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A phenomenological rapid sloshing model for use as an operator guidance system on liquefied natural gas carriers

机译:一种现象学快速晃荡模型,用作液化天然气运输船的操作员引导系统

摘要

A concept for a non-intrusive sloshing guidance system based on a phenomenological Rapid Sloshing Model is proposed to reduce the operational risk of sloshing damage to LNG carriers. A numerical sloshing model is implemented in a commercial Navier-Stokes Computational Fluid Dynamics (CFD) code which uses a volume-of- fluid approach for the simulation of multi- fuid problems. The effect of spatial and temporal discretisation and turbulence is investigated using systematic variation. Dimensional analysis of the multiphase flow regime and examination of the relative velocity at the fluid interface show that an inhomogeneous multiphase model is appropriate for the simulation of a violent sloshing flow. This is conrmed by the good agreement with the experimental data of Hinatsu. The effect of fluid compressibility is investigated for sloshing impacts and a criterion based on wave propagation is developed to assess the importance of compressibility. When modelling sloshing with large air bubble entrainment, the choice of fluid compressibility model is shown to have a significant influence on pressure magnitude and frequency of oscillation required for structural assessment and a thermal energy model is required. The Rapid Sloshing Model (RSM) is based on the observation that the centre of mass of a sloshing fluid tends to follow a particular trajectory. Using a phenomenological modelling approach, the forces affecting the sloshing response are approximated with mathematical functions for restoring force, damping and sloshing impacts. Calculation times for the resulting equations are typically 0.1% of real time on a desktop PC. A case study of sloshing induced by periodic rotation and translation of two-dimensional longitudinal and transverse sections of membrane LNG tanks is carried out using RSM. RSM is set up using one CFD simulation not considered in the case study and the RSM solutions are then compared to the independent CFD solutions. The fluid momentum from RSM is usually within 5%{15% of the CFD solution for excitation at and near the first resonant period at a filling level near the critical depth. An irregular surge motion profile from an ITTC two-parameter spectrum is applied to the tank and the mean error from the RSM solution remains below 15% when using momentum and transverse force. When applied to sloshing with a 10% filling level excited by an irregular seaway a mean error of 9.6% is obtained. Compared to existing phenomenological modelling approaches the RSM methodology reduces the error by an order of magnitude in sloshing scenarios of practical interest. A non-intrusive sloshing guidance system based on the Rapid Sloshing Model which is suitable for installation on existing and newbuild LNG carriers can be implemented by applying motion data measured onboard to the RSM to provide operator guidance on the sloshing severity in partially filled LNG tanks. The RSM is set up for a particular LNG carrier with existing sloshing data from the design and class approval stages.
机译:提出了一种基于现象学的快速晃动模型的非侵入式晃动引导系统的概念,以降低晃动损坏LNG船的操作风险。数值晃荡模型在商业Navier-Stokes计算流体动力学(CFD)代码中实现,该代码使用流体体积方法模拟多流体问题。使用系统变异研究时空离散和湍流的影响。对多相流动状态的尺寸分析和在流体界面处的相对速度的检查表明,不均匀的多相模型适用于猛烈晃动流动的模拟。这与Hinatsu的实验数据吻合得很好。研究了流体可压缩性对晃荡影响的影响,并开发了基于波传播的标准来评估可压缩性的重要性。在对带有大气泡夹带的晃动进行建模时,流体可压缩性模型的选择显示出对结构评估所需的压力大小和振荡频率具有重大影响,并且需要热能模型。快速晃动模型(RSM)是基于以下观察结果:晃动流体的质心趋于遵循特定的轨迹。使用现象学建模方法,使用数学函数来近似影响晃荡响应的力,以恢复力,阻尼和晃荡的影响。所得方程的计算时间通常为台式PC的实时时间的0.1%。利用RSM对LNG储罐的二维纵向和横向截面的周期性旋转和平移引起的晃荡进行了案例研究。使用案例研究中未考虑的一种CFD模拟来设置RSM,然后将RSM解决方案与独立的CFD解决方案进行比较。来自RSM的流体动量通常在CFD解决方案的5%{15%之内,以便在接近临界深度的填充水平下在第一个共振周期及其附近激发。来自ITTC两参数频谱的不规则喘振曲线被应用到储罐,并且在使用动量和横向力时,来自RSM解决方案的平均误差保持在15%以下。当应用于不规则航道激发的充填水平为10%的晃荡时,平均误差为9.6%。与现有的现象学建模方法相比,在实际感兴趣的晃荡情况下,RSM方法将误差减少了一个数量级。可以通过将在船上测得的运动数据应用于RSM上,以提供操作员有关部分装满的LNG罐的晃动严重程度的指导,从而实现适用于安装在现有和新建LNG船上的,基于快速晃动模型的非侵入式晃动指导系统。使用来自设计和类别批准阶段的现有晃动数据为特定的LNG船设置RSM。

著录项

  • 作者

    Godderidge Bernhard;

  • 作者单位
  • 年度 2009
  • 总页数
  • 原文格式 PDF
  • 正文语种 English
  • 中图分类
  • 入库时间 2022-08-20 21:06:20

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