AbstractsBiology & Animal Science

The relative motions of an FLNG and an LNG carrier in side-by-side arrangement: A numerical and experimental analysis :

by W.W. Quast

Institution: Delft University of Technology
Year: 2015
Keywords: mooring
Record ID: 1260028
Full text PDF: http://resolver.tudelft.nl/uuid:62848cb3-a588-4f65-b197-9572b58b3e6c


For future Floating Liquid Natural Gas vessel (FLNG) developments, SBM Offshore is considering system for offloading of Liquid Natural GAS (LNG). The ability to offload LNG at minus 163 degrees Celsius from the Twin-Hull FLNG to an LNG Carrier (LNGC), is of high importance to the overall operability and economic viability of FLNG development. Side-by-side offloading is preferred above tandemoffloading, due to the location of the (off-)loading manifolds on the LNG carrier. Furthermore the maximum distance for transporting the -163 degrees LNG is limited due to mechanical and thermal properties of offloading system components. Traditionally, time-consuming physical model tests are being used to determine the side-by-side relative response of the FLNG and the LNGC, when subjected to specific waves forces. The aim of this thesis is to verify and validate the suitability ofHydroStar and Ariane software models, to predict responses for the FLNG and the LNG carrier, by comparing the vessel response calculations to the results of model tests performed in the MARIN offshore basin. The calculated responses are performed both in frequency domain and in timedomain, which in both cases is much faster obtained compared to responses obtained by physical model tests. The relative manifold motions are a crucial design factor for the (off-)loading system. A description of the MARIN offshore basin setups for soft-mooring and turret-mooring is given. Both setups are without the LNGC, so the FLNG is moored on its own inside the offshore basin. The responses obtained from these experiments are illustrated and compared. This study exposed unexpected outcomes for roll and especially the sway Response Amplitude Operator (RAO). The sway RAO shows an extreme peak value for the turret moored FLNG. This peak value is not observed in the soft mooring experiments. A theoretical description of HydroStar with the respective setups for the FLNG without the LNG Carrier is discussed. HydroStar does not account for a mooring-system so the same model is used both for the soft- as for the turret-mooring. The frequency response calculated by HydroStar corresponds more to the response observed in soft-mooring than to the response observed in turret-mooring. The HydroStar response does not show the extreme sway peak observed in turret-mooring experiments. Furthermore a sensitivity analysis by HydroStar concluded that the extra roll response of the FLNG in soft-mooring can be the result of a different weight distribution between the two vessels. Two different vessel setups were used in the turret- and soft-mooring experiments. The response of the side-by-side setup is analyzed using HydroStar. The FLNG in SBS arrangement shows a similar response as to the FLNG alone, no extreme sway peak response is observed by HydroStar. Likewise, the response of the LNGC is about the same as the FLNG response. However the response obtained from MARIN for the FLNG in side-by-side (SBS) arrangement shows again no correlation for sway in the lower wave frequencies. This…