SOLIDWORKS Simulation Makes Meshing Easy. Too Easy?
Basics of FEA meshing
You can’t run a simulation without meshing; it’s not possible. Meshing is to simulation what chicken is to chicken soup – the core building block. Meshing creates the finite elements that make up a finite element model so that you can do a finite element analysis, or FEA.
What do you have to know about meshing to run a FEA using SOLIDWORKS Simulation? Surprisingly little. But let’s suppose you want to run better simulations, or get the most accurate results.
It is the mesh that determines the accuracy of the results. Read on and you will find enough about meshing to get the most accurate results from your simulations.
What is Meshing?
Meshing is the process of breaking down your model into simple shapes called finite elements. Let’s define basic terms:
- Finite: a certain amount, as opposed to infinite.
- Element: A piece or block of a simple, predefined shape.
The elements are the basic components of the model. Meshing takes a complicated problem and breaks it down into a number of pieces (finite) of a shape that is easily calculated (elements).
Simulation software uses equations to solve for things such as stress on complicated shapes. But it breaks it down into thousands or hundreds of thousands of little pieces of a simpler shape. It works like this:
Creating the Mesh
Creating a mesh is easy in SOLIDWORKS Simulation. To get started, right click on the mesh icon in the Simulation Tree and click Create Mesh.
This will open the mesh interface. Think of meshing in SOLIDWORKS Simulation as having two levels: Level 1 we’ll call Quick Mesh and Level 2 is Advanced Mesh. This isn’t official SOLIDWORKS terminology, but rather the two ways to use the meshing interface.
Level 1: Quick Mesh – The Simplest Way to Mesh your Model
With a quick mesh, you don’t look at any options or even numbers. You only see a slider that controls the density or size of the elements. To the right is fine and to the left is coarse, referring to the element size. A fine mesh will have a greater number of smaller elements, while a coarse mesh will have fewer or larger elements.
You can change the average size of the elements in a part with a mesh slider. A powerful algorithm makes changing all the element sizes at once super easy. But when you create a mesh with the mesh slider, you are putting a lot of faith in its ability to give you a good mesh.
Level 2: Advanced Mesh – Have Control Over the Mesh
To take your mesh from quick to advanced we expand the options. Various options give you more control of your mesh than the mesh slider.
The first choice is the mesh algorithm you want to use. This defines the scheme used to build the mesh from the CAD geometry. There are three choices: standard, curvature-based, and blended curvature-based. As you can see, each one of these algorithms offers different settings.
This is the original meshing scheme of SOLIDWORKS Simulation and a good starting point. It works well for the simplest geometry.
This offers the ability to specify a maximum and minimum element size. While this is great for geometry with a lot of small features, it can add unnecessary elements if used on simple geometry. It is very good at capturing changes in geometry from curved features to prismatic shapes.
Blended Curvature-based Mesh
Introduced to Simulation back in 2016, this is an extension of the Curvature-based mesh in that it offers a more advanced option to capture very small geometric features. This algorithm has one subtle difference, however: the option to “calculate minimum element size.” With this option you can capture small geometric features automatically.
Optional Level 3: Mesh Controls
With SOLIDWORKS Simulation, this is the closest you’ll get to manually building the mesh. Mesh controls are a way to locally define an element size in a particular region. This enables you to focus the resources on a specific area rather than the entire model.
This is especially useful if one area of the model has a small feature such as a radius, like that seen in the example below.
When working with a larger and more complicated models, mesh controls go from an optional step to a required one. In the example below of the industrial equipment, a simulation was done on the boom subassembly to ensure it could withstand the required forces during operation. With all the different components of various sizes, eight different mesh controls had to be used to get a mesh that captured all the geometry.
When working with just the one bracket part from the boom, no mesh controls were required because the geometry was simple—meaning it was consistent and uniform. However, the same could not be said when working with the entire boom assembly. The boom assembly contained many components of varying sizes—some small and others large—so mesh controls are required to get a good mesh. Without mesh controls, the mesh would have at worst completely failed to generate, or at best it would have been a bad mesh.
What’s a Good Mesh?
The secret of a good mesh can be hidden in the details, but SOLIDWORKS Simulation makes it easy to find them. Simply right click on “Mesh” and click “details.” You will be presented with a list from which we can determine the quality of the mesh:
- Maximum aspect ratio
- Percentage of elements with aspect ratio < 3
- Percentage of elements with aspect ratio > 10
What’s the Aspect Ratio?
The aspect ratio tells you the shape of the element. A value of 1 is optimum. The bigger the aspect ratio, the worse the shape of the element.
A good way to understand aspect ratio is to think of it as the element shape; however, the aspect ratio reported by Simulation is more than simply the shape. The simplest way to define the aspect ratio is by looking at the ratio of lines drawn normal from a face to the opposite vertex. As you can see, the higher the aspect ratio the more skewed the element.
How does this tell you if you have a good mesh? Since you know that a perfect element has an aspect ratio of 1, you would ideally want all your elements to have an aspect ratio of 1—but that just isn’t reasonable. The key is to make sure that your elements have low aspect ratios, so you look at the summary percentages; specifically, the percentage of elements with aspect ratio greater than 10 or less than 3. By looking at these values, you can know for sure you have a good mesh or if you need to improve on it.
Now you know how to create a mesh, improve the mesh with mesh controls and even determine if you have a good mesh. These are the three things that make up the foundation of meshing in SOLIDWORKS Simulation.