Aim :

 3D meshing in Hyperworks.

Objective :

To carry out the 3D meshing in hyperworks following the given quality criteria.

Model 1- Housing model

Create the tetra mesh

Elements sizes: Min- 2mm, Target- 5mm,Max- 7mm

Tet collapse: 0.15

Model 2 and 3 - create the 3D mesh with 6mm

Introduction :-

Tetrahedral is a four noded solid element which can be generated through tria elements by creating a volume and also through the existing volume of the geometry.

There are two methods of tetra meshing. 

1) Automatic mesh: 

This approach is limited to simple geometries and the prerequisite is an error free CAD model. The user just has to select the volume and the software automatically carries out the meshing as per the speci"ed element length, quality criteria, etc. 

Advantage: Very quick, no meshing e!orts

Disadvantage: Results in a very high number of nodes and elements. There is no control over the mesh flow and the speci"c mesh pattern requirement (like bolted, welded joints or contact surface simulation). 

2) 2-D (Tria) to 3-D (Tetra): 

This is the most commonly used method. Quad or tria meshing is carried out on all the outer surfaces of the geometry. During the tetra meshing the quads are automatically split into trias which then serve as the “basis” of the tetra elements.

Procedure :

Method 1: 2D to 3D tria 

Step 1 : Opening the file and performing the geometry clean up 

The housing model here is going to be meshed by using the 2D to 3D tria method so it is cleaned in the primary stage to avoid the element failure.

Fig-  housing model (surface model)

 Clean up :

 The  surface is cleaned in the region to remove the any two lines that is having the distance less than 2mm(2 is the minimum size of the element )

For cleaning up we are using the quick edit tool

Points >replace 

Fig-Lines were patched using replace points

Step 2 : Performing the 2d shell mesh :

 Now the 2D meshing is performed using the only tria elements and all the shell kept under the mentioned quality criteria.

Fig- housing model shell meshed with no failed elemnts 

Step3 : 2d to 3d tria conversion 

 After the shell mesh is performed they need to be converted into solid tria elements. So select 3D> tetramesh option 

 Then select the elements under the fixed tria/quad to tetra option  and then do the mesh 

Fixed tria to tetra option ensures the connectivity of the tria  with the tetra.

Use the mask option to see the if the volume mesh is performed correctly

Fig- Tetra meshing for housing model 

Method 2 : Automatic solid meshing 

A- Using the utility option 

 This is one of the approaches to perform the automatic 3D  meshing. The steps to perform are as follows

1. Import the model into the workspace and perform some clean up .

    2.There is no need to delete the solids since this is only the surface geometry.

    3.The click on the view > browsers> hypermesh> utility( we can see the utility tab in the tab bar)

     4.Select the geom/mesh from the utility menu and then select  the quick mesh.

     5.A new sub panel opens for the quick mesh to input the parameters.

• Select the component 
• Input the mesh size as 6 as mentioned 
• Select the element type as tria only and then mesh.
• After the surface mesh is performed a small dialog box pops to ask to perform the tetra mesh. Press OK.

    6.The new tetra mesh model is saved under the name quick test.

Fig- Model2 tetra mesh using utility option

B- Using the volume tetra :

 This method is one of the quickest methods to perform the tetra meshing. The steps to perform the volume tetra are as followed.

1. Import the model into Hyperworks 

     The component here is the suspension assembly and we will be working on one side of the assembly since both the sides are the same. Also there are a number of components so we will be working part by part.

Fig- Chassis model for volume tetra 

    2.The volume tetra requires only the solid model so no need to delete the solid here. Go to 3D> volume tetra 

    3.The volume tetra has the same parameters that needs to be feeded

• Select the solid as available on the workspace 
• Choose the element size as 6 as mentioned
• Also input the minimum element size as 2 
• Switch on the use proximity and use curvature option 

     (These two option are used to refine the mesh in the region of curves or converging parts so that there is smooth transition of the elements.) 

• Then also switch on the element clean up option and then select the mesh.
•  The final component will be obtained with the tetra mesh and then check for the tet collapse and fix using the tools as explained further.

Fig- Chassis component tetra mesh sesction view

Tet collapse

Tet collapse is an important criteria dealing with the volumetric mesh also it is only applicable to the tetra elements only. As we know that tetra element is 4 noded element having 4 sides and 4 nodes.

Tet collapse or TET element is the minimum of (h/√A)÷1.24 

Where h is the perpendicular distance from node to the opposite face of the TET and 

A is the area of the opposite face 

fig

Then if the height of the any tetra element falls below the desired height, it will eventually fail for the Tet collapse 

There are 2 methods to solve the TET collapse as studied in the article 

1. Using the translate option 

This option is a manual method used to solve the tet collapse. Step to perform are as follows 

• Failed elements are stored using the mask option 
• Go to tool > translate > node selection. Pick the node having minimum height and select the N1,N2,N3 as node on opposite planes.

Fig- translating the element

• Move nodes to certain values then again check with the tet collapse. If the elements turn green they are passed, otherwise if it's grey they are failed.
  
  

   2.Using the tetra remesh 

This automatic method to solve the tet collapse at once. Step are as followed 

• The tetra meshed component is checked for the tet collapse. The failed elements are shown in the status bar.
• Now fo to 3D>tetra parameters 
• Select the max and min tetra size and tet collapse value 
• Switch on the fix voids, fix midnodes and smoothing

• Now go tetra remesh > select the 3d elements as the component .
• Click on remesh and after again check for the tet collapse .

Results :

 Fig- housing model 

Fig - model using utility tetra mesh

Fig- chassis model volume tetra 

Conclusions :

  All the model were meshed in 3D using the 2D to 3D , utility and volume tetra mesh respectively along with solving the tet collapse and kinks . The meshed obtained in the utility were not so good as compared to other two. Also the number of elemnts and the tet collapse were more in the volume tetra mesh method.

Link for the model :https://drive.google.com/drive/folders/1JbnjuM2KD6BwxN1_292qCKjRywDVOU8L?usp=sharing

Refrences :https://skill-lync.com/knowledgebase/understanding-tetra-meshing-and-tet-collapse