What are the tips for FEA mesh?

Meshing is an important step in finite element analysis (FEA) as it can significantly affect the accuracy and efficiency of the simulation. Here are some tips and tricks to improve your FEA meshing:

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1. Understand your geometry: Before starting the meshing process, make sure you understand the geometry of your model. Identify areas of high stress or deformation and adjust the mesh density accordingly.
2. Use the appropriate element type: Selecting the appropriate element type can significantly impact the accuracy of your simulation. For example, using shell elements for thin-walled structures can significantly reduce computational time compared to solid elements.
3. Control mesh density: The mesh density should be high in areas where high gradients are expected or in regions of high stress. Controlling the mesh density is important to obtain accurate results without compromising computational efficiency.
4. Use symmetry: Take advantage of symmetry in your geometry to reduce the computational cost of the simulation. You can reduce the number of elements and nodes by using symmetry constraints.
5. Check element quality: After meshing, check the quality of the elements. Poorly shaped or distorted elements can lead to inaccurate results. Tools like the mesh diagnostic tools in FEA software can help identify problematic elements.
6. Refine mesh iteratively: Mesh refinement should be performed iteratively until the results converge to an acceptable level of accuracy. Use solution-adaptive meshing to automatically refine the mesh in areas of high stress.
7. Consider boundary conditions: Boundary conditions should be defined before meshing to ensure that the mesh captures the correct displacement or deformation. This is important to obtain accurate results.
8. Use automatic meshing tools: Modern FEA software often comes with automatic meshing tools that can speed up the meshing process and produce high-quality meshes. These tools can also suggest suitable meshing parameters based on the geometry and material properties.
9. Keep it simple: In general, a simple mesh is better than a complex one. Simple meshes are easier to interpret and lead to faster computation times. Avoid over-meshing and unnecessary complexity.
10. Practice makes perfect: Meshing is a skill that improves with practice. Experiment with different meshing strategies and learn from your successes and failures.

Here are some additional meshing tips and tricks to follow for better quality:

1. Use a structured mesh: A structured mesh, where the mesh elements are arranged in a regular pattern, can provide better accuracy and reduce the computational cost of the simulation. This is especially true for geometrically simple models.
2. Avoid small angles: Small angles between adjacent elements can cause numerical instabilities and reduce the accuracy of the simulation. Try to avoid creating elements with angles less than 15 degrees.
3. Use high-quality elements: Higher-order elements, such as quadratic or cubic elements, can provide better accuracy than linear elements. However, these elements require more computational resources and may not be necessary for all simulations.
4. Use mesh controls: Mesh controls allow you to specify areas where the mesh should be refined or coarsened. This can help optimize the mesh quality and computational efficiency.
5. Check element aspect ratios: Aspect ratio refers to the ratio of the longest side of an element to the shortest side. High aspect ratios can lead to inaccurate results, so it's important to check and control element aspect ratios.
6. Avoid mesh interference: Mesh interference occurs when elements from different regions of the model overlap or intersect. This can cause inaccuracies in the simulation results, so it's important to avoid mesh interference.
7. Check mesh independence: Mesh independence refers to the concept that the results of a simulation should not be dependent on the mesh density. Checking for mesh independence involves performing multiple simulations with different mesh densities and comparing the results to ensure they converge.
8. Use mesh smoothing: Mesh smoothing can improve the quality of the mesh by reducing element distortion and improving aspect ratios. Many FEA software packages include mesh smoothing tools.
9. Consider the physics of the problem: The type of physics being modeled can also influence the quality of the mesh. For example, modeling fluid flow requires a different meshing strategy than modeling solid mechanics.
10. Seek expert advice: If you're new to meshing or need help with a particularly complex model, it can be helpful to seek advice from experts in the field. Many FEA software providers offer consulting services or have online communities where you can ask questions and get help.

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No. 1

The mesh and engineering judgement have a large impact on the quality of the FEA results. After all, FEA is a numerical methods approach towards the real solution. Therefore, hand calculations should always be performed to verify the results. Remember that a static FEA does not consider instability, inertial effects, fatigue, etc. 

No. 2

Meshing the entire structures is not always feasible or particle. A good engineering practice is to break up the structures into simpler elements for inspection and analysis [1]. 

No. 3

At least three mesh layers are required to capture the change in bending stress through the thickness [2]. Five is a desirable lower limit. 

No. 4

Pay special attention to the transitioning between mesh densities, since abrupt transitioning introduces errors of a numerical nature [3]. The results may be overly conservative and non-realistic. Mesh transitions should be located away from the areas of interest in a region.

No. 5

For simple elastic structures, use a coarse mesh for strength analysis and a fine mesh for fatigue analysis [4]. More complex shapes or steep stress gradients may require finer meshes. Brittle materials are defined as materials with a final strain before material rupture of less than 5% (εf < 0.05). They require a much finer mesh as the lack of ductility does not permit localized yielding. 

No. 6

For simple elastic structures, the suggested maximum element dimension is 10 times the smallest element dimension in a strength analysis [4]. Even with more complex shapes, this serves as a good starting point with further iterations of refinement from there.

No. 7

Remember to defeature you model for the mesh. The solid part may contain unnecessary details that should be omitted when you set up your FEA model. Common details to defeature include small holes, faces, engravings, faces, features, etc. 

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No. 8

Use localized mesh controls to fine-tune your mesh to adequately model the transition zones. The standard automatic mesh provides a good starting point, but should be fine-tune through iterations and should be refined at hole locations, curves, corners, etc.

No. 9

Remember to split the face to accurately model load effects, corners, areas of interest, etc. For example, in this bolt-bearing region, the entire interior face of the hole does not bear against the bolt. Rather the bearing zone from the bolt was modeled at a 25° zone and the face was split [2]. The corners and areas of concern where also split to refine the mesh density.

No. 10

Remember to fillet interior corners as sharp re-entrant corners result in stress singularities. The more you refine, the more the stress never converges to the true value. Adding a fillet removes the infinite stress, but interior fillets usually need a reasonable amount of mesh refinement [2]. Exterior corners are less important at getting accurate results. 

If the stress does converge but are still extremely high and unexpected, you may be modeling a stress peak. Stress peaks or concentrations do not significantly affect ductile failure. The effects of stress concentration are ignored since the material will yield locally at the stress-riser while the material further away from the riser remains below yield strength [5]. This is further verified by the allowance of highly localized stress that are blunted by confined yielding [6].

SOURCES

1. ANSYS FEA Best Practices
2. Finite Element Analysis Concepts via SolidWorks &#; J. Ed Akin, Rice University ()
3. DNV-RP-C208 &#; Determination of Structural Capacity by Non-linear FE analysis Methods (). pg. 16
4. API BULL 2V &#; Design of Flat Plate Structures (). pg. 19
5. Stress Concentrations and Static Failure for Common Elements used in Finite Element Analysis &#; J. Rencis, S. Terdalker, University of Arkansas ()
6. AISC 335-89 &#; Specification for Structural Steel Buildings Allowable Stress Design (). pg. 5-127       
7. When Good Engineers Deliver Bad FEA &#; Paul Kurowski, Machine Design Journal ().

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Eric Kuusisto is a registered Professional Engineer (Civil-Structural). He has worked in a wide range of structural engineering projects, from skyscrapers to transmission towers to oil & gas. Currently works for HALFEN USA as an Engineering Technical Representative. Please like and comment!

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