Hi community, I want to use FreeDyn and want to include some flexible bodies in my simulation, but I found that the only way is entering as a “Modal Neutral File used in MSC.Adams”. For what I know some solvers like Nastran and Abaqus can generate such files after runing a modal analysis, but can be done this with Prepomax and CalculiX?
AI Overview
“A Modal Neutral File (MNF) is a binary file format used to transfer flexible body data from a finite element (FE) solver to MSC.ADAMS for multibody dynamics simulations. It contains essential information like geometry (nodes and connectivity), nodal mass and inertia, mode shapes, and natural frequencies, allowing Adams to represent a rigid component as a flexible one in system-level analyses. FE solvers like Nastran and Abaqus can generate these files after an eigenvalue analysis, which are then imported into Adams to simulate small deformations of a part within a larger system.
What it contains:
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Geometry: Information about the nodes and how they are connected.
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Nodal Mass and Inertia: Properties of the component’s mass distribution.
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Mode Shapes: The deformations associated with each natural frequency.
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Natural Frequencies: The inherent frequencies at which the component tends to vibrate.
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Modal Invariants: Properties derived from the stiffness and mass matrices of the FE model.
How it’s used:
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FE Analysis: An FE solver performs an eigenvalue analysis on a meshed component to obtain its natural frequencies and mode shapes.
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MNF Generation: The solver exports this data into the Modal Neutral File format.
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Import to Adams: The generated MNF is imported into Adams, typically the Adams Flex module.
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Flexible Body Representation: Adams uses the data in the MNF to model the component as a flexible body within a larger multibody system.
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Multibody Dynamics Simulation: The system-level simulation uses a modal superposition method, where the flexible body’s motion is a combination of the mode shapes with time-varying scale factors.
Why it’s used:
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Reduced Complexity:
It reduces the many degrees of freedom of a full FE model to a manageable number of modal coordinates for the multibody simulation.
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System Integration:
It enables the integration of flexible components, often originating from different FE codes, into a single, system-level dynamics model.
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Performance:
The modal approximation is suitable for small deformations (typically up to 10% of the part’s size). “