Week 12 - Project-1 - Shell Meshing Of Car Side Door Panel
Shell Meshing Of Car Side Door Panel
Aim: To create the shell (2-D) meshing for the Car Side Door Panel by eliminating geometrical errors and considering the given element quality criteria using Hypermesh
Introduction:
1.Car Side Door Panel
The side door panel is the plastic part. materials used for the door panel is acrylonitrile-butadiene-styrene (ABS), ABS/polycarbonate alloys,Polypropylene (PP).
Properties
1. High weathering resistance
2. High strength and toughness up to 140°C
3. Very good heat resistance
4. good processing characteristics
5. Remail flexible down to -150°C
6. High rigidity
7. Good impact resistance
In the fig0.2 Shows the example for the side door panel.
Fig.0.1: Side Door Panel
2. Finite Element Analysis
The finite element method is a numerical technique for obtaining an approximate solution to a wide variety of engineering problems. FEA (Finite Element Analysis) is done by three phases.
1. Pre-processing
2. Solution
3. post-Processing
This project comes under Pre-processing. The goals of Pre-processing are to develop an appropriate finite element mesh, assign suitable material ID and boundary conditions. ANSA And Hyper-mesh are the example tools and in this project Hypermesh is used. Hypermesh interface is shown in the fig 0.2.
Fig.0.2: Hypermesh Interface.
Types of the elements
1. One-dimensional elements: These elements are suitable for one-dimensional problems such as bar, truss and beams.
Example- Linear elements have 2 nodes etc.
2. Two-dimensional elements:These elements are suitable for Two-dimensional problems such as plane stress and plane strain in sheet metal parts up to thickness of 5mm.
Example- Tria Elements, Quad elements,
2. Three-dimensional elements:These elements are suitable for three-dimensional analysis. uses for solid parts and sheets of thickness more than 5mm..
Example- Tetra elements and hexa elements.
Above all types of elements are done under user defined Quality criteria. for example refer table1.1.
Element Quality Criteria:
| S.No | Quality Criteria | Value |
| 1 | Target/Average length | 5 |
| 2 | Minimum Length | 2 |
| 3 | Maximum Length | 6 |
| 4 | Aspect | 5 |
| 5 | Warpage | 15 |
| 6 | Skewness | 45 |
| 7 | Minimum Quad Angle | 45 |
| 8 | Maximum Quad Angle | 135 |
| 9 | Minimum Tria Angle | 20 |
| 10 | Maximum Tria Angle | 120 |
| 11 | Tria Percentage | 10 |
| 12 | Taper | 0.5 |
Table1.1: Element Quality Criteria
Procedure:
The meshing is done by following steps
1. Import side_door_panel.hm in to Hypermesh
2. CAD Geometry clean up and topology
3. Mid-surface extraction
4. Defeaturing
5. Shell meshing
6. Creating properties and Thickness assigning.
1. Import Side_door.hm in to Hypermesh :file>open>model, browse the file and open. in the figure 1.1 shows the model.
Fig.1.1: Imported file.
From the imported file we can see so many features such as Ribs, Locators etc. So that this component has different thickness on each feature.
2. CAD Geometry clean up and topology: In this step the given model undergoes geometry check. Where all the defects such as collapsed faces, cracks, free edges, T-edges are clear. In the fig.2.1 show description on surface.
Fig.2.1: Description on surface.
Tools used in topology
Tools>Edge Edit Panel
A. Equivalence (multiple edges at a time) Search surfaces for pairs of free edges and combine into shared edges
B. Toggle (edge pair at a time) Select an edge; equivalences with other free edges found within a user specified tolerance
C. Replace (1 edge pair at a time) Select 2 edges to equivalence together. Control which edge to retain and which to move.
D. Geom>Surfaces>Ruled or Geom> Quick edit > filler surface or 2d> spline> surfaces only (to create missing surfaces).
In the given model there are so many defects. fillets which are very small and should be defeated. In the fig. 2.2 shows some defects.
Fig.2.2: Defects
Defeature all small fillets by using
steps
a. Geom>Defeature>surface fillets.
b. Use the Surf Fillets subpanel to identify and remove surface fillets (curved surfaces that create a smooth transition between relatively perpendicular geometric entities). You can identify fillets based on radius, because fillets are always uniform arcs. You can also select a fillet by picking one of the edges that it connects. Once found, fillets can be removed using tools that display automatically after the find process.
c. By clicking on remove all selected fillets will be removed. in the fig.2.3 shows the fillets removed by surface fillets.
Fig.2.3: Remove fillets.
Fill missing surfaces using line drag: Use the Drag Along Line subpanel to create surfaces by dragging lines or a node list along another line, called the "drag line".
Steps
a. Select the lines or node list to drag.
b. Select the lines that the drag will follow. This can also be a series of connected lines.
c. Merge the input lines into smooth lines when possible, and create a surface for each group that forms a tangentially continuous line.Clear this checkbox to create a surface for each input line, with shared edges connecting surfaces where relevant.
d. Choose where to organize the resulting surface component. Show in the figure 3.4
Fig.2.4: Line drag
3. Mid-surface extraction: The given model is a side door panel and before going to the Mid surface extraction check for thickness of entities and measure (Geom>distance). We found different thickness on each feature. For the parent we have T 2.8 units. To simply extraction of mid surface. models divided in to two components shown in the fig 3.1
Fig.3.1: Divided Comp.
Mid surface is done by manually using offset (Geom> surface edit> offset). offset panel shown in the fig bellow
Steps
a. select offset
b. Offset moves the selected surfaces without retaining their connections to surrounding geometry.
c . select the surface and make a duplicate of same surface
d. input the value which is half of the thickness
e. to check the direction click on vector normal so that we can see the offset direction, also one can change the direction by reverse normal shown in the fig. 3.2
Fig.3.3: Check for direction of offset
for all ribs extraction of mid one file final edit tool from Midsurface. (Geom>midsurface>final edit tool) show panel below
Select a surface that represents one side of the solid.
Select a surface that represents the second side of the solid.
Select extraction options accordingly to define which surfaces to take into account when constructing midsurface.
By default, only two surfaces that are selected with the side1 and side2 surf selectors are considered.
To take into account offset directions of the adjacent pre-existing midsurfaces, select the use adjacent midsurfaces checkbox.
To allow modifying pre-existing adjacent midsurfaces, select the combine with adjacent midsurfaces checkbox. In the fig3.4 shows the mid for rib
Fig.3.4: Final Edit Tool
Extend all the ribs to the base surface using Extend.
Select the line of Extend a surface over edges to another surface.
Select the target surface.
in the fig.3.5 shows the mid surface for the model.
4) Defeaturing: Update the Criteria length as per given element Quality criteria which is Target/Average length 5. Removing all unnecessary edges, fillet radiuses etc. also maintain distance between two edges or nodes not less than Minimum Length of 2.
tools to Defeaturing
A. Toggle edge
Left-click a free edge (red) to make it shared (green), or a shared edge to make it suppressed (blue).
Right-click a suppressed edge to make it shared, or a shared edge to make it free.
In either case, the edge must meet the criteria for the type of edge you wish to change it to. For example, toggling a free edge to a shared edge requires the presence of a similar edge within the distance you specify in the tolerance field.
B. Replace (1 edge pair at a time) Select 2 edges to equivalence together. Control which edge to retain and which to move.
C. Geom> Quick edit > filler surface (to create missing surfaces) .
5. Shell Meshing: Before meshing Assign given element Quality criteria in to hypermesh by Preferences>criteria file setting shown in Fig.5.1
here to know more on each criteria
Fig.5.1: Quality Criteria
Start meshing Process by Automesh (2D>Automesh )
steps to mesh
a. Select surfaces for initial mesh and for remesh select elements.
b. select size and bias abd select mesh size which is Target/Average length 5. Use the Size and Bias subpanel to perform size and bias meshing, a flexible and powerful meshing method. A minimum of inputs are required for the element criteria settings. The algorithm options set preferences on how to handle certain situations when encountered in the geometry. When using existing finite elements as the basis for mesh generation, feature recognition settings allow the mesher to break up the areas defined by the selected elements into logical groupings with mesh controls set for each group boundary.
c. Select the type of mesh as mixed (Quad, Tria, mixed, R tria etc) and clock on alin and size in order to get proper mesh near features.
clock on mesh or middle mouse button
Modify mesh flow by changenging surfaces to elements and select the elements. Make sure that while doing mesh all the element Quality criteria must be satisfied. Avid maxim opposite traits and. In fig.5.2 show the mesh flow
Fig.5.2: Mesh Flow
In the fig 5.3 Shows the starting point and end point for components to achieve better flow.
Fig.5.3: Mesh Start and End point
Remove all quality failing elements by smoothing, by changing distance, angle b/w the nodes of failing elements we can see 0 elements are failed
6. Creating properties and Thickness assigning: Not only property we can create components, material, Cross sections etc by right click on Tab area and select requirement shown in the fig 6.1.
Fig.6.1: Create
Before creating properties we need to create components for elements as per the different thickness. right click on the Tab area and select component to create components. in the fig.6.2 shows the components as per the thickness. If we have varying thickness (taper).Then divide that region with respect to mesh flow and assign thickness value from maximum to minimum with equal intervals.
Fig.6.2: Components
Create property as per the components thickness. To create right click on the Tab area and select property to create properties.
a.select property, we can see the properties in the tab area.
b. Click on the property and rename, change the thickness, select material, card image and etc. for each component we need to create property shown in the fig6.3
Fig.6.3. properties.
Each property card has following properties
Slover keyword
Id
color
card image
thickness T etc shown in the fig.6.4
Fig.6.4: properties card
Assign properties to each component by right click on comp> assign> select property. In the graphics area we can see the model after applying properties shown in the fig. 6.5
Fig.6.5: After Applying Properties
In the fig.6.5 2D detailed elements representation as Result
Fig.6.6. 2D detailed elements representation as Result
Find Free Edges: Use the Edges panel to find the free edges in a group of shell elements, find "T" connections in a group of shell elements. Free edges are defined as a pair of nodes identifying an element edge that are not shared with another element. Free edges are normally found around the outer perimeter of a part or around openings within the part.
Free edges found in your model are displayed as red plot elements in their own component called ^edges. Free edges within a field of elements typically indicate a discontinuity within the mesh. Such discontinuities may be intentional, such as crack modeling for durability simulation, or unintentional, due to geometry discontinuities, meshing methods or component boundaries. In cases where the mesh has a discontinuity, there will typically be more than one node at approximately the same location in space. Such nodes are called "coincident". You can use equivalence to remove the coincident nodes, based on a search tolerance which you specify.
Steps
a. Go to tools>Edge
b. Select the elements whose associated edges you wish to find.
c. Specify a spherical search radius around each node in the selected component or group of elements. If multiple nodes are found within this search tolerance they are considered coincident, and can be resolved with the equivalence function. tolerance is approximately60 to 70 % of thickness
d. Click on preview equivalence. and equivalence to join noes.
e. Click on find edges to see the free edeges in Red color for mesh show in the fig.6.6.1
Fig.6.6.1: Find Free Edges
Check for normals: use the Normals panel to display and reverse the normals of elements or surfaces. The orientation of element normals can also be adjusted. The normal of an element is determined by following the order of nodes of the element using the right-hand rule.
Steps
a. Use the Elements subpanel to display and reverse the normals of elements. Select elements indirectly by components or directly by elements, or elect to have all of the displayed 2D elements selected automatically. Click display to review the current normal orientation of the selected elements. Optionally, click reverse to flip the normals to the opposite side (reverse the normals).
b. Adjust normals based on the orientation method you specified
c. Flip all of the normals of the selected elements shown in the fig. 6.6.2
Fig.6.6.2: Normals
Learning Outcome:
- Learnt user interface of Hypermesh.
- Learnt CAD geometry clean up, topology, Mid-surface extraction And Defeaturing for plastic components.
- Learnt shell meshing and making good mesh flow with considering the Quality criteria for plastic components
- Learn how to give Thickness for non-uniform and varying width.
Result:
Shell (2-D) mesh is done Successfully for Side Door Panel model by eliminating geometrical errors and considering the given element quality criteria also assigning thickness using Hypermesh.
In the fig.6.7 Shows the final FE model
Fig.6.7: Result