Creating a powerful and efficient finite element model can be tough for engineers, especially for those new to the practice. It can be frustrating to wait for the model to provide accurate results quickly. But fear not, here are three major tips to improve your finite element analysis.
1.Simplify Your Model
Simplifying your model is the first step in finite element analysis. Although not always possible, try to eliminate unnecessary parts of the design. Simplification can take the form of minor geometric changes (see Figure 1) such as removing small fillets or rounds that don’t affect global displacement calculations. Or it can involve major component reductions (see Figure 2). For example, you don’t need to model an entire chair and person to determine if the chair legs can withstand a maximum load of 1000 N. Instead, you can reduce the forces affecting the legs using remote connections.
Figure 1 Incremental round removal
Figure 2 Simplifying the problem
In more complex cases, advanced simplification can involve submodeling. Figure 3 shows the negligible global and local results when small chip components are excluded from mechanical shock results.
Figure 3 Advanced simplifying in CFD
2. Appropriate Mesh Selection
When it comes to meshing, there are several properties that we can control to improve our simulation accuracy, such as mesh size, proximity, and refinement. However, choosing the correct element type is also crucial for a successful analysis. In FEA models, it may be beneficial to mesh certain 3D bodies with shell elements instead of solid 3D elements.
Figure 4 Solid body (left) replaced with surface body (right) using the Ansys SpaceClaim Midsurface Tool.
Shell elements are 2D approximations of 3D geometry that capture the thickness of a body as a physical property. They are useful for modeling thin-walled geometries with a length much greater than the thickness of the body, such as sheet metal chassis or soda can walls. Shell and beam reinforcement elements can also be used to model the thin copper layers inside printed circuit boards.
While it may seem logical to use solid elements for more detailed results, they can actually create artificially stiff structures and inaccurate simulations for thin-walled geometries. Refining the mesh with enough elements to achieve accurate displacement and stress results can also be difficult. Additionally, solid elements may produce a poor-quality mesh for complex thin-walled structures, resulting in negative effects on results.
2.1 Hex or Tet Elements
When choosing between hexahedral (hex) or tetrahedral (tet) elements for FEA models, it’s important to consider the overall shape and complexity of the object. Hex elements generally provide more accurate results at lower element counts than tet elements, but acute angles or complex geometries may require tet elements. Simplifying the model by removing fillets or splitting the body to allow for hex meshing is recommended.
Figure 5 An identical body meshed with hex elements (left) and tet elements (right).
2.2 Mesh Size and Order
Mesh size, referring to the characteristic edge length of an element, also plays a role in simulation accuracy. A smaller mesh size results in longer run times but more accurate results. The choice between first-order (linear) or second-order (quadratic) elements depends on the level of detail needed for the analysis. It’s essential to balance the order and size of the elements to optimize the simulation accuracy and computational cost.
Figure 6 A quadratic element (left) and a linear element (right). Nodes are highlighted in green. Note the midside nodes in between the corners on the second-order element.
3. Choosing the Right Load Application
Picking the right load application is a crucial step in analysis. Load applications are like the things that test the object being analyzed, such as a hot and cold cycle, a fall or impact, vibrations, or bending.
For example, let’s say an engineer wants to simulate how a structure bends during assembly. If the object is slowly bending, they can use a static displacement model. But if they want to simulate the same bending caused by dropping the object, they need a transient model to capture the faster effects of the impact.
Figure 7 Static or Dynamic?
The real world isn’t the same as the virtual world of finite element analysis. You have to consider the real-world stresses that the object will experience and how that could affect the part you’re interested in. If you input these details correctly, your analysis will be accurate, reliable, and useful.
Finite element analysis is a vast field, and every day you’ll encounter unique challenges. The suggestions we’ve provided will depend on the type of analysis you’re doing and what you want to achieve. But we believe that these basic and fundamental improvements will significantly improve your solution time.