Fluctuating Fluid Froces Acting on a Manipulator Arm Submerged ln Water (Nonrepeatability of Fluctuating Lift Produced by Vortex Formation when Repeatedly Commencing Its Motion In Still Water)

摘要

When a manipulator is operated in water, fluctuating fluid forces produced by vortex formation will cause problems in precised positioning control of the manipulator. However, in this kind of studies to date, people were mainly interested in control theory of linearizing the nonlinear drag evaluated from assumption of constant drag coefficient, and nobody paied attention to the fluctuating fluid forces due to vortex formation. On the other hand, the presence of strong irregularity in vortex shedding from a two dimensional bluff body in uniform flow is reported by number of researchers. Therefore, nonrepeatability of fluctuating fluid forces acting on a manipulator arm repeatedly commencing its motion in still water is expected to appear. In this study, two kinds of circular cross- sectioned manipulator arms were provided. Then, one was towed and the other was swang in still water. In eatch case of motion, variation of fluctuating lift with towed distance or swing angle was measured for one hundred times. From ensembly collected data at particular towed distance or swing angle, presence of nonrepeatability of fluctuating lift was clarified.