Golafshani - Associate Professor, School of Civil Engineering , Sharif University of technology , Tehran , Iran
Golizadeh - phD Candidate, Department of Civil Engineering , Sharif University of Technology

Considering the stress cycles in the joints and members due to the wave induced forces in offshore platform, fatigue analysis is therefore on of the most important analysis in the offshore platforms design. Although most of the steel jacket type platforms located in areas with relatively high ratios of operational seastates to maximum design environmental events, fall in acceptable safety margin in inplace and seismic analysis; but in the fatigue analysis will face with critical condition. Therefore it seems that utilizing control mechanisms with the aim of increasing fatigue life in such platforms will be more preferable to merely deck displacement control. Investigation of tuned mass damper parameters optimality for vibration control of wave excited single degree of freedom systems implies that optimum tuning and damping ratios are strongly dependent to seastate condition to system parameters. Also the efficiency optimally designed friction for fatigue damage mitigation in realistic steel jacket platforms has been evaluated in this study. Full stochastic spectral analysis methods has been employed to estimate the maximum fatigue damage as objection to be minimized also a stochastic linearization technique has been to take the nonlinear of the hysteretic dampers into account.

Steel Jacjet Platforms , Vibration Control , Tuned Mass Damper , Friction Damper , Power Spectral Analysis