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Title: Control Stategy for Marine Riser of Position-Moored Vessel in Open and Level Ice-Covered Sea
Keywords: marine riser, riser end angles, position mooring, control strategy, open water, ice-covered sea
Issue Date: 16-Aug-2010
Citation: NGUYEN HOANG DAT (2010-08-16). Control Stategy for Marine Riser of Position-Moored Vessel in Open and Level Ice-Covered Sea. ScholarBank@NUS Repository.
Abstract: The main objective of the study is to present a control strategy for maintaining small end angles of marine riser during shallow water drilling operations by position-moored systems in open water and level ice-covered sea. Basically, an active positioning control using mooring line tensioning to reduce the riser end angles (REAs) in open sea is first formulated and illustrated numerically. Model experimental tests are then performed to validate the proposed control strategy. In addition, stresses along the riser due to bending are considered numerically, including the case where end bending stiffeners are used, which requires the REA control criterion to be replaced by one with terms related to the stresses at the riser ends. The proposed REA control strategy using line tensioning with vessel set-point chasing algorithm is extended for operation in level ice-covered sea. In the normal drilling and work-over operations, the riser angles at the well-head and top joint must be kept within an allowable limit (ideally within -2 to +2 degree) to prevent the drilling string wearing against the ball joints and guarantee continuous drilling operation. Although this can be achieved by applying sufficient tension at the top of the riser, this may lead to higher stresses, requiring the use of pipes with higher strength or dimensions. Alternatively, the vessel may be moved to reduce the mean offset, and hence the REAs, by tensioning the mooring lines under normal environmental conditions. This minimizes the need for fuel consumption of thrusters? operation.
Appears in Collections:Ph.D Theses (Open)

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