Li, Yanjun

As human explore deeper into ocean, more and more subsea structures need to be installed.
Deployable structures, a folded package which could be drop from surface and at destination morphing
into its final structure form have significant advantages like its counterpart in space structures. More
recently, many space missions have proposed large inflatable structure for different proposes. In lieu of
the difference between outer space and underwater environment, it is necessary to include the fluid
structure interaction in underwater deployable inflatable structures application to study the effect of
dense liquid environment on the inflating dynamics of ocean structures. The purpose for the present
research is to demonstrate, through a numerical simulation and a small scale water tank test, a
Deployable Structure for Intervention on Oil Seeps DISIOS, which could form an underwater dome and
collect lower density chemicals from oil seep. DISIOS prototype are formed by membranes and
inflatable tubes, where tubes act as framework to support the membranes to construct a dome. The
study begin with simulate water injection into flatted structures to verify the ability of LS-Dyna software.
Deflection and velocity of membranes are recorded to compare with experiment data. Then we turned
to inflate process of folded structure by different folded methods. From unfolding process simulation, we
could determine which type of fold method works best for our predesign shape of tube. We are now
conducting the dynamic analysis of inflatable tube, which is the elementary component of DISIOS
framework.

As humans explore greater depths of Earth’s oceans, there is a growing need for the installation of subsea structures. 71% of the earth’s surface is ocean but there are limitations inherent in current detection instruments for marine applications leading to the need for the development of underwater platforms that allow research of deeper subsea areas. Several underwater platforms including Autonomous Underwater Vehicles (AUVs), Remote Operated Vehicles (ROVs), and wave gliders enable more efficient deployment of marine structures.
Deployable structures are able to be compacted and transported via AUV to their destination then morph into their final form upon arrival. They are a lightweight, compact solution. The wrapped package includes the deployable structure, underwater pump, and other necessary instruments, and the entire package is able to meet the payload capability requirements. Upon inflation, these structures can morph into final shapes that are a hundred times larger than their original volume, which extends the detection range and also provides long-term observation capabilities.
This dissertation reviews underwater platforms, underwater acoustics, imaging sensors, and inflatable structure applications then proposes potential applications for the inflatable structures. Based on the proposed applications, a conceptual design of an underwater tubular structure is developed and initial prototypes are built for the study of the mechanics of inflatable tubes. Numerical approaches for the inflation process and bending loading are developed to predict the inflatable tubular behavior during the structure’s morphing process and under different loading conditions. The material properties are defined based on tensile tests. The numerical results are compared with and verified by experimental data. The methods used in this research provide a solution for underwater inflatable structure design and analysis. Several ocean morphing structures are proposed based on the inflatable tube analysis.