Equation Post-Processing - Ultramarine.com

Equation Post-Processing - Ultramarine.com 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, -OPTION

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 option, -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, -OPTION

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. Again, if the option -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

     -E_PERIOD, EP(1), EP(2), .....

Again, the point where moments are referred is the last point specified on a FR_POINT command. The statistical result is the statistic specified with the last -PROBABILITY option on a &DEFAULT command.

The remainder of the commands available for connector forces have a similar syntax in that the final portion of the command is identical to that of the &ENV command. In fact, these commands not only initiate the computation of quantities in an irregular sea, but are also &ENV commands. Thus, when one issues one of these commands with a non-blank ENV_NAME, he is altering the definition of this environment within the database. If ENV_NAME is omitted, then the environment used will be totally defined by the options specified. The options -SEA, -SPREAD and -SP_TYPE are used to define the sea state to which the vessel will be subjected. The -E_PERIOD 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, EP(1), EP(2), ... will be produced.