3.5.4.2 Modeled effective tension forces
In Figure 3.61, effective tension forces at mid-point of the
booms are plotted. This is the force in axial direction of
the boom. Forces in other than axial directions are negligible
at this point and only occur near the mooring where
the boom ends, and are limited in vertical and horizontal
movements. The graph shows the mid-effective tension
for waves and current load only.
For boom lengths used in the simulation, the relation is
fairly linear. The fact that for the Dyneema-tensioned
boom the tension is higher than both the neoprene and
steel boom is due to its high axial stiffness compared to
the other options. The steel boom has neoprene links,
which lower the stiffness significantly.
3.5.4.3 Tension limited boom length
High axial tension in the boom can result in the boom
not being able to follow the wave surface. This effect is
shown in Figure 3.62, where the tension force will cause
wave overtopping and ‘bridging’ of the structure. This
phenomenon did not happen in most of the simulations,
but it is possible that the boom will be designed for longer
lengths than used in the current model.