内孤立波下深水半潜式平台系统动力响应研究

我国南海海域海洋环境条件复杂且海水密度垂直层化现象显著,内孤立波活动频繁,因内孤立波而造成海洋开采平台破坏的案例屡见不鲜。依托水动力计算软件AQWA二次开发功能,采用Kdv方程,借助Fortran语言将深水半潜式平台立柱、浮箱、系泊系统3部分的内孤立波作用力叠加到外力项中,联合求解半潜式平台的6自由度动力响应特性。数值模拟结果表明,在内孤立波作用下,半潜式平台的运动及系泊线张力均受到了显著的影响。在不考虑系泊系统受内孤立波作用时,平台在纵荡和横荡方向上产生较大的漂移运动,最大偏移量较无内孤立波情况下增加了8倍;系泊线最大张力提高了17%,增加了系泊线断裂的风险。在考虑系泊系统受内孤立波作用时,平台的纵荡和横荡运动响应在原响应基础上继续提高15%,但是系泊线张力变化不大。内孤立波不同浪向下的平台纵荡和横荡响应相差也很明显;系泊系统合力在不同方向上的大小决定了平台不同方向上运动的大小。

Research on dynamic response of deep-water semi-submersible platform system under internal solitary wave

The marine environmental conditions in the South China Sea are complex and the vertical stratification of seawater density is significant. Internal solitary waves are frequent. Cases of damage to marine platforms due to internal solitary waves are not uncommon. Relying on the secondary development function of the hydrodynamic calculation software AQWA, the Kdv equation and the Fortran language are used to superimpose the internal solitary wave Morrison force of the three parts of the deep-water semi-submersible platform column, pontoon, and mooring system into the external force term, and the dynamic response characteristics of semi-submersible platform with six degrees of freedom are jointly solved. Numerical simulation results show that under the action of internal solitary waves, the motion of the semi-submersible platform and the tension of the mooring line have been significantly affected. Without considering the effect of internal solitary waves on the mooring system, the platform will produce larger drifting motion in the direction of surge and sway, and the maximum offset is increased by 8 times compared with the case without internal waves; the maximum tension of the mooring line is increased by 17%, thus increasing the risk of mooring line breakage. When considering the effect of internal solitary wave on the mooring system, the platform''s surge and sway motion responses continue to increase by 15% on the basis of the original responses, but the mooring line tension changes little. There is also a significant difference between the platform sway and sway response of the internal solitary wave in different flows; the magnitude of the resultant force of the mooring system in different directions determines the magnitude of the platform''s movement in different directions.