Effects of second order wave load on dynamic response of a TLP under freak waves
LI Yan1,2， TANG Yougang1,2，WANG Bin1,2，QU Xiaoqi1,2
1. School of Civil Engineering，Tianjin University，Tianjin 300072，China；
2. State Key Lab of Hydraulic Engineering Simulation and Safety，Tianjin University，Tianjin 300072，China
Freak waves can cause destructive effects on offshore structures. In order to study the dynamic response of a tension leg platform (TLP) under freak waves, nonlinear equations for its coupled motions were established based on the platform’s 6-DOF motions and the leg’s nonlinear restoring stiffness. Time histories of freak wave surface were generated using the random frequency phase angle modulation method. The 1st order, 2nd order difference frequency and sum frequency wave loads exerted on the platform were calculated under freak waves. The platform’s 6-DOF motions were solved with numerical method. The results showed that freak waves affect both the 1st order and the 2nd order wave loads, increases in amplitude of different wave loads are different in different DOFs; the lower frequency motion, such as, surge of TLP, is mainly affected by the 2nd order difference frequency wave load; the higher frequency motions, such as, heave and pitch of TLP, are mainly affected by the 2nd order sum frequency wave load; under the action of the 2nd order difference frequency wave load, the negative motion caused by motions in horizontal plane of TLP increases significantly to cause an obvious increase in heave motion; therefore, heave motion under freak waves is affected by both the 2nd order difference frequency wave load and the 2nd order sum frequency wave load; besides, due to the impact characteristic of freak waves, the amplitude of each DOF motion appears at different time instants.
李 焱1,2，唐友刚1,2，王 宾1,2，曲晓奇1,2. 畸形波作用下二阶波浪载荷对张力腿平台动力响应的影响[J]. 振动与冲击, 2018, 37(3): 167-173.
LI Yan1,2， TANG Yougang1,2，WANG Bin1,2，QU Xiaoqi1,2. Effects of second order wave load on dynamic response of a TLP under freak waves. JOURNAL OF VIBRATION AND SHOCK, 2018, 37(3): 167-173.
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