# Common mistake in numerical modeling

Common Mistake in Numerical Modeling

However making simplifications is almost always an inevitable part of any modeling, but its accuracy should be the main concern of the user. In this article, I am going to mention some of common mistakes which I have found so frequent in my classes. Briefly, the areas which are extremely prone to errors are geometry, meshing, units, boundary conditions and loading.

Geometry Simplification

Sometimes to reach a higher quality in meshing the user has to simplify the geometry of the objects. In such cases the finite element model does deviate from the reality, which means the analysis results might become inaccurate if the simplification is not reasonable. The simplification of geometric curvatures, for example, is of a significant concern.

Mesh Refinement

Meshing, which is probably the most influential part of any numerical modeling, can results in a misleading  analysis. Whether the size of element, or its family is not suitable, the precision will be sharply reduces. Gaining insight into the proper strategy of meshing is a professional knowledge and is what make a difference between a user and an experienced engineer. It is highly recommended to watch one of our online coarse in which you can find many tips and hints about element and meshing.

Despite the fact that in reality everything is 3 dimensional, under certain conditions 2 dimensional elements not only show a reasonable precision, but also reduce the computational expenses.

Moreover, it is noteworthy that a finer mesh does not necessarily mean a more accurate analysis. Excessively fine elements prolong the analysis time and might cause some numerical errors. The best strategy is to adjust the size of elements based of the relative importance of the area.

Variable Size of Elements

Compatible units

Unlike most of numerical software, ABAQUS runs without any units. Before starting to create your model, you need to decide which system of units you will use. ABAQUS has no built-in system of units. All input data must be compatible with each other. This table shows the compatible units.

Compatible Units

Boundary conditions

Insufficient supports will allow rigid body motion. On the other hand excessive boundary conditions make the results unrealistic. All in all, each of these will result in different displacements, strains and stresses.

Boundary Conditions Window in ABAQUS