​​​​Alban Cobi​

MS Thesis: A Suction-Based Reversible Attachment and Locomotion Mechanism for an Underway Vessel Hull Cleaning and Inspection Robot, 2017-2020

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ABSTRACT: The international merchant vessel fleet is in charge of carrying over 90% of the items that are traded globally. Any vessel down time brings significant additional costs to the industry. A common source of vessel downtime is the colonization of the vessel hull by marine life, known as permanent marine bio growth. Marine bio growth brings significant risks and costs associated with it, the most notable being a hull frictional
drag increase, which significantly increases the annual fuel and maintenance costs of these vessels.

 

To mitigate these risks and costs, merchant vessels such as cargo tankers undergo a thorough cleaning in a dry-dock up to twice every five years. While saving money in fuel costs and mitigating risks such as the introduction of invasive species, dry-docking can cost over $2,500,000 in a five-year period. Research has shown that adopting a more frequent cleaning regimen, eliminates permanent bio growth and saves maintenance costs, in addition to saving costs associated with the other risks.

 

A relatively new cleaning regimen has been made possible by in-port cleaning technologies, such as FleetCleaner and HullWiper that make use of manual and semi-autonomous tethered robots with high power vacuum systems that clean and inspect vessel hulls while they are docked for cargo loading and unloading. These technologies are in their infancy so there are no published studies about the costs associated with
this in-port cleaning regimen.

There are however some downsides to these technologies that have not made them adaptable by all countries due to stringent regulations against cleaning vessel hulls in harbors. Research has shown that the high power vacuum systems used for collecting the cleaned bio growth do not fully eliminate the risk of the leaching of invasive species and toxic hull coatings into the harbor. Additionally, research shows that magnetic attachment systems, employed by many of these technologies can damage the ship hull coatings which can leach the toxic coatings into the harbor and add additional costs for re-coating the vessel hull.

Studies have shown that a new cleaning regimen, that cleans the vessel hull continuously can dramatically reduce risks associated with bio growth. This cleaning regimen could only be made possible by underway vessel hull cleaning (UVHC) with autonomous robots. There are currently no products that can perform UVHC, however in 2009 Raytheon Company patented a new cleaning and inspection concept of a robot that can perform UVHC. Their concept is attractive in theory but there have not been published feasibility analyses and the robot has yet to be realized.

This work assesses the feasibility of using suction-based attachment for UVHC with compliant bio-inspired suction cups, due their reported resistance to high detachment forces. We introduce a model for studying close-proximity suction-based attachment using a compliant suction cup, and experimentally derive scaling relationships for the detachment force, detachment time, and lateral forces on a suction cup. Using these scaling relationships and a thorough literature review of current attachment and locomotion mechanisms, a new low-power, reversible attachment and locomotion mechanism is presented for the UVHC application.

A proof-of-concept prototype of the mechanism is designed, fabricated and tested in-air and the details of the design are presented in this thesis. The technology shows promise that it can be used as an attachment and locomotion system in energyand power-constrained environments. By supplementing the system with an active attachment system, it may increase the reliability of the device. The mechanism maybe useful in other fields such as for inspection and cleaning of underwater structures such as nuclear plants, underwater pipelines, and docked boats.