Trans RINA, Vol 156, Part C1, Intl J Marine Design, Jan - Dec 2014


1 2 3


4 5 6 7


8


9


10


11 12 13


Figure 10: Trimaran force cross section positions Figure 8: Cross section of boat meshed


The material model used is based on a medium grade aluminium alloy with the properties listed in Table 2. As the strain rate effects on aluminium are negligible, a *MAT_PLASTIC_KINEMATIC material model chosen [15].


was


6 FEA CRASH RESULTS As the system is a conservative system, the total energy, which is initially kinetic energy, will convert entirely in deformation, or potential energy. As the boat’s mass is 1580 tonnes and its velocity 20,000mm/s, its total energy is 3.16E8 J, as can be observed in Figure 11. The kinetic energy changing of curvature at 1.0s suggests that the main impact is complete at that time and that the vessel rounds from the rigid wall.


Aluminium (deformable) – structural material


Aluminium (rigid) – for boat boundary condition


3 2.8e-9


70000


0.3 20 2.8e-9 70000 0.3 Table 2: Standard medium grade aluminium


The computer model developed to assess the structural integrity, deceleration levels and hull forces in the vessel. To monitor the boat’s impact deceleration, accelerometers were placed in the lower quill. In order to reduce the ringing due to the vibration of panels to which the accelerometers were attached to, a 20kg masses were added. The location of the accelerometers is shown in Figure 9. To monitor hull forces, section forces have been added to capture the force propagation. The trimaran force cross sections were positioned 10m apart and are displayed in Figure 10.


Figure 11: Computation stability criteria graph


100


1000 N/A N/A


Figure 12: Hull Section Forces (N) – Full Event Figure 9: Trimaran accelerometer positions


The forces in the hull are initially negative as the primary impact generates compressive forces. These values are - 42MN (-4.7E7N) at time 0.021s for cross sections 3, 4 and 5 which appear to be the stiffest part of the ship, as can be observed in Figure 12. Section 1 is weakest and bends and buckles away to absorb the crash event. At 0.06s, after the stress wave has been affected from the back of the


ship causes tension


maximum in the rearwards (21.7MN).


© 2014: The Royal Institution of Naval Architects


forces which are sections 10, 11 and 12


C-143


Material model


Density () (T/mm3)


Young’s Modulus (E) (MPa)


Poisson’s ratio ()


Yield stress (MPa)


Etan (MPa)


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