How Is Hexa Mesh Used in ANSA

Hexa element is a 3D representation of a quad element which will have the thickness measurement that the quad won’t have in reality.

Methods to Generate Hexa Mesh in ANSA:

Below are the two methods to generate Hexa Mesh in ANSA:

1. By using the Volume mesh deck
2. By using the Hexa block deck

Now, we will see how to generate the Hexa mesh by using the volume mesh deck. The Hexa block method is when we convert our geometry to small cuboids, following which ANSA will use those boxes for generating the mesh.

Restrictions while using Hexa Mesh in ANSA:

The common restrictions are as follows:

• It could be used only for sweepable geometries not for complex shapes such as intake manifold, and engine cylinder. That’s because those components will take more time to Hexa mesh and will have a complex profile
• 100% Feature capturing is not possible in complex shapes.
• When compared to tetra mesh, it will take more time to do the mesh
• Getting the proper node connectivity between two different features will be very difficult.

Steps for Creating the HEXA mesh :

Step - 1: Import the geometry.

Step - 2: You have to check the geometry before moving to the mesh to check whether it has any features or not. For our case, we have 4 elliptical features. So we need to project the outer lines of the feature to the bottom surface. We are doing the projection of cons for making proper node connectivity between the base plate and feature.

Step - 3: We need to perform 2D mesh on the base surface and work on the mesh flow. While doing the Hexa mesh, we have to avoid as much tria as we can. Because the tria element will form the Penta element that is not recommended in the structural simulation. You can keep the rotating quad also.

Step - 4: There are so many tools available in ANSA for converting the 2D element to hexa but in this case, the extrude option is Sufficient. (Volume mesh>structured mesh>extrude)

• Select the shells/facets option and select the meshed area. Then click next

• It will move to the target option. If you want, you can select the top surface or else select the none option and then click next.

• Select the guideline option in Rule and select the outer corner edge of the geometry and then click next. (Refer to the image below)

Note: If you are unchecking the box that we had marked in the image, you can control the element or step size of the Hexa element. If you check the option, the element size calculator will measure the length of the selected perimeter/average length.

• It will move to the build option where you can change the number of steps or element length. Here I have taken 4 steps for 2 mm thickness.(Note: if we are increasing the steps, the element size will be very small which will lead to convergence issues while solving the model)

• Click on finish. The hexa mesh is generated for the base plate

• For doing the hexa mesh for elliptical feature, select only the small area that is having the feature outline like below,

• Now, we will try the translate option in the rule panel. It needs the 2 points in which we are going to extrude our element

• We have to define the number of steps for which we want to extrude the feature

• Final meshed model

Reason for projecting the cons :

           Hexa mesh done by projecting the feature cons on bases surface

        Hexa mesh done without projecting the feature cons on bases surface

 

If we are not projecting the cons, the node connectivity goes missing as we can see it in the above image. Here you may ask a question, what is the need of the node connectivity. If it is not there, the force transmission from base plate to feature will not happen so we will end up with the wrong result. This is the one of the major reasons why the hexa mesh is very difficult to execute.