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Solid Edge ST6 First Look: FEA with Solid Edge Simulation

By Attilio Colangelo, Nov 19, 2013

In this First Look article, I look at the FEA (finite element analysis) tools built into Solid Edge ST6 as part of the Premium edition. There is a trend in our industry towards integrating analysis with CAD, and it continues to move forward rapidly. It is a logical progression because prior to the advent of modern GUIs with solid modeling, building models for FEA took a great deal of an engineer’s time. Tools like Solid Edge Simulation allow us to focus more on the analysis, and less on generating and modifying geometry.

Analysis Types

When we sit down to create a new study in Solid Edge Simulation, we are presented with the menu shown in figure 1.

Figure 1: Selecting the FEA study type

Study types are listed in a dropdown menu, and show the various types of physics that can be modeled by Solid Edge. I decided to put the program through its paces by choosing the Linear Static option. This is probably the most common type of FEA performed at the design level.

Geometry

To perform the analysis I used the simple geometry of two hollow cylinders, shown in figure 2. The key feature of this geometry is the set of intersecting cylinders; one cylinder could, for example, represent the outlet nozzle of a tank. The material is carbon steel.

As an engineer, I know that localized effects will occur at the juncture of intersecting cylinders. For this reason, I will examine the area closely using mesh refinement.

Figure 2: Geometry to be analyzed

Loads and Fixtures

The loads and fixtures are collectively known as "boundary conditions," as shown in figure 3. A downward force of 10000 N (Newton) is applied to the end of the nozzle, while the base is fixed.

Figure 3: Setting the model's boundary conditions. Downward force applied evenly across all faces of elements on edge of small cylinder

Upon clicking Solid Edge's Simulation tab, I entered the Simulation environment. I found it straightforward to apply these loads and fixtures. The Simulation tree for this model is shown in figure 4.

Figure 4: Selecting options in the Simulation Tree

The main advantage of using a CAD-based FEA like Solid Edge is that everything is geometry-based. By right-clicking the Loads option, and then clicking through the Structural Loads command, I arrived at the Force input box shown in figure 5. This is where I selected the geometry onto which the loads would be applied. The software's default is to apply the force normal (at a right-angle) to the surface; this, however, can be overridden, which I did using the Direction Type option. Then I chose Components, because it is the most general vector definition which allowed me to specify x-y-z components.

Figure 5: Applying force vector definitions

Since I wanted to have just a downward load Fx and Fy are zero and Fz is the total 10000 N. Having full access to the values for each axis allows for complex loading at a face without having to build additional reference geometry.

Meshing

A proper mesh is critical in achieving good results for a stress analysis. As with most options in the interface, right clicking on the "Mesh" option in the tree brings up the appropriate dialog box. For the mesh command this is shown in figure 6.

Figure 6: Mesh dialog box

Figure 7: Mesh at slider value of 4

The first mesh was performed at a value of 4 on the slider and is shown in figure 7. The degree of mesh resolution is a judgment call for the engineer based on the area of interest in the model. The tradeoffs of finer mesh are greater solution accuracy but increased solution time. Increasing the resolution to a relative value of 8 on the slider gives the finer mesh shown in figure 8.

Figure 8: Mesh at slider value of 8

However, even this mesh may not be sufficient in the area of interest. The potentially high stress area at the junction, shown previously in figure 2, needs refinement. Increasing the mesh for the whole model to capture this local effect is not practical. Fortunately, there are mesh refinement options within Solid Edge that can be done at specific areas of interest.

Figure 9: Mesh edge refinement

Figure 9 shows the submenu when the "Mesh->Edge Size" command is right clicked in the tree. The "Edge Size" dialog box gives a number of parameters for refining just that edge location. I used a value of 50 as a starting point and sometimes the final mesh resolution is iterative based on the results. Figure 10 shows the mesh refinement at this value.

Figure 10: Mesh with edge refinement

We can see that the mesh is refined in the area of interest to capture the likely higher stress gradients. The mesh then transitions into the rest of the model with successfully larger element sizes. The larger meshes allow the model to have a reasonable number of total elements, and reasonable solution time.

Solver

All of the previous work falls into the category of "preprocessing" a stress analysis. With these steps complete, a definition of the nodes and boundary conditions (i.e., loads and fixtures) is now ready to be solved mathematically. Solid Edge uses the NX NASTRAN solver to accomplish this step. (NASTRAN is a robust solution engine developed by NASA, and was one of the first commercial FEA solvers.)

A primary advantage of the NASTRAN solver is it allows custom commands to be issued. This is not something that is going to be readily accessible - or even documented within Solid Edge - but advanced users familiar with NASTRAN commands use this function to tweak the solver. Because it takes some digging to find these native files, for most analyses the default values are sufficient.

Post processing

Probably the most important aspect of an analysis is being able to view and understand the results clearly. In this regard, Solid Edge provides a full complement of tools for post processing. Figure 11 shows one of the main output plots for linear static stress analysis, stress, and deflection.

Figure 11: Outputting a von Mises stress plot

Von Mises stress is the most common way to evaluating the structural integrity of a ductile material. In addition, Solid Edge makes a number of other stress definitions available to the user, as shown in figure 12.

Figure 12: Accessing available stress definitions for plotting

Figure 13 shows the displacement plot for the model.

Figure 13: Generating a displacement plot

One feature that would be helpful in Solid Edge would be the ability to change units display on the fly. For instance, there are times when I prefer to display the stress in psi (pounds per square inch) - as opposed to MPa (megapascals); or inches - instead of mm (millimeters), for the displacement. This feature is incorporated into SolidWorks Simulation. (Siemens PLM says that a workaround is to close the results environment, open the Properties dialog, and change the units. The results will reflect the change.)

Solid Edge has a report generator useful for presenting results. It creates reports in HTML or Word format. The most useful feature I found is that it will echo all user input in a convenient format. This is great for checking material properties, boundary conditions, and so on.

Conclusion

Solid Edge Simulation provides a powerful tool for performing finite element analysis. In addition to the intuitive graphical interface it incorporates a NASTRAN solver, which allows access to advanced features for users familiar with the NASTRAN commands.

Although SolidWorks had an earlier start with CAD/FEA integration and so overall has a more comprehensive package, Solid Edge (with Synchronous Technology in the modeling end and FEMAP/NASTRAN as the FEA engine) is poised to capture the growing base of engineers using integrated CAD/FEA software.

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About the Author

  Attilio Colangelo has over 25 years in design, project management and field experience in chemical, process, ceramic, advanced materials and steel industries. More...

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