Connector Force Post-Processing Connector Force Post-Processing

If connectors were attached to the system when the frequency response was computed, the frequency response of the constraint forces was also computed. To obtain the frequency response of the forces which the connectors exert on the first body to which they are connected, one can issue:


     FR_CFORCE, CONN_NAME

Here, the user is placed in the Disposition Menu with the frequency response of the connector which matches the selector CONN_NAME. He can then proceed to dispose of these results.

To obtain statistics of the forces which the connectors

Many of the commands here compute statistics of quantities and as a result have many common options. In particular:


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

     -SPREAD, EXP

     -SP_TYPE, TYPE

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

     -CSTEEP,  YES/NO

The statistical result is the statistic specified with the last -PROBABILITY option on a &DEFAULT command, and If the original response data was produced with the SRESPONSE command, then no additional sea data can be specified.

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. If -CSTEEP is specified with a YES/NO of YES, then the height of the wave will be altered so that all seastates have the same steepness as the initial one. Otherwise, the wave height will remain constant. exert on the first body to which they are connected, one can issue:


     ST_CFORCE, :CONN_SEL, 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), .....

     -USE_MEAN, YES/NO

The command produces irregular sea results for the first connectors which are selected by the selector :CONN_SEL. This command works exactly as the ST_POINT command, except here the results are for constraint forces instead of motions. Additionally, one can use the -USE_MEAN option to instruct MOSES to add the mean value of the force to the computed deviation with the sign of the mean so that the reported force will be a measure of the total force, and the remainder of the options are discussed above.

When dealing with irregular seas, it is often of interest to know the variation of the sea and frequency response of the constraint forces connector with frequency and period. To obtain results of this nature, one should issue:


     SP_CFORCE, :CONN_SEL , -OPTIONS

where the available options are:


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

     -SP_TYPE, TYPE

     -SPREAD, EXP

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

and they are discussed above.

Fatigue can be computed on the connectors if one has computed frequency response with an SRESPONSE command. This is accomplished with the command


     FAT_CFORCE, -OPTIONS

where the available options are:


     -INITIAL

     -ACCUMULATE, :CONN_SEL

     -REPORT, TIME

This command was designed to accumulate fatigue for several different environments (SRESPONSEs). When the command is issued with the -INITIAL option all fatigue accumulators are zeroed. When it is used with the -ACCUMULATE option, cumulative damage is computed for all connectors which match :CONN_SEL, and this damage is added to that which exists. The duration used for the damage is that specified on the &ENV command. Finally, when the command is used with the -REPORT command, a report of the cumulative damage is written. The TIME (days) variable can be used to scale the damage from the time accumulated to TIME. In other words, if the sum of the durations was T1 and TIME was specified to be T2, then the damage will be multiplied by T2/T1 before reporting.

A command closely associated with fatigue is:


     COUNT_CF, -OPTIONS

where the available options are:


     -F_BINS, T(1), T(2), .....  T(n)


     -ACCUMULATE, :CONN_SEL


     -REPORT, TIME

Instead of accumulating fatigue, however, this command accumulates cycles of tension in specified ranges. The ranges are specified with the -F_BINS option where T(i) is in bforce, and the other options function exactly as for the FAT_CFORCE command.

If some of the connectors are rods, then one has two additional commands available. These commands compute statistics of the internal forces and the stresses in the rod. To obtain the statistics of the internal forces, one should issue:


     ST_RFORCE, ROD_NAME, ENV_NAME,  -OPTIONS

where the available options are:


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

     -SP_TYPE, TYPE

     -SPREAD, EXP

     -USE_MEAN, YES/NO

Here, ROD_NAME is the name of the rod one wishes to investigate. If one is interested in a pipe assembly, then he should use &PIPE for ROD_NAME. When issued, the statistics for the rod internal forces will be computed. One can use the -USE_MEAN option to instruct MOSES to add the mean value of the force to the computed deviation with the sign of the mean so that the reported force will be a measure of the total force. The remainder of the options are discussed above.

Stresses in rods are computed via the command:


     ST_RSTRESS, ROD_NAME, ENV_NAME,  -OPTIONS

where the available options are:


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

     -SP_TYPE, TYPE

     -SPREAD, EXP

     -USE_MEAN, YES/NO

which operates exactly the same as the ST_RFORCE command.