脉冲波作用下竖直弹性板的水弹性响应

基于线性势流理论,将流场分为3个部分:入射势与反射势部分、辐射势的记忆部分、辐射势的瞬时部分,竖直弹性板的时域振动基于模态叠加法,利用傅里叶与拉普拉斯变换求解流场控制方程,与板的振动方程耦合,推导得出波浪作用下竖直弹性板的时域耦合方程,并利用二级四阶隐式Runge-Kutta法求解方程。首先给定竖直板一个初始弯曲,得到的结果与解析解和数值解结果吻合良好,验证了方法的正确性。其次对脉冲波作用下弹性竖直板的响应进行研究,分析了板的刚度系数、质量系数、脉冲幅值和边界条件对其水弹性响应的影响。研究结果表明,刚度系数对板的振动频率影响很大,脉冲幅值与板的振动幅度正相关,两边固定时对竖直弹性板的疲劳损伤最严重。     

非线性遗传优化海域水质耦合模型多参数反演方法研究

通过遗传算法和海域水质模型的有机耦合,提出了基于非线性遗传优化海域水质耦合模型多参数反演的新方法.将海域水质模型嵌入遗传算法模型中,以海域内部验证点位的误差函数为适应度,进行模型多参数的优化反演.文中以渤海湾海域水质模型多参数反演的“孪生”试验来验证方法的有效性.数值结果表明:该反演新方法具有较高的精度.     

海域潮汐模型开边界反演优化方法研究

应用数据驱动模型建立海域潮汐模型开边界条件反演的新方法:分析选择主要分潮作为控制变量并设计计算工况,将海域潮汐模型计算工况结果和控制变量带入数据驱动模型,建立内部观测点潮汐(或潮流)同开边界潮汐之间的关系,利用海域内部的潮汐和潮流观测资料反演开边界条件.以辽东湾海域潮汐模型非耦合与耦合开边界反演验证该方法,通过对反演开边界结果的校验表明耦合开边界反演是有效的,而非耦合开边界反演不具备工程实用性.     

波浪环境中圆形垂向射流的试验研究

使用粒子图像测速技术PIV(particle image velocimetry)对有限水深规则波浪环境下圆形垂直射流进行了试验研究。应用相位分析法从测量结果中分离出时间平均的速度值。试验中用5种不同周期的波浪研究波周期对射流的影响,分析了射流核长度与射流比、射流出口速度与波浪速度之比和波陡的关系,以及一定区域内射流喷口轴线上垂向平均速度的衰减规律和射流宽度的发展规律。结果表明波周期对射流的流场特性有显著影响。     

Lagrangian methods for water transport processes in a long-narrow bay- Xiangshan Bay,China

A better understanding of water transport processes is highly desirable for the exploitation of the ocean resources and the protection of the ocean ecological system. In this paper, the Lagrangian methods are used to study the water transport processes in Xiangshan Bay in China, a typical semi-closed and narrow-shaped bay with complex coastline and topography. A high-resolution 3-D hydrodynamic model is developed and verified, and the results from the model agree well with the field data. Based on the hydrodynamic model, the Lagrangian residual current is computed by using the particle tracking method. A concept based on the dynamical systems theory, the Lagrangian coherent structures （LCSs）, is introduced to uncover the underlying structures which act as the transport barriers in the flow. The finite-time Lyapunov exponent （FTLE） fields are computed from the hydrodynamic model results to extract the LCSs. The results indicate that the LCSs act as the internal structures of the Lagrangian residual current and the Lagrangian residual current displays the residual current speed and direction of different water regimes separated by the LCSs. The water masses with different transport characteristics can be identified and their exchange ability with other water masses can be estimated by combining the Lagrangian particle tracking with the LCSs methods. The comprehensive applications of these Lagrangian methods reveal the underlying structures and the inhomogeneous characteristics of the water transport in Xiangshan Bay.     

海洋环流模式中的二阶湍流封闭格式综述

针对目前海洋环流模式预测能力存在的不足,从雷诺应力方程着手,归纳和阐述了二阶湍流闭合模式中压力项、扩散项和耗散项的改进与发展,分析和讨论了各种改进格式对模型完善和预测能力的影响,同时分析了波浪混合作用对环流封闭格式的影响,并对海洋环流模式中二阶湍流封闭格式发展进行了简要综述。压力项的改进主要集中于压力项中各影响量的添加,使得可以模拟的湍流的理查森数Ri趋近1;扩散项的改进主要通过改善湍流能量扩散的第三稳定函数Sk来完成;对于耗散率的改进更多是基于经验,用与理查德森数相联系的阶梯型函数可以有效模拟强分层流;环流模式中通过模拟波浪对垂向扩散系数的影响和在紊动动能方程中考虑波浪破碎耗散的能量的注入,都可以从物理机制上改善目前模式所模拟的混合层太浅和温跃层强度偏低的共性问题。     

Numerical simulation on influence of jet angle on jet＇s characteristics in flowing ambient fluid

Based on the stress-algebraic model, the turbulent buoyant jet with variable density was studied by the relation between density and concentration. A simple expression for buoyancy coefficient was proposed. The governing equations of turbulent buoyant jet with variable density were closed by introducing the expression of β and the relation between density and concentration. Numerical results for the jet axis with density difference agree well with experimental ones. By finite volume method, the 2 - D vertical jet＇s flow field with different jet angles was studied. The analysis of the relation among the vortex center, the position of separation point and jet angles shows that the circumfluenee field is the largest when the jet angle is 90°. The area turbulent kinetic energy ka is proposed and the relationship between mixing intensity and jet angles is analyzed based on it. Results show that the jet angle of is the optimum condition for jet water mixing with environment water;and the reduced rate of difference between the centerline density of jet and the density of ambient water is the largest at the jet angle of 90°.     

海域组合单元水质模型参数时空反演方法研究

将基于人工神经网络的数据驱动模型同水质模型有机结合,考虑模型参数的时域和地域差异性,建立海域组合单元水质模型参数时空反演的新方法:将研究海域划分为若干单元,模拟总时间划分为若干时段,敏感参数在各单元和各时段内独立赋值;通过水质模型计算多参数匹配设计的工况,构建海域内部观测点的解集;以数据驱动模型建立时空、空间、时间和非时空四种反演方式,并分别确立状态变量(污染物浓度)同多个控制变量(模型参数)之间的非线性关系;将实测资料带入关系中,进行模型参数随时域和地域动态变化的组合单元优化反演研究。以渤海海域水质模型多参数匹配反演为例,采用"孪生"实验验证参数组合单元时空反演新方法的可行性,结果表明该方法是有效的。     

3-D simulations of freak waves based on high-order spectral method

Three-dimensional ( 3-D) directional wave focusing is one of the mechanisms that contribute to the generation of freak waves. To simulate and analyze this phenomenon,a 3-D wave focusing model is proposed based on the enhanced high-order spectral method,which solves the fully nonlinear potential flow equations with a free surface within periodic unbounded 3-D domains. The numerical model is validated against a fifth-order Stokes solution for regular waves. Laboratory-scale freak waves are observed with wave components having equal amplitudes. Investigations of the appearance and propagation of freak-wave events in a 3-D open wavefield defined by a directional wave spectrum are then realized.