Impact Loads on Circular Cylinders
Impact Loads on Circular Cylinders
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发表时间：
2013
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通讯作者：
E. Larsen
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作者：
E. Larsen
在过去，水冲击问题（如破碎波冲击救生艇、水下结构物通过飞溅区下降和自由落体救生艇性能）的测试通过模型试验或简化艾德方法（如经验公式和潜在的波浪计算）进行。简化的艾德方法通常对简单几何形状如楔形体或二维圆柱体给出合理的结果。当需要分析更复杂的结构时，需要进行模型测试，这会显著增加成本和时间。此外，规模效应也可能改变结果。计算机技术和计算流体动力学（CFD）的最新进展使人们能够模拟许多早期只能使用模型试验研究的问题。与模型测试相比，这允许以更低的成本执行更多的测试，并且比简化的艾德方法具有更高的准确性。此外，计算流体动力学模拟通常以全尺寸进行，从而避免了尺寸效应。本文探讨了利用CD-adapco CFD软件STAR-CCM+模拟圆柱入水问题的可能性。选择这种形状的原因是，它是一种简单的几何形状，同时仍然是一个现实的问题，因为这是在海洋海岸工业中最广泛使用的结构构件形状。此外，对于数值方法，圆柱体的冲击的初始阶段在数值上难以求解，因为圆柱体底部上的表面几乎是光滑的。这意味着正确解决圆柱体的水冲击的方法被认为也能够模拟其他几何形状的水进入。二维模拟已经进行了恒定速度和自由下落的圆柱体。计算流体动力学结果与坎贝尔和温伯格（1980）的经验曲线吻合得很好。自由下落圆柱体的计算结果与Greenhow和Lin（1983）的实验数据、Sun（2007）的非线性边界元法结果以及Zhu（2006）的CFD模拟结果相当吻合。对圆柱体在8 °冲击角下的水冲击进行了三维数值模拟。将结果与坎贝尔和Weynberg（1980）的实验结果和条带理论计算结果进行了比较。良好的协议之间的方法。
In the past, testing of water impact problems such as breaking waves impacting on risers, lowering of subsea structures through the splash zone and free fall lifeboat performance has been carried out either by model tests or simplified methods such as empirical formulas and potential flow calculations. The simplified methods generally give reasonable results for simple geometries such as wedges or two-dimensional cylinders. When more complex structures are to be analyzed model tests are required, increasing the cost and time spent significantly. In addition, scale effects may also alter the results. Recent advances in computer technology and computational fluid dynamics (CFD) have made it possible to simulate many of the problems that earlier only could be studied using model tests. This allows for more tests being performed at a lower cost compared to model tests and with higher accuracy than simplified methods. In addition, the CFD simulations are normally performed in full scale, thus avoiding scale effects. This thesis explores the possibility of simulating water entry problems using the CD-adapco CFD-software STAR-CCM+ with focus on circular cylinders. The reason for choosing this shape is that it is a simple geometry while still being a realistic problem, since this is the most widely used shape for structural members in the offshore industry. Also, for numerical methods the initial phase of impact of a cylinder is numerically difficult to solve, because of the almost flat surface on the cylinder bottom. This means that a method solving water impact of cylinders correctly is believed to also being able to simulate water entry of other geometries. Two-dimensional simulations have been performed for constant velocity and free-falling cylinders. Good agreement is found between the CFD results and empirical lines by Campbell and Weynberg (1980). The results for free-falling cylinders show fairly good agreement with experimental data by Greenhow and Lin (1983), nonlinear boundary element method results by Sun (2007), and CFD simulations by Zhu (2006). Three-dimensional simulations have been performed to analyze the water impact of a cylinder with 8 degree impact angle assuming constant velocity. The results are compared to experiments performed by Campbell and Weynberg (1980) and strip theory calculations. Good agreement is found between the methods.