层化海洋中的二阶波散射作用问题

引入Stokes有限振幅水波的多色波作用机制 ,采用二层层化海洋模型 ,分析了层化海洋中非线性波对结构的散射作用问题。提出了二层海洋中二阶水波散射条件的数学表达式 ,进而推导了二层海洋中二阶波对一般型圆柱散射作用的格林积分解式 ,并给出了对解式中自由面及分层界面无限积分的递推算式。     

Autonomous underwater vehicle-based concurrent detection and classification of buried targets using higher order spectral analysis

This paper presents a processing concept for autonomous underwater vehicle (AUV)-based concurrent detection and classification (CDAC) of mine-like objects. In the detection phase, the AUV seeks objects of interest using a simple energy detector combined with a peak tracking mechanism. Upon detection, the processing mechanism changes to a higher order spectral (HOS) classification process. The system is demonstrated through theory, simulation and at-sea experiments to have promise in reducing the false alarm rate of mine detections. The HOS classification mechanism is also shown to have some benefit over classical spectral estimation in all cases. Components of the system concept were also demonstrated live onboard the AUV during the Generic Oceanographic Array Technology Sonar (GOATS 2002) experiment off the coast of Italy, while others are demonstrated using a comprehensive AUV sonar simulation framework.     

Estimation of bottom scattering strength from measured and modeledmid-frequency sonar reverberation levels

Hamilton-type geoacoustic models were developed for Area Foxtrot, a shallow water test bed south of Long Island, for emerging active sonar systems where the surface sediment type is highly spatially variable. Reverberation levels (RL) were modeled using the finite-element parabolic equation (FEPE) propagation model to augment the generic sonar model (GSM) propagation model because the bottom loss model in GSM did not estimate transmission loss (TL) accurately in shallow water. FEPE estimates reveal that there is a greater than 15 dB difference between TL for sand and that for silt-day sediments in Area Foxtrot. The comparison between modeled RL and measured RL (from a 1991 active sonar exercise) enabled bottom scattering strength kernels to be developed for Area Foxtrot. Bottom scattering strength was found to be a function of sediment type. Hard sand sediment has a bottom scattering strength which obeys Lambert's law (sin² &thetas;) while that of silt-clay sediment is consistent with sub-bottom volume scattering (sine). The RLs in Area Foxtrot are azimuth-dependent and are a function of TL and bottom scattering strength (and hence bottom sediment type). Sonar beams steered towards the hard sand show higher RLs than for silt-clay, and knowledge of the sediment type and its spatial variation must be known to model RL accurately. A method to determine sediment type using measured RLs and RL slopes is given     

水下目标方位估计的一种新方法

矢量传感器是一种新型水声传感器。介绍了应用矢量传感器确定目标方位的理论和方法，给出了仿真和实验研究结果，讨论了矢量传感器具体体积小、输出信号多、抗各向同性干扰等特性。最后定性地分析了目标方位的方位估值误差。     

Availability of an equation to evaluate error by optical path discretization in radiative transfer computation based on the successive order of scattering method

The availability of an equation to evaluate the influence of multiple scattering in the single scattering process corresponding to a layer of arbitrary optical thickness was established. In order to confirm the validity of this equation, the radiance distribution in this layer was computed using a plane–parallel layer model based on the successive order of scattering method. The relative errors in a radiance distribution computed were evaluated as a function of optical thickness by the derived equation. It was shown that this equation provides a theoretical background for determining layer thickness using the plane–parallel layer model.     

提高水下GPS定位精度方法研究

水下GPS定位是近几年发展起来的高新技术.承载GPS接收机的海上浮标由于受海浪的影响,使得GPS接收信号附加了海浪信息,最终影响到水下目标的精确定位.针对海浪影响水下GPS定位精度现状,提出基于样条函数的数据分频处理方法,从而有效地分离海浪引起的长周期性漂移误差和短周期性随机误差,提高水下GPS定位精度.通过对实测数据的处理,证明了该方法的有效性.     

On the consistency of the normalized radiances of the Caspian Sea from the ocean color scanners SeaWiFS and MODIS

The consistency of the data of the ocean color scanners SeaWiFS and MODIS is examined using the example of the Caspian Sea as a water basin influenced by external sources of optically-significant admixtures. It was established that the discrepancies of the normalized radiances computed from the scanners’ data depend on the sunlight’s wavelength, grow when passing from the mid-sea to the coastal regions and vary in sign and magnitude within one and the same area under conditions favorable for passive remote sensing from space. Under any conditions, the minimal discrepancy occurs in the green-yellow range. The use of the radiances of this range to derive the oceanological characteristics secures the minimal errors when assessing the long period variability of the aquatic environment based on merging of the SeaWiFS and MODIS data.     

水下滑翔机的海洋应用

<正>水下滑翔机是一种依靠浮力驱动、以锯齿形轨迹航行的新型水下移动观测平台,具有制造成本与使用费用低、续航能力强、自主可控等特点,已经逐渐成为一种有效的海洋观测平台[1]。水下滑翔机是一种新型的海洋环境观测平台,近年来在国内外受到了极大的关注。1995年以来,美国先后研制出Slocum[2]、Seaglider[3]和Spray[4]等多种水下滑翔机,并于2003年前后逐步实现产品化。     

Application of a panel method to hydrodynamics of underwater vehicles

A low-order singularity panel method based on Green's formulation is used to predict the hydrodynamics characteristics of underwater vehicles. The low-order modeling employs constant strength sources and doublets, and the body surface is modeled by quadrilaterals. The method is first applied to predicting the force and moment coefficients of underwater vehicles for the body-alone and finned configurations. Hydrodynamic coefficients of added mass and added moment of inertia are also calculated by modifying the code. Results for several two and three-dimensional bodies show the usefulness of the method for predicting the added mass and added moment of inertia.     

Application of underwater optical data to estimation of primary productivity

We conducted time-series observations of optical fields near the base of the euphotic zone (approximately 40 m) using moored automatic optical sensors at a time-series station in the Western Pacific Subarctic Gyre from March 2005 to July 2006 (with some gaps). We used the ratio of photosynthetically available radiation at the surface (surface PAR) to in situ quantum irradiance (in situ QI) at about 40 m as an index of opacity (surface PAR/in situ QI), which began to increase in the middle of April and peaked between the end of June and the middle of July 2005. This ratio then decreased toward winter. The ratio increased again beginning in January 2006, and large peaks were observed in June and July 2006. As an index of chlorophyll abundance we used the ratio of spectral irradiance at wavelengths of 555 and 443 nm (Ed₅₅₅/Ed₄₄₃) at about 40 m; seasonal variability of this ratio synchronized well with the attenuation coefficient “k” estimated with surface PAR, in situ QI, and BLOOMS depth. We estimated primary productivity (PP) using Ed₅₅₅/Ed₄₄₃ and an empirical equation based on a previous model but improved on the basis of shipboard observations. Estimated PP agreed well with observed PP. Seasonal variability of estimated PP was synchronized with that of organic carbon flux observed by sediment traps from approximately 150, 540, 1000, and 5000 m. This study demonstrates that time-series observations of in situ optical fields could contribute to the estimation of primary productivity and the study of the biological pump in the ocean.     

Dynamic response of cylindrical shell structures subjected to underwater explosion

This study investigated the linear and nonlinear dynamic responses of three cylindrical shell structures subjected to underwater small charge explosions in a 4 m×4 m×4 m water tank. The dimensions of the cylindrical shell structures were 90 cm×30 cm×1 mm (length×diameter×thickness). Both ends of the cylindrical shell were mounted with thick plates to provide support and create an enclosed space. The three cylindrical shell structures were un-stiffened, internally stiffened and externally stiffened, respectively. The experiments involving the dynamic response of cylinders subjected to underwater explosion (UNDEX) were performed under different standoff distances, varying from 210 to 35 cm. A small quantity of explosives was used to generate the shock loading. The plastic deformation of the cylindrical shell was observed at a standoff distance of less than 50 cm. Other conditions were tested to examine cylinder linear response. Dynamic analyses were performed for the experimental model using FEM and compared with the test results. The accelerations and dynamic strains of cylindrical shells obtained from the experiment were compared with those obtained by FE analysis. Finally, problems related to small-scale UNDEX experiments performed in small water tanks were analyzed.     

Contribution of Raman scattering to upward irradiance in the sea

Measurements of underwater irradiance revealed that the vertical attenuance in upward irradiance for wavelengths above 520 nm decreased with increasing depth, while the attenuance in the remaining wavelength region and also the attenuance in the downward irradiance in the whole wavelength range kept almost constant values. In this paper, it is suggested that the decrease in the attenuance for the upward irradiance above 520 nm can be ascribed to the Raman scattering of water molecules excited by the intense blue-green light in the downward irradiance. The pure water Raman scattering function at a scattering angle of 90° is measured and the results are used for the theoretical computation of upward irradiance generated by Raman scattering. Then, the difference between observed upward irradiance and the upward irradiance obtained by extrapolation from that in the shallow layers is computed under the assumption of constant irradiance attenuance. Since this difference is expected to represent the upward irradiance generated by Raman scattering, its value is compared with the upward irradiance due to Raman scattering obtained by theoretical computation. The similarity between the two upward irradiances so evaluated supports the view that Raman scattering makes a significant contribution to upward irradiance in the longer wavelength region.     

Correlation of the distribution of normalized spectral radiances as an indicator of the features of water exchange in the Black Sea

A set of 128 images of the Black Sea obtained using the SeaWiFS color scanner data in 1998–2004 was processed to estimate the new capabilities of indication of the vertical inhomogeneity of the upgoing normalized radiance. The basin of the sea was divided into 430 frames with a size of 30 × 30 km. Correlation coefficients R between all the spectral radiances were calculated for all the frames of all the images. The correlation between the radiance distributions at 490 and 670 nm was most sensitive to the conditions of the radiance formation. This allowed us to find the situations in which the variations in the shortwave and long wave radiances in the frame appear opposite and are characterized by estimates R < ?0.7. It was shown that such distributions are indicators of the water exchange between the coastal and open sea areas. They are caused by a special optical stratification during the events of such exchange. A conclusion is made about the prospective of applying the estimates of the correlation of spectral radiances for diagnosis of the water exchange based on the current and archive materials of ocean color scanners.     

Shock responses of a surface ship subjected to noncontact underwater explosions

In combat operations, a warship can be subjected to air blast and underwater shock loading, which if detonated close to the ship can damage the vessel form a dished for hull plating or more serious holing of the hull. This investigation develops a procedure which couples the nonlinear finite element method with doubly asymptotic approximation method, and which considers the effects of transient dynamic, geometrical nonlinear, elastoplastic material behavior and fluid–structure interaction. This work addresses the problem of transient responses of a 2000-ton patrol-boat subjected to an underwater explosion. The KSF=0.8 is adopted to describe the shock severity. Additionally, the shock loading history along keel, the acceleration, velocity and displacement time histories are presented. Furthermore, the study elucidates the plastic zone spread phenomena and deformed diagram of the ship. Information on transient responses of the ship to underwater shock is useful in designing ship hulls so as to enhance their resistance to underwater shock damage.     

The evaluation method of total damage to ship in underwater explosion

Whipping response will happen when a ship is subjected to underwater explosion bubble load. In that condition, the hull would be broken, and even the survivability will be completely lost. A calculation method on the dynamic bending moment of bubble has been put forward in this paper to evaluate the impact of underwater explosion bubble load on the longitudinal strength of surface ships. Meanwhile the prediction equation of bubble dynamic bending moment has been concluded with the results of numerical simulation. With wave effect taken into consideration, the evaluation method of the total damage of a ship has been established. The precision of this evaluation method has been proved through the comparison with calculation results. In order to verify the validity of the calculation results, experimental data of real ship explosion is applied. Prediction equation and evaluation method proposed in this paper are to be used in ship structure design, especially in the preliminary prediction of the ultimate withstanding capability of underwater explosion damage for the integrated ship in preliminary design phase.     

Stokes' expansion of internal deep water waves to the fifth order

Stokes' expansion is applied to the internal waves of finite amplitude, which propagate on the interface between two layers of infinite thickness. Stream function, wave profile, phase velocity and mass transport velocity are given in the fifth order approximation. It is shown that (a) phase velocity increases with increase of wave steepness, (b) mass transport appears in the direction of the wave propagation in both layers as in the case of the surface waves, and (c) when the density difference is very small, the wave profile is flattened not only at the troughs but also at the crests.     

水下模块化自重构机器人对接导引

给出一种水下自重构机器人的基本构成模块,针对模块化自重构机器人的对接要求,设计一套基于蓝光波段的可见光定位系统,检测需要对接的两个面之间的位置与姿态关系.在主动连接面呈正三角形安装三个蓝光LED光源,在相应的被动连接面中心安装一个光敏二极管作为光强接收传感器,利用光强接收传感器接收到的信息,设计一套位置检测算法,根据计算出的相对方位误差,修正两对接面的方位.实验结果表明,所设计的蓝光波段可见光导引系统能够在水下准确检测两对接面相对方位,误差小于2cm.     

Development and experiments of the Sea-Wing underwater glider

Underwater gliders,which glide through water columns by use of a pair of wings,are efficient long-distance,long-duration marine environment observatory platforms.The Sea-Wing underwater glider,developed by the Shenyang Institute of Automation,CAS,is designed for the application of deep-sea environment variables observation.The system components,the mechanical design,and the control system design of the Sea-Wing underwater glider are described in this paper.The pitch and roll adjusting models are derived based on the mechanical design,and the adjusting capabilities for the pitch and roll are analyzed according to the models.Field experiments have been carried out for validating the gliding motion and the ability of measuring ocean environment variables.Experimental results of the motion performances of the glider are presented.     

Formation control of multiple underwater vehicles subject to communication faults and uncertainties

This paper proposes a novel approach to analyze and design the formation keeping control protocols for multiple underwater vehicles in the presence of communication faults and possible uncertainties. First, we formulate the considered vehicle model as the Port-controlled Hamiltonian form, and introduce the spring-damping system based formation control. Next, the dynamics of multiple underwater vehicles under uncertain relative information is reformulated as a network of Lur’e systems. Moreover, the agents under unknown disturbances generated by an external system are considered, where the internal model is applied to tackle the uncertainties, which still can be regulated as the Lur’e systems. In each case, the formation control is derived from solving LMI problems. Finally, a numerical example is introduced to illustrate the effectiveness of the proposed theoretical approach.