Roll performance of an LNGC with partially-filled spherical tanks

Wenhua Zhao, Mike Efthymiou, S. Wille, F. McPhail

    Research output: Chapter in Book/Conference paperConference paper

    Abstract

    Copyright 2016, Offshore Technology Conference.Objective/Scope: Roll performance of an LNG carrier (LNGC) plays a critical role in side-by-side offloading. Liquid cargo motions can couple with the global motions of an LNGC, affecting the roll response and affecting the operational window for side-by-side offloading. In this study, a series of model tests has been conducted in a wave basin, and the roll characteristics of the LNGC are studied with liquid cargo in spherical tanks. Methods/Procedures: Scale model tests were conducted with an LNG carrier-like model under waves in an artificial wave basin, whereby the model was positioned in the centre area of the wave basin through four horizontally arranged spring lines. The time series of the vessel motions and the internal liquid cargo motions were measured. To quantify the liquid cargo effect, several sets of tests were performed for which the tanks were empty, but the vessel properties modified to a 'frozen' approximation. Decay tests were conducted with the model oscillating freely in calm water, excitation by a given initial heel angle. Results/Conclusions: Spectral analyses have been conducted to obtain the response amplitude operators (RAO) from the test results. Based on the obtained RAOs, short-term spectral analyses were conducted to understand the most probable maximum roll response in side-by-side offloading sea states. For the first time, the effects of cargo motion have been clarified for LNGCs with partially-filled spherical tanks. The findings reveal that the operational window may not be estimated robustly using a simplified method which ignores the liquid cargo and considers only the ballast condition. Based on the results in five different loading conditions, the most responsive loading condition is examined for spherical cargo tanks. It is suggested that intermediate load conditions with explicit inclusion of the effects of cargo motions to be utilised in side-by-side operability studies to robustly ascertain offloading availability. To facilita
    Original languageEnglish
    Title of host publicationProceedings of the 2016 Offshore Technology Conference
    EditorsDarrel Harvey, Charles Knobloch
    PublisherSociety of Petroleum Engineers (SPE)
    Pages2353-2366
    Number of pages14
    Volume3
    ISBN (Print)9781510824294
    DOIs
    Publication statusPublished - 2016
    EventOffshore Technology Conference 2016 - Houston, United States
    Duration: 2 May 20165 May 2016

    Conference

    ConferenceOffshore Technology Conference 2016
    Abbreviated titleOTC 2016
    CountryUnited States
    CityHouston
    Period2/05/165/05/16

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