Application of the mixed finite-element method to rotor blade modal reduction

A mixed finite element is investigated as a means for achieving accurate modal reduction of rotor blades in finite-element software. A rationale for mixed finite elements is developed by investigating the modal reduction accuracy of a series of blade analysis methods that introduces, in a step-by-step fashion, the key features of the mixed element. During this investigation, the shortcomings of classical, displacement-based finite elements are examined qualitatively and through calculations of articulated blade response. The formal derivation of the mixed element starting from a mixed variational principle is then summarized, and finally, numerical examples are presented to demonstrate the elementʹs modal reduction accuracy.