Sesam Converters

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How to convert and import Nastran models?

Version: All

See the Best practice for hull modelling using Sesam GeniE (also attached) chapters 2.9 and 3.9 for both overview and details about how to convert typical ship models in Nastran .bdf file format to Sesam T#.FEM files and import them into GeniE.

Please see the attached document Best practice for hull modelling in Sesam GeniE V7 - Rev 4

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How to convert Sesam wave loads (L#.FEM) to Nastran bdf format?

Nastran does not handle complex numbers (e.g. wave loads) the way Sesam does, thus Sesam wave loads can’t be easily converted to and calculated in Nastran.

However, in a “snapshot” (point in time) of a wave from Wasim (on L-file format), the imaginary parts are all zero on both the BRIGAC and BEUSLO cards, and it is therefore possible to convert this information to equivalent Nastran format.

Nevertheless, there are some differences between the Sesam and Nastran implementation of relevant cards, so conversion is not straightforward. NastranToSesam (discontinued) and Sesam Converters only partially support such conversion.

Here are some details: 

  • Real rotational accelerations on Sesam BRIGAC cards are converted to Nastran RFORCE cards. (Supported, at least for global coordinate system.)
  • Real translational accelerations on Sesam BRIGAC cards need to be converted to Nastran ACCEL/GRAV cards. (Not supported.) 

For translational accelerations (real values, not imaginary) in Nastran, either the GRAV or ACCEL cards can be used, see the attached notes from the Nastran manual. Since BGRAV is applied to the whole model, it is natural to use GRAV since it also applies to the whole model.

Workaround:

The workaround is to use Sestra instead of Nastran for the structural analysis.

Please see the attached document ACCEL.

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Limitations to line loads on beams

Version: All

This applies to conversion from Sesam to Nastran.

The beam element line loads defined on the Sesam BELOAD1 cards can have arbitrary end node offsets, but the similar Nastran PLOAD1 beam element line load can only have arbitrary end node offsets on node 2. Node 1 can't have a negative offset in element x-direction (overhang).

In version 2.1-02 and earlier any BELOAD1 card with partial loading are not converted and there are no warnings about this. Thus this load will be missing in the analysis.

In version 2.2-01 the Partially loaded cards are converted, but with a negative value for X1, which gives an error message in Nastran. Alternative workarounds are:

  • Manually edit X1 to zero. This will then omit the load outside end 1.
  • Manually divide the element in two and reverse the element at end 1 such that it has it's end 2 at the original position of end 1. Then the load has to be updated manually.

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Separate load file (L#.FEM) is not supported

Version: All

There is no support for conversion from/to a separate Sesam load file (L#.FEM). The workaround is to include all loads in the input file (T#.FEM file or .bdf) before conversion.

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