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Methodology Behind the ANSYS-ADAMS Interface

file can then be imported using the /INPUT command. A simple static analysis can be started in Mechanical APDL after the import of this file.

Export Mode Shapes: The toolkit writes a Mechanical APDL input file that can be used to compute the orthonormalized or unorthonormalized eigenmodes of the component. By using the Export of Modal Coordinates option, these eigenmodes can be scaled in Mechanical APDL, and the stresses in the component can be computed for every time step.

Export Nodal Loads: Using this feature, you can write a Mechanical APDL input file to perform stress recovery as a superposition of unit force load steps. This method ignores the inertia load contribution to the flexible body deformation, so it may be inaccurate when interpreting dynamic effects.

Note

The MSR toolkit features described here are not supported by the ANSYS-ADAMS Interface.

12.7. Methodology Behind the ANSYS-ADAMS Interface

Some tasks performed by the ANSYS-ADAMS Interface involve substantial “behind-the-scenes” work. Two tasks in particular fall in this category: the creation of the modal neutral file (Jobname.MNF) and the addition of weak springs via the WSPRINGS command.

The following sections provide details concerning how Mechanical APDL performs those tasks.

12.7.1.The Modal Neutral File

12.7.2.Adding Weak Springs

12.7.1. The Modal Neutral File

The algorithm used to create the modal neutral file (.MNF) is based on a formulation called component mode synthesis (also known as dynamic substructuring). ADAMS uses the approach of Craig Bampton with some slight modifications. According to this theory, the motion of a flexible component with interface points is spanned by the interface constraint modes and the interface normal modes. Constraint modes and interface normal modes together are referred to as component modes.

Because the algorithm relies on the component mode synthesis method, which is based on the modal analysis, only linear properties are considered during the formation of the modal neutral file. All geometric and physical nonlinearities are ignored. If significant geometric nonlinear effects are present in your component, you must subdivide the component into several smaller components and transfer each one separately. You can then assemble the subdivided components in ADAMS to form a flexible component with geometric nonlinearity.

The modal neutral file contains the following information:

Header information: date, ANSYS version, title, .MNF version, units

Body properties: mass, moments of inertia, center of mass

Reduced stiffness and mass matrices in terms of the interface points

Interface normal modes (the user requests the number of modes generated)

Interface constraint modes

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of ANSYS, Inc. and its subsidiaries and affiliates.

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