A UNIFIED PROBABILISTIC APPROACH TO PREDICTING THE RESPONSE OF OFFSHORE STRUCTURES, INCLUDING THE EXTREME RESPONSE

It is of crucial importance for the design of an offshore structure, floating or fixed, to make accurate predictions of the maximum responses which may be expected to occur during its service life. This refers in particular to the response due to wave action. The procedures in use for such predictions vary from case to case, but they have in common that they attempt to identify one or more sets of environmental conditions which are supposed to produce the required maximum responses. In other words, designs are at best based on a consistent choice of environmental conditions rather than on a consistent level of individual responses. This paper discusses important developments towards a new procedure to overcome the above shortcomings. It is based on the calculation of long-term statistical distributions for each and every response parameter of interest, which include all response magnitudes experienced during a structure's lifetime. To enable this to be achieved a notional '1000 year wave scatter diagram' is introduced. A procedure for deriving such a diagram from an actually measured wave scatter diagram covering, typically, a period of a few years is indicated. The procedure allows a comprehensive probabilistic analysis of the response of offshore structures to wave action and is illustrated by four examples.