[en] A mathematical model is proposed to describe the dynamic behavior of square and hexagonal cylinder bundles immersed in a liquid. First, the hydrodynamic forces associated with cylinder motions are examined, and then equations of motion of the spring-mounted cylinder motions are examined, and then equations of motion of the spring-mounted cylinders including liquid coupling are derived. 9 refs

[en] In the design of an off-shore tower-like structure, which consists of two pipe sections assembled with universal joints and attached to a buried sinker block on the sea bed, enough buoyancy can be provided to keep the structure vertical. It is desirable to reduce both the structural oscillations due to random wave excitation forces and the reaction forces acting on the sinker block. Assuming that the motion of the structure is two-dimensional in the vertical plane, these design requirements can be effectively satisfied if appropriate restoring and damping coefficients are provided at the joints. In this study, the authors employed the statistical equivalent linearization technique to linearize a nonlinear fluid drag force, and applied a sub-optimal control theory with control sturctural constraints to obtain the optimal stiffness and damping coefficients required at the joints after a trade-off between the rms valves of control moments at the joints. The presented examples showed that the hollowness of the pipe sections and the length ratio of the two pipes are important design considerations

[en] The dynamical behavior of an elastic control rod inserted into a vibrating rigid thimble, which is filled with a viscous fluid, was studied in a theoretical manner. In this problem the excited mode shape of the rod varies unsteadily with the time elapsed, because the span of the rod increases during vibration. The maximum deflection of the rod becomes small, if the higher mode appears with the insertion of rod. Although only a linear model was treated in this study, the position of the first collision between the rod and the thimble was examined for a relatively higher input acceleration. The time required for the insertion of the rod increases as the input acceleration increases. But its increasing rate is very small, because the effect of fluid force on the falling motion of the rod is small compared with those of the dead weight of the rod. (orig.)