Wind Effect Estimation and Navigational Effect in Side by Side Offloading Operation for FLNG and LNG Carrier Ships
Authors: Fujiwara Toshifumi , Yukawa Kazuhiro , Sato Hiroshi , Kato Shunji 
Published: April 2012

The side by side offloading operation for a Floating LNG facility (FLNG) and aLNG carrier ship (LNG) is expected efficient way of offloading rather thantandem style one, since the ondeck equipment is easily installed using thecommon facility used in the port terminal. In case of considering the LNGapproaching to the FLNG, however, it is needed to pay attention for the weathercondition like wind, waves and current. Rapidly change of those weatherconditions causes the difficulty of manoeuvring of the LNG, and in worst theLNG may crash to the FLNG. In particular a conventional LNG has largesuperstructures and the operating speed of the LNG is very slow at the closednavigational area for the FLNG. Wind effect becomes larger than the otheroperational situation in the ocean. Then the operational capability evaluationof the LNG would be needed to grasp the operational weather limitation. Theeffect of each element on weather conditions, that is wind etc. givingmanoeuvring difficulty to ships as external load, is expected to assessexactly. Wind interaction effect under the operating condition that a FLNG anda LNG are in same closed area, however, is not clearly understood. This papertreats and proposes one estimation method of wind load including interactioneffect of a FLNG and a LNG for the operation of side-by-side offloading. Theproposed wind load estimation method based on the wind tunnel experimentssufficiently represents the shielding effect of interaction of the LNG behindthe FLNG. Operational assessment on ship manoeuvring under strong wind iscalculated using the proposed wind load estimation method in the finalstage.

1 Introduction

The gross area of the sea on the earth is vast and the percentage whichaccounts for a whole surface of the earth is about 71%. In considering thesecuring of resources on Liquid Natural Gas (LNG), the region of thedevelopment spreads out from land to the sea recently and sea excavating pointsof that are expanded from shallow sea area to deep ocean gradually. Whengetting LNG in the ground under the sea distant from land, it will be necessaryto transfer the LNG from the excavating and production facility to a transportship after producing it at those points.

In such a situation, LNG offloading critical limitation under rough sea isimportant information for the operation of transferring storage LNG resourcefrom a Floating LNG facility (FLNG) to a LNG carrier ship (LNG as a ship). Theside by side offloading operation, see Figure 1 as the image, to supply liquidgas from the FLNG to the LNG is adopted frequently with easier operationalreason rather than tandem style operation. In the side by side offloadingoperation, however, weather condition must be paid attention enough to preventthe collision accident between the FLNG and the LNG.

The authors have focused on the wind shielding effect in side by sideoffloading situation of operating ships in this paper. In the past presentedpapers by another authors [1]~[4], general information noted the importance ofconsideration for the wind shielding effect was pointed out, and in some cases, CFD (Computational Fluid Dynamics) calculations in the ship shieldingconditions had conducted[4]. Detail analysis of the effect based onexperimental or the wind shielding effect on calculated results, however, havenot generally presented in them. Easier estimation method or logic of assessingon ship shielding conditions is expected to get information for operationalrisk from the viewpoints of practical use.