﻿ 基于全船建模的航速对船首外飘砰击影响研究
 舰船科学技术  2016, Vol. 38 Issue (8): 23-28 PDF

Effect of ship speed for the flare slamming of ship bows based on the whole ship modeling
XIAO Kao-kao, GAO Xiao-peng
Naval University of Engineering, Department. of Naval Architecture & Ocean Engineering, Wuhan 430033, China
Abstract: The impact of one rigid wedge subject is calculated to verify the reliability of the slamming simulation method. Modeling a whole ship, import the ship's motion parameters, including pitching motion. In simulation, the fluid is represented by an Euler formulation with 8-nodes brick elements, the ship structure is represented by a Lagrange grid, and simulate the whole ship model's slamming problems by using General coupling. The results show that: In case of high speed, moderate sea conditions, the bow's slamming pressure is higher than the other conditions; the longitudinal deadrise angle of the bow will be changed in whole model simulation, resulting in a greater influences the ship speed to the bow's slamming pressures, and the higher of ship speed, the higher of the bow's slamming pressure and the ship speed also makes slamming pressure peak position changes.
Key words: flare slamming     whole ship modeling     general coupling     longitudinal deadrise angle
0 引言

1 基本理论 1.1 拉格朗日有限元法

MSC.Dytran是瞬态动力学流固耦合领域的高端软件，它的求解方法在时间域上采用显式时间积分法。设当前时间步是n，显式积分方法是将运动微分方程

 $M{a_n} + C{v_n} + K{d_n} = F_n^{ext}$ (1)

 $M{a_n} = F_n^{ext} - F_n^{int},$ (2)

 ${a_n} = {M^{ - 1}}F_n^{residual}.$ (3)

 ${a_{ni}} = {F_{ni}}^{residual}/{M_i}$ (4)

 ${v_{n + 1/2}} = {v_{n - 1/2}} + {a_n}(\Delta {t_{n + 1/2}} + \Delta {t_{n - 1/2}})/2,$ (5)
 ${d_{n + 1}} = {d_n} + {v_{n + 1/2}}\Delta {t_{n + 1/2}}.$ (6)

1.2 欧拉有限体积法

 ${u_b} = 1/2({u_1} + {u_2}),$ (7)

 $\begin{gathered} \Delta M = {\rho _2}\Delta V,\hfill \\ \Delta Mom = {\rho _2}{u_2}\Delta V,\hfill \\ \Delta TE = {\rho _2}\left( {{e_t}} \right)\Delta V. \hfill \\ \end{gathered}$ (8)

1.3 拉格朗日-欧拉流固耦合

MSC.Dytran中的流固耦合计算就是拉格朗日域（固体）与欧拉域（流场）的耦合计算。本文采用的一般耦合法大多是拉格朗日的固体在欧拉的流场范围内运动，即拉格朗日域驱动欧拉域。流场虽有速度，但在流固耦合过程中欧拉网格不移动也不变形。

2 仿真方法可靠性分析

 图 1 计算模型 Fig. 1 Calculation model

 ${W_T} = 12{L_m}.$ (9)

 图 2 水域的压力云图 Fig. 2 Pressure cloud image

 图 3 斜底最大砰击压力时历曲线 Fig. 3 The curve of the maximum pressure

 图 4 楔形体入水自由液面变化情况 Fig. 4 The change of the water level of the wedge into the water

3 船舶砰击计算模型

3.1 计算工况

3.2 参数设置

 图 5 全船模型 Fig. 5 Whole ship model

 图 6 有限元模型 Fig. 6 Finite element model

4 结果分析

 图 7 外飘砰击预报点位置示意图 Fig. 7 A sketch map of the prediction point of the flare slamming

 图 8 航速0 kn下2–1点时历曲线 Fig. 8 2–1 point time history curve at speed of 0kn

 图 9 航速10 kn时2–1点时历曲线 Fig. 9 2–1 point time history curve at speed of 10kn

 图 10 航速18 kn时2–1点时历曲线 Fig. 10 2–1 point time history curve at speed of 18kn
4.1 航速对砰击压力极值大小的影响

 图 11 极值沿舷侧高度分布曲线 Fig. 11 Extreme value side along the height distribution curve

4.2 航速对砰击压力极值分布的影响

 图 12 极值沿船长方向分布曲线 Fig. 12 Extreme value side along the direction of ship distribution curve
4.3 原因分析

 ${p_i} = \rho {K_w}V_n^2/text"$ (10)

5 结语

1）全船入水仿真时，纵摇运动导致船型纵向斜升角变小，从而导致航速对于船首外飘砰击压力大小的影响较大，其规律为航速越高，船首砰击压力越大。

2）全船入水仿真时，航速越高，船首砰击压力极值发生点越向船尾推移。

3）与船首局部建模或二维船体剖面建模相比，本文中尝试的将船舶的航速与纵摇运动考虑进去的全船建模仿真方法能更贴近实船运动模式，考虑的因素更多，更全面。

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