Vessel Position Holding Controller Feedforward Wave Drift Compensation
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Solution Overview
Problem
Conventional dynamic positioning systems fail to accurately control vessel position and heading in rough seas due to the lack of consideration for wave drifting forces and moments, leading to delays and increased positional deviations, as there are no means to easily estimate these forces and moments.
Innovation Solution
An automatic vessel position holding control method that estimates and compensates for wave drifting forces and moments using methods like Hsu's or Pinkster's, incorporating wave incident angle estimation and pitch response coefficients, and performs feedforward control to reduce positional deviations and heading errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If feedback control is performed after detecting positional deviations, then the vessel can be held in position, but delays in control are generated and positional deviations increase in rough sea conditions
Solution Approach 1:
The patent applies preliminary action by estimating wave drifting forces and moments before they cause significant positional deviations. The feedforward control component calculates anticipated wave forces based on wave spectra and vessel characteristics, then pre-compensates for these forces before they manifest as positional errors, eliminating the need to wait for feedback detection.
Solution Approach 2:
The patent implements feedback by continuously monitoring actual vessel position and comparing it with the target position. The feedback control component uses detected positional deviations to adjust control forces, ensuring the vessel returns to the desired position after any disturbances, thereby maintaining position holding reliability.
2Manufacturing precision
If wave drifting forces and moments are not considered in control, then the control system is simpler, but positional deviations and heading deviations increase significantly
Solution Approach 1:
The patent introduces an intermediary component that estimates wave drifting forces and moments based on wave spectra, vessel motion responses, and hydrodynamic characteristics. This intermediary estimation system bridges the gap between measurable quantities (wave parameters, vessel motion) and the unmeasurable wave forces, enabling accurate feedforward compensation without requiring direct wave force measurement equipment.
Solution Approach 2:
The patent replaces the need for direct mechanical measurement of wave forces with a computational estimation system. Instead of using complex mechanical sensors to measure wave drifting forces directly, the system uses mathematical models and signal processing to estimate these forces from readily available data such as wave spectra and vessel motion responses.
3Manufacturing precision
If feedforward control compensating for wave drifting forces is implemented, then positional deviations are drastically reduced, but the control system becomes more complex
Solution Approach 1:
The patent segments the control system into distinct functional components: wave parameter measurement, wave spectra analysis, wave force estimation, feedforward control calculation, and feedback control. This segmentation allows each component to be optimized independently and facilitates implementation using standard control system modules, reducing the practical complexity despite the advanced functionality.
Data Source
AI summary
An automatic vessel position holding control method for holding a vessel position and a vessel heading of a vessel on the ocean in order to reduce a positional deviation and a heading deviation sharply as compared with the conventional automatic vessel position holding control by performing feedforward control for estimating and then compensating for at least one of a wave drifting force and a wave drifting moment that act on the vessel, wherein a vessel position holding control is performed that includes such controls as estimating waves entering the vessel from motion thereof, calculating at least one of the wave drifting force and the wave drifting moment from the estimated waves and performing feedforward control for at least one of the calculated wave drifting force and the calculated wave drifting moment.