Flexcom Analyses |
 
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Flexcom Analyses |
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If you intend to use LifeFrequency in the RAOs mode of operation, you must perform a Flexcom random sea analysis for every combination of reference seastate and wave direction with non-zero percentage occurrence. Additionally, you must also postprocess the Flexcom analyses to generate RAOs of axial force and bending moment at the locations of interest (i.e. the hot spots). LifeFrequency subsequently postprocesses the results to obtain stress RAOs (transfer functions). The stress RAOs for a particular reference seastate and wave direction are then used to produce stress spectra for all of the remaining seastates within that block for that direction. In this way stress spectra are produced for every combination of seastate and wave direction in the long-term environmental data. Note that the assumption implicit in this procedure is that stress RAOs are invariant with respect to seastate over short “distances” within the scatter diagram.
If you intend to use LifeFrequency in the Stress Spectra mode of operation, you must perform a Flexcom random sea analysis for every combination of all seastates and wave direction with non-zero percentage occurrence. Obviously the result of doing a Flexcom random sea analysis for every seastate for every wave direction is that you have immediately the axial force and bending moment spectra that are required for the fatigue analysis. In this context, the next section covering Computation of Stress Spectra is not relevant for the Stress Spectra mode.
After the Flexcom analyses (including postprocessing) for each reference seastate/direction combination have been completed, LifeFrequency proceeds to the fatigue life prediction process proper. The fatigue life at a particular location is found by looping over all of the seastates in the scatter diagram and all of the storm approach directions, and computing and accumulating the fatigue damage due to each combination.
•*SEASTATE FILES is used to specify all of the Flexcom random sea analyses on which the LifeFrequency calculations are to be based, and to tabulate the percentage occurrences of the corresponding seastates.
•*BLOCK is used to input the fatigue analysis wave scatter diagram, including the definition of blocks and/or reference seastates as appropriate.
•*DIRECTION is used to specify long-term directionality data.
•*SPECTRUM is used to specify the wave spectrum type to use for fatigue life calculations.
•*RAO is used to request the creation of RAO plots.