FPSO (Floating Production, Storage and Offloading) has become used increasingly for off-shore gas fields. Most tall pressure vessels such as columns installed in the FPSO are surrounded by topside structures. In general, columns in on-shore plants are supported only by bottom skirts; on the other hand, some of the tall columns on FPSO hulls require intermediate supports in addition to bottom skirts because of large accelerations they are subject to due to ship motion induced by wave loading. In this paper, the effects of the support were investigated considering acceleration distributions and structure deformation (drift), then the ideal elevation of the support was determined to minimize bending moment throughout the columns under the combined conditions. A dimensionless controlling parameter related to the acceleration, structure drift, and column properties was proposed and graphs (called N-Charts) were proposed to understand effects in reducing the maximum bending moment with respect to the elevation of the guide.
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