A Two-Dimensional Study of Green-Water Loading
A Two-Dimensional Study of Green-Water Loading
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发表时间：
2001
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通讯作者：
M. Greco
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作者：
M. Greco
船与水之间的大的相对运动可能导致主甲板上的水上航行。在这篇论文中，研究了甲板上水现象的基本特征，以及船首区域甲板室上的“绿色”水载荷。本文的研究是针对顶浪中的浮式生产储油船（FPSO）这类静止船舶，采用势流理论对包含船舶中心平面的平面内的二维非线性问题进行数值研究。通过多种试验案例对模型进行了验证，并利用已发表的和新的试验数据进行了验证，研究了波浪参数、船舶运动和船体几何形状对模型的影响。三维效应的相关性进行了讨论。专门的二维模型试验已经完成，既阐明了水航运中涉及的流体力学和验证的数值方法。研究发现，水上航行是以波浪冲击甲板的形式开始的。这可能会造成结构性破坏。最常见的情况是，下倾是局部的船首区域，并不影响主流在稍后阶段。在少数情况下，已经观察到较大的水块直接冲击甲板。后者与3D实验中很少报告的观测结果一致，即大而陡的波浪直接扑到甲板上。更常见的情况是，水沿着桥面流动类似于溃坝后的水流。这两种类型的事件进行了研究数值。通过对船首垂直壁面上的冲击压力的测量，并与边界元法进行了比较，验证了溃坝模型和浅水近似法研究水在甲板上传播的可靠性。前者只能定性地描述流场的演变，后者原则上也可以使用，但需要外部流场的信息，因此需要求解完整的船波相互作用问题。使用的相似性解决方案的水楔击中刚性壁在90 °的完全数值解进行了比较。该方法预测正确的第一阶段的影响与较小的计算工作。讨论了局部水流条件和壁面坡度对水动力荷载的影响。水弹性的重要性进行了调查的情况下，现实的结构参数的甲板室。这表明结构变形在确定最大载荷方面的作用是有限的。
Large relative motions between the ship and the water may cause water shipping on the main deck. In this thesis, the fundamental features of water-on-deck phenomena are in vestigated, together with the "green" water loading on a deck house in the bow region. The studies are relevant for a stationary ship like a FPSO in head sea waves.Potential flow theory is used to study numerically a nonlinear two-dimensional problem in a plane containing the ship's centerplane. The developed model is verified by various test cases, and validated by published as well as new experimental data.The influence of wave parameters, ship motions and hull geometry is investigated. Relevance of three-dimensional effects is discussed.Dedicated two-dimensional model tests have been performed, both to elucidate the fluid mechanics involved in the water shipping and to validate the numerical method. It is found that the water shipping starts in the form of a plunging wave hitting the deck. This could cause structural damages. Most often, the plunging is localized in the bow region and do not affect the main flow at a later stage. In a few cases, larger masses of water bluntly impacting with the deck have been observed. The latter is consistent with seldom observations reported in 3-D experiments, with large and steep waves plunging directly onto the deck. More often the water flow along the deck resembles the one subsequent to a dam breaking. Both types of events are investigated numerically. The impact pressures on a vertical wall in the bow area are measured and compare well with the boundary element method.The reliability of a dam-breaking model and shallow-water approximation to study the propagation of water on the deck is examined. The former can only qualitatively describe the flow evolution.The latter can in principle be used but needs information from the exterior flow and, thus, the solution of the complete ship-waveinteraction problem.Water impacts with a deck house in the bow area are studied in details. Use of a similarity solution for a water wedge hitting a rigid wall at 90o is compared with the fully numerical solution. The method predicts correctly the first stages of the impact with a smaller computational effort. Inuence of local flow conditions and wall slope on hydrodynamic loads is discussed. Importance of hydroelasticity is investigated in case of realistic structural parameters for the deck house. This shows a limited role of structural deformations in determining the maximum loads.