Week 4 Challenge : CFD Meshing for BMW car
AIM: CFD MESHING FOR BMW CAR MODEL.
PROBLEM STATEMENT:
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.
- Target lengths for the different parts of a model are as follow:
- Body - 3 mm
- Lights - 4 mm
- Grills - 1 mm
- Rims and Tyres - 2 mm
- Optical Rear view mirror - 2 mm
- Window - 2 mm
- Silencer - 3 mm
- Logo - 1 mm
PROCEDURE:
> Open the file in ANSA window by clicking on the file menu present at top left corner of the ANSA window.
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Assign the perimeter length as 1mm for the file due to which the curves present at the body become circular or simply use FINE option.
To assign the perimeter length follow CLASSIC MESH > PERIMETER > LENGTH > SELECT PERIMTER > BOX SELECTION > MIDDLE KEY > ENTER TARGET LENGTH AS 1MM > OK.
To use fine option follow TOPO > AUXILLARIES > FINE.
To perform the topological cleanup first delete half portion of car body and then perform the topological cleanup after performing it use TRANSFORM option to redrew the deleted surface
To use the transform option use the layout
TRANSFORM > COPY > SELECT ENTITY > SYMMETRY > 3 POINT MIRROR PLANE > SELECT 3 NODES > OK > FINISH.
After deleting half of the body using the checks manager check the geometrical errors by following the layout.
CHECKS > CHECKS MANAGER > CFD CHECKS GEOMETRY > EXECUTE.
All the geometrical errors will appear on the screen as shown in image below.
> Perform the topological cleanup such as elimination of the single cons,tripple cons,penetration,needle,corner cracks etc.
> To start the topological cleanup start with the grill portion.
> eliminate all the tripple cons and single cons and penetration error by simply deleting the surfaces.
> To check whether the topological cleanup completed use CHECKS by following the layout
CHECKS > CHECKS MANAGER > CFD CHECKS GEOMETRY > EXECUTE.
> In this grill portion remove all the tripple cons by deleting the extra surfaces and overlapping surfaces, confirm the selection ogf the surfaces by using wire frame model.
> Before performing the topological cleanup checks the error using the checks manager.
To remove this type of penetration errors first create the small cut at the parent surfaces by following the laout given below and then then delete those small surface by using the universal delete option.
TOPO > FACES > CUT > SELECT ONE POINT > SELECT ANOTHER POINT > MIDDLE KEY.
After eliminating of the penetration error fill the surfaces by following the layout
TOPO > FACES > NEW > SELECT FITTED OPTION > SELECT LOOP MODE > SELECT SURAFCES > OK.
After performing the topological cleanup checks for the errors using the checks manager.
In the above image after performing the topological cleanup for all the parts of the grills checks the errors using the checks manager. follow the same procedure for all other PIDs.
Isolate the particular pid in this case optical rear view mirror using the boolen operator NOT and then use LOCK option.
check all the errors using checks manager.
perform all the topological cleanup for eliminating the errors.
After performing topological clean up checks the geometrical errors using checks manager.
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> Delete all the small edges whose dimensions are less the target length.
> To measure the distance use measure option presen at top of the ANSA window
MEASURE > EDGES > SELECT EDGE
> Delete all the edges whose length are less then the target length using univaersal delete option and create the surface using TOPO > FACES > CONS > ENT > SELECT CONS > OK.
In the above image after performing the topological cleanup use the check manager where it shows all the geometrical errors has been resolved.
After the completion of topological cleanup assign some PIDs by following the layout
PROPERTY > PID MANAGER > RIGHT CLICK > NEW > ASSIGN NAME > OK > RIGHT CLICK ON PID > APPLY > SELECT THE PID USING BOX SELECTION > MIDDLE KEY.
Assign eight pids as shown in image below.
A
> Perform the meshing on each pids by hiding the other pids by turning off the bulb button present in the pid manager.
> for performing the pids floows the four steps.
1) MESH PARAMETER > CFD MESH > MINIMUM LENGTH AS 0.5 MM > MAXIMUM LENGTH AS 2MM > ELEMENT TYPE AS TRIA .
2) QUALITY CRITERIA > DISABLE ALL THE PARAMETER EXCEPT ASPECT RATIO, SKEWNESS , MINIMUM LENTH AS 0.5MM, MAXIMUM LENGTH AS 2MM > APPLY > OK.
3) CLASSIC MESH > PERIMETER > LENGTH > MACROS > BOX SELECTION OF THE PID > MIDDLE KEY > ASSIGN TARGET LENGTH AS 1MM > OK > PERIMETER > SLECT THE PID USING BOX SELECTION > MIDDLE KEY > TARGET LENGTH AS 1MM > OK.
4) CLASSIC MESH > MESH GENERATIONS > LONG PRESS ON CFD > SELECT VISIBLE.
After performing the mesh in grill porttion freeze this pid using freeze option by following the layout.
CLASSIC MESH > MACROS > FREEZE/UN > BOX SELECTION USING LEFT KEY.
Freezing of the pids are done because of diffrent target lengths present at the intersection of two PIDs.
> perform the meshing over the tyres, windows, optical side view mirror having the target length as 2mm.
classic mesh > perimeter > length > perimeter > box selection > assign target length as 2mm > macors > box selection > middle key > assign target length as 2mm > ok.
classic mesh > mesh generations > cfd > visible.
> If there are off elements then remove them by using the
RIGHT CLICK ON OFF ELEMENTS > IMPROVE > RESHAPE > SELECT EDGES > OK
> After performing the improve options if there are still off elements are present and if present off elements are due to the maximum length then change the maximum length in Quality criteria and change maximum length from 2mm to 2.5mm. follow the layout
QUALITY CRITERIA > MAXIMUM LENGTH > CHANGE 2mm TO 2.5mm > APPLY >OK.
> After changing the maximum length as 2.5mm if there are still some off elements are present due to the maximum length then eliminate them manually by following the layout
classic mesh > elements > splits > select edges > middle key.
> check the dimension using MEASURE tool present at top of ANSA window.
After performing the mesh in tyre. window , optical side view mirror porttion freeze these pids using freeze option by following the layout.
CLASSIC MESH > MACROS > FREEZE/UN > BOX SELECTION USING LEFT KEY.
Freezing of the pids are done because of diffrent target lengths present at the intersection of two PIDs.
> QUALITY CRITERIA > DISABLE ALL THE PARAMETER EXCEPT ASPECT RATIO, SKEWNESS , MINIMUM LENTH AS 0.5MM, MAXIMUM LENGTH AS 3MM > APPLY > OK.
> perform the meshing over the body and silencer having the target length as 3mm.
classic mesh > perimeter > length > perimeter > box selection > assign target length as 3mm > macors > box selection > middle key > assign target length as 3mm > ok.
classic mesh > mesh generations > cfd > visible.
> If there are off elements then remove them by using the
RIGHT CLICK ON OFF ELEMENTS > IMPROVE > RESHAPE > SELECT EDGES > OK
> After performing the improve options if there are still off elements are present and if present off elements are due to the maximum length then change the maximum length in Quality criteria and change maximum length from 3mm to 3.5mm. follow the layout
QUALITY CRITERIA > MAXIMUM LENGTH > CHANGE 3mm TO 3.5mm > APPLY >OK.
> After changing the maximum length as 3.5mm if there are still some off elements are present due to the maximum length then eliminate them manually by following the layout
classic mesh > elements > splits > select edges > middle key.
> check the dimension using MEASURE tool present at top of ANSA window.
After performing the mesh in body and silencer freeze these pids using freeze option by following the layout.
CLASSIC MESH > MACROS > FREEZE/UN > BOX SELECTION USING LEFT KEY.
Freezing of the pids are done because of diffrent target lengths present at the intersection of two PIDs.
> QUALITY CRITERIA > DISABLE ALL THE PARAMETER EXCEPT ASPECT RATIO, SKEWNESS , MINIMUM LENTH AS 0.5MM, MAXIMUM LENGTH AS 4MM > APPLY > OK.
> perform the meshing over the body and silencer having the target length as 4mm.
classic mesh > perimeter > length > perimeter > box selection > assign target length as 4mm > macors > box selection > middle key > assign target length as 4mm > ok.
classic mesh > mesh generations > cfd > visible.
> If there are off elements then remove them by using the
RIGHT CLICK ON OFF ELEMENTS > IMPROVE > RESHAPE > SELECT EDGES > OK
> After performing the improve options if there are still off elements are present and if present off elements are due to the maximum length then change the maximum length in Quality criteria and change maximum length from 4mm to 4.2mm. follow the layout
QUALITY CRITERIA > MAXIMUM LENGTH > CHANGE 4mm TO 4.2mm > APPLY >OK.
> After changing the maximum length as 4.2mm if there are still some off elements are present due to the maximum length then eliminate them manually by following the layout
classic mesh > elements > splits > select edges > middle key.
> check the dimension using MEASURE tool present at top of ANSA window.
> unfreeze all the pids by using the layout.
CLASSIC MESH > MACROS > FREEZE/UN > BOX SELECTION USING RIGHT KEY.
> Create the close contors of following dimensions.
> front domain of the close contour will be at a distance of 4 times of the length of the car from the car frontal portion that is at a distance of 5200mm.
> rear domain of the close contour will be at a distance of 6 times of the length of the car from the car rear portion that is at a distance of 7800mm the large porion at the rear end due to the bake area and Negative pressure region present at back side of the car.
> Top domain of the close contour will be at a distance of 3 times of the height of the car from the car top portion that is at a distance of 1050.
> Bottom domain of the close contour will be at a distance of 80mm from the car bottom area.
> Both side domain of the close contour will be at a distance equal to width i,e, 500mm from the car side portion i,e, extreme portion of optical side view mirror.
> create the close contour by following the steps.
1) Create the 3D points.
TOPO > POINTS > RELATIVES > SELECT THE POINT AT THE BOTTOM OF THE CAR > MIDDLE KEY > ENTER DIRECTION AS dy =-1 > enter distance as 80mm > ok.
By following this procedure a 3D points at 80mm below the bottom of the car will be created.
Create the 3D points at the rear end of the car.
TOPO > POINTS > RELATIVES > SELECT THE 3D POINT > MIDDLE KEY > ENTER DIRECTION AS dZ =-1 > enter distance as 9100mm( Length of the car as 1300mm+ 6 times the length of the car) > ok.
Create the 3d point at a approximate distance of 1550mm( height of the car as 350+ 3 times the height of the car+ 80mm) from the 3D points those have been created.
TOPO > POINTS > RELATIVES > SELECT THE ALL FOUR 3D POINTS > MIDDLE KEY > ENTER DIRECTION AS dY =1 > enter distance as 1550mm( height of the car as 350+ 3 times the height of the car+ 80mm) from the 3D points those have been created > OK.
Delete the 3d points those are present at middle.
2) Create the curves/ edge for creating the surface between the 3D points.To create the edges follow the layout
TOPO > CURVES > CREATE > SELECT TWO 3d POINTS > PRESS MIDDLE KEY.
> Create the surface using the layout
TOPO > FACES > NEW > FITTED > SELECT EDGES > OK
Delete the edges and 3D points using the universal delete option before deleting the 3D points and edges hide the surafce using boolen operator NOT and then select the 3D points using box selection and then delete them using using universal delete option.
> Assign the target length as 20mm for the bottom domain and 100mm for the top domain of the close contour.
classic mesh > perimeter > length > perimeter > box selection of the bottom domain by hiding all other pids using bulb button > assign target length as 20mm > macors > box selection > middle key > assign target length as 20mm > ok.
classic mesh > perimeter > length > perimeter > box selection of the Top domain by hiding all other pids using bulb button > assign target length as 100mm > macors > box selection > middle key > assign target length as 100mm > ok.
> Use spacing option, for gradually increasing the mesh element size from 20mm to 100 mm spacing option is used.
CLASSIC MESH > PERIMETERS > SPACING > SELECT Bi- Geometric as biasing > start factor as 1.1 > dstart as 20mm > dlimit as 100mm > select at the bottom portion at the cons present at all four edges near the bottom domain of the close contour for deciding the direction for gradual increase in the mesh element size.
> perform meshing over the surfaces by hiding the car body using the bulb window present at the pid manager.
check the target length of the mesh whether it is gradually increasing from bottom to top from 20mm to 100mm using the MEASURE tool.
Eliminte off elements by RIGHT CLICK ON OFF ELEMENTS > IMPROVE > RESHAPE > SELECT EDGES > OK.
So in the above image it is clear that mesh element size is gradually increasing from 20mm to 100mm from bottom to top domain of the close contour.