Simcenter 3D Files and Modelling Approach for Finite Element Analysis


Andrew Berndt


One of the uniquely powerful aspects of Simcenter 3D is the strong geometry creation, editing, and clean-up foundation on which it is based. The approach to Finite Element Analysis (FEA) adopted by Simcenter 3D draws on the strengths of the CAD (Computer Aided Design) modeling approach and is thus rather unique. This article will provide an overview of the different files and the modeling approach used by Simcenter 3D for FEA.

The Part File (.prt)

A Simcenter 3D structural analysis typically starts with a Part (.prt) file. The Part file is simply CAD geometry that can be:

  • Sourced from NX
  • Created within Simcenter
  • Imported from another modeling package (Parasolid, STEP, Solid Edge etc.)

The Part file is typically used for design and manufacturing purposes. A typical part file is illustrated in Figure 1, showing numerous small features in the form of blended faces

FEA Part fileFigure 1: A typical Part file

The Idealised Part File (.prt)

The Idealised Part is an optional interim CAD model based directly on the Part file. It is intended specifically for simulation purposes and enables geometry modifications to be made without affecting the Part file. Updates performed on the part will be propagated to the Idealised Part, but any modifications conducted on the Idealised Part will not change the Part file. This one-way flow of information allows the FEA model to always be based on the latest Part file while neatly separating the FEA specific geometry from that used for design and manufacturing.  Figure 2 shows the result of the idealisation of the part shown in Figure 1. The blended faces have been removed and the body split up to facilitate meshing.

Note that the Idealised Part is not a necessary step in the analysis process. If the analyst prefers, all modifications can be performed directly on the Part.

Idealised Part fileFigure 2: An Idealised Part file

The FEM File (.fem)

The FEM file stores all finite element data (nodes, elements, connections, material properties, element properties) for a specific entity. The finite element data is, by default, associated to the geometry of the Idealised Part or Part used for the construction of the mesh. The FEM file can contain all finite element data for a specific analysis, but this approach is inefficient for large models because it does not take advantage of the important Simcenter 3D functionality. It is usually beneficial to break the model down into logical separate entities, each with its own FEM file. Figure 3 shows the mesh constructed based on the idealised geometry of Figure 2.

A FEM fileFigure 3: A FEM file

The Assembly FEM File (.afm)

In the same way that a typical CAD assembly forms a logical grouping of appropriately positioned geometrical parts, an Assembly FEM does this using FEM parts. Several types of connections between the various FEM parts can be defined within the Assembly FEM file.  An example of an Assembly FEM is provided in Figure 4.

The Assembly FEM organisation technique can greatly reduce model setup effort by ensuring that subassemblies used repeatedly in a model only need me meshed and connected/assembled once. It also serves as a valuable method to break very large models down into smaller, more manageable portions. It is an optional modeling technique that can be used at the analyst’s discretion.


Figure 4: Assembly FEM example

The SIM File (.sim)

The SIM file contains information on the loads, boundary condition and solver/solution settings for a specific model. It is the top-level item in the Simulation Navigator and references all FEM and Assembly FEM files used to construct the complete Finite Element model. The SIM file can be thought of as the means of drawing the various Simcenter 3D analysis files together into a form that is ready for solving.

Modeling Approach

The Finite Element Analysis approach used by Simcenter 3D uses a strong coupling between the CAD geometry and the mesh. The modeling methodology adopted by the analyst should take this into account, making use of Idealised Parts, FEM files, and Assembly FEM files, to benefit from Simcenter 3D’s unique strengths. Some practice will be required to acquire these skills. To facilitate this process, several tutorials have been set up to guide the interested analyst.