SCIENCE & ENGINEERING NEWS
San Diego, CALIF. — You are in a submarine somewhere in the ocean. Your mission is to seek out and follow an enemy submarine. However, your sonar only extends so far so you load the lower torpedo tube with an Unmanned Underwater Vehicle (UUV) and fire it. After a few hours of searching, you instruct the UUV to return to the submarine. As the UUV approaches, you extend an arm from the upper torpedo tube. An unsteady flow develops around the extended arm causing the UUV to fluctuate. Finally after several attempts, the arm snags the vehicle and shoves it into the lower torpedo tube. Sound far-fetched. Well it could happen and sooner than you think.
Drs. Stephen Huyer and John Grant are currently involved in studying the unsteady flow fields that occur when a UUV is in close proximity to a docking structure. By using the High Performance Computing Modernization Program’s high performance computing resources and computational fluid dynamics (CFD) code, Huyer and Grant are able to simulate UUV recovery hydrodynamics. The CFD code allows the computational points to move with the local flow and to be continuously generated. This allows worst case scenarios to be modeled and the resulting impact examined.
A 45-degree cone was used to simulate the docking module and a standard 21″ diameter UUV was placed immediately downstream of the cone. The cone and UUV simulation revealed the generation of vortex rings in the wake of the cone. These vortex rings can have large amounts of energy and become unsteady when coming in contact with nearby vehicles. If the nose of the cone and the nose of the UUV lie along the same line, then the vortex rings are shed above or below the UUV and the UUV will remain steady. However, if the UUV is aligned either to the left or right of the cone, the vortex rings break apart and are consumed in the UUV’s wake causing the UUV to become unsteady and making it difficult to capture, possibly impacting the sub. If the UUV impacted the sub, the UUV would not breach the hull of the submarine. Worst case, however, is that the UUV loses control and it impacts the submarine control surface or propulsor.
All UUV applications associated with the submarine are in the design phase. The retrieval system is currently being developed and the feasibility of deploying an extendable arm from the upper torpedo tube is being examined. Drs. Huyer and Grant are designing a test fixture for examining the extendable arm concept. If they are successful, this type of retrieval system will be placed on a submarine. It is anticipated that in the near term, the UUV will be used in mine warfare for reconnaissance missions of mine fields. In the future, it is expected that UUVs will have extended missions in oceanographic mapping, reconnaissance, surveillance of enemy submarines, and generally extending the reach of the submarine.