淤泥质粉砂海底典型平台桩基冲刷

通过黄河三角洲埕岛海域2个典型平台桩柱周围实测水深及海流、波浪资料,研究了淤泥质粉砂海底桩柱周围局部冲刷坑的特征及其发展演化情况,并结合水动力条件对其形成机制进行分析。     

Numerical Simulation of Wave Scour Around A Large-Scale Circular Cylinder

A numerical model is developed for estimation of local scour around a large circular cylinder under vvave action. The model includes wave diffraction around structures, bed shear stress calculation inside the vvave boundary layer and topo-graphical change model. The vvave model is based on the improved Boussinesq equations for varying depth. The vvave boundary layer is calculaled by solving the integrated momentum equation over the boundary layer. The bed shear stress due to streaming, an important factor affecting the sediment transport around a large-scale cylinder, is calculated. The Lagrangian drift velocity is included in calculation of the suspended sediment transport rates. The model is implemented by a finite element method and the results from the present model, which agree well with experimental data, are com-pared vvith those from other methods.     

Numerical Simulation of Local Scour Around A Large Circular Cylinder Under Wave Action

A horizontal two- dimensional numerical model is developed for estimation of sediment transport and sea bed change around a large circular cylinder under wave action. The wave model is based on an elliptic mild slope equation. The wave-induced current by the gradient of radiation stress is considered and a depth integrated shallow water equation is applied to the calculation of the current. The mass transport velocity and the bed shear stress due to streaming are considered, which are important factors affecting the sediment transport around a structure due to waves, especially in reflective areas. Wave-current interaction is taken into account in the model for computing the bed shear stress. The model is implemented by a finite element method. The results of this model are compared with those from other methods and agree well with experimental data.     

海口湾人工填海前后冲淤演变数值模拟

为了解近年的人工填海工程主要包括南海明珠项目、葫芦岛、秀英港扩建工程等人工填海工程对海口湾冲淤变化的影响,基于FVCOM海洋数值模型,对研究区人工填海前后潮流场、波浪场及冲淤变化进行了数值模拟。人工填海后,综合各条件下的冲淤情况,海口湾受潮流和波浪共同作用大部分区域处于淤积状态,年淤积量预测值为0.1~1.0m;白沙角等局部区域处于侵蚀状态,年冲刷量预测值为0.1~0.3m;受海口湾人工填海工程的影响,秀英港航道的水动力条件减弱,对通航条件改善有利,需加强航道的水深监测和定时的清淤工作;在南海明珠人工岛南侧波影区泥沙堆积会形成向海的舌状的突出体,其两侧海岸形成侵蚀后退带,需人工补沙等措施以保证岸线稳定。     

堤前远破波运动与冲淤形态

利用数值波浪水槽,对远破波作用下堤前波浪运动进行了数值模拟。分析了堤前速度场的变化,指出堤前波浪运动在一个波周期内可分为向堤波和离堤波。波浪在距堤约L/2处破碎后向堤冲击并沿堤面爬升,称为向堤波;波浪从堤面最高处回落与向堤波相遇并破碎,称为离堤波。堤前远破波的前半个周期的向堤波速度场大于后半个周期的离堤波速度场,且堤前波浪运动在一个波周期内的前半个周期和后半个周期完全不同。床面某点(L/4,3L/4)的速度在一个波浪周期内随时间呈向堤和离堤变化,向堤速度最大值大于离堤速度的最大值。利用堤前速度场的研究成果,进一步分析了远破波作用下堤前海床冲淤形成过程,完善了冲淤机理。     

A Study of Lift Force and Instantaneous Velocity Field Around an Oscillating Circular Cylinder

-Force measurements of oscillatory flow acting on a single circular cylinder have been carriedout.The experiments were done by oscillating a circular cylinder in still water.Instantaneous forces and ve-locity fields around the cylinder were measured by Particle Image Velocimetry(PIV).The Keulegan-Car-penter number(KC)varied in the range from 5 to 20 and the viscous parameter β=Re/KC was set at500(Re is Reynolds number).It was found that the strength and frequency of the lift force increased withKC number,the main frequency of the lift force being three times the frequency of the oscillatory flow atKC=20.The movement and strength of the vortices around the cylinder are discussed for differentKC numbers.     

Suppression of Flow Separation Around A Circular Cylinder by Utilizing Lorentz Force

Both experimental and numerical investigations on the flow past a cylinder under the influence of Lorentz force （electromagnetic force） were conducted in an electrically low-conducting fluid. The Lorentz force is applied beth locally, wholly and periodically on the surface of the cylinder, and their control effects for flow ,separation were investigated Both experimental and numerical results show that Lorentz force can suppress the flow separation with Lorentz force applied on beth local and whole surface of the cylinder. However, when the periodic and opposite Lorentz force adopted, the cylinder wake cannot be stabilized.     

Numerical Simulation of Viscous Flow Around a Rolling Cylinder with Ship-Like Section

Two-dimensional unsteady incompressible viscous flow around a rolling cylinder with ship-like section is numerically simulated by employing the computational scheme previously developed by the authors, in which the continuity and momentum equations are satisfied simultaneously at each time step for oscillating flow. The numerical results show that the motion of vortices around a rolling ship hull is cyclical. It is found that the location of the vortices is very similar to the existing experimental result. Using these simulation results, we can calculate the roll damping of ships including viscous effects.     

三沙湾潮滩涨落潮和大小潮冲淤特征及其动力机制

潮滩不同尺度的变化规律一直是地表过程研究的核心之一。利用声学多普勒流速仪（ADV）、温盐深（CTD）、光学后向散射浊度计（OBS）对三沙湾潮滩涨落潮和大小潮冲淤及动力变化进行了高精度的观测。结果发现,潮周期内,潮滩冲淤呈现涨潮初期冲刷-落潮末期淤积-中间时段稳定的特征,涨潮初期水深<1 m 的30 min内平均冲刷4.05 mm,落潮末期水深<1 m 的30 min内平均淤积3.72 mm,中间时段动态稳定;大小潮周期内,呈现中潮到小潮平均淤积3.4 mm,小潮到大潮平均冲刷8.2 mm的特征。通过流速、紊动能、水深、悬沙浓度等因子与冲淤的相关性分析发现,潮周期内,流速和紊动能的增减决定涨潮初期冲刷和落潮末期淤积的变化;大小潮周期内,涨潮冲刷大于落潮淤积的特性决定了大潮到小潮阶段的冲刷, 涨潮冲刷小于落潮淤积决定了小潮到大潮阶段的淤积。涨落潮周期和大小潮潮周期的冲淤机制为潮滩动力地貌和动力沉积学研究提供了一定的参考。     

高雷诺数下近壁圆柱绕流数值模拟与分析

近壁圆柱绕流问题在海底悬跨管道的研究中具有重要的意义。在绕流阻力、升力以及海底土壤的耦合作用下,海底管道所发生的移位、悬跨等现象对于海底管道的安全运行构成了很大的威胁。正确预测各种绕流条件下管流之间的作用力是保证油气管道安全的首要任务。海底管道在极端海洋环境条件下的管、流相互作用为高雷诺数绕流问题,处于高雷诺数下的绕流模拟比处于低雷诺数下的绕流模拟要复杂很多,它需要更精细的网格以及合适的湍流模型。此文对处于悬跨状态下的海底管道进行数值研究,给出不同间隙比下海流绕流海底管道的流场结构形态,分析了间隙比对绕流阻力和绕流升力的影响,为进一步研究海底悬跨管道的受力和变形提供载荷边界数据。     

含水合物沉积物相对渗透率研究进展

气-水相对渗透率是天然气水合物现场试采的关键参数。如何测量和评估储层相对渗透率是提高产气效率、实现天然气水合物产业化需要解决的基础问题。从含水合物沉积物相对渗透率的实验测试、数值模拟和模型建立3个方面,总结了含水合物沉积物相对渗透率的研究进展,研究发现,现有含水合物沉积物实验测试大多采用非稳态法,相对渗透率曲线图显示：在同一含水饱和度下,水合物饱和度越大,水的相对渗透率越小,气的相对渗透率变化规律较为复杂;水合物饱和度的变化改变了沉积物的孔隙空间结构,进而影响气-水相对渗透率。数值模拟大多利用孔隙网络模型或持水曲线进行相对渗透率计算,探索水合物生长习性、孔隙赋存特征,并揭示颗粒尺寸、水合物饱和度、润湿性、表面张力等不同因素对气-水相对渗透率的影响差异。梳理多种相对渗透率模型,发现新近提出的考虑毛细作用和孔径分布的含水合物介质相对渗透率模型在模拟含水合物沉积物中的多相流以及解释水合物饱和度的变化方面具有优势。建议下一步克服该模型计算成本较高的缺陷,实现含水合物沉积物多相流物理精确建模。     

海底水平管线回流区水流特性研究

针对管线绕流剪切层区的水流特征,利用射流分析的类似方法,通过简化控制方程,从理论上探讨了剪切层区的时均速度分布规律。物理试验中采用ADV测速仪对回流区流场进行了测量,对各流区流速和紊动强度变化趋势进行了讨论,并将试验结果与理论推导进行对比,二者基本吻合,为进一步研究海底管线防护措施提供了理论依据。     

防波堤建设对海底泥沙冲淤环境影响研究

以烟台八角海域为例,分别采用数值模拟计算与实测值对比两种方式分析评价防波堤建设对海底冲淤变化的影响。研究结果表明,防波堤建设导致研究区海底沉积物由原来的平衡状态转变为"浅水冲深水淤"的态势,冲刷及淤积速率均为0~0.06m/a。除构筑物附近等边界区域外,模型计算结果与实测泥沙运移趋势基本一致。     

Three-Dimensional Instability of Flow Around Two Circular Cylinders in Tandem Arrangement

The spatial evolution of vortices and transition to three-dimensionality in the wake of two circular cylinders in tandem arrangement have been numerically studied. An improved virtual body method developed from the virtual boundary method is used here. A Reynolds number range between 220 and 270 has been considered, and the spacing between two cylinders is selected as L/D = 3 and L/D = 3.5. When L/D = 3, the secondary vortices of Mode-A are seen to appear at Re = 240 and persist over the range of the Reynolds number of 240 - 270. When L/D = 3.5, the similar critical Reynolds number has been found at Re = 250. No obvious discontinuity has been found in the Strouhal-Reynolds number relationship, and this is different from three-dimensional flow around a single cylinder at the critical Reynolds number. The spanwise wavelength is about four times the diameter of the cylinder, and it is the characteristic wavelength for ModeA instability. This paper can give some foremost insight into the three-dimensional instability of flow by complicated geometrical configuration.     

近海湍流三维数值模拟中的重整化群模式

利用重整化群理论来确定近海湍流数值模式中的垂向涡动粘性系数，并对冬末春初琼州海峡的潮流场特征进行数值模拟。结果表明，重整化群模式的待定常数少，应用方便可行，其计算结果也比常用的湍流封闭模式的计算结果更加合理。     

海山对水动力场影响的数值实验

采用普林斯顿海洋模式对海峡中过海山的流场变化进行模拟。通过数值分析不同条件下海山周围的流场分布变化特征,并讨论了其相应的形成机制。在无海山存在的平底海峡中,无论是否考虑科氏力,海流流向均不发生偏转,但水位分布有明显差异。海山存在的情况下,若考虑科氏力效应,则会形成环绕海山的顺时针环流,并在海山周围有泰勒柱形成。当入流速度不同时,流场特征发生明显变化,流速越小,泰勒柱越明显,在合适入流条件下,在海山后方的尾流区会有涡生成。     

Hydraulic Modeling of A Curtain-Walled Dissipater by the Coupling of RANS and Boussinesq Equations

A hybrid numerical method for the hydraulic modeling of a curtain-walled dissipater of reflected waves from breakwa-ters is presented. In this method, a zonal approach that combines a nonlinear weakly dispersive wave (Boussinesq-type equation) method and a Reynolds-Averaged Navier-Stokes (RANS) method is used. The Boussinesq-type equation is solved in the far field to describe wave transformation in shallow water. The RANS method is used in the near field to re-solve the turbulent boundary layer and vortex flows around the structure. Suitable matching conditions are enforced at the interface between the viscous and the Boussinesq region. The Coupled RANS and Boussinesq method successfully resolves the vortex characteristics of flow in the vicinity of the structure, while unexpected phenomena like wave re-reflection are effectively controlled by lengthening the Boussinesq region. Extensive results on hydraulic performance of a curtain-walled dissipater and the mechanism of dissipation of reflected waves     

Numerical Study on Characteristics of Supercavitating Flow Around the Variable-Lateral-Force Cavitator

A control scheme named the variable-lateral-force cavitator, which is focused on the control of lift force, drag force and lateral forces for underwater supercavity vehicles was proposed, and the supercavitating flow around the cavitator was investigated numerically using the mixture multiphase flow model. It is verified that the forces of pitching, yawing, drag and lift, as well as the supercavity size of the underwater vehicle can be effectively regulated through the movements of the control element of the variable-lateral-force cavitator in the radial and circumferential directions. In addition, if the control element on either side protrudes to a height of 5% of the diameter of the front cavitator, an amount of forces of pitching and yawing equivalent to 30% of the drag force will be produced, and the supercavity section appears concave inwards simultaneously. It is also found that both the drag force and lift force of the variable-lateral-force cavitator decline as the angle of attack increases.     

潮汐河口桥墩群对波浪传播影响的数值研究

为研究河口桥墩群的消波作用,以李村河口段胶州湾快速路桥墩群为例,建立了基于波作用守恒方程的二维波浪模型,精细模拟了100年一遇高潮耦合100年一遇波高情况下,波浪通过河口桥墩群后波浪变化及波高分布,并利用物理模型试验结果对其进行了验证,二者吻合较好。数值模拟结果显示:桥墩群对河口波浪具有明显的消减作用,其透射系数随桥墩挤压面积比的增大呈线性减小趋势。     

油气混输系统的实验研究与实验模拟准则

描述了油气混输系统的实验研究,特别是多相流的流态、增压、计量系统的实验研究,并用动力相似理论分析了油气混输两相管流实验模拟所需满足的相似参数,提出了各种简化条件下的相似规律,讨论了用水和空气的两相流动来模拟原油和天然气的两相流动的可靠性和提高实验精度的手段和方法。