Project 2 [ Floor Panel ] Hypermesh

OBJECTIVE

To perform 2D shell mesh on the the Floor panel of car by following below quality criteria:

MODEL

FIG:1

FIG:2

THEORY

A structural shear panel for forming a floor panel for support by a vehicle frame is formed by a composite of top and bottom sheets and a core with a vacuum infused resin. The core is formed of top and bottom layers each formed from a honeycomb panel defining an array of hexagonal tubular cells with walls which extend in the thickness direction filled with a foam material. A third layer is located between the first and second layers and is formed of a material such as foam, rubber or cork which is free from tubular cells in the thickness direction and free from rigid structural members in the thickness direction to reduce communication of sound through the panel.

METHODOLOGY

 i. Open the file in Hypermesh from the file source folder in the system 

 ii. After importing the model perfrom Topology repair on the model. It consist of correcting connectivity error between adjacent surfaces. Possible errors include :

• Unconnected adjacent surfaces
• Duplicate surfaces
• Missing surfaces

   The goal of topology repair is to restore the surface data to a perfectly clean representation of the parts.

 iii. In this given model some areas are having some surface issues, it is sloved by Geom-> Quick edit. If the surface is having deformations can be solved by using Quick edit option which is located in Geom option. In quick edit option use the commands Replace the points and Toggle option used to remove this deformations.

FIG:3 [Topology Error in the surface]

 iv. The above error is solved by quick edit option

FIG:4 [Surface is reworked]

 v. Similar surface problems are shown Below, all the below issues are solved using Quick edit panel commands

FIG: 5

FIG:6

 vi.  In the given model free edge is denoted as Red colour, in this it is associated with only 1 surface. For shared edge it is denoted by Green colour, here it is associated with 2 surface and for T junction edges is denoted by yellow colour. In here it is associated with 3 or more surfaces.

 vii.After solving all the Topology cleanup on the parent surface go with extracting the Mid Surface of the model, so a better Mid surface will be getting. By this we can save time working on the Mid surface. Eventhough if we worked on the parent body there will be some small cleanup need to be done on the Mid surface.

 viii. As the model is a sheet metal, the model is having uniform thickness. So for extracting the mid surface go with Auto mid surface. In Automid surface command panel select the offset command from Extract option. In Offset command it create pieces of the middle surface by offsetting the model's side surfaces towards the middle

FIG:7 [Auto Mid surface command Panel]

 ix. In auto extraction option select the full model and performed Auto Mid surface option, here the thickness value is 0.75mm

 x. After extracting the Mid surface, Check for any Ribs in the model. In this model no Ribs are there to be extracted so extension of any ribs to the surface is not there.

 xi. Defeature the Mid surface for Minimum length areas, inorder to capture the area without failing for quality values.

FIG:8 [Mid Surface]

 xii. Next main step is to generate 2D mesh elements on the Mid surface.

 xiii. During meshing somes things need to care about:

1. The tria elements should never be opposite each other.
2. No tria elements should be connected back to back.
3. No tria elements should be in the edge of the geometry.
4. No tria elements should be near the hole
5. No tria elements should be on the feature and fillet areas.
6. There should be less tria concentration    

 xiv. This steps allowed to have good mesh for analysis in the slover deck inorder to get better results.

 xv. Before starting to do the meshing input the quality criteria values 

FIG:9 [Quality criteria panel]

 xvi. Before start with the meshing some details of quality criterias:

1. Warp angle (Warpage): It is not applicable for triangular elements. It is a way to measure how far is a Quad element being planar
2. Aspect Ratio : Maximum element edge length / Minimum element edge length
3. Skewness ( Ideal value = 45 degree) : Skew for quad= 90 deg - Min angle between 2 lines joining opposite mid side and Skew for Tria element= 90 deg - Min angle between the lines from each node to the opposing mid side and between 2 adjacent mid sides at each node of the element. 

 xvii. Meshing is carry out inorder to have finite element method to reduce Degree of freedom from infinite to finite with the help of discretization 

 xviii. Mesh can be generated by 2D-> Automesh-> Select the surface-> Mesh

FIG:10 [Automesh panel]

FIG:11 

 xix. As the meshing is completed look for quality issues in the quality index, 2D-> Quality Index

 xx. In quality index it consist of all the cleanup tools for clearing the quality issues in meshing

FIG:12 [Cleanup tools]

 xxi. Tool details:

a. Place node tool: Choose which direction to node move

FIG:13

  b. Swap edge tool: Use the Swap Edge tool to consider the elements to which the edge belongs, and find alternative orientations for it. Each time you click an edge, it switches to the next valid configuration. If an edge swap will not improve element quality, a message to that effect displays in the status bar. To force the swap anyways, click the edge a second time. Additional clicks will cycle through the possible edge positions. The number of possible edge positions depends on the types of elements involved.

FIG:14

  c. Node optimize tool: se the Node Optimize tool to automatically move a selected node to optimize the overall quality of its surrounding elements. The options along surface, normal to surface, and along and normal to surface work exactly as described for the place node tool. The only difference is that node optimize moves the node automatically, while place node requires you to choose the location manually.

FIG:15

  d. Element optimize tool: Use the Element Optimize tool to automatically optimize the shape of the selected element and the elements surrounding it. It is similar to Node Optimize, except that its effects are wider-spread.

FIG:16

  e. Smooth tool: Use the Smooth cleanup tool to improve element quality in a surface-based mesh. This cleanup tool uses one or more algorithms to adjust node positions to moderate sharp variations in size or quality in adjacent elements, and to adjust the position of the free nodes of the selected shell elements to smooth out variations in element quality and size.

  f. Split/Collapse edge tool: Use the split/collapse edge cleanup tool to split or collapse the edges of elements in your model.

FIG:17

  g. Drag Tria elements: Use the drag tria element cleanup tool to drag a tria element to a different location in the model, or out of the model completely. To use the drag tria element cleanup tool, left-click on a tria element and drag it to a desired location. HyperMesh highlights the selected tria element in pink.

FIG:18

  h. Split Quad element tool: Use the split quad element cleanup tool to split a quad element into two tria elements.

FIG:19

  i. Combine Tria elements tool: Use the combine tria elements cleanup tool to combine two tria elements into one quad element.

FIG:20

 xxii.In this model all this tools are used at a time inorder to achieve a good mesh flow. For converging areas in the model, trias can allowed to come 

 xxiii. Some of the areas will have Warpage issues. Inorder to clear this issue try with the Translate command. 2D-> Translate select the nodes which is going downwards in comparison with other nodes. And select the plane N1 and N2 and give tolerance value to be 0.01 , 0.02 as minimal value and 0.05 , 1 for large . By doing this command warpage can be cleared, here it is trying to distribute the  angle values to the adjacent quads and trias.

 xiv. In this model some areas are similar in both sides, so to save time in meshing go with the option position. Changing position is accomplished by picking six nodes that define a transformation for the selected entities. Three nodes represent the entities' starting position, and three corresponding nodes define the selected entities' ending position. 

FIG:21 [Select the elements that need to be positioned on the other side]

xxv. Select the nodes from both sides, with respect to the nodes only the elements will place in the correct place.

FIG:22 [Nodes are selected on both sides]

 xxvi. By clicking position all the elements will move to other side. Before selecting the nodes duplicate the elements so that the orginal elements will be in their respective position.

FIG:23 [All elements are positiones to other side]

xxvii. After performing this all the elements need to be projected to the boundary line of the elements. This is carry out using Project command.

FIG:24 [All the elements are projected to the outer boudary]

 xxviii. Using Translation and Cleanup tools will clear the Quality issues in the whole model.

FIG: 25 [Full body mesh is generated on the whole model]

 xxix. Assign the thickness for the Mid surface. Here the thickness is 0.75mm. To assign the thickness create Property in the tree structure and in the property panel input the thickness value.

FIG: 26 [Thickness value assigned in the property]

 xxx. Assign the property for the mid surface.

FIG: 27 [Property assigned]

 xxxi. Last step is to setup the Normals for the surface, for that Normals command is present in tool panel. 

FIG:28 [When checking the normals]

xxxii. After this all the blue region need to changed to Red area. So select the elements and display the normal colour and just reverse the colour to Red.

FIG: 29 [Select the elements]

FIG:30 [ Display the elements]

FIG:31 [Reverse the display elements to RED]

RESULT

2D mesh is generated on the Floor panel of the car

FIG:32