Underwater Robotics

🫠Underwater Robotics Unit 4 – Underwater Robot Propulsion Systems

Underwater robot propulsion systems are crucial for navigating aquatic environments. These systems convert energy into thrust, allowing robots to move through water while overcoming drag forces. Efficiency, cavitation prevention, and power management are key considerations in propulsion system design. Various propulsion types exist, including propellers, thrusters, and biomimetic systems. Designers must consider factors like robot size, mission requirements, and power sources when selecting a system. Advanced control and navigation technologies enable precise maneuvering and autonomous operation in diverse underwater applications.

Key Concepts and Terminology

  • Propulsion generates thrust to move an underwater robot through the water
  • Thrust is the force that propels the robot forward and overcomes drag
  • Drag is the resistance force acting on the robot as it moves through the water
  • Efficiency is the ratio of useful work performed to the total energy expended
  • Cavitation occurs when bubbles form and collapse around a propeller, causing damage and reducing efficiency
  • Bollard pull is the maximum static thrust a propulsion system can generate
  • Propulsive power is the power delivered by the propulsion system to the water
    • Calculated as the product of thrust and velocity P=T×vP = T \times v
  • Advance ratio is the ratio of the robot's speed to the propeller's rotational speed
    • Affects propeller efficiency and cavitation

Underwater Propulsion Basics

  • Propulsion systems convert energy into thrust to move the robot through the water
  • Thrust is generated by accelerating a mass of water in the opposite direction of desired motion
  • Conservation of momentum explains how the acceleration of water produces a reaction force (thrust) on the robot
  • Propulsive efficiency depends on factors such as propeller design, motor efficiency, and hydrodynamic losses
  • Drag forces, including skin friction and form drag, oppose the robot's motion and must be overcome by thrust
  • Streamlining the robot's body can reduce form drag and improve overall efficiency
  • Matching the propulsion system to the robot's size, weight, and intended speed is crucial for optimal performance
  • Propeller selection involves considering diameter, pitch, number of blades, and material

Types of Propulsion Systems

  • Propellers are the most common type of propulsion system for underwater robots
    • Consist of rotating blades that push water to generate thrust
    • Can be fixed-pitch or variable-pitch for improved control and efficiency
  • Thrusters are self-contained propulsion units that include a motor, propeller, and nozzle
    • Provide precise control and maneuverability
    • Can be positioned and oriented in various configurations (e.g., vectored thrust)
  • Jet propulsion systems use a pump to expel water through a nozzle, creating thrust
    • Offer high efficiency and low noise compared to propellers
    • Suitable for high-speed applications and environments with debris
  • Biomimetic propulsion systems mimic the swimming mechanisms of aquatic animals
    • Examples include undulating fins, oscillating foils, and jellyfish-inspired pulsed jets
    • Offer high maneuverability and efficiency at low speeds
  • Hybrid propulsion systems combine multiple propulsion technologies for improved performance
    • Example: a combination of propellers and thrusters for hovering and long-range travel

Design Considerations

  • Propulsion system selection depends on the robot's size, weight, speed, and mission requirements
  • Matching the propulsion system to the robot's hydrodynamic characteristics is essential for optimal performance
  • Propeller design factors include diameter, pitch, number of blades, and material
    • Larger diameters and higher pitch generate more thrust but require more power
    • Increasing the number of blades improves efficiency but may increase complexity and cost
  • Thruster placement and orientation affect the robot's maneuverability and stability
    • Vectored thrust configurations allow for precise control in multiple degrees of freedom
  • Streamlining the robot's body reduces form drag and improves overall efficiency
  • Proper sealing and waterproofing of the propulsion system components are critical for reliable operation
  • Vibration and noise reduction techniques, such as using balanced propellers and isolation mounts, improve stealth and minimize interference with sensors
  • Modularity and ease of maintenance should be considered for field operations and repairs

Power Sources and Energy Efficiency

  • Underwater robots typically rely on batteries or tethered power for propulsion
  • Lithium-ion batteries are commonly used for their high energy density and long cycle life
    • Proper battery management systems ensure safe and efficient operation
  • Tethered power systems provide a continuous power supply but limit the robot's range and maneuverability
  • Fuel cells and hybrid power systems are emerging technologies for extended endurance missions
  • Energy efficiency is crucial for maximizing mission duration and range
  • Propulsive efficiency can be improved through optimized propeller design, motor selection, and hydrodynamic streamlining
  • Power management techniques, such as duty cycling and sleep modes, conserve energy during periods of low activity
  • Regenerative power systems, such as solar panels or turbines, can harvest energy from the environment to extend mission duration
  • Minimizing the robot's weight and drag reduces the power required for propulsion

Control and Navigation

  • Propulsion control systems regulate the speed, direction, and thrust of the robot
  • Motor controllers, such as electronic speed controllers (ESCs), provide precise control of propeller or thruster motors
  • Feedback systems, including tachometers and current sensors, monitor the propulsion system's performance and enable closed-loop control
  • Navigation systems, such as inertial measurement units (IMUs) and Doppler velocity logs (DVLs), provide position and velocity information for autonomous operation
  • Acoustic positioning systems, like ultra-short baseline (USBL) or long baseline (LBL), enable precise underwater localization
  • Sensor fusion techniques combine data from multiple sensors to improve navigation accuracy and robustness
  • Autonomous control algorithms, such as proportional-integral-derivative (PID) controllers or model predictive control (MPC), enable the robot to maintain desired trajectories and adapt to environmental disturbances
  • Remote control interfaces allow operators to manually control the robot's propulsion and navigation during tethered operations

Real-World Applications

  • Underwater robots with advanced propulsion systems are used in a variety of industries and research fields
  • Offshore oil and gas exploration and maintenance
    • Inspection, repair, and maintenance of subsea infrastructure
    • Surveys and mapping of seafloor for pipeline routing and site selection
  • Marine research and conservation
    • Monitoring and sampling of marine ecosystems and habitats
    • Tracking and studying marine life behavior and migration patterns
  • Underwater archaeology and cultural heritage preservation
    • Documenting and exploring submerged historical sites and shipwrecks
    • Non-invasive imaging and mapping of delicate artifacts
  • Military and defense applications
    • Mine countermeasures and explosive ordnance disposal
    • Surveillance and reconnaissance missions in contested waters
  • Aquaculture and fisheries management
    • Inspection and maintenance of fish farms and aquaculture facilities
    • Stock assessment and habitat mapping for sustainable fisheries
  • Environmental monitoring and disaster response
    • Monitoring of water quality, pollution, and climate change impacts
    • Rapid deployment for search and recovery operations in underwater environments
  • Advances in materials science and manufacturing techniques enable lighter, stronger, and more efficient propulsion components
  • Biomimetic propulsion systems inspired by aquatic animals offer new possibilities for efficient and maneuverable underwater locomotion
  • Swarm robotics and cooperative control algorithms enable coordinated operation of multiple robots for large-scale surveys and monitoring
  • Integration of artificial intelligence and machine learning techniques for adaptive and autonomous propulsion control
  • Development of hybrid propulsion systems that combine the advantages of different technologies for improved performance and versatility
  • Wireless underwater power transfer and charging technologies extend the operational range and endurance of untethered robots
  • Advancements in energy storage and harvesting technologies, such as high-capacity batteries and fuel cells, enable longer mission durations
  • Miniaturization of propulsion components allows for the development of smaller, more agile, and cost-effective underwater robots for a wider range of applications


© 2024 Fiveable Inc. All rights reserved.
AP® and SAT® are trademarks registered by the College Board, which is not affiliated with, and does not endorse this website.

© 2024 Fiveable Inc. All rights reserved.
AP® and SAT® are trademarks registered by the College Board, which is not affiliated with, and does not endorse this website.