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Investigations regarding the dynamic response of a novel heave-compensated floating platform have been carried out. The concept consists of a semi-submersible floating platform with an air chamber below its hull, aiming to keep the static platform buoyancy constant, thus effectively reducing heave motion and enabling its use under harsh environmental conditions as in the North and Norwegian seas. This work develops a dynamic response model for the concept platform in which hydrodynamic coefficients calculated using potential flow theory and mooring lines effects are considered. Calculations in both the frequency and time domain are performed, and results show that the air chamber and effects of the mooring lines are the most beneficial scenario to reduce the dynamic response, especially in terms of heave motion reduction at lower wave frequencies. Another observed benefit is the change of the heave resonance peak away from the typical observed frequency range of sea waves. [ABSTRACT FROM AUTHOR]

A heave compensation system combined with a vibration absorber and accumulator is proposed, with regard to the requirement for poly-metallic nodule mining systems at an ocean depth of 6,000 m in China. The principle of the compensation system was analyzed, its main parameters were designed, and its mathematical model was established. The system performance was simulated and analyzed in MATLAB, and the frequency domain characteristics and compensation rate of the system with different volume accumulators, and with or without vibration absorbers, were compared. A simulation test of the compensation system was conducted. The proposed compensation system had a better compensation effect for a random wave interference under level-6 sea conditions, and the compensation rate being more than 72% with optimal system parameters. [ABSTRACT FROM AUTHOR]

The heave compensation system is essential for the installation of subsea equipment. A new semi-active heave compensation system is designed and the control system is analysed, with the aim of solving heave movement problems during deep-water installation. The heave compensation is implemented with a pulley block system and actuated by a compound hydraulic cylinder. The control system can switch between passive compensation mode and semi-active compensation mode. The state-space equations of both modes are set up based on the mechanical and hydraulic system models of the compensation system. With the state-space equations, three control strategies are compared based on the classic Proportion Integration Differentiation (PID) control, and the limitations of PID control are also analysed. In order to avoid defects of the PID controller, the active disturbance rejection control (ADRC) technology is introduced, and a newly developed second-order ADRC controller is applied in the tension control strategy for heave compensation, which results in improved compensation effect. [ABSTRACT FROM AUTHOR]

This article describes the design, operation, and field testing of the depthimeter. The depthimeter merges heave and acoustically derived vessel depth to form estimates of instantaneous vessel depth and instantaneous sea surface height, both relative to mean sea level. Results from sea trials held in December 1997 demonstrate successful operation of the system. [ABSTRACT FROM AUTHOR]