水下模糊图象维纳滤波和卡尔曼滤波恢复算法研究

该文将海水中图象传输特性的研究与用此传输特性进行水下模糊图象恢复结合起来 ,得到一套测量水体传递函数及进行水下图象处理的方法。采用维纳 (Wiener)滤波和卡尔曼 (Kalman)滤波算法 ,对模糊图象进了恢复。结果表明 ,利用计算机采用一定的算法对散射性质已知的水体造成的图象模糊可以进行有效的复原 ,且良好效果。     

基于复contourlet域隐马尔科夫树模型的海面溢油合成孔径雷达图像相干斑抑制

海面溢油SAR图像中的相干斑噪声严重影响了后续的图像分割、特征提取和分类.为了更有效地抑制海面溢油SAR图像相干斑,文中提出了一种基于复contourlet域隐马尔科夫树模型的海面溢油SAR图像相干斑抑制方法.首先对观测图像取对数并进行复contourlet变换;然后在复contourlet域中用隐马尔科夫树模型对相邻尺度间的带通方向子带系数进行建模,并依据贝叶斯最小均方误差准则估计无噪系数;最后进行逆复contourlet变换和指数变换,得到相干斑抑制后的图像.大量实验结果表明,与Lee、Kuan、Frost及Gamma Map等4种经典滤波方法以及小波域和contourlet域隐马尔科夫树模型方法相比,文中方法从主观视觉和客观定量评价两方面来看综合性能更为优越,是一种行之有效的SAR遥感图像海面溢油检测的预处理方法.     

Pressure image assimilation for atmospheric motion estimation

The complexity of the laws of dynamics governing 3-D atmospheric flows associated with incomplete and noisy observations make the recovery of atmospheric dynamics from satellite image sequences very difficult. In this paper, we address the challenging problem of estimating physical sound and time-consistent horizontal motion fields at various atmospheric depths for a whole image sequence. Based on a vertical decomposition of the atmosphere, we propose a dynamically consistent atmospheric motion estimator relying on a multilayer dynamic model. This estimator is based on a weak constraint variational data assimilation scheme and is applied on noisy and incomplete pressure difference observations derived from satellite images. The dynamic model is a simplified vorticity-divergence form of a multilayer shallow-water model. Average horizontal motion fields are estimated for each layer. The performance of the proposed technique is assessed using synthetic examples and using real world meteorological satellite image sequences. In particular, it is shown that the estimator enables exploiting fine spatio-temporal image structures and succeeds in characterizing motion at small spatial scales.     

Optimized support vector regression algorithm-based modeling of ship dynamics

This study contributes to solving the problem of how to derive a simplistic model feasible for describing dynamics of different types of ships for maneuvering simulation employed to study maritime traffic and furthermore to provide ship models for simulation-based engineering test-beds. The problem is first addressed with the modification and simplification of a complicated and nonlinearly coupling vectorial representation in 6 degrees of freedom (DOF) to a 3 DOF model in a simple form for simultaneously capturing surge motions and steering motions based on several pieces of reasonable assumptions. The created simple dynamic model is aiming to be useful for different types of ships only with minor modifications on the experiment setup. Another issue concerning the proposed problem is the estimation of parameters in the model through a suitable technique, which is investigated by using the system identification in combination with full-scale ship trail tests, e.g., standard zigzag maneuvers. To improve the global optimization ability of support vector regression algorithm (SVR) based identification method, the artificial bee colony algorithm (ABC) presenting superior optimization performance with the advantage of few control parameters is used to optimize and assign the particular settings for structural parameters of SVR. Afterward, the simulation study on identifying a simplified dynamic model for a large container ship verifies the effectiveness of the optimized identification method at the same time inspires special considerations on further simplification of the initially simplified dynamic model. Finally, the further simplified dynamic model is validated through not only the simulation study on a container ship but also the experimental study on an unmanned surface vessel so-called I-Nav-II vessel. Either simulation study results or experimental study results demonstrate a valid model in a simple form for describing the dynamics of different types’ ships and also validate the performance of the proposed parameter estimation method.     

基于声呐图像的深海采矿车组合定位导航算法

实现高精度的定位导航是深海采矿车完成海底工作任务的基础条件。在采矿车行进过程中,声呐设备生成的图像信息能够反映海底场景的变化,从而体现采矿车本身的运动,由此建立了一种声呐图像里程计,并将其与轮式里程计和USBL测量数据相结合提出了一种深海采矿车组合定位导航算法。首先对多波束前视声呐图像进行预处理,然后使用Canny算法进行特征检测并对特征点云进行配准,再结合声呐成像原理构建了声呐图像里程计运动模型,最后通过轮式里程计运动模型推导预测方程、声呐图像里程计运动模型和USBL测量数据推导更新方程,利用EKF（extended Kalman filter）算法实现基于多传感器融合的定位与姿态估计。海试数据验证了该组合定位算法能实现轮式里程计、声呐里程计和超短基线在速度、位置、艏向角估计、定位速率的精度互补,具有一定的有效性和精确性,该算法为深海采矿车的定位与导航算法研发提供了参考。     

导航雷达近海回波图像丢帧内插技术研究

研究了在连续的X波段导航雷达图像序列中丢失一帧图像状态下的一种快速修复算法.该算法主要采用基于运动估计与运动补偿的视频序列修复技术进行插帧修复.具体步骤是根据雷达图像中像素点的运动特点,采用改进的三步搜索算法并结合双向运动估计进行搜索,然后对矢量场进行后续处理,最后内插出重建帧.为了提高图像修复的精度,还引入了亚像素运...     

Influence of weight distribution on rolling of an LNG carrier

The paper discusses the various effects of the weight distribution on the roll motion of an LNG carrier based upon model tests results. The tests consisted of extinction tests in calm water as well as roll response tests in regular beam waves.The results of the wave tests were compared with those calculated with the much used simplified equation for pure rolling.     

Assimilation of the climatic hydrological data in the σ-coordinate model of the black sea by the algorithm of adaptive statistics

We realize the algorithm of adaptive statistics of forecasting errors for the assimilation of the climatic fields of temperature and salinity in the σ-coordinate model of the dynamics of the Black Sea. The principal relations of this algorithm and its simplified version based on the Kalman filter are presented. The distinctive features of realization of the algorithm specified by the model are discussed. We also present the results of comparison of the hydrophysical fields of the Black Sea reconstructed according to the algorithm of adaptive statistics and a simplified scheme of assimilation of the climatic data. It is shown that the dependence of sources in the transport equations (heat and salt diffusion) on the four-dimensional variances of forecasting errors and threedimensional measurement errors enables one to reconstruct the mutually adapted climatic parameters of the sea more exactly.     

开孔沉箱式结构内部波浪冲击压力试验研究

为研究在不同比尺模型下,透空式海洋结构中开孔沉箱内部受力与入射波浪的关系及差异,针对简化的上部开孔箱体海洋结构,选取两组不同尺寸模型进行了多组规则波物理模型试验。首先采用低通滤波方法分析了冲击力的不同组分,然后对比了两组模型内部所受冲击力的分布及波要素与箱体内部受力的关系。研究发现,波面对开口的淹没程度是影响冲击过程的主要因素;当模型尺寸发生变化时,开孔箱体内部所受波浪力与入射波要素的关系也发生了变化。     

利用简化PIV方法测量水底浮帘后方流场

粒子图像测速（PIV）是一种快速全流场测量方法。为克服PIV设备昂贵和操作复杂等缺点，文中介绍一种新的简化PIV方法。它是根据PIV测速原理，并利用现有的连续抓图软件，CAD和Origin等绘图软件对示踪粒子进行捕捉及图像处理，并将其应用于水底浮帘截留促淤装置的实验中，成功获得了浮帘后方回流区的瞬时流场分布图。     

基于深度卷积神经网络的海洋牧场岩礁性生物图像分类

水下视频可直观记录和反映海洋牧场生物资源的现状和变动,目前亟待开展基于图像的海洋牧场生物识别分类方法研究,以充分发挥图像处理技术在海洋牧场生物群落监测领域的应用潜力。利用采集自我国北方烟威地区包含鱼礁、藻床和泥沙三种图像背景的水下视频,开展了图像增强、图像分类数据集的建立和3种分类模型的应用。对比了基于绿通道的色彩补偿和限制对比度的自适应直方图均衡等方法在海洋牧场水下图像增强上的效果。建立了北方海洋牧场常见岩礁生物图像分类数据集,包括花鲈(Lateolabraxjaponicus)、(Lizahaematocheilus)、许氏平鲉(Sebastes schlegelii)等鱼类11种、棘皮类3种和蟹类1种,共23 211张图像。基于飞桨深度学习框架和PaddleX全流程开发工具,选择AlexNet、MobileNetV3和ResNet50三种图像分类卷积神经网络进行迁移学习,并分别验证了其在含噪音水下图像上的鲁棒性。结果表明,三种模型在测试集的类准确率分别达到96.64%、94.75%和99.23%,其中ResNet50模型在含有高斯噪音的图像集验证具有更好的鲁棒性。综之,基于深度学习的计算机视觉技术在我国海洋牧场生物群落监测中具有较大应用潜力,可为我国海洋牧场监测和管理提供新的思路和方法。     

Discussion of “Experimental investigation of impact generated tsunami; related to a potential rock slide,Western Norway” by G. Sælevik,A. Jensen,G. Pedersen [Coastal Eng. 56 (2009) 897–906]

This paper is a discussion of Sælevik et al. (2009). Their comparison between block and granular model results is described in more detail, along with a discussion of five parameters which may be in general responsible for deviations between block and granular models. New small scale physical model tests have been performed to support some of the statements made. Finally, it is argued that the use of physical model testing based on simplified geometries are justified in practice and normally produce results that are considerably better than an order of magnitude.     

Analysis of a simplification strategy in a nonhydrostatic model for surface and internal wave problems

This paper examines the simplification strategy of retaining only the nonhydrostatic effect of local acceleration in a three-dimensional fully nonhydrostatic model regarding the submesoscale wave phenomenon in the ocean.Elaborate scale analysis of the vertical component of the Reynold-averaged Navier–Stokes(RANS) equation was performed, confirming the rationalization of this simplification. Then, the simplification was implemented in a RANS equation-based nonhydrostatic model NHWAVE(nonhydrostat...     

Optimal Active Control of Wave-Induced Vibration for Offshore Platforms

An obvious motivation of this paper is to examine the effectiveness of the lateral vibration control of a jacket type offshore platform with an AMD control device, in conjunction with H2 control algorithm, which is an optimal frequency domain control method based on minimization of H2 norm of the system transfer function. In this study, the offshore platform is modeled numerically by use of the finite element method, instead of a lumped mass model. This structural model is later simplified to be single-degree-of-freedom (SDOF) system by extracting the first vibration mode of the structure. The corresponding "generalized" wave force is determined based on an analytical approximation of the first mode shape function, the physical wave loading being calculated from the linearized Morison equation. This approach facilitates the filter design for the generalized force. Furthermore, the present paper also intends to make numerical comparison between H2 active control and the corresponding passive control using a T     

Application of T-bar in numerical simulations of a monopile subjected to lateral cyclic load

A series of centrifuge tests were performed to investigate the response of a free-head monopile due to cyclic lateral loading in normally consolidated clay. By linking the maximum reaction-force point of the final cycles in all tests with various amplitudes, a postcyclic reaction-force curve is obtained, which can be used to assess the postcyclic remolded lateral stiffness. To numerically analyze the tests, a strength degradation model of the clay is calibrated by the T-bar cyclic test. However, this model is T-bar-dependent, which is unable to capture the degrading behavior of the monopile stiffness. Thus, a modification approach is proposed based on the upper bound theory, and the modified model is further combined with finite element analysis to simulate the cyclic behavior of the model pile. The simulation results show similar degrading trend and consistent postcyclic remolded lateral stiffness with the model tests. This further demonstrates that the remolded lateral stiffness mainly depends on the soil remolded strength, which is one of the parameters calibrated by the T-bar tests. Based on this finding, a simplified numerical analysis is proposed, which can predict the postcyclic reaction-force curve by performing one monotonic loading instead of modeling the whole process of cyclic loading.     

In Situ Underwater Electronic Holographic Camera for Studies of Plankton

In this paper, we describe an underwater electronic holographic camera (eHoloCam) that has been developed for in situ studies of the distribution and dynamics of plankton and other marine organisms and particles. The eHoloCam uses an Nd-YAG pulsed laser to freeze-frame fast moving particles and a complementary metal-oxide-semiconductor (CMOS) sensor for high-resolution image capture. Digital holograms and holographic videos are recorded at rates from 5 to 25 Hz over a period of several hours. Data is stored locally on an embedded computer. The eHoloCam is capable of recording all organisms and particles located in a water volume of 36.8 cm³ in a single hologram frame. The recorded holographic videos may subsequently be reconstructed numerically at a desired image plane. The main optical and mechanical specifications for eHoloCam are also described. To record electronic holographic videos of marine organisms, the eHoloCam was deployed from a towed sampling frame [autorecording instrumented environmental sampler (ARIES)] on the research vessel RV Scotia at speeds up to 4 kn (about 2 mldrs^-1) in the North Sea off the Shetland Isles. Various images of marine organisms obtained from this deployment are shown, together with preliminary measurements on the distribution of Calanus copepods.     

3-D shape recovery of planar and curved surfaces from shading cuesin underwater images

Automatic construction of high-resolution topographical maps, or determining the shape of man-made objects, targets, and obstacles for localization, identification, and/or recognition, is an important capability in the application of autonomous or intelligent underwater vehicles. In this paper, we investigate the application of underwater image models for the reconstruction of three-dimensional object shapes from the shading cues in two-dimensional optical images. We first present the results of a sensitivity analysis in support of a simplified model for a Lambertian surface illuminated by a point source in an attenuating medium, proposed in earlier work. We then generalize a closed-form solution for planar scenes, previously proposed for negligible source-camera baseline, to the case where the baseline may be increased to minimize backscatter effects. For curved surfaces, we propose two techniques based on different iterative updating strategies to recursively improve the recovered surface shape. We study the performance of various methods using synthetic data and real images acquired under different turbidity conditions     

Computer modeling and the design of optimal underwater imagingsystems

A computer model to simulate the formation of underwater images has been developed. The model incorporates the inherent and apparent properties of the propagation of light in water. An image is approximated as a linear superposition of several image components. The model has been used to simulate the relative advantages of different camera/light configurations. The results indicate that extremely large gains in image contrast can be obtained by careful design of beam patterns and the manipulation of camera and light locations. The performance of range-gated systems is explored, and it is demonstrated that these systems are presently power limited. In order to obtain better quality images at larger distances, an imaging configuration which consists of scanning an incoherent light beam across the field of view of a camera is proposed. The incoherent light-scanning system is shown to have advantages over both conventional imaging techniques and range-gated methods     

Study on key performance parameters of hydro-pneumatic tensioner for top tensioned riser

In this paper an improved mathematical model of a hydro-pneumatic tensioner (HPT) system for top tensioned riser (TTR) is derived by consideration of friction, mass of piston and piston rod, tension loss in hydraulic oil piping, and compressibility of hydraulic oil. The vertical motion of the riser string is also considered. Subsequently, the proposed detailed model and the conventional simplified model are comparatively studied. Finally, the tension characteristic and performance parameters of the HPT are analyzed based on the proposed model. Results show that the conventional simplified model indeed overestimates the tension of tensioner as it neglects some performance parameters resulting in tension loss. The diameters of piston and piston rod and the initial pressure of high pressure (HP) gas have the most significant influence on the tension of the tensioner. The initial volume of HP gas and the initial pressure of low pressure (LP) gas also have some impact. The influence of the initial volume of LP gas and the inner diameter and length of the piping is relatively small. The research has some reference value for HPT and TTR design.