Submarine Test Capsule: Surface Motion Analysis of Capsule with Simple Damping Mechanism
United States submarines scheduled for release in 2020 will be fitted with vertically launching capsules that will ascend to the surface and perform a mission. These capsules are designed to carry a universal payload, allowing the mission objective to range from missile launching to data gathering. In order to successfully deploy the capsule and complete its mission at the surface, the hydrodynamic properties of the capsule must be evaluated and, possibly, improved.
The purpose of this project was to study the dynamics of a similar test capsule and observe how adding a simple appendage altered the motion. A test capsule was developed and fitted with a motion monitoring instrumentation package in order to evaluate the surface motion of these capsules. After motion analysis of the capsule alone was finished, a passive damping mechanism was designed with hopes of improving the sea keeping characteristics of the capsule. The proposed damping mechanism was a simple cantilever post extending from the aft end of the capsule, with a mass-plate attached to the extreme end of this post.
Using the onboard instrumentation, the hydrodynamic improvements of the capsule, with attached damping mechanism, were analyzed. The free response of three different capsule-damper systems, in both heave and pitch, was tested in a 20-foot tank. From these tests the natural periods of oscillation and damping ratios were extracted and used to calculate additional parameters of motion. These results were used to form conclusions about the effectiveness of the tested damping mechanism. It was found that the simple damping mechanism does have a noticeable effect on the capsule's surface motion. This mechanism tended to increase the heave period and decrease the tilt period, while increasing the damping ratios of both motions. A functional damping mechanism concept design is proposed for possible future implementation on the real capsules.
Available from the National Sea Grant Library (use NHU number to search) or NH Sea Grant
- SubTeC Submarine Test Capsule: Surface motion analysis of capsule with simple damping mechanism (2003). Rebecca Conrad, William Gillard and Kevin Soucy. Advisors: Lloyd Huff and Barbaros Celikkol.