Car hood meshing in Ansa

OBJECTIVE

check the geometrical errors of the hood,geometry clean up the model,extract the mid surface and mesh the model in ANSA according to the given quality criteria with the target element size 5mm.

PROCEDURE : To fullfill the above objective folllowing steps are performed

1. Geometry Clean up the model.
2. Extract the mid surface.
3. Assign the new pid to the model.
4. Mesh the model according to the given quality criteria.

1.clean up the model : 

First we import a cad model into ansa as shown in below fig. 1. and this model is divided into three part.

a. inner hood panel

b. outer hood panel

c. latch portion.

                                              fig.1 hood model (shadow mode)

 Geometry clean up

   The geometry checkup is done  using the check box and selecting a geometry option.then the image shown there are several errors in the geometry so we will rectifying all the errors and surface cleaning is needed.

 There were unchecked faces, needle faces, crack between cons and single cons which were then eliminated and fixed completely.

Now the surface was completely error free. The Geometry checks was run again and no error was found.now the next step is extracting midsurface.

2.Extracting the midsurface - 

Now using the Offset command we are going the extract the mid surface .

TOPO>Faces>Offset>Faces

Select the offset command from the faces toolbar and then select the offset surface as shown in figure .Now enter the value of distance which is half to the thickness of the sheet.Click Ok to produce the surface but do not delete the parent surface.The pannel of the hood was offset by -0.75/2. The negative value was given to have the offset in the opposite direction of the arrow and here we are using a featured area 40 degree angle option.beacause it selected all the faces together below the angle value is entered in box.

                                                                      fig. Inner pannel (inprocess of extraction of mid surface)

Now, The created mid surface taking only visible using iNOT option select the one element and click neighbour all option to get them all extracted surface.

3. Assign a new pid to model 

After that, we will define the new PID for the  hood midsurface. And also define the new material ID for it.

TOPO>Faces>Set Pid.                                                                            

after that next step is to defeaturing.

Defeaturing  

It is the process of removing unnecessary surface radius,pinholes,edges,unwanted lines.very small entites can be a problem. if you have very small faces with sharp angles the surface meshing might fail.

4.Meshing 

Now we are ready for the meshing process but before meshing we have to mention the following quality criteria  and mesh lengths.

Here the mesh length is 5 and the quality criteria values are as follow

Now we can mesh the model using the tool MESH>Mesh Generation>Best.

Meshing was done by using BEST mesh as it uses all the mesh algorithm and then keeps only the mesh of best quality.

Now try to remove the mesh errors as much as possible to improve the mesh quality and reduce the tria percentage.

now you can seen in below image the mesh is fail for quality criteria and there are some opp.tria and tria present at edge .

there are some quality criteria issues which are shown as off elements which can be cleared using the following tools.

• Mesh>Elements>Swap- This function rotates the shell edge picked by the user, inside the two shells which have that edge as common.

                        fig. (before swap command)  

                                       fig. (after using swap)

• MESH>Shell Mesh>Reconstruct- This function is a powerful tool for the creation of a high quality surface mesh.

                                                fig.(before reconstruction)  

                           fig.(after reconstruction)

• MESH>Shell Mesh>SMOOTH- This function automatically applies Smoothing attributes so as to 'relax' the mesh on already meshed Macro Areas.

• MESH>Elements>Split- This function splits quadrilateral and triangular shell elements into smaller ones.

                                  fig.(before split two opp.tria.) 

                                    fig.(using split command)

                                    fig.(after split)

• MESH>Grids>paste- This function is to paste a two nodes of triangle or quadrilateral .

                                        fig.(before paste)  

                               fig.(after paste)

 After following all the above steps correctly we will get the result as shown below. As we can see in the image that there are no OFF elements and all the mesh elements are within the mesh quality criteria.

                                   fig. (final meshing of inner pannel)    

                            fig.(final meshing of outer pannel)

                                      fig. (final meshing of latches reinforcement)

                            fig. ( final assembly of hood model)

Learning outcome :

    we learned to clear topological errors.

    we learned to extract mid surface by feature angle .

    we learned how we do meshing the mid surface.

    we also learnt to rectify the mesh quality parameters and improve the mesh flow.