Marine Vessel Dynamic Positioning Using Riser Angle and Velocity Fusion
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Solution Overview
Problem
Dynamic positioning systems for marine vessels face challenges in maintaining accurate position measurements, especially in deep water, where acoustic systems are noisy and GPS is susceptible to ionospheric perturbations, and riser information is unreliable due to unknown shapes and current variations.
Innovation Solution
Combining riser bottom angle measurements with vessel velocity data, possibly using a Kalman filter, to produce a stable and reliable position estimate, eliminating the limitations of individual measurements without requiring top angle measurements or modeling the riser shape and current profiles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If acoustic position measuring equipment is used in deep water, then position measurement is possible, but measurements become noisy and accuracy decreases
Solution Approach 1:
The patent combines multiple independent position measurement systems (acoustic PME, GPS, and velocity logs) into a unified estimation system using a Kalman filter. This merging allows the system to leverage the strengths of each sensor while compensating for their individual weaknesses, particularly using velocity logs to reduce acoustic measurement noise in deep water conditions.
2Reliability
If GPS is used for position measurement, then cost and convenience are improved, but the system becomes vulnerable to ionospheric perturbations causing complete loss of measurements
Solution Approach 1:
The patent integrates GPS with independent position measurement systems (acoustic PME and velocity logs) in a unified Kalman filter framework. This combination ensures that when GPS measurements are lost due to ionospheric perturbations, the system can maintain position estimation using the other independent sensors, thereby improving overall reliability and availability.
3Reliability
If multiple redundant measurement systems are deployed, then system reliability is improved, but device complexity and cost increase
Solution Approach 1:
The patent combines multiple measurement systems (PME, GPS, velocity logs) into a single integrated estimation framework using a Kalman filter. This approach achieves redundancy and reliability through software-based fusion rather than requiring multiple complete independent systems, thereby reducing overall device complexity while maintaining measurement availability.
4Measurement precision
If riser information is used for position measurement, then additional position data is available, but the measurements become unreliable due to unknown riser shapes and current variations
Solution Approach 1:
The patent integrates riser bottom angle measurements with other position measurement systems (PME, GPS, velocity logs) in a unified Kalman filter framework. This combination allows the system to use riser information as one data source among others, where the filter can weigh and combine measurements according to their reliability, thereby improving position estimation without being solely dependent on unreliable riser data.
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 provides a stable and accurate vessel position estimation, enabling effective dynamic positioning by integrating riser bottom angle and velocity measurements, thus maintaining vessel stability within required limits without the need for complex modeling or redundant systems.
Implementation Method 1
They operate by measuring the Doppler shift of high-frequency acoustic signals reflected either from the sea-bed (known as 'bottom lock') to derive the vessel's speed relative to the sea bed; or from particles in the water below the keel (known as 'water lock') to derive the vessel's speed relative to the surrounding water.
Data Source
AI summary
Dynamic positioning of a vessel 10 connected to the seafloor 14 by a riser 12 utilizes a measurement of riser 12 bottom angle combined with a measurement of vessel 10 velocity, optionally obtained from a Doppler log 16. These two signals are combined to produce a single position estimate using an algorithm such as a Kalman filter. Using riser bottom angle only would result in an unstable control system, since the bottom angle lags the vessel motion by a considerable amount and the relationship is non-linear. Using the velocity measurement alone would result in a slow drift of position. The combination of the two eliminates the disadvantages of the individual measurements.