Continuous Stabilizing Fin Motion for Low-Speed Ship Roll Control
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Solution Overview
Problem
Current methods for controlling ship roll motion at null or low speed, such as those using stabilizing fins, often result in unstable balance, requiring continuous correction and causing uncomfortable transverse jolts due to non-continuous fin motion, which limits maximum dampening and comfort.
Innovation Solution
A process where the stabilizing fin starts moving when the roll motion begins and continues with a speed proportional to the roll rate, stopping at a stable position when the roll rate is zero, and re-starting when the roll motion resumes, using a continuous motion law to oppose the roll motion without creating jolts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the stabilizing fin moves in maximum roll rate zone (bang-bang control), then maximum roll energy dissipation is achieved, but the ship becomes unstable and requires continuous correction
Solution Approach 1:
The patent inverts the conventional control timing by activating the stabilizing fin not at maximum roll rate (passage from zero), but at maximum roll angle. This reversal of the control trigger point allows energy dissipation while maintaining stability, as the fin acts when the ship is at extreme positions rather than during rapid motion through the neutral position.
Solution Approach 2:
The fin is activated in advance at maximum roll angle before the ship reaches maximum roll rate. This preliminary action allows the stabilizing force to be applied during the roll motion development phase, preventing instability before it occurs while still achieving energy dissipation.
2Loss of energy
If the fin moves non-continuously (bang-bang control), then maximum dampening is achieved, but transverse jolts (jerk) are generated causing discomfort
Solution Approach 1:
The patent transitions from static bang-bang control to dynamic continuous control. The fin position is continuously adjusted according to the ship's roll angle and roll rate, creating a smooth control action that dissipates energy without generating harmful jolts. The control law varies the fin deflection dynamically based on real-time ship motion parameters.
Solution Approach 2:
The stabilizing fin operates continuously rather than in discrete bang-bang pulses. The continuous control action smooths out the force application, maintaining roll dampening effectiveness while eliminating the transverse jolts that occur during abrupt fin movements and stops.
3Object-affected harmful factors
If the fin is moved continuously, then comfort is improved, but roll energy dissipation is reduced
Solution Approach 1:
The continuous control system applies stabilizing force in advance during the roll development phase (at maximum angle), rather than waiting for maximum rate. This timing allows effective energy dissipation to occur during the motion itself, not after, thereby maintaining dampening effectiveness while ensuring comfort through continuous smooth operation.
Solution Approach 2:
The control system dynamically changes the fin deflection parameter based on ship motion parameters (roll angle and roll rate). This parameter adaptation allows the fin to provide sufficient stabilizing force for energy dissipation while varying the control intensity to maintain passenger comfort, avoiding excessive or abrupt movements.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach achieves greater roll dampening and improved comfort by maintaining the ship in a stable balance point, reducing the workload of the fins and eliminating unpleasant jolts, while effectively dampening both large and small roll motions.
Implementation Method 1
The reduction of the roll motion of a ship with null or low ship speed is obtained by rotating the fins in order to create a roll motion capable of braking the roll motion of the ship. It is well known, in fact, that the force, with null or low ship speed, is developed from the rotation speed of the fins
Data Source
AI summary
A process is described for controlling the roll motion of a ship, with null or low ship speed, through at least one stabilizing fin. The process comprises the following steps: starting the movement of the stabilizing fin when the roll motion starts; impressing a motion law of the stabilizing fin depending on the roll rate; and ending the movement of the stabilizing fin when the roll motion ends.