Trans RINA, Vol 157, Part C1, Intl J Marine Design, Jan –Dec 2015 Max stress = 157MPa
Yield stress of structural steel (S460N) = 380MPa Design factor = 2.4
4.1(b) FEA of Storage Fr ame
The FEA of the storage frame is shown in Figure 38. The weight of the 90tonne Mainprize vessel when loaded, including a heave loading factor to account for rough sea conditions resulted in a load of 1471.5kN. The resultiing maximum stress was 3.2MPa. For standard structurral steel (Ys=262MPa) results of initial FEA analysis show the current design has a high safety factor of 81, which ced to 10 and the design would still be
could be reduc
acceptable. The frame could be optimize d for weight by removing unloaded members, reducing the number of sub-frames and using smaller beam sections.
σdesign = yield stress/5 = 262/5MPa = 52.4MPa Which requires the beam to have
sectional area.
A = 368kN/52.4MPa = 70.299cm s
5. DISCUSSION
A key objective in O&M is the reduction in operational cost. In this SOV proposal it is achieved through a multi vessel O&M strategy, in which Cabin RIBS can operate in 1.5m Hs or possibly higher with the use of innovative fendering and motion seats. Offering both a significant fuel cost saving and an acquisitiion cost which is less than 10% that of a catamaran WFSV. Advances in catamaran design could potentially result in vessels capable of 3.0m Hs, which currently is only achievable by using a SWATH type vessel, which have significantly higher fuel consumption than a catamaran.
The critical design challenge of this SOV was the launch/recovery of the catamarans and Cabin RIBs. Here gn compromi se between
there was a need for
F 4
igure 38: FEA of storage frame .1(c) FEA of Turntable Lifting Bars desig
operational safety and mothership stability. Having sufficient wet deck height to saffely lift the WFSV above the waves through a horizontal door in the wet deck would make the vessel unstable. The initial concept of a transom mounted cantilever davit solved the wave height produce a significant increase in significant
issue but
moment requiring loading bay with fe
loading ballasting. The wide f ndering is a compromise significantly
reducing ballasting requirements and addressing risk of impact relating to vessel movement caused by high sea states. In the initial proposal there was a significant risk of the vessel grounding on the horizontal bar of the bollards. The revised proposal re
he esolves this issue through
the implementation of a retractable structurally stabilized bollard structure capable of supporting an appropriate level of side load. To lift under designed load sea conditions the WFSV must be lifted rapidly out of the air/water interface to avoid impact loading after the contact. The winches installed should be
initial lift
tension compensated to ensure the load on the lifting system does not exceed the design load off the lifting equipment. There should also be a latching system implemented between the hulls
s and the lifting cradle so Figure 39: FEA of lifting bar
The full load of the Mainprize M002 in 2.5m Hs is 150tonne in 2.5Hs. As there are 4 lifting bars, the force on each bar is 37.5tonnes (368kN). The design stress elow is based on a safety factor of 5.
be
that they are in constant contact, this would avoid snap loading. These features will be developed in the further work of the authors.
The transfer of cr ew and equipment to the turbine is a critical part of the process for safety of the personnel and for
the transfer of the maintenance equipment. The turbine structure is fixed to the seabed while the transfer vessels are subjec t to wave motion. Current operations
2
The closest standard beam ha s 76.9cm cross section, resulting in a maximum stress of 48.1MPa, shown below in Figure 39.
2
e the following cross
C-120
© 2015: The Royal Instittu
ution of Naval Architects
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