﻿ 独立B型LNG船液舱晃荡强度分析方法
 舰船科学技术  2017, Vol. 39 Issue (9): 59-63 PDF

1. 海洋工程国家重点实验室 上海交通大学，上海 200240;
2. 高新船舶与深海开发装备协同创新中心 船海协创中心，上海 200240

Strength analysis measures of LNG ship with independent type B tanks under sloshing load
ZHANG Ming-juan1,2, LIU Jun1,2, XUE Hong-xiang1,2, TANG Wen-yong1,2
1. State Key Laboratory of Ocean Engineering Shanghai Jiao Tong University, Shanghai 200240, China;
2. Collaborative Innovation Center for Advanced Ship and Deep-Sea Exploration, Shanghai 200240, China
Abstract: In order to ensure that the sloshing strength of the new independent type B tanks in LNG ship with large capacity and free loading limit meets the requirements, a new direct analysis method for the sloshing strength assessment of the tank is proposed. Sloshing loads were calculated according to formulas recommended in rules. The coarse gird analysis of the tank was carried out according to the direct calculation method. Then the region which exceeded the allowable stress was filtered and fine mesh analysis on the target region in rolling condition was done. The result shows that the method can be used to evaluate the sloshing strength of the independent tank effectively, and the result of the fine mesh calculation can reflect the stresses distribution state of the high stress gradient region truly. The analysis results can provide reference for the evaluation of the tank sloshing strength, optimization of the tank structure and further design of the similar LNG ships.
Key words: independent type B tank     sloshing     fine mesh analysis
0 引　言

1 液舱晃荡局部强度直接计算

1.1 工况选择及载荷计算组合

1）对于距离横向制荡横舱壁和端部横舱壁0.25 lb范围内的构件，压力为：

 $p = \rho \left[ {4 - \frac{L}{{200}}} \right]{l_b}\;{\rm{kN/}}{{\rm{m}}^2},$ (1)

2）对于距离纵向制荡横舱壁和舱边舱壁0.25 bb范围内的构件，压力为：

 $p = \rho \left[ {3 - \frac{B}{{100}}} \right]{b_b}\;{\rm{kN/}}{{\rm{m}}^2}\text{。}$ (2)

3）与制荡横舱壁和端部舱壁邻近的强框架或桁材构件，压力为：

 $p = {P_{bhd}}{\left[ {1 - \frac{s}{{{l_s}}}} \right]^2}\;{\rm{kN/}}{{\rm{m}}^2},$ (3)

 $p = {P_{bhd}}{\left[ {1 - \frac{s}{{{b_s}}}} \right]^2}\;{\rm{kN/}}{{\rm{m}}^2}\text{。}$ (4)

1.2 有限元模型

1.3 应力衡准

2 目标船液舱晃荡强度分析 2.1 粗网格分析

 图 1 目标液舱有限元模型及内部构构件示意图 Fig. 1 Finite element model of the tank and internal components

 图 2 对称装载横摇工况载荷云图 Fig. 2 Scalar pressure of symmetrical loading rolling motion condition

 图 3 典型构件应力云图 Fig. 3 Von mises stress of typical components

1）横摇工况下的液舱舱壁强度基本符合强度要求；

2）液舱结构中超许用值区域主要集中在水平桁材、横舱壁垂直桁材以及横框架的拐角处，桁材的较大应力是由于舱壁的变形引起桁材拐角处的拉伸从而产生应力集中现象；

3）水平桁材越低，应力水平越高，最大应力出现在距离底部14 437BL处的水平桁材拐角处；因为理想化的原因，液舱底部约束附近区域有应力集中现象。

2.2 局部细化分析

 图 4 细化区域模型 Fig. 4 Model of typical refined mesh area

 图 5 细化分析典型构件应力云图 Fig. 5 Von mises stress of typical refined mesh components

1）由于网格尺度较小，细化分析的最大应力一般大于粗网格，但是细化之后同面积的平均应力一般小于粗网格，这是由于细化网格对局部加强或是改善应力集中的构件模拟更加真实的原因；

2）大部分构件在细化之后能满足许用应力要求，但是距离液舱底部较近的14 437BL处的水平桁材腹板拐角处应力仍然超出许用值（应力分布见图6），同时因为粗网格的简化处理加强了均化效应，细化后应力平均值反而大于粗网格的结果，这是因为该处为结构形状变化部位，属于容易产生应力集中的区域，考虑到结构安全性，后续设计中可从增大板厚和骨材尺寸两方面对此处进行结构加强。

 图 6 水平桁材拐角处细化分析应力云图 Fig. 6 Von mises stress of refined mesh area in horizontal web plates
3 结　语

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