Numerical simulation and analysis of periodically oscillating pressure characteristics of inviscid flow in a rolling pipe

Abstract

Floating liquefied natural gas (LNG) plants are gaining increasing attention in offshore energy exploitation. The effects of the periodically oscillatory motion on the fluid flow in all processes on the offshore plant are very complicated and require detailed thermodynamic and hydrodynamic analyses. In this paper, numerical simulations are conducted by computational fluid dynamics (CFD) code combined with user defined function (UDF) in order to understand the periodically oscillating pressure characteristics of inviscid flow in the rolling pipe. The computational model of the circular pipe flow is established with the excitated rolling motion, at the excitated frequencies of 1–4 rad/s, and the excitated amplitudes of 3°–15°, respectively. The influences of flow velocities and excitated conditions on pressure characteristics, including mean pressure, frequency and amplitude are systematically investigated. It is found that the pressure fluctuation of the inviscid flow remains almost constant at different flow velocities. The amplitude of the pressure fluctuation increases with the increasing of the excitated amplitude, and decreases with the increasing of the excitated frequency. It is also found that the period of the pressure fluctuation varies with the excitated frequency. Furthermore, theoretical analyses of the flow in the rolling circular pipe are conducted and the results are found in qualitative agreement with the numerical simulations.

Keywords

pressure fluctuation / rolling / floating production storage and offloading unit for liquefied natural gas (LNG-FPSO) offshore

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Acknowledgements

This work was supported by the National High-Tech Research and Development Program of China (863 Program) (No.2006AA09Z317), and the Program for Distinguished Young Scholars of the Ministry of Education (NCET-07-0544).

Notation

a_{\mathrm{0}}	Acceleration of kinetic system/(m·s-2)
f	Body force/ (N·kg-1)
fi	Body force component/(N·kg-1)
BoldItalic	Normal vector
\mathrm{d}{\mathit{l}}^{\prime }	Pipe segment in kinetic system/m
P	Pressure/(N·m-2)
qw	Heat flux of wall/W
BoldItalic0	Vector of origins from inertial and kinetic systems/m
BoldItalic	Vector in kinetic system/m
t	Time/s
T	Temperature of fluid/K
BoldItalic	Flow velocity/(m·s-1)
ui	Velocity component/(m·s-1)
BoldItalicn	Normal velocity/(m·s-1)
BoldItalicr	Relative velocity/(m·s-1)
xi	Direction component/m
{\delta }_{ij}	Kronecker delta
ϵ	Surface force/(N·m-3)
{\theta }_{\mathrm{0}}	Amplitude of rolling/rad
\rho	Density/(kg·m-3)
\omega	Angular velocity/(rad·s-1)
{\omega }_{\mathrm{0}}	Angular velocity of rolling/(rad·s-1)

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