﻿ 流固耦合分析下的船体高速入水冲击数值模拟
 舰船科学技术  2023, Vol. 45 Issue (19): 60-63    DOI: 10.3404/j.issn.1672-7649.2023.19.011 PDF

Numerical simulation of high-speed water entry impact of ship hull under fluid structure coupling analysis
CHI Tie
Harbin Engineering University, Harbin 150001, China
Abstract: A numerical simulation method for high-speed underwater impact of ship hull under fluid structure coupling analysis is proposed, providing an effective means for studying the impact of ship hull entering water. This method uses the ALE algorithm to conduct fluid structure coupling analysis on the high-speed water inflow impact of the ship hull, and treats the ship hull as a cylindrical shape. A finite element numerical simulation model of the ship hull is established. After setting the high-speed water inflow conditions of the ship hull, the simulation results of the high-speed water inflow impact number of the ship hull are obtained through the fluid structure coupling analysis method. The experimental results show that at the moment when the ship enters the water at high speed, a huge acceleration is generated and transmitted to the ship structure. Under the impact of acceleration, the ship structure is discharged from the water surface, and the water medium is squeezed by the ship structure, causing the horizontal plane to rise and produce water splashes. After the ship structure enters the water, super cavitation is formed. When the hull structure comes into contact with the water surface, it bears the maximum impact load, and the acceleration curve shows a straight upward trend.
Key words: fluid structure coupling analysis     water impact     numerical simulation     finite element analysis
0 引　言

1 船体高速入水冲击数值模拟方法 1.1 基于ALE的流固耦合分析方法

$g$ 表示船体结构第 $i$ 个入水空间坐标， ${\rho _w}$ 为流体密度，利用ALE方法建立质量守恒方程，表达公式为：

 $\frac{{\partial {\rho _w}}}{{\partial t}} + {c_i}\frac{{\partial {\rho _w}}}{{\partial {g_i}}} + {\rho _w}\frac{{\partial {z_i}}}{{\partial {g_i}}} = 0 ，$ (1)
 ${c_i} = {v_i} - {w_i} 。$ (2)

${b_i}$ 表示流体体积，则动量守恒表达式为：

 ${\rho _w}\left[ {\frac{{\partial {z_i}}}{{\partial t}} + {c_i}\frac{{\partial {z_i}}}{{\partial {g_j}}}} \right] = {\varphi _{ij}} + {\rho _w}{\eta _i} 。$ (3)

 ${\varphi _{ij}} = - {Q_s}{\delta _{ij}} + {\mu _d}{z_{ij}} + {\mu _d}{z_{ji}} 。$ (4)

 $M = \psi d。$ (5)

 $\psi = \varepsilon rE \cdot \frac{1}{V} 。$ (6)

1.2 船体有限元数值仿真模型构建

 图 1 船体简化后圆筒结构有限元模型 Fig. 1 Finite element model of simplified cylindrical structure of ship hull

 $P = (\gamma - 1)\rho e 。$ (7)

 $P' = {h_1}\mu + {h_2}{\mu ^2} + {h_3}{\mu ^3} + {\rho _0}e'{f_0} + {\rho _0}e'{f_1}\mu ，$ (8)
 $\mu = \frac{{\rho '}}{{{\rho _0}}} - 1 。$ (9)

 $P' = {h_1}\mu + {f_0}{\rho _0}e' + {f_1}\mu {\rho _0}e'。$ (10)

 图 2 船结构高速入水有限元仿真模型 Fig. 2 Finite element simulation model of ship structure entering water at high speed

2 性能测试与分析

 图 3 流固耦合状态下水介质飞溅和超空泡情况 Fig. 3 Splash and supercavitation of water medium in fluid solid coupling state

 图 4 加速度冲击响应曲线 Fig. 4 Acceleration impact response curve

Y方向船体结构应力变化为分析目标，模拟船体结构高速入水后，其Y方向应力变化情况并绘制曲线，结果如图5所示。分析可知，在船体结构高速入水的瞬间，船体结构碰击水面后，船体和水介质之间碰撞持续时间较短，但瞬时产生的冲击力较大，冲击力迅速在船体结构内传播。船体结构在入水时间为1 ms左右时，其结构应力达到−150 MPa左右，随着船体结构持续入水，其水平方向的冲击波在船体结构与水面不断接触过程中产生震荡情况，结构应力也随之震荡，但结构应力始终在0 MPa左右震荡，震荡数值较小。

 图 5 船体结构应力变化曲线 Fig. 5 Stress change curve of hull structure
3 结　语

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