Shell Meshing Of Dash Board Sub Part 

Shell Meshing Of Dash Board Sub Part

Aim: To create the shell (2-D) meshing for the Dash board sub part eliminating geometrical errors and considering the given element quality criteria using ANSA.

Introduction:

The finite element method is a numerical technique for obtaining approximate solution to a wode variety engineering problems. FEA (Finite Element Analysis) has 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 ANSA is used. ANSA interface is shown in the fig 0.1.

Fig.0.1: ANSA Interface.

Types of the elements

1. One-dimensional elements: This elements are suitable for one-dimensional problems such as bar, truss and beams.

Example- Linear element has 2 nodes etc.

2. Two-dimensional elements: This 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: This elements are suitable for three-dimensional analysis. uses for solid parts and sheets of thickness more then 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	4
2	Minimum Length	2
3	Maximum Length	6
4	Aspect	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

Table1.1: Element Quality Criteria

Procedure:

The meshing is done by following steps

1. Import Ip.IGS in to the ANSA

2. CAD Geometry clean up and topology

3. Mid-surface extraction

4. Setting the PID

5. Defeaturing

6. Shell meshing

7. Thickness assigning.

1. Import Ip.IGS in to the ANSA: Import the given Ip.IGS in to the ANSA Shown in the fig.1.1. Make orientation of all visual faces and change the element length on perimeter to 4 (Target/Average length) in both perimeters and macros (MESH>Perimeters>Length). In work area on the screen we can see the component is not stitched so the all nodes are connected by single cons and 243 unchecked faces.

Fig.1.1: Imported File Ip.IGS

To stich all faces together by Topo TOPO>Faces>Topo. This function automatically creates topological conditions between selected adjacent CONS shown in the fig1.2.

Fig.1.2: After Topo

Here we can observe thickness is uniform but all ribs has varing thickness. and ribs are connected by circular pillar.

2. CAD Geometry clean up and topology: In this step the given model undergo geometry check (Tools>Checks>Geometry).

A. Activate the Check Geometry function.

B. The Checks Manager window pops up. The selected Check is loaded to an Auto generated Template.

C. Select on which entities the check should be executed "Visible", "Model" or "All Entities".

D. Activate the respective options in order to perform the check. select Unchecked Faces, Needle Faces, Collapsed Cons, Triple Cons, Overlaps and Cracks

E. Press Execute to run the check shown in the fig 2.1.

Fig.2.1: Geometry Check Manager

F. Where ANSA check for any geometrical errors such as collapsed faces, cracks, single con, triple con etc. those errors are shown in fig. 2.2.

Fig.2.1: Geometry Errors

Geometrical errors are cleared by using release triple cons and topo, deleting the overlapped faces and creating new faces. Here some geometrical errors auto fixed, some are done by deleting faces and re creating faces by NEW (TOPO>Faces>New>COONS)Fig.2.2 shows the fixed all Geometrical errors.

Fig.2.2: Geometry Clean Up

3. Mid-surface extraction: The given model is plastic component and before going to the Mid surface extraction check for uniform thickness entities and measure (Utilities>Measure). found uniform thickness for outer face and ribs are varying thickness.

Mid-surface extraction done by manually. Because in auto mid-surface not process and for casting ANSA is not responding.

The following procedure is used to extract mid-surface by manually

1. Activate the Offset Faces function.(TOPO>Faces>Offset>Faces)

2. Select the facess of same thickness value using the right mouse-button

3. Press the middle mouse-button to confirm selections. An arrow appears showing the offset-direction.While extracting the mid-surface by Offset method it will ask for the offset distance along with direction. With respect to direction input the value. The value may be +ve or -ve depending on direction. Input an offset value as -0.3mm because here thickness of selected faces is 0.6mm shown in the fig 3.1.

Fig.3.1: Offset

4. Decide whether to delete or not the original faces by pressing the relative button in the Confirmation window. The new Faces are defined.

To capture all the features part is divided in to four sub pars in order to capture all features without missing shown in the fig 3.1.1 with separate PID's. omce all the features are captured then put all 4 PID's in to single PID before meshing.

Fig.3.1: Sub Divided

Mid-Surface extraction for all ribs are done by Middle (TOPO>Faces>Middle>Single) select first face then select 2nd face and middle mouse button shown in the fig.3.2. Make sure that selected surfaces by middle must have same cuts. if not means we have to project the cons to other surfaces before using Middle option.

Fig.3.2: Mid-Surface By Middle

Similarly Mid-surface extracted for different features on given model.

for circular pillers mid surface exracted in the shape if pluse shown in the fig 3.3.

Fig.3.3: Mid-Surface for Pillers

Once extraction done for all features extend all rib to parent mid-surface by following steps

1. Activate the Extend (TOPO>Faces>Extend>Target)

2. Select the single cons from the face which is to be extend

3. Middle mouse button and select the target faces

4. Confirm selection by middle mouse button and the faces will extend shown in the fig 3.4

Fig.3.4: Extend Faces

4. Setting the PID: setting PID (Property ID) for each mid surface done by using Set PID (Topo>Faces>Set PID) This function assigns selected Faces, Shells or Groups of entities to an existing or new PID. The following steps for setting PID

1. Activate the Set PID ANSA asked to select faces

2. Conforming the faces, A Property Help window will pop up, in that window create new PID by right clicking mouse button and select New>PSHELL.

3. Another PSHELL window will popup there we can assign the Name, MID (material ID) and thickness. We can modify the colors of each PID. (But in this case we have different thickness at different region so we need to set PID according to the thickness after mesh and for initially we are going to set PID for reference purpose)

4. Press OK and Double click on current PID. New PID created shown in the fig.4.1

Fig.4.1: Mid Surface

5) Defeaturing: Update the element length as per given element Quality Criteria (Mesh>Perimeters>Length) which is Target/Average length 4. Removing all unnecessary edges, fillet radiuses etc. also maintain distance between two cons or nodes not less than Minimum Length of 2. Shown in the Fig.5.1. In this project Defeaturing and meshing done simultaneously.

To defeature the fillet edges wich have arc length less the 2mm byfollowing steps

1. Activate the Dach TOPO>Faces>Dach

2. select the fillet faces and confirm by middle mouse click

3. Mark on delete fillet and join macros. fillite will replace single edge shown in the fig 5.1

Fig.5.1: Dach

6. Shell Meshing: Assign given element Quality criteria in to the ANSA (Utilities>Quality criteria) and Mesh Parameters (Utilities>Mesh Parameters) shown in Fig.6.1. Here we are going to Generate Shell Mesh which is preferred for 2D mesh.

Fig.6.1: Quality Criteria & Mesh Parameters.

Start meshing Process by Best Mesh (MESH>Mesh Generation>Best).

1. Activate the Best Mesh MESH>Mesh Generation>Best>Select and select faces.

2. Confirm the selected faces by middle mouse button.

3. The mesh will generate shown in the fig 6.2

4. Modify mesh flow using Reconstruct (MESH>Shell Mesh>Reconstruct), Smooth (MESH>Shell Mesh>Smooth) and Split (MESH>Elements>Split). Make sure that while doing mesh all the element Quality criteria mush satisfied. Avid maximum opposite trais and quad elements.

Fig.6.2: Best Mesh

To get better mesh Flow the mrssing process start from one end and ends with other end without any skipping which is show in the fig 6.3. in bottom the numbers 1,2 & 3 shows the filling mesh

Fig.6.3: Meshing process flow

Over all mesh flow also show in the fig6.4 we can see the data of quads, trias, off elements and total elemens.

Fig.6.4: Mesh flow

Thickness assigned to the parts by selecting Draw Shell As Solid (Utilities>Quality criteria>Presentation Parameters). each and sheet and ribs mush measure and set PID for each varying thicknes Feature. shown in the fig.6.5.

Fig.6.5: Thickness Assigned

Assigning separate PIDs for different thickness region. If we have varying thickness (taper).Then divide that region with respect mesh flow and assign thickness value from maximum to minimum with equal intervals.

Learning Outcome:

1. Learnt user inter face of ANSA.
2. Learnt CAD geometry clean up, topology, Mid-surface extraction And Defeaturing for plastic components.
3. Learnt shell meshing and making good mesh flow with considering the Quality criteria for plastic components.
4. Learnt how to give Thickness for non-uniform and varying width.

Conclusion

Shell mesh is done successfully for Dash board sub part by eliminating geometrical errors and considering the given element quality criteria using ANSA.

(Find the attached file of Ip 1_midmesh1.igs).