﻿ 基于LS-dyna的平台定位系统结构强度数值计算方法
 舰船科学技术  2019, Vol. 41 Issue (10): 129-133 PDF

Numerical calculation method for structural strength of platform positioning system based on LS-dyna
YAN Bo, DONG Hai-fang, ZHU Gang, YUAN Wei, LI Jian, YAO Bai-lian
Wuhan Second Ship Design and Research Institute, Wuhan 430064, China
Abstract: The floating stack platform adopts a small stack type for offshore power generation, and provides power energy and hot water resources for offshore facilities such as oil production platforms. Its positioning system can ensure that the floating platform can withstand the harsh sea conditions of wind and waves and thus float stably at sea. Combining the motion characteristics of the floating platform and analyzing the inherent characteristics of the positioning system, an analytical method for hull displacement based on hydrodynamic calculation and an overall rigid-flexible coupling model based on LS-dyna is proposed. The kiln displacement is used as input to calculate the dynamic coupling of the structure, and with analyzing the force of each system module and motion pair, it can obtain the stress time history curve of key parts and motion pairs. And the calculation method of the motion posture of each motion pair is given, which provides a reference for engineering application.
Key words: platform positioning system     dynamics     numerical method     strength
0 引　言

 图 1 平台定位系统 Fig. 1 Platform positioning system
1 平台定位系统建模方法

 图 2 平台位移计算流程 Fig. 2 Process of platform displacement calculation

 图 3 整体动力学计算流程 Fig. 3 Process of overall dynamics calculation
2 平台定位系统数值模型 2.1 船体位移计算

 ${S_x}\left( \omega \right) = {\left| {{H_x}\left( \omega \right)} \right|^2}S\left( \omega \right)\text{，}$ (1)

 ${S_F}\left( \mu \right) = 8\int_0^\infty {S\left( {\omega + \mu } \right)} S\left( \omega \right){T^2}\left( {\omega + \mu ,\omega } \right){\rm d}\omega \text{。}$ (2)

 ${{\bar F}_{WD}} = 2\int_0^\infty {S\left( \omega \right)T\left( {\omega ,\omega } \right)} {\rm d}\omega \text{，}$ (3)

 $\sigma _{xl}^2 = \frac{{\text{π}} }{{2b{C_{11}}}}{S_F}\left( {{\mu _c}} \right)\text{，}$ (4)
 ${X_{max,lf}} = \sqrt 2 {\sigma _{xl}}\sqrt {lnN} \text{。}$ (5)

 图 4 平台位移分析模型 Fig. 4 Model of platform displacement analysis

 图 5 平台纵荡位移 Fig. 5 Turbulent displacement of platform
2.2 动力学建模

 $[{ M}]\left\{ {\ddot u} \right\} + [{ C}]\left\{ {\dot u} \right\} + [{ K}]\left\{ { u} \right\} = \left\{ {F\left( t \right)} \right\}\text{。}$ (6)

LS-dyna是著名的通用显示动力分析程序，以拉格朗日算法为主，具有强大的非线性处理功能，结合软刚臂系统运动的多结构耦合非线性问题，采用此软件能较好的处理模型计算问题[810]。如上述流程所示，前处理采用hypermesh建模，系泊支架采用管单元与梁单元，系泊腿采用管单元，两端设置球铰接转动副，系泊刚臂采用壳单元及梁单元，旋转塔台采用板单元，平台与固定塔架设置为刚体，建立整体有限元动力学模型。

 图 6 整体动力学模型 Fig. 6 Overall dynamics model

 图 7 整体动力学计算结果 Fig. 7 Result of overall dynamics model

 图 8 上铰接点纵向位移 Fig. 8 Longitudinal displacement of the upper hinge point

 图 9 上铰接点垂向位移 Fig. 9 Vertical displacement of the upper hinge point

 图 10 下铰接点纵向位移 Fig. 10 Longitudinal displacement of the lower hinge point

 图 11 下铰接点垂向位移 Fig. 11 Vertical displacement of the lower hinge point
2.3 局部构件建模

 图 12 系泊腿有限元模型 Fig. 12 Finite element model of mooring leg

 图 13 t=2 s系泊腿应力云图 Fig. 13 Mooring leg stress cloud of t=2 s

 图 14 t=20 s系泊腿应力云图 Fig. 14 Mooring leg stress cloud of t=20 s

 图 15 t=100 s系泊腿应力云图 Fig. 15 Mooring leg stress cloud of t=100 s

 图 16 单元1应力云图 Fig. 16 Stress cloud of unit 1

 图 18 单元2应力云图 Fig. 18 Stress cloud of unit 2

 图 17 单元1应力曲线 Fig. 17 Stress curve of unit 1

 图 19 单元2应力曲线 Fig. 19 Stress curve of unit 2
3 结　语

1）结合浮动平台定位系统的固有特性，提出了一种以水动力计算得到船体位移，将船体位移作为输入对结构进行动力学耦合计算，分析各分系统模块、运动副的受力，求得关键部位和运动副的应力时程曲线以及关键节点的位移时程曲线的方法。

2）基于LS-dyna显示动力学，建立了平台船体、软刚臂系统、固定塔架整体刚柔模型，计算得到节点位移，并以节点位移建立局部模型，得到了结构应力时程曲线，验证了建模思路的可行性。

3）通过分析节点位移曲线，结构应力时程曲线，可得软刚臂系统系泊腿运动规律，以及其结构薄弱环节，并后续可将应力结果作为输入进行结构疲劳强度校核，具有一定的工程应用价值。

4）建立的整体刚柔耦合模型计算速度较为缓慢，模型网格、构件简化等方面还有改善空间，后续针对这方面会进行相关优化，提高模型计算效率。

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