Shell Meshing on a Wheel Floor Panel using Hypermesh.

Project 2 Report.

• Aim: To successfully extract a mid surface and mesh the given component.
  
  
  
  
  Initial Model.
  
  
  
  
  
  
  
  
  
• Objectives: 1. To geometrically clean the model for any error on it.
  
  2. To extract a mid-surface of the component.
  
  3. To clean and defeature the Midsurface so as to avoid any minimum lenght errors while meshing.
  
  4. To mesh the midsurface while trying to minimize the number of trias and its concentration.
  
  5. Clear all elements that are failing any Quality criteria that was set.
  
  6. To assign thickness to the mesh according the component.
  
  
  
  
  
  
  • Procedure:
    
    1. To begin with the meshing process on the model, the very first step is to geometrically clean the model after we import it. There might be presence of some errors during the importing process. An added step during the geometric clean up is the process of defeaturing all the fillets that will fail for the minimum length criteria when we mesh on it. So we can either remove these kind of fillets in the parent surface or we can remove them seperately in the mid-surface.
    
    
    
    
    Geometry -> Defeature
    
    
    
    
    
    Defeature command.
    
    
    
    By this process, we can make the extraction of mid surface much more easier and the improve the mesh flow overall. After the Defeature command is done, we then need to switch to the surface view to "By Topo" to view for any free edges and then thus resolve them if necessary.
    
    
    
    2. After the Geometry clean up is performed, then we go on to extract the mid surface of the component. Since the component is more or less of an uniform thickness, we can use the Midsurface command available in the Geometry tab. In the midsurface command, we need to change the extraction option to "Skin offset" to get a much better mid-surface.
    
    
    
    Geometry -> Midsurface
    
    
    
    Midsurface command.
    
    
    
    Skin offset command.
    
    
    
    
    
    
    
    Final Mid-surface.
    
    
    
    
    After the mid-surface is extracted, then we need to proceed to clean the midsurface for anywhere we might get a minimum length error. To do this, we firstly need to measure the distance between two points on the surface where we might get an element which might fail for minimum length. To measure the distance, we need to use the Distance command under the Geometry tab (shortcut-F4).
    
    Then we select the two points and view the distance between them. If the distance is below the minimum element length then we either toggle the line or take a mid-line of the feature so that the feature is also captured.
    
    
    
    
    Geometry -> Distance.
    
    
    
    
    Distance command.
    
    
    
    To take the mid line, we need to use the Lines command under the Geometry tab. In the lines command, we will see the mid-line option. After this option is selected, we then select the two lines between which we need to extract the mid-line.
    
    
    
    
    Lines -> Mid-line
    
    
    
    To toggle any specific line, we need to use the Quick edit tab (shortcut- F11) and use the Toggle edges command.
    
    
    
    
    Quick Edit tab.
    
    
    3. Before we can strat meshing, we need to set the Quality criteria for the meshing process. To do this, we need to use the Preferences tab and use the option of Criteria File Setting. In this option, we need to fill in all the necessary Quality criteria values such as the value of minimum and maximum length or and even the value for warpage etc.
    
    
    
    Preferences -> Criteria File Setting.
    
    
    
    
    
    Quality Criteria.
    
    
    
    4. After the Quality criteria is set, we then need to proceed to mesh the midusrface. To perform meshing on the component, we need to use the command of Automesh (Shortcut-F12) under the 2D Tab. In this command we need to change the element type to "Mixed" and change the average element length to 5mm (as given in the Quality criteria)
    
    
    
    
    Automesh Command.
    
    
    Always keep the flow Align and size option ticked as it will give a much better mesh flow on the component. The basic rules while meshing are to be followed here, such as that there should be no tria element on a feature line and even to avoid the rotational Quad elements in the mesh. We also need to keep the tria count as low as possible because Tria elements are much more stiffer than Quad Elements, but Tria elements are to be given preference over the presence of Rotational Quad Elements. If we get any Fixed/Pattern Tria we simply need to remesh these regions. Or we can simply resolve the Rotational Quad elements into two seperate tria elements in two different directions or even resolve the Fixed/pattern tria elements into three different directions as well.
    
    For better mesh flow and control over the nodal number, we can divide the geometry into much smaller segments that can be meshed individually.
    
    After meshing the entire mid surface, the mid-surface should look something like the following:
    
    
    
    
    Final Meshed component.
    
    
    
    
    
    5. After the Meshing is done, the next step is to check for elements that have failed the Quality criteria set earlier. To check this, we need to see at two different places, the first one being in the 2D tab under the command of Quality check. Here we can see all the elements that are failing for any Quality criteria such as the minimum length or even the aspect ratio.
    
    
    
    
    2D -> Quality Index
    
    
    
    
    
    Model under the Quality check.
    
    
    The other place is to check for Quality check (shortcut-F10). We need to give in all the values according to the Quality criteria set. We then click on the Quality criteria individually and view the total number of elements that have failed that particular Quality criteria. All the Elements that are failing for the set Quality criteria are to be resolved before going ahead with the further steps.
    
    
    
    
    No element is failing for the set Quality criteria.
    
    
    
    
    6. Now that the model has cleared all the Quality criteria, the next step is to assign thickness to the model. The first step when assigning thickness is to measure the thickness at various spots in the model and storing them using the dimension tool under the Geometry tab.
    
    
    
    
    Geometry -> Dimesioning.
    
    
    
    
    Dimensioning command.
    
    
    This tool will save all the dimensions measured on the parent surface and will show the same dimensinos on the mid surface. This will easily help us identify the thickness at different locations on the geometry. It will only make the process of assigning the thickness much easier.
    
    After the Thickness was measured, we then need to seperate all the components according to their thickness and put them into seperate components.
    
    
    
    
    7. To create a component, we need to right click in the tree and select the Create option.
    
    
    
    
    Create -> Component.
    
    
    Like for example if two components areahving thickness as 2mm, then we need to use the organize tool and move these elements and name the component as comp_2mm.
    
    Now to assign proper thickness to the elements, we need to create properties and change the value of thickness for that property. To create a property, we again right click on the tree and select the create option and under this option we need to select the option of Property.
    
    
    
    Create -> Property
    
    
    After we create the property, we then need to change the value of thickness for this property. The value of thickness for a property is under the value of "T" under the property tab. So if the thickness of the component is 2mm, then we need to change the value of "T" to 2.
    
    
    
    Thickness assigned as 2
    
    
    After the property is created, we then need to assign this property to the component for it to reflect onto the elements. To do this, we simply need to right click on the component and select the option of assign.
    
    
    
    Assign the property.
    
    
    
    
    
    
    
    
    8. Now that the property is assigned, we can view the 3D elements with the thickness assigned by changing the view from "2D Traditional Element Representation" to "2D Traditional and Element Representation". This can be done by changing the view by the following way.
    
    
    
    
    Element Viewing tab.
    
    
    
    The final Thickened mesh will look something as the following. (only a certain part of the mesh is shown)
    
    
    
    
    
    Thickened Mesh.
    
    
    
    
    9. The final Step in the meshing process is to check for free edges on the component. To check for free edges on the component we need to use the shortcut of Shift+F3 and select the option of free edges. We then need to select all the elements and then search for Free edges on the component. If there are Free edges present in the middle of the model (except in the cases of holes), then we need to check the connectivity between the nodes and fix them by using the Equivalence command or by using the node connectivity command (shortcut-F3). This connectivity is important as it shows how the energy will flow when the model is being put under certain loads and Boundary conditions.
    
    
    
    
    Free Edges command.
    
    
    
    
    
    Free Edges on the model.
    
    
    
    
    
    
    
    
    
    
    
    
• Conclusion: In conclusion, I would like to state that, this project helped me get a better review of all the meshing steps and how to resolve a particular problem, be it Quality clearing or even Geometry Clean up.