Numerical prediction of MODUs drift during Hurricane Katrina     

G.V. Tahchiev  J. Zhang   《Ocean Engineering》2008,35(10):995-1005

Severe hurricanes, such as Katrina, broke the mooring lines of a number of mobile offshore drilling units (MODU) deployed in the Gulf of Mexico and some of those MODUs went adrift. A drifting MODU may damage other critical elements of the offshore oil and gas infrastructure by colliding with floating or fixed production systems and transportation hubs, or by rupturing pipelines owing to their dragging anchors over the seabed. To avoid or mitigate the damage caused by a drifting MODU, it is desirable to understand the mechanics of the drift of a MODU under the impact of severe wind, wave and current and have the capability of predicting the trajectory of the drift. To explore the feasibility and accuracy of predicting the trajectory of a drifting MODU based on hindcast met-ocean conditions and limited knowledge of the condition of the drifting MODU, this study employed a simplified equation describing only the horizontal (surge, sway and yaw) motions of a MODU under the impact of steady wind, current and wave forces. The simplified hydrodynamic model neglects the first- and second-order oscillatory wave forces, unsteady wind forces (owing to wind gustiness), wave drift damping, and the effects of the body oscillation on the steady wind and current forces. It was assumed that the net effects of the oscillatory forces on the steady motion are insignificant. To verify the accuracy and feasibility of our simplified approach, the predicted drifting trajectories of two MODUs were compared with the corresponding measurements recorded by the global positioning system (GPS).  相似文献   

Three-dimensional liquid sloshing in a tank with baffles   总被引：1，自引：0，他引：1  

Dongming Liu 《Ocean Engineering》2009,36(2):202-52

A numerical model has been developed to study three-dimensional (3D) liquid sloshing in a tank with baffles. The numerical model solves the spatially averaged Navier-Stokes equations, which are constructed on a non-inertial reference frame having six degree-of-freedom (DOF) of motions. The large-eddy-simulation (LES) approach is employed to model turbulence by using the Smagorinsky sub-grid scale (SGS) closure model. The two-step projection method is employed in the numerical solutions, aided by the Bi-CGSTAB technique to solve the pressure Poisson equation for the filtered pressure field. The second-order accurate volume-of-fluid (VOF) method is used to track the distorted and broken free surface. The baffles in the tank are modeled by the concept of virtual boundary force (VBF) method. The numerical model is first validated against the available analytical solution and experimental data for two-dimensional (2D) liquid sloshing in a tank without baffles. The 2D liquid sloshing in tanks with baffles is then investigated. The numerical results are compared with other results from available literatures. Good agreement is obtained. Finally, the model is used to study 3D liquid sloshing in a tank with vertical baffles. The effect of the baffle is investigated and discussed.  相似文献   

Nonlinear random wave-induced drag force on a vegetation field     

Dag Myrhaug  Lars Erik HolmedalMuk Chen Ong 《Coastal Engineering》2009

This paper provides a practical method by which the drag force on a vegetation field beneath nonlinear random waves can be estimated. This is achieved by using a simple drag formula together with an empirical drag coefficient given by Mendez et al. (Mendez, F.J., Losada, I.J., Losada, M.A., 1999. Hydrodynamics induced by wind waves in a vegetation field. J. Geophys. Res. 104 (C8), 18383–18396). Effects of nonlinear waves are included by using Stokes second order wave theory where the basic harmonic motion is assumed to be a stationary Gaussian narrow–band random process. An example of calculation is also presented.  相似文献   

Numerical Simulation of Large Diameter Cylindrical Structure Slamming     

许靖  王德禹 《中国海洋工程》2008,22(3):513-520

The water entry of large diameter cylindrical structure is studied by applying numerical simulation method. The processes of different diameter cyhndrical structures impacting water with various constant velocities are calculated numerically. Thereafter, analyzed are the distribution of slamming pressure on structure during slamming course and the influence of slamming velocity and cylindrical diameter on slamming process. Furthermore, presented herein is an equation being used to forecast the peak slamming force on a large diameter cylindrical structure.  相似文献   

带横隔板局部开孔沉箱在斜向波作用下的受力研究          下载免费PDF全文

刘勇  李玉成  滕斌  吴浩 《海洋学报》2008,30(2):137-146

基于线性势流假定,对斜向波作用下带横隔板局部开孔沉箱防波堤的水平波浪力进行了理论研究。给出了开孔沉箱法向水平力和横隔板受力的理论计算方法,在极限情况下波浪力的计算结果与文献中的已有结果一致。利用数值算例分析了开孔沉箱总水平力的主要影响因素。开孔沉箱法向总水平力的减小主要集中于结构上半部分波浪影响范围以内。增加单个开孔沉箱的长度有利于减小结构所受总水平波浪力。当波浪入射角或沉箱前开孔墙孔隙影响系数幅值较大时,开孔沉箱横隔板上总水平力的最大值要超过相应的沉箱法向总水平力,此时要注意横隔板的强度问题。  相似文献   

The role of Coriolis in sandbank formation due to a headland/island system   总被引：2，自引：0，他引：2  

Simon P. Neill   《Estuarine, Coastal and Shelf Science》2008,79(3):419-428

Tidal flow past a headland was modelled and the resulting sandbank formation due to bedload transport by eddy systems was examined with particular emphasis on the role of Coriolis. The headland configuration was extended to the more complex case of a headland with a detached island and the role of Coriolis in sandbank formation was again examined. In the headland case, the contribution of Coriolis resulted in the expected change in bed level at the centre of the residual eddies (positive contribution for the cyclonic eddy and negative change for the anticyclonic eddy). In the headland/island case, the role of Coriolis in the resulting bed level change was a function of eddy shedding from the island, defined by the island wake parameter. When eddy shedding occurred, the inclusion of Coriolis had a large magnitude effect on creating flood/ebb sandbank asymmetry. When eddies remained attached to the island, Coriolis had a minor role in the magnitude of this asymmetry.  相似文献   

利用卫星云图资料制作热带气旋预报路径的一种算法   总被引：1，自引：0，他引：1  

潘杰丽  朱明  朱敬海  李永平  郭兴业  卢保祥 《台湾海峡》2009,28(3):425-431

根据台风生成后在云场中移动的环境条件，引入一个环境作用于台风中心的热力梯度力方向，用该热力梯度力方向与当前台风的移动方向相结合，研究台风移动过程的变化规律，寻找一种简易可行的台风路径预报方法．经过多年实践，本文揭示出台风中心未来沿着当前移动方向与环境作用于台风中心的热力方向合成移动的基本规律：当前台风中心移向与前方晴空区中轴线相交时，台风沿着当前移向前进到与阻挡轴线相交点相距4个纬距的位置时便发生偏转，逐渐与阻挡轴线走向趋于一致；若当前台风中心距相交点的距离小于或等于4个纬距时，则从当前位置发生偏转．文中利用以上规律研制出台风移向变化方程和移动轨迹方程．  相似文献   

济南市建成区扩展的时空特征及驱动力分析     

陈淑兴  韩波  柯长青  闫弘文 《地理空间信息》2009,7(5):117-120

以山东省济南市为例，以1979—2005年5个不同时相的遥感图像为数据源，利用遥感信息提取技术，获取了城市扩展的空间信息。结合济南市社会经济统计数据，从扩展方向、重心转移等方面综合分析了济南市建成区扩展的时空特征，并从人口、经济、地理区位、政策导向等4个方面探讨了城市扩展的驱动力。结果表明，济南市城区扩展的整体趋势是东西向的带状扩张，向东扩张明显，城市重心向东北方向转移；1979年济南市城区面积是52．7km^2，2005年达到311．6km^2，是1979年的5．9倍。  相似文献   

Model Test Study on Ice-Induced Vibrations of Compliant Multi-Cone Structures     

黄焱  史庆增  宋安 《中国海洋工程》2009,23(2):317-328

For the study on the ice-induced vibration of a compliant mono-cone structure,a series of model tests were performed from 2004 to 2006.In these tests,the ice sheet before the compliant conical structure was found to be failed in two-time breaking.Based on this important finding,model tests study of the ice force on a compliant multi-cone structure were performed from 2006 to 2007.in these tests,the ice sheet broke before each single cone non-simultaneously.The exciting energy of the total ice force was found to be in a wide range of frequencies,and the structure can be easily excited with nonlinear resonance.  相似文献   

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陆明勇 《大地测量与地球动力学》2007,27(4):105-111

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