Simulation Solves the Mystery of the Titan’s Missing Viewport

The viewport was expected to wedge itself from the pressure, but a simulation shows that it popped out.

Forward titanium hemisphere of the Titan submersible hoisted shows that the acrylic viewport is missing. Image from YouTube video by The Telegraph.

Titan submersible’s viewport is lost at the bottom of the ocean. The massively thick acrylic viewport had a refractive index that was close to water. Great for seeing the Titanic but hard to see on the dark ocean floor. Image from YouTube video by Jeff Ostroff.

On June 18, 2023, OceanGate’s deep-sea submersible, the Titan, imploded on a mission to see the Titanic shipwreck, killing all five on board. Though the U.S Coast Guard investigation is still studying the wreckage for clues as to the cause of the tragedy, the consensus of the engineering community, such as input found on Eng-Tips, points to structural failure. The main suspects in the structural failure have emerged as (1) the cylindrical hull, made of carbon fiber reinforced plastic (CFRP); (2) an acrylic viewport that was rated for a much shallower depth than where the Titanic lies; and (3) the carbon fiber/titanium interface.

Neither the cylindrical hull nor the viewport have been recovered, either in whole or in part, at the time of this writing. The parts that have been recovered are being studied for clues out of the public eye by the Coast Guard, but news reports of the crane lifting several parts recovered from the ocean depths shows the forward titanium endcap intact—but missing its viewport.

In the previous simulation by Dr. Ronald Wagner, results that showed the titanium rings fracturing were not supported by photographic evidence of Titan debris that included the titanium rings intact. Upon request, Wagner redid the simulation with different geometry for the rings, acrylic viewport and titanium endcaps. The resulting simulation is consistent with the intact titanium rings that were recovered and continues to support the theory that the occupants had no time to sense the implosion.

At 48.4 milliseconds, the hull cylinder shows its first sign of necking.

At 49.2 milliseconds, a pinhole opens in the hull cylinder and could have introduced a jet of water. A waterjet cutter, operating at much higher pressure (4,000 atmospheres, 10 times higher than outside the Titan submersible) can cut through a steel plate.

By 50 milliseconds, the hull cylinder has disintegrated. Missing in this analysis are fragments near the middle on the outside of the hull that indicate the carbon fiber on the outside was failing from compression due to the necking of the hull cylinder. Here, the carbon fibers fail in tension. Although the volume defined by the remaining pieces of the hull cylinder could still be considered a survivable volume, the force of the inrushing water and the hydrodynamic pressure (400 atm) would have killed the occupants.

At 50.7 milliseconds, the simulation shows high stress spots in the forward endcap. As this simulation did not account for fluid flow and water rushing in, could the stress spot be the result of a strike from hull fragments?

Hot spots appearing on titanium rings. Again, these are possibly from collisions with debris. Note that the endcaps are moving together.

At 57.4 seconds, we see the viewport (appearing in blue –no stress) has popped out.

The missing viewport set off a popular theory of the reason the Titan sank was that water at extreme pressure rushed in after the viewport failed. But a simulation shows that although the viewport did indeed fail, it failed in the opposite direction: outward instead of inward. The expected worst case, the extreme external pressure found at a depth of almost 4,000 meters—a pressure of 400 atmospheres—was not the cause. Instead, an unforeseen worst-case scenario emerges from the revised simulation. The viewport pops out of the titanium hemispherical endcap like a champagne cork.

The massively thick viewport with its convex external shape was designed to thwart external pressure. Increased pressure would only make the viewport wedge itself into the titanium hemisphere and prevent water ingress. The viewport had only adhesive and a retaining ring to keep it from falling out.

Although the revised simulation reveals an unforeseen worst-case scenario for the viewport, which is helpful in explaining its separation from the endcap, it would not have mattered to the occupants of the Titan. In either failure mode, from external pressure that shatters the carbon fiber hull in the previous simulation or internal forces that pop out the viewport, death would have been swift and painless.

The viewport was made for OceanGate but only rated for a depth of 1,300 meters by its manufacturer, sufficient for looking at coral reefs in the Bahamas, for example, where the depths of 500 meters gave the submersibles that preceded the Titan a comfortable safety margin of 2.6. But the Titanic lies at a depth of almost 4,000 meters.

Stockton Rush, CEO of OceanGate, who was piloting the ill-fated Titan when it imploded, was known to flaunt conventional wisdom and avoid regulation. He might have thought the viewport, such as it was, was in no danger of failing in bending or compression, even at pressures 3 times above the pressure it was rated to withstand. Failure in compression would not be an issue because acrylic changes optically before it cracks and, besides, the submersible was plastered with sensors—part of a hull monitoring system of Rush’s own invention—that would warn him of impending failure.

Although the revised simulation settles the direction the viewport took in the implosion (outward rather than inward), the exact mechanisms of failure remain in question—and will continue to be so until a simulation can analyze the fluids (water and air) as well as the structure.

Without fluid/structural interaction, the hydrodynamic effects of water at tremendous depths as it forces its way into a submersible can only be imagined. Would it be like a waterjet cutter, slicing through whatever is in the submersible and going out the other side? Did the tremendous pressure cause an explosion, as suggested by U.S. Navy submariners, that popped out the viewport? Or was it the water hammer?

Next: Titan Submersible Had No Margin of Safety, Says Structural Expert

Corrected August 13, 2023: Changed “Titan shipwreck” to Titanic shipwreck.”