Extreme-response analysis of jack-up platforms

The extreme wave and current response of a typical North Sea jack-up drilling platform has been calculated using nonlinear, stochastic, time-domain analysis techniques. A statistical treatment of the response-time histories has been performed. Appropriate probability distributions have been fitted to simulated response amplitudes and extrapolated to determine extreme values in storms of 3 or 6 h duration. Nonlinear geometric effects and dynamic effects are also addressed.

The results of the nonlinear time-domain analyses are compared to the results of more simplified methods used in jack-up designs.     

On nonlinear ship waves and wave resistance calculations

A finite difference method based on the Euler equations is developed for computing ship waves and wave resistances. Time marching is carried out using a time-splitting fractional-step method. The second-order central difference is used to discretize the spatial differentials, while the convection terms are discretized by the QUICK scheme. A body- and free-surface-fitted grid system with a cell-centered stencil is used. A Poisson equation for the pressure increment at each time step is solved to enforce mass conservation. The method is validated by comparing the numerical results with the experimental data for a Wigley parabolic hull. The characteristics of ship waves, such as the wave profile along the hull, the wave pattern on the free surface, the pressure distribution on the hull surface, and the wave-making resistance are reasonably predicted. The calculated results are in good agreement with the experimental data. Received for publication on Oct. 13, 1998; accepted on Jan. 20, 1999     

高速欠膨胀射流结构及推力特征研究

为了研究水下发动机不同工作状态射流结构变化及原因,利用轴对称及VOF模型对水下发动机射流进行仿真,研究发现高马赫数、欠膨胀状态下射流发生准回击现象;与具有四个典型过程的过膨胀状态下的射流结构相对比,发现高度欠膨胀下,射流的激波结构阻断了断裂与回击使得回流无法到达壁面完成回击;发动机推力因准回击现象骤变,因在激波及膨胀气体共同作用下回击力度受限无法到达壁面而被来流气体带往下游;对长时间射流流场结构研究发现,高度欠膨胀下的射流边界为成一定角度的倾斜直线。     

带横隔板开孔沉箱所受波浪力的研究

研究了斜向波与无限多开孔沉箱的相互作用。依照结构物的几何形状,整个流域被分成无限多个子域,在每个子域内应用特征函数展开法求解速度势。对于沉箱内的波浪运动,引入相位差概念;同时,在构造反射波模型时,考虑了结构物的几何形状影响。进行了数值试验,分析了开孔沉箱水平波浪力及横隔板受力特点,详细讨论了波浪入射频率、入射角度、相对消浪室宽度及开孔影响系数对开孔沉箱波浪力的影响。     

长江口半圆型沉箱导堤试验研究

论述了长江口深水航道治理工程南、北导堤一期及二期工程部分标段半圆型沉箱导堤结构的一系列试验研究成果。有关研究成果为设计方案的优化和结构计算提供了依据,并成功地应用于长江口深水航道治理工程实践中。     

SWT方法在内部充水弹性球壳散射的应用

采用Sommerfeld-Watson变换(SWT)方法研究了内部充水弹性球壳的散射,应用绕数积分求根方法在频率域复平面和波数域复平面求解环绕波的频散方程。比较了弹性球壳在内部真空和内部充水两种情况下环绕波相速度曲线和衰减曲线,结果表明内部流体负载使得相对于内部真空情况有大量流体环绕波产生,相邻流体环绕波相速度曲线的"排斥"现象是明显的,流体波向周围媒质的再辐射作用在其相速度接近内部真空球壳弹性环绕波相速度的时候达到局部极值。用镜反射波和环绕波的叠加合成反向散射形态函数,与简正级数解符合良好。     

船舶结构疲劳评估设计波法

以散货船船舯内底与底边舱斜板折角处节点为例,对船舶结构疲劳评估的设计波法进行研究.论述了设计波法的基本原理,给出了确定设计波的流程。通过分析该节点的受力情况,确定5个控制载荷参数及设计波参数。以谱分析法得到的参考应力范围为目标值,对5个控制载荷参数对应的设计波作用下的节点应力范围结果进行回归分析,从而得到了用于疲劳评估的设计波组合,并利用该方法对1艘散货船的船舯内底与底边舱斜板折角处的节点进行了计算。结果显示,设计波法与谱分析法的结果吻合较好,计算量大幅减少。     

波浪对潮流影响的数值模拟及其应用

文章将水动力因素分为潮流特征周期与波浪特征周期两部分,建立了考虑波浪影响的潮流方程。通过考虑波浪引起的辐射应力、表面和底部边界层、Stokes漂流以及Coriolis波浪应力等因素,利用数值方法分析了波浪对潮流场的影响,并将其应用到渤海区域中,分析渤海内波浪对于潮流的影响。     

Nonlinear hydrodynamic responses of submerged moving payload in vicinity of a crane barge in waves

The wave interaction with a submerged cylindrical payload subjected to constrained motions in presence of a nearby floating crane barge is investigated in the three-dimensional numerical wave tank using a fully nonlinear potential flow model in the time domain. Numerical simulations are carried out to investigate the hydrodynamic features of this submerged payload under pendulum motion in water waves as well as while it moves towards the sea bed at a constant vertical velocity. It is known that the presence of multiple side by side floating bodies in waves can create significant drift motion. In the present study the similar drift motion is observed for the side by side floating barge and submerged payload and it appears that the submerged payload under constrained motions may face a very large mean drift motion of nearly seven times that of the incident wave amplitude in the beam sea upstream condition. Emphasis is also given towards investigating and understanding the influences of natural frequency of the payload and shielding effect due to the presence of the floating barge. It is found that natural frequency coupled with shielding effect generates remarkable low frequency components in payload responses both in the head sea and the beam sea situations. The effect of different cable lengths, wave maker frequencies and downward moving velocities on payload responses under several geometric setups are studied and compared, and interesting features such as increased low frequency movement of the payload near the natural frequency region and existence of considerable low frequency motions even at a greater depth (while the payload is quite below the free surface) are observed.     

两层流中潜体运动与诱发内波特征关系研究

在两层流体中潜体运动会激发生成内波。文章通过编程控制潜体运动,使用动态分层法保证潜体运动时边界层不受影响,基于RANS方程多相流模型,采用求解相的体积分数方式捕捉内界面波形。潜体定常运动计算结果与实验结果相符,通过此方法,对比不同潜深下潜体诱发内波波高和波长随密度Froude数的变化特征,得到了诱发内波波高最大处的临界密度Froude数,重点研究了在临界密度Froude数处潜体加速运动和减速运动对诱发内波幅值及其波动过程的影响。