Models

The drawbacks of three-dimensional CAD models in structural mechanical calculations

Three-dimensional CAD models have become an indispensable part of modern design practice. They enable the precise visualisation of components and structures and provide a valuable basis for manufacturing processes. However, when it comes to structural mechanical calculations, they also present a number of challenges and drawbacks that are often underestimated.

High level of detail complicates calculations

A major disadvantage of CAD models in calculations is their high level of detail. Whilst finely detailed geometries are advantageous for design, they can be problematic in finite element analyses (FEA):

• Complex geometries lead to complex meshes: Small radii, bores or delicate structures result in very fine mesh structures, which significantly increase computation time and memory requirements.
• Unnecessary details distort the analysis: Not all design details are relevant for mechanical calculations. However, neglecting such elements often involves a great deal of manual effort.

The need for model simplification

Model reduction is necessary to make CAD models suitable for calculations. However, this simplification presents its own challenges:

• Time required for model adjustments: Engineers often have to invest a considerable amount of time in cleaning up and simplifying CAD models.
• Loss of accuracy: During simplification, essential structural properties may be unintentionally altered or overlooked.
• Manual post-processing required: Many calculation programmes require specially prepared geometries, which entails additional steps.

Numerical problems caused by CAD models

A further problem lies in the numerical implementation of CAD geometries in calculation tools:

• Poor element quality: Direct import of CAD models can lead to degenerate or poorly shaped finite element meshes, which negatively affect the convergence and accuracy of the calculation.
• Inconsistencies between CAD and FEA models: Geometric tolerances and rounding errors can result in connections or boundary conditions not being transferred correctly.
• High computational costs: Detailed CAD models result in extremely large finite element models, which significantly increase computation times and require high-performance hardware.

Conclusion

Although three-dimensional CAD models form an important basis for design and manufacturing, they present significant challenges for structural analysis. Their high level of detail, the simplification required, and numerical issues often make direct use impractical. Efficient analysis therefore requires targeted model reduction and optimised meshing to achieve accurate and cost-effective results.