船舶海浪中非线性随机运动的可视化技术

研究船舶海浪中运动的可视化技术.通过采用船舶在海浪中运动的可视化技术,可以使船舶设计人员能够更直观地了解船舶的运动性能.采用具有平台独立性的OpenGL图形库对船舶在波浪中运动的可视化进行描述,讨论了建立船舶模型的可行方法和如何建立三维波浪的数学模型.考虑随机波浪及船舶的非线性阻尼、非线性恢复力矩,建立船舶横摇运动的非线性微分方程.采用Runge-Kutta方法求解非线性微分方程,根据数值模拟结果,应用OpenGL中的函数来生成船舶在海浪中运动的动画.所开发的程序模拟的船舶和波浪是三维的,可以对不同有义波高的波浪和不同船舶的运动进行模拟.     

水面舰艇CGF系统的若干关键技术研究

水面舰艇计算机生成兵力，是海战模拟中的重要环节，是模拟海战场的重要组成部分。通过建立水面舰艇的运动、动力学数学模型，同时建立舰艇上有关情报侦察系统、武器系统的数学模型，实现这些模型的仿真运行，建立水面舰艇CGF，并将该CGF置于战术模拟训练仿真环境中，对于提高战场环境的仿真可信度，提高模拟训练的效果具有重要意义。该文对水面舰艇CGF系统的工作原理、物理模型、智能决策模型等关键技术进行了研究，并给出了水面舰艇CGF系统简化的舰艇机动模型、舰空导弹弹道模型、对空警戒雷达的功能仿真模型。对完善水面舰艇CGF系统，进一步研究海军训练DIS系统有很重要的意义。     

基于CFD的船舶斜浪三自由度运动仿真研究

针对船舶在斜浪中的多自由度耦合运动问题, 建立了三维粘性流耐波性数值波浪水池, 采用边界条件造波法生成高精度的斜向规则波, 通过同时求解RANS方程和刚体运动学方程, 结合网格整体移动方法和滑移网格方法, 实现了船舶斜浪航行的垂荡、纵摇及横摇三自由度耦合运动数值模拟。给出了DTMB5512船模斜浪中的垂荡、纵摇及横摇的频率响应函数, 与线性切片理论计算结果进行比较, 吻合良好。该方法可为船舶斜浪航行的耐波性预报提供一种有效的途径。     

Synoptic mapping of internal-wave motions and surface currents near the Lombok Strait using the Along-Track Stereo Sun Glitter technique

A multi-component satellite remote sensing program is required to track the response of the world's oceans, lakes and rivers to climate change. Central to this endeavor is the ability to detect the motions of internal waves, swell waves and currents and hence follow energy transport and exchange. However, the present methods of monitoring the motions of water bodies from space, such as those based on altimetry or gravity measurements, are geared mostly toward applications on large spatial scales, whereas the capacity to map the fine details of hydrospheric flows is limited. This paper describes a satellite-based method of detecting wave motion and surface currents at high (in principle metric) resolution that can be applied under specific circumstances in the confined environs of narrow sea straits, lakes and rivers and that compliments the use of other high-spatial resolution techniques such as those based on Synthetic Aperture Radar (SAR). The Along-Track Stereo Sun Glitter (ATSSG) technique makes use of images of water bodies that are separated in time by roughly 1 min and are gathered in the forward-, nadir- and backward-looking directions by space-borne optical sensors performing along-track observations. When sensor viewing geometries lead to the presence of Sun glitter in these images, surface slicks, internal waves, swell waves and other phenomena become highlighted through the surface roughness changes they induce, since these in turn modulate the reflected glitter radiance. Measurement of the differential displacements between congruent sections of the surface roughness signatures present within image pairs of the stereoscopic sequence then enables internal wave or swell wave motions to be determined, while surface currents can be deduced if “passive” tracers of the flow in the form of surface roughness structures (such as slicks) are present. The application of the ATSSG technique described herein makes use of data acquired at a spatial resolution of 2.5 m by the Panchromatic Remote-sensing Instrument for Stereo Mapping (PRISM) to provide the first along-track fine-scale synoptic mapping of the surface motions of individual components within a large group of internal waves and to generate supporting surface-current measurements. The PRISM data we employ were acquired to the south of the Lombok Strait (Indonesia), where highly energetic internal-wave growth takes place and where through-flow surface-current data, of the type derived by the ATSSG technique, can be of value in climate studies.     

Review Article. The imaging of waves by satelliteborne synthetic aperture radar: the effects of sea-surface motion

The effects of sea-surface velocities in the imaging of waves by synthetic aperture radar (SAR) are considered using the ‘facet’ concept of the backscattering process. It is shown that if the sea wave spectrum is divided at the nominal limit of resolution of the SAR the effect of the long and short wavelength parts can be considered separately, the former being treated by numerical simulation and the latter by statistical methods. It is found that the motions due to: the short wavelengths produce an azimuthal smearing which can be represented by a Gaussian low-pass filter acting on the azimuthal component of wavenumber in the image. The cut-off wavelength is typically some hundreds of metres in moderate winds. Images obtained with the SEASAT SAR frequently show such an effect.     

基于干扰观测器的SWATH船运动非线性预测控制

针对带有海浪干扰和参数不确定的SWATH船运动控制问题, 提出基于干扰观测器的SWATH船运动非线性预测控制. 首先对SWATH船运动进行建模、参数求解和海浪干扰仿真; 然后根据运动模型设计非线性预测控制律, 对SWATH 船升沉和纵摇进行控制, 同时利用干扰观测器对海浪干扰进行观测, 并从理论上证明了所设计的控制器可以保证SWATH 船运动的稳定性. 仿真结果表明, 所设计的控制器提高了SWATH船运动控制效果, 且能对海浪干扰进行抑制.

     

Vessel motion thresholds for maintaining physical and cognitive performance: a study of naval personnel at sea

Methods and results are reported from a study of ships companies' exposure to low-frequency motions on three vessels of the Royal Navy. The aim of the study was to investigate relationships between deck accelerations and the incidence of problems such as difficulties with physical tasks, cognitive activities, motion sickness, and work effort. Ship motions were recorded continuously during sea patrols of 10-14 days. The data collected from the three vessels comprised 105 days of ship motions over 12 patrols, with 779 associated daily diaries from 78 participants. Problems most strongly associated with vessel motions were related to the difficulties with physical tasks. Some cognitive aspects of task performance and motion sickness were associated with vertical acceleration magnitudes, but the correlations were less strong than with physical tasks. Practitioner Summary: Little is known about the severity of ship motions that degrade physical and mental performance. The paper offers preliminary estimates of the motion threshold values below which the performance will not be degraded by motion.     

A sub-grid air entrainment model for breaking bow waves and naval surface ships

Direct numerical simulations (DNS) of air entrainment by the breaking bow waves of naval surface ships are outside of the computational reach of the most powerful computers in the foreseeable future. This creates a need for physically-based models of air entrainment for applications in numerical simulations for ship design. Due to the non-linear dependence of the terminal bubble velocity with diameter most air entrainment flows have a high void fraction region immediately below the free surface. We present a model that locates this region employing the local liquid velocity and the distance to the interface. Using this model and the bubble size distributions measured by Deane and Stokes [Deane BD, Stokes MD. Scale dependence of bubble creation mechanisms in breaking waves. Nature 2002;418:839-44] we have simulated the air entrainment in the breaking wave experiments of Wanieski et al. [Waniewski TA, Brennen CE, Raichlen F. Measurement of air entrainment by bow waves. J Fluids Eng 2001;123:57-63]. Comparison against these experimental data is good. We then apply this model to simulate the flow around naval combatant DTMB 5415 and the research vessel Athena. The model predicts air entrainment in regions where it was actually observed at sea, namely the breaking bow wave, along the water/air/hull contact line and in the near-wake. To the best of our knowledge this is the first model of air entrainment that compares favorably with data at laboratory scale and also presents the right trends at full-scale.     

基于模糊控制的船舶自动导航仿真系统

在介绍船舶运动特性和分析船舶运动的基础上,建立船舶运动质点方程,研究基于模糊控制的船舶自动导航仿真系统。针对船舶偏航量的控制,设计位移模糊控制器和航向模糊控制器,对船舶在波浪中的运动进行数值仿真。船舶在各种不同外界条件下的运动状态数据,应用数据库技术,进行存储,作为后续数据分析来源。采用VC＋＋,在VS2005开发环境下使用GDI编程,实现可视化仿真。     

Removal of azimuth ambiguities and detection of a ship: using polarimetric airborne C-band SAR images

Synthetic aperture radar (SAR) imagery from the sea can contain ships and their ambiguities. The ambiguities are visually identifiable due to their high intensities in the low radar backscatter background of sea environments and can be mistaken as ships, resulting in false alarms in ship detection. Analysing polarimetric characteristics of ships and ambiguities, we found that (a) backscattering from a ship consisted of a mixture of single-bounced, double-bounced and depolarized or diffused scattering types due to its complex physical structure; (b) that only a strong single- or double-bounce scatterer produced ambiguities in azimuth that look like relatively strong double- or single-bounce scatterers, respectively; and (c) that eigenvalues corresponding to the single- or double-bounce scattering mechanisms of the ambiguities were high but the eigenvalue corresponding to the depolarized scattering mechanisms of the ambiguities was low. With these findings, we proposed a ship detection method that applies the eigenvalue to differentiate the ship target and azimuth ambiguities. One set of C-band JPL AIRSAR (Jet Propulsion Laboratory Airborne Synthetic Aperture Radar) polarimetric data from the sea have been chosen to evaluate the method that can effectively delineate ships from their azimuth ambiguities.     

Global structure of extreme wind and wave climate derived from TOPEX altimeter data

Sea surface wind speed and significant wave height (SWH) are two basic parameters, in addition to sea surface height, which can be inferred from satellite altimeter measurements. Traditionally, altimeter-derived wind and wave data are less extensively used compared to sea surface height, as they are sometimes considered as by-products of satellite altimetry (in contrast to, for example, the dedicated scatterometer missions for marine wind observations). However, it is clear that altimeter-based wind and wave data have the unique advantage of being concurrent and collocated with each other. Using eight years (1993–2000) of TOPEX altimeter data with unprecedented accuracy and continuity, the 10-, 50- and 100-year return values of global wind speed and SWH are derived, their characteristics are discussed in relation to wind climatology and wind variability. Validations against in situ observations indicate that the uncertainties of altimeter-derived extreme winds and waves are at the levels of 10% and 5%, respectively. These results suggest that satellite altimeter data, with present quality and duration, can be very useful in many aspects of coastal engineering and marine technology such as design of offshore facilities, ship routing, and preparation of other sea-going activities.     

An application of dynamic positioning control using wave feed forward

The paper presents the results of model tests for a large tanker in which wave drift force feed forward was applied in the dynamic positioning control system. The estimation method of the nonlinear (second order) wave drift forces from the measurement of relative water motions at the side of a ship hull is presented. The estimated wave drift forces are used in the DP control system, to enhance the filter process of the extended Kalman filter, and in the required thruster set‐points. The EKF uses the nonlinear equations of low‐frequency ship motions on the horizontal plane, which are also presented. The results of the model tests show that the use of wave drift force feed forward significantly improves the positioning accuracy in sea states with 3.5 m significant wave height or higher. Copyright © 2001 John Wiley & Sons, Ltd.     

联合显著性特征与卷积神经网络的遥感影像舰船检测

目的 针对高分辨率遥感影像舰船检测受云雾、海浪以及海岛等复杂因素干扰,存在虚警率高、漏检率高、目标检测和识别困难等问题,提出一种联合视觉显著性特征与卷积神经网络的海面舰船目标检测方法。方法 基于频率域相位谱显著性检测能够有效抑制高分辨率遥感影像上云层、海面杂波干扰的特点,计算影像多尺度显著图并进行加权融合。采用对数变换对融合后的图像进行空间域灰度增强以提高目标与背景的区分度,利用灰度形态学闭运算填充舰船目标孔洞,采用大津分割法来提取疑似舰船目标作为兴趣区域。最后构建舰船样本库,利用迁移学习的思想训练卷积神经网络模型,对所有兴趣区域切片进行分类判断和识别,得到最终检测结果。结果 利用多幅不同背景下的高分辨率遥感影像,分别从视觉显著性检测、舰船粗检测与船只类型识别3个方面进行实验验证,选取检测率、虚警率、识别率3个指标进行定量评价。结果表明,本文方法相比于其他方法能有效排除云雾、海岛等多种因素的干扰,检测率、虚警率、识别率分别为93.63%、3.01%、90.09%,明显优于其他算法,能够实现大范围影像上多种类型舰船的快速准确检测和识别。结论 本文将图像视觉显著性检测快速获取图像显著目标的特点与卷积神经网络在图像分类的优势相结合,应用于遥感影像的海域舰船目标检测,能够实现对复杂背景下舰船目标的检测和船只类型的精细化识别。     

Ship motions using single-phase level set with dynamic overset grids

The problem of surface ships free to pitch and heave in regular head waves is analyzed numerically with an unsteady Reynolds averaged Navier Stokes (URANS) approach. The unsteady single-phase level set method previously developed by the authors was extended to include six degrees of freedom (6DOF) motions. The method uses rigid overset grids that move with relative motion during the computation, and the interpolation coefficients between the grids are recomputed dynamically every time the grids move. The motions in each time step are integrated implicitly using a predictor-corrector approach. An earth-based reference system is used for the solution of the fluid flow, while a ship-based reference system is used to compute the rigid-body equations of motion. Predicted results for sinkage and trim and resistance at two Froude numbers (medium, Fr = 0.28 and large, Fr = 0.41) were compared against experimental data, showing good agreement. Pitch and heave motions were computed for near-resonant cases at Fr = 0.28 and 0.41, with regular linear head waves with slope ak = 0.025 and wavelength λ = 1.5L, with L the ship length. The predicted motions compare favorably with existing experimental data. A solution for a large amplitude head wave case (ak = 0.075) was also obtained, in which the transom wave breaks and extreme motions are observed. The medium Froude number case was subject to a verification and validation analysis. A problem with two ships pitching and heaving one behind the other is demonstrated.     

船舶运动状态下风速风向测量补偿与数字仿真

为了研究船舶运动状态下的风速风向精确测量,设计了一种船舶风速风向动态测量及误差补偿的数字仿真系统。通过对船舶航行状态下的风速风向测量原理进行分析,建立了船舶平面运动的相对风速风向和真风风速风向的解算模型,并根据船舶空间运动的风速风向测量及其误差补偿算法,对船舶横摇、纵摇状态下的风速风向的动态测量和误差补偿进行了数字仿真。数字仿真结果表明,该方法能够消除船舶航行时的运动姿态对风速风向测量带来的影响,为船舶的操纵控制和航行安全提供了精确和可靠的风速风向数据信息。     

高分辨率遥感图像投影分析的靠岸舰船检测

目的 高分辨率遥感图像中,靠岸舰船检测有着广泛的应用前景,其主要难点在于舰船与港口陆地在空间上紧邻,在颜色和纹理特征上相似,舰船与港口陆地难以分割。针对这种情况,利用港口岸线平直的几何特点和靠岸舰船多为舷靠的停泊特点,提出一种基于投影分析的靠岸舰船检测方法。方法 首先,对原始图像进行预处理,利用K-means聚类算法与区域生长算法相结合的方式得到海陆分割图像,利用Sobel算子与Otsu分割结合的方式获取边缘图像;然后,通过改进的Hough变换提取直线特征,结合港岸几何特性定位港口岸线;再将海陆分割后的二值图像向沿岸线和垂直岸线两个方向进行投影,根据沿岸线方向投影形态确定和分离并靠舰船,根据垂直岸线方向的投影形态定位舰船目标;最后,利用舰船尺寸、长宽比、最小外接矩形占空比特征去除虚警。结果 在15个港口场景不同分辨率的遥感图像测试集上,本文方法整体检测率达到85.4%,虚警率达17.2%;限定分辨率范围在24 m的情形下,检测率提高到93.5%,虚警率降低至5.3%。结论 本文方法简单有效,无需港口先验信息,适用于多尺度和多方向的靠岸舰船目标检测任务,对不同类型舰船形态差异具有鲁棒性,且能够分离并靠舰船。     

船舶零航速减摇鳍控制系统研究

船舶零航速减摇鳍是指在来流速度为0的流场中依靠鳍的主动摆动产生升力,以对抗海浪的作用力,从而减小系泊状态下船舶摇摆的减摇。设计了伺服控制系统,增加了升力限位环节。通过对有义波高分别为1,2m,浪向角均为90°海况下的仿真研究,减摇效果分别达到了78．30％和56．92％,优于减摇水仓减摇效果,证明所设计系统能够满足船舶零航速减摇的要求。     

Deep Neural Network Based Detection and Segmentation of Ships for Maritime Surveillance

In recent years, computer vision finds wide applications in maritime surveillance with its sophisticated algorithms and advanced architecture. Automatic ship detection with computer vision techniques provide an efficient means to monitor as well as track ships in water bodies. Waterways being an important medium of transport require continuous monitoring for protection of national security. The remote sensing satellite images of ships in harbours and water bodies are the image data that aid the neural network models to localize ships and to facilitate early identification of possible threats at sea. This paper proposes a deep learning based model capable enough to classify between ships and no-ships as well as to localize ships in the original images using bounding box technique. Furthermore, classified ships are again segmented with deep learning based auto-encoder model. The proposed model, in terms of classification, provides successful results generating 99.5% and 99.2% validation and training accuracy respectively. The auto-encoder model also produces 85.1% and 84.2% validation and training accuracies. Moreover the IoU metric of the segmented images is found to be of 0.77 value. The experimental results reveal that the model is accurate and can be implemented for automatic ship detection in water bodies considering remote sensing satellite images as input to the computer vision system.     

Investigation of the Nonlinear Rolling of a Ro-Ro Ship with Slipping of Heavy Loads

The common effect of waves and the slippage of internal heavy loads will cause a ro-ro ship to roll seriously. This is one of the important reasons when ro-ro ships capsize. The multibody system with a floating base is composed of a ro-ro ship and slipping heavy load. This paper takes the rolling angle of the ship and the transverse displacements of the heavy loads on deck as degrees of freedom. The equations of motion of the system are derived, including the influence of the nonlinear restoring and damping moments due to the influence of the waves. Taking a certain channel ferry as an example, a set of numerical calculations have been carried out for the synchronous effect of slipping heavy loads on a rolling ro-ro ship, the nonlinear rolling response of the ship and the displacement response of the slipping heavy load under the common effect of synchro-slipping heavy loads and wave. The conclusions are that the motion of the numerous freely slipping vehicles synchronize in most cases and the nonlinear rolling angle of the ro-ro ship will increase when considering the nonlinear characteristics.     

Deterministic and probabilistic ship pitch prediction using a multi-predictor integration model based on hybrid data preprocessing,reinforcement learning and improved QRNN

The deterministic and probabilistic prediction of ship motion is important for safe navigation and stable real-time operational control of ships at sea. However, the volatility and randomness of ship motion, the non-adaptive nature of single predictors and the poor coverage of quantile regression pose serious challenges to uncertainty prediction, making research in this field limited. In this paper, a multi-predictor integration model based on hybrid data preprocessing, reinforcement learning and improved quantile regression neural network (QRNN) is proposed to explore the deterministic and probabilistic prediction of ship pitch motion. To validate the performance of the proposed multi-predictor integrated prediction model, an experimental study is conducted with three sets of actual ship longitudinal motions during sea trials in the South China Sea. The experimental results indicate that the root mean square errors (RMSEs) of the proposed model of deterministic prediction are 0.0254°, 0.0359°, and 0.0188°, respectively. Taking series #2 as an example, the prediction interval coverage probabilities (PICPs) of the proposed model of probability predictions at 90%, 95%, and 99% confidence levels (CLs) are 0.9400, 0.9800, and 1.0000, respectively. This study signifies that the proposed model can provide trusted deterministic predictions and can effectively quantify the uncertainty of ship pitch motion, which has the potential to provide practical support for ship early warning systems.