Flexible body analysis

Typical motion simulations represent mechanisms using rigid bodies that move in prescribed degrees of freedom according to constraints. These rigid-body motion simulations cannot represent certain dynamic characteristics, especially those resulting from conditions such as sharp impacts, sudden changes in motion, or when the component is flexible enough to affect the motion of the mechanism. For these situations, you can use a flexible body analysis to combine both elastic deformation and rigid body motion.

Simcenter 3D lets you use the finite element method of flexible body analysis using Motion with the Simcenter 3D Motion Solver or RecurDyn solver, and Pre/Post with the Simcenter Nastran, ANSYS, or Abaqus solver. You can also model finite element flexible bodies using Motion with the Simcenter 3D Motion Solver and an imported Simcenter Nastran, ANSYS, MSC Nastran, or Abaqus Simulation or results file.

Note:

If you switch motion solvers (for example, from RecurDyn to Simcenter 3D Motion Solver), the flexible bodies defined in the original solver environment become invalid and must be redefined. You cannot successfully solve the solution without redefining the flexible bodies.

Flexible body solutions in Pre/Post

To set up a flexible body analysis for a component in your mechanism, you create a finite element model on the component and define stiffness at the points where it is connected to the mechanism (typically at joint locations). When you create the FEM file, you can define 1D elements for the components you want to use as flexible bodies. This allows you to create an ERFEM representation of the component when you create the flexible body. The ERFEM representation consists of reduced modal results and wireframe visualization that reduce file size, reduce solve time, and create animations more quickly with the same level of accuracy as a flexible body without the ERFEM representation.

You can use one of the following solutions to perform the analysis. The solutions reduce the dynamic behavior of the flexible body to a set of mode shapes, which are stored in an output file, depending on the type of solver.

• Simcenter Nastran SOL 103 Flexible Body solution

• ANSYS Modal Flexible Body solution

• Abaqus Modal Flexible Body solution

Note:

For information about the correct version of the solver to use, see Integration with solvers and applications. In addition, if you are using a solver other than Simcenter Nastran, you might have to set up your solver environment. In Pre/Post, in the Simulation Navigator, right-click a solution, and choose Edit Solver Parameters. See the following for more information:

• Solver Parameters dialog box (ANSYS)

• Solver Parameters dialog box (Abaqus)

Flexible body association in Simcenter 3D Motion Solver

After you solve the modal solution, you associate the flexible body Simulation or results file with the motion body on which the component is defined in the motion simulation. If the Simulation file contains more than one solution, you can choose the solution to use to represent the flexibility of the body. You can also use the Open Pre/Post Model command to open the Simulation file in Pre/Post so you can edit it.

When you solve the motion simulation with the RecurDyn solver, the solver communicates with Simcenter Nastran and recovers the FE results. When you animate the mechanism, a contour plot for the flexible component is animated along with the rigid body animation.

Where do I find it?

Pre/Post environment

Application	Pre/Post
Prerequisites	A Simulation file as the work part and displayed partOne of the following:Simcenter Nastran as the specified solver and SOL 103 Flexible Body as the specified solution ANSYS as the specified solver and Modal Flexible Body as the specified solutionAbaqus as the specified solver and Modal Flexible Body as the specified solution
Command Finder	Solution

Motion environment

Application	Motion
Prerequisites	Simcenter 3D Motion Solver or RecurDyn as the specified solverFor the Simcenter 3D Motion Solver, a solved Simulation or results file, and a Simcenter 3D Motion Flexible Body licenseFor the RecurDyn solver, Analysis Type is set to Dynamics and the Flexible Body Dynamics check box is selected under RecurDyn Solution Options in the Environment dialog box; a solved .rfi file; and an NX Motion Flexible Body licenseType is set to Finite Element Method in the Flexible Body dialog box
Command Finder	Flexible Body

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Flexible body analysis

Flexible body analysis, Simcenter 3D 2021.1 Series

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