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Presenter: Brad Buckham - Department of Mechanical Engineering, University of Victoria
Supervisor:

Date: Tue, March 5, 2002
Time: 11:00:00 - 12:00:00
Place: EOW 430

ABSTRACT

Abstract:

A vast majority of industrial and scientific activity in the world's oceans is conducted using tethered remotely operated undersea vehicles (ROVs). These vehicles are generally outfitted with numerous thrusters and multiple robotic appendages that result in a highly maneuverable vehicle that is well suited for a wide variety of undersea intervention tasks. To provide high-bandwidth, real-time communication with the vehicle and supply power to allow the vehicle to stay at a work site indefinitely, a neutrally buoyant tether (or umbilical cable) connects the vehicle to a pilot station on the surface. However, as an ROV follows an omni-directional path during operation it deploys a twisted lay of low-tension (or slack) tether along the path. Travel to the limits of the tether, sudden movements of the ROV and/or environmental forces can cause the tether to become taut. During such tensioning, the ROV response is dominated by the rate of and direction of tensioning, complicating the already intricate job of the human pilot. In order to train ROV pilots to handle such circumstances, or avoid them through mission planning, an ROV simulator is being developed that accurately models the low-tension cable dynamics and the dynamics of re-tensioning, in a computationally efficient manner.

In this talk a non-linear finite tether element is presented that is derived using a weighted residuals approach. This element allows for the evaluation of the higher order flexural and torsional internal effects generated within the tether while maintaining the minimal state information of a lumped mass strategy. Using a lumped mass strategy, the state of the ROV tether is defined strictly in terms of node positions. It is the minimal size of this system state vector that enhances the utility of this finite element approach. Results of early experimental validation are to be presented which show good agreement between the finite element model results and observed low-tension tether motion. An overview of ongoing experimental validation is also given which discusses how fibre optic shape sensing technology is being used to capture the state of an actual ROV tether during ROV operation in order to quantitatively describe general tether motion during three dimensional ROV operation.