Self-localization is one of the most challenging problems for deploying micro autonomous underwater vehicles (μAUV) in confined underwater environments. This paper extends a recently-developed self-localization method that is based on the attenuation of electro-magnetic waves, to the μAUV domain. We demonstrate a compact, low-cost architecture that is able to perform all signal processing steps present in the original method. The system is passive with one-way signal transmission and scales to possibly large μAUV fleets. It is based on the spherical localization concept. We present results from static and dynamic position estimation experiments and discuss the tradeoffs of the system.
The ship capsizing problem is one of the major challenges in naval architecture. The
Current stability criteriaCurrent stability criteria are based on static assumptions. The roll-restoring moments, called righting moments in calm water, are calculated at various heeling angles. By dividing the righting moment by the weight of the ship the righting lever curves, Figure 1, are obtained. The slope of the righting lever curve at 0• is called initial stability or metacentric height GM . National and international rules on intact stability -which consider non-damaged-ships -make demands on minimum values and characteristics of these curves [1]. The rules require a minimum area of the righting lever curve between 0• and 30• and between 0 • and 40• , the minimal size of the righting lever at 30 • , the minimum metacentric height at 0• , and that the maximum righting lever has to lay at 25 • or higher.Model tests and practical experience show that the current stability criteria do not always correspond to the danger of capsizing. Large-amplitude motions, which neither can be predicted accurately by static criteria nor by linear theory are associated with nonlinear dynamic effects. Consequently, we propose to develop a criterion taking these nonlinear effects into account.
Mathematical modelConsider that a ship freely floating in regular waves can be considered as a rigid body with six degrees of freedom. The equations of motion are obtained from the principle of linear and angular momentum. Denoting the position vector of the center of gravity with respect to the space-fixed frame with r CG and the ship's angular velocity with omega one obtains in coordinates of the body-fixed frame K S : {CG, x S , y S , z S }, Figure 2:where m is the mass of the ship, S J is the 3 × 3 inertia matrix with respect to CG and K S , S f and S m are the vectors of applied forces and moments acting on the ship due to radiation and diffraction, head and beam resistance,
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