Date of Award

2019

Degree Type

Capstone Project

First Advisor

Bahram Nassersharif

Abstract

The objective of Project Message in a Bottle is to design a variable buoyancy deployment capsule capable of housing generic payloads. The capsule is designed to deploy from a submersible host vessel at a depth of 65 feet below sea level. Once deployed, the capsule will sink horizontally with about 10% negative buoyancy until it is two capsule lengths from the host vessel. It then reorients vertically and rises to the surface with positive buoyancy. Once the capsule reaches the surface, the payload can be ejected without having been in contact with the water. A primary benchmark of the capsule is its cycle time; it must sink, reorient, and rise to the surface in under a minute.

The main function of the capsule is to alter its buoyancy, which was accomplished using a drop weight mechanism. Initially, the team developed an Euler simulation to accurately evaluate the position and time of the capsule during descent and ascent. The simulation was corroborated with an in-water demonstration of a scaled version of the capsule. This model was constructed of PVC. The water demo was performed in two phases: ascent and decent, where weights were manually removed and added between trials. Position versus time plots were compared from both the simulation and water demonstration in ascent and descent. The experimental results of descent were exactly in accordance with the simulation results. The ascent values for the simulation and experiment were slightly off, however the team determined that the simulation’s lack of dynamic reorientation of the capsule is to blame. The water demo revealed that the product sinks horizontally with roughly -2% buoyancy, and rises to the surface with positive buoyancy in a matter of seconds. These results prove the drop weight method is feasible.

During the Spring semester, another scaled prototype was designed and constructed. It was made of four inch diameter Schedule 40 PVC, with a threaded male adapter and female end-cap on each end. The drop weight was constructed using low-carbon steel for its magnetic properties. Deployable fins keep the capsule vertical on ascent, and were made using spring hinges. Both items were held in place using rubber straps and pin clevises. The drop weight mechanism consists of an internal motor, which rotates a spool on the exterior of the capsule. The spool is attached to pins, that once pulled, release the straps, deploying the drop weight and fins. This system was governed using an Arduino Uno, breadboard, and depth sensor. Once the capsule has reached the desired depth, the mechanism is triggered. An Euler simulation was completed for this capsule, and it featured reorientation. Flow simulation was completed to calculate drag coefficients at different angles for this simulation. The capsule was tested in a 14 foot dive pool. Five usable trials were recorded, and their results were compared to the simulation data. The simulation proved accurate, and the predicted time to surface of 9.87s was only 8.6% different from the average experimental value of 10.76s.

Comments

Sponsor: Naval Undersea Warfare Center

Sponsor Representative: Peter Phelps

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