Surface Meshing Of BMW M6 & Creating A Wind Tunnel || ANSA

OBJECTIVE:

The objective of this project is:

• To perform geometry cleanup of the BMW M6 model.
• To create surface mesh with different length of each individual part.
• To create a wind tunnel.

GEOMETRY CLEANUP:

Fig 1- Shadow Mode Fig -2 Wire Frame Mode

The above figure shows the BMW M6 in shadow mode on left side and wire frame mode on right side.

Performing geometry check:

Fig 3 - Geometry Check

We can see a lot of errors such as:

• There are single cons around the tyres.
• The car is not well defined it is poorly detailed.
• The styling lines which was used for designing purpose is present.
• The car has several PID we need to assign them accordingly to our convenience.

It is also found that the length of the element is 30 mm so to make it more detailed we change the length to 1 mm.
Doing this it enhances the geometry of the BMW M6 model. Even the BMW logo was of square shape and now it becomes a complete circle.

Fig 5 - BMW Logo before and after correction

The contour lines which were used for the contour designing of the vehicle were present, deleted the contour lines as it is not needed for meshing.
Switching of the macros and deleted the unnecessary contour lines.


Fig - 6 - Vatrioua Topo Errors

The above fig 6 shows errors such as tripple cons, faces overlaped, cracked faces, needled faces
cracked cons, unwanted faces etc.
So carrying out different operations to do geometry cleanup such as:

Faces -> Cut : creates a small partition in the surface.
Cons-> Project: connects the cons to surfaces.
Cons-> Release: disconnects cons from the surfaces.
Cons-> Paste: joins two or more cons segments that lie close to each other, which usually are boundaries of different faces.
Faces->New (surface type: existing surf, planar, fitted, coons) : creates new faces
Faces-> Delete: instantly deletes the face without selecting.
Universal delete: highlights the surface and does not delete the surface instantaneously.
Hot Points-> Insert: will insert hot point in cons whereever needed.
Surfaces-> Extrude-> Glide: the glide uses one con and one direction and extends the line.
Face->Zone cut: creates a cut to the con.

The below figures will show before and after correction of topo errors:

Only the outside surface is important for the surface mesh:

The windows:

Fig 7: windows

SIDE GRILL:

Fig 8 - Side Grill

CENTRAL GRILL:

Fig 9 - Central Grill

LOWER GRILL:

Fig 10 - Lower Grill

LIGHTS:

Fig 11 - Lights

The above corrections were made on the left side of the model.
The model being symmetric can be mirrored. Deleting the right half of the model, correcting the left half and mirroring it to right.

MODEL SEGREGATION:

The model has many features the body is one pid, the tyres are another set of pid's, the rims being another set of pid's and etc.
Entire model consists of different set of pids.

To make it easy we segregate them into different parts with the help of model manager:

• Windows
• Wheels
• Lights
• Body
• Exhaust
• Grills

Fig 12 - Model Browser

Fig 13 - bottom chassis

Fig 13 shows the bottom side of the chassis after cleaing all the topo errors and patching the geometry.

ORGANISING THE PID'S:

Fig 14 - unnecessary pid

Setting up the pids. Earlier they were not named properly so it was difficult to distinguish them. Naming them accordingly and also using the compress option to delete the unwated surafces, nodes etc which are not needed.

Fig 15 - Assigning the pid properly

WHEELS:

Unlike other body parts the wheels are special because they incorporate rotatory motion. There are a lot of topo errors on the wheels. Single cons running around the tyres, unwanted surfaces present, also there are missing tyres.
After performing checks it is found that the wheels are symmetric in nature.

Fig 16 - wheels

The rims and tyres are found to be sperate volumes which is not convenient for meshing so making it one volume by deleting the upper rim suface and the lower suface of the tyre after projecting the con of the rim to the tyre making it a tripple con.

After these steps we perform geometry check and now we are left with the single cons which is our known error and would get fixed once we perform the symmetry.

Fig 17 - known errors

After fixing all errors and performing symmetry:

Fig 18 - Wheels after geometry cleanup

Fig 19 - successfully completed geometry checks

2 DIMENSIONAL MESHING:

Selecting each part from the model browser & assigning the mesh length given in the table below :

Table 1 - mesh length of each individual part

Fig 20 - Mesh Parameter Box

The mesh parameter is basically used for improvement of mesh generation.
The minimum target length is given 0.9 mm while the maximum target length is given 5 mm, distortion angle is set to be zero and distortion distance distance is kept 15%.

SURFACE MESH CHECKS:

After performing 2 dimensional surface checks we perform surface mesh checks.

Fig 21 - Mesh Check Dialogue Box

• Geometry: Unmeshed Macros: Shows the entities which are yet to be meshed.
• Penetration: Intersections: Checks whether two elements are intersecting or not.
• Mesh: Sharp Edges: If there are two meshes angled up between each other it restricts the angle if it is
  more than 160 degrees. Also checks whether the two angles are also very close to each other and if it is, then will give an error.
• Penetration: Proximities: It is not an error but a warning whether two elements are very close to each other. If there is a fluid flow going to happen, it won't get calculated because one element would be very close to the other element.
  It check for 2 surfaces which could be grey surfaces or yellow to yellow surfaces or surfaces of both orientation.
• Mesh: Trias On Corner: Checks the mesh of the Tria element on the corner & whether the mesh quality could be increased or not.
• Mesh: Mesh Quality: Checks the quality of the Tria element by various parameters such as skeweness, warping aspect ratio etc.
• Duplicate: Checks whether same space is occupied by any different element.

RESULT MESH CHECK:

Fig 22 - mesh check errors

To eliminate the errors we create new faces but before that we perform parametric cut with enabled remesh macros across the unwated surfaces and then delete those surfaces by universal delete.

MESH QUALITY CHECK:

Mesh quality check is used to check each individual element and how each element is well defined.
Quality Criteria-> Shells: To check the mesh quality of 2 dimensional element.
Quality Criteria-> Solids: To check the mesh quality for 3 dimensional element.

Quality Criteria:

Setting the quality criteria. The dialogue box below shows the quality criteria which has been set up:

Fig 23 - Quality Criteria dialogue box

Skewness:

Fig 24 - Green Trias represent skewness

Skewness is the irregularity of the element.

Minimun length:

The length which has been set in minimum length under quality criteria (Fig 22).

Maximum length:

The length which is greater than the maximum length length set.

Warping:

Warping is a criteria related to quad elements and how the element can bend as quad elements has four points so there is a possibility that three points lie in the same plane while the fourth on the other plane.

Fig 25 - Red elements show min length

To eliminate the quality criteria errors the tools which were used:

• RECONSTRUCT:Reconstructing the surface mesh by using the reconstruct funtion enabling the remesh macros target length was chosen to be average it enhances the quality of the surface mesh.
• MV SURF: It helps to move the point along to the node on which is lying.
• CUT UNDER MACROS: As it is used to create partition within the surface enabling the parametric cut, heal cut & remesh macros.

Fig 26 - After fixing all quality criteria errors

Total trias = 1166736 generated.

CREATING WIND TUNNEL:

Dimensions of wind tunnel:

Fig 27 - Dimensionsnof the wind tunnel (mm)

WIND TUNNEL:

Wind tunnel is a device for producing airflow relative to the body under test. Wind tunnel provide uniform flow condition under test. Majority of experimental data needed in aerodynamics is generated using wind tunnels.

Fig 28 - wind tunnel

Fig 29 - wind tunnel enclosed

Conclusion:

• Geometry cleanup done of BMW M6 model.
• Deleted the right side of the model and after fixing all the topo errors on the left side done the symmetry successfully.
• Performed surface mesh with different length of each individual part.
• Created a wind tunnel.