Week 4 Challenge : CFD Meshing for BMW car

Aim: For the given model, check and solve all geometrical errors on half portion and Assign appropriate PIDs. Perform meshing with the given Target length and element Quality criteria. After meshing the half model, Do symmetry to the other side.

Software Used: ANSA Pre-processor

Given data:

1. Target lengths for the different parts of a model are as follow:
2. Body - 3 mm
3. Lights - 4 mm
4. Grills - 1 mm
5. Rims and Tyres - 2 mm
6. Optical Rear view mirror - 2 mm
7. Window - 2 mm
8. Silencer - 3 mm
9. Logo - 1 mm

Given Model:

Fig 1: BWM car model

First click on topo in faces selection for converting single cons into double cons.

Fig 2 : After topo

Cons Resolution:

For getting the actual shape instead of irregular cons using Auxiliaries-Fine

Fig 3 : before and after cons resolution

For doing Cons configuration to entire model is difficult and time consuming process, so go to mesh - select entire model - given perimeter and macro length as 1 mm.

Fig 4 : Cons Configuration using Mesh

The given model is Symmetry, , so we delete half of the part and we do topo for geometry clean up using delete option in top the GUI.

Fig 5 : deleted half of the symmetry part of the car

Front grill area:

Delete all the extra parts to have a single volume throughout the car.

Now remove the single and triple cons and to maintain single volume.

To create a single volume we need to have double cons everywhere, so we need to perform different operations like resurfacing of parts and few cuts to maintain single volume.

Fig 6 : Front gill region

Fig 7 : Creating new surfaces

Fig 8 : Geometry cleaned grill

After performing the cuts and removing the triple cons by using the delete and other options, we can re-meshing the create surfaces and maintain a single volume.

Fig 9 : Creating new surface

Fig 10 : Wire frame mode

Rear lights, Windows, Roof region and logo:

Delete the triple cons and extra surfaces, double surfaces are not necessary since we need to have a single volume.

Rear lights and roof area where having extra internal parts, so which is not used to create surface or volumetric mesh.

The logo of the car is under a single surface, therefore using project cons, create a separate surface and delete the extra surfaces to maintain a single volume.

Fig 11 : Geometry cleaned Rear lights

Fig 12 : Logo geometry clean up

Design Feature and Mirror:

Perform topo and identify the triple and single cons.

Delete the extra unwanted surface to maintain a common volume.

Fig 13 : Design feature of car

Use the intersect option to identify the triple cons at the intersection area and can delete the smaller surfaces individually

Extended the single cons on the adjacent surface to create triple cons and delete the unwanted surfaces.

Delete and recreate the surfaces accordingly to have a smooth and perfect shape at tight corners. Also uncut the lines which are necessary which might cause trouble during meshing.

Fig 14 : Design Feature with Wire Frame Model

Isolate the mirror and perform topo clean up, hide the surfaces blocking the triple cons view.

Fig 15 : Optical rear view mirror

Delete the extra surfaces and create a single volume, also at the car and mirror connection region perform extend on the car surface and create a single volume by deleting he extra surfaces.

Wheels and Base Region:

Isolate the wheels to perform geometry clean up, to rectify the triple cons, hide the surface blocking the view and delete the overlapping surfaces causing triple cons.

Create larger surfaces after deleting smaller surfaces which are parallel to each other.

Fig 16 : Tyre wire frame model

The base of the car is intersecting with the tyre, therefore we need to delete the excess surface and also delete the extra design surfaces which cause smaller edges, this causes problems while creating mesh.

Fig 17 : Curve feature topo clean up

Therefore we need to clean the entire base and create new surfaces accordingly having smooth edges.

Fig 18 : Base Geometry Clean up

After making the surface changes, we need to check if the base surfaces have no intersection with the tyre region.

Fig 19 : Checking Interface between tyre and body

After checking and performing topo clean up for the entire half car model. We need to perform geometry checks to find small cracks are unchecked faces extra which are not good for the geometry; therefore we need to perform checks and clean the geometry accordingly.

Fig 20 : Geometry Checks

PID's:

Once the geometry is checked and has no errors, we can now assign names to different components using PID.

Fig 21 : Assigning PID's

Fig 22 : PID Table

After assigning the PID names, Now we perform Quality criteria.

Fig 23 : Quality criteria table

Used the measure tool for calculate the smallest distance between to cons or hot points.

Assign the minimum and maximum length accordingly in the mesh parameters for meshing.

Fig 24 : Using Measure tool

Surface Meshing:

We need to do the mesh for components individually because given mesh targets are different for each PID regions.

Assign the Mesh parameters and quality parameters for each PID accordingly.

Fig 25 : Surface Mesh Logo

Fig 26 : Grill Surface Mesh

Fig 27 : Grill surface mesh close view

Rims and tyres, window and Rear view mirror surface mesh:

Surface Mesh:

Fig 28: Surface mesh on Windows

Fig 29 : Surface mesh on tyres

Fig 30 : Surface mesh on rear view mirror

Silencer and lights:

Fig 31 : Surface mesh on silencer

Fig 32 : Surface mesh on lights

Fig 33 : Car body Mesh

Body PID region is in contact with various other PID, the Mesh length variation at the boundary region of 2 different PID cause the mesh to erase or cause mesh failure. Therefore, While entering the perimeters under length in mesh drop down.

Select the regions which are not in contact with the other meshed PID regions. This helps in avoided the mesh to be erased and can later be edited to erase the off elements.

Fig 34 : Checking for off elements in entire car body

After meshing, we can choose re-construct under shell mesh to reduce the off elements. later the remaining off elements can be edited manually.

Fig 35 : Using Re construct option to reduce off elements

Final Surface mesh of car model:

Fig 36 : complete car elements with O off elements

Performing symmetry on the car model:

Perform symmetry under transform option to create a exact same opposite body of the car to create a full body car.

Use the copy option and select the half body of car and deselect the logo since we don’t need a copy of the logo.

After choosing the model, middle click the mouse, we get a window, choose the symmetry and choose mirror 3 points plane and choose 3 points on the edge to be performed symmetry.

After choosing 3 points, middle click twice and the symmetry is performed, click middle to confirm the geometry and complete the process.

There will be few single cons present near the middle section, use paste or other tools to solve the problem.

Fig 37 : Symmetry conditions window

Fig 38 : Surface mesh of full body after performing symmetry

Fig 39 : Full car model

Creating Wind Tunnel:

First, we need to create reference points to create wind tunnel surfaces.

Select relative under points in topo mode, create a point below the car taking one reference point and entering the correct values.

Fig 40 : Using relative points tool

Calculating the wind tunnel dimensions appropriately, we can create the wind tunnel accurately.

The wind tunnel dimensions are (standard distance of the tunnel w.r.t to car model = 1306 mm as x times)

Front surface distance (from reference points) = 5875 mm (4x).

Back surface distance = 8480 mm (6x)

To surface distance = 4323 mm (3x)

After creating the bottom surface use the curves for having the reference of cons, we can delete all the hot points and curves.

Create the other entire wind tunnel surface using the new surface option.

Fig 41 : Wind Tunnel

Surface Meshing of wind tunnel:

We need to apply surface meshing depending the mesh length near the car and regions far away from it.

Therefore we need to apply different mesh lengths at the bottom and top wind tunnel surfaces.

We need to use spacing option to have a mesh length varying from the small mesh length sie to larger mesh length.

Surface meshing can be achieved by doing this accordingly.

Fig 42 : Surface Mesh on Wind tunnel

Volumetric mesh of wind tunnel car volume:

We are interested only the volume between the car model and wind tunnel, we can delete other volumes of the car model which is not necessary.

Since performing the volumetric mesh takes 2-3 days, volumetric mesh is not performed as given by the challenge question.

Fig 43 : Volume between Wind tunnel and Car model

Fig 44 : Car body single volume

Fig 45 : Tyres volume

Fig 46 : Silencer volume

Conclusions:

Performed the given BMW car model topo clean-up and Surface mesh appropriately.

Create surfaces using the reference hot points by using relative points.

Surface meshing is done for different components and varying their mesh lengths.

Wind tunnel is created, Different volumes of the car model is created.

Single volume is created of the car body so that it can be avoided at one go when creating a volumetric mesh.