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http://hdl.handle.net/1947/10167
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| Title: | Trim Calculation Methods for a Dynamical Model of the REMUS 100 Autonomous Underwater Vehicle |
| Report number: | DSTO-TR-2576 |
| AR number: | AR-015-046 |
| Classification: | Unclassified |
| Report type: | Technical Report |
| Authors: | Hall, R.
Anstee, S. |
| Issue Date: | 2011-08 |
| Division: | Maritime Operations Division |
| Abbreviation: | MOD |
| Release authority: | Chief, Maritime Operations Division |
| Task sponsor: | DGMD
DGNHM
COMMHP |
| Task number: | NAV 07/088 |
| File number: | 490-6-395 |
| Pages or format: | 45 |
| References: | 4 |
| DSTORL/DEFTEST terms: | Autonomous vehicles
Control systems
Stability
Dynamic characteristics |
| Abstract: | The calculations given in this work demonstrate that the trimmed state for a dynamical model of the REMUS 100 autonomous underwater vehicle is readily found using a numerical zero-finding procedure based on Newton-Raphson iteration. This work also presents approximate analytical expressions for the trimmed state that can be used as a starting point for the numerical procedure. The procedure should be applicable to a range of hydrodynamic parameters corresponding to other configurations of the REMUS 100 vehicle and to similar vehicles from other vendors. |
| Executive summary: | Survey-class autonomous underwater vehicles (AUVs) are used to investigate the seabed and the water column with high resolution and navigational accuracy. The Royal Australian Navy (RAN) is in the process of acquiring AUVs for use in mine countermeasures, Rapid Environmental Assessment and Advance Force operations. AUVs are potentially major components of acquisition projects SEA 1778 Phase 1 Deployable MCM – Organic Mine Countermeasures and JP 1770 Phase 1 Rapid Environmental Assessment. They may also be components of off-board mission systems that will be acquired as part of future projects SEA 1180 Phase 1 - Patrol Boat, Mine Hunter Coastal and Hydrographic Ship Replacement Project and SEA 1000, Future Submarine.
The DSTO acquired two commercial AUVs in 2007, in collaboration with the Directorate General of Maritime Development and the RAN. One of the AUVs was a REMUS 100, manufactured by Kongsberg Hydroid Incorporated of the USA. Many navies have one or more REMUS 100 vehicles in their inventory and the number of REMUS 100s that has been produced is of the same order as the number of all other commercial AUVs in existence, combined. Although the DSTO vehicle has been extensively tested, its high value precludes testing in waters where currents are strong, or shallow and wave-driven, since the vehicle might be damaged, lost or destroyed. However, operating areas in which such conditions occur are potentially of high military value and there is considerable interest in being able to predict the limiting conditions for use of the vehicle. As a consequence, the DSTO has begun to investigate techniques by which the dynamics of the vehicle may be simulated with appropriate fidelity, using so-called ‘low-level’ simulation models based on estimates of the governing equations of motion for the vehicle.
Accurate low-level simulations of vehicle behaviour rely on well-behaved numerical implementations. One component of such implementations is the ‘trim’ state of the model, which, for a given speed, is the combination of vehicle orientation and control settings in which the unperturbed vehicle will maintain straight-line, level flight in a state of dynamic equilibrium. The trim state is used to analyse the stability of the numerical model – its response to perturbations away from the trim state – and to initialise simulations.
This work describes a robust, parametric process to estimate the trim state of a dynamical model of the REMUS 100 AUV based on equations of motion originally developed by Prestero [1] and extended by Sgarioto [2]. The method is based on direct solution of the governing equations of motion, using an iterative Newton-Raphson zero-finding algorithm. The algorithm is initialised using second-order analytical approximations to the Prestero-Sgarioto equations of motion. The relative accuracy of the analytical expressions is better than 1% at speeds near the cruising speed of the vehicle, but decreases by 1 to 2 orders of magnitude at lower speeds. Other methods of initialisation were also investigated and a reduced set of analytical expressions was found to be effective as a starting point for the iterative calculation.
A parametric investigation showed that the iterative algorithm was convergent for speeds from 1 knot to at least 6 knots; in comparison, the physical vehicle operates within a range of speeds between 2 knots and 5 knots. The variation of the trimmed state conformed to expectations over the latter range. Unexpected behaviour was seen at lower speeds, but this did not originate from a failure of the trim calculation.
In summary, this work has resulted in a procedure for finding the trimmed state of the Prestero AUV dynamics model using a straightforward numerical method with a parametric initialisation procedure. With appropriate parameters, the method should be applicable to variations of the REMUS vehicle; for example, extended versions, and to other REMUS-like vehicles.
References cited in this section:
1. Prestero, T. “Verification of a Six-Degree-of-Freedom Simulation Model for the REMUS Autonomous Underwater Vehicle”, MSc/ME Thesis, Massachusetts Institute of Technology, Sept. 2001.
2. Sgarioto, D. “Steady State Trim and Open Loop Stability Analysis for the REMUS Autonomous Underwater Vehicle”, Defence Technology Agency, New Zealand Defence Force, DTA Report 254, March 2008. |
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