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Other Points to Note

Incidentally, it is worth pointing out that the situation where you specify both a boundary condition from vessel motion and a boundary condition from a user-subroutine is one of only two situations where you can combine two types of boundary condition at the same node and DOF. For example, it is not valid to combine a constant boundary condition and a vessel boundary condition, or a constant boundary condition and a user-subroutine boundary condition. The only valid combinations at the same node and DOF are, as outlined above, combining a vessel boundary condition and a user-subroutine boundary condition, or combining a sinusoidal boundary condition with any other boundary condition.

All applied loads and displacements in Flexcom are optionally ramped or gradually increased up to the full values over a time period (the ramp time) you define. Further information on load ramping is provided in Load Ramping. However, with regard to user-programmed boundary conditions, it is important to note that a ramp is not applied to the value you assign to the variable disp after the return from usrdsp. If you want the value of disp to be gradually ramped on, then the responsibility for applying the ramp is yours and you should do so in the user-subroutine coding. This generality is necessary, since you have no way of indicating to the program whether the application of a ramp is appropriate or not.

Note that the values of dispx, dispy and dispz will already have been ramped prior to the call to subroutine usrdsp, so any value calculated on the basis of the current values of these variables will automatically include the effect of the ramp. This is illustrated in the example to follow..