Week 4 Challenge : CFD Meshing for BMW car

CFD MESHING FOR BMW CAR:-

Objective-

• Do topo cleanup for BMW car
• Do 2D meshing, check quality criterias
• Use hidden mode to check failed meshes on quality criteria
• Use reconstruct option to  view and  clear failed meshes
• Do 3D Meshing for car
• Create a wind tunnel , either in 2D or 3D mesh depending on capacity of your system

NOTE: Due to lot of challenges faced while working on this geometry, repeated changes have been done to solve different parameters and I have recorded as much as possible so that I  can paste those on challenge page to do an explaination for them. Minute details are  not captured as there are multiple such changes which had to be done in order to fix this geometry, only few initial and final steps are captured in order to give an overview of what you have to do and challenges you require to overcome while working on this project.

Steps involved in complete process-

• Topo cleanup - topo cleanup is basically cleaning geometry by removing unwanted surfaces and solving triple and double cons
• Geometry is irregular in shape after we exported file to ansa. Irregular means surface irregularities , removing these is our first step
• Start with topo cleanup for eachh parts eg: tyres, grills, logos, windows, lights and batteries
• Use entity mode while working.
• Divide geometry into half as geometry is symmetric.
• Start with 2D meshing after topo cleanup
• Start with 3D meshing after 2D meshing

Original Geometry-

 Single and Double cons-

Cons which we see above picture needs to be solved in order to complete topo cleanup.

STEP 1 - TOPO CLEAN-UP

Original geometry first error is that cons are irregular, this is overcome by going into mesh tool

• Go to mesh tool and select length perimeter of 1mm for complete body, this will resolve all irregularities in cons alignment and body will appear in proper shape.

Divide Car into half

Problems in which there is symmetry on both sides it is prefered to divide body into half and then work on half body and then do symmetry to create other half of body withh available half body. This eases our work by half as there is only geometry to work with and the rest can be part can be created by symmetry tool.

 Geometry divided into half

 

 CONS to be solved for half geometry

Parts to be solved 

• Side mirrors
• Grills 
• Tyres 
• Body
• Lights 
• LOGO

SIDE MIRRORS

• Isolate side mirror by using Inot tool
• Remove all overlapping surface by identifying them using boolean operation tool
• Removing overlapped and extra surfaces will solve triple cons
• Use paste option to solve single cons if any.

side mirrors after topo cleanup done

 

GRILLS

Three grills are present in half body. We will solve each of them seperately.

Grill-1

Steps involved 

• Start with deleting extra surfaces
• There is large single con on front of grill, project that con on longitudnal grill you see, and after that delete upper part of longitudnal grill.
• Create hot points where there is requirement, so that it would be easy to create new surface with those hot points.
• Delete sharp edges from both corners of grills. Seperate sharp edges by creating cuts and then delete them
• Next step is to close grill geometry from inside or from back
• Use face tool to create new surfaces to close geometry.

Deleting extra and overlapped surfaces

Creating new surfaces to close geometry.

Geometry closed

All single and double cons solved

Front view of grill

Grill- 2

This part was hard to complete that is why very less content is recorded for this part.

Steps involved

•  Start with deleting overlapped surfaces and extra surfaces
• We have to remove triple cons, triple cons are form when there is volume formed, so delete surfaces which are contributing towards volume creation.

•  After deleting outer overlapped surface, there is another surface behind it, project cons of grills on this surface so that we can delete those surfaces
• In below right side image you can see a long surface been deleted, that surface was in alignment with grills. In same way project cons from grills to this surface and delete them.

   

•  After deleting all extra and unrequired surfaces we are left with few single and double cons
• use topo on those cons most of them will convert to double cons and some which are left are either there because of extra hot point or because of two single cons which are not pasted together, paste them using paste tool.
• Use delete tool to delete triple con because that surface is not creating a volume still there was a triple. Always assume there is very fine extra surface present there in such situation, you can just use delete tool to get rid of those triple con.

    

• Geometry cleanup is complete and we are left with only double cons

•  Use wire frame mode to get a better view 

 

 Grills -3

Steps involved-

• Start by deleting extra and overlapped surface. After deleting all overlapped surfaces you will find you geometry like show in below image.
• Zoom into geometry and delete fine extra edges by creating cuts around them
• Use cut tool to creates cuts where there is required in order to refine geometry
• After creating cuts delete unrequired surfaces
• now use new tool to create new surface using fitted option

• In below image you can observe curved shaped single cons, create cuts from top hot point to bottom hot point.

 

• After creating cuts delete surface in order to get smooth geometry

• Deleting sharp edges which is seen after zooming into geometry

• Start creating new surface using fiited option to close the geometry from inside

• Geometry clean up is done and use wire frame mode to confirm there is no single or double cons.

LOGO-

Steps involved

• Focus on two faces of logo, top & bottom.
• Start with bootom surface , delete overlapped surfaces. You will see logo hollow from bottom after deleting bottom surface
• Then go to top surface there you will another overlapped surface and delete it.
• Use not tool and hide top surface inside you will and extended surface attached with top surface inside logo, delete it.
• There is circular strip surface on top logo along boundary, delete that surface and use coons option to create a new surface at the gap created between boundary and middle part of logo.

 

• Geometry cleanup for logo is done

WINDOWS & LIGHTS-

• Windows of car contains volumes, delete surfaces forming volumes from inside of car.

 

• Deleting surfaces

 

• Deleting surface which are forming volumes at back of front light.

BODY-

• Start with door handles, start by deleting overlapped surface as hown in image.
• there are some surface behind deleted surface, delete them too.
• After deleting them create new surface by selecting single cons.

Next step involved in body cleanup is cleaning lower portion, as we can see surfaces are penetrating in tyres which needs to resolved.

• Drectly delete surfaces which are penetrating with tyres or create cuts to create seperation between surfaces which are required to be kept and which are required to be deleted.
• There are lot of uneven surfaces at bottom part of car, I advise you to delete and all those surfaces and create a blank area, there we will create new surfaces by using coons option.
• You can use construct curves option to create boundary line of surfaces before deleting so that while creating new surfaces you can use those lines as references.
• Another approach here is you create a new surface at edge of car, and you can take that surface as areference line and can delete that surface after creating surfaces.

• One take away while solving this region is that its better if you delete half of area between front and rear tyres and recreate them, as it would be easiest approach according to me.

Geometry checks

• Do geometry check after doing topo cleanup to see if there is any songle or triple cons left.
• I have checked my geometry and there is no such cons present, so my topo cleanup is properly done.

PIDs Assigned

 Step 2- START 2D MESHING-

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

Start with meshing of smaller parts

REAR VIEW MIRROR-

•  Mesh length is 2mm
• After giving quality criterias, give length parameters and macros
• select length parameters and choose PID by doing right click and dragging cursor over PID. Then do middle click
• Dialogue box will appear, give mesh length 2mm and click ok
• Similar do for macros
• Then select spot mesh and choose visible mesh, you can see mesh on PID
• In order to check if geometry is failing on quality criteria go to hidden mode and go to entity mode while using hidden mode.
• you will off elements. select reconstruct option and choose visible and execute reconstruct option. Reconstruct option will solve most of off elements and remaining off elements needs to be solved by findind why mesh is failing, mainly this happens due to formation of meshes smaller than specified criteria.
• Go to topo mode and use cut options to cut or recreate cons where mesh is failing. 

 

 

• Inside hidden mode we can see off elements as below and we can also see on which criteria it is failing.

GRILLS Meshing-

•  Mesh length is 1
• mm
• After giving quality criterias, give length parameters and macros
• select length parameters and choose PID by doing right click and dragging cursor over PID. Then do middle click
• Dialogue box will appear, give mesh length 2mm and click ok
• Similar do for macros
• Then select spot mesh and choose visible mesh, you can see mesh on PID
• In order to check if geometry is failing on quality criteria go to hidden mode and go to entity mode while using hidden mode.
• you will off elements. select reconstruct option and choose visible and execute reconstruct option. Reconstruct option will solve most of off elements and remaining off elements needs to be solved by findind why mesh is failing, mainly this happens due to formation of meshes smaller than specified criteria.
• Go to topo mode and use cut options to cut or recreate cons where mesh is failing. 

  

• Measure distance betweens nodes and cons where you believe meshes can fail
• For value of min length you can see by measure tool where length is minimum and give min length less than that in order for mesh not to fail on quality criterias.

• Meshing done and quality criterias checked

LOGO Meshing-

•  Mesh length is 1mm
• After giving quality criterias, give length parameters and macros
• select length parameters and choose PID by doing right click and dragging cursor over PID. Then do middle click
• Dialogue box will appear, give mesh length 2mm and click ok
• Similar do for macros
• Then select spot mesh and choose visible mesh, you can see mesh on PID
• In order to check if geometry is failing on quality criteria go to hidden mode and go to entity mode while using hidden mode.
• you will off elements. select reconstruct option and choose visible and execute reconstruct option. Reconstruct option will solve most of off elements and remaining off elements needs to be solved by findind why mesh is failing, mainly this happens due to formation of meshes smaller than specified criteria.
• Go to topo mode and use cut options to cut or recreate cons where mesh is failing. 

While using measure tool we find some lenghth on logo which are smaller than minimum length, so delete and create new surfaces on BMW so that minimum length problem is solved.

 

  

 

 Meshing done and quality criterias checked.

Logo fulfills quality criteria

LIGHTS-

•  Mesh length is 4mm
• After giving quality criterias, give length parameters and macros
• select length parameters and choose PID by doing right click and dragging cursor over PID. Then do middle click
• Dialogue box will appear, give mesh length 2mm and click ok
• Similar do for macros
• Then select spot mesh and choose visible mesh, you can see mesh on PID
• In order to check if geometry is failing on quality criteria go to hidden mode and go to entity mode while using hidden mode.
• you will off elements. select reconstruct option and choose visible and execute reconstruct option. Reconstruct option will solve most of off elements and remaining off elements needs to be solved by findind why mesh is failing, mainly this happens due to formation of meshes smaller than specified criteria.
• Go to topo mode and use cut options to cut or recreate cons where mesh is failing. 

 Meshing and quality check done. PID fulfills quality criteria.

SILENCER Meshing-

•  Mesh length is 3mm
• After giving quality criterias, give length parameters and macros
• select length parameters and choose PID by doing right click and dragging cursor over PID. Then do middle click
• Dialogue box will appear, give mesh length 2mm and click ok
• Similar do for macros
• Then select spot mesh and choose visible mesh, you can see mesh on PID
• In order to check if geometry is failing on quality criteria go to hidden mode and go to entity mode while using hidden mode.
• you will off elements. select reconstruct option and choose visible and execute reconstruct option. Reconstruct option will solve most of off elements and remaining off elements needs to be solved by findind why mesh is failing, mainly this happens due to formation of meshes smaller than specified criteria.
• Go to topo mode and use cut options to cut or recreate cons where mesh is failing. 

  

 

 

WINDOWS & Tyres Meshing-

•  Mesh length is 2mm
• After giving quality criterias, give length parameters and macros
• select length parameters and choose PID by doing right click and dragging cursor over PID. Then do middle click
• Dialogue box will appear, give mesh length 2mm and click ok
• Similar do for macros
• Then select spot mesh and choose visible mesh, you can see mesh on PID
• In order to check if geometry is failing on quality criteria go to hidden mode and go to entity mode while using hidden mode.
• you will off elements. select reconstruct option and choose visible and execute reconstruct option. Reconstruct option will solve most of off elements and remaining off elements needs to be solved by findind why mesh is failing, mainly this happens due to formation of meshes smaller than specified criteria.
• Go to topo mode and use cut options to cut or recreate cons where mesh is failing. 

BODY-

There is a concept  we have to follow while meshing body which is

• When there are PIDs with different mesh length and they are in direct contact with each other meshes on one PID disappear when me mesh other PID. This problem is overcomed by deleting perimeter lines that are in contact with other PID
• As we can see in image after selecting perimeters white color lines appeared on body, so we will delete perimetric lines that are in direct contact with other PIDs and then do right click and give mesh length

Steps for meshing

•  Mesh length is 3mm
• After giving quality criterias, give length parameters and macros
• select length parameters and choose PID by doing right click and dragging cursor over PID. Then do middle click
• Dialogue box will appear, give mesh length 2mm and click ok
• Similar do for macros
• Then select spot mesh and choose visible mesh, you can see mesh on PID
• In order to check if geometry is failing on quality criteria go to hidden mode and go to entity mode while using hidden mode.
• you will off elements. select reconstruct option and choose visible and execute reconstruct option. Reconstruct option will solve most of off elements and remaining off elements needs to be solved by findind why mesh is failing, mainly this happens due to formation of meshes smaller than specified criteria.
• Go to topo mode and use cut options to cut or recreate cons where mesh is failing. 

We can observe that even after using reconstruct tool there are 557 off elements. There is no problems with these off elemnts as they are appearing on areas where there is change of mesh length or where Body is in contact with other PIDs so this is scompletely fine.

PIDs name assigned after meshing

 

Step 3- CREATING OTHER HALF BODY USING SYMMETRY OPTION-

• Go to transform tool at top-right and choose copy option from transform tool.
• Choose Mirror 3 Points Plane from dropdown menu.
• There are options X1 X2 & X3, these box is required to be filled with coordinates 
• choose three points as shown in image and those boxes will automatically take coordinates of those points after that do middle click and then another dialogue box will appear which will ask you to give offset distance as we dont want our copy to be created at an oaffset distance so leave that part and click ok
• Your symmetry body is created and geometry is now complete.

• After symmetry is done there are single cons between old and newly created part. Use paste tool to paste those cons and convert them to double cons.

Do geometry check with cons and umeshed macros on.

Our model is completely fine and ready to go for 3D meshing and creating wind tunnel

 

Step 4- WIND TUNNEL CREATION

We will create a wind tunnel around car

Measurment for wind tunnels are-

• Consider length of car as X
• Keep wind tunnel at 75mm distance from bottom of car
• Length of wind tunnel from front of car should be 4X, total length of tunnel in front is half length of car added to 4X length
• Length of wind tunnel from back of car should be 6X, total length of tunnel from rear side is half length of car added to 6X length
• Height of wind tunnel should be 3X

Steps Involved-

• Enable cons 
• select relative points option from point tool and select a point in middle of car from bottom side
• A dialogue box will appear, see your coordinate axes, To create a point at bottom of car I will give 75mm with negative sign.
• With reference to that point create a point in front of car at distance 5820 in Z direction

 

 

• Do middle click and point is created in front of car

• Similarly measure distance from middle to back of car and create a point at 6X added to this distance in negative Z direction

• Point at back of car is created 
• Now with reference to this bottom point create a point at 3X distance in positive Y -direction. This is height of wind tunnel
• Next step is to create points on both side of car with help of front and back points at a distance X which is 1300mm.

• Points created at both sides of car
• Now you can use offset option to offset points created at sides of car in upward direction at 3X distance or you can select those points and create another set of points at 3X distance in ositive Y-direction.
• Use Create  curve tool to create lines to connect points which are created.
• Select create curve select one point and then select another point and do middle click. In this way joint all points so that we can create wind tunnel using them
• After creating wind tunnel delete points and curves which were created earlier.

• After creating wind tunnel its time for meshing
• Top surface of wind tunnel would be meshed with 100mm mesh length
• Bottom surface would be meshed with 20mm mesh length

USE OF SPACING TOOL-

After creating top and bottom meshes it time for meshing sides of tunnel. In order to mesh sides of tunnel we will use spacing tool.

Basically what spacing tool does is it will vary mesh length from bottom to top, give min length as 20mm and max limit as 100mm and select factor of 1.1 and click ok.

Steps involved

• choose spacing tool give dmin and dlimit and spacing factor 1.1. spacing factor varies length from bottom top by factor of 1.1
• click on ok and select faces and do middle click.

3D-MESHING TOOL-

• Choose define option available in volumes tool and select wholedb(whole database) and click on ok.
• Volumes created for 3D meshing will appear in a dialogue box

• From dialogue Box select first volumes this is the volume of tunnel and this is what we require.
• All oher volumes are car volumes which is not required so delete them.

 

 

 

 

 

 

CONCLUSION-

• Working on BMW model gave ideas about different meshing tools available in ANSA.
• Learned surface meshing and Geometry cleanup in much detailed manner. Challenges faced helped to understand tools better
• Learned how to use curve tool, how to create win tunnel with help of points and curves
• Learned about dimensions of wind tunnel, like what dimesnions to give based on model size
• Learned how to de meshing when there are different PIDs with different mesh length in contact with each other
• Advance topo-cleanup