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SPAWAR GPS Tracking Buoy
Project Overview
In order to combat ocean pollution, Space and Naval Warfare Systems Command (SPAWAR) will introduce several new instruments to its environmental restoration program. One such instrument is a system consisting of an underwater drogue that will move with the ocean current and a surface buoy that will relay information about its location. This will deal directly with the problem of stormwater runoff, which contains many harmful particles. Because these contaminants are swept into the ocean following each storm, this has become a major hindrance to SPAWAR's attempts to decontaminate the coastal ocean floor. But by determining the settling locations of these particles, SPAWAR can take further measures to prevent the ocean's recontamination. Therefore, in order to better understand where this stormwater pollution settles, SPAWAR has proposed the drogue and buoy system that will simulate the behavior of these particles as shown in Figure 1.
Figure 1: The path of the submersible
The goal of this project is to create an oceanography instrument which simulates the behavior of particles as they descend from the ocean surface to the ocean floor. The instrument consists of three parts: a surface buoy equipped with a Global Positioning System transmitter, a large, high drag drogue equipped with a pressure transducer and range-finding equipment, and a waterproof electromechanical winch to raise and lower the drogue at a controlled rate. The layout of the entire system can be seen in Figure 2.
Figure 2: Overall layout of the drifter system
Project Objectives
The primary objective of this project is to design and build a system that can precisely lower the drogue at any speed between 0.1 to 10 mm/s to depths of up to 18.2 meters (60 ft). It will also be required to raise the drogue back to the surface. The system will need to survive for at least 3 days while fully submerged in the ocean in order to conduct a successful run.
In order to simulate different-sized particles, and therefore different settling rates, the descent speed must be easily configurable for each deployment. In addition, auxiliary ports should be incorporated for additional sensors and to facilitate access to data.
The winch is constrained to work within a Pacific Gyre 3' x 3' SVP drogue tethered to an 8" diameter surface float1. The goal is to send several of these systems out at once, so they should be designed with the production of 10 or more identical instruments in mind. Finally, in order to mimic the sinking particles, the drag of the drogue must be at least 40 times that of the rest of the assembly2.
Final Design
Figure 3: Design of the electromechanical winch.
The final design, displayed in Figure 3, will consist of a level wind to evenly wrap the line around the spool diameter. This is important because if the line wraps around itself, the spool diameter will be changed. By making sure that the line fully coils around the spool before starting another pass, the diameter change can be modeled and the descent speed can be kept constant.
Operation
1For more information on Pacific Gyre's SVP Drogue see: http://www.pacificgyre.com/files/svp.pdf
2For more information on drag area ratio see Pacific Gyre's drag area ratio calculator at: http://www.pacificgyre.com/DragAreaRatioCalculator.aspx