Extraction Mid Surface and Meshing of the Car Dashboard Subparts using ANSA Workbench

Extraction Mid Surface and Meshing of the Car Dashboard Subparts using ANSA Workbench

Aim:

To check the geometrical error of the component and Extract the Mid Surface of the given model and to do the 2D meshing for the component considering given quality criteria.

Introduction of Finite Element Analysis:

• The Finite Element Analysis (FEA) is a numerical method for solving problems of engineering and mathematical physics.
  
  
• Useful for problems with complicated geometries, loadings, and material properties where analytical solutions can not be obtained.

1. Introduction to Meshing

1.1 What is Descritization??

Model the componet by dividing it into an equivalent system of many smaller bodies or units (finite elements) interconnected at points common to two or more elements (nodes or nodal points) and/or boundary lines and/or surfaces.

1.2 Why Do we Carry out Meshing?

Basic theme of FEA is to make calculation at limited number of points and then interpolate the results for entire domain.Any Continues object has infinite degrees of freedom and its just not possible to solve the problem in this format.Finite Element method reduces degrees of freedom from infinite to finite with the Help of Descritization i.e Meshing

Types of Finite Elements:

There are 3 types of Element Namely 1D,2D and 3D Element.

• 1D Element:

It is used for the geometry having one of the dimensions are very large compared to the rest two. Shape of the 1D Element is line.

Example:Beam Element,Truss Element

• 2D Element:

It is used for the geometry having two of the dimensions are large compared to the third dimension.2D Meshing is carried out on the midsurface of the part.

Why 2D Meshing is Carried out on the Mid Surface?

Mathematically the Element thickness specified by the user is assigned half on element top and half on bottom side.Hence in order to represent the geometry appropriately it is necessary to extract mid surface and then mesh on the mid surface.

Example:All sheett metal Componets,Plastic Components.

• 3D Element:

It is used when all the three dimension are comparable.

Example:Transmission Casing,Intake manifold,Connectong Rod,Clutch Housing etc

As the given model is a Sub part of Instrumental Panal and it is a Plastic Component.So here we are going to extract the Mid Surface of the Dashboard Sub Assy and Carry out the Meshing in the Beta CAE ANSA v19.1.6 Software

Given Quality Criteria:

Sl No	Quality Criteria	Value
1	Target Lenghth	4
2	Minimum Length	2
3	maximum Length	6
4	Aspect Ratio	3
5	Warpage	15
6	Skewness	45
7	Jacobian	0.7
8	Minimum Quad Angle	45
9	Maximum Quad Angle	135
10	Minimum Tria Angle	30
11	Maximum Tria Angle	120
12	Tria Percentage	15

Overview on given Quality Parameters :

• Aspect Ratio:

The ratio between largest and smallest characteristic dimension of an element is known as the Aspect Ratio.Large aspect ratios increase the inaccuracy of the finite element representation and have a detrimental effect on convergence of Finite Element Solutions.

• Warpage:

The warpage of the quadrilateral elements is defined as the deviation from a best-fit plane that contains the element. It is not always a case to define a plane with 4 nodes. Therefore, a node of the quadrilateral element may be formed outside of a plane.The warpage is a measurement how this node has been deviated, and as it gets closer to 0, the element become more planar.

• Skewness:

Skewness is the Angular Measure of Element quality with respect to the Angles of Ideal Element Types.It is one of the Primary Qualities Measures of FE Mesh. Skewness determines how close to ideal (i.e., equilateral or equi-angular) a face or cell is.

• Jacobian Ratio:

The Jacobian calculation is done at the integration points of elements commonly known as Gauss Point. At each intergration point, Jacobian Determinant is calculated, and the Jacobian ratio is found by the ratio of the maximum and minimum determinant value.

Procedure

1) Importing of the .IGS File of the IP Substrate in to the ANSA WorkBench

2) Geometrical Clean up and Topology

3) Extraction of Mid Surface

4) Assigning New Property ID

5) Defeaturing of the Component

6) Meshing.

7) Assigning thisckness to the Mesh and Enabling shell as Solid

Let us study te extraction of Mid Surface and Meshing of Ip Substrate

1) Importing of the .IGS File of the IP Substrate in to the ANSA WorkBench

• Import the IP Substrate.IGS into the ANSA Workbench as shown in fig 1.1

• Change the Mode to Topo and Entity

• Set the proper orientation as shown

• Change the perimeter length to 1(MESH>PERINETER>LENGTH) as shown in fig 1.2

fig 1.1 .IGS file of IP Substrate

fig 1.2 Length Change to 1mm

2)Geometrical Clean up and Topology

• Check all the geometry errors in the checks manager(Checks>Geometry>Execute) as shown in Fig 2.1
• Eliminate All the Triple Cons and Cracks between 2 Surafces by releasing thr triple cons and applying topo as shown in Fig 2.2

Fig 2.1 Geometrical Errors

Fig 2.2 Geometrical Cleanedup Component

Now the Component is error free and is ready for mid surface extraction.

3) Extraction of Mid Surface

• Mid surface has taken manually as the component has varying thickness which is too less which causes quality criteria failure in the auto mid.

• Manual mid surface is taken by using 2 commands

a)Offset Command (Topo Mode>Faces>Offset) in which we have to select the faces for which we need the mid surface and later we need to input the offset value(Half the thickness).Negetive and positive signs indiactes the direction in which the value need to offset.

b)Middle Command (Topo Mode>Faces>Middle) in which we need to selct the 2 faces for which we need mid surface and on confirmation it will automatically generate the midsurface.

• In this model the Main Body has thickness of 0.6 and we are taking the mid surface by Offset Command as shown in the fig 3.1.After Entering the Offset Value Click Ok.Mid Surface will be generated.
• Mid surface of all the Ribs are taking by using Middle Command . Select 2 faces of the Ribs and Click OK as shown in fig 3.2.
• Mid surface of all the circular feature are taking by using Curve Middle (Topo Mode >Curves >Middle ) or Command.
• To Check he Mid Surface from the Parent Model,Enable PID Region and using INOT command hide the parent object.Thus Visible model on the screen will be your Mid Surface.

fig 3.1.1 Selecting the Faces for Offset

fig 3.1.2 Mid Surface

fig 3.2.1 Mid Surace Extraction of the Ribs

fig 3.2.2 Mid Surace of the Ribs

• Now all the Mid Surface of the Ribs has to be extended to the Base Surace using Extend Command.((Topo Mode>Faces>Extend ).
• Select the Edge of the Rib which is to be extended.
• On Center Mouse click,Select the faces on which the ribs has to be extended.
• On Confirmation,the Ribs have been extended till the Base surace which we have selected shown in fig 3.3

Fig 3.3.1 Selection of Rib Edges Fig 3.3.2 Selection of Base Surface

Fig 3.3.3 Extended Ribs

Thus all the Component Midsurface is taken and is shown in the fig 3.4

fig 3.4 Mid Surface of the IP Substrate(Dashboard)

4) Assigning New Property ID

• Once after the extraction of Mid surface,We need to assign the new property ID for the Component.

• To give new property ID go to SET PID Command(Topo Mode>Faces>Set PID)
• Select the portion for which you need to assign new PID.On Confirmation the property Tab will popup on the Screen as shown in fig 4.1
• On Right Click,Go to New>PSHELL the new prperty Card will popup on the Screen as shown in fig 4.2
• Enter the Required data and thickness and click OK.The new PID is created and thickness is assigned to the selected faces as in Fig 4.3

fig 4.1 Seletion of the Component for new PID

fig 4.2 Property Card

Fig 4.3 New Proprty for the Main Body Mid Surface.

Likewise we have to assign the new properties to the all Features ,Ribs Etc.

5) Defeaturing of the Component

• As we find there are so many cons in the component and the disstance between some of those cons are below the minimum length which cause the minimum lenghth error after Meshing.So we need to eliminate all those unwanted cons,Edges and fillets using Cut Command (Topo Mode>Faces>Cut).
• In Fillet portion where the minimum length quality criteria fails,there we need to defeature by using Dach Command(Topo Mode>Faces>Dach ).It replaces the filletts with Corner a)Select the Fillet Faces as shown in fig 5.1

b)On Confirmation,Small window will popup.Enable the Join Macros as shown in fig 5.2

c)On Confirmation the Fillet have been replaced with adjacent macros as shown in fig 5.3

fig 5.1 Selection of fillet fig 5.2 Enabling the Join Macros

fig 5.3 Defeaturing of Fillet using DACH

6) Meshing of the Component

Once geometry cleanup cleanup is completed and Extracting the Midsuraface and defeaturing (e.g. surfaces are stitched stitched geometry), meshing is next.

Some rules before starting meshing

• The mesh should look rather smooth and regular.We should keep in mind that the analysis is based on our Mesh Flow and mesh quality is the key.
• Use the simplest element type suited for the problem
• Try to keep mesh related uncertainties to a minimum as much as possible.
• Opposite trias should be avoided as shown in fig below.

• No mesh transition on constant transition on constant radius fillets / curvatures.

• Avoid tria elements tria elements on outer edges er edges or holes.

• What is not acceptable acceptable at a professional level ?

• What is Accepted?

• Instead of a zig-zag distribution,a structured structured or smooth mesh is recomanded.

Use Smooth Command for the above Problem.

• Rotating quads are n uads are not allowed

Let us start the meshing of the Component.

• Go to Mesh mode from Topo Mode.
• Enter the Mesh Parameters (Utilities>Mesh Parameters) and Quality Crieteria (Utilities>Quality Criteria) as shown in Fig 6.1

Fig 6.1 Quality Criteria and MEsh Parameters Tab

• Change the Permieter Length to given target length(Mesh Mode>Perimeter >Length).
• Now Mesh the Component.(Mesh Mode>Mesh Generation>)
• Select the Faces and on Midldle click the mesh will be generated as shown in fig 6.2

fig 6.2 Meshing

• If need any modification in meshing Use Reconstruct Command (Mesh Mode>Shell Mesh>Reconstruct)
• If need any Smoothness in meshing Use Smooth Command (Mesh Mode>Shell Mesh>Smooth).
• To move the Trias to upward direction use Split command (Mesh Mode>Elements>Split ) and to move trias to right or left use Swap Command(Mesh Mode>Elements>Swap) .
• To move the trias to downward direction use Paste Command(Mesh Mode>Grids>Paste).
• Avoid Rotating Quads by splitting teh rotating quads in to two trias.
• While meshing all the given quality criteria must be satisfied.
• Overall Component Meshing is hown in fig 6.3

fig 6.3 Overall Meshing of the Component

7) Assigning thisckness to the Mesh and Enabling shell as Solid

• Now the Mid surface is Visualize in th solid shell by Enabling Draw as Solid Command(Utilities>Quality Parameters>Presentation Parameters>Draw shell as Solid) as shown in Fig 7.1

Fig 7.1 Visualizing the model As Solid

Learning Oucomes:

1. Able to fix Hepmetrical Errors and Geometric Cleanup of the Component.
2. Able to Creating and extracting of Mid Surface from the Parent Geomtery of the plastic Component.
3. Defeatiring of the Component
4. Meshing of the Component considering all given quality Criteria.
5. Removing Trias and Rotating Quads.

Conclusion:

In the above Project Model we can conclude that the Meshing process is very similar to the any complex geometry and it is observd that Before meshing we need to observe and study the model carefully as it has varyig thickness and need to assign new property to each of them with respect to their thickness.Now the Mesh is generated for the IP Substrate(dashboard) and all the Elements meets the given quality criteria .Thus the Model can be given for next Solver Process.

Google Drive Sharable link of the IP Substrate Model:

https://drive.google.com/file/d/1iNQ_c9kRedcKZkpaPANyj2oB3DH474Hr/view?usp=sharing