Trans RINA, Vol 153, Part A4, Intl J Maritime Eng, Oct-Dec 2011


reinforcement of the helideck and aft mooring deck structure through Finite Element (FE) modelling and analysis of the local structure, see Figure 9a. Figure 9b shows a drawing of an FE model element plot depicting the upper part of the helideck structure together with the additional reinforcement supports. A simplified forced damped analysis is performed in order to ensure that both the modal strength is reduced and the natural frequencies move at higher values.


3.2


CAVITATION REDUCTION USING VORTEX GENERATORS (VG’s)


In order to mitigate the uncomfortable vibration level in steering deck and after mooring deck as indicated earlier (see Figure 3), propeller excitation forces are required to be further reduced through wake flow improvement in front of the propeller. In this specific case, it is found that the main cause of the uncomfortable vibration on stern structures stems from adverse stern wake quality in front of propeller. Instead of the most common cause, usually


Figure 9a: Proposed local reinforcement plan to change the natural frequency of the helideck and aft mooring deck of the structure.


Figure 9b: FE Model of the local reinforcement to change the natural frequency of the helideck and aft mooring deck.


Cooling Water Discharge Hole affecting the flow


Vortex Generator (VG)


Propeller


Figure 10: Cooling water discharging hole in front of propeller. ©2011: The Royal Institution of Naval Architects A-267


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64