CLEANING UP AND MESHING THE BMW M6 MODEL USING ANSA

OBJECTIVE:

To cleanup and meshing the given geometry model and also perform the wind tunnel set up.

Given geometry:

Fig.Given BMW M6 geometry model in PID mode.

Fig.Given BMW M6 geometry model in wireframe mode.

METHODOLOGY:

As we seen that the given geometry has several topological errors,missing faces which are indicated by single cons and triple cons but for cfd analysis only the double cons are preferred even triple cons are not acceptable. Let\'s do a systematic approach to solve these errors and mesh the given model.

1)

i)

• The given car model has a symmetry on a central axis ,the best way to approach is deleting the half of a model.
• eliminating the topological errors and meshing on one side and finally perform the symmetry.

ii)

Fig.inner view

• For an external flow analysis we don\'t need a volume of the features or parts .
• Therefore, deleting the thickness of a part,unnecessary faces to get rid of single cons and triple cons in this feature of the model.

Fig.exterior view of the feature after eliminating errors.

2)

fig.exterior view of a window

• Triple cons are appearing in a window where the edge is shared by three surface.

Fig inner view of a window

• Deleting the thickness of a glass which is present inside to get rid of a triple con.
• Same procedure is proceeded for rest of the windows(front,back and side).

Fig. exterior view of a window after eliminating the triple cons.

3)

fig.side grill feature

fig.grill feature of the model(centre grill)

• To get rid of these error, First delete the overlapping surfaces and thickness of a grill which is not necessary for analysis.
• Delete the inner surface and recreate it inorder to make it as a one whole volume.

fig.grill feature of the model after eliminating errors.

4)

fig.given model browser window

• Given model browser contains all the parts and features in a one folder.
• In order to get easy access, segregation of parts accordingly by using not option and creating the new folder by clicking right mouse button on a model browser window.

fig.edited model browser window

5)

• Set the PID for each feature of a model in the properties window.
• Compress it to make all PID is visible.

6)

Fig.geometry check window

• After get rid of the single and triple cons,Geometry checkup has made to check whether there is a needle face,triple cons,single cons are present in the geometry.
• Only the single cons are present at the symmetry edge of a car which will be fix automatically after performing a symmetry operation.

7)

Meshing:

Given element length size:

fig.trias surface mesh as per the given element length size

8)

surface mesh checks:

Excluding the penetration proximity,trias on corner and mesh quality all other mesh checks have done perfectly without any errors.

i)

fig.penetration proximity error showing on a grill

• This error occurs when the elements are very close to each other(distance b/w the two adjacent element is lesser than specified).It may cause problem in flow analysis,the flow characteristics calculated in this region will not be so accurate.
• To get rid of this error, using cut option in macros and delete the elements or change the specified length in the parameters list.

ii)

Mesh:Trias on corner warning and Mesh quality error arises when the specified mesh quality criteria and mesh parameters is not satisfied.

fig.mesh quality criteria as per our requirement

• Quality criteria is a tool where we can change the individual element quality.
• In our case we check it for skewness,length and angle under the shells.Any element that occupies in a 2D space called shells.

• Red colour shows that the error in min length or max length of a element.This error is rectified by either make changes in quality criteria or using the cut option to delete the elements and make a new surface elements but in our case this approach is not valid we can change the min length 0.9 to 0.2 . shell mesh>reconstruct to get rid of these errors.
• These error occurs when mesh element length differs as it grows towards inside ,this error can be controlled by target element length.
• Green colour indicates the skewness element.Skewness refers to the deviation of tri element to a line(equilateral triangle have a skewness of 0).

fig skewness error showing in top of the grill

This error is eliminated by using three options,

• Grids>paste option to join the nodes manually.
• Elements>split option to split the element into smaller.
• Grids>MV surf option to move the single mesh node.
• similiarly, same procedure has proceeded for entire model where these errors exists.

9)

After eliminating the skewness and length errors .Symmetry option is performed by using Transform>copy>symmetry>mirror 3 points plane.

fig.performing symmetry operation

fig.BMW M6 model after performing a symmetry.

10)

Wind tunnel setup:

Given wind tunnel setup dimensions:

• In order to create a wind tunnel, first create a relative point along the axis of given size and create a surface>plane.

fig.wind tunnel in a wire frame mode

fig.wind tunnel in a PID mode.

LEARNING OUTCOMES:

While doing this project i\'ve came to know about how to

• perform symmetry,rotation,translation and scaling option under Transform tool.
• use model browser.
• perform surface mesh checks and also learnt surface check manager.
• use quality criteria tool and also learnt various options under the shell parameters(skewness,warping,min length,max length,min angle,max angle etc).
• eliminate the errors such as penetration proximity,skewness,min and max length using various tools.
• setup wind tunnel as per the given dimension.

RESULTS:

• The entire geometry has meshed correctly ,only the unmeshed region is wind tunnel setup which it\'s not necessary for this project.Volumetric mesh is not done for this project as it may too cost and takes much time for meshing.

CONCLUSION:

The given BMW M6 geometry model has cleaned up and meshed perfectly.

LINK: https://drive.google.com/open?id=1NUv9lb52Ds92rn-iCXpcbUH-xzdW3Jbl