Modal Updating of Tail of a Military Helicopter

Abstract

Modal updating is a method to correct the dynamic behavior of FEM which contain uncertainties because of the boundary conditions, partial modeling, joint and contact stiffness values etc. Conducting structural dynamic analysis which represent different modal behavior than the real structure can produce considerable different analysis results like displacement, stress and fatigue life response in addition to the natural frequency and mode shape results. In this study, modal updating technique using natural frequency and mode shape differences as residual values is applied to the tail of a military helicopter. The finite element model by using beam and shell elements is created in Altair HYPERMESH® and modal analysis results are obtained using Altair RADIOSS® solver. Modal test, which is called ground vibration test (GVT) for the aerospace structures, is conducted by using LMS SCADAS® data acquisition system and modal test results are obtained using LMS TESTLAB® Polymax. Modal updating is conducted using LMS VIRTUAL LAB® together with NASTRAN SOL200® solver and point mass values assigned for some parts of the tail together with stiffness values for the fuselage-tail connection assigned by using CBUSH elements are updated.