Chloe Zhang
HyperMesh is a leading meshing software developed by Altair that is used for pre-processing and finite element analysis (FEA). It is a crucial tool for engineers who want to create high-quality meshes that enhance the accuracy of simulations. Before meshing, it is important to clean and prepare the geometry by removing unnecessary features and inconsistencies. For plastic components, it is essential to extract the mid-surface manually and perform 2D meshing according to quality parameters. This process is an important step in performing FEA and can be applied to complex 3D structural components, such as automotive plastics and sheet metal applications.
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What You'll Learn
Pre-processing
Geometry Cleanup
The first step in pre-processing is geometry cleanup, which involves refining the CAD model to ensure it is suitable for meshing. Small features and holes that are typically expected in the design phase are removed. This step may also involve manually cleaning up the surface to avoid distortion, as relying solely on the Auto-mid-surface option can lead to surface distortion in complex geometries.
Mid-Surface Extraction
The next step is to extract the mid-surface of the plastic component. This is particularly important for plastic parts with variable thicknesses, such as the car side door plastic component mentioned in the example. By extracting the mid-surface, you can then assign the appropriate thickness to the component.
Refine Topology
Refining the topology of the plastic component is crucial to achieving a high-quality mesh. This step involves understanding how topology affects the mesh and making any necessary adjustments. It includes working with the complex 3D structural components to ensure the mesh accurately represents the geometry.
Element Properties and Materials
In this step, you define the element properties and materials for the plastic component. HyperMesh offers various element formulations and material cards with different applications and failure criteria. You need to assign the thickness to the component and understand the parameters available in the property card, such as boundary conditions and loading conditions (e.g., force or constraint on the degree of freedom).
Quality Checks
Before finalizing the mesh, it is essential to perform quality checks to ensure the mesh meets the required standards. This includes understanding the significance of element quality and maintaining it throughout the geometry. Different quality parameters and criteria files need to be optimized according to the specific requirements of the project.
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Geometry clean-up
For example, in the case of a BMW M6 car model, the objective was to perform a geometry clean-up and mesh the outer surface of the car for external flow analysis. This was done in preparation for a wind tunnel test. Another example is the clean-up and 2D meshing of a clip repair mounting bracket, which involved extracting and cleaning the midsurface geometry and creating a 2D mesh with a specified target length.
The process of geometry clean-up can be done manually or with the help of tools available in HyperMesh. One such tool is the Auto-mid-surface option, which automatically generates the mid-surface of a model. However, for complex geometries, it may be necessary to manually clean up the surface to avoid distortion. This can be achieved by extracting the mid-surface and assigning thickness to the components.
It is important to note that plastic parts have variable thicknesses, which is why extracting the mid-surface and defining the thickness is a crucial step in the geometry clean-up process for plastic components.
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2D meshing
To mesh plastic components in HyperMesh, you must first understand the fundamentals of Finite Element Analysis (FEA) and the importance of pre-processors. This includes refining topology, geometry editing, and mid-surface extraction, especially when dealing with complex 3D structures.
When working with plastic parts, it is essential to consider their variable thickness. This is where 2D meshing comes into play. First, generate a mid-surface using geometry tools to clean up any distorted geometry. This step may require manual intervention to ensure an accurate surface.
For 2D meshing, you will need to create three 2D surfaces for two parts in contact (A and B). These surfaces are:
- Surface of A excluding the surface in contact with B
- The surface where A and B are in contact
- Surface of B excluding the surface in contact with A
Ensure that these three surfaces are in exact contact to create your 3D mesh.
In HyperMesh, you can also explore manual mesh generation using different meshing options. This involves understanding element quality and maintaining it throughout the geometry. Various element formulations are available for different types of elements in HyperMesh, allowing you to assign thickness to components and explore the parameters in the property card.
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Quality checks
Aspect Ratio
The aspect ratio is the ratio of the longest edge of an element to the shortest edge or the shortest distance from a corner node to the opposing edge (also known as the "minimal normalized height"). This check helps evaluate the element's shape and proportions.
Warpage
Warpage refers to the angle formed by the normals of two planes created by splitting a quad element along its diagonals. It indicates how much an element deviates from being planar. Warpage of up to five degrees is generally considered acceptable.
Skew
Skew is calculated differently for quad and triangular elements. For a quad, subtract the minimum angle between the lines joining the opposite mid-sides of the element from 90 degrees. For a triangular element, calculate the minimum angle between the lines from each node to the opposite side. Skew is an important measure of the element's orientation and distortion.
Taper Ratio
The taper ratio specifically applies to quadrilateral elements. It is determined by first finding the area of the triangle formed at each corner grid point and then comparing it to half of the quadrilateral's area. As the taper ratio approaches 0, the shape becomes more rectangular.
Jacobian Evaluation
HyperMesh CFD evaluates the Jacobian matrix at each element's integration points (Gauss points) or corner nodes, reporting the ratio between the smallest and largest values. Values of 0.7 and above are typically considered acceptable.
Minimum Element Length
The minimum element length is calculated using one of two methods. The first method is the shortest edge of the element, applicable to non-tetrahedral 3D elements. The second method is the shortest distance from a corner node to its opposing edge or face for tetrahedral elements.
It is important to note that these quality checks are not exhaustive, and there may be additional considerations depending on the specific requirements and complexity of the plastic components being meshed in HyperMesh.
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Element types
HyperMesh is a leading meshing software developed by Altair, which is used for pre-processing and making models ready for analysis. It offers a wide range of element types, each with its own applications, which are crucial to accurately represent the geometry and physics of the problem.
The element type chosen for meshing depends on the problem at hand. Tetrahedral, hexahedral, and shell elements are some of the types offered by HyperMesh. For instance, for objects in contact with each other, mesh connectivity between them is preferred. In such cases, a conforming mesh is usually used.
The quality of the elements is also of utmost importance. HyperMesh provides various mesh quality checks and tools to identify and fix problematic elements. It is important to maintain the quality of the elements throughout the geometry and take measures to achieve a good quality of elements.
For 2D meshing of plastic components, the first step is to extract the mid-surface manually, followed by performing 2D mesh as per the quality parameters. The mid-surface extraction is an important phase in performing FEA and is used to assign thickness to the components.
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Frequently asked questions
Meshing is a crucial step in the finite element analysis (FEA) process, which involves dividing a plastic component into a finite number of elements. Effective meshing is essential for accurate and reliable analysis, enhancing the accuracy of simulations.
Before meshing in HyperMesh, it is important to clean and prepare the geometry by removing unnecessary features and repairing inconsistencies. Then, you can extract the mid-surface manually and perform 2D meshing according to the quality parameters. Finally, you can use HyperMesh's mesh quality checks and tools to identify and fix any problematic elements.
It is crucial to accurately define boundary conditions and contact interfaces to capture realistic behaviour in simulations. Additionally, choose the appropriate element type, such as tetrahedral or hexahedral elements, to accurately represent the geometry and physics of the problem.
