Structural and hydrodynamic analysis of a gas-filled membrane structure submerged in water

In the last two decades there has been an increasing interest in the development of inflatable structures on account of their potential applications in the erection of space and under-water structures. The stability of inflatable structures for use in the fluid environment is founded on such advantages as light weight, ability to carry the environmental forces efficiently by direct tensile stress and abiIity to utiIize the water pressure to counterba lance the gas pressure. The
extensive possible applications of inflatable structures in ocean technology have emphasized the demand for investigations aimed at better understanding of the structural and hydraulic behaviour of these structures.
The present study is concerned with the structural and hydraulic analysis of a gas-inflated membrane structure fully submerged in water. The structural analysis of such a structure involves the determination of the profile shape and
the tension in the membrane for given inflation and load conditions. This is carried out by the numerical solution of the differential equations of equilibrium of the membrane. The results have been confirmed by an experimental investigation.
The incorporation of a two-way set of reinforcing cables has also been considered. The effect of the spacing of the reinforcing cables for various membrane geometries is studied. Also, the effect of partially drawing-off the internal
gas of the inflated structure as a result of which, water enters the container, is examined.
The hydraulic aspect of this study is mostly concentrated on the investigation of the effect of waves and currents on the proposed structure. Models of the proposed structure have been tested using wind tunnel and wave flume. The results show the effects of currents and waves on the pressure distributions around the models and on the inertia forces. The changes in the shape of the structure and the tension in the membrane due to the effect of a uniform current are assessed. The scouring action of the current has also been investigated experimentally and qualitative results have been obtained.
A general computer program has been developed which can handle structures with up to 300 joints and can be used efficiently for the analysis of many types of cable and suspended structures under different loading conditions.
Numerical results are generated for the proposed inflated cable-reinforced structure.
Finally, the application of such structures for the storage of hydrogen produced from the electrolysis of water using surplus electricity and the storage of associated gas from offshore oil wells is considered. The work carried out in this thesis shows that the proposed structure is feasible and the results presented may be used as a gUidel ine in the design.
However, more investigation is required before a final design can be attained.