﻿ 计及水-空气-结构耦合的结构砰击载荷预报方法研究
 舰船科学技术  2016, Vol. 38 Issue (6): 31-36 PDF

Research on the prediction method for structural slamming loads considering water-air-structure coupling
PENG Dan-dan, LIU Kun
School of Naval Architecture and Ocean Engineering, Jiangsu University of Science and Technology, Zhenjiang 212003, China
Abstract: While ships sail in rough sea condition, slamming will happen between the hull and waves, which could damage local structure and reduce the longitudinal strength in severe cases. With the innovation of industrial technology and the needs of developing marine resources, modern ships continuously develop toward high speed and large scale, so the probability of slamming becomes increasingly higher. It has important significance for the navigation of ships and personnel safety to study the slamming characteristics of structure and predict the slamming loads accurately. This paper set water-airstructure coupling models and analyzed the slamming characteristics of wedges by the numerical simulation based on FineMarine. Moreover, the influences caused by different deadrise angles and different entry speeds on slamming loads have been studied.
Key words: slamming     wedges     Fine/Marine     numerical simulation
0 引言

1 砰击压力峰值理论计算方法 1.1 经典理论计算方法

Von Karman [4]将水上飞机的降落过程简化为二维楔形体砰击水面的模型。设斜升角 为楔形体以垂直速度 V 冲击水面，冲击过程在极短时间内发生，忽略流场速度平方的二阶小量，将自由面的边界条件作线性化处理，应用动量守恒定理，求得楔形体上的最大压力为：

 ${P_{\max }} = \frac{1}{2}\rho {V^2}\frac{\pi }{{\tan \beta }} \text{。}$ (1)

Wagner [5]考虑到了结构冲击时液面的升高现象，引入了湿表面的概念。设二维楔形刚体以等速入水，按浸湿半宽的“平板拟合”势流求解，在楔形体浸湿半宽的边缘，接近喷溅根部处出现的最大压力为：

 ${P_{\max }} = \frac{1}{2}\rho {V^2}\left( {1 + \frac{{{\pi ^2}}}{{4{{\tan }^2}\beta }}} \right) \text{。}$ (2)

Ochi 和 Motter[6]通过分析和总结上百个船模在波浪中的砰击试验数据，提出了在船舶剖面底部的砰击压力公式，整理可得：

 $P = K \cdot {V^2} \text{。}$ (3)

1.2 砰击压力峰值系数的比较

 $\text{VonKarman}:K=\frac{{{P}_{\max }}}{{{V}^{2}}}=\frac{\rho \pi }{2\tan \beta };$ (4)
 \begin{aligned} {\text{Wagner}}: K = \frac{{{P_{\max }}}}{{{V^2}}} = \rho \left[{\frac{1}{2} + \frac{{{\pi ^2}}}{{8{{\tan }^2}\beta }}} \right] \text{。} \end{aligned} (5)

 $K = \left\{ \begin{array}{l} \displaystyle \frac{\pi }{{2\tan \beta }} ,\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \beta \geqslant {10^ \circ },\\ 141{\rm{-}}\tan (2\beta )) ,\ \ \ \ \ \ \beta < {10^ \circ } \text{。}\\ \end{array} \right.$ (6)

 图 1 理论和规范中K~曲线比较 Fig. 1 Comparison of K~ curves in theories and rules
2 有限元模型建立 2.1 有限元模型

 图 2 几何模型 Fig. 2 Geometric models

 图 3 有限元模型 Fig. 3 Finite element model
2.2 测点分布

 图 4 测点分布（单位：mm） Fig. 4 Distribution of measuring points
3 计算参数设置 3.1 基本参数设置

3.2 网格自适应技术

Fine/Marine 的自由液面网格自适应准则，指的是网格只在自由液面附近即气-水掺混的区域进行网格自适应：细化或粗化。这种方法对于破碎波的自由演化等复杂自由液面的高精度预报问题可以实现合理的网格布局、减小网格总量、提高计算效率。本文采用的细化标准是自由液面张量标准，它类似于自由液面定向标准，只是在计算缓冲层时会稍有不同，在泡沫和破波区域的细化次数更少，适用于非稳定流的计算，如图 5 所示。

 图 5 自由液面张量标准 Fig. 5 Free surface tensor criterion
3.3 自适应库郎特数法则

4 计算结果分析及结论 4.1 计算结果分析

4.1.1 不同速度下的砰击压力及峰值

 图 6 不同速度下的砰击压力曲线 Fig. 6 Slamming pressure curves of different speed

4.1.2 不同斜升角下的砰击压力及峰值

 图 7 不同斜升角楔形体砰击压力 Fig. 7 Slamming pressure of different bottom angle of wedges
4.1.3 计算砰击压力峰值系数 K 与理论值对比

 图 8 砰击压力峰值 K 系数与理论值对比 Fig. 8 Comparison between peak slamming pressure coefficient K and the theoretical value
5 结语

1）二维楔形体以某一速度冲击水面，在速度达到最大值的瞬间，出现砰击压力峰值。在斜升角相同时，随着入水速度的增大，砰击压力及峰值明显增大。

2）在一定范围内，楔形体的砰击压力及其峰值随着斜升角的增大而减小。在斜升角较小时，砰击压力峰值从 P1 ~ P5 先增大后减小，说明砰击压力峰值会受到水面抬升及射流的影响，而在斜升角较大时，从 P1 ~ P5 的砰击压力峰值逐渐减小，表明射流的影响不明显。

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