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To measure loads induced by nonimpacting waves on a vertical piercing cylinder, tests were performed in a 17 m long wave tank at the École Centrale Marseille. Different configurations of the cylinder (shape and size of the section and length) were studied for two focusing waves. Wave loads as calculated by the Morison equation were compared with measurements. The context for this experiment is the assessment of the hydrodynamic loads as a result of sloshing on the pump tower in liquefied natural gas tanks on floating structures. The comparisons turn out to be good in all cases studied, provided the Morison equation is used with relevant time series of liquid velocities and accelerations.

Introduction

Liquefied natural gas (LNG) membrane tanks are largely used on different kinds of floating structures such as LNG carriers, floating liquefied natural gas vessels, floating storage regasification units, LNG-fueled ships (LFSs), LNG bunker vessels, and all small-scale related applications. In these tanks, the liquefied gas remains in conditions close to thermodynamic equilibrium (-162°C at atmospheric pressure). Depending on the application, the volume of LNG tanks for floating structures ranges from a few thousand cubic meters for LFS or small-scale applications to about 55,000 m3 for tanks of the largest LNG carriers. Whatever the application, the shapes of these tanks are always prismatic, with large upper chamfers and smaller lower chamfers. The tanks do not include any structure that could mitigate LNG sloshing except a pump tower. As can be seen in Fig. 1, the pump tower is a tubular, vertical, stainless steel structure that enables the loading and unloading of the LNG, thanks to pumps located at its base. It is mainly made of three large vertical pipes: the emergency pipe at the front and two discharge pipes at the rear, connected together by struts. Located at the rear of the tank, in the central part but not necessarily exactly in the middle, it hangs from the liquid dome and is horizontally guided at its base by the pump tower base support.

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