RESEARCH ARTICLE Yan GU, Yonglin JU Numerical simulation and analysis of periodically oscillating pressure characteristics of inviscid flow in a rolling pipe © Higher Education Press and Springer-Verlag Berlin Heidelberg 2012 Abstract Floating liquefied natural gas (LNG) plants are gaining increasing attention in offshore energy exploita- tion. 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 simula- tions 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 produc- tion storage and offloading unit for liquefied natural gas (LNG-FPSO) offshore 1 Introduction In recent years, a large number of floating plants for oil production are applied in offshore energy exploitation. Compared to fixed units, floating plants have the advantages of portability, reusability, and low cost. Floating production storage and offloading unit for liquefied natural gas (LNG-FPSO) is a floating unit with the functions of production, storage and offloading for LNG, which has received wide attention from countries interested in offshore natural gas resources [1]. However, many unique characteristics and rigorous factors, induced by the periodically oscillatory platform motion originated from variable wind and dynamic ocean wave, are restricting the construction of a real floating LNG plant. The fluid flow in the processes on LNG-FPSO will be inevitably influenced by the periodically oscillatory plat- form motion. The induced instabilities of the fluid flow are harmful to the operation of the transport equipment and the performance of the transfer process. For example, the LNG offloading process, one of the most important parts on LNG-FPSO, is carried out between two floating plants of the LNG-FPSO and LNG carrier. When the LNG is transferred between the two, the pipelines move together with the platform, inducing flow instability. As a result, the pressure fluctuations of the cryogenic fluid will cause resonance and vaporization, which are harmful to the pipeline and the LNG transport. There are high demands on the safety and economics of LNG offloading [2]. Thus the effects of the periodically oscillatory motion on the fluid flow require to be investigated systematically, to gain quantitative information for different situations. Some research has been conducted on the pressure fluctuation of the flow and thermal hydraulic induced by such oscillatory motions. Richardson and Tyler [3] experimentally investigated the cross-sectional velocity distribution in an oscillatory pipe and found that the maximum velocity occurred near the wall, not in the center of the pipe in steady flow. Sexl [4], Womersley [5] and Uchida [6] verified that the velocity profile was different Received July 8, 2011; accepted October 10, 2011 Yan GU, Yonglin JU (✉) Institute of Refrigeration and Cryogenics, Shanghai Jiao Tong University, Shanghai 200240, China E-mail: yju@sjtu.edu.cn Front. Energy 2012, 6(1): 21–28 DOI 10.1007/s11708-012-0173-2