Achieving Mesh Perfection: Quality Checks in SALOME 9.14.0
In the world of Computational Fluid Dynamics (CFD) and Finite Element Analysis (FEA), the quality of your mesh is paramount. A poorly constructed mesh can lead to inaccurate results, convergence issues, and wasted computational resources. Fortunately, powerful meshing tools like SALOME provide robust quality control features to ensure your simulations are built on a solid foundation.
This post delves into the essential mesh quality checks available in SALOME version 9.14.0, with a particular focus on Scaled Jacobian, Skewness, and Aspect Ratio. We’ll also touch upon how you can leverage these capabilities on cloudHPC instances, as demonstrated in their tutorial.
Why Mesh Quality Matters
Think of your mesh as the discretization of your physical domain. Each element in the mesh represents a small piece of the whole, and the accuracy of your simulation heavily depends on how well these elements represent the underlying physics. Poorly shaped elements can introduce numerical errors, leading to:
- Inaccurate Results: Solutions may not converge or might be significantly off from reality.
- Solver Instability: Many solvers struggle or fail to converge with low-quality meshes.
- Increased Computation Time: The solver might take longer to achieve a solution, or it might not find one at all.
- Difficulty in Post-processing: Visualizing and interpreting results from a compromised mesh can be challenging.
Key Mesh Quality Metrics in SALOME 9.14.0
SALOME 9.14.0 offers a suite of tools to analyze and improve mesh quality. Let’s highlight some critical metrics:
1. Scaled Jacobian: The Cornerstone of Tetrahedral Quality
The Scaled Jacobian is a crucial quality indicator, especially for tetrahedral meshes. It measures the deviation of an element from an ideal, regular tetrahedron.
- What it measures: For a tetrahedral element, the Scaled Jacobian is defined as the ratio of the determinant of the Jacobian matrix at the element’s center to the determinant of the Jacobian matrix of an ideal tetrahedron with the same volume.
- The Limit for Tetrahedral Meshes: A commonly accepted threshold for a good Scaled Jacobian in tetrahedral meshes is 0.75. Values below this can indicate highly distorted or “collapsed” elements, which can severely impact simulation accuracy and convergence.
- How SALOME helps: SALOME allows you to define minimum limits for Scaled Jacobian, flagging any elements that fall below your specified threshold. This helps you identify and rectify problematic elements during the meshing process.
2. Skewness: Minimizing Angular Distortions
Skewness quantifies how much an element deviates from being “regular” in terms of its angles. High skewness can lead to numerical diffusion and inaccuracy.
- What it measures: Skewness is typically defined based on the angles within an element, comparing them to the angles of an equilateral or equiangular element.
- The Limit for Surfaces: For surface meshes, a common guideline for acceptable skewness is below 40. Higher values suggest elements that are too “stretched” or have sharp angles, which can be detrimental, especially in boundary layer meshing.
- How SALOME helps: SALOME allows you to set limits for skewness on your mesh groups. This is particularly useful for identifying problematic elements on boundaries or in regions where high gradients are expected.
3. Aspect Ratio: Balancing Element Dimensions
The Aspect Ratio of an element is the ratio of its longest dimension to its shortest dimension. While not as universally critical as Scaled Jacobian or Skewness, a very high aspect ratio can still pose problems.
- What it measures: It indicates how “stretched” or “compressed” an element is.
- Suggested Limit: While there isn’t a strict universal limit, a suggested aspect ratio below 4.5 is often recommended for good quality meshes. For certain types of elements or specific simulation needs, higher aspect ratios might be tolerable, but it’s generally best to keep them within reasonable bounds.
- How SALOME helps: You can set criteria for the maximum aspect ratio to ensure your elements are not excessively elongated, promoting better numerical behavior.
Leveraging SALOME on CloudHPC Instances
The ability to run complex meshing operations on powerful cloud infrastructure is a significant advantage. As highlighted by the cloudHPC tutorial, you can seamlessly utilize SALOME 9.14.0 on static instances. This means you can:
- Access Pre-configured Environments: Launch a static instance with SALOME 9.14.0 pre-installed.
- Upload Your Geometry: Transfer your CAD models to the cloud instance.
- Perform Meshing and Quality Checks: Utilize SALOME’s powerful meshing algorithms and quality control tools within the cloud environment.
- Leverage More Resources: Benefit from increased CPU and RAM capacity for handling large and complex meshes.
- Save and Download Results: Store your meshed geometry and results on the cloud storage for later use or download them to your local machine.
The tutorial demonstrates how to create a new simulation on cloudHPC, select the appropriate SALOME version (e.g., SALOME 9.8.0 as seen in the demo, but 9.14.0 would follow a similar process), choose your resources (vCPU, RAM), specify a folder, and select the meshing script. This workflow allows for efficient and scalable meshing without needing powerful local hardware.
Implementing Quality Checks in SALOME
Within SALOME’s SMESH module, you can access and apply these quality controls through the mesh object’s properties. You typically:
- Create a Mesh: Generate your mesh using your preferred algorithms.
- Compute Quality: Right-click on the mesh in the study tree and select “Compute Quality”.
- Set Criteria: Access the “Mesh” properties and navigate to the “Quality” tab. Here, you can define minimum values for “Scaled Jacobian” and “Skewness,” and maximum values for “Aspect Ratio.”
- Visualize Issues: SALOME will then color-code the elements based on these criteria, making it easy to identify problematic areas. You can further refine these settings and re-compute the quality until your mesh meets your desired standards.
Conclusion
Mastering mesh quality is a critical skill for any simulation engineer. SALOME 9.14.0 provides the essential tools to achieve this, with robust metrics like Scaled Jacobian, Skewness, and Aspect Ratio to guide your meshing process. By understanding these metrics and utilizing powerful platforms like cloudHPC, you can ensure the reliability and accuracy of your CFD and FEA simulations, leading to more trustworthy results and efficient workflows.
Remember to always check your mesh quality thoroughly before proceeding with your simulations – it’s an investment that pays dividends in accuracy and stability.
CloudHPC is a HPC provider to run engineering simulations on the cloud. CloudHPC provides from 1 to 224 vCPUs for each process in several configuration of HPC infrastructure - both multi-thread and multi-core. Current software ranges includes several CAE, CFD, FEA, FEM software among which OpenFOAM, FDS, Blender and several others.
New users benefit of a FREE trial of 300 vCPU/Hours to be used on the platform in order to test the platform, all each features and verify if it is suitable for their needs
