Dynamics of Dynamic Positioning Systems
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Questions and Answers

What are the three horizontal degrees of freedom that a DP system typically controls?

  • Surge, sway, and yaw (correct)
  • Surge, heave, and yaw
  • Pitch, roll, and yaw
  • Roll, sway, and yaw

What is the primary function of the mathematical model in a DP system?

  • To directly control the movement of the vessel's thrusters
  • To predict the vessel's heading, position, and speed based on forces acting on it (correct)
  • To generate the exact thrust required for each thruster
  • To track the vessel's position and movement in real-time

What factors are used as input to the mathematical model?

  • Wind speed and direction, thruster/propeller pitch/rpm and direction
  • Vessel's heading, position, and speed
  • Sea current and wave forces
  • All of the above (correct)

What is the purpose of the Kalman filtering technique in a DP system?

<p>To continuously correct and improve the accuracy of the mathematical model (A)</p> Signup and view all the answers

How are wind forces calculated in a DP system?

<p>As a function of measured wind speed and direction (A)</p> Signup and view all the answers

How does a DP system determine the forces the thrusters should produce?

<p>By calculating the forces needed to minimize the deviation between the vessel's actual position and its required position (A)</p> Signup and view all the answers

What is the primary limitation of the mathematical model in a DP system?

<p>It is not able to account for all the forces acting on the vessel (A)</p> Signup and view all the answers

How does the DP system use the data from gyrocompasses and position-reference systems?

<p>To update the mathematical model with real-time information about the vessel's position and heading (B)</p> Signup and view all the answers

What are the main components of the DP system?

<p>Power supply system, Thruster system, Reference systems, Sensor, Control system, Steering console and System operator (B)</p> Signup and view all the answers

What are some of the key characteristics of the power supply system?

<p>High flexibility, high reliability, continuity of work, high accuracy (D)</p> Signup and view all the answers

What type of propeller is most commonly used in DP systems?

<p>Controllable Pitch Propeller (C)</p> Signup and view all the answers

What is a Becker rudder?

<p>A type of steering gear used in DP systems (D)</p> Signup and view all the answers

What is the purpose of manoeuvring thrusters?

<p>To provide propulsion in lateral directions (B)</p> Signup and view all the answers

What are Azipod thrusters?

<p>A type of thruster used in DP systems (A)</p> Signup and view all the answers

What are the main characteristics of reference systems used in DP systems?

<p>High accuracy, high reliability, continuity of work (A)</p> Signup and view all the answers

What is the minimum time that the control system, control console, displays and alarm systems, and reference systems of the DP system must be able to operate for in the event of a failure of the main power system?

<p>30 minutes (C)</p> Signup and view all the answers

What significant development occurred in the United Kingdom in 1977 regarding drilling technology?

<p>First semi-submersible drilling rig launched (C)</p> Signup and view all the answers

Which company was responsible for the first research on DP systems in Norway?

<p>Kongsberg Vapenfabrikk (D)</p> Signup and view all the answers

What percentage of the world market for DP systems did Kongsberg capture by 2012?

<p>75% (B)</p> Signup and view all the answers

Which of the following is NOT an application of DP systems?

<p>Emergency Response Vessels (A)</p> Signup and view all the answers

What is a primary factor in determining the required equipment class for a DP system?

<p>Risk analysis of position loss (D)</p> Signup and view all the answers

What does FPSO stand for in the context of DP applications?

<p>Floating Production Storage and Offloading (C)</p> Signup and view all the answers

Which type of vessel is primarily associated with underwater cable laying and repair using DP technology?

<p>Cable Lay/Repair Vessels (D)</p> Signup and view all the answers

What is the main purpose of developing redundancy in DP systems?

<p>To ensure position keeping capability (B)</p> Signup and view all the answers

What occurs in equipment class 1 in the event of a single fault?

<p>A loss of position and/or heading may occur. (A)</p> Signup and view all the answers

Which class does not allow a loss of position and/or heading in the event of a single fault?

<p>Equipment class 3 (A)</p> Signup and view all the answers

What type of components may be accepted in systems of equipment class 2?

<p>Common static components without immediate positioning effects (D)</p> Signup and view all the answers

Which of the following describes 'rolling' movement of a ship?

<p>Tilting side to side on the X-axis. (B)</p> Signup and view all the answers

What is measured by the position-reference systems on a seagoing vessel?

<p>Changes in position, heading, and speed (C)</p> Signup and view all the answers

In the context of equipment classes, what is meant by 'single failure criteria'?

<p>Any active or static component that may cause immediate impact on position keeping. (D)</p> Signup and view all the answers

Which of the following components would classify as normally static and potentially affect position keeping?

<p>Cables and pipes (D)</p> Signup and view all the answers

What does the phrase 'six degrees of freedom' refer to in maritime movement?

<p>The range of motion involving translations and rotations. (B)</p> Signup and view all the answers

What factors influence the choice of reference systems in a dynamic positioning system?

<p>The level of risk associated with the operation (B)</p> Signup and view all the answers

Which of the following is NOT a commonly used reference system in dynamic positioning?

<p>GPS (A)</p> Signup and view all the answers

What is the primary function of heading sensors in dynamic positioning systems?

<p>To determine the ship's motion parameters and course (C)</p> Signup and view all the answers

Which type of sensor measures movements in the vertical plane for stabilization purposes?

<p>Attitude sensor (B)</p> Signup and view all the answers

What is an advantage of pendulum devices when used in dynamic positioning systems?

<p>Low cost (A)</p> Signup and view all the answers

Which disadvantage is associated with pendulum devices in dynamic positioning systems?

<p>Poor performance under marine dynamics (A)</p> Signup and view all the answers

What improves the performance of pendulum devices in dynamic positioning systems?

<p>Implementing them in a dampened environment (D)</p> Signup and view all the answers

Which of the following sensors can provide additional heading data in DP systems?

<p>Satellite compasses (D)</p> Signup and view all the answers

What are the disadvantages of using a pick up coil in a VRU?

<p>Size and handling restrictions, life cycle costs, installation difficulties, latency (C)</p> Signup and view all the answers

Which of these is NOT a disadvantage of using VRU with solid state inertial sensors?

<p>Good accuracy for GPS and Acoustic Stabilization, range of performance / price sensors available, relatively low cost (A)</p> Signup and view all the answers

What is an advantage of using a VRU with GPS?

<p>Heading and Position Information, Good Accuracy (D)</p> Signup and view all the answers

Which of these is a disadvantage of using a VRU with GPS?

<p>Heading is GPS dependent, relatively high cost (C)</p> Signup and view all the answers

What are the two main types of anemometers mentioned?

<p>Mechanical and ultrasonic (B)</p> Signup and view all the answers

What are the possible wind speeds and direction errors in an anemometer?

<p>The anemometer could be affected by the wind direction and speed, as well as the location and the direction of the ship. (D)</p> Signup and view all the answers

Which of the following is NOT a factor that can potentially distort wind measurements from an anemometer?

<p>The color of the anemometer (C)</p> Signup and view all the answers

What are the two main types of waves sensors mentioned?

<p>Hydrometeorological buoys and logs (D)</p> Signup and view all the answers

What are the two types of current sensors mentioned?

<p>Hydrometeorological buoys and logs (B)</p> Signup and view all the answers

Which of the following are not the main source used for ships’ speed, according to the text?

<p>Depth sensors (C)</p> Signup and view all the answers

When were microprocessors first used in DP systems?

<p>Since 1980 (D)</p> Signup and view all the answers

What type of technology was used in the first DP systems?

<p>Analogue techniques (B)</p> Signup and view all the answers

Which of these is NOT mentioned as a factor influencing the accuracy of wind measurements from an anemometer?

<p>The color of the anemometer (E)</p> Signup and view all the answers

What is the primary benefit of using digital techniques over analogue techniques in DP systems?

<p>Digital techniques are more reliable than analogue techniques (B), Digital techniques are more easily adaptable to new technology (C), Digital techniques are more accurate than analogue techniques (F)</p> Signup and view all the answers

Which of these is a possible benefit of using a VRU with solid state inertial sensors over a pick-up coil VRU (select all that apply)?

<p>Lower cost (A), Smaller size and handling restrictions (B), Higher accuracy (C)</p> Signup and view all the answers

Flashcards

Equipment Class 2

Equipment class where a single fault in any active component or system will not cause loss of position or heading.

Equipment Class 3

Equipment class where a single fault, including failures in certain static components, will not cause loss of position or heading.

Equipment Class 1

Equipment class where a single fault in an active component or system might result in loss of position or heading.

Heaving

Movement of a ship along the vertical axis.

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Swaying

Movement of a ship along the horizontal axis, from left to right.

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Yawing

Turning of a ship around its vertical axis.

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Surging

Movement of a ship along the horizontal axis, forward and backward.

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Pitching

Tilting of a ship forward and backward around its horizontal axis.

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First DP Systems

The first dynamic positioning (DP) systems were developed and deployed in 1971 by British GEC Electrical Projects Ltd. in the United Kingdom. These early systems marked the beginning of a revolution in offshore operations, enabling vessels to maintain a precise position even in challenging sea conditions.

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First DP Vessel

The first vessel equipped with a Norwegian-designed DP system, the Seaway Eagle, launched in 1977. The Kongsberg DP system, lauded for its reliability and performance, quickly gained popularity, making Kongsberg a leading manufacturer in the DP systems market.

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Diving Support Vessels Use DP

DP systems are widely used to support specialized diving operations, ensuring the diving platform remains stable even with ocean currents or waves.

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Pipelay Vessels Use DP

Pipelay vessels rely on DP to maintain accuracy in laying pipelines, ensuring the pipeline is positioned correctly on the seabed. This prevents damage to the pipeline and helps ensure its long-term integrity.

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ROV Support Vessels Use DP

ROV Support Vessels utilize DP so that the ROV can conduct operations, such as inspecting or repairing subsea infrastructure, in a stable and precise manner.

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Crane Vessels Use DP

Crane Vessels equipped with DP offer a stable platform for heavy lifting and installation operations, ensuring the crane can operate with precision even in harsh conditions.

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Float-over Vessels Use DP

Float-over Vessels employ DP for the safe and precise installation of large structures. The DP system allows the vessel to carefully position the structure over its foundation without risk of damage or misalignment.

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Accommodation Vessels Use DP

DP systems in Accommodation Vessels are crucial for providing comfortable and safe living quarters for offshore personnel. These vessels are often located in remote areas and require a stable platform for the crew to live and work comfortably.

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Deviation in DP

The system calculates the difference between the vessel's actual position and its desired position.

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Thrust Force Calculation

The system calculates the forces required by the thrusters to minimize deviation and maintain position.

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External Forces

The system accounts for the forces of wind, waves, and currents acting on the vessel.

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Degrees of Freedom in DP

The system controls the vessel's movement in three dimensions: forward/backward (surge), sideways (sway), and rotation (yaw).

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Mathematical Model in DP

DP systems use a mathematical model to simulate the vessel's behavior under different forces.

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Inputs to the Model

The model uses variables like wind speed, thruster details, and ocean conditions to predict vessel movement.

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Outputs from the Model

The model provides estimates of the vessel's heading, position, and speed in each degree of freedom.

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Model Correction

By comparing actual measurements to model predictions, the system continuously corrects the model for accuracy.

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Dynamic Positioning (DP)

The ability of a DP system to maintain a ship's position and heading despite external forces like wind, waves, and currents.

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Position and Heading Measurement

The process of measuring a ship's actual position and heading using reference systems like GPS and compasses.

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Position Error

The difference between the predicted position of a ship and its actual measured position.

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DP Control System

Systems that use the ship's position and heading data to calculate the thrust required from the propellers to maintain position.

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Reference Systems

The systems that provide information about the ship's position, heading, and other relevant parameters.

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Azimuth Thrusters

Propellers that allow the ship to move in any direction, even sideways.

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Dynamic Positioning System (DPS)

A system of thrusters, propellers, and control systems that allows a ship to maintain its position and heading without anchors.

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Station Keeping

The ability of a ship to hold its desired position and heading despite external forces.

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Factors Affecting Reference System Choice

Reference systems used in DP systems are chosen based on the level of risk associated with the operation, required redundancy, system availability, and the potential consequences of losing a reference system.

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Traditional Navigation Systems for DP?

Traditional navigation systems like GPS and Glonass are inadequate for DP operations.

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Common DP Reference Systems

Devices like taut wires, Artemis, RADius, RadaScan, Miniranger, Trispondeur, Fanbeam, CyScan, differential satellite systems, and hydroacoustic systems are commonly used reference systems in DP.

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DP Sensor System

Sensors gather data on ship motion, heading, external disturbances, and other parameters vital to dynamic positioning.

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Primary Heading Sensors

Gyrocompasses, often used in pairs or triples, provide the primary source of heading information for DP.

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Satellite Compass Role

Satellite compasses can supplement gyrocompasses providing an additional source of heading information.

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DP Attitude Sensors

Attitude sensors measure the ship's roll, pitch, and heave, providing essential data for stability and dynamic positioning control.

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Pendulum Sensors

Pendulum devices (inclinometers) are a simple and cost-effective method for measuring roll and pitch, but have limitations in dynamic conditions.

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Oil-bath attitude sensor

A type of attitude sensor that uses a pick-up coil floating in an oil bath to detect rotation around fixed coils.

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Size and handling restrictions

A disadvantage of oil-bath attitude sensors due to their physical size and the difficulty of handling them.

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Life cycle costs

A disadvantage of oil-bath attitude sensors due to the costs associated with maintaining the sensor and its components.

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Strapdown attitude sensor

A type of attitude sensor that uses an orthogonal array of accelerometers and gyroscopes to compute roll and pitch, deploying a vertical reference algorithm.

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Accuracy for GPS and Acoustic Stabilization

A significant advantage of strapdown attitude sensors, offering high accuracy for GPS and acoustic stabilization.

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VRU/GPS attitude sensor

A type of attitude sensor that combines information from a Vertical Reference Unit (VRU) and GPS.

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Heading and Position Information

A key advantage of the VRU/GPS attitude sensor, providing both heading and position information.

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Heading and Position GPS-dependent

A disadvantage of the VRU/GPS attitude sensor, relying entirely on GPS for heading and position.

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Anemometer

An instrument that measures wind speed and direction.

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Mechanical anemometer

A type of anemometer that uses mechanical cups or vanes to measure wind speed.

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Ultrasonic anemometer

A type of anemometer that uses sound waves to measure wind speed.

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Wave sensor

A device that measures the height and motion of waves.

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Current sensor

A device that measures the speed and direction of ocean currents.

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Draft sensor

A sensor that measures the depth of a vessel in the water.

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Ship's speed sensor

A sensor that measures the speed of a vessel through the water.

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Study Notes

Dynamic Positioning (DP) Systems

  • DP is a vessel capability to maintain its position automatically using its propulsion system
  • A DP system is a hydrodynamic system that controls or maintains the vessel's position and heading
  • Dynamically positioned vessel (DP vessel) means a vessel that automatically maintains its position and/or heading (fixed location, relative location or predetermined track) using thruster force
  • DP systems are strongly linked to the development of the oil industry in sea areas

History of DP Systems

  • 19th century: First oil well in the Caspian Sea, 30m from shore, using wooden pier
  • 1925 Caspian Sea: First self-elevating drilling and production platforms ("Jack-up" type), operating in waters up to 60m deep
  • Vessels stabilized position using anchor ropes, enabling drilling and exploitation of wells up to 600m deep
  • 1960 California: CUSS (Continental, Union, Shell & Superior oil consortium) attempted core drilling at 180m water depth and up to 3500m
  • Equipment included four azimuth thrusters, manual control, visual observations, and sonar tracking
  • 1961 USA: Launching of the first drilling vessel with fully functional automatic DP system (Eureka) for Shell, drilling at depths up to 1300 meters. Wave up to 6 meters, wind up to 21 m/s.
  • 1963 France: Launching of two DP ships (Salvor and Terebel) intended for laying pipelines on the seabed and securing underwater works
  • 1964 USA: Launching of DP vessel Caldrill (Caldrill Offshore Company), drilling up to 2000 meters
  • 1971 UK: British GEC Electrical Projects Ltd. constructed first DP systems
  • 1974 UK: Conversion of commercial ship Wimpey Sealab into a drilling vessel for hard coal deposits
  • 1977 UK: Launching of the first semi-submersible drilling rig (Uncle John)
  • 1975 Norway: First research on DP systems at the request of Stolt Nielsen by Kongsberg Vapenfabrikk (KV)
  • 1977 Norway: Launching of Seaway Eagle, the first vessel with the Norwegian DP system

DP Vessel Applications

  • Diving Support Vessels
  • Pipelay Vessels
  • ROV Support Vessels
  • Crane Vessels
  • Float-over Vessels
  • Accommodation Vessels
  • Drilling Vessels
  • FPSO Vessels
  • Shuttle Tankers
  • Trenching Vessels
  • Cable Lay/Repair Vessels
  • Jack-up Vessels
  • Offshore Supply Vessels
  • Anchor Handling Vessels/Tug
  • Well Stimulation Vessels
  • Rock Placement Vessels
  • Dredging Vessels

DP System Classes

  • DP equipment class 1: A single fault may lead to a loss of position and/or heading
  • DP equipment class 2: A single fault within any active component or system does not lead to a loss of position/heading. Common static components are accepted, as long as there's adequate protection for failure and is documented
  • DP equipment class 3: A single fault or failure does not lead to a loss of position/heading. This includes components listed in class 2 and components and systems in a single compartment or fire sub-division. All components/systems potentially affected by fire or flooding need to meet the requirements of class 2.

Degrees of Freedom

  • A ship's motion at sea, described as six degrees of freedom:
    • Translations: Surge (forward/backward), Sway (left/right), Heave (up/down)
    • Rotations: Roll (side-to-side), Pitch (forward/backward), Yaw (left/right turn)

Main Principles of Operation

  • Forces affecting seagoing vessels: wind, waves, currents, and propulsion
  • DP systems measure deviations between desired and actual positions
  • Forces are calculated to counteract deviations, to maintain stability
  • Mathematical models describe how vessels react to external forces (wind, waves, currents) such as mass and drag
  • Kalman filtering technique helps continuously correct models, improving accuracy
  • Input data compares predicted position/heading to actual values, adjusting the model.
  • DP system components: power supply, thrusters, reference systems, sensors, control systems, steering console, and operator

DP Construction Components

  • Power supply system (high flexibility due to potential sudden changes in demand)
  • Thruster system:
    • Propellers (often Controllable Pitch Propellers - CPP)
    • Rudders (modified steering gear, e.g., Becker, Schilling rudders, Kort nozzles)
    • Manoeuvring thrusters (transverse propulsion units fitted to ship bow or stern)
    • Azimuth thrusters (propellers with rotatable units)
    • Azipod thrusters (thrusters with propeller housed in pod units)
    • Voith-Schneider thrusters (axial thrusters)
  • Reference systems (high accuracy, reliability, and continuity)
    • Mechanical systems
    • Taut wires
    • Microwave systems (e.g., Artemis, RADius, RadaScan, Miniranger, Trispondeur)
    • Laser systems (e.g., Fanbeam, CyScan)
    • Differential satellite
    • Hydroacoustic
  • Sensors: Measuring devices to determine ship motion, course and external factors:
    • Heading sensors (gyrocompasses, satellite compasses)
    • Attitude sensors (pendulum devices, fluid-stabilized devices, VRUs/GPS)
    • Anemometers (Mechanical, ultrasonic)
    • Wave sensors (hydrometeorological buoys)
    • Current sensors (logs)
    • Draft sensors (ships' speed, additional sensors)
  • Control system (analogue or digital techniques)
  • Steering console
  • Operator

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Dynamic Positioning (DP) Systems PDF

Description

Explore the critical components and functionalities of Dynamic Positioning (DP) systems through this quiz. Test your knowledge on how these systems maintain position, utilize mathematical models, and employ various thrusters and filters. Ideal for engineering students and professionals in marine technology.

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