Three stochastic procedures using hydroelastic and structural analyses as itemized in the following are proposed to calculate stresses of detailed local structures for VLFS (e.g. a Mega-Float) in irregular waves. Values including stresses in irregular waves in each procedure are obtained by the ordinary short-term prediction. - [Procedure-l]: This is an ordinary stochastic method employing hydroelastic analysis and structural analysis. - [Procedure-21: This is applicable when a single load item such as shear force or bending moment determines stresses. A short-term predicted stress is simply obtained by multiplying a short-term predicted internal load by a stress factor that is calculated by a local structural model. - [Procedure-31: This is applicable when concurrent multiple load items determine stresses. Firstly, each internal load in the complex mode of an individual load item is multiplied by the corresponding stress factor to obtain the complex amplitude of stress of a single load item. They are then added together to obtain the complex amplitude of the combined stress of which the absolute amplitude is the stress RAO. - By applying Procedures-2 and -3, stresses of structural details at any locations of a floating structure can be easily obtained. - Some examples of calculation for the above are shown.
Since elastic behavior in waves of a wide and shallow very large floating structure (VLFS) including the Mega-Float is very complicated, it is difficult to express wave-induced loads governing global strength by a simple formula as used for a ship's classic longitudinal wave bending moment. Accordingly, the hydroelastic analysis is an essential process to obtain design materials including bending moments and shear forces. Many studies have been made on hydroelastic analysis and some analytical codes for practical use have been presented [Yasuzawa, Kawano, Kagawa and Kitabayashi (1997); Nagata (1997); Ohmatsu (1997); Seto and Ochi (1998)].
