Flexible Multibody Dynamics
Flexible Multibody Dynamics: Theoretical Foundations
What is Flexible MBD?
Professor, what does flexible MBD add to rigid body dynamics?
A combination of rigid bodies + CMS-reduced flexible bodies. Handles large rigid body motion + small elastic deformation simultaneously.
CMS + MBD
1. Reduce FEM model via CMS using the Craig-Bampton method
2. Integrate the reduced flexible body into the MBD solver
3. Joint connection + dynamic analysis
Summary
The theory of flexible body MBD is based on NASA's Shabana paper
The rigorous formulation of flexible multibody systems is based on the "Floating Frame of Reference (FFR)" method established by Ahmed Shabana (University of Illinois) in his 1982 PhD thesis. NASA's Goddard Space Flight Center's implementation of Shabana's theory for analyzing the deployment of solar array paddles on space structures was one of the earliest practical applications. The current ANCF (Absolute Nodal Coordinate Formulation) is an extended version published by Shabana himself in 1996, which significantly improved the analysis accuracy of large-deformation flexible bodies.
Computational Methods for Flexible Multibody Dynamics
Implementation of Flexible MBD
Summary
The Craig-Bampton method is the world standard for mode reduction
In flexible body MBD (MFBD), the "Craig-Bampton method" for reducing finite element models to a small number of modes is the de facto standard. This method, published by Roy Craig Jr. and Mervyn Bampton in the AIAA Journal in 1968, combines fixed-interface modes and constraint modes, resulting in high mode accuracy at connection points. For automotive crankshaft analysis, Craig-Bampton reduction is standardly used to reduce FEM models with over 100,000 total modes to tens or hundreds of modes for integration into MBD.
Flexible Multibody Dynamics in Practice
Flexible MBD Practice
Stress evaluation of automotive suspension components, crane boom deflection, robot accuracy evaluation.
Practical Checklist
MFBD is essential for satellite solar array paddle deployment
Deployable space structures (solar array paddles, antennas) are typical applications of MFBD analysis. The deployment analysis for the solar array paddles of JAXA's Hayabusa2, launched in 2014, was conducted using coupled RecurDyn and Nastran (indirect information from JAXA press release). MFBD analysis was used to pre-evaluate the risk of deployment vibration interfering with attitude control thrusters, reportedly aiding in optimizing the deployment sequence. The importance of MFBD analysis in zero-gravity environments, where ground testing is difficult, will only increase.
Flexible Multibody Dynamics: Software & Solver Comparison
Flexible MBD Tools
MSC Adams, founded in 1977, is the industry's oldest MBD solver
The predecessor of MSC Adams, "DADS (Dynamic Analysis and Design System)", was developed by Professor Orlandea at the University of California, Davis in 1977 and later transferred to MSC. Flexible body functionality (AdamsFlexible) was added in the late 1990s, and the workflow automating Craig-Bampton reduction in conjunction with Nastran became the industry standard. Currently under HexagonMSC, Adams 2023 features enhanced Python script APIs, making integration into ML optimization loops easier.
Advanced Technology
Advanced Flexible MBD
Related Topics
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