Print Email Facebook Twitter The relative motions of an FLNG and an LNG carrier in side-by-side arrangement: A numerical and experimental analysis Title The relative motions of an FLNG and an LNG carrier in side-by-side arrangement: A numerical and experimental analysis Author Quast, W.W. Contributor Brinkel, T. (mentor) Faculty Mechanical, Maritime and Materials Engineering Department Offshore Engineering Programme Floating structures Date 2015-04-08 Abstract 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 exceptional sway peak also applies for the sway response for the LNGC, observed in the offshore basin. The natural frequency of the turret mooring system does not come near this sway peak. Therefore the mooring system does not seem to be responsible for the observed sway motion amplification. Investigation on the effects of weight distribution, epsilon damping and linear viscous damping, showed that also these are not the source for the sway motion amplification. Possibly viscous phenomena are causing the observed sway behavior, which are neglected in HydroStar. HydroStar is not capable of calculating the sway RAO’s for this typical mooring set-up. In order to "fit" the computed RAO’s with the obtained experimental RAO’s, the model has been tuned. The "tuned" RAO’s are the RAO’s computed by HydroStar except for the sway RAO. The "tuned" sway amplitude RAO and the "tuned" sway phase RAO are obtained from MARIN. Subsequently, using Ariane multiple time domain analysis are executed, with the "untuned" and "tuned" RAO’s as input. Their results consist of time traces of the relative manifold motions, which are compared with the manifold motions obtained from the MARIN experiments. The time domain analysis with "untuned" RAO’s show satisfying correlations in X- and Z-direction, however the Y-direction (relative sway) does not correlate with the relative sway obtained in the offshore basin. For the "tuned" RAO’s all six Degree of Freedom (DOF)’s do correlate, including the sway motions. Due to insufficient experimental data, a true validation of the HydroStar SBS model and Ariane SBS model is not possible. Therefore it is recommended to perform additional side-by-side experiments in the MARIN offshore basin, which include appropriate parameters purposely designed for calculating the HydroStar SBS and Ariane SBS mdoels. Subject mooring To reference this document use: http://resolver.tudelft.nl/uuid:62848cb3-a588-4f65-b197-9572b58b3e6c Embargo date 2020-01-17 Coordinates 51.999112, 4.370564 Part of collection Student theses Document type master thesis Rights (c) 2015 Quast, W.W. Files PDF report2.pdf 9.66 MB Close viewer /islandora/object/uuid:62848cb3-a588-4f65-b197-9572b58b3e6c/datastream/OBJ/view