﻿ 船首外飘砰击载荷的数值预报
 舰船科学技术  2018, Vol. 40 Issue (3): 35-41 PDF

1. 大连海事大学 交通运输装备与海洋工程学院, 辽宁 大连 116026;
2. 中船重工船舶设计研究中心有限公司, 辽宁 大连 116001

Numerical prediction of bowflare slamming loads
YU Peng-yao1, LU Lei2, ZHEN Chun-bo1, WANG Tian-lin1
1. Transportation Equipment and Ocean Engineering College, Dalian Maritime University, Dalian 116026, China;
2. China Ship Design and Research Center Corporation, Dalian 116001, China
Abstract: An explicit finite element method is adopted to forecast bowflare slamming loads. By comparing the free falling test values of a small-scale bowflare model with the corresponding numerical simulation results, the numerical method proves reliable to forecast bowflare slamming loads. Through simulating the slamming process of two different bowflare sections of real ship scale, on the condition that the track of the sections is consistent with the relative movement between the hull and the wave, the secondary slamming phenomenon after flow separation is studied and the effects of mesh density and contact stiffness parameters on bowflare slamming loads are further explored.
Key words: explicit finite element method     bowflare slamming loads     flow separation     secondary slam
0 引　言

1 基本理论 1.1 控制方程

 $\frac{{\partial \rho }}{{\partial t}} = - \rho \frac{{\partial {v_i}}}{{\partial {x_i}}} - {w_i}\frac{{\partial \rho }}{{\partial {x_i}}}\text{，}$ (1)
 $\rho \frac{{\partial {v_i}}}{{\partial t}} = \frac{{\partial {\sigma _{ij}}}}{{\partial {x_j}}} + \rho {b_i} - \rho {w_i}\frac{{\partial {v_i}}}{{\partial {x_j}}}\text{，}$ (2)
 $\rho \frac{{\partial E}}{{\partial t}} = {\sigma _{ij}}\frac{{\partial {v_i}}}{{\partial {x_j}}} + \rho {b_i}{v_i} - \rho {w_j}\frac{{\partial E}}{{\partial {x_j}}}\text{。}$ (3)

 ${\sigma _{ij}} = - p{\delta _{ij}} + \mu (\frac{{\partial {v_i}}}{{\partial {x_j}}} + \frac{{\partial {v_j}}}{{\partial {x_i}}})\text{。}$ (4)

1.2 材料模型与状态方程

1.3 耦合算法

 ${{P}} = {{kd}}{\text{。}}$ (5)

2 数值模型 2.1 网格域

 图 1 数值模型 Fig. 1 Numerical model

 图 2 网格密度示意图 Fig. 2 Schematic diagram of mesh density
2.2 边界条件

3 数值模拟中的主要影响因素 3.1 网格密度

3.2 接触刚度

3.3 二次砰击

4 算例分析

 图 3 实船尺度剖面 Fig. 3 Section of an actual ship
4.1 数值方法验证

 图 4 落体模型剖面 Fig. 4 Section of the free-drop model

 图 5 理论值与试验值对比 Fig. 5 Comparison between numerical results and experimental results

 图 6 船舶与波浪相对运动 Fig. 6 Relative motion between the ship and the wave
4.2 不同网格密度仿真模型计算结果

 图 7 不同网格密度下砰击力 Fig. 7 Slamming forces with different mesh densities

 图 8 不同网格密度下P1处砰击压力 Fig. 8 Slamming pressure of P1 with different mesh densities

 图 9 t=0.8 s时流场液面 Fig. 9 Water elevation of the fluid at t=0.8 s
4.3 不同接触刚度仿真模型计算结果

 图 10 不同接触刚度下砰击力 Fig. 10 Slamming pressures with different contact stiffness

 图 11 不同接触刚度下的砰击压力 Fig. 11 Slamming forces with different contact stiffness

4.4 不同剖面形状计算结果

 图 12 不同型线下的砰击力 Fig. 12 Slamming forces of different sections

 图 13 不同型线下的砰击压力 Fig. 13 Slamming pressures of different sections
5 砰击压力系数与规范值的比较

 图 14 砰击压力系数理论值与规范值 Fig. 14 Numerical and rule results of the slamming pressure coefficient
6 结　语

1）通过对比数值预报结果与落体砰击模型试验结果，验证本文在网格划分和接触刚度等参数选取的合理性。

2）通过研究不同网格密度、接触刚度下2种型线的砰击力与砰击压力载荷的数值预报，可以看出对于型线2，在网格密度相对稀疏，dmax约为模型宽度的0.002，pmax约为剖面可达到的最大砰击压力时，即可得到稳定的砰击载荷数值结果；由于二次砰击现象，导致型线1砰击力和砰击压力载荷的峰值受网格密度和接触刚度的参数影响更加敏感，但不同参数下，砰击力与砰击压力载荷的变化趋势一致，后续可从结构响应的角度对二次砰击现象中的网格密度和接触刚度的收敛性进行研究。

3）在相同网格密度和接触刚度参数下，型线1在二次砰击发生时（1.0~1.2 s），砰击力和砰击压力P1P2明显要大于型线2的值，1.2 s之后2种型线砰击载荷变化几乎一致。可见，二次砰击现象会导致局部位置砰击载荷的增加，应该引起结构设计的关注。

4）由砰击压力系数与规范值的比较看出，对于未发生二次砰击（型线2的P1P2P3）和不受二次砰击影响的位置（型线1的P3），砰击压力系数与规范值相差不大。但对于受二次砰击压力较大的位置（型线1的P1P2），砰击压力系数明显大于规范值，可见当前规范仍需更合理地考虑二次砰击现象对砰击载荷的影响。

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