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MAE156B 2017 Winter Team #2
MAE156B 2017 Winter Team #2
Alan Duong, Harry Miller, Tung Nguyen, Aaron Spanner, and Kendra Toy
SPAWAR Velocity Float
Project Overview
The overall system consists of three main parts: the drive float, the cart, and the velocity float (or depth logger float in the figure above). When the test begins, the drive float is released and will rise to the surface. It is connected to the cart and the velocity float by a system of pulleys. As the drive float rises to the surface, the cart is pulled along the track with the velocity float being pulled down behind it. The project is focused on developing the velocity float, which will house a sensor from which pressure data will be used to determine velocity. The velocity float will be used to calibrate the adjustable buoyancy of the drive float to the velocity of the cart.
The overall system consists of three main parts: the drive float, the cart, and the velocity float (or depth logger float in the figure above). When the test begins, the drive float is released and will rise to the surface. It is connected to the cart and the velocity float by a system of pulleys. As the drive float rises to the surface, the cart is pulled along the track with the velocity float being pulled down behind it. The project is focused on developing the velocity float, which will house a sensor from which pressure data will be used to determine velocity. The velocity float will be used to calibrate the adjustable buoyancy of the drive float to the velocity of the cart.
Functional Requirements
Per direction of the sponsor, the Sea Dragon Velocity Float and other related deliverables, such as the program to achieve velocity, would need to meet the following requirements:
Calculate the velocity of the cart to within ± 0.15 m (± 0.5 feet) of accuracy
House multiple sensors to reduce potential for failed tests
Minimize and correct for line tilt angle (<5 degrees of tilt considered negligible)
Minimize drag
Be stable prior to and during the experiment
Be simple, inexpensive, rugged, and user-friendly
Involve little to no electronics besides the pressure sensor (passive system)
Convert change in pressure to position and velocity with an algorithm
Determine the pressure signature from waves and current and remove this from the data, perhaps with a filter
Operate in an assumed environment of 0.51 m/s (½ knot) current
Operate at a maximum depth of approximately 24.4 m (80 ft) of seawater
Operate for velocities up to 4.25 m/s (14 ft/s)
Transport a depth-logging sensor that can be easily and securely retrieved by a diver
Design Solution
The float body was designed with PVC to be rugged, significantly buoyant to increase tension in the line and thus minimize the line tilt angle, horizontal at rest to minimize the effect of ocean current drag prior to testing, and vertical when being pulled down for increased aerodynamic stability. A bail was added to allow the float body to change from the horizontal position at rest to the vertical position when being pulled down. The location of the bail was determined such that the float would be statically trimmed horizontally. To ensure that multiple sensors could be transported with the float and retrieved safely by divers, a separate sensor housing component was fabricated out of 3d printed material and a protective PVC sleeve to be attached with cable and carabiners to the bail attachment. In this way, divers could attach the housing to themselves, preventing an accidental drop of the sensors.
Testing and Analysis
Static tests in which a prototype of the float was placed in a freshwater pool with bail position adjusted to trim horizontally. Dynamic tests in which a prototype of the float was released into a deeper freshwater pool were used to support predictions that the float would indeed turn from the horizontal (static) position the vertical (dynamic) position and travel in a stable manner.
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