Engineering Technique Follow. Design Efficiency Improvement Through Collaboration. Related Books Free with a 30 day trial from Scribd. Uncommon Carriers John McPhee. The Art of War Sun Tsu. Related Audiobooks Free with a 30 day trial from Scribd. Elizabeth Howell. Views Total views. Actions Shares. No notes for slide. The basic idea of FEA is to make calculations at only limited Finite number of points and then interpolate the results for the entire domain surface or volume.
Finite Element Method reduces the degrees of freedom from infinite to finite with the help of discretization or meshing nodes and elements. You need these elements to be able to apply Finite Element since Finite Element is all about having a basis local to an Element and stitching a bunch of local solutions together to build the global one. If you did not mesh and just assumed some basis that covered the whole domain that would be a Spectral Method.
One other aspect of meshing is the accuracy of your solution. Due to these contributors to accuracy, it's important to be careful about how you implement your mesh to ensure angles within elements are larger smaller angles hurts accuracy and that you get it sufficiently refined to get the accuracy you wish.
Solid Mesh 3D Element : The program creates a solid mesh with tetrahedral 3D solid elements for all solid components. However, adding more elements to a Finite Element Model adds computational expense in two ways:.
To avoid this unnecessary expense, 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. Other geometric features, such as fillet radii, that have large stress concentrations also require 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 in the entire model as well as local size controls that allow refinement in areas of interest. Check out this webinar on FEA meshing. 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 a specified number of solutions is achieved. The images below show this tool in action.
One image summarizes each solution; it shows the number of nodes and elements in the mesh for each solution as well as the change in stress in each solution.
In this example, you can see 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. 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.
Another common source of stress singularities occurs at regions where there is a discontinuity in stiffness in the model. For the hex-parametric meshing method, maintaining an overall grid size that keeps the skewness ratio low is a simple but effective way to increase the accuracy.
This can be done by first selecting the intended cell size via literature or referenced works before the domain distance is calculated and divided by the number of cells. For example, if the user requires a cell size of 0. This tip ties into the balance between computational cost and mesh fineness. Say you have a specific general cell size to maintain, but you require additional accuracy near critical parts that, if adjusted through overall cell size, would be much too computationally expensive to simulate.
A way to get around this would be to designate the area at or around the critical part with a higher refinement in that particular region. This effectively decreases the cell size of only the target area but does not increase the computational cost dramatically.
This method can be applied to further increase the accuracy of the simulations that have not opted to do so and is often used in applications like wake prediction or vortex generation. To perform this with SimScale, a geometrical box needs to be created first and then a region refinement applied to that geometrical box. Boundary layer refinement or inflation is a critical meshing parameter that is sometimes overlooked by those who are new to CFD online simulations.
The final tip concerns optimizing and determining the ideal mesh to be used for further simulations. A mesh convergence study dictates that a general mesh is created for the problem case, a simulation is run, and the results are obtained. Afterward, the process is repeated with a continuous increase in mesh fineness. Once the results have deviated within the required criteria, the coarsest mesh produced that is still within the criteria is deemed the base mesh and, as such, the results obtained are then as accurate as possible for the given mesh.
A proper mesh convergence study will not only ensure that your mesh is as accurate as possible, but that is also optimal. This means you are balancing computational time with accuracy, which is crucial when it comes to large and complex meshes. This not only leads to better convergence, but also more accurate results from your simulations. While this article does not cover all the criteria that need to be considered for a highly qualitative and accurate mesh, I hope it helped you gain some valuable insight into such a critical part of the simulation.
Piqued your interest? With the smallest wavelength calculated, more elements per wavelength nepw can be used to increase accuracy; however, this will increase model size. For example, in 3D models, doubling the number of elements per wavelength will multiply the model size by a factor of eight as there are double the number of elements along all three axes of the structured grid.
Accuracy is subjective and it is up to the user to determine what is required to obtain the best solution. At a minimum, we recommend starting at 15 elements per wavelength, but all users should perform mesh convergence studies to understand how meshing affects their results. As part of our engineering team Chloe assists with developing applications, improving our existing software and providing technical support to our customers.
By accepting our cookies, you consent to the use of cookies in accordance with our Cookies Policy. Accept Learn more. Log in. Simulate Now. Log in Simulate Now. By Chloe Allison 18 March
0コメント