Optimal Control for Response Reduction of Single Hinged Articulated Tower Using an MR Damper

An articulated leg platform (ALP) is a compliant offshore structure deployed in deep waters for extraction of crude oil and natural gas. Under extreme wave conditions, the response of ALP can go beyond the expected limit, causing discomfort to occupants and creating unfavourable working conditions. Therefore, it is necessary to control the dynamic response of ALP to keep it safe and workable under extreme ocean conditions. Owing to several advantages and the popularity of the magnetorheological damper (MR damper) in structural control, a numerical study is carried out to investigate the performance of the MR damper for response control of ALP. The use of semiactive control techniques with the MR damper for response control of flexible structures such as ALP is not available in literature. In the present study, the linear quadratic regulator technique is used to find the desired optimal control force. The voltage supply to the MR damper is obtained using four well-established control algorithms (Passive-on, Passive-off, Direct control, and Clipped optimal), and their efficiency in response control of ALP is discussed. It is observed that the Passive-on works better than does the Direct control and Clipped optimal algorithms in the case of flexible structures such as ALP under random ocean waves.