Structural Vibration Control Technique For Offshore Platforms

The offshore platform in ice area suffers from serious impact by ice force in winter, the continuous ice force causes severe structural vibration, which influences the offshore platform's safety and comfort, and have a direct impact on production. With the further development of offshore oil and gas resources exploitation in China, it is more anxious for designing new anti-vibration ice offshore platform and taking measures on the offshore platform's vibration control method. This paper focuses on the offshore platform's vibration control, including the validity test of passive control device and the simulation compute the active control.First, this paper reviews some of civil engineering vibration control strategies and devices in order to find a suitable passive control device and active control strategy for ice-induced offshore platform's vibration control. Then does feasibility test for passive control device including isolation, TMD and TLD. Adopts Matlab / Simulink make a program for simulating offshore platform then connects the real isolation, TMD and TLD devices to built a hardware in the loop simulation (HILS) experiment by dSPACE, uses random ice function and the determined ice function simulating the real ice excitation to verify the device's validity .The experimental results show that under certain conditions passive control device can play a great role in vibration control.In the pursuit of better control effectiveness and wider application, this paper studies active control method and designs two feedforward-feedback control systems. 1). First, assign the desired pole according to the system's performance requirements and compute state feedback coefficients. Second, choose proper disturbance servo coefficient as feedforward matrix which can make the output and the state independent of the disturbance input. At last, combining the two control forces to attenuate the structure's vibration. 2). By using online measured data and an AR model with time-varying coefficients, the future ice force can be estimated accurately. Combing this AR model with a discrete-time state space model of the platform and the AMD, an augmented state space model is constructed. With this model, the active control force, consisting of feed-forward and feedback control, can be evaluated according to discrete linear quadratic regulator theory. The simulation shows that these two feedforward - feedback compound control approaches are better than passive control and feedback control.