Post-Processing Cases Post-Processing Cases

In all commands in the Structural Post-Processing Menu, one has the option to specify precisely which cases to consider. One always has the "basic" cases obtained directly from the structural solution available, but one of the more powerful capabilities of MOSES is the ability to combine the results of the fundamental load cases to obtain new cases for post-processing. For most situations, this capability is exercised via the CASES command.

As mentioned above, most of the control of post-processing cases is accomplished with the command:


     CASES_POST, -OPTIONS

where the available options are:


     -DELETE, :CASE_SEL(1), ........., CASE_SEL(n)

     -COMBINE, NEWNAME, CASE(1), MULT_F(1), MULT_P(1) ...,

     -AMOD, MULT, NAME(1), ........., NAME(n)

     -NOMINAL, NAME, MULT

     -PRELOAD, NAME

     -TIME, ENV_NAME, NEWNAME(1), T(1), .........., NEWNAME(i), T(i)

     -PROCESS, PRC_NAME

     -MEAN, MLCNAME

     -FATIGUE, DURATION_NAME, TOTTIME, TOW_VEL

     -SPECTRA, ENV_NAME(1), ............., ENV_NAME(i)

If one has defined some cases which he no longer needs, he can delete them by using the option -DELETE, which will delete all cases which match any of the selectors CASE_SEL(i).

The -COMBINE option is used to define a simple linear combination of previously defined cases (either fundamental or combinations themselves). Here NEWNAME is the name the user wishes to give to this combination, CASE(i) is the name of the cases to be combined, and MULT_F(i) and MULT_P(i) are the multiplier for this case for loads and pressure respectively. One really should not have two multipliers here, but some codes require multiplying the static loads by a factor. If one also multiplies the pressures by the same factor, one gets unreasonable code pressure checks. If MULT_P is omitted, then it is set to the value of MULT_F.

Some codes allow one to employ an "allowable stress modifier". This is a number which is multiplied by the allowable stress in the computation of a code check. If the user takes no action, these factors are set to 1. To alter these multipliers, one should use the -AMOD option. Here, MULT is the new allowable stress modifier for cases which match any of the names NAME(i) and it can contain wild characters.

The allowable stress modifiers operate on "cases", either load cases or combine cases. They do not operate on the constituents of a combine. Thus, suppose one issues the following:

     CASES -AMOD   1.3   @
     CASES -COMBINE DOG CAT .5 BIRD .5

Since the combine case, DOG, was defined after the definition of the allowable stress modifiers, a default modifier will be assigned. If one wishes DOG to have a different modifier, he must either issue another CASES -AMOD command, or define DOG before the -AMOD.

The -NOMINAL and -PRELOAD options define load cases and multiplier to be considered as the nominal and pre-load cases during a foundation code check. They play the same role here as the -SET_STATE option on &CONNECTOR play for a Process Post-Processing FOUNDATION check. If either of these are not defined the values defined via &CONNECTOR will be used.

The -TIME option is used to produce a time domain "snap-shot" from results obtained via a frequency domain structural solution. Here, ENV_NAME is a seastate name which has been previously defined on an &ENV command, and NEWNAME(i) is the name given to the snapshot of the system at time T(i).

All of the other options deal with converting response operator solutions into something more meaningful. MOSES associates a process name with each set of response operator loads cases. The -PROCESS option tells MOSES to use the response operators associated with process PRC_NAME for all options which follow. Normally, one wishes to combine the response operators with the mean to obtain the results. Without any other action, MOSES will use the "frequency mean" load case for this process in the combination. Use of the -MEAN option instructs the program to use the case MLCNAME instead of FRQMEAN(i) for all cases defined after the -MEAN option is encountered until a new -MEAN is encountered. -MEAN will not accept a case name created via -COMBINE.

The -FATIGUE option can be used to alter the total time of exposure to a given environment or the process to which it is applied. If this option is used, then whenever the duration DURATION_NAME is used to compute fatigue, the actual exposure for a given component will be WTIME * TOTTIME / SUMTIME where TOTTIME (days) is that specified with the option, WTIME is the time specified when the component was defined, and SUMTIME is the sum of WTIME(i) for the duration. If TOW_VEL is specified, the length of the tow will be computed as the tow velocity times the duration of the tow, where TOW_VEL is in ft/sec or m/sec, and the duration of the tow is determined by summing the durations. When this option is used, the process associated with the duration is also changed to be the one specified by the preceding -PROCESS option.

The -SPECTRA option allows one to combine the frequency domain results to obtain spectral ones. Here, ENV_NAME(i) are the names of environments which have been previously defined via &ENV commands or in the &DATA Menu. The cases defined by this option will have the same names as the environments. These cases will be formed as follows: First, the RMS of each force or deflection will be computed based on the spectrum. The statistic selected by the -PROBABILITY option on the &ENV command will then be computed. Finally, if the -USE_MEAN option was selected when the environment was defined, the statistical result will be added to the mean using the sign of the mean. In other words, the mean and the deviation will be combined by adding the absolute value of the two quantities and using the sign of the mean. Here, the mean is either the appropriate FRQMEAN or MLCNAME.