Ultra-quiet Autonomous Underwater Vehicle

WINTER 2023 MAE 156B SENIOR DESIGN PROJECT

UNIVERSITY OF CALIFORNIA, SAN DIEGO

SPONSORED BY JULES JAFFE (PhD), JAFFE LABORATORY FOR UNDERWATER IMAGING

Why is this important?

San Diego's coasts are home to unique species of marine life. These species are integral parts of the kelp forest ecosystem in both the La Jolla and Point Loma Kelp Forests. Being able to unobtrusively study and monitor these species' populations using a location independent method would help advance the understanding of these species' roles and behaviors in the ecosystem.

How are we going to approach this?

Dr. Jules Jaffe, our sponsor, had the idea for an ultra-quiet autonomous underwater vehicle capable of tracking and recording fish without disrupting their environment.

AUV Objectives

After discussion with our sponsor, we have determined the primary objectives for the project to be as follows:

Minimally invasive to a fish’ environment
Must have a failsafe to resurface
Don't tangle in the kelp
Record fish (images and acoustics)
Withstand 100m depth
Move at slow speeds
Hand deployable
Autonomous function

Team Final Design

Full CAD of AUV

IMG_9317.MOV

Detailed descriptions and information can be found in the Final Design section.

Summary of Results

Before completing the design, the team researched various propulsion methods to determine which propulsion method was the quietest and least likely to tangle. After research, the most promising propulsion method appeared to be a rim driven hubless thruster. To verify this, the team tested a rim driven hubless thruster and a traditional propeller in a hydrophone tank.

Hubbed

Blue Robotics T100 Marine Thruster

Hubless

Hydromea DISKDRIVE Thruster

Setup

The test environment consisted of a hydrophone mounted at one end of a test tank with the propulsion method mounted at the opposing end.

The thrusters were connected as shown above with the overall speed controlled by the potentiometer.

Experimental Results

Ductless Hydromea Hubless Thruster Sound Profile

Blue Robotics T100 (Hubbed) Thruster Sound Profile

The audio recordings were analyzed with a reference pressure of 1 micropascal and an average profile of each sound pressure level was made. The profiles depict the average decibel level for 1/3 octave frequency ranges for the thrusters being powered up to 30% of their maximum power, which is the intended operating range for the AUV.

According to Popper, et. al., the majority of fish can only detect up to 800-1000Hz. To minimize disturbances to the fish, it was determined that the AUV should not exceed typical ambient noise conditions in that frequency range as the fish would be accustomed to that level of noise. The ambient noise limits were determined using the Wenz curve, shown below, which depicts the ambient ocean noise at the same reference pressure as the audio recordings.

Wenz Curve depicting Ocean Noise

As shown in the sound profiles above, for both the hubbed and hubless thrusters, within the 0 to 1000 Hz range, the number of decibels emitted by the thrusters stays well below the decibel limits of sea state 1 and usual traffic conditions on the Wenz curve. Usual traffic and sea state 1, ocean on a calm day with some wind, are fairly typical conditions for ocean ambient noise. As the noise level for both thrusters is below this level, the noise is sufficiently masked. The noise profile between the thrusters in the relevant range is very similar, however, hubless thrusters were chosen for the final design as they reduce the risk of tangling compared to hubbed thrusters.

Final Design Review

Executive Summary