What Are the Core Technologies Used in Underwater Robotics?

Fremont, CA: Underwater robotics represents a multidisciplinary domain that combines mechanical engineering, computer science, electronics, and oceanography. These robots are designed to perform in challenging underwater conditions, utilizing various essential technical components and systems to operate efficiently.

Hull Design and Materials

The structure of an underwater robot must be engineered to endure the significant pressures found in deep-sea settings, where pressures can surpass 100 MPa (megapascals). Typically, underwater robots are constructed using titanium or aluminum alloys for their primary framework, as these materials provide an excellent balance of strength and weight while also being resistant to corrosion in saline conditions.

Effective buoyancy control is also of paramount importance. Syntactic foam, which consists of hollow glass microspheres embedded within an epoxy resin matrix, is frequently utilized to achieve neutral buoyancy, thereby reducing energy consumption during operation. Additionally, the hydrodynamic shape of the hull is designed to minimize drag, enabling the robot to navigate efficiently through dense aquatic environments while conserving energy.

Propulsion Systems

Underwater robots are equipped with thrusters and propellers specifically designed to optimize thrust in water, which is more viscous than air. Typically, multiple thrusters are utilized to facilitate movement in six degrees of freedom (DOF): forward and backward, left and right, up and down, and rotational movements such as pitch, yaw, and roll.

Contemporary autonomous underwater vehicles (AUVs) incorporate energy-efficient thrusters that support prolonged operational durations. Low-noise electric thrusters are commonly favored in deep-sea operations to reduce acoustic interference with sonar systems. The strategic positioning of these thrusters is crucial for ensuring balance and stability during intricate maneuvers in unpredictable underwater currents.

Navigation and Control:

Underwater robots differ significantly from their surface or aerial counterparts. They cannot utilize global positioning system (GPS) signals due to the attenuation of these signals in water. Instead, they use Inertial Navigation Systems (INS), Doppler Velocity Logs (DVL), and acoustic positioning systems to ascertain their location. INS employs accelerometers and gyroscopes to estimate positional changes in the robot.

Conversely, DVL systems gauge velocity about the seabed, thereby enhancing short-term location accuracy. For extended missions, underwater robots frequently depend on acoustic positioning systems such as ultra-short baseline (USBL) or long baseline (LBL) systems, which utilize fixed transponders located on the seabed to provide reference points for positioning.

Power Supply and Energy Management:

Energy limitations considerably restrict the operational capabilities of underwater robots, particularly Autonomous Underwater Vehicles (AUVs), which depend on onboard power sources. Lithium-ion batteries are frequently utilized due to their high energy density and relatively lightweight. Nevertheless, the increasing need for extended missions has prompted investigations into alternative energy solutions, including fuel cells and ocean thermal gradient energy harvesting.