Equation Post-Processing

The commands discussed in this section allow one to post-process the data used to compute the response. Basically, two types of data are used: added mass and damping matrices, and exciting forces. MOSES always uses these properties about the vessel origin, but all commands discussed here will produce data applicable to the point specified on the last FR_POINT command. In other words, if one wants the results for the vessel origin, then he should issue a FR_POINT command with a point of 0, 0, 0 before issuing any command discussed here.

While commands are discussed below which give one complete control over the results he wishes to obtain, a single command has been provided which produces a set of "standard results" which suffice in many circumstances. The form of this command is:

     EQU_SUM

When this command is issued, MOSES will simply generate reports of all of the equation results. The Disposition Menu will not be entered.

Alternately, one can have the option of disposing of the data for the matrices by issuing:

     MATRICES, -FILE

When this command is issued, the program will compute the added mass and damping matrices about the point specified on the last FR_POINT command. If the -FILE option is used, then the matrices will also be written to the PPO file. In the file, the full 6x6 matrices will be written. Care is needed here. The results reported for damping are not the ones really used, but are the maximum over all headings. This is correct for a spectral linearization, but not for a steepness one. Also, a report to paper gives the radii of gyration while the report to file gives the actual terms of the matrix.

To obtain the exciting forces about the point specified on the last FR_POINT command, one uses:

     EXFORCE, -FILE

When this command is issued, the program will compute the forces operators at the specified location for every period and heading where response was computed. If the -FILE option was used, the forces will also be written to the PPO file. In the file, the forces will be real and imaginary parts instead of the magnitude and phase elsewhere.

When placed in the Disposition Menu, the results for all headings are available. The names of the variables are followed by HEDXXX where XXX is the heading angle in degrees. When using the REPORT command in the Disposition Menu, one can selectively report the response operators. If there is no data on the REPORT command, all headings will be reported. To report data for only some headings, one should specify the angles of the heading to be reported on the REPORT command.

To compute statistics of the exciting forces in irregular seas, one issues the command:

     ST_EXFORCE, ENV_NAME, -OPTIONS

where the available options are:

     -SEA, SEA_NAME, THET, HS, PERIOD, GAMMA

     -SP_TYPE, TYPE

     -SPREAD, EXP

     -NPERIOD, PER_INC, NUM_PERIOD

Again, the point where moments are referred is the last point specified on a FR_POINT command. The options -SEA, -SP_TYPE, and -SPREAD are used to define the seastate to which the vessel will be subjected and are the same as if they were specified on an &ENV command. The -NPERIOD option can be used to generate results for seas of several different periods. If this option is omitted, then a single period of PERIOD will be considered. With the option, periods of PERIOD, PERIOD+PER_INC, ..., PERIOD+NUM_PERIOD*PER_INC will be produced. Here, PER_INC is the period increment, and NUM_PERIOD is the total number of periods. The statistical result is the statistic specified with the last -PROBABILITY option on a &DEFAULT command. As with the &ENV command, the meaning of PERIOD and PER_INC depend on either the setting of TYPE specified with the -SP_TYPE option or with -SP_TYPE specified on if they were specified on an &ENV command. If the original response data was produced with the SRESPONSE command, then no additional data can be specified.