Creating and Simulating Flexible Bodies in MotionView and MotionSolve

Welcome to the Multibody Dynamics for Automotive Applications using MotionView and MotionSolve blog series. In this blog, we will explore the FlexPrep Utility in MotionView software, which is used to generate flexible bodies for multibody simulation software. Additionally, we will discuss quasi-static analysis, a critical method used in automotive engineering simulation. 

How to Generate Flexible Bodies in MotionView? 

MotionView provides multiple ways to generate flexible bodies for automotive simulation tools: 

Using the FlexPrep Utility: 

• Automates the creation of flexible bodies from FE models. 
• Runs OptiStruct in the background to generate h3d files. 
• Using HyperMesh and OptiStruct: 
• Allows manual control over mesh and modal analysis settings. 

Manually Editing FE Input Files: 

• Suitable for advanced users who want to reduce model size and optimize performance. 

For this tutorial, we will focus on the FlexPrep Utility, which simplifies the process of creating flexible bodies for MotionSolve certification courses. 

Understanding the FlexPrep Utility in MotionView 

The FlexPrep Utility is found under the Flex Tools menu in MotionView. This tool allows users to: 

• Create flexible bodies from FE models. 
• Translate file formats (e.g., Adams MNF to h3d). 
• Mirror flexible bodies, useful in automotive suspension modeling. 
• Specify interface nodes and CMS methods for accurate simulation. 

Key Settings in the FlexPrep Utility 

• CMS Method Selection: Choose from Craig-Bampton, Craig-Chang, or Craig-Bampton Geometric Stiffness methods. 
• Specify Interface Nodes: Use a + symbol to separate multiple nodes (e.g., 9887+9898). 
• Set Frequency Cutoff: Determines the number of modes retained in the flexible body model.
• Enable Stress and Strain Recovery: Ensures the flexible body can be used for durability analysis. 

To prevent CMS method failures, RB3 spiders should be converted into RB2 spiders using HyperMesh before running the simulation. 

Understanding Quasi-Static Analysis in MotionSolve 

Quasi-static analysis is an essential feature in multibody dynamics training and certification. It helps analyze slow-moving dynamic systems, where inertia effects are negligible. 

Key characteristics of quasi-static analysis: 

• Used when forces/motions change slowly over time. 
• Solves equilibrium configurations at each time step. 
• Does not account for acceleration-based dynamics. 

This method is useful for: 

• Simulating suspension movement under static loads. 
• Analyzing deformation in flexible structures. 
• Performing stress and strain analysis in automotive components. 

Step-by-Step Process for Flexible Body Simulation 

In MotionSolve for automotive engineers, we follow these steps to create and analyze flexible bodies: 

• Use the FlexPrep Utility to generate a flexible body. 
• Convert RB3 spiders to RB2 spiders in HyperMesh. 
• Ensure interface nodes are correctly defined. 
• Run OptiStruct to generate an h3d flexible body file. 
• Import the h3d file into MotionView. 
• Use the FlexPrep Utility to mirror flexible bodies (e.g., left and right lower control arms). 
• Replace rigid bodies with flexible bodies in MotionSolve. 
• Run quasi-static analysis and view stress-strain results in HyperView. 

Conclusion 

Creating flexible bodies in MotionView using the FlexPrep Utility is an efficient way to integrate finite element models into multibody dynamics automotive simulations. By understanding quasi-static analysis, engineers can accurately simulate structural deformations and load distribution in real-world vehicle dynamics analysis. 

In our next blog, we will explore how to visualize and interpret stress-strain results from flexible body simulations in HyperView. Stay tuned for more insights into multibody dynamics certification courses and MotionSolve training! 

This blog is part of our ongoing Multibody Dynamics blog series. If you missed the previous posts, check them out here.  

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