Saturday, November 5, 2016

Research Blog 2: Unmanned Maritime Systems

Review on "A Concept for Docking a UUV With a Slowly
Moving Submarine Under Waves"
 The research for this week's blog, has brought me to unmanned underwater vehicles and their uses for the military and how they are deployed and retrieved by the vessel that houses the system. Unmanned underwater vehicles (UUVs) in military applications have been used or are in the planning stages for the following applications: Intelligence, surveillance, and reconnaissance, mine countermeasures, anti-submarine warfare, inspection/identification, oceanography, communication/navigation network nodes, payload delivery, information operations and time-critical strike. (Ervin 2014). Most of the UUVs are deployed and retrieved from a floating vessel above the water. The retrieval process in many cases are the same as the ABYSS AUV is retrieved: 
Retrieved from http://www.vosizneias.com/news/photos/view/493514038

"Once the scan is complete (roughly 20 hours or less)  the nose float pops off when triggered through an acoustic command. The float and the ca. 25 m long recovery line drift away from the vehicle so that a grapple hook can snag the line. The UAV is then brought aboard the vessel and the information is downloaded and analyzed.”(Linke & Lackschewitz, 2016). This retrieval system works well when the ship is stationary, above water, has the proper docking facilities, is not in a hostile region or an area with rough water that could possible damage the UAV or the ship when retrieving the vehicle. What if though a retrieval system was needed that could not fit the above criteria? This problem has been discussed in the Journal of Oceanic Engineering with the article title "A concept for docking a UUV with a slowly moving submarine under waves.": 

                            Docking an unmanned underwater vehicle (UUV) with a submerged submarine in littoral waters in high sea states requires more dexterity than either the submarine or streamlined UUV possess. The proposed solution uses an automated active dock to correct for transverse relative motion between the vehicles. Acoustic, electromagnetic, and optical sensors provide position sensing redundancy in unpredictable conditions. (Watt 2016).

Docking with a moving submarine does provide challenges, the UUV and dock must make physical contact precisely so that the UUV can be captured and parked. At the time being countries are in the process of developing methods for launching and recovering UUVs through torpedo tubes. This approach can work well in launching smaller UUVs for reconnaissance work, though retrieval with this approach is not fully discussed in this article, simulations of how recovery of these UUVs is discussed. " the active dock approach by using remotely operated vehicles (ROVs). This relies on operator control using video feedback and is probably time consuming, but it provides flexibility and minimizes docking infrastructure on the UUV itself." (Watt 2016)

There are however limitations with this recovery system. One is that the size of the UUV has to be smaller than the torpedo tube, also with the UUV being small the endurance and the payload would be less, making the UUV have to continuously be returned, charged and resent constantly. This increases work and cost that would be offset by creating a larger UUV which would have a larger payload and endurance. The other problem that could come from this is the occupation of the torpedo tubes. If the submarine has been outfitted to become a research vessel then there is no problem in this. Yet if the submarine is being used for wartime efforts, having one or more of the torpedo tubes occupied could mean the difference between life and death of the crew on the submarine. This is where the idea from this article comes into play. A docking system located on the underside of the submarine, this would allow for a larger UUV to be deployed also this would free the torpedo tubes to be used for their mandated purpose.

The process of docking while forward movement has 3 benefits:
"1) Submariners prefer to keep moving and submarines are designed to do so quietly at low speed. Hovering, the deep water stationary docking alternative, is a potentially noisy operation relying on pumps and will lose effectiveness under high sea states.
2) Constant forward speed throughout the docking process reduces the impact of environmental disturbance by superposing a stabilizing steady velocity component on the disturbance and by providing hydrodynamic control for both the UUV and submarine. Although hydrodynamic control for submarines at the top speeds of many commercial grade UUVs (2 m/s) is not great, it is better than at zero speed.
3)With stationary docks, failed docking attempts require the UUV to ‘go-around’ to try again, a lengthy process,whereas when both vehicles are moving in parallel a simple speed adjustment by the UUV can quickly reset conditions for a new docking attempt." (Watt 2016)

Docking is perceived in the following figure: 

(Figured obtained from Watt 2016)

To wrap up this discussion, the use of a full docking unit attached to the bottom of the submarine while in forward motion to dock with the UUV as it too moves in the forward motion would be beneficial to launch a recover a UUV. The only problem that I can see with this is loss of the UUV if damage was done to the docking port by either rough water or unforeseen underwater terrain and organisms that could attach themselves to the docking port. 
                    
References: 
Ervin, W. P., Madden, P., & Pollitt, G. W. (2014). Unmanned Underwater Vehicle Independent Test and Evaluation. APL Technical Digest, 32
Linke, P., & Lackschewitz, K. (2016). Autonomous underwater vehicle „ABYSS“. Journal of large-scale research facilities JLSRF, 2, . doi:10.17815/jlsrf-2-149
Watt, G. D., Roy, A. R., Currie, J., Gillis, C. B., Giesbrecht, J., Heard, G. J., . . . Jeans, T. L. (2016). A concept for docking a UUV with a slowly moving submarine under waves. IEEE Journal of Oceanic Engineering, 41(2), 471-498. doi:10.1109/JOE.2015.2424731

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