Effect of Wave on Current |
 
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Effect of Wave on Current |
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In early versions of Flexcom (prior to Version 6.1), the current velocity at any point below the MWL was time-invariant (unless the point was above the instantaneous water surface at any stage), and calculated from the user-specified velocity distribution in the usual way.
In more recent versions of Flexcom, if you input a piecewise linear current profile, then that profile is stretched or compressed so that the current at the instantaneous water surface remains constant throughout an analysis, as does the velocity as a proportion of the instantaneous depth. This is done by factoring the profile you specify at each solution time by (d/d+η), where d is the water depth and η is the instantaneous wave elevation.
In practice this means that Flexcom has to calculate the water surface elevation at each integration point on each element at each iteration at each solution time. In the vast majority of analyses this is not sufficiently onerous to adversely affect runtimes. However in a very small number of random sea analyses, particularly where a multi-directional sea was specified, runtimes can increase substantially.
The procedure of stretching user-defined piecewise linear current distributions remains the default in the latest version of Flexcom. However an option is provided to over-ride this default, and to instruct the program to return to the earlier method of using a time-invariant current variation with depth.
•*CURRENT is used to specify current loading. Specifically, the LEVEL= input is used to define the current stretching algorithm.