How to Reduce Virtual Simulation Study Time

SHELL BLOG 3
The process of discretization or “meshing”

 

Using SOLIDWORKS Simulation to optimize designs is a cost & time-saving practice, but generating those studies can sometimes be time consuming. When creating a simulation study one of the first steps is to take our SOLIDWORKS solid model and turn it into a mesh model. This process of meshing is also known as “discretization”.

When running a SOLIDWORKS SIMULATION study and creating a meshed solid model, this mesh is made up of many solid ELEMENTS. These solid elements are 4 sided, with each side taking the shape of a triangle. Each edge of the solid element contains a NODE at both ends and a NODE at the midpoint for a total of 10 NODES per element.

 

A solid ELEMENT with 10 NODES
A solid ELEMENT with 10 NODES

An important concept to recognize when working with SOLIDWORKS SIMULATION is that each of these nodes represents the unknown variable of an equation. In linear static stress analysis we are typically running a study to determine the stress imposed on a model. This stress is derivative of strain, which is a derivative of DISPLACEMENT. Therefore, each node of a solid element represents the unknown variable of displacement, which we are solving for when we run our SOLIDWORKS Simulation Study.

A single solid element before and after displacement equations are solved
A single solid element before and after displacement equations are solved

If we apply a force to the lower face of this model and mesh using solid elements, we can see that the maximum stress is 83.349 MPa, and that the maximum displacement is 2.112 mm.

Max Stress is calculated at 83.349 MPa
Max Stress is calculated at 83.349 MPa
Max Displacement calculated at 2.112 mm
Max Displacement calculated at 2.112 mm

We can also see that the total number of nodes used to solve this study was 80052

Mesh Details of Solid Element Mesh
Mesh Details of Solid Element Mesh

Since a single node represents an unknown variable for displacement, and we are solving equations for displacement, it stands to reason that less nodes in a study will result in a shorter time to calculate our results. While there are several techniques to reduce the amount of mesh in a model, one technique is known as a SHELL MESH.

 

A shell mesh differs from a solid mesh in that the elements are 2 dimensional rather than 3 dimensional. A shell mesh element is a single triangular face with nodes at each corner and at each midpoint, for a total of 6 nodes per element.

A 2D SHELL Element with 6 NODES
A 2D SHELL Element with 6 NODES

Some models are good candidates for utilizing shell elements. Some are not. The most important qualifier in deciding to use a shell element mesh is the material thickness being uniform. If the material wall thickness is NOT uniform, the model is NOT a good candidate for a shell element mesh.

 

In the example of the bracket we are using, the wall thickness IS uniform so this IS a good candidate for shell meshing. In order to turn a model with uniform wall thickness into a shell element mesh, we must first create a surface model, in this case using the mid-plane option. Once this surface model is generated, we are ready to turn our surface model into a shell element mesh.

The process of discretizing or “meshing” using shell elements
The process of discretizing or “meshing” using shell elements

After shell element meshing and applying forces and fixtures to our model, we run the model and find the following results:

Max Stress is calculated at 90.422 MPa
Max Stress is calculated at 90.422 MPa
Max Displacement calculated at 2.112 mm
Max Displacement calculated at 2.112 mm

When examining the results we can see the following comparisons to our solid element study:

MAX STRESS:

Solid Elements – 83.349 MPa

Shell Elements – 90.422 MPa

 

MAX DISPLACEMENT:

Solid Elements – 2.112 mm

Shell Elements – 2.057 mm

 

These results show a variance of less than 10%, which is within our range of tolerance.   However, when we examine the total nodes in the shell element study we see the following:

SHELL BLOG 13

When we created our Solid Element mesh we had a total of 80,052 nodes. We have reduced that number to just 6,352, without sacrificing the quality of the results of our study. This reduction in nodes will result in a significant reduction in the number of calculations, and ultimately a reduction in the amount of time it takes to reach a solution for this study.

 

I hope that you find this summary of why we use shell elements to be a helpful explanation of what nodes truly represent in a SOLIDWORKS Simulation study, and how using a shell element mesh to reduce the total number of nodes can reduce the total amount of time required to solve a study. Remember that for a model to be a good candidate for a shell element mesh, it must have uniform wall thickness.

Prism Engineering, Inc.
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