Simplification of FEA by Symmetry

Simplification of FEA by Symmetry

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For irregular geometry, classical B31.3 rules cannot be applied. As a result, a Finite Element Analysis (FEA) is required, meeting ASME VIII-2 guidelines as permitted by B31.3.

Ultraflo brochure

In many cases, the geometry of the part is symmetrical about one or more base planes.

Valve showing symmetry

In this case, one of Ultraflo’s wafer valves requires CRN registration. The valve is symmetrical about the centre of the valve from left to right, and front to back.

Solid model extracting 1/4 of model

Because of this symmetry the entire valve need not be analyzed. One quarter of the model can be extracted and used. This reduces the complexity of the mode and the time required to perform the analysis.

Applying constraint of symmetry to model cut planes.

How is this symmetry accounted for in the analysis? When running the FEA one of the constraints is symmetry about the model cut planes.

Applying contraints and loadings

The remaining constraints and loadings are applied as if the whole model is included. This is possible when the loadings are symmetrical about the same planes the geometry was sectioned. In this case internal pressure and surface contacts on the interface between the two halves (and bolt) are applied (for explanation of multi-body part analysis see below).

FEA results

The results are interpreted the same as if the entire model were analyzed. Ultraflo’s wafer valve analysis was accepted by the jurisdiction and Ultraflo obtained their CRN#.

A special thanks to Ultraflo Corporation, #8 Trautman Ind. Dr. Ste. Genevieve, MO for allowing use of their valve geometry for this exercise.

(Note: the stress results show do not represent actual stresses under operating conditions, arbitrary loadings were applied and arbitrary stresses are shown.)