Working with Units in MOSES

This document explains how to set up and interchange the working units in MOSES.

Two sets of files are used to demonstrate the unit definition and units interchange to assess the longitudinal strength of a barge. The two sets of files can be found on ...\hdesk\runs\samples\how_to directory.

MOSES v10.14 was used in generating results for this work.

Specify Analysis Units

The analysis units are specified with the &DIMEN command and they are usually defined at the top of the file. The command syntax is

&dimen -options

and the available options are

 -dimen, -save, or -remember

The three options will be discussed with two examples below. Let us see the first set.

Long_str.cif and Long_str.dat

The -dimen option controls the current analysis dimensions and in long_str.cif we see

&dimen -dimen meter k-nts

When a -dimen option is used, any input that follows is to be consistent with meters and kilonewtons and all output will also be consistent. With this option available one can define input data in a system different than meters and kilonewtons. This feature is used in the second set of files.

In long_str.cif and long_str.dat all input is consistent in meters and kilonewtons and no further discussion is made. The results from this set of files will be used for comparison with the output from the second set.

Long_str_mtons.cif and Long_str_mtons.dat

In these files the same analysis is carried out but this time metric tonnes force are used instead. The syntax in the command and the data file is specific to demonstrate how analysis units are changed, data is specified, and then return to the initial units.

Let us look at Figure 1 where the implemented units in the command file can be seen better.

• On top of the file, step A, we see
  &dimen -save -dimen meters k-nts
  This command defines the “computational” units and MOSES is informed that all data that follows is to be in meters and kilonewtons.
• In step B, the INMODEL command reads the information contained in the data file.
• In step C, the &DIMEN command is used again, this time to change the input units from meters and kilonewtons to meters and metric tonnes. Any subsequent input is to be in meters and metric tonnes until a new &DIMEN command is encountered. The -save option used here instructs MOSES to save the current dimensions so that when the -remember option is issued, the previous units saved, in step A, will be recalled.

• In step D, the &DIMEN command is used again, this time to alter the input units from meters and metric tonnes to meters and kilonewtons. Anything that follows is to be in meters and kilonewtons until a new &DIMEN command is encountered in step E.
• Finally, in step E the -remember option is invoked to revert to the initial units defined in step A.

Remember that MOSES stores all the data in neutral format. It is the user’s responsibility to ensure that the units are consistent in each step. MOSES will not convert input data in any of the above steps. The benefit of the above scheme is that one can input a model using different units for various definitions. For example, a barge may be defined in metric units, while a jacket in English units.

Post processing results from the above two analyses shows that the banding moment and shear curves are identical even though in long_str_mtons the flexural rigidity EI was converted from kN-m² to Te-m² in

&describe body barge -section 113e11/9.81 0 75.333

Note that the above change from kN-m² to Te-m² is not automatic but the user has to responsibly carry out conversion. The above interchange can take place as many times as necessary as long as one respects the units chosen with the -dimen option.

Do not forget to issue the -remember option last (step E) to revert to the primary analysis settings (step A)

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