Investigation of Low-Frequency Pitch Motion Characteristics for KRISO Standard Offshore Structure (K-Semi) Moored with a Truncation Mooring System

Investigation of Low-Frequency Pitch Motion Characteristics for KRISO Standard Offshore Structure (K-Semi) Moored with a Truncation Mooring System

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In this study, a model test was carried out to evaluate the station-keeping performance of Korea Research Institute of the Ships and Ocean Engineering (KRISO) standard semi-submersible, K-Semi in the Deep Ocean Engineering Basin (DOEB).The test was performed using a 1/50 scaled model with 12 mooring lines.The water depth was set to 3.2 m using a moveable bottom structure and truncated mooring lines.The dynamic behavior of the K-Semi was examined using a free decay test and regular wave as well as irregular wave tests of 1800.

Large surge, heave and pitch due to drift motion Miscellaneous from second-order effect were observed.The reason for the excessive low-frequency pitch motion is attributed to the restoring force and moment related to the mooring system as excessive surge occurred.The numerical model of K-Semi with the truncated Wax stick mooring system was tuned and calibrated using model test results such as free decay and regular wave tests.Through numerical analysis, the motion characteristics of the K-Semi were compared with irregular model test results.In the case of a semi-submersible using a mooring system, it is observed that excessive pitch motion due to vertical restoring force and moment may occur when large horizontal displacement occurs.

The effect of low-frequency pitch motion related to surge motion is an important factor in upwell estimation as well as second-order motion in referred DNV-GL OTG13.