Dynamic Positioning for Dummies - Controller & Estimator (5)

Summary

This video provides an in-depth explanation of dynamic positioning (DP) systems, focusing on how vessel controllers, such as gain damping tracks and joysticks, work to maintain vessel stability. It discusses the role of Kalman filters in estimating position and heading, the impact of force calculations (wind, drag, and external forces), and different control models (linear, relaxed, and green control). The video also covers joystick control options, the role of draft input for accurate mass calculation, and how the DP system adjusts for environmental factors to maintain station-keeping under various conditions.

Takeaways

• 😀 The DP system uses a simplified dynamic positioning block diagram, with an emphasis on the controller and its components like gain damping, joystick, and tracking.
• 😀 A Kalman filter helps compare estimated data with actual measurements, adjusting the trust between them based on the residuals from forces like wind, current, and drag.
• 😀 The vessel's estimated position is compared with the setpoint to calculate the gain factor, which can be adjusted to optimize station-keeping capabilities.
• 😀 High gain settings lead to faster response, more precise maneuvering, and smaller position windows, but at the cost of higher power consumption and wear on equipment.
• 😀 The non-linear models like relaxed control and green control provide smoother station-keeping at the expense of precision, with green control optimized for precision in all weather conditions.
• 😀 The system calculates instantaneous setpoints when the DPO changes the setpoint, which helps the vessel approach the desired position in a controlled manner.
• 😀 Drag force, which results from the vessel's motion through water, plays a significant role in position estimation, but it's not fed forward into the DP system due to complexities in modeling.
• 😀 Joystick controls allow for manual adjustments of thrust in different axes, with scaling options for high-speed or low-speed maneuvers, affecting how much force is applied.
• 😀 Environmental compensation can be used with joystick controls to account for external forces like wind, current, and wave forces acting on the vessel.
• 😀 The Kalman filter continually updates estimates of the vessel's position and heading, using new measurements and forces, ensuring the DP system's accuracy and minimizing errors in real-time.

Q & A

What is the role of the gyrocompass and position reference system in Dynamic Positioning (DP) systems?

The gyrocompass and position reference system are used to measure the vessel's heading and position. These measurements are compared to the estimated position and heading, with the difference being processed through a Kalman filter to determine the trustworthiness of the data and adjust the control system accordingly.

How does the Kalman filter function in the DP system?

The Kalman filter combines both measured data (such as from a gyrocompass and position reference system) and estimated data to create a more accurate position estimate. It continuously adjusts the trust level between measured and estimated data by considering unmeasured forces and compensating for errors.

What is the significance of the gain factor in the DP system?

The gain factor in the DP system determines how much force is applied to correct any deviation from the setpoint position. A higher gain provides faster response and greater accuracy but at the cost of power consumption and wear on machinery, while a lower gain offers slower response with less power use and less wear.

What are the differences between linear and non-linear gain models in DP systems?

The linear gain model is used in high precision control, providing a quick response to changes in the vessel's position with minimal oscillation. Non-linear models, such as relaxed control and Green control, offer smoother operation but are less precise and slower in response. Green control is optimized for power efficiency and can be used in various weather conditions.

What happens when the DP system is given a new setpoint, such as a 500-meter move?

When a new setpoint is introduced, the DP system calculates two types of setpoints: the co-setpoint (the ultimate goal position) and the instantaneous setpoint (a dynamic target that changes based on the vessel's current position). The system adjusts the vessel's movement gradually towards the co-setpoint while calculating forces needed for each step.

How does the DP system manage external forces like wind and drag?

The DP system uses models to estimate external forces like wind and drag, integrating them into the overall calculation. These forces are used to adjust the thrust needed to maintain the vessel's position. Wind force, drag, and other external forces are considered when calculating the required forces to keep the vessel stationary.

What is the importance of the joystick control in DP systems?

Joystick control allows the operator to manually control the vessel's thrust when automatic control is not active. There are two types of joystick settings: full thrust and reduced thrust. The joystick can also be configured for high or low-speed maneuvers, giving the operator precise control over the vessel's movements.

How does the DP system handle environmental compensation using joystick control?

When using joystick control, the DP system can compensate for environmental forces, such as wind, sea currents, and wave forces. The system adjusts the thrust allocation to counteract these forces and maintain the vessel's position. This helps the vessel respond to changes in environmental conditions without requiring manual adjustments from the operator.

Why is the draft input crucial for the DP system's calculations?

The draft input is vital for accurately calculating the vessel's displacement, which is essential for estimating the mass of the vessel. This mass is used in calculations of acceleration and other forces. Incorrect draft readings can significantly affect the accuracy of the DP system's position estimates and force calculations.

How does the DP system estimate the vessel's motion based on forces like wind or drag?

The DP system estimates the vessel's motion by calculating the residual forces from the previous second and adding them to the current estimate. For example, if wind force increases, the system computes the corresponding change in force and adjusts the vessel's position accordingly. The calculation involves using Isaac Newton's formula, F = m * a, where force equals mass multiplied by acceleration.