Marine Vessel Station Keeping With Sea-State Adaptive Deadband
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Solution Overview
Problem
Existing marine vessel positioning systems face challenges in maintaining precise station-keeping and auto-heading under rough sea conditions, as they are prone to frequent corrections due to recurring disturbances like waves and wind, leading to increased wear and noise in propulsion systems.
Innovation Solution
A control module that filters actual velocities based on attitude measurements and roughness conditions, calculating desired velocities to minimize position and heading errors, and adjusts propulsion system operations to maintain target positions and headings, using sensors for pitch, roll, and heading data, and implementing a PID control algorithm with gain scheduling and deadband adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the propulsion system frequently corrects position and heading under rough sea conditions, then positioning accuracy is maintained, but wear and noise in propulsion systems increases
Solution Approach 1:
The control system dynamically adjusts the deadband threshold based on measured sea state conditions. When rough seas are detected through attitude measurements, the deadband increases, allowing larger position and heading deviations before correction is triggered. This dynamic adaptation reduces unnecessary propulsion corrections during rough conditions while maintaining accuracy when seas are calm.
Solution Approach 2:
The system changes the control parameter (deadband value) based on external conditions (sea state). By monitoring pitch, roll, and heading measurements, the system adjusts the deadband parameter to optimize the balance between positioning accuracy and propulsion system usage, reducing wear and noise during rough conditions.
2Measurement precision
If the control system responds to every position and heading deviation, then positioning accuracy is improved, but the frequency of corrective actions increases
Solution Approach 1:
The deadband acts as an intermediary filter between position/heading measurements and corrective actions. By introducing this intermediate threshold, the system only triggers corrections when deviations exceed the deadband, filtering out minor fluctuations that would otherwise cause frequent unnecessary corrections.
Solution Approach 2:
The system intentionally allows partial deviations from the target position and heading by implementing a deadband zone. Within this zone, no corrective action is taken, accepting small positioning errors to avoid excessive corrective actions. This partial action approach reduces the frequency of propulsion system activations.
3Object-generated harmful factors
If the deadband is increased to reduce corrective actions, then propulsion system wear is reduced, but positioning accuracy deteriorates
Solution Approach 1:
The deadband is made dynamic rather than fixed, adjusting based on real-time sea state measurements. During calm conditions, the deadband is small to maintain high positioning accuracy. During rough conditions, the deadband increases to reduce corrective actions and propulsion wear, accepting that larger deviations may occur due to environmental forces.
Data Source
AI summary
A method for maintaining a marine vessel at a global position and/or heading includes receiving measurements related to vessel attitude and estimating water roughness conditions based on the measurements. A difference between the vessel's actual global position and the target global position and/or a difference between the vessel's actual heading and the target heading are determined. The method includes calculating a desired linear velocity based on the position difference and/or a desired rotational velocity based on the heading difference. The vessel's actual linear velocity and/or actual rotational velocity are filtered based on the roughness conditions. The method includes determining a difference between the desired linear velocity and the filtered actual linear velocity and/or a difference between the desired rotational velocity and the filtered actual rotational velocity. The method also includes calculating vessel movements that will minimize the linear velocity difference and/or rotational velocity difference and carrying out the calculated movements.