UFC 4-159-03
3 October 2005
3-3.2
Dynamic Mooring Analysis. Conditions during Mooring Service Types
III and IV, and during extreme events can be highly dynamic. Unfortunately, the
dynamic behavior of a moored ship in shallow water can be highly complex, so
dynamics cannot be fully documented in this UFC. An introduction to dynamics is
provided in Chapter 8. Information on dynamics is found in: Dynamic Analysis of
Moored Floating Drydocks, Headland et. al. (1989); Advanced Dynamics of Marine
Structures, Hooft (1982); Hydrodynamic Analysis and Computer Simulation Applied to
Ship Interaction During Maneuvering in Shallow Channels, Kizakkevariath (1989); David
Taylor Research Center (DTRC), SPD-0936-01, User's Manual for the Standard Ship
Motion Program, SMP81; Low Frequency Second Order Wave Exciting Forces on
Floating Structures, Pinkster (1982); Mooring Dynamics Due to Wind Gust Fronts,
Seelig and Headland (1998); and A Simulation Model for a Single Point Moored Tanker,
Wichers (1988). Some conditions when mooring dynamics may be important to design
or when specialized considerations need to be made are given in Table 3-10.
The programs AQWA DRIFT and AQWA NAUT (Century Dynamics, Houston, TX) are
examples of software tools that can be used to simulate highly dynamic mooring
situations.
3-4
RISK. Risk is a concept that is often used to design facilities, because the
probability of occurrence of extreme events (currents, waves, tides, storm surge,
earthquakes, etc.) is strongly site dependent. Risk is used to ensure that systems are
reliable, practical, and economical.
A common way to describe risk is the concept of `return interval', which is
the mean length of time between events. For example, if the wind speed with a return
interval of R = 100 years is given for a site, this wind speed would be expected to occur,
on the average, once every 100 years. However, since wind speeds are probabilistic,
the specified 100-year wind speed might not occur at all in any 100-year period. Or, in
any 100-year period the wind speed may be equal to or exceed the specified wind
speed multiple times.
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