Page 119 - The ROV Manual - A User Guide for Remotely Operated Vehicles 2nd edition

Vehicle Design and Stability 5 CHAPTER CONTENTS
5.1 Vehicle design..............................................................................................................................108
5.1.1 Frame......................................................................................................................108
5.1.2 Buoyancy.................................................................................................................109 5.1.2.1 Lightweightfoam..................................................................................................109 5.1.2.2 Syntactic foam ..................................................................................................... 110 5.1.2.3 Ceramicspheres..................................................................................................113 5.1.2.4 Summary.............................................................................................................114
5.2 Buoyancy and stability ..................................................................................................................116 5.2.1 Hydrostaticequilibrium.............................................................................................116 5.2.2 Transversestability...................................................................................................118 5.2.3 Water density and buoyancy ...................................................................................... 119
This section, along with several others in this manual, will investigate the effect that vehicle geom- etry and stability have on the motive performance of an ROV, especially when taking into account the effect of the tether. Vehicle geometry is driven primarily by the vehicle’s mission, e.g., pipeline survey vehicles require long straight travel distances while construction vehicles require close- quarter maneuverability. Such mission-related considerations affect the frame design and thus the accommodation of the buoyancy material required to float the vehicle. The overall shape of the vehicle determines the drag it will experience not counting the effect of the tether. Then the impact of the tether upon the vehicle’s dynamic stability and the thrust to drag capability have to be taken into account. Just as one would use a leash to walk and control where his/her dog is going, so goes the tether’s effect on the vehicle.
Accordingly, the perfect ROV would have the following characteristics:
• Minimal tether diameter (for instance, a single strand of unshielded optical fiber)
• Powered from the surface having unlimited endurance (as opposed to battery operated with
limited power available)
• Very small in size (to work around and within structures), yet extremely stable
• Have an extremely high data pipeline for sensor throughput
Unfortunately, the perfect ROV is hard to develop, especially when considering the many tasks required by the WCROVs. ROV systems are a trade-off of a number of factors including cost, size,
The ROV Manual.
© 2014 Robert D Christ and Robert L Wernli. Published by Elsevier Ltd. All rights reserved.
107
CHAPTER