In this video, learn about the motivation for preparing the geometry ready for the FE analysis.
- [Instructor] The CAD geometry in SolidWorks is the definitive representation of the component. However, when we create the FE analysis, we need additional definition of both geometry and coordinate systems to be able to apply loads and boundary conditions. This video gives an overview of how and why we want to manipulate the CAD geometry further. I've opened the SolidWorks model of the con rod, we can see the geometry in its as delivered state, coming from the CAD. When we review this geometry to see how applicable it is going to be for the FEA workflow, we can break it down into three task areas, loading, boundary conditions, and meshing.
We'll go and look at the little end. The loading is going to be applied at the little end shown here. We're going to have the two load cases, one in tension, and one in compression. The loading is going to be applied as a pressure distribution on the inside of the bearing face of the little end. We're going to use conventional engineering principles and apply the tensile bearing load as a cosine distribution over 180 degree arc. The compressive bearing load will be applied as a constant pressure over 120 degree arc.
At the moment, there's no way to delimit either the tensile or compressive loading distributions. There's no geometry available to handle those loadings, so we need to split the original SolidWorks CAD geometry, ready to accept this form of loading. This is a fairly common task in FE analysis, and in some cases, there are many loading scenarios. We can have a requirement for a lot of regions to be imprinted into the CAD geometry. We also need to define a local coordinate system to be able to apply the bearing load.
Again, this is not something needed in the CAD definition, it is an FEA specific requirement. One of the things you need to consider is how you're going to manage the FEA friendly variant of the CAD model as I call it. It may exist only within the analysis discipline, or you may check it in and control it within the overall CAD management system. Let's look at the big end. The constraints are going to be applied at the big end shown here. In an actual project analysis, we would probably replace these constraints with equivalent, opposing reaction forces.
A minimum constraint set, or inertia relief method would be used to stabilize the model. There are two reasons for doing this in a real project. The first reason is that reactions will be created at opposing bearing faces, dependent whether we have compressive or tensile load cases. We have to choose a different constraint boundary condition for each load case. This implies that we would need two analyses, one for each loading condition. The second reason is that the presence of the constraint in the big end here will give very harsh and unrealistic local stress condition.
Stress distribution in the big end can't be used to assess the strength of the component. For the con rod analysis in this course, we're going to simplify the reaction system by fixing the con rod to ground at the big end in both load cases. We accept that this means we have to ignore the stresses around the big end, it does however mean that we don't have to apply any further geometry manipulation, we can run just one analysis. Let's look at the standard view. Finally, we want to be able to guide the mesh, so that the elements are small and well shaped in regions of high stress.
Simple geometry regions with brick-like shapes are the easiest to mesh. Splitting the solid geometry up, or imprinting curves on surface is a very powerful technique to help create this kind of brick-like geometry. And in our case, we're going to limit this mesh control to putting split lines running longitudinally along the con rod. So we've seen how the SolidWorks geometry needs to be manipulated to allow an effective workflow to take place.
- Setting up Simulation properties and defined views
- Preparing the geometry
- Setting up a local coordinate system
- Splitting surfaces
- Defining the constraint and the loads
- Running analysis
- Contour control
- XY plots