Trans RINA, Vol 154, Part A2, Intl J Maritime Eng, Apr-Jun 2012
(within any time-window) but also its probability of exceedance. It substantially reduces the probability of exceedance of the class societies’ design MW (or any other given limit) when the EVT is applied. All steps in the proposed procedure are discussed and examples are provided to illustrate its application when records of the random process are available.
The most probable extreme value in extreme value theory depends on the number of observations (e.g., number of cycles of wave induced load) within a given service life. The design MW in class rules is a fixed value which is determined with the individual amplitude statistics and has an extremely improbable probability of exceedance (around 10-8). It does not follow any change of the most probable extreme value (derived by the extreme value theory). That is why one should not use the design MW in class rules as equal probable extreme value. The
to the most calculated 63.2%
probability of exceedance of class rules by some authors is incorrect because the assumptions in the calculations is that the design MW is always equal to the most probable extreme value.
Data from real random processes is not always available, especially at the design stage. Obviously, additional work should be done to develop a procedure that allows for taking into consideration the probability of occurrence of the maximal values of
the random variable. After
verification and calibration against real records, such a procedure could contribute to more realistic assessment of the structures’ reliability.
Considering the sensitive nature of this issue as well as its importance to all involved in shipping, shipbuilding and ship repair, it deserves critical discussion by experts in the field in order to develop a reasonable procedure for practical application of the extreme value theory in ship strength calculations. Therefore, any
constructive
criticism or proposal for improvement of the proposed procedure described in this Technical Note is welcome.
5. 1. 2.
3. 4. 5. REFERENCES
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©2012: The Royal Institution of Naval Architects
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