于布放该磁场测量系统的基阵结构。 通过海上试验验证,该基阵入水姿态平稳,着底姿态良好,满足测试要求,为水下装备磁场指标评估提供依据和方法。     

数字ADCP波束偏转公式的解算

波束偏转是由基阵旋转引起的.将Janus结构数字ADCP基阵旋转进行横滚、纵倾、航偏分解考虑,进而推导了波束偏转公式.     

圆阵低频超增益波束形成用于水下目标探测研究

针对小尺度基阵难以取得低频空间增益的问题,研究了圆阵超增益波束形成技术检测低频目标的方法。利用小尺度基阵低频噪声的空间相关性,求出基阵的相关系数矩阵,该矩阵对常规波束形成的权系数进行加权,产生超增益波束形成器的最优加权向量。计算机仿真与实测数据处表明：超增益波束形成技术能够在较低的工作频率上形成波束,获得更好的探测定位性能,有良好的应用前景。     

水声信道高速率数据传输的换能器研制

在复杂的水声信道中 ,实现高速率的数据传输 ,水声换能器的带宽是一个重要的技术问题。实验中 ,为了拓宽换能器的带宽 ,我们利用圆柱形压电换能器的径向振动与液腔振动相耦合原理研制自由溢流式换能器和利用纵向振动与前盖板弯曲振动相耦合原理研制纵向振动复合棒换能器。本文介绍适应于复杂的水声信道中 ,进行高速率数据传输的两种宽频带换能器的研制     

水声定位

用水声设备确定物体 (例如船只 )的方位和距离。在预定海域的海底布放 3个以上声应答器 ,组成应答器阵。在定位的船上装有询问声发射系统和应答接收系统 ,以接收海底应答器 ,在收到询问脉冲后发出的具有不同频率的应签脉冲。根据脉冲到达时间 ,可测得船与各应答器距离 ,从而确定船位。用这种方法定位的绝对误差约为数米。另一种方式是在海底布设定时辐射声脉冲的声源或海底应答器 ,另在被定位的船底或者布设由 3个水听器组成的接收基阵 ,或者安装一个收发两用换能器和两个水听器 ,由脉冲到达时间 (必要时还须利用由测深仪测得的水深数据 )确…     

20~40kHz压电圆管换能器设计及测试

提出了一种水声测量领域常用的压电圆管换能器的设计,并应用有限元方法对压电圆管换能器进行研究。利用有限元分析软件ANSYS建立了圆管换能器的有限元模型,旨在优化换能器结构,分析换能器振动特性、电导特性和辐射特性。在此基础上,设计和制作了一个宽带无指向性圆管换能器.结果表明:换能器工作带宽为20~40 kHz,发射电压响应最大值为142 dB,发送电压响应起伏不超过±5 dB,具有良好的水平无指向性的发射性能。     

一种优化多通道声波束形成的方法

因基阵各通道不均衡,使得水声接收系统波束形成时,目标检测、方位估计等性能经常达不到预期。分析了各通道信噪比、辐值、相位影响波束信噪比的机理,提出了一种减小基阵各通道不均衡的方法,并利用实测数据进行了仿真。仿真结果表明：该方法可有效地提高水声接收系统的目标检测、方位估计等性能。     

多孔结构换能器等效质量的计算方法

利用多孔结构增加换能器频带宽度,是换能器设计方面的一个新的理论问题。本文指出,换能器辐射块钻孔引起等效质量的减少,是导致频带变宽的主要原因。 对园台形辐射块钻孔的换能器,用一般解析法求其振速分布是困难的。本文采用有限元方法求其振速的数值解,并算出了换能器的等效质量及带宽变化。该计算方法同样适用于辐射块前端或中间沿轴向钻孔的复合式和夹心式压电换能器等效质量的计算。     

海上大直径钢管桩打桩过程中桩周土强度弱化研究

海上大直径钢管桩打桩过程中,桩周土体受到强烈扰动而发生强度弱化,掌握桩周土体强度弱化规律对于准确预测打桩过程、保证工程安全具有重要意义。为研究土体强度弱化规律,开展了环剪试验模拟打桩对桩周土体的扰动,测试土体强度随剪切速率的变化规律,建立了描述土体强度弱化规律的拟合公式,引入到打桩分析软件中。研究结果表明：土体的强度折减程度不仅与土体本身的性质有关还受到土体的埋深和剪切速率的影响,埋深越深土体强度折减程度越低,剪切速率越高土体强度折减越高,在打桩分析中可采用这里推荐的线性折减方法来模拟不同深度处土体强度的折减规律。     

A Tidal Flow Model for the Gulf of Kachchh, India

A vertically integrated model has been used to study the tidal circulation and currents in the Gulf of Kachchh along the west coast of India. The model is fully nonlinear and uses a semiexplicit finite difference scheme to solve the basic hydrodynamic equations on a staggered grid. The model is forced by prescribing the tides along the open boundary of the model domain. The flow is simulated both with and without the presence of the proposed tidal barrage across the Hansthal Creek in the Gulf of Kachchh. The results show a considerable change in the behavior of the tidal flow in the presence of the barrage.     

The role of syntectonic sedimentation in the evolution of doubly vergent thrust wedges and foreland folds

This paper shows the evolution of time-constrained two-dimensional scaled analogue models of doubly vergent thrust systems in the presence of syntectonic sedimentation. Two sets of experiments were considered: (1) the addition of a syntectonic layer composed of a polymer and overlying sand in the prowedge; and (2) the addition to the previous condition of a progradational sedimentary load. Results from the first set of experiments indicate that the foreland fold-and-thrust belt has a strong relationship with the competence of the syntectonic layers. When the competence is low, the deformation produces tight asymmetric detachment-folds. As the competence increases, the fold-and-thrust belt shows break-trough folds with longer and better defined foreland-vergence. Results from the second set of experiments indicate that structural vergence is determined by the sense of progradation of the syntectonic layers, and in the case of strong aggradation at the prowedge, extension and reactive diapirism form contemporaneously with the contraction. Three end-members are proposed for mountain front thrust systems formed in the presence of syntectonic polymer and sand sedimentation: (1) outcropping fold-and-thrust belt sequence, in the case of no syntectonic sedimentation; (2) long displacement blind-thrust sheets, in the case of under-filled basins and (3) short displacement blind-thrust sheets, in the case of over-filled basins. All results indicate that ductile units at the base of syntectonic layers increase the displacement of the underlying frontal thrusts at the prowedge, and reduce the critical taper. Results also indicate that at very high sedimentary rates and hyper-critical taper conditions the prowedge collapses. Conclusions drawn from this research may be applied as an analogue to foreland evolution and to evaluate hydrocarbon generation, migration, and entrapment in thrust belts in areas where seismic imaging is generally poor.     

Seasonal variability of water transport through the Straits of Gibraltar, Sicily and Corsica, derived from a high-resolution model of the Mediterranean circulation

The variability of the water transport through three major straits of the Mediterranean Sea (Gibraltar, Sicily and Corsica) was investigated using a high-resolution model. This model of the Mediterranean circulation was developed in the context of the Mercator project.The region of interest is the western Mediterranean between the Strait of Gibraltar and the Strait of Sicily. The major water masses and the winter convection in the Gulf of Lions were simulated. The model reproduced the meso-scale and large-scale patterns of the circulation in very good agreement with recent observations. The western and the eastern gyres of the Alboran Sea were observed but high interannual variability was noticed. The Algerian Current splits into several branches at the longitude of the Strait of Sicily level, forming the Tyrrhenian branch, and, the Atlantic Ionian Stream and the Atlantic Tunisian Current in the eastern Mediterranean. The North Current retroflexed north of the Balearic Islands and a dome structure was observed in the Gulf of Lions. The cyclonic barotropic Algerian gyre, which was recently observed during the MATER and ELISA experiment, was evidenced in the simulation.From time-series of 10-day mean transport, the three straits presented a high variability at short time-scales. The transport was generally maximum, in April for the Strait of Gibraltar, in November for the Strait of Sicily, and in January for the Strait of Corsica. The amplitudes of the transport through the Straits of Gibraltar (0.11 Sv) and Sicily (0.30 Sv) presented a weaker seasonal variability than that of the Strait of Corsica (0.70 Sv).The study of the relation between transport and wind forcing showed that the transport through the Strait of Gibraltar is dependent on local zonal wind over short time-scales (70%), which was not the case for the other straits (less than 30%). The maximum (minimum) of the transport occurred for an eastward (westward) wind stress in the strait. An interannual event was noticed in November–December 2001, which corresponded to a very low transport (0.3 Sv), which was characterised by a cyclonic circulation in the western Alboran Sea. That circulation was also reproduced by the model for other periods than winter during the interannual simulation.The transport through the Strait of Sicily is not influenced by local wind.The wind stress curl of the northwestern Mediterranean influenced the transport through the Strait of Corsica.     

大亚湾红树林与海岸植物叶片气孔特征及其发育

光镜下观察了大亚湾地区红树林及海岸20种植物叶片气孔的结构特征及部分植物气孔器的发育过程。结果表明：大部分植物仅下表皮具气孔；气孔类型有无规则、平列、环绕、横列和四轮列型；气孔指数和气孔密度不同植物间变化较大；保卫细胞以卤蕨最大，阔苞菊最小；气孔开张度以桐花树最大，阔苞菊最小。高盐度对秋茄、木榄幼苗叶片气孔器的发生发育有一定抑制作用。海芒果、海漆的气孔器发育为周源型，而木榄、秋茄为中源型。多数真红树植物气孔在表皮下陷，发生于保卫细胞形成之后，气孔特征及其发育表现出生活于相同海岸带的不同植物既有相似性又有多样性。     

Numerical Simulation of Extreme Sea Levels Using Location Specific High Resolution Model for Gujarat Coast of India

Although the frequency of tropical cyclones is less in the Arabian sea compared to that of the Bay of Bengal, there are several severe tropical cyclones which caused extensive damage along the Gujarat coast. In view of the high tidal range in the funnel-shaped gulfs of the Khambhat and the Kachch, it is very useful to study the surge response in these regions. There is always a possibility of abnormal rise of sea level when the occurrence of surge coincides with high tide, which may eventually cause inundation of vast stretches of shallow coastal areas. In view of this, a location specific fine resolution model is developed for the Gujarat coast. The east-west and north-south grid distances for the model are 5.1 km and 5.2 km, respectively. Several numerical experiments are carried out to compute the extreme sea levels using the wind stress forcings representative of 1982, 1996, and 1998 cyclones, which crossed this region. The model-computed extreme sea levels are in good agreement with the available observations.     

养殖文蛤体内寄生的一种吸虫幼虫及宿主组织病理学

作为文蛤吸虫病害研究的基础资料,报道了寄生在文蛤体内的1种复殖吸虫幼虫的形态结构及宿主由此所产生的组织病理学变化。研究表明：该吸虫分别为咆蚴和尾蚴。咆蚴圆筒形,内含不同发育阶段的尾蚴。成熟尾蚴体成扁平舌状,具有口吸盘、腹吸盘,1对眼点和1条细长无刺的尾巴。该吸虫主要侵占生殖腺,少部分幼虫进入附近的消化盲囊、鳃、肾等部位。轻微感染者,生殖滤泡萎缩,生殖细胞发育滞后;严重感染的宿主,生殖腺完全被侵占并耗尽。消化盲囊、鳃、肾等器官组织也因幼虫感染呈现不同程度的病理学变化;严重者上皮细胞水肿或脱落,肌肉组织结构紊乱或溶解等。本工作同时显示,吸虫寄生可诱发宿主血淋巴细胞大量增生,并产生凝集、组织浸润及形成包囊等免疫反应。     

Estimation of Sediment Properties during Benthic Impact Experiments

Sediment properties, such as water content and density, have been used to estimate the dry and wet weights, as well as the volume of sediment recovered and discharged, during benthic impact experiments conducted in the Pacific and Indian Oceans. The estimates show that the weights of dry (355-1332 t) and wet sediment (1651-4888 t) recovered during the experiments, are not only a function of the total duration and distance covered during the experiment, but also depend on water content and density of the sediment. Estimation of dry sediment and its volumetric ratio in the discharge, are key parameters for calculating the discharged volume. The estimated volume of wet sediment recovered (1427-4049 m 3 ) as well as discharged (2693-6951 m 3 ) during the experiments, provide important inputs to evaluate the sediment resettlement and migration. Using these estimates, the average depth of excavation on the seafloor, can also been calculated. However, the stages of sediment recovery and discharge are expressed differently in some of the experiments. In order to standardize these, different stages have been identified, and definitions of certain terms have been suggested, for use in the future. The methods of calculating different properties, as well as weight and volume of discharged sediment are described in the paper for use in other applications concerning deep-sea discharges.     

Development of storm surge which led to flooding in St. Bernard Polder during Hurricane Katrina

Hurricane Katrina caused devastating flooding in St. Bernard Parish, Louisiana. Storm surge surrounded the polder that comprises heavily populated sections of the Parish in addition to the Lower 9th Ward section of Orleans Parish. Surge propagated along several pathways to reach levees and walls around the polder's periphery. Extreme water levels led to breaches in the levee/wall system which, along with wave overtopping and steady overflow, led to considerable flood water entering the polder. Generation and evolution of the storm surge as it propagated into the region is examined using results from the SL15 regional application of the ADCIRC storm surge model. Fluxes of water into the region through navigation channels are compared to fluxes which entered through Lake Borgne and over inundated wetlands surrounding the lake. Fluxes through Lake Borgne and adjacent wetlands were found to be the predominant source of water reaching the region. Various sources of flood water along the polder periphery are examined. Flood water primarily entered through the east and west sides of the polder. Different peak surges and hydrograph shapes were experienced along the polder boundaries, and reasons for the spatial variability in surge conditions are discussed.     

Transport of salt and suspended sediments in a curving channel of a coastal plain estuary: Satilla River, GA

This study describes the transport of salt and suspended sediment in a curving reach of a shallow mesotidal coastal plain estuary. Circulation data revealed a subtidal upstream bottom flow during neap tide, indicating the presence of a gravitational circulation mode throughout the channel. During spring tide, landward bottom flow weakened considerably at the upstream end of the channel and changed to seaward in the middle and downstream areas of the reach, suggesting the importance of tidal pumping. Salt flux near-bottom was landward at both ends of the channel during neap tide. At spring, however, the salt flux diverged along the bottom of the thalweg suggesting that tidal pumping caused a transfer of salt vertically and laterally into the intertidal zone. Thus, landward flux of salt is maintained even in the presence of subtidal seaward flow along the bottom at the downstream end of the channel.Landward bottom stress is greater than seaward stress, preferentially transporting suspended sediments upstream. Compared with salt, however, the weight of the suspended sediments causes less upward transfer of sediments into the intertidal zone. Flood flow carried more suspended sediments landward at the upstream end compared with the downstream end. We speculate that secondary flow in the curving channel picks up increasing amounts of suspended sediments along the sides during flood and adds them to the axial flow in the thalweg. Since the landward flow along the bottom of the thalweg weakens and even reverses during spring tide, there appears to be a complex re-circulation system for sediments re-suspended in curving channels that complicates the picture of a net transport of sediments landward.