3D Numerical Simulation of Overbank Flow in Non-Orthogonal Curvilinear Coordinates

1.Introduction Riverflowsinacompoundchannelofteninundatetheadjacentplainsathighdischarges.This generatesacomplicatedflowstructurebetweenthemainchannelflowandthefloodplainflow.In straightchannels,thevelocitydifferencebetweentheflowinthemainchannelandthatontheflood plainisoneofthemostdistinctivecharacteristics.Thisintroducesseveralphysicalandphenomenologi calfeaturesaroundthejunctionbetweenthemainchannelandthefloodplain,namely,theformation ofahighhorizontalshearlayerandstreamwiseandverticalvorti…     

Numerical Investigation of Flow Motion and Performance of A Horizontal Axis Tidal Turbine Subjected to A Steady Current

Horizontal axis tidal turbines have attracted more and more attentions nowadays, because of their convenience and low expense in construction and high efficiency in extracting tidal energy. The present study numerically investigates the flow motion and performance of a horizontal axis tidal turbine with a supporting vertical cylinder under steady current. In the numerical model, the continuous equation and incompressible Reynolds-averaged Navier-Stokes equations are solved, and the volume of fluid method is employed to track free surface motion. The RNG k-ε model is adopted to calculate turbulence transport while the fractional area/volume obstacle representation method is used to describe turbine characteristics and movement. The effects of installation elevation of tidal turbine and inlet velocity on the water elevation, and current velocity, rotating speed and resultant force on turbine are discussed. Based on the comparison of the numerical results, a better understanding of flow structure around horizontal axis tidal turbine and turbine performance is achieved.     

Spoiler自埋技术特点及其在杭州湾海底管道运行情况分析

海底管道阻流板(Spoiler)自沉埋技术是一种新型管道自埋技术,为深入了解其作用机制及其效果,本文通过分析安装有阻流板的杭州湾海底管道历年检测资料,结合管道附近海域海床、潮流动力特性,深入探讨了阻流板装置在实际工程中的运行效果,分析了其作用机制及其适用条件。研究发现安装阻流板装置的杭州湾海底管道在往复潮流作用下逐渐埋入海床,其埋入段长度由2005年的50%增加到2013年的80%以上,而且平均埋入深度超过2.6 m,自埋效果较好;而在管道路由与海流平行段或管道敷设于抗冲刷强海床上时,阻流板作用不能有效发挥,管道仍然呈现裸露状态。     

Vertical 2D Modeling of Free Surface Flow with Hydrodynamic Pressure Using SIMPLE Arithmetic in σ Coordinates

A numerical model for shallow water flow has been developed based on the unsteady Reynolds-averaged Navier-Stokes equations with the hydrodynamic pressure instead of hydrostatic pressure assumption. The equations arc transformed into the a-coordinate system and the eddy viscosity is calculated with the standard k -ε turbulence model. The control volume method is used to discrete the equations, and the boundary conditions at the bed for shallow water models only include vertical diffusion terms expressed with wall functions. And the semi-implicit methed for pressure linked equation arithmetic is adopted to solve the equations. The model is applied to the 2D vertical plane flow of a current over two steep-sided trenches for which experiment data are available for comparison and good agreement is obtained. And the model is used to predicting the flow in a channel with a steep-sided submerged breakwater at the bottom, and the streamline is drawn.     

疏浚土倾倒后悬浮泥沙扩散输移的数值模拟

疏浚土的处置是航道疏浚整治中需要解决的问题.疏浚土在倾倒区倾倒之后,大部分疏浚土会沉积在抛泥区附近,其余泥沙将在抛泥点的局部区域形成高浓度悬沙,在重力、波浪、潮流、风生流等因素作用下扩散输移.建立了平面二维潮流、悬沙浓度增量输移扩散的数学模型,采用有限单元法离散求解,研究了虾峙门口外航道整治工程中疏浚土倾倒后悬浮泥沙在水体中的扩散输移,以此分析抛泥后不同悬沙浓度增量的悬浮泥沙的扩散范围.虾峙门口外外海处设置了1#、2#、3#倾倒区,模型计算结果表明,各悬沙浓度增量的悬浮泥沙扩散最大面积的最小值及包络线面积的最小值均发生在3#倾倒区抛泥的工况,原因在于3#倾倒区位于外海,水深明显大于1#、2#倾倒区,其倾倒区容积最大.可见,在水动力条件相当的情况下,水深条件形成的各倾倒区容积对悬浮泥沙的扩散和输移是有影响的.倾倒区容积越大,对悬浮泥沙扩散和输移越有利.从经济因素来看,疏浚船的运输距离所发生的运费是不可忽略的,疏浚航道至1#、2#倾倒区的距离要短于至3#倾倒区的距离,把疏浚土运至1#和2#倾倒区的运行费用明显低于运至3#倾倒区的运行费.研究结果建议,选择1#和2#倾倒区为疏浚土倾倒区,并根据潮流方向灵活安排施工作业,可将1#倾倒区作为落潮时疏浚土的倾倒区,2#倾倒区作为涨潮时疏浚土的倾倒区.     

1959—2019年杭州湾南岸滩涂演变规律及机制

掌握滩涂演变规律是保护和开发滩涂资源的重要依据,杭州湾水沙条件复杂,人类活动强度大,滩涂演变机制复杂。基于杭州湾近60 a（1959—2019年）水文地形监测资料,结合促淤围涂进程,分析了杭州湾南岸滩涂在水沙变化和人类活动影响下的演变规律及其机制。结果表明:近60 a来,杭州湾南岸滩涂普遍淤高,1959—2003年淤积速率约6.70 cm/a,2003—2019年淤积速率加快,约12.59 cm/a;大规模围涂和潮差增大是滩坡坡度增大的主要原因;庵东浅滩平面形态的周期性演变与径流的丰枯周期有关,呈现“丰水走弯,枯水趋直”现象;长江来沙减少尚未对杭州湾南岸滩涂淤涨产生明显影响;围涂工程是杭州湾南岸滩涂近期淤涨速率加快、潮滩宽度减小的主要原因。     

基于FVCOM模式钱塘江河口涌潮三维数值模拟研究

应用FVCOM模型进行钱塘江涌潮的二维和三维数值模拟,并使用2007年10月大潮期间的现场观测结果进行模型验证。结果表明,平面二维模拟结果与实测值吻合较好,与基于Godunov算法求解钱塘江涌潮二维特征的结果基本一致。三维计算结果再现了流速在垂向上的差异,以及在落潮转向涨潮时刻,涨潮先从底部开始,垂向上从底层向表层逐步从落潮流转为涨潮流。敏感性分析显示模型网格大小和曼宁系数的选取对模拟结果有较大的影响。     

REFINED RISK ASSESSMENT OF STORM SURGE DISASTER IN COASTAL PLAIN: A CASE STUDY OF PINGYANG COUNTY

As the risk of storm surge on coastal plains increases, the research on disaster risk assessment is fundamental for disaster management. Disaster risk assessment tends to develop towards the direction of refinement and it gradually plays a more important role. As regards the characteristics of storm tide disaster in coastal plain, the paper uses refined floodplain numerical model which combines typhoon, flood, astronomical tide and waves. The model also considers influencing factors of dike-breaking, micro-topography and buildings. Precise calculation is executed for the range and the submerged depth caused by floodplain flow in coastal plain. Based on 3S technology, disaster-bearing bodies are subdivided into the smallest unit of the ground object, and the vulnerability of these units is evaluated. Refined risk assessment of storm surge disaster for the coastal plain is obtained, and the detailed distribution of risk areas at different risk levels is achieved. These results can be widely applied in many fields, such as disaster prevention and mitigation, urban planning, industrial arrangement, disaster insurance and so on.     

FVCOM模型关键参数的处理及其在涌潮模拟中的应用

通过改进海床阻力系数和设置合适的垂向紊动背景系数,应用FVCOM模型成功再现了钱塘江河口强涌潮的演进过程。海床阻力系数采用Manning公式形式,取值随水深、地形在0.000 2~0.002 9之间变化;垂向紊动背景系数取1×10^-4 m²/s。模拟结果较好地复演了涌潮到达时刻、涌潮高度及涌潮抬升过程、涌潮水平流速以及其沿垂向分布规律,表明阻力系数及垂向紊动背景系数等关键参数的改进和处理是合理的,可应用于涌潮三维潮流运动特征模拟。     

非粘性沙坝溃决数学模型及求解

考虑一维陡坡浅水方程与Exner方程耦合构建漫顶溃坝数学模型,利用Roe格式黎曼近似解法求解,并用预测-校正法处理源项保证水流、泥沙侵蚀输运和底床演变过程的计算稳定.模型实例计算结果表明,该方法能较好地计算非粘性模型沙坝漫顶溃决问题,可为溃坝数值计算提供新的思路.