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__=m__a__STEP 1

INTERNAV sets

Integration time-frame for ODE solution from

time T to TEND

STEP 2

DIVPAG called to determine solution of the

XX system vector between T and TEND

STEP 3

DIVPAG uses FCMANVR to calculate derivatives of

XX which it stores in DXDT vector at intermediate time-step 't'

STEP 4

FCMANVR combines all vessel forces and uses DLSLRG

to solve F=ma for velocity components at intermediate time 't'

STEP 5

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!

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