How to Add Element Biasing in Altair HyperMesh

An FEA Analyst is always looking for ways to more efficiently model their finite element simulations. Analysts are typically worried about getting a model to solve as quickly as possible, while retaining optimum accuracy. The more elements a simulation typically has, the longer it will take to solve. Therefore, it is imperative to efficiently model elements in simulations to ensure accuracy.

With Altair HyperMesh, analysts have numerous tools to ensure accuracy for models while reducing element count, such as customizable mesh templates, batch meshing, mesh controls, manual mesh manipulation, different element types, and a variety of other options to utilize. In today’s blog I am going to step through one of these options in HyperMesh, called “Element Biasing”, which helps reduce overall mesh density while helping with element accuracy.

Figure 1: Example of a Meshed Model in HyperMesh

What Is Element Biasing?

So firstly, what is element biasing, and how can I utilize it in HyperMesh? Element biasing is the option to set the element size ratio distribution between a fixed number of elements at a location. Simply put it will adjust the element edge size across an edge, without changing the element density. For example, you have ten elements distributed on an edge and the biasing will determine the mesh size between those ten elements. By default, HyperMesh will automatically uniformly distribute element size if you do not set biasing.

The beauty of biasing is it allows you to change this setting, so those elements are not uniformly distributed. An analyst may do this, because they want to have more elements closer to one edge, without changing the total number of elements. Through biasing, you keep the same element count, but more elements are located at the critical location, an example of biasing and non-biasing is shown below in Figure 2.

Figure 2: Example of a Non-Biased and Biased-Model (Left Non-Biased, and Right Biased)

How to Bias on a 2D Mesh in HyperMesh

I am going to work through the process of how to bias a 2D surface with a basic bracket I have designed in Altair Inspire. After importing the CAD file into HyperMesh, I can click on the 2D Mesh menu and first designate the element Density to create the mesh, and then after I create the mesh, I will see the Biasing icon appear.

Figure 3: Initial Mesh Density of Bracket and Location of Biasing Option

With our initial mesh density set, we can click on the Biasing icon and begin to set the Biasing settings, in our case we will set the one vertical edge as the edge to bias (Figure 4). You will see after clicking on the Biasing icon, we have three different options to set biasing: Linear, Exponential and Bell curve.

Figure 4: Setting Bias Options

• Linear Biasing works by adjusting the element density by the slope of a line, so the greater the biasing value the more elements will be applied at the one end, note you can flip the end which it biases from by typing in a negative value.
• Exponential Biasing works by exponentially distributing the element distribution.
• Bell Curve Biasing, looks at the mid point of the line and distributes elements that are symmetric about the midpoint of the line (Figure 5).

Figure 5: Linear Biasing (Left), Exponential Biasing (Center), Bell Curve Biasing (Right)

Note with HyperMesh, we can apply as many or as little edges with biasing, and we can see the effect of biasing in preview mode before accepting the mesh. This makes it very easy to iterate and build meshes in Altair HyperMesh!

How to Bias on a 3D Mesh in HyperMesh

Models can also be biased directly with 3D Hex Meshing in HyperMesh. The caveat of this approach is you need to make sure your models are initially mappable (i.e able to be Hex Meshed). In HyperMesh, we can easily check if an object is mappable, by turning on the mappable visualization option (Figure 6).

Figure 6: Mappable Visualization Location

In our case, we can see that our model is mappable, so we can jump to the 3D Mesh menu and apply the Map mesh option which has Biasing built into it. You will note that once we specify the Map mesh option you will see the Biasing option appear (Figure 7).

Figure 7: 3D Solid Map Mesh Option

Once we select the mesh density, we can key in our Biasing, like the 2D Biasing option we have the capability to key in Linear, Exponential and Bell curve Biasing. The one unique thing with the 3D Biasing option is you select an edge and it will look for all of the other appropriate mappable edges, since a mapped mesh is an extruded mesh. In our case, I will try a Linear bias with a size of 20, and then create the mesh (Figure 8).

Figure 8: Biasing Options (Left), Finished Biased 3D Mesh (Right)

With both the 2D and 3D biasing options, I never had to change the overall element count, I just adjusted the location of finer elements through the Mesh Biasing options. I hope this blog has illustrated the power and ease of use with Biasing in Altair HyperMesh, and how easy it is to create your own unique element Biases. If you have any more questions about Altair HyperMesh or any Altair solution, please reach out to us!