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:
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 strucrural rigidity of the upper deck is relatively small and therefore hydroelastic responses are dominant, which must be taken into account in the analysis.
- 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.
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) 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 right-lower figure is one example of the wave elevation (measured at a position between No.10 and No.11 cylinders), 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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