Meshing of Car Hood

Preprocessing of Hood Model Using Hypermesh

 

Objective :

• Make proper geometric clean up on the surfaces.
• To extarct a proper mid surface from the parent components.
• Maintain Proper mesh flow with less tria concentration.
• To achieve exact quality criteria as given in the question.
• Mesh the component properly with clean up tools to get proper mesh flow.

 

Procedure :

 

 Phase 1- Importing

1. Hence we are importing a given CAD geometry into hypermesh.
2. There are file formates like IGES,STEP,Parasolid where we can import these file formats into any CAD,CAE Softwares.
3. But in hypermesh we can only import three file formates like

• IGES [Initial Graphics Exchange Specification].
• STEP [Standard for the Exchange of Product Model Data].
• Solidworks.

IGES,STEP,These two are standard file formats which are used most in industries.But now a days in industries,they are aslo using parasolid file format.

 

Figure 1

 

Phase 2- Examining

•  Before working on the model.We have to check the geometry if there are any errors like 

1. Damaged Geometry.
2. Free edges in unnecessary areas.
3. Unnecessary points on the lines. 
4. Unnecessary Connections and connectivity error. 

• By assessing the hood model.We can see there will be five components in the hood.

• Inner Extract
• Outer Extract
• Two Hinge's and 
• Latch                       

     

Figure 2-Inner Extract

Figure 3-Outer Extract

Figure 4-Hinge

 

Figure 5-Latch

 

Phase 3- Extracting the Mid Surface

 

  3:1 How to Extract Mid Surface ?

• Before extracting the mid surface,Delete the solids and then extract the midsurface cause we are not going to mesh on the solid model.We are going to mesh on the surface.Ensure whether you have deleted the solids or not.
• In Geometry`>`Mid Surface`>`Auto Mid Surface.
• Extraction Options`>`Use Skin Offset.This option will be able to capture the features properly.

 

  3:2 Why to Extract Mid Surface ?

• Before extracting the mid surface for every component,We should measure the thickness of the component and then we have to proceed to extract the mid surface.If the component thickness is less than 6mm then we will come to know it is a sheet metal component.
• For sheet metal and plastic components,Mid Surface extraction is must.

 

  3:3 Assigning a property and Material for the components.

• To assign a property,Right click on the feature tree panel/right click`>`create`>`property.
• Do the same thing for the material also.
• After creating property and material.Select the property and give the material which you have created and thickness to the property.
• And then go and assign the property to the component which you have exracted the mid surface from it.

 

Figure 6-Assigning a property to the component for which the midsurface has been extracted

 

  3:4 Checking symmetry for the component's.

• By examining the components,we have only two symmetric components called

• Inner Extract 
• Outer Extract

• Other two called hinge and latch,For this two components,we don't have symmetry.
• In case,We can do one thing for the hinge,Cause hinge have two parts.In that we can mesh on one part and we can mirror it on other one using reflect tool.

 

  3:5 Why checking symmetry is necessary for the component's ?

• Cause we can save the time.
• If we have symmetry in the components.We can cut into half and we can reflect the surface and mesh on the other side.By doing like this,we can save lot of time instead of doing both sides.

 

  3:6 How to reflect ?

• First cut the component surface into half using delete tool.

 

Figure 7-Selecting the surfaces which we want to delete according to symmetry.

 

Figure 8-Half of the surface has been deleted according to symmetry.

 

Phase 4 : Manual Clean Up

• Manual clean up is necessary to achieve a things like 

• Proper mesh flow.
• Feature capturing.
• To eschew the elements failing for the minimum length.
• For surface deformations.
• For connectivity errors.

 

  4:1 Defeaturing the Regions

• We can defeature the fillet regions if it is necessary.
• The purpose of defeaturing is to get a good mesh flow.
• It will eliminate the fillet regions and it will bring sharp corners instead of curves.

 

Figure 9-Defeaturing the fillet regions to remove.

 

Figure 10-Fillet's have been removed.

 

• How to use defeature tool ?

• Geometry`>`Defeature`>`edge fillets`>`Select the surface/where the fillet regions are present`>`Give min radius`>`click find`>`and click remove.
• The fillet regions will be removed.

 

Figure 11-How to defeature.

 

  4:2 Extracting the midline for outer extract surface

• We have to toggle all the split lines which are less than minimum length.
• We have to go [Midline option`>`geom`>`lines`>`midline].
• We have to select two fillet edges on the hemming portion and then create a mid line.

[Note : If it is necessary to extract the midline in the hemming regions of outer extract.You can extract or it's fine.]

 

Figure 12-Hemming region where we want to exract mid line.

 

 

Figure 13-Extracted mid line in hemming region

 

• After extracting the mid line in the hemming region.Trim the line with (trim with lines) tool.
• We are trimming the line to get shared edge.

 

 

Figure 14-After trimming.We got shared edge.

 

• Grey line is there in the hemming region.If you want to get rid off that.Switch to the wire frame and delete that grey line.It will be perfect.

 

 

Figure 15-Grey line in hemming region.

 

  4:3 Toggling Edges and Purpose of it.

• If there is any unnecessary lines,We can toggle that edges to get a proper mesh flow.
• In give quality criteria,The minimun length for this component is 2.If it fail's for the minimum length.Then toggle that edges also.If we mesh without toggling the edges,the element's will fail.

 

 

Figure 16-Before and after toggling edges

 

  4:4 Fixing Damaged Geometry in surfaces.

• We can fix the geometry by following tools called

• geometry → quickedit → split surface node

•  Select two locations of the nodes to split the surface and then select an additional node to continue to split the surface.

• geometry → quickedit → Split surf-line

•  In this,select a node and select a line to split the surface,here the split will be perpendicular to the line chosen.

 

Figure 17-Splitted lines to get proper mesh flow.

 

• Geometry → quick edit → Adjust/set density.

 

• After meshing a particular surface.We can adjust the mesh density by using this tool.While meshing we will increase the nodes to get a proper mesh flow.We can also increase nodes after meshing by using this tool.

 

Figure 18-Adjusting mesh density.

 

• Geometry → quick edit → release points.

• Drag and select the surface,where you want release the points.After releasing the points.The free edges will exsists.

 

Figure 19-Releasing the points.

 

• Geometry → quick edit →replace points

• Move points from their current locations to the locations of other points,where we want them to replace it.

• Geometry → quick edit → add/remove points

• Use window selection (with the left mouse button and right mouse button ) to add and remove any points within the selection box.

• Geometry → quick edit →add points on line

• Specify the number of points that we wish to add to that line, and then select the desired line in our model. 

• Geometry → quick edit → delete surface

• Select the surface which we need to eliminate and delete it.

[Note : These tools are used to fix the damaged geometry]

 

Figure 20-Before fixing geometry.

 

Figure 21-After fixing geometry.

 

Phase 5 - Perform Mesh on the surfaces

 

  5:1 Enter the quality criteria what they given for the component's

• Tool bar → preferences → criteria file settings → checks for the element criteria →Enter values → apply → ok

[Note : Save the criteria file settings for that component and save it any other drives,Cause whenever we open that component,we can open the element criteria file and criteria will be applied habitually instead of entering again.]

 

Target Element Length = 5 Units

S.N	Quality Criteria	Value
1	Aspect Ratio	5
2	Skewness	45
3	Warping	15
4	Taper	0.5
5	Min. Length	2 Units
6	Max. Length	8 Units
7	Min angle Quad	45
8	Max angle Quad	135
9	Min angle Tria	20
10	Max angle Tria	120
10	Tria %	10

 

• Aspect Ratio

This is the ratio of the longest edge of an element to either its shortest edge or the shortest distance from a corner node to the opposing edge ("height to closest node").

• Skewness

Skew of triangular elements is calculated by finding the minimum angle between the vector from each node to the opposing mid-side, and the vector between the two adjacent mid-sides at each node of the element.

• Warping

This is the amount by which an element (or in the case of solid elements, an element face) deviates from being planar. Since three points define a plane, this check only applies to quads. The quad is divided into two trias along its diagonal, and the angle between the trias’ normals is measured.

 

Figure 22-Warpage

 

• Taper

Taper ratio for the quadrilateral element is defined by first finding the area of the triangle formed at each corner grid point.These areas are then compared to one half of the area of the quadrilateral.

 

• Minimum and Maximum Length

The shortest distance from a corner node to its opposing edge (or face, in the case of tetra elements) referred to as height to closest node.

 

5:2 Conditions to be followed while meshing

• Feature Capturing

• Feature capturing is must while meshing.All the nodes must be connected to the shared edges. 

 

Figure 23- Feature Capturing

 

• Mesh Flow

 

Figure 24-Proper Mesh Flow

 

• Quality Criteria

• Maintain exact quality criteria given.

 

Figure 25-Achieved Quality Criteria.

 

• Tria Management

• Avoig higher number of trias.
• Tria mangement.

 

• Important Parameter's in tria management

• No trias in corner's or edge's.
• No opposite trias.
• No back to back trias.
• No trias in fillets or hemmings(We can have minimum but anyhow try to avoid).
• No rotational quads.
• No trias should share a boundary with feature line.
• Connectivity between elements.
• Split and perform the mesh.
• Use mixed type mesh for irregular shaped surfaces and quads only for rectangular/square surfaces(Opposite sides should be parallel and equal).

 

  5:3 Begin meshing the surfaces

 

• Start meshing from the centre regions or from least free edges.You will get proper mesh density and proper mesh flow.

 

Figure 26-Meshed Region

 

• If the mesh is not proper since remesh or rebuild the mesh by using this two tools.
• Remesh (F12) 2D → automesh → mesh type → mixed → mesh

 

Figure 27-Mesh Panel.

• After meshing try to eliminate the trias and capture the feature lines properly as per the conditions while meshing a component.
• Rebuild mesh → 2D → rebulid mesh → elements → select elements → rebuild.

 

Figure 28-Rebuild Mesh.

• If we want to select the particular surface and to mesh Right click on elements → select geometry → surface add to selection.

 

Figure 29-By selecting particular surface and meshing.

 

  5:4 Using quality index clean up tools

 

 

SI.NO	Tool	Purpose of the tools
1	Place Node	Move the node along the plane or curvature of the surface or away from surface.
2	Swap Edge	Each time if we click an edge, it switches to the next valid configuration.
3	Element Optimize	To move the midnodes attached to the element we are optimizing, enabled the with attached midnodes checkbox.
4	Smooth	It is used to improve the element quality of the surface.
5	Split/Collapse Edge	To use the split edge tool, left-click on an edge. HyperMesh splits the elements that share the selected edge in a way that will achieve the optimum quality.
6	Drag Tria Element	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.Drag both trias to combine when they are facing opposite direction.
7	Split Quad Element	To split a quad element, left-click on the quad element you wish to split. HyperMesh splits the quad element into two tria elements.
8	Combine Tria Element	To combine two tria elements, left-click on their shared edge. HyperMesh combines the two tria elements into one quad element.

 

  5:5 Manual Clean Up

• Distance
• Translate
• Align Nodes

 

Distance

• Geometry → Distance → two nodes → enter the value 
• The Distance panel to determine the distance between two nodes/points or the angle between three nodes/points, or to change distances or angles.

 

Figure 30- Before

 

Figure 31-After

 

Translate

• Tool → Translate → Nodes → N1,N2,N3 → Translate +/-
• This tool is used to fix the warpage.

 

Figure 32- Before

 

Figure 33- After

 

Align Nodes

• Geometry → Node edit → align mode → 1st node → 2nd node → 3rd node → align
• Select a node that defines one end of the imaginary line.
• Select a node that defines the other end of the imaginary line.
• Once both nodes are selected,  now we can pick the nodes that we wish to align.

 

Figure 34- Aligning nodes

 

Phase 6 : Reflecting the component

• Once the mesh is done completley,we need to reflect the component.
• Tool → reflect → select the element's as duplicate → current component → select y axis (In which direction we want to reflect it) → base node → reflect

Figure 35- Outer Extract Before reflecting

 

Figure 36- Outer Extract After reflecting

 

Figure 37- Inner Extract Before reflecting

 

Figure 38- Inner Extract After reflecting

 

Check Nodes :

• Tool → Count → Nodes → right click select all → press selected ( no of nodes will be displayed)

 

Figure 39- Checking Nodes Count

 

Why checking Nodes ?

• Cause if we have more mesh density in our surfaces,Nodes will be higher,So when we try to save the model,The software will be stating [Hyperworks Student Edition can have only 100000 nodes].If the nodes exsist more than 100000.We cannot save the model.It will show some error like 

 

Figure 40- Error [Note:The Figure shown above is for only example].

 

• To get rid off this.We should have nodes less than 100000.If we cannot able reduce the nodes.Delete the one hinge surface to get nodes less than 100000.I done this for my model,cause there was no way to solve this,So I deleted that one,cause we have two.It's not a issue in deleting that.

 

Check for Normals

• Top side of surface must be in blue colour.
• Bottom side of surface must be in red colour.

The model should exsist these two things,Then it is ok.

 

Figure 41-Check for normals

 

Check tria percentage

 

• Check whether the tria percentage is within the given tria concentratio in the quality criteria.

 

 

Figure 42- Tria %

 

• Here the tria percentage is less than the given tria percent,so it is ok.

 

Check for duplicates 

 

Figure 43-Check for duplicate element's

 

• There is no duplicate elements in the model,thn it is ok.

 

Final Cad Model Image : 

Figure 44-Final cad model image

 

Result : 

•  Hence the mid surface for every individual component has been extracted and every component has been meshed with proper good mesh flow and attained the quality criteria as per given.Every tria conditions has been followed in this model and completed successfully.

Conclusion :

In this week 6 challenge.I came to know how to mesh a component properly with proper mesh flow,proper,feature capturing,avoid trias as much as,avoid rotational quads(rotational quads in hemming regions),quality criteria,manual clean up,check for the duplicates,nodes,normals,and tria percentage.