In late December 2015, the OceanGate team conducted a pressure test of a 1/3 scale model of the manned submersible, Cyclops 2.
The objective of the test was to validate that the pressure vessel design is capable of withstanding an external pressure of 6,000 psi -- corresponding to operating in the ocean at a depth of about 4,200 meters (13,800 feet). See the chart below for other pressure-to-depth comparisons.
The results of the test will be used in the final design of the full sized pressure vessel that is slated for commercial debut in 2017.
To begin, the scale model was lowered vertically into the pressure test chamber and suspended by way of a harness. Lead ballast was attached to the bottom of the model to prevent it from floating and contacting the pressure chamber end cap once the chamber was filled with water. The chamber was then partially filled with water and air pumped into the chamber to increase the internal pressure.
The test was conducted as a series of steps where the pressure was increased to pre-determined levels and held at each pressure level for a period of time (dwell time) to monitor results. The engineering team installed 19 strain gauges inside the pressure vessel and monitored them throughout the test.
About 75 minutes into the test, the model successfully reached the pressure of 4000 psi -- equivalent to a depth of about 2800 meters. This was a significant milestone because worldwide only seven manned submersibles are capable of descending to that depth.
At a pressure of nearly 4300 psi, the stainless steel insert in one of the end domes separated from the carbon fiber. This allowed water intrusion into the vessel and aborted the test. The end caps were thought to be the most likely area of failure as the use of carbon fiber for hemispheres such as these is pushing the boundaries of carbon fiber design and fabrication. The use of carbon fiber for hemispheres has never been done at this size or to this depth.
This ititial test provides valuable proof that filament wound carbon fiber hemispheres are viable to depths of 10,000 feet and demonstrates that the benefits of carbon fiber are real. As a result, we remain very confident that we will overcome the extreme technical challenges needed to achieve a design operating depth of 20,000 feet.
Coincidentally, the day of the test we received an article titled the Innovation's Understanding Gap, from Aviation Week and Space Technology, that directly addresses the development process we have undertaken and reminds us all that these setbacks challenge us to learn from the questions raised and find the best possible means to reach our goals.
Anthony Velocci: Editor-in-Chief, Aviation Week and Space Techology.
The next step for us is to apply what we learn from this first test and then build the next test model.
|Pressure||Depth||Pounds on Hull|
|PSI||Bar||Feet||Meters||Scale Model||Full Size Hull|
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Weight: 275 lbs.
Displacement: 8.2 cu. ft.
The pressure vessel was designed and fabricated in collaboration with the University of Washington Applied Physics Lab Collaboratory, and Spencer Composites.
The scale model is approximately 1/3 of the size of the full sized vessel. The walls of the scale model are made of multiple layers of carbon fiber material and resin. The vessel is assembled from three main components: a center cylinder, and two dome end caps. Fabrication of the end caps required 28 unique winding patterns of the carbon fiber material to form a sperical shape. After the carbon fiber cured, the sphere was cut in half to form the two dome end caps.