The Study On Complex Mode Analysis And Technique Of Damping Layer To Reduce Vibration For Offshore Platform Under Random Loads

Jacket is the most widely used offshore platform structural style. First of all, the paper summarizes the present achievements of dynamic analysis for offshore platform, and studies both the vibration isolation system for jacket and vibration-suppressed effectiveness. Considering the style and character of jacket, and in order to make best use of dampers to reduce vibration, a damping isolation scheme, in which the damping layer is laid between the jacket cap and deck is put forward. Then a simplified computational modal of damping isolation systems is established for a platform structure, and the relationships between the parameters of isolation layer and structural damping ratio, including their vibration-suppressed effect on the whole structure and the relative displacement of isolation layer are studied, and the simulation analysis under several representative load case of random wave force and earthquake affairs is performed. Under random wave force, using complex mode theories, non-classically damp problems considering the interaction between the structure and wave, lying in deepwater, are studied. And the resolution solution of structural response are achieved.The results of calculating and analysing show that adding damping isolation to a jacket is an effective way to reduce vibration for offshore platforms. The problem of non-classically damp, after the structure's damp and linear water's damp are added up, are solved by way of complex mode transformation, and the dynamic responses of a offshore platform are studied under the circumstances of thinking about the mutual effect or not. Because the complex mode analysis takes mutual effect between the structure and water into account, the better precise and reasonable responses of the offshore platform under random loads can be achieved.