Overspeed Analysis Best Practices
Best practices for nonlinear overspeed analysis — elastic-plastic material, large deformation, incremental loading and margin assessment.
Material model
Use the elastic-plastic stress-strain curve at the overspeed temperature. Include the yield strength, hardening and ultimate tensile strength. For large deformation, use true stress-true strain. The material model must be valid at the strains encountered at overspeed.
Large deformation
Include large-deformation (geometric nonlinearity) effects if the radial growth is significant relative to the radius. The geometry change affects the stress distribution and the load. The analysis should use the updated geometry at each increment.
Incremental loading
Apply the centrifugal load incrementally up to the overspeed value. Monitor the plastic strain at the critical locations at each increment. If convergence is difficult, use smaller increments or automatic stabilisation.
Margin assessment
Compute the burst margin and yield margin. Check the plastic strain is within the allowable. Check the clearance at overspeed. Report the margins with the material properties and temperature used.