Reliable and Effective Operations of Underwater Vehicles Subjected to Wave-Induced Loads

Abstract

Underwater vehicles have the potential to perform numerous long duration, near-surface missions such as undertaking intelligence, surveillance, and reconnaissance (ISR), acting as communication hubs, and tackling shallow water mine clearance. However, for these vehicles to effectively carry out such missions, wave-induced loads need to be accounted for in their design and controllability. They also need durable and potentially replenishable power to perform continuously for extended time periods. Wave-induced loads are important because a submerged vehicle operating close enough to the surface in a seaway will experience them. We seek a broad understanding of the parameters that affect the severity of these loads and the ability to predict these loads accurately. Currently we are investigating the parameters of vehicle geometry, depth, and speed along with the wave height and length. Once the generation of wave-induced loads is understood and able to be predicted accurately over a wide wave environment, we aim to exploit this knowledge for improved operational capability of underwater vehicles. One example of this would be the determination of the minimum operating depth for a given vehicle in a given seaway such that the wave-induced loads are negligible. Another example is harnessing the periodic vertical wave forcing, and resultant periodic vehicle motion, so that the vehicle can internally generate electricity to prolong its mission time. A third example is the identification of hull cross-sectional geometries that reduce the wave-induced loads compared to the typical circular cross-section. The final example is the creation of advanced control algorithms that predict the upcoming wave-induced loads to compensate for them. This would provide for much better near surface depth keeping performance of the vehicle. This research effort involves both experiments and simulations. The experiments utilize small vehicle models that are tested in the towing tank with wave generation capabilities at the Naval Postgraduate School. The simulation work involves both creating high-fidelity simulations that complement the tow tank experiments as well as exploring the fidelity of existing government owned hydrodynamic prediction software. The knowledge gained from this research effort could be utilized to increase the mission capabilities and effectiveness of unmanned underwater vehicles. Since these wave-induced loads are mostly potential driven with very little viscous effects, these results should scale and be applicable for submarines as well.