Structural Mode Sensitivity to Local Modification

An efficient approximate technique for vibration mode re-analysis of a locally damaged or altered structure is introduced. The method employs a truncated set of original structure modes, augmented by an appropriate set of residual vectors, to form a reduced description of the damaged structure. The desired lowest frequency modes of the locally changed structure are computed on the basis of the reduced representation. Practical test cases, consisting of complex offshore oil platforms, illustrate the value of the new technique to accurately predict modal parameter changes at very substantial computational savings with respect to complete re-analysis of the structure.