Free Surface Effects on Viscous Hydrodynamic Forces Acting on Offshore Structure

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We carried out the research project of the free surface effects on the viscous force acting on an off shore structure from July of 1995 to March of 1997. As the basic study for this topics we have carried out following theoretical and experimental studies.(1) A numerical study on the wave forces acting on a circular cylinder.(2) An experimental study on the viscous hydrodynamic forces acting ob a inclined circular cylinder.(3) An theoretical and experimental study on the viscous damping forces for the slow drift oscillation of a horizontal submerged cylinder.On the basis of these studies two application researches were carried out as follows ;(4) The field experiment and numerical prediction on dynamics of a floating structure moored in deep ocean.(5) An theoretical and experimental study on the thruster assisted mooring system controlled by H* controller.The main conclusions obtained from these researches are as floolws ;(1) The viscous wave forces obtained using the numerical simulat … More ion method developed in the research shows good agreements with experiments.(2) The viscous hydrodynamic force acting on an inclined circular cylinder does not depend on the inclined angle when the inclined angle is taken into consideration into the nondimension form.(3) The slow drift damping force acting on a circular cylinder obtained from two-harmonic oscillation tests coincides with that from forced oscillation tests in waves, but for a rectangular cylinder the latter one is larger than the former.(4) An estimation technique for the hydrodynamic forces on an offshore structure has been developed in this study, in which the interference effects and Reynolds effects are taken into consideration. Hydrodynamic forces of an offshore structure estimated using the method show good agreements with those obtained from total model tests.(5) Motions of an offshore structure predicted using the viscous hydrodynamic forces obtained on the basis of this study and linear theory agreed well with those measured in the field test.(6) The dynamic positioning system based on a mathematical model for motions developed in this study can control the displacement of an offshore structure very accurately. Less