Reliability assessment of offshore platforms exposed to wave-in-deck loading

1a) Model testing: A large model tests program, financed by EU, has been completed in February-April 2001 in the large wave channel (GWK) at Forshungszentrum Kuste in Hanover. Regular waves with wave height up to 2.5m can be generated. The experimental data have been used for verification of the numerical model (Task 1b) and as input for Task 2. 1b) Numerical Simulations: A very detailed numerical study for the force variation for two vertical plates placed after each other has been completed. The model has, very convincingly, been able to calculate how the water that passes above the first plate is disconnected and results in an extra peak force, as it hits the second plate. A large number of simulations of the wave impact on a row of profiles have been completed. Those results have been compared with the experimental results and have been used to determine 'engineering' expressions for the shielding. Those expressions can be used to determine how much the hydrodynamic forces are reduced when an element is placed behind other elements. 2) Implementation: The load and shielding coefficients determined in activities 1a) and 1b) have been built into DHIWID programme. This program has been used together with the non-linear structural program RONJA, for Pushover analyses to gradually increasing water depth. 3) Reliability Analyses: Using the 'model-correction-factor-method' a method is developed for reliability analysis of jacket structures with a complicated estimation of the load on jacket and deck and with a non-linear computational model (RONJA) for pushover analyses. The reliability assessment can be performed with only 10-15 RONJA calculations, and can therefore be used in practical applications