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Abstract:In this paper, residual sway control of objects that are moved underwater is investigated. The fuel transfer system in a nuclear power plant transfers the nuclear fuel rods underwater. The research on the dynamics of the loads transferred in different mediums (water and air) and their control methods have not been fully developed yet. The attenuation characteristics of the fuel transfer system have been studied to minimize its residual vibration by considering the effects of hydrodynamic forces acting on the fuel rod. First, a mathematical model is derived for the underwater fuel transfer system, and then experiments have been conducted to study the dynamic behavior of the rod while it travels underwater. Lastly, the residual vibration at the end point is minimized using the input shaping technique.

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For efficient mechanical system optimization, a new two-point approximation method is presented. Unlike the conventional two-point approximation methods such as TPEA, T ANA, TANA-l, TANA-2 and TANA-3, this introduces the shifting level into each exponential intervening variable to avoid the lack of definition of the conventional exponential intervening variables due to zero-or negative-valued design variables. Then a new quadratic approximation whose Hessian matrix has only diagonal elements of different values is proposed in terms of these shifted exponential intervening variables. These diagonal elements are determined in a closed form that corrects the typical error in the approximate gradient of the TANA series due to the lack of definition of exponential type intervening variables and their incomplete second -order terms. Also, a correction coefficient is multiplied to the pre-determined quadratic term to match the value of approximate function with that of the previous point. Finally, in order to show the numerical performance of the proposed method, a sequential approximate optimizer is developed and applied to solve six typical design problems. These optimization results are compared with those of TANA-3. These comparisons show that the proposed method gives more efficient and reliable results than TANA-3.

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Input shaping is a feed-forward control technique which is used for generating shaped commands to suppress the residual vibrations of a system. In this paper, an underwater weight positioning system (WPS) and a fuel handling system have been considered as a pendulum system. It has been simulated to match the experimental response, giving the information required for designing the input shaper. A zero vibration (ZV) shaper has been designed to suppress the residual vibration. Underwater experiments have been implemented by transforming the payload straight in the water with command velocity. A trapezoidal controller has also been used to compare with the ZV shaper. The effectiveness and applicability of each method have been analyzed through experimental results.

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