4.3.4.1 The determination
of dynamic loads should take account of the long-term distribution
of ship motions, including the effects of surge, sway, heave, roll,
pitch and yaw on irregular seas which the ship will experience during
its operating life (normally taken to correspond to 108 wave
encounters). Account may be taken of reduction in dynamic loads due
to necessary speed reduction and variation of heading when this consideration
has also formed part of the hull strength assessment.
4.3.4.2 For design against
plastic deformation and buckling the dynamic loads should be taken
as the most probable largest loads the ship will encounter during
its operating life (normally taken to correspond to a probability
level of 10-8). Guidance formulae for acceleration components
are given in 4.12.
4.3.4.3 When design against
fatigue is to be considered, the dynamic spectrum should be determined
by long-term distribution calculation based on the operating life
of the ship (normally taken to correspond to 108 wave encounters).
If simplified dynamic loading spectra are used for the estimation
of the fatigue life, those should be specially considered by the Administration.
4.3.4.4 For practical application
of crack propagation estimates, simplified load distribution over
a period of 15 days may be used. Such distributions may be obtained
as indicated in figure 4.3.
4.3.4.5 Ships for restricted
service may be given special consideration.
4.3.4.6 The accelerations
acting on tanks are estimated at their centre of gravity and include
the following components:
| vertical acceleration:
|
motion accelerations of heave, pitch and, possibly,
roll (normal to the ship base);
|
| transverse acceleration:
|
motion
accelerations of sway, yaw and roll; and gravity component of roll;
|
| longitudinal acceleration:
|
motion accelerations of surge and pitch; and gravity
component of pitch.
|