ABATRACT: In this paper we propose a projection based observer that can be used to estimate state vectors such as position and velocity for its motion control using non-uniform interval multi-sensor outputs. The output measurement we will use in estimating the state is a series of known multi-sensor asynchronous outputs. The idea for the proposed projection based observer is that each measurement output give us a piece of information which we can use to project the state vector onto the null space of C (output matrix) in order to reduce the error of state estimation. We will explain how to construct the projection operator in a Hilbert space and show the noise rejection of this algorithm by using Lyapunov method. The applicability of the proposed based observer to SAUV (semi-Autonomous Underwater Vehicles) navigation system is demonstrated through computational analysis with theoretical data. Its comparison with traditional Kalman filtering is assessed for computer simulations of the KRISO SAUV and experiments of the FAU Ocean Voyager II Autonomous Underwater Vehicle. INTRODUCTION There are numerous applications where the usage of an Autonomous Underwater Vehicle is desired. Born from the military requirements for stand-off weapons, remote sensing, mine field mapping and clearance, and coupled with the rapid commercialization of microcomputer technology, it is now possible to foresee some civilian use for AUVs in ocean science, offshore operations, environmental monitoring and underwater inspection. One continuing issue is the precise navigation of such vehicles underwater. While differential GPS (DGPS) is widely used for survey ships and underwater vehicle while surfaced, the navigation problem underwater requires the fusion of data from sensors such as Doppler sonar in a ground locked mode, compass data (a three axis magnetometer), acoustic systems like a SSBL and low cost inertial units.

ABSTRACT: A brief overview is given of researches on the prediction methods of hydrodynamic force on a body moving in waves and having a steady -advance speed. Then two methods developed by the present author for computing hydrodynamic forces are presented and their results are discussed. These two methods are based on different assumptions of the steady flow field around the body. OVERVIEW Prediction of hydrodynamic forces on off-shore structures in current as well as in waves or towed in waves must be based on the correct understanding of current-wave interaction effect. There are other less obvious contexts in which this effect must be considered. Slow drift oscillation in waves is of so large amplitude and long period compared with wave motions that it may be considered as a quasi-steady movement. Damping of the motion may be predicted as a steady force when assuming they move at a steady speed in waves backward or forward. Tilt moment on the structures in waves is caused by vertical steady force. This will be affected when they make slow drift oscillations. That means the tilt moment is also to be predicted taking into consideration that the structures are moving in waves at steady speed. In this chapter I give a brief, I never intend it complete, review of recent researches on prediction of hydrodynamic forces on bodies moving at constant speed in waves. Description is restricted to the potential theories. Correct prediction of hydrodynamic forces on a floating body moving at steady velocity in waves has been mainly a concern of ship hydrodynamics. In the contexts-of seakeeping of ship, however, ship" s geometrical form is often assumed very slender. Prediction of those forces on bluff bodies such as off-shore structures is quite a different problem.