Extension of the Frequency-Domain pFFT Method for Wave Structure Interaction in Finite Depth

To analyze wave interaction with a large scale body in the frequency domain, a precorrected Fast Fourier Transform (pFFT) method has been proposed for infinite depth problems with the deep water Green function, as it can form a matrix with Toeplitz and Hankel properties. In this paper, a method is proposed to decompose the finite depth Green function into two terms, which can form matrices with the Toeplitz and a Hankel properties respectively. Then, a pFFT method for finite depth problems is developed. Based on the pFFT method, a numerical code pFFT-HOBEM is developed with the discretization of high order elements. The model is validated, and examinations on the computing efficiency and memory requirement of the new method have also been carried out. It shows that the new method has the same advantages as that for infinite depth.     

Wave Breaker Indices in Finite Water Depth

Based on the analysis and comparison of wave breaker indices defined by geometric, kinetic as well as dynamic stabilities and verified by observation, the value a, which is equal to H / Lthkd by Miche's result and may be modified by Goda's results, is" suggested as the wave breaking criteria. The applicable values of a for pure waves or wave-current co-existing field are given in this paper. They are smaller than Miche's result (0.142), and they have been verified by model tests.     

An Efficient Model for Transient Surface Waves in Both Finite and Infinite Water Depths

A numerical model is developed to simulate fully nonlinear extreme waves in finite and infinite water-depth wave tanks. A semi-mixed Eulerian-Lagrangian formulation is adopted and a higher-order boundary element method in conjunction with an image Green function is used for the fluid domain. The boundary values on the free surface are updated at each time step by a fourth-order Runga-Kutta time-marching scheme at each time step. Input wave characteristics are specified at the upstream boundary by an appropr...     

An Efficient Model for Transient Surface Waves in Both Finite and Infinite Water Depth

A numerical model is developed to simulate fully nonlinear extreme waves in finite and infinite water-depth wave tanks. A semi-mixed Eulerian-Lagrangian formulation is adopted and a higher-order boundary element method in conjunction with an image Green function is used for the fluid domain. The boundary values on the free surface are updated at each time step by a fourth-order Runga-Kutta time-marching scheme at each time step. Input wave characteristics are specified at the upstream boundary by an appropriate wave theory. At the downstream boundary, an artificial damping zone is used to prevent wave reflection back into the computational domain. Using the image Green function in the whole fluid domain, the integrations on the two lateral walls and bottom are excluded. The simulation results on extreme wave elevations in finite and infinite water-depths are compared with experimental results and second-order analytical solutions respectively. The wave kinematics is also discussed in the present study.     

Statistical Distribution of Depth-Integrated Local Horizontal Momentum for Second-Order Random Ocean Waves in Finite Water Depth

Based on the second-order random wave solutions of water wave equations in tinite water depth, statistical distributions of the depth-integrated local horizontal momentum components are derived by use of the characteristic function expansion method. The parameters involved in the distributions can be all detemained by the water depth and the wavenumber spectrum of ocean waves. As an illustrative example, a fully developed wind-generated sea is considered and the parameters are calculated for typical wind speeds and water depths by means of the Donelan and Pierson spectrum. The effects of nonlinearity and water depth on the distributions are also investigated.     

New Derivation of Ordinary Differential Equations for Transient Free-Surface Green Functions

Based on the Laplace transform, a direct derivation of the ordinary differential equations for the three-dimensional transient free-surface Green function in marine hydrodynamics is presented. The results for the 3D Green function and all its spatial derivatives are a set of fourth-order ordinary differential equations, which are identical with that of Clement (1998). All of these results may be used to accelerate numerical computation for the time-domain boundary element method in marine hydrodynamics.     

基于遥感海浪信息的近岸水深反演模型

基于遥感影像的测深技术具有易获取、成本低和覆盖率大等优势,是目前的研究热点问题之一。为在波浪折射的基础上,进一步综合考虑绕射及非线性的影响,本文提出了一种基于海浪波数和波高信息的近岸水深反演模型。将模型与Berkhoff 椭圆形浅滩理想试验对比,平均误差为0.13%,显著小于现有基于频散关系反演水深的方法。进一步应用模型反演三亚湾近岸地形,通过与海图对比,平均误差为11.58%,且大部分区域的误差小于10%。部分区域误差较大,主要是由于遥感影像获取的波数空间分辨率和精度较低。以上结果表明该模型可以利用遥感海浪信息较准确推算近岸水深。本文对于近岸浅海区的水深反演工作具有一定的参考价值。     

Wave-Induced Loads on Very Large FPSOs at Restricted Water Depth

The effects of water depth on the wave-induced vertical bending moment and shearing force on a very large FPSO are studied by experiments and computations for regular and irregular waves. The restricted water depth composite Green function is employed to develop a program for the computation of the hydrodynamic coefficients of the very large FPSO at shallow water. A thrce-segment model with 1 : 100 scale is tested in the State Key Laboratory of Ocean Engineering at Shanghai Jiao Tong University for the verification of the nmnerical method. The experimental and computational results show that the water depth has a substantial effect on wave-induced loads. The wave-induced vertical loads increase with the decrease of water depth for shallow water. Especially, for ultra-shallow water these loads increase very evidently with the decrease of water depth. The long-term prediction values of wave-induced vertical loads increase with the decrease of the ratio of water depth to draught. The long-term prediction values of wave-induced vertical loads are about 8% larger than those for deep water when the ratio of water depth to draught is 3.0. However, water depth hardly affects the longterm prediction values of wave-induced loads when the ratio of water depth to draught is larger than 5.0.     

多光谱遥感水深反演及其水下碍航物探测技术

针对采用传统海洋测量手段难以获取危险及争议海区的水深和水下碍航物信息,提出了基于卫星遥感进行水深反演和水下碍航物探测的新思路。探讨了多光谱遥感水深反演的数据预处理方法、遥感水深反演模型的构建及水下碍航物遥感探测方法,并开展了相应的实验验证。实验表明,采用卫星遥感手段可以快速地获取测量船只不易到达海区的水深和水下碍航物信息,研究成果对海洋测绘技术的发展具有一定的指导意义和应用价值。     

Hybrid Model Testing Technique for Deep-Sea Platforms Based on Equivalent Water Depth Truncation

In this paper,an inner turret moored FPSO which works in the water of 320 m depth,is selected to study the so-called "passively-truncated numerical-simulation" type of hybrid model testing technique while the truncated water depth is 160 m and the model scale λ=80.During the investigation,the optimization design of the equivalent-depth truncated system is performed by using the similarity of the static characteristics between the truncated system and the full depth one as the objective function.According to the truncated system,the corresponding physical test model is made.By adopting the coupling time domain simulation method,the truncated system model test is numerically reconstructed to carefully verify the computer simulation software and to adjust the corresponding hydrodynamic parameters.Based on the above work,the numerical extrapolation to the full depth system is performed by using the verified computer software and the adjusted hydrodynamic parameters.The full depth system model test is then performed in the basin and the results are compared with those from the numerical extrapolation.At last,the implementation procedure and the key technique of the hybrid model testing of the deep-sea platforms are summarized and printed.Through the above investigations,some beneficial conclusions are presented.     

大辽河流域水生态系统功能区划研究

为了明确大辽河流域范围内主要的生态环境问题、生态环境脆弱区和对流域生态安全非常重要的区域,根据流域湿地景观格局的变化及驱动机制分析、流域生态环境敏感性评价和水生态系统服务功能重要性评价,运用定性分区与定量分区相结合的方法和自下而上的划分方法得到大辽河流域水生态系统功能分区图,将大辽河流域划分成5个一级区和13个生态亚区。按照"水体类型+干扰类型+功能类型"对每个生态功能区进行命名,明确了每一个生态功能区的特征,为大辽河流域产业布局、生态环境保护与规划建设提供了科学依据。     

Numerical Treatments and Applications of the 3D Transient Green Function

How to evaluate time-domain Green function and its gradients efficiently is the key problem to analyze ship hydrodynamics in time domain.Based on the Bessel function,an Ordinary Differential Equation(ODE)was derived for time-domain Green function and its gradients in this paper.A new efficient calculation method based on solving ODE is proposed.It has been demonstrated by the numerical calculation that this method can improve the precision of the time-domain Green function.Numerical research indicates that it is efficient to solve the hydrodynamic problems.     

水深对超浅吃水拖轮系柱拖力的影响

超浅吃水拖轮在浅海对钻井平台进行拖带和井位定位时,必须了解超浅吃水拖轮浅水系柱拖力特性,才能充分利用海潮条件和自身能力完成钻井平台的拖带和定位任务。     

Second-Order Potentials and Forces for Two-Dimensional Diffraction Problem of Finite Water Depth

-In this paper, an analytical solution in the outer region of finite water depth is derived for the second-order diffraction potential, which gives a clear physical meaning of the wave transmission and reflection characteristics in the far field. A numerical method-simple Green's function technique-for calculating the second-order diffraction potential in the inner region is also described. Numerical results are provided for the second-order wave forces on a semi-submerged cylinder. It is found that the contribution of second-order diffraction potential to second-order wave forces is important. The effect of water depth and submerged depth on the wave force is also discussed.     

机载海洋激光雷达测量叶绿素a浓度、悬移质浓度和浅海深度的性能估计

以14:00时离水辐亮度作为背景光强度,模拟355nm激光雷达测量不同深度水层叶绿素a荧光的信噪比.分析体积衰减系数c、辐照度衰减系数k、散射系数b和透明度盘深度(SDD)的关系.最后模拟532nm激光雷达测量悬移质浓度的最大测量深度和误判率小于10%时的最大海底探测深度随SDD的变化.     

利用多波段卫星数据进行浅海水深反演方法研究

以遥感反演水深的基本原理为基础,利用我国南海永暑礁景区的TM数据和实测水深资料,通过TM多波段数据辐射校正、图像与海图地理配推、底质类型分区、潮汐改正和实测水深数据与相应的图像辐射值回归分析,建立了浅海水深反演模型,并进行了浅海岛礁水深的实际计算,总标准误差为2．14m。对我国南海30m以浅岛礁水深地形研究有很好的应用价值。     

A new ordinary differential equation for the evaluation of the frequency-domain Green function

Clément (2013) derived a second order ordinary differential equation (ODE) satisfied by the free-surface Green function in the frequency domain. Since then, similar ODEs for the gradient of the Green function have been developed. Unfortunately, all these ODEs degenerate at zero frequency. Therefore, it is not possible to initialize the numerical solution of these ODEs from this zero frequency. Alternative methods based on the shifting of the initial condition to frequencies strictly greater than zero have then been developed.The present paper describes an alternative approach to address this issue. It involves a new function which is the solution of a modified ODE which can be solved from the zero frequency.Finally, comparisons with evaluations of the Green function using the classical direct integration method are provided. They show that the new ODE can provide accurate estimates of the Green function.     

四阶波动方程的有限体积元法

建立一类四阶色散耗散方程全离散有限体积元格式,并给出格式的收敛性和误差估计,同时还给出数值结果。     

Hydroelastic Analysis of Very Large Floating Structures Using Plate Green Functions

1 .IntroductionRecentlygreatinteresthasbeenshowninthedevelopmentofverylargefloatingstructuressuchasMegaFloatofJapan (Isobe ,1 999)andMOBofUSA (Remmers ,1 999) .Owingtotheirextremelargesizeandgreatflexibility ,thecouplingbetweenthestructuraldeformationandfluidmotionissignifi cant.Thisisatypicalproblemofhydroelasticity .Efficientandaccurateestimationofthehydroelasticresponseofverylargefloatingstructuresinwavesisveryimportantfordesign .Manymethodshavebeenproposedinliteratureforthepredictiono…     

中等水深轻型张力腿井口平台运动研究

本文提出了一种中等水深轻型张力腿井口平台的型式。研究了该种型式平台的六个自由度的运动响应以及所受到的波浪力、二阶漂移力、系索回复力和系索张力等特性。分析了平台运动响应与水深以及系索预张力大小的关系。文中得出的结论可供张力腿初步设计时参考。