Ch 7 – Pressure Vessel Stresses
A naturalist, William Beebe, wished to construct a manner submersible that would help him explore the ocean at a depth far greater that previously reached. His proposal was to have cylindrical shaped pressure vessel. However, the submersible would be subjected to huge external pressure. Otis Barton would then suggest what he felt was the most practical design was spherical pressure vessel, which was later known as “Bathysphere.” The bathysphere has windows of 8 inches in diameter and 3 inches in thickness. The submersible was accessible using an opening that is 14 inches in diameter, and it was secured with a watertight door that is fastened by 10 bolts. Further, oxygen was supplied to internal tanks and the quality of air enhanced using trays of powered chemicals meant to absorb both moisture and carbon dioxide. To lower the vessel into the ocean, it was tethered by a steel cable, and there was also another cable, electric cable, to supply lighting and allow communication with the ship.
One of the objectives in this study was to determine the water pressure that act on the submersible as the function of the submerged depth while a specific weight for seawater. Also, another objective is to relate the submerged depth of the maximum stress that is allowed, using the equation for thin-walled spherical pressure, in order to determine the maximum permissible depth of submergence. In this regard, the Bathysphere was determined to have maximum allowable depth of submergence of 2990 feet was calculated using the equation of thin-walled spherical pressure.
The image above illustrates the half-sphere diagram obtained after passing a section through the vessel’s center C, in which all force arrows have demonstrated to have changed direction.