Fin Stabilizer Angle of Attack Control for Vessel Rolling
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Solution Overview
Problem
Conventional fin stabilizers for vessels fail to accurately control the fin angle to achieve the required lifting force for suppressing rocking motion due to mismatch between the angle of attack and fin angle, especially under wave disturbances.
Innovation Solution
A fin stabilizer system with a hydraulic cylinder-driven fin, including a pressure detection section, torque calculation section, and command generation section to estimate and control the fin angle of attack, ensuring accurate lifting force generation by matching the estimated angle with a target angle for counteracting rocking motion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the fin angle is controlled based on the assumption that angle of attack equals fin angle, then the control system is simple, but the control accuracy deteriorates under wave disturbance
Solution Approach 1:
The patent replaces direct mechanical angle measurement with a computational approach. A detection device measures the fin angle, and a calculation device computes the angle of attack by combining this measurement with vessel motion data (roll angle, pitch angle, heave acceleration). This substitution of mechanical direct measurement with a sensor-fusion calculation system resolves the contradiction by providing accurate angle of attack information without requiring complex mechanical angle-of-attack sensors.
Solution Approach 2:
The patent introduces an intermediary calculation process that acts as a mediator between the fin angle measurement and the lifting force control. The angle of attack is calculated as an intermediary parameter that bridges the gap between the controllable fin angle and the performance-determining angle of attack. This intermediary calculation allows the control system to account for wave-induced motions without directly measuring angle of attack, thus improving accuracy while maintaining system simplicity.
2Speed
If the fin angle is controlled to match target angle directly, then the response is fast, but the lifting force accuracy deteriorates due to angle mismatch
Solution Approach 1:
The patent applies preliminary action by calculating the angle of attack in advance before generating the fin angle command. The detection device continuously measures the fin angle, and the calculation device pre-computes the angle of attack using this measurement combined with vessel motion data. This preliminary calculation ensures that when the control command is generated, the accurate angle of attack information is already available, allowing the system to achieve both fast response and accurate lifting force control.
Solution Approach 2:
The patent implements feedback by using the detected fin angle as input to the calculation device, which continuously updates the angle of attack calculation. This feedback loop ensures that the control system constantly adjusts the fin angle command based on the actual fin position and vessel motion conditions, maintaining accurate lifting force generation while responding quickly to changes in sea state and vessel motion.
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
The system achieves high accuracy in anti-rolling control by directly controlling the fin angle based on the angle of attack, ensuring the required lifting force is obtained to effectively suppress vessel rocking motion.
Implementation Method 1
a fin driving device having a hydraulic cylinder for adjusting an angle of the fin with respect to the vessel body
Implementation Method 2
a pressure detection section that detects a pressure in the hydraulic cylinder; a torque calculation section that calculates a torque of the fin
Implementation Method 3
by controlling an angle of this fin a lifting force is generated to suppress the rolling motion of the vessel body
Data Source
AI summary
An object is to suppress the rocking motion of a vessel body with a high level of accuracy by obtaining a required lifting force. A torque calculation section 27 calculates a torque of a fin 11 based on the pressure of a hydraulic cylinder 12. This torque is inputted to an angle of attack computing unit 24 via a torque adjusting unit 28, and based on this torque, a fin angle with respect to a flow of sea water, that is, an angle of attack of the fin is estimated. Then a command generation section 23 generates a fin angle command value θ3 for matching the estimated angle of attack θ2′ with a target fin angle θ1. Based on this fin angle command value θ3, a flow rate adjusting mechanism 14 controls a flow rate Q of hydraulic fluid applied to the hydraulic cylinder 12, to thereby adjust the angle of the fin 11. Thus, the fin angle is controlled based on the angle of attack, which directly relates to lifting force.