MPS-DEM耦合方法的多段系泊浮体波浪响应分析
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摘要
针对大型海上浮体平台常采用分段式结构以保证平台在海浪冲击下结构的稳定性,分段式结构使得浮体平台的水动力特性变复杂的问题,通过耦合移动粒子半隐式法(MPS)与离散单元法(DEM),在全拉格朗日框架下建立了二维造波水池模型。本文比较并修正了造波模型,提高了造波的准确度,并对消波模型进行了改进,改进后的计算量下降了12.1%;对含有不同数量子平台的分段浮体平台在规则波影响下的运动进行了数值模拟,探讨了分段浮体平台运动时子平台间的动态关系。研究结果表明,子平台位置靠近整体平台下游时,其垂荡和纵摇响应逐渐衰减,纵荡响应成为主导特征。大型分段浮体平台在设计时需注意减小前部子平台的垂荡和纵摇,并增加连接部件对尾部子平台的约束力,防止尾部子平台相互碰撞或脱离主浮体平台。
In recent years, more and more attention has been paid to the development of ocean resource. Especially in the deep ocean, the development of the resource and energy usually depends on the large floating structures. Multibody platforms are usually used in VLFS(very large floating structure) to ensure the stability of the floating structure under the impact of sea waves. Because of the multibody structure, the hydrodynamic characteristics of the platform are very complex. This paper proposes a full Lagrangian algorithm by coupling moving particle semi-implicit method(MPS) and discrete element method(DEM). A two-dimensional numerical wave tank was established and the wave generation model was modified to enhance the accuracy of the numerical wave. Moreover, the wave absorption model was improved and the computation cost was reduced by 12.1%. Furthermore, the motion response of moored multibody platforms under the influence of regular waves was analyzed, and the dynamic relationship between sub-platforms was discussed. It was found that the closer the sub-platform is to the end of the main platform, the smaller are the heave and pitch responses, and the larger is the surge response. In conclusion, the design of large multibody floating platform should pay attention to reducing the heave and pitch of the front sub-platform and increasing the bonding force of the end sub-platform to prevent its collision with and leave from the main platform.
In recent years, more and more attention has been paid to the development of ocean resource. Especially in the deep ocean, the development of the resource and energy usually depends on the large floating structures. Multibody platforms are usually used in VLFS(very large floating structure) to ensure the stability of the floating structure under the impact of sea waves. Because of the multibody structure, the hydrodynamic characteristics of the platform are very complex. This paper proposes a full Lagrangian algorithm by coupling moving particle semi-implicit method(MPS) and discrete element method(DEM). A two-dimensional numerical wave tank was established and the wave generation model was modified to enhance the accuracy of the numerical wave. Moreover, the wave absorption model was improved and the computation cost was reduced by 12.1%. Furthermore, the motion response of moored multibody platforms under the influence of regular waves was analyzed, and the dynamic relationship between sub-platforms was discussed. It was found that the closer the sub-platform is to the end of the main platform, the smaller are the heave and pitch responses, and the larger is the surge response. In conclusion, the design of large multibody floating platform should pay attention to reducing the heave and pitch of the front sub-platform and increasing the bonding force of the end sub-platform to prevent its collision with and leave from the main platform.
引文
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[13] NI X,FENG W,HUANG S,et al.A SPH numerical wave flume with non-reflective open boundary conditions [J].Ocean Engineering,2018,163:483-501.
[14] 孙一颉,孙中国,曹文瑾,等.系泊型远海浮体平台水动力特性数值研究 [J].工程热物理学报,2018(2):307-313.SUN Yijie,SUN Zhongguo,CAO Wenjin,et al.Numerical study on hydrodynamic characteristics of moored offshore floating platform [J].Journal of Engineering Thermophysics,2018(2):307-313.
[2] SUN P,MING F,ZHANG A.Numerical simulation of interactions between free surface and rigid body using a robust SPH method [J].Ocean Engineering,2015,98:32-49.
[3] ZHANG Y,WAN D.MPS-FEM coupled method for sloshing flows in an elastic tank [J].Ocean Engineering,2017:S0029801817307308.
[4] ZHE S,DJIDJELI K,XING J T,et al.Coupled MPS-modal superposition method for 2D nonlinear fluid-structure interaction problems with free surface [J].Journal of Fluids & Structures,2016,61:295-323.
[5] ZHANG S,MORITA K,FUKUDA K,et al.An improved MPS method for numerical simulations of convective heat transfer problems [J].International Journal for Numerical Methods in Fluids,2006,51(1):31-47.
[6] LEE B H,PARK J C,KIM M H,et al.Step-by-step improvement of MPS method in simulating violent free-surface motions and impact-loads [J].Computer Methods in Applied Mechanics & Engineering,2011,200(9):1113-1125.
[7] CHEN X,SUN Z,LIU L,et al.Improved MPS method with variable-size particles [J].International Journal for Numerical Methods in Fluids,2015,80(6):358-374.
[8] 曹文瑾,孙中国,席光.移动粒子半隐式法流固耦合模型及自由浮体数值研究 [J].西安交通大学学报,2014,48(8):136-140.CAO Wenjin,SUN Zhongguo,XI Guang.Fluid-structure interaction models in MPS method and its numerical simulation for floating bodies [J].Journal of Xi’an Jiaotong University,2014,48(8):136-140.
[9] CUNDALL P A.A discrete numerical model for granular assemblies [J].Geotechnique,2008,29(30):331-336.
[10] POTYONDY D O,Cundall P A.A bonded-particle model for rock [J].International Journal of Rock Mechanics & Mining Sciences,2004,41(8):1329-1364.
[11] ZHANG X P,WONG L N Y.Cracking processes in rock-like material containing a single flaw under uniaxial compression:a numerical study based on parallel bonded-particle model approach [J].Rock Mechanics and Rock Engineering,2012,45(5):711-737.
[12] 曹文瑾,孙中国,席光.系泊型浮体运动的无网格法数值模型 [J].西安交通大学学报,2015,49(3):62-66.CAO Wenjin,SUN Zhongguo,XI Guang.Numerical models of moored floating bodies using meshless method [J].Journal of Xi’an Jiaotong University,2015,49(3):62-66.
[13] NI X,FENG W,HUANG S,et al.A SPH numerical wave flume with non-reflective open boundary conditions [J].Ocean Engineering,2018,163:483-501.
[14] 孙一颉,孙中国,曹文瑾,等.系泊型远海浮体平台水动力特性数值研究 [J].工程热物理学报,2018(2):307-313.SUN Yijie,SUN Zhongguo,CAO Wenjin,et al.Numerical study on hydrodynamic characteristics of moored offshore floating platform [J].Journal of Engineering Thermophysics,2018(2):307-313.