MPS与GPU结合数值模拟LNG液舱晃荡

NUMERICAL SIMULATION OF LIQUID SLOSHING IN LNG TANK USING GPU-ACCELERATED MPS METHOD

液舱晃荡是一种在外部激励作用下部分装载的液舱内液体的波动现象,它会对液舱结构强度和运输船舶稳性产生危害.移动粒子半隐式法(moving particle semi-implicit, MPS)是一种典型的无网格粒子类方法,可以有效地模拟剧烈的液舱晃荡问题.但MPS方法存在计算效率低的缺点,难以模拟大规模三维问题,而GPU并行加速技术已广泛应用于科学计算领域.因此,本文将MPS方法与GPU并行加速技术相结合,采用CUDA程序语言编写,自主开发了MPSGPU-SJTU求解器,对三维液化天然气(liquefied natural gas, LNG)型液舱晃荡进行了数值模拟.通过三种不同粒子间距的数值模拟,验证了求解器的收敛性,其中最大计算粒子数达到了200多万.与其他研究结果相比,MPSGPU-SJTU求解器能够准确地预测壁面砰击压力,并且捕捉晃荡过程中自由面的大幅度变形和强非线性破碎现象.相比CPU求解器的计算时间,GPU并行加速技术可以大幅度地减小计算时长,提高MPS方法的计算效率.本文将LNG型液舱与方型液舱的晃荡进行对比,结果表明在高充液率下LNG型液舱可以有效地减小晃荡幅值和壁面砰击压力.但在中低充液率下,LNG型液舱则会加剧晃荡,自由面呈现明显的三维特征.本文还进一步研究了水和LNG两种不同介质的液舱晃荡现象,数值模拟结果表明二者的流场基本相似,砰击压力则正比于液体密度.

Liquid sloshing is a common phenomenon induced in partially filled tanks under external excitations,which may destroy the tank structure and vessel stability.Moving particle semi-implicit(MPS)method is a typical meshfree method which can effectively simulate violent liquid sloshing problem.However,the low computational efficiency of MPS is the bottleneck of its application in large-scale three-dimensional problems.In the past years,GPU parallel acceleration technique has been widely used in the field of scientific computing.In this work,GPU parallel acceleration technique is introduced into MPS method and an in-house solver MPSGPU-SJTU is developed by using CUDA language.Then this solver is used to simulate 3-D liquid sloshing in liquefied natural gas(LNG)tank.The convergent validation of particle spacing is carried out to verify the accuracy of present solver.The maximum particle number of simulation model is over two million particles.MPSGPU-SJTU solver can accurately predict the impact pressures by comparing with other results.In addition,the violent flow phenomena such as large deformation and nonlinear fragmentation of free surface can be observed in these simulations.The comparison of computation time between GPU and CPU solvers demonstrates GPU parallel acceleration technique can significantly reduce the computation time and improve the computational efficiency of MPS.The phenomena of liquid sloshing in LNG tank and rectangular tank are compared.The results show that LNG tank can reduce the sloshing amplitude and impact pressure in high filling level.However,the sloshing is more violent and the free surface presents three-dimensional feature in LNG tank with middle and low filling level.Finally,the investigation of the effect of different fluids such as water and LNG on sloshing phenomena is also conducted in this paper.It shows that the flow fields of both liquids are almost similar and the impact pressure is proportional to the liquid density.