BMW M6 geometry clean up and meshing

Aim:- Meshing and geometry clean up of the BMW M6 model.

Procedure:-

1. Work on the topological errors in the half portion of body first.
2. Mesh the half portion and then perform all the error corrections on it.
3. Use the symmetry option to get the other half of the geometry.
4. Create a wind tunnel for further CFD analysis in the future.

Geometry cleanup

• To improve the resolution we are increasing the mesh length to get a detailed model
• Now to remove modeling errors we have to remove the styling lines which were left by the CAD modeler.
• To remove styling lines disable macros and then use a universal delete option.
• This clean up is done by isolating different PIDs of the geometry and cleaning each one by one.
• First is the body of the car, here there is a large single con along both the sides of the geometry, to delete it first create a partition and then create a new face using coons option.
• Now isolate the feature in the sides of the body along with the body and then lock the working geometry.
• First, convert the single cons on the front side to triple cons using project option under cons then use extend option to fill the gap in between the feature geometry.
• Now at the backside of the feature use intersection option and then use delete option to remove unnecessary surfaces.
• Now on the front side again use the surface creation option and then go for fitted option and then use the intersection option between the new surface and the PID region within the box.
• Lastly, use the projection option to remove single cons and delete the option to remove unrequired surfaces and then fill the cavity at the front side using the fitted option in new under faces option.
• Coming to the windshields of the car, convert the volume elements to surface elements by using the delete option and then convert the triple cons to single cons by release and paste operation.
• Next is the front grill in the left corner of the car, isolate the surface first and then start by deleting extra unwanted surfaces, after which use the cut option to remove the unrequired projections and also delete the option to remove any anomalies. Now recreate the surface such that the outer feature will appear as mold with reference to the inner surface by using face creation and conversion of triple and single cons to double cons.
• Now use the F1 view in ANSA so that the right half of the car is deleted easily without the symbol circle. Use a universal delete option to do so. Make sure the outer lines of the cut have a single con to them.
• Now we have to work on the central grill which is now half before that we have to clear headlight volume, Then either create a new surface between gap or cut the previous surface from gap and delete it, then recreate surface using filled option.
• Now isolate the central grill and then remove the extra surfaces and then work on the fins by deleting its unrequired hot points and then use intersect option on the bottom portion from the upper end of the curved portion at the bottom.
• Now delete the back wall of fins so as to convert it to a surface element rather than the volume element. Then use the glide option under extrude in the surface menu along with paste option so that all the triple cons and single cons can be converted to double cons.
• Now we can delete the half portion of the car so that we can correct it easily and then use the symmetry option to get the full body.

Geometry Segregation

• In this different PIDs are arranged to there utility where 6 folders have to create consisting of body, grills, lights, tires, windows, and exhaust under model browser window.
• In this windows will consist of front windows, side windows, back windows and ORVM, Body is a single entity, tires are divided into rims and tires, Lights are divided into front headlights and rear headlights, grills are divided into intake grill side grill and central grill.
• Now we can on each error individually depending on the part of the car first we will work on the body of the car.

Body corrections

• Start by deleting unrequired parts in the tire casing of the body then after patching it up we will delete the unrequired surfaces at the bottom of the car and then patch it by creating a new surface option.
• After this, the exhaust portion of the is patched up so that space is created to contain the exhaust along with the body.

Wheels correction

• First, isolate the wheels and then work on each of them to convert the triple cons to double cons by deleting the common surface between the rim and the tire.
• Error corrections
• Run the geometry check on the model and make sure only single con errors are present on the cut portion of the car, patch any other errors in the geometry before moving into the mesh mode.

Meshing

• Now go to the mesh menu and then give the following specifications to the mesh creation per PID as given below.

Body=3mm

lights=4mm

Grills=1mm

Tires and rims=2mm

ORVM( Optical Rear View Mirror)= 2mm

Windows=2mm

Exhaust=3mm

Logos=1mm

• While inputting these values give a 15% distortion and distortion angle as 0.

Mesh creation

• Go to mesh parameters and then go to basic and select general mesh, give target length as perimeter, Min target length as 0.9, max target length as 5 and distortion distance, as well as distortion angle, is of the same value.
• Now select the free option under mesh generation and then create the mesh.
• Now perform a mesh check and remove the errors using delete option or reconstruct option depending upon the error.
• After this under quality parameters enable only skewness, min length, and max length option only. Disable all other options on the menu. This will lead to the total number of off surfaces to be displayed in the mesh detail menu if there are any errors.
• Now work on each error by right-clicking on each parameter and then select show only so that each type of error can be worked on separately.
• In the error, the correction step provide the min length parameter to be 0.2 so that useful features of the grill can be retained in the geometry.
• The skewness error can be corrected by a combination of options like MV surface, paste, cut and reconstruct options according to the error found.
• One can also go to a topological mode so that if unnecessary protrusions are present or a surface is missing in the geometry which can be corrected there and in mesh mode such areas can be remeshed and error can be removed from mesh.
• Now after removing all off surfaces that is errors in all forms one can use symmetry option to get back the other half of the car by going to transform icon and go for copy option and then select the symmetry tab and provide the three-point mirror form to set the plane for symmetry after selecting the entire half portion of the car.

Wind tunnel

• After all the errors have been patched, we have to create a wind tunnel so as to perform a CFD analysis on the car.
• We can create a wind tunnel by using these specifications:-

Inlet=4x car length

Outlet=6x car length

Top wall= 3x car length

Bottom wall= close to the tires in the geometry

• The distance can be measured of the car body using the measure tool and then effective points can be created using the relative option of the point menu and then form three additional points in the plane which is perpendicular to the direction of measurement in each of the plane formation. Then create the required plane using the three points.
• One can also use translate option as well as symmetry option for mesh generation, if any of the planes are not intersecting then one can use resize option to do so.
• After all, planes are created then on can use the intersect option and remove the unrequired surfaces by using universal delete option.
• Now we have to provide point space on the wind tunnel according to the following configuration:

Bottom= 20 divisons

Pillars=50 divisions

Top=100 divisions

• In pillars, we have to use the spacing option to create increasing mesh length. Under spacing, menu give biasing as geometric , factor=1.1,dmin=20 and dmax=100

Results:-

Learnings:-

1. The release option is used to disconnect the cons.
2. Symmetry option in the transform menu option can be used to move or copy the geometrical parts so that only one half of the geometry has to be corrected by using a plane of symmetry as per the type of geometry.
3. F1 to F8 are different view options in the ANSA.
4. For a CFD analysis, a mold of the features of the external geometry is only required rest all of the unnecessary features can be deleted so as to reduce the size of the mesh based on the type of study conducted.
5. Cut option is useful for segregating the unwanted surfaces and deleting them at once.
6. Some tools can be used in a stack like cut and delete options one after the other.
7. Tires of the geometry may or may not be symmetrical, one has to take care of the threads of the individual tires after symmetry option is complete
8. Reverse cut can be used for deleting stray cuts
9. Cut and project cuts are straight cuts while zone cuts are along a plane cut.
10. Split X option is used to split the elements while the swap option is used to change diagonals, Both of these options are used in mesh corrections.
11. The default plane in ANSA is the plane of the isometric view.
12. If facing mesh error problems perform error correction from mesh check and then go for mesh quality check correction.

Conclusion:-

1. The given geometry of the BMW has been cleaned from all the topological errors.
2. The given geometry has been meshed as well as all its mesh errors are also resolved effectively
3. A wind tunnel has also been created as well as meshed so that effective CFD analysis can be done in the future.