How to reduce your MNF file size by up to 97%

Published 2020-03-06

Flex bodies in Adams are very powerful and if used correctly, could mean the difference between a right and wrong answer. One of the most popular ways to create a flex body in Adams is to create an MNF (Modal Neutral File) with your FEA (Finite Element Analysis) package and import that file into Adams.

However, these files can be quite large and since they are not written out in ASCII format, they are impossible to decipher. Fortunately, MSC Software has a tool that can assist you with your MNF files, it is called the Adams Flex Toolkit, or just Adams Flex as shown in the image below.

In this toolkit you can browse the information contained in your MNF file, convert your MNF file if you wish to and even optimize your MNF file to make it more manageable within Adams. The following paragraphs will go through the Toolkit and expand on what can be done within the tool.

Adams Flex Toolkit is a program in which you can browse your MNF file, translate an MNF file to an Adams matrix file or optimize your MNF file. The Adams Flex Toolkit interface looks as follows:

The default tab is the MNF Browser interface. From here you can select from the check boxes which information you wish to see from the MNF file.

By selecting your MNF file and the check boxes selected as shown in the image above, you have two options to view the results. The first option is to open another window with the information shown as below, or you can choose to save the results to a text file. The image below shows what the results will look like if viewed in the GUI (Graphical User Interface) browser. Feel free to experiment with the various tick boxes to see what information you can extract from your MNF file.

The next tab over shows the MNF to MTX Translator window. In this pane you can translate your MNF file to an Adams Matrix file. A matrix file is used by Adams Solver to describe the properties of a flex body. It is not required to create a matrix file to generate a flex body in Adams.

For more info on the Matrix file refer to the Adams help file section Flexible Body Modelling with Adams Solver.

The third tab in the Flex Body Toolkit is probably the most useful. This is the MNF Optimizer tab. Using this tab, you can reduce the size of your MNF file and make it more efficient for use in Adams.

As you can see in the image below there are a few options that you can play around with when optimizing your MNF file.

  • Invariants
    • Fast Set – With this option the toolkit does not compute invariants 5 and 9. This corresponds to the Partial Coupling formulation for modal flexibility. Invariants 5 and 9 provide the second order correction for the flex body inertia tensor and is responsible for significant CPU load. By disabling them you can reduce the CPU effort drastically, while impacting the results of your flex body only marginally.
    • Full Set – Use this method when you want full accuracy.
    • None – Adams Flex Toolkit does not perform any invariant calculations and they must be calculated each time you save an Adams Solver dataset.
  • Units
    • Original – Selecting this option Adams Flex Toolkit performs the unit scaling as it performs different operations. This can degrade the Adams Flex Toolkit performance.
    • SI – This converts all data to SI units.
  • Formatting
    • Standard Portable – This keeps the MNF file platform independent.
    • Platform Specific – This turns off the encoding that make the MNF file platform independent. This option can reduce the computational overhead if you are not interested in using the MNF file on other platforms.
  • Precision
    • Double – All data is stored in 64-bit floating point values.
    • Single – All data is stored in 32-bit floating point values. A single precision MNF file is about half the size of a double precision MNF file and the results will not be adversely affected if you chose either Fast Set or Full Set at the Invariants drop down menu. However, if you chose None for the Invariants drop down and opt to use single precision some accuracy will be forfeit.
  • Stress & Strain Modes
    • Sparse – The optimized MNF will only store stresses/strains for nodes that was retained in the optimized MNF file. If a node had zero values associated to it and is retained in the optimized MNF, the zeros will be written to the optimized MNF. Remember that the stress/strain recovery will only be available if it was requested in the FEA program that generated the original MNF file.
    • Full – The optimized MNF will store the nodal stress/strain information for all the nodes that are retained.
    • Remove Zero Entries – If you select this option the MNF will store only non-zero stresses/strains for nodes that exist in the optimized MNF. If your model has several zero entries in the stress/strain modes, then this option can drastically reduce the optimized MNF file size.
  • Rigid-Only MNF – Use this option if you want to create a temporary rigid MNF file that you can use to setup and debug your model, before replacing it with the original intended MNF file.
  • Remove Internal Solid Element Geometry – Ticking this check box will greatly improve the graphics performance in Adams. Note that if you intended to use an internal node as a reference point that that node will no longer be available. However, interface nodes will be retained.
  • Optimize Modal Load (MFORCE) Nodes – Leaving this box unchecked will result in all modal load nodes being retained, so that detailed MFORCE plots can be generated. If detailed MFORCE plotting is not required, this box can be checked.
  • Apply Mesh Coarsening Algorithm
    • Mesh Resolution – This slider determines below which size Adams Flex Toolkit will remove the detail of the mesh. For example, if your model is approximately 1m in size, then a 15% Mesh Resolution will result in a mesh with 0.15m wide mesh shells.

Source: Adams Help File - Working with the Adams Flex Toolkit GUI

    • Face Smoothing – this slider determines the angle below which Adams Flex Toolkit will merge faces. For a Face Smoothing value of 15° any faces that are less than 15° out of plane of their adjacent face will be merged with that face.


Source: Adams Help File - Working with the Adams Flex Toolkit GUI

    • Colinear Point Removal – This option removes colinear points from the MNF file.

Source: Adams Help File - Working with the Adams Flex Toolkit GUI

A test MNF file was generated with an original file size of 2.5GB, after using the Adams Flex Toolkit to optimize the MNF file it was reduced to 76MB without the stress/strain data or 678MB with the stress/strain data.

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