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Underwater Vehicles Part 10

Tham khảo tài liệu 'underwater vehicles part 10', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Chemical Signal Guided Autonomous Underwater Vehicle 349 2. Background Chemical signal guided search is complicated by the nature of fluid flow and the resulting odor plume characteristics. An initial approach to designing an AUV chemcial plumetracing strategy might attempt to calculate a concentration gradient. Gradient following based plume navigation algorithms have been proposed for a few biological entities that operate in low Reynolds number environments Berg 1990 however gradient based algorithms are not feasible in environments with medium to high Reynolds numbers Elkinton et al. 1984 Jones 1983 Murlis et al 1992 . At low Reynolds numbers the evolution of the chemical distribution in the flow is dominated by molecular diffusion resulting in a chemical concentration field that is reasonably well-defined by a continuous function with a peak near the source. At medium and high Reynolds numbers the evolution of the chemical distribution in the flow is turbulence dominated Shraiman Siggia 2000 . The flow contains eddying motions of a wide range of sizes that produce a patchy and intermittent distribution of the above threshold chemical Jones 1983 . For an image of the plume the gradient is time-varying steep and frequently in the wrong direction. Even so such plume images are not available to the AUV. Due to the rate of spatial and temporal variations in the flow and plume relative to the maneuvering limitations of existing AUV gradient computation and following is not practical. If a dense array of sensors were distributed over an area through which a turbulent flow was advecting chemical and the output of each sensor were averaged for a suitably long time i.e. several minutes then this average chemical distribution would be Gaussian Sutton 1947 Sutton 1953 however the required dense spatial sampling and long timeaveraging makes such an approach inefficient in a turbulence dominated environment Naeema1 et al. 2007 . It is known that the instantaneous chemical .