Simulation of wave power devices

Classical frequency and time domain models of a single degree of freedom wave power device are presented. In the time domain, a convolution integral is conventionally used to represent the fluid dynamic radiation force, characterised by added mass and damping in the frequency domain. This integral is replaced by an approximate ordinary differential equation (ODE) model which is faster and more convenient in simulations. A time domain model of the fluid dynamics of an oscillating water column (OWC) device is derived to illustrate the technique. Digital simulations of the OWC are used to compare the accuracy of the classical and ODE models. The simulation of the ODE model runs about six times as fast as the classical model based on convolution, yet characterises the fluid dynamics accurately.     

Numerical Study on Instantaneous Discharge of Unsorted Particle Cloud in Cross Flow

The mixing characteristics of particles such as dredged sediment of variable size discharged into cross flow are studied by a 3D numerical model, which is developed to model the particle-fluid two-phase flow. The Eulerian method with the modified k-ε parameterization of turbulence for the fluid phase is used to solve fluid phase, while a Lagrangian method for the solid phase (particles), both the processes are coupled through the momentum sources. In the model the wake turbulence induced by particles has been included as additional source term in the k-ε model; and the variable drift velocities of the particles are treated efficiently by the Lagrangian method in which the particles are tracked explicitly and the diffusion process is approximated by a random walk model. The hydrodynamic behavior of dumping a cloud of particles is governed by the total buoyancy of the cloud, the drag force on each particle and the velocity of cross-flow. The computed results show a roughly linear relationship between the displacement of the frontal position and the longitudinal width of the particle cloud. The particle size in the cloud and the velocity of cross flow dominate the flow behavior. The computed results are compared with the results of laboratory experiments and satisfactory agreement is obtained.     

人工鱼礁工程的风险评估

对台风暴潮影响下的嵊泗海域人工鱼礁工程做了风险评估,考虑了台风暴潮中出现的大浪和风暴潮减水对鱼礁联合作用的危害。风险评估分为危险灾害识别、失效概率计算、失效后果评估、风险准则评定和风险管理决策几个主要的步骤。在失效概率的计算中采用基于应用设计点的重点抽样法随机模拟的技术,这一随机模拟技术可以广泛的应用与海洋工程结构的风险评估当中。     

黄、东海环流的数值研究Ⅲ——正压环流的数值模拟

依据黄、东海环流的的动力学模型 ,运用“流速分解法”对黄、东海正压环流进行了数值模拟。计算结果表明冬季黄海正压环流主要受风应力影响 ,基本形态为黄海暖流由济州岛西南进入南黄海中部 ,其东西两侧分别为两支向南流动的沿岸流 ;夏季主要受到潮致体力的影响 ,为一逆时针涡旋。东海环流主要是边界力作用驱动的结果 ,东海黑潮、台湾暖流和对马暖流较稳定。冬季风应力对东海环流表层流场有消弱作用 ,在夏季则有一定增强作用。     

A model of the formation and development of ocean shear wave

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闽江河口潮流数值模拟

应用边界拟合坐标系统，解决了闽江河口河道曲折汊道多造成的计算方向与河底走向交角过大的难点；针对闽江河口长宽比相差较大的特点，移植了通常用于河道计算的沿纵向求解大尺度矩阵问题转化为沿横向小尺度矩阵求逆的水流方程求解方法，采用全隐差分格式，使闽江口数模网格步长最小控制在50m左右，时步长达3min，潮位、流场与实测拟合良好。     

Numerical Simulation of Multi-Directional Random Seas

Multi-directional irregular waves are simulated on the basis of the given directional spectrum using a double summation model, a single direction per frequency model and a single summation model. Their results are compared. It is shown that the single direction per frequency model proposed in this paper can generate a realistic wave field. The effects of the model parameters on the simulated results are also studied in this paper and corresponding suggestions are given.     

东中国海环流及其季节变化的数值模拟

关于东中国海环流的研究，国内外学者已做了大量的工作。早期科学家们主要依赖于对温盐资料和少数测流资料的分析研究对渤、黄、东海的环流结构有了较系统和深入的认识。东中国海环流是由一个气旋式的“流涡”组成，东侧主要是北上的黑潮-对马暖流-黄海暖流及其延伸部分；西侧为南下的沿岸流系。黑潮对东中国海环流的影响是如此之大，以致于除了某些局部区域外，上述海域主要流系的冬、夏季分布形式比较相似而无本质上的差异(胡敦欣等，1993)。但本文所研究海域正处于世界上最显著的季风区，冬、夏季盛行风向基本相反，过渡季节(春、秋季)风向多变，风力减弱；海洋热盐结构季节变化明显(如冬季混合强，而夏季层化明显等)，这些因素都使得东中国海环流存在着较明显的季节变化。 自20世纪80年代以来，东中国海环流的数值模拟工作逐步展开，并已成为研究环流结构及其形成机制的强有力工具。但由于数值模式本身以及计算方案的缺陷(如有些学者用固定的风场、温盐场对东中国海环流进行诊断模拟等)和观测资料的不足，数值模拟的结果难以得到验证，渤、黄、东海的环流研究中仍有大量的问题存在争议，以待澄清。例如，台湾暖流的来源、流径;对马暖流的来源;夏季黄海暖流的流径以及黄海冷水团环流等均有不同的论述。对黄、东海环流季节变化的数值模拟工作也较少，多用冬、夏典型月份的风场强迫积分至稳定态，给出冬、夏季环流，这种做法值得商榷。三维环流模式很难在1个月内达到稳定态，尤其是夏季层化明显、风力减弱的情况下，非常定风场的影响更应引起人们的重视。 本文采用比较符合实际的计算方案，用年循环风场和海面热通量场为外强迫，对渤、黄、东海的环流及其季节变化进行了模拟，并对一些争议问题进行了探讨。