All About 2D Meshing

Whenever the thickness of the component falls to 5 mm or below we opt to mesh them with the 2D elements. Why? Can we mesh them with the 3D elements? Yes, you can very well mesh them with the 3D elements but when we look at the results there is not going to be much difference, the only difference will be the number of elements and time taken to solve the problem.

So just to avoid wasting time-solving 3D elements, we can use the 2D element and still get the same result. 

To understand this, a cantilever beam has meshed with 2D and 3D elements and the results are summarized.

 

 

Meshing with 2D elements

After assigning the thickness to the mesh, it captures the geometry with one row of elements.

 

 

Meshing with 3D elements:

The thickness is captured with 2 rows of elements.

 

 

A 100N of the load is applied to the free end of the beam,

 

 

You can see the error percentage is less than 5% which is acceptable. You can also notice that the time taken to solve the problem with the 2D element is 25% faster than the time taken to solve the problem with the 3D elements.

If you are working on a big model like a full car model, this is going to make a huge difference in the time taken to solve the problem.

Depending on the accuracy needed, you can go for 2D mesh for higher thicknesses.

 

1. Knowing your Geometry:

Once you get a geometry for meshing it is very important that you should do a visual inspection to get a better idea about what it is. In case you don't get any idea about what the geometry is, at least you should be able to identify if it is a plastic or sheet metal component. You can also measure the thickness at multiple places to understand if the component is sheet metal or plastic. 

If the thickness is the same throughout the geometry, it is sheet metal and if the thickness is varying then it is plastic.

 

 

This is a plastic part where you can see four different thicknesses and this is how the thickness will change in a Plastic component.

 

2. Cleaning up the Errors:

After understanding the geometry, now is the time for you to spot the errors in the geometry. Most of the time the errors will be on the surface i.e, the surfaces will be distorted heavily or the surface will have small cracks. 

You need to figure out a way to fix them, you can either spend time and work on the distorted surface to get it fixed or you can delete the surface and recreate it. Choosing to edit the surface or recreating the surface totally depends on the complexity involved and the availability of tools in your software.

 

3. Creating the Middle Surface: 

    You need to extract a surface right in the middle of the surface in order to mesh. Now, why is that? Take a look at the sketch below, 

 

 

In this image, the square plate is the actual geometry with thickness and length as a and b respectively. 

Whenever you mesh and assign thickness, the software is going to define it in the +ve and in the -ve Y in the thickness direction(a reference to the above image ). Because of this constraint, you can only mesh in the middle of the geometry to represent it accurately when the thickness is assigned.

Now, we have a clear understanding of why we need mid-surface. Let’s now see how they can be extracted. In all the pre-processing packages you will have an option where the automatic algorithm will extract the mid-surface with a single mouse click. On the other hand, you can extract the middle surface manually by offsetting the surface, either top or bottom to half of its thickness. 

Split before Mesh: 

You need to split the middle surface into small patches before deploying the mesh in the patches. You can try the auto mesh option where the algorithm itself does the meshing, then you can do the required changes to get a perfect mesh. Since it is an algorithm, sometimes it fails to give us a proper mesh in a complex region, only for those areas you can do a manual mesh. 

A few tips for auto meshing, always spit the geometry in a known shape like a square, or rectangle. The algorithm works best for this kind of shape. This is because the number of nodes for the square or rectangle will be equal in both length and breadth. Thus it will give you a mesh which has only quad. You can attain a good mesh flow by smoothing the mesh. You should also check the quality and mesh flow right after meshing a patch so that it will be easy for you to control the mesh quality.

Before splitting the geometry you need to be aware of the Feature and Construction lines.

Feature Line:

Any line which helps or is directly involved in defining a feature is said to be a feature line. A line which is responsible for a plane change is as well called a feature line.

Construction Line:

Any line which does not involve defining the feature is said to be a construction line.

 

 

Here is an example of a Hood where you can see how the splitting of the geometry will significantly improve the mesh flow and quality.

 

 

This outer part of the hood has its surface split into small surfaces with different shapes. Whenever we have sharp edges the probability of having a Tria element will be high so it is always advisable to avoid the sharp as much as possible.

 

 

Here I have split once half of the hood and meshed it, from this you can understand the meshflow and reduction of the tria element is high on the left side as it is split in squares.

 

 

Proper Mesh Flow:

 

 

Improper Mesh Flow:

 

 

Whenever you have the node number the same on all the sides of the surface you will end up having only Quads and when you have a mismatching number of nodes on the surface you will have Trias, provided you are in the mixed mode of the mesh.

When a surface is converging then having only the Quad elements will increase your mesh density, to overcome this high-density mesh you need to have some tria elements which are facing toward the convergence direction.

Two final checks:

After meshing, there are a few checks you need to do like free edges and normal checks. Free edge checks are something which is really important to do once you mesh a component, this will give a clear idea about the mesh connectivity. 

Secondly, you need to check the element's normal as many beginners fail to do so. 

The elements normal are something that can play a vital role, it is always important to keep the elements normal aligned in one direction.