Underwater Robotic Propulsors Inspired by Jetting Jellyfish

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Virginia Tech

Underwater surveillance missions both for defense and civilian applications are continually demanding the need for unmanned underwater vehicles or UUVs. Unmanned vehicles are needed to meet the logistical requirements for operation over long distances, greater depths, long duration, and harsh conditions. In order to design UUVs that not only satisfy these needs but are also adaptive and efficient, there has been increasing interest in taking inspiration from nature. These biomimetic/bio-inspired UUVs are expected to provide significant improvement over the conventional propeller based vehicles by taking advantage of flexible bodies and smart actuation. In this thesis, jetting jellyfish were utilized as the inspiration to understand the fundamentals of this new form of propulsion and subsequently translate the understanding onto the engineered platform to validate the hypothesis and construct robust models. Jetting jellyfish species are generally smaller in dimensions than rowing jellyfish, consume lower energy for transport, and exhibit higher proficiency.

In the second chapter, a bio-inspired stationary jet propulsion mechanism that utilizes an iris diaphragm actuation system was developed. Detailed discussion is provided on the design methodology and factors playing the leading role in controlling the vortex formation. The propulsion mechanism was intended to mimic the morphological and deformation features of Sarsia sp. jellyfish that measures approximately 1 cm in diameter. The performance of experimental model was analyzed and modeled to elucidate the role of structure and fluid displacement.

Utilizing the results from Chapter 2, a free-swimming jellyfish-inspired robot (named JetPRo) was developed (also utilizing an iris diaphragm) in Chapter 3 and characterized for relevant propulsive metrics. A combination of theoretical modeling and experimental analysis was used to optimize the JetPRo's gait for maximum steady-state swimming velocity.

Next, an attempt was made towards creating a free-swimming jetting robot (named JP2) using a guided cable mechanism to achieve the desired actuation and improve the propulsion while simplifying the drive mechanism. Using JP2 robotic model, a systematic set of experiments were conducted and the results were used to refine the theory. Based upon the comprehensive computational analysis, an optimized swimming gait was predicted and then validated.

A modular robot inspired by siphonophores was developed and initial efforts were made in laying down the foundation for understanding of this complex locomotion mechanism. Siphonophores are colonial organisms consisting of several jetting bodies attached to a central stem. An experimental model was developed mimicking the multimodal swimming propulsion utilized by Siphonophores. Several swimming gaits inspired by the natural animal were replicated and the preliminary performance of the experimental model was quantified. Using these results, an analysis is presented towards further improving the design and assembly of a siphonophore-inspired robot.

Jellyfish, robotics, biomimetics, jet propulsion, siphonophores