Abstract
The response control of a very large floating structure (VLFS) is a crucial issue that affects the stability and safety of the structure. This paper presents a vibration control method for stabilizing the motion of a multi-modular VLFS by using a set of stiffness-adjustable connectors. The proposed connector consists of a cylindrical spring with an embedded actuator, making its stiffness adjustable. In a case study, a layout for such connectors is suggested to reduce the surge, heave, pitch, and yaw motions of the VLFS in random seas. To control the vibration responses of the VLFS, a mathematical model of the floating structure with the proposed connectors is established. A state feedback control scheme is developed using Sequential Quadratic Programming, which is able to adapt to varying wave conditions. Numerical studies indicate that the control method based on the stiffness-adjustable connectors was able to greatly reduce the responses of the modules when compared to flexible connectors and was also able to reduce the connector loads when compared to hinged connectors. Most importantly, this control method enables the elimination of resonant responses by changing the system stiffness.
Highlights
Academic Editor: Rosario PecoraA very large floating structure (VLFS) is a unique concept for an oceanic structure that embraces a range of unprecedented parameters, being thousands of meters long, weighing several tons, and costing between USD 5000~15,000 million, etc., [1]
We proposed a novel stiffness-adjustable connector and a related vibration control method for multi-modular VLFS
The novel connector is composed of an annular spring to provide basic flexibility and an embedded hydraulic actuator to provide control force
Summary
A very large floating structure (VLFS) is a unique concept for an oceanic structure that embraces a range of unprecedented parameters, being thousands of meters long, weighing several tons, and costing between USD 5000~15,000 million, etc., [1]. A semi-active control method [23] was proposed to reduce the vibration of a floating airport by intermittently tuning the stiffness of the connectors based on the amplitude death mechanism. This method can greatly reduce the vibration responses of a VLFS, but it may fail to perform in certain sea conditions. A vibration control method is developed based on the mathematical VLFS model and is connected by the novel connectors and Sequential Quadratic Programming to determine feedback gains of the different states and the hydraulic parameters of the actuators.
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