﻿ 变载荷作用下船舶板架结构冲击评估方法
 舰船科学技术  2023, Vol. 45 Issue (13): 44-47    DOI: 10.3404/j.issn.1672-7649.2023.13.009 PDF

Impact assessment method for ship grillage structures under variable loads
NI Jun
Wuhan Institute of Shipbuilding Technology, Wuhan 430050, China
Abstract: Ships are in the marine environment, and they are often subjected to impacts such as dry/wet alternating erosion, ocean salt spray corrosion, and waves beating due to complex sea conditions during navigation. As a result, it will not only cause huge economic losses to the maintenance and overhaul of the ship, but also affect the service life and safety of the ship's equipment. Some ships (such as warships) also have carrier-based aircraft in service. During each lifting process, the impact load will also cause damage and cracks to the ship’s frame structure, which will not only reduce the mechanical properties of the aircraft, but also cause It results in a shortened structural life due to impact loads when dropped. Accordingly, this paper takes 38CrMoAl steel material as the research object, and analyzes the impact dynamic mechanical behavior of 38CrMoAl steel material in the marine environment from the perspective of the mechanism of variable load, so as to improve the evaluation method of the impact of ship plate structure, and provide the structure for the ship to withstand the impact load. Lay the necessary foundation for life assessment.
Key words: variable load     ship grillage     structural impact     evaluation method
0 引　言

 $\sigma (t) = \frac{{{A_1}}}{{2{A_0}}}E({\varepsilon _{\text{i}}} + {\varepsilon _{\text{r}}} + {\varepsilon _{\text{t}}}) = \frac{{{A_1}}}{{{A_0}}}E{\varepsilon _{\text{t}}} \text{，}$
 $\varepsilon (t) = \frac{c}{{{l_0}}}\int_0^t {({\varepsilon _{\text{i}}} - {\varepsilon _{\text{r}}} - {\varepsilon _{\text{t}}}){\text{d}}t} = - \frac{{2c}}{{{l_0}}}\int_0^t {{\varepsilon _{\text{r}}}} {\text{d}}t \text{，}$
 $\dot \varepsilon (t) = \frac{c}{{{l_0}}}({\varepsilon _{\text{i}}} - {\varepsilon _{\text{r}}} - {\varepsilon _{\text{t}}}) = - \frac{{2c}}{{{l_0}}}{\varepsilon _{\text{r}}} \text{。}$

1 显式动力学算法

ABAQUS有限元软件中的显式非线性动态求解方法，可以应用在变载荷作用下的相关数据求解。在具体研究思路上，可以采用差分处理的方式对运动方程进行时间积分。通过应用前一个时步的运动条件直接求解下一个时步的运动条件，相对于隐式算法，该算法不需要进行迭代计算，计算速度快，计算所需资源少，稳定性好，也不存在收敛问题。因此被广泛应用于动态力学的仿真计算中，获得了很好的效果。显式动力学有限元算法的计算过程如下：

 $M\ddot u = P - I \text{，}$

 ${\ddot u_{(t)}} = {(M)^{ - 1}}{(P - I)_{(t)}} \text{。}$

 ${\dot u_{(t + \frac{{\Delta t}}{2})}} = {\dot u_{(t - \frac{{\Delta t}}{2})}} + \frac{{\Delta {t_{(t + \Delta t)}} + \Delta {t_{(t)}}}}{2}{\ddot u_{(t)}} 。$

 ${u_{(t + \Delta t)}} = {u_{(t)}} + \Delta {t_{(t + \Delta t)}}{\dot u_{(t + \frac{{\Delta t}}{2})}} 。$

 ${\sigma _{(t + \Delta t)}} = f({\sigma _{(t)}},{\rm{d}}\varepsilon ) \text{。}$
2 有限元模型的建立

 图 1 准静态拉伸试验件有限元模型 Fig. 1 Finite element model of quasi-static tensile test piece

SHPB模型如图2所示，模拟变载荷冲击长度为300 mm，入射杆和透射杆长度为1 250 mm，直径均为15 mm。模拟变载荷冲击和杆系材料均为18Ni钢，材料密度为7800 kg/m3，弹性模量为210 GPa，泊松比为0.3。采用C3D8R六面体网格，并对中心杆附近的网格进行加密，共设置网格数196200个。

 图 2 SHPB试验有限元模型 Fig. 2 SHPB test finite element model

SHTP模型如图3所示，该模型的网格密度较为稀疏，但是仿真速度可以获得成倍的提升，有利于提升仿真效率。

 图 3 SHTP试验有限元模型 Fig. 3 SHTP test finite element model

 图 4 SHTP试验件有限元模型Y密度分布图 Fig. 4 Y density distribution diagram of SHTP specimen finite element model
3 变载荷作用下的船舶板架结构有限元计算结果与分析

 ${D_0} = \sum (\Delta \varepsilon _{eq}/\varepsilon _f) \text{。}$

 ${\varepsilon _f} = \ln ({A_2}/{A_{{f}}}) \text{，}$

 ${\sigma ^*} = \frac{1}{3} + \ln \left( {1 + \frac{{{d_0}}}{{4R}}} \right) \text{。}$

 图 5 入射波反射率分布曲线 Fig. 5 Incident wave reflectivity distribution curve

 图 6 试验件数值模拟与J-C本构模型对比 Fig. 6 Comparison between numerical simulation of test piece and J-C constitutive model

4 断裂韧性计算结果与评估分析 4.1 准静态断裂韧性计算结果

 图 7 准静态断裂韧性力-位移曲线 Fig. 7 Quasi static fracture toughness force displacement curve

4.2 动态断裂韧性评估分析

 图 8 38CrMoAl钢试验件裂纹尖端附近应变片所测应变与数值模拟结果对比 Fig. 8 Comparison between the strain measured by strain gauge near the crack tip of 38CrMoAl steel specimen and the numerical simulation results
5 结　语

 [1] 李怿, 李典, 侯海量, 等. 螺栓连接结构对舰船复合材料夹芯板架冲击动响应的影响[J]. 兵器装备工程学报, 2022, 43(9): 343-350. LI Yi, LI Dian, HOU Hai-liang, et al. Influence of Bolted Connection Structure on Shock Dynamic Response of Ship Composite Sandwich Panel Frame[J]. Chinese Journal of Ordnance Equipment Engineering, 2022, 43(9): 343-350. [2] 郭德松, 纵帅, 王秀飞, 等. 集装箱坠落载荷作用下甲板板架结构响应理论预报方法研究[J]. 振动与冲击, 2021, 40(21): 142-149+193. GUO De-song, ZONG Shuai, WANG Xiu-fei, et al. Research on Theoretical Prediction Method of Deck Grid Structure Response under Container Falling Load[J]. Vibration and Shock, 2021, 40(21): 142-149+193. [3] 王鹏飞. 含腐蚀损伤板架结构极限强度评估及工程应用[D]. 大连理工大学, 2020 WANG Peng-fei. Ultimate Strength Evaluation and Engineering Application ofStiffened Panel with Corrosion Damage [D]. Dalian University of Technology, 2020. [4] 杨正伟, 赵志彬, 李胤, 等. 压-压疲劳载荷下CFRP层合板表面红外辐射特征[J]. 航空学报, 2021, 42(5): 231-241. YANG Zheng-wei, ZHAO Zhi-bin, LI Yin, et al. Characteristics of infrared radiation on the surface of CFRP laminates under compression-compression fatigue loads[J]. Acta Aeronautica Sinica, 2021, 42(5): 231-241. [5] 王逸南, 姚熊亮, 王治, 等. 基于物质点法的船体板架结构高速侵彻毁伤模式研究[J]. 爆炸与冲击, 2021, 41(10): 90-102. WANG Yi-nan, YAO Xiong-liang, WANG Zhi, et al. Research on high-speed penetration damage model of hull grillage structure based on material point method[J]. Explosion and Shock, 2021, 41(10): 90-102. [6] 赵松涛, 王南, 王鑫, 等. 水下爆炸作用下船舶结构与燃气轮机动态响应的数值研究[J]. 船舶力学, 2021, 25(6): 815-827. ZHAO Song-tao, WANG Nan, WANG Xin, et al. Numerical study on dynamic response of ship structure and gas turbine under underwater explosion[J]. Ship Mechanics, 2021, 25(6): 815-827.