Analysis of full-scale sea-trials manoeuvring data and development and validation of a motion-simulation model for the AUV MUN Explorer

Issac, Manoj Thomas (2011) Analysis of full-scale sea-trials manoeuvring data and development and validation of a motion-simulation model for the AUV MUN Explorer. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Autonomous Underwater Vehicles (AUVs) are free-swimming underwater robots capable of navigating on its own by means of the various sensors it carries onboard. AUVs are rapidly emerging as an important tool in ocean exploration. Designers of AUVs rely increasingly on hydrodynamic models as a design tool particularly for the initial phases of vehicle development. These models allow the designer a means for determining the inherent motion behaviour of a proposed vehicle even before its construction and testing. -- The research work addressed in this thesis is aimed at evaluating the performance of a hydrodynamic motion simulation model developed based on the component build-up method for torpedo-shaped underwater vehicles. The model is derived in a form that only requires the specification of the vehicle's geometry, and the lift, drag and moment characteristics of its constituent elements: the hull, control surfaces, propulsion system etc. The total hydrodynamic load acting on the vehicle is obtained by summing up the loads from each of these components. Such a model, developed by previous researchers at Memorial University of Newfoundland (MUN) for a streamlined AUV was available for use in this research. However, this model was never validated against experimental data. In order to validate the model and establish the performance envelope it was necessary to test the simulation model against all possible mission scenarios that a typical AUV would encounter. This required an extensive set of manoeuvring data from real vehicles that resembled a wide range of mission scenarios. -- The availability of a new Explorer class AUV at Memorial University (the MUN Explorer) facilitated the performing of a series of free-running manoeuvring trials at sea. This included straight-line tests, turning circles, zigzags in horizontal and vertical planes and helix manoeuvres. The responses of the vehicle to different manoeuvres are reported in detail in this thesis and formed a major portion of this research. This formed a database, which encompass a range of mission scenarios, against which the simulated response of the vehicle could be compared. Apart from providing a dataset for validation purpose, these manoeuvring trials also provided valuable information on the performance and capabilities of the Explorer, which belongs to the class of a large commercial AUV, and is one of the only seven Explorers operational around the world to date. -- In order to simulate the above manoeuvres, it was necessary to modify the existing hydrodynamic model to one that can capture the specific features of the new AUV - the MUN Explorer. A second model of the MUN Explorer, with a different tail plane configuration from the original, was also developed to study and compare the control plane actions between the two configurations. The ease with which the model was adapted from one vehicle to another as well as the ease with which the model can be reconfigured exemplifies the overriding advantage of using the component build-up method and the generic nature of the hydrodynamic model as well. -- A select number of manoeuvres were simulated using one of the models. Preliminary results from the simulation of steady state manoeuvres show reasonable-to-good agreement with the measured data. The vehicle responses to manoeuvring trials, simulation of a few of these manoeuvres and their comparisons and validation are considered to be some of the main contributions made in this research work.

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