Spread Moored Vessel Thruster Control for Position Maintenance

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Solution Overview

Problem

There is a need for a method to control the position of a spread moored vessel that minimizes unnecessary thrust and energy usage without requiring anchor force measurements or models, while maintaining the vessel within acceptable limits, especially during large environmental forces that move the vessel outside these limits.

Innovation Solution

Implementing an ID control algorithm that applies position correcting thrust when the vessel is outside a target area and reduces or maintains zero thrust when inside, with the integral term calculated towards an aim position on the boundary of the target area when outside and decayed when inside, and optionally applying damping thrust to prevent oscillations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If continuous position correcting thrust is applied to maintain vessel position, then the vessel remains within target area, but energy consumption increases unnecessarily when vessel is already inside target area

Engineering Contradiction:

Improvevessel position maintenanceVSAvoidthrust energy consumption

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The control system applies thrust periodically or intermittently rather than continuously. When the vessel enters the target area, the controller reduces or stops applying position correcting thrust, allowing the vessel to drift naturally within the target area without continuous energy input, while still maintaining position bounds through occasional corrective actions.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The system allows the vessel to use its own momentum and environmental forces to maintain position within the target area. Once the vessel is inside the target area, the controller reduces thrust intervention, letting the vessel's natural dynamics and environmental conditions keep it within acceptable position limits without continuous active control.

Inventive Principle:

Principle #25Self-service

2Stability of the object's composition

If high thrust is applied to counteract environmental forces, then vessel position stability improves, but stress on anchor lines increases excessively

Engineering Contradiction:

Improvevessel position stabilityVSAvoidanchor line stress

Core Design Contradiction:

Stability of the object's compositionVSStress or pressure

Solution Approach 1:

The controller dynamically adjusts the thrust parameter based on the vessel's position relative to the target area and the magnitude of environmental forces. When the vessel is near the center of the target area, the controller reduces thrust magnitude to minimize anchor line stress. The control parameter (thrust force) is changed according to position feedback, applying higher thrust only when necessary to bring the vessel back toward the target area.

Inventive Principle:

Principle #35Parameter changes

3Manufacturing precision

If thruster assisted mooring is used to hold vessel position, then position control accuracy improves, but system complexity increases due to additional control mechanisms

Engineering Contradiction:

Improveposition control accuracyVSAvoidcontrol system complexity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The patent extracts and removes unnecessary control components from the system. By implementing a simplified control logic that only applies thrust when the vessel is outside the target area, the system eliminates the need for complex continuous control mechanisms, advanced algorithms, or additional sensors, achieving effective position control with minimal system complexity.

Inventive Principle:

Principle #2Taking out (Extraction)

4Manufacturing precision

If position correcting thrust is continuously applied, then vessel remains precisely at target position, but unnecessary thrust causes increased energy usage

Engineering Contradiction:

Improveposition precisionVSAvoidthrust energy loss

Core Design Contradiction:

Manufacturing precisionVSLoss of energy

Solution Approach 1:

The control system applies partial action rather than full continuous correction. When the vessel is within the target area, the controller applies reduced or zero thrust, accepting some position variation within the target area bounds. This partial action approach maintains adequate position control while avoiding the excessive energy consumption that would result from continuous full-strength position correction.

Inventive Principle:

Principle #16Partial or excessive action

Data Source

PatentUS8857357B2Method of controlling the position of moored marine vessels

Publication Date: 2014.10.14 GE ENERGY POWER CONVERSION TECHNOLOGY LTD(GB)

AI summary

The present invention provides a method of controlling the position of a spread moored marine vessel (1). In particular, the method of the present invention substantially maintains the position of a spread moored vessel (1) in, or on the boundary of a target area (2) using thruster assistance. This is done by monitoring the position of the vessel and when the vessel (1) is positioned outside of the target area (2) applying a position correcting thrust (7) to the vessel (1) in the direction of an aim position located on the boundary of the target area (2) and when the vessel (1) is positioned within the target area (2) reducing the position correcting thrust (7) applied to the vessel (1) or maintaining the position correcting thrust (7) applied to the vessel (1) at zero. The present invention may also apply a damping thrust (7) to the vessel (1) in order to damp the positional variation of the vessel (1). The present invention also provides a thruster assisted mooring system for a spread moored vessel (1) operating according to the method of the present invention.