To illustrate how the Fortran code operates an overview of the differential equation solution mechanism used by the code is outlined below. This solution mechanism uses standard IMSL (International Mathematics and Statistics Library) functions to solve the equations of motions for the vessel under study both in navigation and mooring modes.
Two IMSL functions are at the core of the code, these are;
ñ DIVPAG (Double precision IVPAG routine) which uses a predictor-corrector or Adams-Bashforth-Moulton method to solve the set of ODE's (Ordinary Differential Equations) that are used to calculate the vessel's various position and velocity parameters.
ñ DLSLRG (Double precision LSLRG routine) which is used to solve the linear set of equations for the various forces acting on the vessel using the equation set F =ma
Integration time-frame for ODE solution from
time T to TEND
DIVPAG called to determine solution of the
XX system vector between T and TEND
DIVPAG uses FCMANVR to calculate derivatives of
XX which it stores in DXDT vector at intermediate time-step 't'
FCMANVR combines all vessel forces and uses DLSLRG
to solve F=ma for velocity components at intermediate time 't'
DIVPAG moves solution forward from T to TEND
through intermediate time-steps 't'
Return to STEP 1
A familiar set of procedures at last - continuing the journey!