Finding Floating Equilibrium Finding Floating Equilibrium

The method for finding an equilibrium position is fundamental to the manner in which MOSES considers hydrostatics. Instead of using a specified draft and trim to determine the weight, ballast, and cargo for a vessel system, MOSES allows the user to input these weights and ballasts directly via internal commands discussed earlier. After the system has been defined, the question remains as to where the vessel will float. This question can be answered by issuing the following command:


     EQUI_H, -OPTIONS

and the available options are:


     -ECHO, YES/NO

     -FIX, DOF(1), ..., DOF(N)

     -NUMITER, ITER_MAX

     -TOLERANCE, HE, RO, PI

     -WAVE, WLENGTH, STEEP, CREST

When this command is issued, MOSES will iterate until equilibrium is found. The program simply iterates until the center of buoyancy is above or below the center of gravity, and the buoyancy equals the weight. If one wishes to see the details of the resulting position, he should issue the &STATUS command afterward.

The -ECHO option controls the trace of iterations which is printed at the terminal. If YES/NO is YES, then the trace will be printed, otherwise it will not. The option -FIX fixes the specified degrees of freedom during the iteration. Here, DOF(i) can be HEAVE, ROLL, and/or PITCH. The option -NUMITER is used to override the default (20) number of iterations, and -TOLERANCE is used to override the default closure tolerances for heave, roll, and pitch respectively. The values are a percentage of weight for heave, and arms for the angular motions. The defaults are 0.0001, 0.01, 0.01. Finally, the -WAVE option controls the static wave as discussed previously.