Why is Meshing Important for Engineers?
Meshing has a significant role when it comes to the engineering simulation process. Creating a high-quality mesh is one of the most critical factors that should be considered to ensure simulation accuracy.
Creating the most appropriate mesh is the foundation of engineering simulations because the mesh influences the accuracy, convergence, and speed of the simulation. Computers cannot solve simulations on the CAD model’s actual geometry shape as the governing equations cannot be applied to an arbitrary shape.
Mesh elements allow governing equations to be solved on predictably shaped and mathematically defined volumes. Typically, the equations solved on these meshes are partial differential equations.
Due to the iterative nature of these calculations, obtaining a solution to these equations is not practical by hand, and so computational methods such as Computational Fluid Dynamics (CFD) and Finite Element Analysis (FEA) are employed.
What are the Different Types of Meshing?
Ansys Meshing Solutions
Creating the most appropriate mesh is the foundation of engineering simulations. Ansys Meshing appropriately adapts to the type of solutions that will be used. Defining the project and setting respective criteria to create the best suited mesh is critical.
For a quick analysis or for the new and infrequent user, a usable mesh can be created in a few short steps. Where possible, Ansys Meshing automatically takes advantage of the available cores in the PC. Utilizing parallel processing via Finite Element Analysis (FEA), and significantly reducing the time to create a mesh.
CONSIDERATIONS FOR MESHING STRUCTURAL MODELS
FEA Meshing of structural models in Ansys Mechanical is all about balancing accuracy versus computational expense. Typically, finer meshes with smaller elements produce more accurate results. However, finer meshes take longer to solve.
However, there is a point where the mesh is refined enough to accurately capture the results. In effect, making additional computational expense unnecessary. This level of refinement is usually problem dependent. In addition, requiring both experience and engineering judgement to determine.
As a general guide, the considerations listed below will help you to create an accurate and efficient mesh in a structural analysis of your own.
BEST PRACTICES WHEN CREATING FEA MESHING
1. Mesh Density
Generally, in a Finite Element Analysis (FEA), a finer mesh produces more accurate results. The smaller elements in a finer mesh can more accurately capture stress gradients across the element.
However, adding more elements to a Finite Element Model adds computational expense in two ways:
- More elements mean that more equations need to be solve at each time step, increasing both solution time and memory requirements.
- The results files from these analyses take more disk space to store.
Of course, managers and engineers alike would like to avoid this unnecessary expense. Consequently, users can restrict areas of high mesh density to areas of interest in their analysis. This is usually confined to areas in the load path of the model, where there is a significant stress level.
FEA Meshing | Unique Geometric Features
Other geometric features, such as fillet radii, may be deployed. This pre-set is often used for large stress concentrations requiring a dense mesh to be able to accurately predict stress. Areas away from the load path or stress concentrations can be meshed with larger elements.
Generally, these areas have insignificant stress levels and can be accurately modelled with large elements.
Ansys Mechanical offers a wide array of tools to help you control your mesh density. There are global mesh controls that control the mesh size. This setting may be established for the entire model as well as local size controls, allowing refinement in areas of interest.
- Check out this webinar on FEA meshing.
2. Convergence and Stress Singularities
To identify the level of mesh density that provides accurate results, we must first understand convergence. When a result has converged, further mesh refinements in that area will no longer produce a meaningful change in that result. With experience, engineers can determine when they have a sufficiently dense mesh to achieve convergence.
Ansys Mechanical also includes a built-in tool that aids in identifying convergence. Ansys Mechanical will first solve the model with the mesh generated by the user.
Then, the mesh will be refined in locations with high stress. Ansys Mechanical repeats this process until the change in results between each solution reaches a sufficiently low value. Or, based on custom user input, a specified number of solutions is achieved.
The images below show this tool in action. One image summarizes each solution. In effect, demonstrating the number of nodes and elements in the mesh. This pertains to each solution as well as the change in stress in each solution.
In this example, engineers will observe the change in stress growing smaller and smaller with each mesh refinement, converging on a result.
It is also important to note that a result may not necessarily be able to achieve convergence.
In the case of stress, we refer to this as a stress singularity. These singularities are artificial “hot spots” of stresses that are usually due to modelling assumptions or simplifications. Stress singularities can be caused by geometric features such as sharp corners or edges.
Stress can be thought of as the amount of force transferred through a specific area. In these geometric features, as the element size decreases, the “area” approaches zero, causing the stress to diverge to an infinite value.
Another common source of stress singularities occurs at regions where there is a discontinuity in stiffness in the model. These regions can include things like the boundary where two bodies are in contact or the boundaries of a support.
It is important for a user to be able to identify which areas of stress are artificial stress singularities and which areas are real and need a sufficient mesh to be able to capture the results properly.
In the example below, the convergence tool was used in a location with a stress singularity. In this case, refining the mesh does not result in smaller change in stress at each solution; it increases the change.
If we continued to refine the mesh in this location, the stress would never converge on a value. Instead, it would diverge, approaching an infinite value.
3. Element Shape and Quality
There are two main element shapes used in structural analysis in Ansys Mechanical, hexahedral (hex) or tetrahedral (tet) elements. Other element shapes such as pyramid or wedge-shaped elements also exist, mainly as transitional elements between tet and hex elements.
The ideal element shape for an analysis is usually determined by the geometry that is being represented in the analysis. In general, it is easier to use tet elements than hex elements on highly complex geometry.
To be able to use a hex mesh on complex geometry, the geometry must be divided up into small, more easily meshed sections. This can greatly increase the amount of time spent on an analysis.
However, there is also a trade off in efficiency for tet element. More tet elements need to be used to represent the same geometry than hex elements. It is up to the user to best judge which element shape will be best for an analysis.
Meshing Considerations | Quality of Shape Elements
The quality of the shape of elements used in a structural analysis is also an important consideration. Elements with a distorted or skewed shape can produce inaccurate results. Ansys Mechanical includes many different mesh quality criteria that allows the user to check the shape of element.
These quality criteria include element quality, aspect ratio, Jacobian ratio and more . The user can plot each of these mesh quality criteria on their mesh to be able to identify elements of poor quality.
BEST PRACTICES FOR SIMULATING FLUID MODELS
1. Using Geometry Wrapping to Create Watertight Fluid Models
The geometries that design engineers send to analysis engineers are rarely clean enough to import into a fluids modeling program. Fixing these gaps and leaks in the geometry can traditionally take hours, even days.
Therefore, you (as the analysis engineer) should use a CFD software that can wrap a surface mesh around discontinuous geometry.
This automated meshing capability will quickly fill in all the gaps, leaving more time for simulation and results analysis.
2.Combining Overlapping Geometry to Quickly Create a Flow Boundary
When performing a fluid analysis, an inverse fluid volume needs to be created. Generating a fluid volume is achieved by wrapping a box around watertight geometry and combining all the overlapping faces between the solids into one face.
This resolves the intersections between the box and source geometry. The volume can then be extracted and imported into a fluids model.
Employing the “share topology” function creates the requisite flow geometry using Ansys SpaceClaim. With Fluent’s “surface mesh” operation, extracting the flow volume from the void between the boundaries in the geometry is achieved. Follow the corresponding link for more on Operation Engineering.
3.CONFORMALLY CONNECT MESHES TOGETHER TO AVOID GAPS
Reducing computational times is achieved by creating fluids models with coarse meshes for large areas and finer meshes for more detailed geometries.
The challenge then becomes linking these disparate meshes into a continuous mesh or sacrificing accuracy by creating non-conformal (mismatching) mesh interfaces.
Conformally linking meshes is a tedious job. It typically requires cleaning up the geometry and manually correcting the meshes so everything fits nicely together.
How do you Leverage Different Meshing Approaches and Element Types in a Single Mesh?
The concept of subdividing a geometry into multiple meshed bodies to leverage strengths of different meshing approaches has existed for a long time. The process of connecting different meshes (whether conformal or not) had varying levels of automation available to the user.
Past approaches, even when automated, were often limited to element type variation on a global level. This resulted in conformal and non-conformal connections between large separately meshed regions.
Additionally, recent Ansys updates to Fluent Meshing take the concept of “The right mesh for the right” job to the next level by introducing Mosaic Meshing.
Ansys Fluent’s Mosaic-enabled meshing technology can automatically generate different mesh and element types in different localized or global regions and link these grids conformally.
This approach currently results in a poly-hexcore mesh leveraging the following element types as needed:
- Hexcore (Hex Elements with Cut-Cell Refinement)
- Polyhedral Elements
- Wall Inflation (Inflated Poly and Prisms)
It automatically blends between these element types to give you a mesh which is optimized for accuracy and meshing speed. The resulting mesh will have an inflated boundary layer near the walls and a hexahedral core in the fluid free stream.
Ansys Meshing & Boundary Layers | Near Wall & Free Stream
The two regions (near wall and free stream) will then be blended with a layer of polyhedra. This novel approach means a user is be able to quickly obtain a highly robust, high quality mesh optimized for accurate and stable solutions.
Detailed Meshing | 3D CAD Models in Ansys
Finally, the more detailed a mesh is, the more accurate the 3D CAD model will be, allowing for high fidelity simulations.
- Learn more about Structural Meshing
- Learn more about Fluid Meshing
For more information about Ansys Software, FEA Meshing, Stress Singularity, or general inquiries on Fluids Engineering, contact us.
What is the importance of meshing in FEA? ›
Meshing is one of the most important steps in performing an accurate simulation using FEA. A mesh is made up of elements which contain nodes (coordinate locations in space that can vary by element type) that represent the shape of the geometry.Why is meshing important in CFD? ›
Meshing is important because it allows designers and engineers to create predictive models of real-world situations computationally—the more accurate the mesh, the more performant the simulation will be. Both FEA and CFD are mathematical methods that rely on high-quality meshing.What is the use of meshing in Ansys? ›
Ansys meshing capabilities help reduce the amount of time and effort spent to get to accurate results. Since meshing typically consumes a significant portion of the time it takes to get simulation results, Ansys helps by making better and more automated meshing tools.What are the advantages of structured meshing? ›
Structured meshes offer simplicity and efficiency. A structured mesh requires significantly less memory — say a factor of three less — than an unstructured mesh with the same number of elements, because array storage can define neighbor connectivity implicitly.What is mesh analysis and when is it effective to use? ›
Mesh analysis (or the mesh current method) is a method that is used to solve planar circuits for the currents (and indirectly the voltages) at any place in the electrical circuit. Planar circuits are circuits that can be drawn on a plane surface with no wires crossing each other.How can you tell if mesh is Ansys good? ›
A good rule of thumb is that the maximum skewness for tetrahedral cells should less be than 0.95. The maximum cell squish index for all types of cells should be less than 0.99. Cell size change and face warp are additional quality measure that could affect stability and accuracy.What is the role of a mesh? ›
Meshing is a technique used for software-based simulation for Finite Element Analysis (FEA) and Computational Fluid Dynamics (CFD). It is a very important process as the size and shape of the mesh directly impacts the accuracy of the solution.How does mesh size affect FEA? ›
In Finite Element Analysis the accuracy of the result obtained is determined by size of the mesh. According to the theory of Finite Element Analysis, finite modal with small element size yields high accuracy as compared to the modal with large element size.What is structured mesh in CFD? ›
Structured meshes are meshes with implicit connectivity whose structure allows for easy identification of elements and nodes. Often structured meshes have orthogonal quadrilateral (2D) or hexahedral (3D) elements.What are the different meshing techniques used in FEA? ›
- Tetrahedral - tetrahedral cell shape based core mesh.
- Polyhedral - polyhedral cell shape based core mesh.
- Trimmed - trimmed hexahedral cell shape based core mesh.
What types of meshes that are commonly encountered in CFD? ›
Most popular 3D mesh elements are hexahedra (also known as hexes or hex elements), tetrahedra (tets), square pyramids (pyramids) and extruded triangles (wedges or triangular prisms), shown below.Which meshing type gives more accurate solution? ›
Quadratic order meshing might be more accurate than linear order meshing. Checking Orthogonal quality of elements (higher the better) and skewness of elements is necessary before proceeding for solution iterations.What is the difference between structured and unstructured mesh CFD? ›
Typically a structured mesh is comprised of hex (brick)elements (quads in 2D) that follow a unifrom pattern. An unstructured mesh does not follow a unifrom pattern, usually comprised of tet elements (tris in 2D).What type of meshing gives accurate results? ›
Mesh density is a significant metric used to control accuracy (element type and shape also affect accuracy). Assuming no singularities are present, a high-density mesh will produce results with high accuracy.What are the benefits of mesh analysis? ›
The primary advantage of mesh current analysis is that it generally allows for the solution of a large network with fewer unknown values and fewer simultaneous equations. In our example circuit, it requires three equations to solve the branch current method and only two equations using the mesh current method.What is mesh analysis generally used to determine? ›
Explanation: Kirchhoff's Voltage Law is used in mesh analysis to find all the mesh currents. Hence, a mesh analysis method is used to determine the current.What is the basic concept of mesh analysis? ›
What is Mesh Analysis? The method in which the current flowing through a planar circuit is calculated. A planar circuit is defined as the circuits that are drawn on the plane surface in which there are no wires crossing each other. Therefore, a mesh analysis can also be known as loop analysis or mesh-current method.How to improve mesh quality in Ansys? ›
- Reduce the 'Number of layers': Use at least 1 layer. ...
- Increase the 'Overall relative thickness': Keep the range between 10-60%. ...
- Reduce the 'Growth rate': Keep the range between 1.1-1.5.
If the accuracy is of the highest concern then hexahedral mesh is the most preferable one.What is a good meshing? ›
Meshes that are “good enough” are ones that produce results with an acceptable level of accuracy, assuming that all other inputs to the model are accurate. Mesh density is a significant metric used to control accuracy (element type and shape also affect accuracy).
Is a mesh system necessary? ›
The mesh outlay of a whole home Wi-Fi system is also ideal for spaces with multiple floors. Regular routers, even with extenders, may struggle to cover such spaces. Therefore, you may need a mesh Wi-Fi network if you live in a mid-sized, large, or multi-story home.What are the advantages and disadvantages of mesh? ›
|Almost impossible to take down||Complex structure|
|Easy to add new devices||Difficult to set up initially|
|Scalability is simple||Costly compared to others|
|Adding new devices does not affect the network||the risk of redundant connections|
The Mesh Sizing can be used to set the following:
The element size for a selected body, face, or edge. The number of divisions along an edge. The scale factor for a selected body, face, or edge.
As mesh size decreases, the maximum principal stress values converge toward the calculated value. Also worth noting is that hexahedral elements are generally not the most appropriate elements to use in simulations involving bending since they are prone to shear locking.How do I choose mesh size in FEA? ›
- Perform chosen analysis for several different mesh sizes.
- Notice where high deformations or high stresses occur, perhaps it is worth to refine mesh in those regions.
- Collect data from analysis of each mesh: outcome, number of nodes in the model, computing time.
Unstructured Meshing of Control Volumes
Unstructured grids have the advantage of generality in that they can be made to conform to nearly any desired geometry.
The difference between mesh and nodal analysis is that nodal analysis is an application of Kirchhoff's current law, which is used for calculating the voltages at each node in an equation. While mesh analysis is an application of Kirchhoff's voltage law which is used for calculating the current.Why do we mesh in HyperMesh? ›
Meshing is a process that helps create proper elements that are computable out of irregular 3D shapes. It breaks down complex structures into shapes, such as polygons and polyhedral. Meshing is done on a CAD model using computer software.