In order to describe the AUV motion and set up a 6-DOF nonlinear mathematical model, a special reference frames have been established (Shi, 1995). There are two reference frames: fixed reference frame E-§nZ (or inertial coordinate system) and motion reference frame o-xyz (or body-fixed coordinate system), which are shown in Fig.1.
Considering the shape characteristic of most AUVs, the mathematic model is based on the hypothesis that the AUV is symmetric about its xoz plane.
Defining generalized position vector R, generalized velocity vector V and generalized force vector t , the motion vector include
2. Linear and angular velocities (in o-xyz)
3. Force and moment parameters (in o-xyz)
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