Project 1 : CFD Meshing for Tesla Cyber Truck

AIM :

To perform the volumetric mesh for the given tesla cyber truck model over the the fluid domain region for doing CFD analysis in the model.

OBJECTIVES :

• To check every geometrical errors in the given cyber truck model and to perform respective topological clean up in it.
• To assign PIDs ( Propertty identifiers) for given cyber truck model.
• To surface mesh each PIDs with different mesh target lengths, which is as follows,

1. Body - 3 mm
2. Windows - 3 mm
3. Lights - 3mm
4. Rims and tyres - 2mm

• To create a fluid domain enclosure for the given cyber truck model and to perform surface mesh on it.
• To perform the volumetric mesh in the fluid domain for doing CFD analysis ( Since, performing volumetric mesh for the given truck model may take more computational time, only the surface mesh is performed for the fluid domain ) 

Tools used :

MENUBAR>Drawing Styles>Shadow - This flag turns on and off the shadow drawing style.

MENUBAR>Drawing Styles>Wire - This flag activates the wire model representation of the geometry and the FE-Model.

MENUBAR>Faces Draw>Cross Hatches - This flag activates and deactivates the visibility of Faces' cross-hatches. As this flag is activated, green isoparametric lines that lie on the visible Faces appear. If the Faces are linked Faces the color of the crosshatch is orange.

MENUBAR>Tools>Checks>Checks Manager - This function opens the Checks Manager. It is used to execute massively a number of checks.

MENUBAR>Tools>Checks>Geometry - This function locates geometrical problems of the model such as Unmeshed Macros, Unchecked Faces, Needle Faces, Collapsed Cons, Triple Cons, Overlaps and Cracks.

MENUBAR>Tools>Checks>Penetration [Intersections] - This function checks all visible shell elements, macros, solids skin (the outer area of a solid volume), thick-shells, gaskets and all combinations of them to locate any intersections. For this check, the shell elements' thickness is not taken into account. The results are reported in the 'Checks' list window that appears.

MENUBAR>Faces Draw>Single - This flag activates and deactivates the visibility of single (red) CONS.

TOPO>CONS>Project - 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, in a user controlled direction. The selection of the CONS or 3D-curves can be assisted by the 'Corner Angle', 'PID Neighbs' for line elements or 'Path'.

MENUBAR>Utilities>Delete - The Delete function of the Geometry Group can be used to delete various ANSA entities (Curves, Faces, FE-Model entities etc.).

TOPO>Hot Points>Insert - This function creates or projects Hot Points by hovering positions on CONS or 3d curves or 1d FE elements.

TOPO>CONS>Fill Hole - This function fills holes on Faces. The holes can be of any shape. Such internal openings can be selected individually, or automatically among the visible ones if they fall below a user specified diameter value. There is the option to create automatically 3D Curves, Points or Connection Points of the removed holes, in order to mark their shape and position for reference.

TOPO>Hot Points>Project - This function defines a new Hot Point that lies on a CONS (or a Node on a 3D-curve) as the projection of an existing Node, 3D-point, Hot Point, Weld Spot etc.
This function also defines a new Weld Spot that lies on a face as the projection of an existing node, 3D-point etc. to this face.

TOPO>CONS>Release - This function releases CONS which have been automatically joined (pasted) or were joined by the CONS>Paste function.

TOPO>Hot Points>Release - This function releases Hot Points that lie on the limit of two or more faces. When a Hot Point is released, the adjacent CONS of the faces' limits are also released and become single CONS (marked in red). As a result, the local topology changes

TOPO>Faces>New - 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.

New [COONS] -

This function defines a new multi-patch Face and Surface, using the COONS interpolation principal. This is an easy way to define a new surface by its boundary curves. After the mathematical definition is finished, the calculated surface appears as a net. A relative window gives the ability to accept or to reject the calculated surface. When only three boundary sides are selected, there is the ability to choose between two alternative definitions for the fourth generated side, one is to be straight and the other is to have a shape similar to its opposite side.

New [EXISTING SURF] -

This function defines a new Face laying on an existing surface.

New [PLANAR] -

This function defines a new planar face. The underlying surface is automatically created.

New [FITTED] -

The FITTED option is used for the definition of a non-planar Face. The created Face fits to the selected boundaries.

TOPO>Faces>Cut - This function cuts (splits) an existing Face or joins faces if inverse operation is applied (right mouse button).
It does not require the existence of Hot Points since it can be applied directly on an arbitrary position of a CONS.

TOPO>Faces>Proj.Cut - This function is used to cut (split) a Face by combining the Hot Points>Project and Faces>Cut functions. In other words, it splits a face between a selected hot point and its projection on a selected CONS.

MENUBAR>Feature Selection>Line Options>Loop - Selects a closed loop of edges, perimeters or curves. Any internal or external perimeter is considered a loop.

MENUBAR>Feature Selection>ENT - Selects any kind of entity (the kind of entity depends on the ANSA function which is in use) one by one or multiple entities by box selection.

MENUBAR>Feature Selection>Surface Options>PID Region - If the 'PID Region' flag is activated, then by picking an element (shell or solid) of a particular PID, ANSA automatically selects all the connected visible elements, which are assigned with the particular PID.

MENUBAR>Focus>Or - Keep visible only the selected entities.

MENUBAR>Focus>And - Select one or more already visible entities, in order to also bring to visible any neighbor entities which may exist.

MENUBAR>Focus>Not - Hide one or more selected entities.

MENUBAR>Focus>!Not - Select entities that will remain visible. The selected entities temporarily (during selection) are excluded from the visible ones, but as soon as 'Enter' or the middle mouse is pressed (selections' termination) then they will only be the ones to remain visible in the graphics area.

MENUBAR>Focus>Invert - Inverts the current visibility status. This means that visible entities become non-visible and non-visible entities become visible. If one or more Parts are Locked then this function operates exclusively in the Locked Parts.

MENUBAR>Focus>All - Bring to visible all entities of the database. If the Lock flag button is active, then the function brings to visible only the entities that belong to the active locked view.
If there are numerous stored locked views, then they will be displayed as a sub-options list of the All button.

MENUBAR>Focus>Lock - This function locks the current working area view. This working area view is kept locked until the flag is turned off. There is also the ability to store different kinds of views of the same model. The status and the content of the working area influence the result of the All function.

MENUBAR>Focus>Neighb - Logical operation that brings to visible all the 1st level neighboring items attached to the already visible ones.

TOPO>Hot Points>Release - This function releases Hot Points that lie on the limit of two or more faces. When a Hot Point is released, the adjacent CONS of the faces' limits are also released and become single CONS (marked in red). As a result, the local topology changes.

TOPO>Faces>Topo - This function automatically creates topological conditions between selected adjacent CONS.

TOPO>Faces>Orient - 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.

TOPO>CONS>Paste - This function pastes (joins together) two or more CONS segments that lie close to each other, and which usually are boundaries of different Faces. A new topological condition is created and these Faces become neighboring. 

TOPO>Faces>Undelete - 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.

TOPO>Faces>Intersect - 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.

TOPO>Hot Points>Delete - This function deletes Hot Points lying on a CONS segment. After deletion, the adjacent CONS segments sharing the Hot Point become one.

TOPO>Points>Relative - 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.

TOPO>Curves>Cons2Curves - This function defines 3D-curves from existing CONS, shell/solid edges, Line Elements end Cross-sections.

TOPO>Curves>Create - This function creates smooth 3D-curves, polylines, circles and ellipses, by defining a number of points with the help of geometric and element entities (e.g., Faces, CONS, Curves, Nodes, Elements, Working Planes e.t.c).

MENUBAR>Lists>Properties - This function facilitates property management. A list of the properties existing in the file is available. Management windows, such as this one, provide filtering, sorting and selection capabilities on the listed entities as well as definition of new entities.

MENUBAR>Utilities>Mesh Parameters - This function opens the 'Mesh Parameters' window, where the user can define the parameters for the Reconstruction, Reshape and Fix functions.

MENUBAR>Utilities>Quality criteria - 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.

MESH>Perimeters>Length - 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.

MESH>Mesh Generation>CFD - This function is recommended after the user has applied the Perimeters>Spacing(Auto CFD) on the selected perimeters.
This algorithm meshes with variable element length, depending on the local curvature of the underlying CAD surface, under tight user-controlled specifications. It generated the less possible elements taking into account all small details of the geometry. This algorithm is an advanced meshing algorithm tailor made to meet CFD specs or other application areas where a variable size mesh is required.

MESH>Perimeters>Spacing[Manual] - In cases where there are element length variations in the model between neighboring Macro Areas, it is useful to control this transition and make it smooth using biasing (Spacing) functions along Perimeter Segments. There are three available node-biasing modes in ANSA, linear, geometric and bell curve. This function can be applied only on CONS, if there is no CONS in the model, the function is not activated.

MENUBAR>Utilities>Measure - This function performs various measurements according to the corresponding Selection Mode. The applied measurements can be saved and viewed at a later stage.

MESH>Shell Mesh>Improve - 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.

Reshape,

The Shell Mesh>Reshape function is applied on either meshed Macro Areas or FE models to improve mesh quality. The function performs automatically a combination of the following actions:

- Joins Perimeters
- Inserts or Deletes Hot Points
- Reconstructs the mesh
- Creates quad zones around holes based on predefined rules.

Reconstruct,

The Re-construction function is a powerful tool for the creation of a high quality surface mesh. It examines a given mesh and performs re-meshing to correct problematic areas and optimize the overall quality of the mesh according to the mesh parameters. For Geometry Mesh (Macro Areas) all modifications are made on the underlying CAD surface.

For FE-model mesh, all modifications are made on the surface defined by the shell elements. The function may be applied to selected or to all visible meshed Macro Areas and FEM mesh according to the chosen option.

With the option "Advanced" the Advanced Selection window opens where the user selects where to apply the Reconstruction. Note that the option "Violating" is associated with the Mesh Quality criteria in the F11 card whereas, all the rest obey to the Mesh Parameters. The Expand Level controls the number of zones around the affected elements.

Applied on Geometry mesh the perimeters will be visible as feature lines, which cannot change, but the user can add or remove more edges as perimeters. Applied on FE mesh, the user is able to modify all feature lines during preview stage.

MESH>Elements>Split - 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. The function can be applied on individual or groups of shell elements in order to improve the mesh orientation, reduce the number of triangles, or refine locally or globally the mesh of a part. Refer to ANSA User's Guide for a detailed description of the use of the function.

MENUBAR>Utilities>Compress - This function is used to compress an ANSA database. Compression may be selectively applied either on geometric entities only (faces, curves 3D-points) or on the entire database. By this operation, all information concerning deleted entities is lost. Therefore no undelete operation can be made upon entities which were deleted prior to the compress operation. This function relieves the database from unwanted information. Also, this function removes from the database all grid points, coordinate systems, properties and materials that are defined but not used in the model element definition.

MESH>Macros>Freeze/Un - This function locks/unlocks the selected Macro Areas and their boundary segments. In this way, the Macro Areas' condition is stabilized and no participation to functions that might alter their topology or meshing (if any) is permitted. If any function tries to alter the Macro Area, or a Macro Area's component is selected to participate to another function, a relative message appears in the text window.

VOLUME MESH>Volumes>Define[Auto Detect] -  This function automatically defines multiple volumes using already meshed macros or FE-model mesh.

VOLUME MESH>Volumes>List - This function enables the handling of the defined volumes in the database.

VOLUME MESH>Unstructured Mesh>Tetra CFD - The Tetra CFD algorithm is most suited for geometries of thick volumes, large domains with significant variation in length of the surface mesh (say more than 2 orders of magnitude). Most met in CFD applications.
Activate Tetra CFD and select either one or more already defined volumes or some specific solid elements.

MENUBAR>Utilities>Snapshot - Take snapshots from the drawing area or from any ANSA window. Depending on the selected option the image can be: POSTSCRIPT, RGB, TIFF, JPEG, PNG or BMP.

PROCEDURE :

Step 1 : Open the given tesla cyber truck model using MENUBAR>File>Open

Step 2 : Use TOPO>Faces>Topo option on the given model to resolve some of the single con errors.

Step 3 : Since the volumetric mesh needs to be performed on the external surface of the given cyber truck model for flow analysis, the external surfaces need to be on the positive side which is done by using TOPO>Faces>Orient

STEP 4 : Check for all the geometric errors in the given model using MENUBAR>Tools>Checks>Checks Manager

Step 5 : Create new surfaces using TOPO>Faces>New , where single cons present due to missing surfaces. 

Step 6 : Create a cut in the surface using TOPO>Faces>Cut, delete the sharp edge surface using MENUBAR>Utilities>Delete and create new surface using TOPO>Faces>New

Step 7 : Delete the penetrating surfaces and the unwanted internal surfaces in the given model and create new surfaces where it is needed.

Step 8 : Delete the sharp edge surface by making a cut using TOPO>Faces>Cut, and create new surface to enclose it.

Step 9 : Since there is a sharp edge at the rear lights region, it should be resolved, First make a cut using TOPO>Faces>Cut

Step 10 : Use TOPO>Curves>Cons2Curves option to create the curves on the cons.

Step 11 : Now, delete the surfaces and create new surfaces using the curves that are created.

Step 12 : Delete the overlapping surfaces and unwanted internal surfaces present in the shaft of the tyre region.

Step 13 : Before deleting the unwanted shaft surfaces, project the cons to the shaft surface using TOPO>CONS>Project

Step 14 : Now, delete the unwanted surface and repeat this for all the shaft regions.

Step 15 : Delete the overlapping surfaces and the unwanted internal surfaces.

Step 16 : Since there is a sharp corner near the window region which will affect the mesh, resolve it by creating create new surfaces and deleting the sharp edge surfaces. 

Step 17 : Resolve all the sharp edge regions by using same steps as discussed above.

Step 18 : After performing all topological clean up, again check the model for any geometric errors, the below shown concave errors in the tyre regions can be ignored, since deleting it may affect the geometry of the given model and also the mesh. 

Step 19 : Assign PIDs using MENUBAR>Lists>Properties, and delete the leftover PIDs using MENUBAR>Utilities>Compress 

Step 20 : For the Rims and Tyres PID, Give the maximum and minimum target lengths as 0.5 mm and 2.5 mm in the mesh parameters using MENUBAR>Utilities>Mesh Parameters and respective quality criterias. 

Step 21 : Give the perimeters and macros length as 2 mm for the PID using MESH>Perimeters>Length

Step 22 : Now, perform surface mesh using MESH>Mesh Generation>CFD . After meshing, since there are many off elements for the given quality criteria, use MESH>Shell Mesh>Improve to reduce the off elements to zero.

Step 23 : Since different mesh target lengths are to given for different PIDs, Freeze the PID using MESH>Macros>Freeze/Un 

Step 24 : For Body and Windows PIDs, Give the maximum and minimum target lengths as 0.5 mm and 3.5 mm in the mesh parameters using MENUBAR>Utilities>Mesh Parameters and respective quality criterias. 

Step 25 : Give the perimeters and macros length as 3 mm for the PID using MESH>Perimeters>Length . Now, perform surface mesh using MESH>Mesh Generation>CFD . After meshing, since there are many off elements for the given quality criteria, use MESH>Shell Mesh>Improve to reduce the off elements to zero.

Step 26 : Since different mesh target lengths are to given for different PIDs, Freeze the PID using MESH>Macros>Freeze/Un 

Step 27 : For lights PID, Give the maximum and minimum target lengths as 0.5 mm and 3.5 mm in the mesh parameters using MENUBAR>Utilities>Mesh Parameters and respective quality criterias. 

Step 28 : Give the perimeters and macros length as 3 mm for the PID using MESH>Perimeters>Length . Now, perform surface mesh using MESH>Mesh Generation>CFD . After meshing, since there are many off elements for the given quality criteria, use MESH>Shell Mesh>Improve to reduce the off elements to zero.

Step 29 : Since different mesh target lengths are to given for different PIDs, Freeze the PID using MESH>Macros>Freeze/Un 

Step 30 : After performing surface mesh to all the PIDs, Measure the mesh element lengths for checking.  

Step 31 : The fluid domain enclosure should be of length,

• for the front domain, 4*length of the car model(x) = 4 * 5870 = 23480 mm, distance taken from the front of the car model. 
• for the rear domain, 6*length of the car model(x) = 6 * 5870 = 35220 mm, distance taken from the front of the car model .
• for the top domain, 3*height of the car model(y) = 3 * 1540 = 4620 mm, distance taken from the top surface of the car model.
• for the bottom domain, since the CFD analysis is not important compared to others surfaces, it can be held near to the bottom surface.
• for the side domains, width of the car model(z) = 1880, distance taken from each respective sides.   

Step 32 : First, Measure the dimensions of the model using MENUBAR>Utilities>Measure, inorder to create the fluid domain. 

Step 33 : Now, Create 3D point relative to the hot point for the reference using TOPO>Points>Relative

Step 34 : Create 3D point relative to the previous point to the distance described to create the fluid domain. 

Step 35 : Similarly, Create 3D points which are needed to create the fluid domain at the respective distances as shown above. 

Step 36 : Create curves to connect those 3D points using TOPO>Curves>Create  

Step 37 : Now, with the help of those curves, create new surfaces for the fluid domain using TOPO>Faces>New

Step 38 : Assign PIDs for the Fluid domain to mesh the regions with different target lengths.

Step 39 : For the Bottom domain PID, Give the perimeters and macros length to be 20 mm.

 Step 40 : For the Top domain PID, Give the perimeters and macros length to be 100 mm.

Step 41 : Now, use MESH>Perimeters>Spacing[Manual] option and select the four cons as shown below and choose geometric biasing, give the 'factor' as 1.1, the 'dmin' as 20 mm and the 'dlimit' as 100 mm.

Step 42 : Perform the surface mesh using MESH>Mesh Generation>CFD for the fluid domain. 

Step 43 : Define the volume using VOLUME MESH>Volumes>Define[Auto Detect] for performing the volumetric mesh.

Step 44 : Since the CFD analysis is to be done to the external surface of the given model, the volumetric mesh is performed on the fluid domain. Therefore, the unwanted internal volume of the cyber truck model is deleted. 

Step 45 : Finally, Choose the type of elements as Tetra CFD under VOLUME MESH>Unstructured Mesh>Tetra CFD ,and perform the volumetric mesh. 

RESULTS :

Google drive link for the final surface meshed cyber truck model with the fluid domain enclosure :

https://drive.google.com/file/d/1aAGonIhq7sJ507pAXK8FcVZyzcXTvl4Z/view?usp=sharing

1. Screenshot for the given tesla cyber truck model after performing surface mesh with diffferent mesh target lengths for different PIDs, 

2. Screenshot after performing surface mesh on the given cyber truck model as well as its fluid domain, 

3. Final screenshot before performing volumetric mesh for the fluid domain,

CONCLUSION :

Hence, the total mesh elements (trias) produced is 15796248 after performing the surface mesh. Therefore, the volumetric mesh for the fluid domain takes more computational time for the given Tesla Cyber truck model with the given mesh target lengths. So, in order to reduce the computational time, the fluid domain can be created near to the model and mesh lengths can be provided smaller near to that as given and, away from it, in the fluid domain, larger mesh lengths can be provided. This generates finer mesh elements near to the external surface of the given cyber truck model and coarse mesh away from it.