Stabilizing Fin Control for Low-Speed Ship Roll Damping
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Solution Overview
Problem
Current ship roll stabilization methods, such as those using stabilizing fins, face challenges in achieving maximum comfort and roll dampening at low ship speeds, as they often result in transverse jolts and inadequate dampening of small roll motions, leading to discomfort and inefficient energy dissipation.
Innovation Solution
The process involves starting the movement of stabilizing fins when roll motion begins and controlling their motion based on the roll rate, using a continuous motion law that stops the fins at a non-null position, ensuring they only move when the roll rate is non-zero, thereby creating a gradual stabilizing moment without jolts and maximizing dampening.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If stabilizing fins are moved at the passage of roll from zero or near zero (maximum roll rate zone), then maximum roll dampening is achieved, but transverse jolts and jerk are generated reducing passenger comfort
Solution Approach 1:
The fin motion is synchronized with the roll periodicity, but the activation timing is shifted from maximum roll rate to when roll angle exceeds a threshold. The fin performs periodic strokes that are phase-shifted relative to conventional systems, creating a periodic stabilizing moment that avoids the harmful jerk while maintaining dampening effectiveness through continuous rather than impulsive action.
Solution Approach 2:
The fin motion law is made dynamic and adaptive, transitioning from fixed bang-bang control to a continuous motion law that adjusts fin position based on real-time roll angle and roll rate. This dynamic control allows the fin to move gradually rather than abruptly, reducing jerk while maintaining the ability to counteract roll motions effectively.
2Loss of energy
If stabilizing fins are moved in maximum roll rate zone with bang-bang control, then maximum energy dissipation is achieved, but the ship cannot be stabilized at zero roll angle and control runs after continue
Solution Approach 1:
The control system incorporates feedback from both roll angle and roll rate sensors to determine fin position continuously. This feedback mechanism allows the fin to adjust its position based on the current state of the ship, enabling stabilization at zero roll angle while maintaining energy dissipation. The feedback loop ensures that the fin stops at the appropriate position rather than continuing to stroke, eliminating control run-after effects.
Solution Approach 2:
The control parameters are changed from fixed bang-bang switching based on roll rate to continuous adjustment based on both roll angle and roll rate. This parameter change allows the system to transition from maximum energy dissipation at the cost of stability to a balanced state where both energy dissipation and roll angle stability are achieved simultaneously.
3Object-affected harmful factors
If fins are moved continuously based on roll rate, then transverse jolts are reduced improving comfort, but roll dampening effectiveness may be reduced
Solution Approach 1:
The fin motion is activated partially based on roll angle threshold rather than continuously at all roll rates. When roll angle exceeds the threshold, the fin performs a stroke that is sufficient to counteract the roll motion without excessive action. This partial action approach maintains comfort by avoiding continuous high-frequency motion while preserving dampening effectiveness through targeted intervention.
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 effectively dampens roll motions, providing greater comfort and increased roll stabilization efficiency, especially for small roll angles, by continuously adjusting fin position based on roll rate, reducing transverse jolts and workload, and enhancing overall ship stability at low speeds.
Implementation Method 1
the force, with null or low ship speed, is developed from the rotation speed of the fins or of other devices
Data Source
Figure 1~2
Figure 3~4
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.