Welcome to Adams/Solver Subroutines - Kxcad.net

Welcome to Adams/Solver Subroutines
each user-defined variable depends. Adams/Solver determines these functional dependencies at the
beginning of the simulation by calling CFFSUB with the argument iflag set to true. Adams/Solver does
this once for each CONTACT statement with a
FRICTION_FUNCTION=USER() argument.
During each call to CFFSUB, Adams/Solver records which calls you make to SYSARY and SYSFNC.
Adams/Solver assumes that the CONTACT components depend on those Adams/Solver variables that
are accessed through SYSARY and SYSFNC.
Using the DFLAG Variable
The use of the DFLAG variable is optional. Its purpose is to simply let you know that CFFSUB is being
called to evaluate a partial derivative. One of the states on which the CFFSUB depends has been
perturbed very slightly. In many situations, it is likely that major calculations in the CFFSUB are
insensitive to small changes in state, and therefore, need not be recalculated. In such situations, you can
structure the CFFSUB not to redo these calculations.
Tip: If the SYSARY or SYSFNC subroutines are called to access angular displacements, the
values returned by CFFSUB may contain discontinuities. Discontinuities occur if there is
an Euler singularity. To avoid the Euler singularity (and thus the discontinuities), use the
RCNVRT utility subroutine to convert the rotational angles from Euler angles to some
other coordinate system that does not encounter a singularity.
Fortran - Prototype
• If the calculations always use the same SYSARY and SYSFNC calls through the
whole simulation, and you have no initialization to do, you do not need to check
the flag argument at all. You can just call SYSARY and/or SYSFNC, compute the
user-defined variable value, and return to Adams/Solver (FORTRAN)
Caution: When the iflag argument is true:
• You must make all the calls to SYSARY and SYSFNC as they are made to
compute the component values of the CONTACT statement. This ensures that
Adams/Solver has the proper functional dependencies. In general, failure to
account for dependencies in the CONTACT statement components can make it
difficult for Adams/Solver to converge to a solution and/or can force
Adams/Solver to take small integration steps, potentially causing large increases in
execution time.
• SYSARY and SYSFNC return zero values for system and user-defined variables.
When you use Adams/Solver, computations that divide by these values result in
fatal errors. You should check for nonzero values, or ensure the iflag argument is
set to false, before dividing by these values.
A sample structure for CFFSUB is shown next. The comments explain how the subroutine works.
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