A column-supported type is regarded as a good candidate for the very large floating structure (VLFS), because the wave forces and thus the motion in waves are expected to be small relative to a pontoon type VLFS.
However, we have to study the followings in this type:
  1. The strucrural rigidity of the upper deck is relatively small and therefore hydroelastic responses are dominant, which must be taken into account in the analysis.

  2. Hydrodynamic interactions among a great number of columns are complicated and sometimes very large wave loads are exerted at some critical frequencies, which must be properly accounted for by a calculation method.
In this research, a new hierarchical interaction theory is developed for treating hydrodynamic interactions among a great number of cylinders. The elastic motion of the upper deck is expressed by a superposition of elastic modal functions, and the amplitude of each modal function is determined by solving the motion equation of a thin plate by means of a Galerkin scheme.
The right-upper figure shows the coordinate system and notations used in the theory.

Experiments are also conducted using 64 truncated cylinders (shown in the top figure and also above) arranged in 4 rows and 16 columns with equal separation distance both in the x- and y-axes. The wave-induced 3-component forces on an element cylinder and the wave elevation along the longitudinal center line are measured. The figure below is one example of the wave elevation measured at 16 position along the center line, showing good agreement with measurements. We can see also that the measured values near the resonant frequency (about Ks=1.26) are smaller than computed values, which may be attributed to viscous effects due to, for instance, development of the oscillating boundary layer on upwave cylinders.

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