不同尺度DDM的深度保证率变化规律研究

针对当前高密度多波束水深数据抽稀后所构建数字水深模型(digital depth model,DDM)的航海安全性缺少估计这一问题,分别以最浅点法、最近点法和平均值法3种常用方法抽稀水深数据并构建DDM,在此基础上,分析不同抽稀方法所构建DDM随尺度变化的深度保证率变化规律,采用统计分析的方法建立DDM深度保证率与抽稀尺度、海底地形复杂因子之间的数学回归模型。实验表明:该回归模型不仅可用于估算基于不同抽稀方法所构建DDM的深度保证率,也为确定满足适合的DDM深度保证率所需要的抽稀尺度提供了理论依据。     

岸基GNSS反射信号延迟多普勒图变化特征分析

GNSS-R(Global Navigation Satellite System-Reflections)技术是一种可用于海面参数遥感探测的新兴技术,是当前国内外的研究热点之一。GNSS海面反射信号的延迟多普勒图像(DelayDoppler Map,DDM)是GNSS-R技术应用的重要理论基础。基于Z-V模型确定了岸基GNSS反射信号DDM的理论仿真方法和流程,并进行了实验验证,实验结果显示,仿真DDM与实测DDM之间具有很好的一致性。同时,全面系统地分析了风速、风向、接收天线高度和卫星仰角4个参数对DDM变化特征的影响规律,仿真结果显示:风速和接收天线高度的影响呈单调特性;风向的影响呈周期特性;卫星仰角的影响则比较特殊,在30°以下时呈现明显的单调性,大于30°时误差几乎相同,即具有窗函数选择特性,这种变化特征为利用DDM反演海面波浪、风场数和海面粗糙度等参数提供了理论依据和参考。     

基于核密度和Voronoi算法的点选取模型

为了清晰有效表达不同尺度下的点状应急态势符号,使其能够适应尺度变化,提出了一种基于核密度和Voronoi算法的点选取模型,通过核密度分析、建立Voronoi图的方法对同类点进行选取。实验表明,该模型有效保持了应急态势符号的空间分布特征和属性信息,解决了因比例尺缩小而导致的压盖、重叠等问题;同时降低了大数据量下符号选取的计算难度,提高了选取效率,保证了应急态势图的清晰易读性。     

基于半参数回归的DDM内插方法

提出了一种基于半参数回归的数字水深模型(DDM)内插方法。将原始水深数据误差和内插函数的逼近误差分别视作数字水深模型的偶然误差和系统误差部分,构建DDM内插的半参数回归模型;基于距离法与L曲线法,分别确定正规化矩阵R与平滑因子α;采用按方位取点的加权平均法,估计内插函数在任意节点处的逼近误差。实验结果表明:所提方法提高了DDM的构建质量;海底地形复杂程度越大,所提方法对DDM构建质量的提高程度越大。     

基于不完全四叉树的数字水深模型多尺度表达

空间数据的多尺度表达问题是GIS领域研究的重点和难点问题之一。以数字水深模型(DDM)为研究对象,从DDM的几何形态角度出发,通过挖掘水深点之间的空间几何关系,构建了基于不完全四叉树的DDM多尺度表达模型。实验证明,该模型在符合DDM多尺度表达基本原则的前提下,能较好地保持DDM的基本地形特征,同时具有较高的计算效率。     

基于深度学习的海温观测数据质量控制应用研究

基于国家海洋信息中心质量控制后的西太平洋 10 度方区约 100 万站次温盐实测历史调查资料,对经过 26 种严格质量控制方法的综合海温质量符进行分类分析,首次将深度学习技术应用于海洋数据质量控制多分类 （multiclass classification）算法与应用研究。通过人工合成少数类样本和加权损失函数方法减少多数类的频率来降低数据的不平衡,并构建了多层感知器 （Multi-Layer Perceptron, MLP） 和深度神经网络 （Deep Neural Network, DNN） 两个海温资料质量符分类深度学习模型。分类结果表明本文构建的两个深度分类模型能够较准确快速地识别该海域海温数据质量,在 20 975 条温盐剖面资料测试集中分类准确率分别达到 99.63%和 99.69%。海温资料的分类精度评分有着较好的表现,其中正确数据 （QC1） 和数据缺失（QC9） 的正确识别率均达 100%。MLP 和 DNN 多分类质量控制模型可大幅降低传统质量控制方法的工作量,提升海量数据处理速度和分析能力,为海温观测资料在海洋研究与工程中应用提供参考。     

基于航海应用的海图数据库比例尺分级研究

介绍了我国海图生产现状及基于数据库的海图制图技术,针对以航海图生产为主要目的的海图数据库建设中的比例尺分级问题,依据统一的样本海图选择原则,计算海部要素载负量,计算结果表明,海图载负量数值受地形、人为等因素影响大。定义一个全水深的理想海部区域,通过确定水深注记间距和载负量之间的关系、参考现有海图水深注记最小间距值和航海应用对海图比例尺分级的需求等因素,最终确定了海图数据库比例尺分级方案。     

基于聚类过程的多比例尺GIS空间数据模型设计

在面向对象的数据模型的构造基础上,提出一种基于聚类过程的多比例尺空间数据模型,并得到尺度依赖的空间数据表达。以图斑数据为实例,通过空间分布与距离信息的聚类过程,建立了图斑数据的多比例尺分层分区的数据模型,从而由数据本身实现多尺度表达与综合的模型化,降低或消除了制图综合过程中的主观影响和不稳定性,改进和提高了多尺度表达与综合的效果和质量。     

海洋浅层土质剪切波速与深度的关系分析

剪切波速是工程场地地震安全性评价最重要的参数之一。应用测试的大量海洋浅层土质的剪切波速数据,利用最小二乘法通过三种模型探讨了不同土质类型的剪切波速与深度的关系,给出了不同土质类型的剪切波速与深度拟合最佳的统计公式。并与《构筑物抗震设计规范》的推荐公式在某一海域工程场地的测试结果进行对比分析,结果表明:本文所建立的统计公式对剪切波速的预测效果明显好于规范所推荐的统计公式。所推荐的海洋不同土质类型的剪切波速与深度间的统计公式,可供无波速测试的海洋工程场地使用。     

波能测试区波浪运动数学模型研究

为研究位于大万山岛南部的波能测试区新增发电机组对该水域波浪场产生的水动力作用,将自主建立的二维Boussinesq波浪模型应用于该测试区,模拟了不同波浪要素下装置布设前线性波的运动传播,装置布设后无锚固时其在波浪中的自由运动、有锚固时其对波浪场的影响。结果表明,装置布设前的波浪传播,低潮位时波峰线相较高潮位时更为明显,且受陆域影响更大;装置无锚固时的自由运动,低潮位时其运动速度、旋转角速度均小于高潮位时;装置有锚固时,其对波浪场的影响主要集中在背波面,会形成一道顺波向的"扇形"衰减区,其影响程度随波高、波周期的增大而减小。因此,根据研究结果所得到的相对波高衰减范围,可对后期2,3号发电装置的规划与布设提供科学依据,即尽量避开由1号装置引起的波高衰减区,以免造成波能利用率的降低。     

长航道乘潮水位计算新方法研究及应用

随着航道建设规模和航道里程增加,长航道乘潮水位的计算成为航道设计遇到的新技术难题之一。针对多潮位站控制长航道乘潮水位计算问题,提出了乘潮水位计算的多站联合典型潮曲线法。通过构建典型潮曲线,使乘潮累积频率、乘潮历时、潮波传播延时和潮波变形等关键要素同时呈现。基于构建的典型潮曲线,进一步探讨了长航道全程同一乘潮水位、分段变乘潮水位,以及进港、出港等不同情况下乘潮水位的设计取值方法,并以珠江崖门航道为例进行了实例分析,进一步说明了本方法的实用可行。     

Large eddy simulation of spilling and plunging breakers

A Navier–Stokes solver with a free surface model is used for simulating wave breaking, undertow, and turbulence in breaking waves. The free surface model is based on the Volume of Fluid concept. Turbulence scales larger than the grid scale are simulated directly while turbulence scales smaller than the grid scale are represented by a sub-grid scale model. Two different approaches for the sub-grid scale model have been applied, which are the Smagorinsky model and a model based on a k-equation for the sub-grid scale turbulence. The waves approach the shore in shore-normal direction and break on a plane constant sloping beach. Periodic spilling and plunging breakers are simulated for 20 and 16 wave periods, respectively. The set-up, undertow, and turbulence levels are compared to experimental results. Despite the rather coarse resolution of the computational domain, satisfactory results for the wave height decay and undertow have been obtained. However, the turbulence levels are over-predicted when using the standard values of the model parameters and a complete answer to this problem has not been found. Furthermore, the evolution of vorticity over the wave period has been studied. It shows that at the initial breaking point vorticity is generated around the vertical as well as around the transverse axis. Later vorticity around the longitudinal axis (offshore–onshore direction) is generated, probably through deformation of vorticity around the other axis.     

Influence of Spur Dike on Hydrodynamic Exchange Between Channel and Shoal of Generalization Estuary in Physical Model Test

Widely applied in maintaining estuarial waterway depth, the spur dike has played an important role in currents and sediment exchange between channel and shoal and sediment back-silting in the channel. Through establishing a generalized physical model at a bifurcated estuary and conducting current tests under the joint action of runoff and tide, the influence of the spur dike length on current exchange between channel and shoal is analyzed. Results show that when the spur dike length reaches a certain value, the direction of the flow velocity shear front between the channel and shoal will change. The longer the spur dike, the larger the transverse fluctuating velocity at the peak of flood in the channel shoal exchange area, while the transport of the transverse hydrodynamics is obvious in the process of flood. There is an optimum length of spur dike when the shear stress in the channel and the longitudinal velocity in flood and ebb reach the maximum, and the flow velocity will decrease when the spur dike length is smaller or larger than the optimum. For a certain length of spur dike, the larger the channel shoal elevation difference, the larger the peak longitudinal flow velocity in the middle of the navigation channel in flood and ebb. However, the transverse flow velocity will first decrease and then increase. The transverse transportation is obvious when the channel shoal elevation difference increases.     

GNSS-R观测下的海面飓风风速反演

利用全球导航卫星系统在地球表面的反射信号（GNSS-R）进行海面风速反演已经被广泛研究并作为一种重要的遥感手段。目前,该L波段微波信号的相关功率已可以在多普勒频率和时延码片空间进行多普勒时延图像的成像。由于该图像的图像特征与海面粗糙度有较高的相关性,因此能够用来进行海面风场反演。然而,对于该遥感手段而言,其双基雷达前向散射截面（BRCS）理论上与海面粗糙度有更高的相关性,如同目前合成孔径雷达使用后向雷达散射截面而非相关功率。所以,本文通过改进已有的GNSS-R的双基雷达散射截面方程,代替相关功率在多普勒时延空间进行成像,得出了与海面粗糙度相关的双基雷达散射截面图像（BRCS map）。基于该图像,本文提出了三种与其形状特征相关的观测量,通过2005年Dennis飓风GNSS-R机载数据生成的16000多幅图像进行地球物理模式函数建模并与经典的一维时延波形匹配方法得出结果进行对比分析,得出更为精确的风速反演结果。     

离散群中Mbius变换的公共不动点与极限球和超球的关系

研究了Mbius变换f,g不动点的关系对它们的极限球或超球之间位置的影响。证明了,在〈g,f〉离散群且二者的不动点集合相等时,当g,f为抛物变换时,范数越大,极限球越小;当g,f为双曲变换时,迹越大,超球越小;当g,f为椭圆变换时,旋转角越大,超球越小。如果〈g,f〉是离散群且二者没有公共不动点,并且f,g共轭时,则存在一个正数,使得f,g的极限球或超球不相交。     

Wave pattern induced by a moving atmospheric pressure disturbance

A moving low atmospheric pressure is a main feature of tropical cyclones, which can induce a system of forced water waves and is an important factor that cause water level rise during a storm. A numerical model based on the nonlinear shallow water equations is applied to study the forced waves caused by an atmospheric pressure disturbance moving with a constant velocity over water surface. The effects of the moving speed, the spatial scale and the central pressure drop of the pressure disturbance are discussed. The results show that the wave pattern caused by a moving low-pressure is highly related with its moving speed. The wave pattern undergoes a great change as the moving speed approaches the wave velocity in shallow water. When the moving speed is less than the wave velocity, the distribution of water surface elevation is nearly the same as that of the pressure disturbance, and the maximum of the water surface elevation is located at the center of pressure. When the moving speed is larger than the wave velocity, a triangle shaped wave pattern is formed with a depression occurs in front of the pressure center, and the maximum of the water surface elevation lags behind the center of pressure. As the moving speed increases, the maximum of the water surface elevation firstly increases and then decreases, which reaches a peak when the moving speed is close to the wave velocity. The maximum of water surface elevation is approximately in proportion to the central pressure drop, and slightly affected by the spatial scale of pressure disturbance. Both the central pressure drop and the spatial scale of the pressure disturbance do not significantly affect the forced wave pattern. However, a clear difference can be noticed on the ratio of the maximum water surface elevation in moving pressure situation to that in static situation, when the moving speed is close to the wave velocity. A pressure disturbance with smaller spatial scale and smaller central pressure drop will give a larger ratio when the moving speed is close to the wave velocity.     

顾及海底地形变化的狄洛尼三角网构建

数字水深模型是对海底表面形态的数字化表达,传统的网格数字水深模型存在不能根据海区水深变化情况自动调节内插水深间隔的不足,提出了以深度极限误差作为判断标准,顾及海底地形变化的补深补浅方法,并在此基础上构建了相应的狄洛尼三角网。 实验证明:与传统的最浅点抽稀规则格网方法相比,所提方法更能合理的反映出海底地形的实际变化情况,并明显改善 DDM 精度。     

移动式海上基地多模块间相互作用对连接器载荷的影响

移动式海上基地(MOB)一般由多个模块构成,模块间的相互作用对连接器载荷可能有影响,但在许多现有文献中通常被忽略。计算了考虑模块间相互作用的5模块MOB的模块运动和连接器载荷响应,并与不考虑模块间相互作用的结果进行了比较。结果表明模块间相互作用对不同连接器刚度的MOB连接器载荷的影响不同,在浪向角较小尤其在迎浪时十分明显且不可忽略;当浪向角较大尤其是横浪时,模块间相互作用力较小。     

The elemination of re-reflected waves by a porous medium of finite thickness

The elimination of re-reflected waves in a wave channel by installing a porous medium in front of the wavemaker is investigated. The thickness of the porous wall required to eliminate the re-reflected waves is shown to be related to th porosity, friction coefficient, and wave period, as well as to both the positions of the porous medium and the test structure. However, this study indicates that the goal of eliminating re-reflected waves can be achieved by simply varying the thickness of the porous medium according to the wave period, with all the other factors arbitrarily selected.Assuming that the oscillation amplitude of the wavemaker board is constant, the primitive wave amplitude, before reaching the porous medium, becomes smaller as the wave period is increased. In addition, the study found that the required thickness of the porous medium for eliminating the re-reflected wave becomes larger as the wave period is increased. This results in a trend which further reduces the wave amplitude after the wave passes through the porous medium. In consequence, the oscillation amplitude of a wavemaker board has to be adjusted in a larger scale if the wave period is to be increased.