A Statistical Analysis of Modal Parameters for Uncertainty Quantification in Structural Dynamics D. A. Pape 1 , S. Adhikari 2 1 Department of Engineering and Technology, Central Michigan University, Mt. Pleasant, MI, 48859, USA 2 School of Engineering, University of Wales Swansea, Singleton Park, Swansea SA2 8PP, UK Abstract This paper presents modal parameters which have been extracted from frequency response data from one hundred nominally identical systems. The experimental setup used is a fixed-fixed beam arrangement, with multiple randomly placed masses added to simulate mass matrix errors, published by Adhikari et. al. [1]. In that work, they present the probabilistic characteristics of the amplitude and phase of the measured frequency response functions. These FRFs are discussed in the low, medium and high frequency ranges. In the current paper the previous work is extended to include modal parameters estimated from each of the one hundred sets of frequency response data. Statistical information, including mean and standard deviation are compiled and discussed for the low frequency (up to 1000 Hz) range. The results obtained in this work may prove useful in uncertainty quantification investigations. 1 Introduction Uncertainty Quantification (UQ) is becoming increasingly important in establishing confidence in results obtained from finite element models. Uncertainties may be broadly classified as aleatoric or epistemic. Aleatoric uncertainty arises from inherent variability in system parameters, whereas epistemic uncertainty arises from lack of knowledge of the system. In the low frequency range, stochastic finite element methods [2-10] involve parametric uncertainties. In this work a probabilistic approach is used with the goal of enhanced understanding of the effect that variation in system parameters has on the frequency response of a model. 2.1 Experimental Procedure A complete description of the experimental procedure has been previously published [1]. In this section the relevant information from that work is summarized. The reader is referred to the original paper for further experimental details. A steel beam with uniform rectangular cross section, clamped between two massive fixed supports, was instrumented with three accelerometers and excited by an electromagnetic shaker, as shown in Figure 1. Pertinent data for the beam is given in Table 1. Accelerometers are placed at 230 mm (point 1), 500 mm (point 2), and 1020 mm (point 3) from the left end of the beam. The driving point 2 is actuated by impacts generated by an electromagnetic shaker outfitted with a steel tip. The result is clean FRF Baseline data for each of the measuring points to an upper limit of 4.2 kHz, with a resolution of 1 Hz [1]. Property Value Length (L) 1200 mm Width (b) 40.06 mm Thickness (t h ) 2.05 mm Mass Density () 7800 kg/m 3 Elastic Modulus (E) 2.0 x 10 5 MPa Table 1: Pertinent Beam Data