Page 36 - 6634

These structures are typically designed to have their lowest modal frequency to

be below the wave energy, as opposed to the fixed structures, which have a first

modal frequency greater than the frequency of wave energy.

Figure 3.7 – Gravity-Paled Structure

The most common among elastic platforms are:

3.2.1 Articulated Platforms (13%). One of the earliest compliant structures

that started in relatively shallow waters and slowly moved into deep water is the

articulated tower. An articulated tower is an upright tower, which is hinged at its

base with a cardan joint and is free to oscillate about this joint due to the

environment.

The base below the universal joint on the seabed may be a gravity base or may

be piled. The tower is ballasted near the universal joint and has a large enough

buoyancy tank at the free surface to provide large restoring force (moment). The

36