Week 4 Challenge : CFD Meshing for BMW car
Title :- CFD Meshing for BMW car
Aim / Objective:- 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 as mentioned in the question. After meshing the half model use symmetry to the other side and also mesh the wind tunnel only surface mesh not volume as it will take more than 2 days to perform.
Given PIDs and target length for the different parts of the model:
- 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
Topo cleanup - Set of tools for Geometry clean-up and for setting up of PIDs.
Surface mesh - A surface mesh or 2 D mesh consists of a set of polygonal faces, often triangles, that, taken together, form a surface covering of the object.
Volume mesh - In 3D computer graphics and modeling, volumetric meshes are a polygonal representation of the interior volume of an object.
In our case topo and surface mesh will be performed .
Tools to import the object -
1. Function Name : Open
Summary :
This function activates the File Manager and enables the input of data from a neutral format file or an ANSA database file. The neutral CAD formats currently supported are the VDA_FS, the IGES and the STEP format.
Then go to check manager to check the existing errors( Like - single coons, triple coons, unfinished surface , hollow, etc) in the given model.
Required tools for topo cleanup -
1. Summary:
This function defines a new surface by selecting its boundary curves and creates a corresponding face that covers the new surface. The calculated surface appears as a net.
Function List :
New [COONS]
New [EXISTING SURF]
New [PLANAR]
New [FITTED]
2. Function Name : Cut
Summary :
This function cuts (splits) an existing Face or joins faces if inverse operation is applied (right mouse button).
3. Function Name : Project
Summary :
This function projects, as CONS or 3D Curves, a number of selected 3D-curves, CONS, element edges, line elements or Hexa Box edges on a number of selected Faces, WPLANEs and CROSS_SECTIONs, in a user controlled direction.
4. Function Name : Parametrical
Summary :
This function defines a new Node or Hot Point parametrically on a 3D-curve segment or a CONS segment.
5. Function Name : Topo
Summary :
This function automatically creates topological conditions between selected adjacent CONS.
6. Function Name : Fill Hole
Summary :
This function fills holes on Faces.
7. Function Name : Fine
Summary :
This function increases or decreases the presentation resolution of a selected 3D-curve or CONS segment.
8. Function Name : Transform
Summary :
This function defines new 3D Curves as transformation of a number of selected consecutive 3D Curves, CONS or Cross Section segments.
9. In order to give name to the available properties in the model we use
Function Name : Properties
Summary :
This function facilitates property management. A list of the properties existing in the file is available.
9. To delete the unwanted PIDs
Function Name : Compress
Summary :
This function is used to compress an ANSA database.
10. To delete the unwanted and overlapping surface we can use ..
Function Name : Delete
Summary :
The Delete function of the Geometry Group can be used to delete various ANSA entities (Curves, Faces, FE-Model entities etc.).
11.Function Name :Undelete
Summary :
This function recovers a Face that was previously deleted, provided that the COMPRESS command was not used since the Face was deleted. As the Faces>Undelete function is activated, all deleted Faces still in the database become highlighted and can be selected for recovery.
12.Function Name : Orient [Visible]
Summary :
This function sets a uniform orientation direction to all visible Faces according to the orientation of the majority of the Faces. The mesh elements that will be generated, or those already existing, also obtain a uniform orientation.
13.Function Name :Intersect
Summary :
This function defines the intersection between two groups of Faces and/or FE elements that penetrate each other. Topology can be applied automatically if required. In case that the two groups can define a closed volume between them, Boolean operations can be applied.
Using this tools we can deal with the errors like single coons, triple coons, unfill hollow, intrsection errors, convex cons, concave coon, overlapping surface ( If we enable PID draw mode , overlapping surface will be shown clearly) .
Required tools for surface Meshing:-
1. Function Name : Mesh Parameters
Summary :
This function opens the 'Mesh Parameters' window, where the user can define the parameters for the Reconstruction, Reshape and Fix functions.
2. Function Name : Quality criteria
Summary :
Select and set the respective quality criteria for the corresponding elements to perform the Quality Checks (Hidden Mode). Also set the general presentation settings concerning the ANSA workspace.
3. Function Name : Length
Summary :
This function defines the element length on selected perimeter segments or macro areas. The element length may be explicitly declared or may be declared as a factor to be multiplied by the existing element length.
4. Function Name : Spot Mesh [Select - Re-Generate - Visible]Summary :
This function automatically meshes Macro and FE shell mesh areas using a special meshing method for Macro-Areas that have 'weld spot' nodes on their surface.
In order to give target length for the Meshing, we used mainly Mesh parameters, Quality Criteria, Macros and Perimeters in length tool within Perimeters manager.
5.Function Name : Spacing [Manual]
Summary :
Manual control of nodal spacing and distribution on perimeter segment. There are five available node-biasing modes in ANSA, Linear, Geometric, Bi-Geometric, Bell Curve and User Defined. This function can be applied only on CONS, if there is no CONS in the model, the function is not activated.
6.Function Name : Free [Select]
Summary :
This function automatically meshes Macro Areas and FE shell areas using the Free meshing method, taking into account the element type already selected and the defined meshing parameters.
In order to clear the off elements this tools are strongly recommended :
1.
Function Name : Move
Summary :
This function can be used to move nodes. Selected nodes can be moved/slid freely in space with respect to global or a local coordinate system, on a geometrical or FE model surface, along a perimeter or can be offset from a perimeter.
2.
Function Name : Split [Shells]
Summary :
This function splits quadrilateral and triangular shell elements into smaller ones. Element splitting is performed between selected nodes and/or inserted nodes along selected element edges.
3.
Function Name :Improve
Summary :
The function is applied on either meshed Macro Areas or FE models in order to improve the existing mesh. The user can select one of the embedded algorithms: Reconstruct, Reshape, Smooth or Fix Quality.
4.
Summary :
This function defines a new number of edges or nodes on a selected Macro Area's perimeter segment. The same number can be transferred to other indicated perimeter segments.
Tools for creating the wind tunnel:-
1.
Function Name :Relative
Summary :
This function defines new 3D-points that lie on a given relative position from a number of selected 3D-points, Hot Points, Weld Points etc. The input of a (dx, dy, dz) vector, or an indication by the mouse is required for the definition of the relative position.
2.Function name : Create
Summary :
This function streamlines legacy functionality for Planar and 3-D curves, including primitive planar shapes (circles and ellipses, rectangles) and adds corner fillet, trim and offset capabilities. Support may be derived from geometric and element entities (e.g., Faces, CONS, Curves, Nodes, Elements, Working Planes e.t.c).
Procedure to Clean all geometrical errors for the given model:-
1. First of all impotr the object and go to check manager to see what are the errors presendt in the model . As the given model is almost same from the two side except the silencer part and logo we can go first for thr half portion of the car and then using symmetry tool in transform to join the model. So in order to do that !Not ,Not tool has been used.
2. Then we have isolated the grill part and resolve the erros for the grill part. you can see here the triple cons , single cons also there are many needle face, intersection erros, overlapping surfaces...
In order to do that we have splitted the grill in theree part and then cleaned all erros as you can see in the following snapshots.
There is only single cons because there is another surface which we have isolated in order to perform topo easily.
3. Then we have cleared the erros for light , window, optical view mirror, tyres, cylenser, etc.
Logo part -
Tyres -
Cylenser -
4. Then after clearing all the eros in the first portion of the car , in order to join the another half , we have used symmetry tool in transform.
After using the symmetry tool we have given back the original bmw model.
As you can see there is no more geometrical error like single cons, triple cons or any intersection erros, convex cons, etc.
We have cleaned all the errors .
5. Now in order to set pids SET Pid in Faces option has been used. We have given the eight pids for this model.
- 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
6.And to delete the unnecessary pids compress tool is used.
Now , our model is all set to go for surface mesh.
Procedure for surface Meshing :-
1. We have meshed the model by the given pids and target length one by one.
First we meshed Grills and logo as the target legth is same for these pids. We have given min and max target length in Mesh Parameters and Quality Criteria. In quality criteria we have checked the Aspect ratio, Skewness, min and mix length.
2.Surface mesh for Grills and Logo
Here you can see that there is no more off elements. And to do that Improve tool in Shell Mesh , Split in Elements etc tools has been used. Usimg improve tools ANSA will autometically reshape or reconstruct the mesh elements in order to clear the off elements.
Mesh for Window,Rims and tyres,optical rear view mirror-
Freeze tool in Macros has been used after performing mesh so that the other meshing surface is not affect by this meshing surface because the target length are different .
Surface mesh for Body and Silenser -
Target length is same for both 3 mm .
Surface mesh for the last part Light-
BMW car model afetr sueface mesh:-
And you can see , in this way mesh for BMW car model has been performed and there is no more off elements . By clicking on the hidden in the below you can see the offelements, Here we have cleared all offelements.
Now create wind tunnel or you can say CFD domain to calculate the drag forces , and the speed of the car , surface is being affected by the drag force , etc. Here we have performed only perform surface mesh on wind tunnel not volume mesh as it will take more times.
Procedure to create the wind tunnel:-
1. Before creating we need to measure the length, width and height of the car.
2. Create in curve , Relative in points has been used to create the wind tunnel.
First using Relative tools in topo we have to create a curve in y direction and then create the surface using curve tool, Fitted in New.
In this way we created the wind tunnel. Then set pids for the Top , Bottom, Side , Front and Rare domain in wind tunnel.
3. Now we meshed the winned tunnel by length 20 mm for Bottom and 100 for Top domain . And at last using spacing we meshed all the PIDs in wind tunnel . In spacing we have used Dstart = 20 and Dlimit = 100.
Snapshot of the wind tunnel:-
Conclusion:- So we have performed the topo on the half portion and then used symmetry tool to join the other portin of the car. After topo surface mesh has been performed by the given target length and atlast we created a wind tunnel and meshed it .There is no offelements in my BMW car modeland wind tunnel.
Link for the BMW car model:- https://drive.google.com/file/d/1rLWMQMd0Q1aZmjRyNfUHzXEInT8kO9F0/view?usp=sharing