Dynamic Positioning for Dummies - Wind (2)

Summary

In this video, Eva Paganini discusses the role of wind in dynamic positioning (DP) systems, explaining how wind sensors measure wind speed and direction. The video highlights the scaling of wind speed measurements, the use of filters to smooth data, and the wind model's impact on the vessel's position. It also covers how to handle errors from inaccurate wind sensors and explains critical modes for safe DP operations. The video emphasizes the importance of adjusting the system based on environmental factors, offering examples of scenarios where manual wind input might be necessary.

Takeaways

• 😀 Wind is the only environmental force measured by dynamic positioning (DP) systems using sensors for speed and direction.
• 😀 There are two types of wind sensors: static ultrasonic and mechanical vane type, designed for harsh environments.
• 😀 Wind speed needs to be scaled to a common level, usually 10 meters above sea level, due to factors like pressure gradient and surface friction.
• 😀 A formula or a scaling table is used to adjust wind measurements based on height coefficients, ensuring accuracy at different heights.
• 😀 Dynamic positioning systems require filtered wind data to avoid inaccurate readings, often using low-pass filters to smooth out noise.
• 😀 Low-pass filters smooth data by removing high-frequency noise and allowing low-frequency, relevant signals to pass through.
• 😀 Filter timing is crucial: too short of a filter time can lead to imprecise data, while a longer time provides more accuracy but causes delay.
• 😀 Wind force is calculated using wind speed and direction, and applied to the vessel's dynamic positioning system for accurate position control.
• 😀 Wind models use sets of coefficients for different directions, taking into account factors like vessel orientation and draft changes.
• 😀 In certain conditions, such as gusty winds or obstructions, operators may switch off the wind sensor and input wind data manually to avoid overcompensation.
• 😀 Critical activity mode (CAMO) and task-appropriate mode (TAM) help configure the DP system depending on the operational environment and risk factors.

Q & A

What are the two types of wind sensors used in dynamic positioning systems?

The two types of wind sensors are the ultrasonic-based static sensor and the mechanical cup and vane type sensor. Both are designed to function in harsh environmental conditions.

Why is the wind speed measured at 10 meters above sea level?

Wind speed increases with height from the surface due to factors such as the pressure gradient, surface friction, and air density. Measuring at 10 meters above sea level provides a standardized reference for comparison.

How does air density affect wind speed measurements?

Air density decreases with height, and less dense air requires less force to move at the same speed as denser air. This results in higher wind speeds at higher altitudes.

What method is used to scale wind speeds to a common reference height?

Wind speeds are scaled using a formula or a table with height coefficients, adjusting the measured wind speeds to a common reference height, usually 10 meters above sea level.

How is noisy wind measurement data typically filtered in a dynamic positioning system?

Noisy wind measurement data is filtered using a low-pass filter, which smooths the data by removing high-frequency noise. This process helps provide more accurate wind speed and direction data for the system.

What is the purpose of a low-pass filter in dynamic positioning systems?

A low-pass filter removes high-frequency noise from the raw measurement data, allowing only low-frequency components to pass through, which results in smoother and more accurate data used by the dynamic positioning system.

Why might the operator choose to manually input wind data instead of relying on the wind sensor?

An operator may choose to manually input wind data if the wind sensor is malfunctioning or if environmental factors, such as wind gusts or obstructions, cause inaccurate readings that interfere with dynamic positioning.

What is the role of the wind model in the dynamic positioning system?

The wind model calculates the wind force based on wind speed and direction, using coefficients for various angles of attack. This information is essential for the dynamic positioning system to adjust the vessel's position accordingly.

What factors can cause errors in the wind model?

Errors in the wind model can arise from inaccurate wind sensors, changes in the environmental profile, such as vessel draft or the shape of the platform, and incorrect wind area settings.

How is the wind force calculated in dynamic positioning systems?

The wind force is calculated by using a coefficient from the wind model for a specific angle of attack, multiplying it by the square of the wind speed, and dividing by 9.81 to account for the wind's force in kilonewtons.