Research Of Vertical Vibrationcontrol Of Tension Leg Platform By Using TMD

Tension leg platform (TLP) is an offshore structure which is suitable to deep-searesource development with high performance. As a deep-sea platform, TLP offers threeprofound advantages:1) The range of water depth is around200~2500m and has highcompetitive in600~1500m;2) It can be used as a cheap dry type of oil production system;3)It has low cost for installation and maintenance. The structural characteristics of TLP is that1)its motion in plane (surge, sway, and yaw) is flexible and the motion out of plane (roll, pitch,heave) is rigid; and2) The period of the vertical vibration is2~4s. These specificcharacteristics of TLP lead it to showing some special motion responses which other offshorestructures do not have, such as the high frequency vertical vibration. These special motionscan result in the structure to occur resonances under some wave force excitation. The verticalvibration of TLP in resonances can cause damage of TLP structure and tension legs, the bestway to handle this is vibration control.Tuned mass damper (TMD) is a passive vibration control device that can be introducedon a host structure to reduce the dynamic response at the targeted resonance frequency.Because of its simple structure, easy to installation, convenient to maintenance, and norequirement to power, TMD has been widely used in the vibration control of buildings,bridges, and machines.In this paper, the TMD is used to control the vertical vibration of the TLP. AQWAsoftware system is also used to calculate wave force and hydrodynamic parameters infrequency domain. Then FORTRAN code is used to convert these parameters from frequencyto time domain. And finally, the vertical response of TLP is obtained from numericalcalculation. To evaluate the control performance of TMD, numerical analysis is also carriedout to calculate the vertical response of the TLP with/without TMD. Further investigation isconducted to examine the effect of TMD parameters to its control performance. It is knownthat: Working frequency of TMD significantly influences its control performance. The TMDmust be well designed to match the targeted frequency under control. The damping ratio ofTMD is another critical parameter and has an optimal value for best control performance. Themass ratio of the TMD and the host structure is also important. Based on the research,4~5%is a good ratio. The control study shows that TMD can significantly reduce the verticalvibration of TLP after appropriately designed.