David Hopkin

UNCLOS under ice survey - An historic AUV deployment in the Canadian high arctic

In March and April 2010, an ISE Explorer Autonomous Underwater Vehicle (AUV), built for Natural Resources Canada (NRCan), was deployed to Canadas high Arctic. Its mission was to undertake under-ice bathymetric surveys in support of Canadas submission to establish the outer limits of its continental shelf under the United Nations Convention on the Law of the Sea (UNCLOS). During this deployment several under-ice records were broken and several new technologies were demonstrated.

A Behavioral Probabilistic Risk Assessment Framework for Managing Autonomous Underwater Vehicle Deployments

The deployment of a deep-diving long-range autonomous underwater vehicle (AUV) is a complex operation that requires the use of a risk informed decision-making process. Operational risk assessment is heavily dependent on expert subjective judgment. Expert judgments can be elicited either mathematically or behaviorally. During mathematical elicitation experts are kept separate and provide their assessment individually. These are then mathematically combined to create a judgment that represents the group view. The limitation with this approach is that experts do not have the opportunity to discuss different views and thus remove bias from their assessment. In this paper a Bayesian behavioral approach to estimate and manage AUV operational risk is proposed. At an initial workshop, behavioral aggregation, reaching agreement on distributions of risks for faults or incidents, is followed by an agreed initial estimate of the likelihood of success of proposed risk mitigation methods. Post-expedition, a second workshop assesses the new data, compares observed to predicted risk, thus updating the prior estimate using Bayes’ rule. This feedback further educates the experts and assesses the actual effectiveness of the mitigation measures. Applying this approach to an AUV campaign in ice-covered waters in the Arctic showed that maximum error between the predicted and the actual risk was 9% and that the experts’ assessments of the effectiveness of risk mitigation led to a maximum of 24% in risk reduction.

A fully interactive dynamic simulation of a semi-submersible towing a large towfish

ISER and DREA are collaborating on the development of SIMRNIS, a fully interactive nonlinear submersible/cable/towfish six degree-of-freedom (DOF) time domain simulation. This capability is not found in standard tow system codes. SIMRMS is a meshing of the DREA Submersible Simulation Program (DSSP) and the DYNTOCABS tow cable/towfish simulator. DSSP is a nonlinear 6 DOF vehicle simulator that models control, propulsion, and ballasting. DYNTOCABS provides a three-dimensional, nonlinear, 3 DOF, finite segment simulation of the cable and includes a nonlinear 6 DOF model of an active towfish. The two programs have been merged so that the equations of motion for all system components are simultaneously integrated in time. New features and capabilities have also been developed. SIMRMS is used as a test bed to minimize technical risk for further development of a remote minehunting system. This paper discusses, and presents full scale sea trials data validating, the programs capabilities.

Modeling Autonomous Underwater Vehicle (AUV) operations in mine hunting

As part of the new Underwater Warfare Program, DRDC has started a new project on Task Group Mine Field Avoidance. While the long-term objective of the work is to demonstrate a Task Group Mine Field Avoidance capability using Autonomous Underwater Vehicles (AUVs) and Autonomous Air Vehicles (AAVs), the first project is focused on developing a realizable and cost effective concepts of operations for this system. This involves looking at a variety of sensor and vehicle configurations, and for predefined mission scenarios, determine the systems measures of effectiveness (MOEs).

Effectiveness of a two-part tow for decoupling ship motions

Two-part tow configurations are becoming more widely used for stabilization of towed bodies, but there have been few experiments to quantify performance. Two-part tows consist of a depressor at the bottom of the main tow cable, followed by a connecting cable and a towfish which are both close to neutral buoyancy. Because the angle between the two cables at the depressor is large, ideally a right angle, heave of the main tow cable caused by ship motions is markedly attenuated before affecting the towfish. This paper describes a full scale, detailed study of motions of the connecting cable and towfish with vertical excitation of their tow point. For oscillatory excitation, the amplitude ratio of the towfish heave with respect to the tow point heave was found to decrease with increasing frequency or cable length and with decreasing tow velocity. The trial results are compared to simulation with DYNTOCABS, a fully dynamic three-dimensional cable simulation program.<<ETX>>

Modelling variable length tows and altitude-keeping with the Canadian Remote Minehunting and Disposal System

The minehunting scenario of a surface water platform towing, and mutually interacting with, its towbody in a maneuver with variable cable lengths and altitude-keeping to an arbitrary terrain is a realistic yet challenging dynamic situation to model. This paper describes and reports on developments of the SIMRMS modelling tool with emphasis on this scenario. The methodologies used are discussed as well as their validation against full scale sea trials data. To date, the authors have not seen such modelling capabilities for interactive tow cable systems reported in the literature.