In this paper, we present a motion control method of oscillatory-base manipulators, which are associated with mechanical systems installed on vessels or ocean structures. The typical property of such systems is strong and persistent disturbance due to the base oscillation to be overcome. Therefore, we attempt to exploit the sliding mode control (SMC) concept which is known to be a powerful tool to develop a robust control system against disturbances and model uncertainties. Specifically, we propose a novel approach based on SMC by introducing a nonlinear sliding surface with variable-gain integral control. We address control system design and stability analysis for the proposed SMC, and demonstrate its control performance by simulations. The results show that the proposed control method can achieve successful control performance for oscillatory-manipulators and further exhibits advantageous features with respect to control performance and control inputs when compared with the conventional SMC.
Water hammer pumps can effectively use the water hammer phenomenon for water pumping. They are capable of providing an effective fluid transport method in regions without a well-developed social infrastructure. The results of experiments examining the effect of the geometric form of water hammer pumps by considering their major dimensions have been reported. However, these conventional studies have not fully evaluated pump performance in terms of pump head and flow rate, common measures of pump performance. The authors have focused on the effects on the pump performance of various geometric form factors in water hammer pumps. The previous study examined how the hydrodynamic characteristics was affected by the inner diameter ratio of the drive and lift pipes and the angle of the drive pipe, basic form factors of water hammer pumps. The previous papers also showed that the behavior of water hammer pump operation could be divided into four characteristic phases. The behavior of temporal changes in valve chamber and air chamber pressures according to the air volume in the air chamber located downstream of the lift valve was also clarified in connection with changes in water hammer pump performance. In addition, the effects on water hammer pump performance of the length of the spring attached to the drain valve and the drain pipe angle, form factors around the drain valve, were examined experimentally. This study focuses on the form of the lift valve, a major component of water hammer pumps, and examines the effects of the size of the lift valve opening area on water hammer pump performance. It also clarifies the behavior of flow in the valve chamber during water hammer pump operation.
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