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Limiting Values
•Assume the following limiting values for the responses:
–Significant single amplitudes:
•Ship roll: 5 deg.
•Ship pitch: 3 deg.
•Absolute vertical velocity at ramp: 2 m/sec
–Depends on ramp (x,y) location
–Expected number of events per hour:
•Wetness (relative vertical motion hits zero) events at ramp: 30
–Depends on ramp (x,y,z) location
All limiting values for the responses were based on standard design limits for helicopter operations.
All values are given in terms of significant single amplitudes; i.e., the average of the highest one-third of all values in the random process.
Responses considered were ship’s roll and pitch, the vertical velocity at the ramp location as well as the relative motion between the ramp’s lower point and the sea.
This relative motion can be used to calculate the expected number of wetness events in a random sea, and it depends heavily on the vertical location of the lower point of the ramp.