Dynamic Positioning for Dummies - Overview (1)

Summary

This video introduces the dynamic positioning (DP) system used to control a vessel’s position in the face of environmental forces such as wind, waves, and currents. It explains the process of using the Kalman filter and vessel model to estimate the vessel’s position and correct deviations using thrusters. The system factors in forces like wind, external environment forces, drag, and speed to maintain the vessel’s set position. Additionally, it covers the importance of accurate position reference systems and the role of manual controls in certain conditions.

Takeaways

• 😀 The Dynamic Positioning (DP) system controls a vessel's position using inputs like wind force, thruster commands, and Kalman filters.
• 😀 The Kalman filter combines measurements and estimations to provide a more accurate position estimate for the vessel.
• 😀 Environmental forces, including wind and current, are constantly measured to adjust the vessel's position accordingly.
• 😀 Trust allocation converts calculated forces into thruster commands, ensuring the vessel counteracts external forces.
• 😀 The system uses feedback from thrusters, like RPM and pitch, to update the vessel’s position estimation.
• 😀 The vessel’s position can be affected by unknown forces, which the DP system detects and compensates for through force calculations.
• 😀 The system automatically adjusts to return the vessel to its set position by applying force proportional to the deviation.
• 😀 Drag force, a resistance force from water, is also considered in the system’s calculations for accurate speed control.
• 😀 Manual control of the DP system can be done via a joystick when automatic control is not applied in certain axes.
• 😀 The DP system uses pre-processed data from position reference systems to ensure accurate vessel positioning by adjusting weights based on variance.
• 😀 The system is designed for various operational modes, including specific scenarios like heavy lifts and other specialized vessel operations.

Q & A

What is the main purpose of a Dynamic Positioning (DP) system as described in the script?

The DP system controls the vessel's position by counteracting external forces such as wind, waves, and currents. It uses a variety of sensors and models to estimate the position and apply corrective actions via thrusters to maintain the required position.

How does the Kalman filter function in the DP system?

The Kalman filter combines measurements from position reference systems with the vessel's model to estimate the true position. It adjusts the weight given to the measurement and the model based on their reliability, providing a more accurate position estimate.

What is the role of the trust allocation in the DP system?

The trust allocation takes the calculated external forces (like wind) and converts them into thruster commands (RPM, load, pitch) to counteract those forces, ensuring the vessel stays in the required position.

What external forces are considered by the DP system?

The DP system primarily considers environmental forces like wind, waves, and currents, along with forces generated by the vessel’s propulsion system. However, wind is the only external force that is directly measured and used for calculation.

What happens if the DP system detects an error in the vessel's position?

When the DP system detects an error, it calculates the required corrective force (known as the air force or error force) to bring the vessel back to the desired position. This corrective action is then sent to the thrusters.

How does the system prevent a blackout during operation?

The power overload control checks whether there is enough power to perform the necessary thrust before sending the commands to the thrusters. If there is enough power, the set point is forwarded to the thrusters; otherwise, it prevents overloads or blackouts.

What role does the vessel’s model play in position estimation?

The vessel’s model acts as an estimator to predict the position of the vessel based on known forces like wind and thruster-generated forces. The model helps provide an accurate estimate of the position, which is then adjusted based on measurements from position reference systems.

What is the purpose of damping control in the DP system?

Damping control is used to calculate the force demand based on the deviation between the desired speed and the actual speed of the vessel. It helps in correcting and minimizing speed fluctuations to keep the vessel stationary.

What is drag force and how is it involved in the DP system?

Drag force is the resistance the vessel experiences when moving through water. It acts in the opposite direction of the vessel’s motion and is an important factor in calculating the vessel's speed and the required thrust to maintain position.

How does the DP system validate the accuracy of the position reference systems?

The DP system performs tests on each position reference system to ensure their measurements are accurate. It then assigns a weight to each system based on its reliability, with higher variance systems receiving less weight, ensuring the best possible position estimation.