Modal testing

About: Modal testing is a research topic. Over the lifetime, 4047 publications have been published within this topic receiving 64772 citations.

Eliminating the Influence of Harmonic Components in Operational Modal Analysis

Abstract: Operational modal analysis is used for determining the modal parameters of structures for which the input forces cannot be measured. However, the algorithms used assume that the input forces are stochastic in nature. While this is often the case for civil engineering structures, mechanical structures, in contrast, are subject inherently to deterministic forces due to the rotating parts in the machinery. These forces are seen as harmonic components in the responses, and their influence should be eliminated before extracting the modes in their vicinity. This paper describes a new method based on the well-known Enhanced Frequency Domain Decomposition (EFDD) technique for eliminating these harmonic components in the modal parameter extraction process. For assessing the quality of the method, various experiments were carried out where the results were compared with those obtained with pure stochastic excitation of the same structure. Good agreement was found and the method is shown to be an easy and robust tool for enhancing the EFDD technique for mechanical structures.

Using Modal Analysis for Estimation of Anisotropic Material Constants

Abstract: A dynamic method is presented for the estimation of the in-plane elastic properties of structural panels modeled as thin orthotropic plates. The method utilizes the concept of modal analysis. Results from experimental modal testing are matched with theoretical modal analysis calculations for a set of plate bending modes and one in-plane mode of the compression type. The elastic constants \iE\d1, \iE\d2, and \iG\d1\d2 are estimated by minimizing the relative errors between corresponding experimentally and theoretically determined eigenfrequencies. A ratio of two chosen mode shape values of an in-plane compression mode yields an estimate of the Poisson ratio ν\d2\d1. The other in-plane Poisson’s ratio ν\d1\d2 is calculated on the basis of \iE\d1, \iE\d2, and ν\d2\d1 using Hooke’s generalized law. Some redundant information gained from the experimental modal testing is used to minimize possible errors in the test and evaluation process. The method is applied to one type of wood panel material, namely oriented strand board.